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Landslides in the Charlie Lake map sheet, Fort St. John Severin, Jordan M. 2004

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LANDSLIDES IN THE CHARLIE LAKE MAP SHEET, FORT ST. JOHN by JORDAN M. SEVERIN B.Sc, The University of Waterloo, 2001 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Earth and Ocean Sciences) (Geological Engineering Program) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September, 2004 © Jordan M. Severin, 2004 JUBCl THE UNIVERSITY OF BRITISH COLUMBIA FACULTY OF GRADUATE STUDIES Library Authorization In presenting this thesis in partial fulfillment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Name of Author (please print) /JO /2Qoy Date (dd/mm/yyyy) Title of Thesis: _A^a>^L<o>£S >^ Th(^ <Lj\c\QJ-\^ HAP SH££T } Po R T ST. 3~O y A/ Degree: Year: Department of £A£-TH A^->T) OC(£r/\-^v/ ^ C_ / CL(= S The University of British Columbia Vancouver, BC Canada grad.ubc.ca/forms/?formlD=THS page 1 of 1 last updated: 2-Oct-04 Abstract Many large, deep-seated landslides have occurred along the Peace River Valley and its steep-sided tributary valleys. These failures mostly occur within the Lower Cretaceous Shaftesbury Formation, a horizontally-bedded marine shale and the interglacial silt and clay beds in the Quaternary sequence. A detailed inventory of landslides was compiled in the Fort St. John area, using air photo interpretation and engineering-geological field mapping. The study area is on NTS Map Sheet 94A, comprising 14,000 km2 of terrain. Practically all slope activity in the study area occurs on slopes of stream valleys. The observed landslides were separated into a series of failure types, involving bedrock, Quaternary deposits or both. The estimated areas of individual slide units range up to approximately 10,000 m2 and volumes to 10,000,000 m2. The result of the inventory is a digital landslide map at a 1:20,000 scale and a corresponding database of landslide characteristics. The main focus of the typological classification is the failure mechanism. The classification was reinforced by more detailed field study of selected type cases. There is a prevalence of multi-level failures, approximately 48%, utilizing weak surfaces at multiple levels. This type of failure occurs extensively both in the Quaternary sequence and the Cretaceous bedrock. An activity classification was implemented based on field observations and dated air photographs. The classification comprises landslides that are very active, active, of low activity, ancient, and anthropogenically modified. Results indicate that approximately 90% of the total length of valley slopes in the study area are involved in mass movements. Approximately 15% are occupied by very active or active landslides and 61.0% are Inactive - Dormant. Four areas were chosen to be studied in detail due to their accessibility from Fort St. John, diverse failure mechanisms, and diverse local stratigraphies. A generalized stratigraphic column and landslide model was produced for each area. These were generated from the detailed landslide investigations done. ii TABLE OF CONTENTS ABSTRACT ii LIST OF FIGURES.... vLIST OF TABLES x LIST OF APPENDICES x ACKNOWLEDGEMENTS xi 1.0 Introduction 1 1.1 Objectives 2 1.2 Area Introduction 3 2.0 Literature Review 5 2.1 Landslides in Shale2.1.1 Falls2.1.2 Topples 6 2.1.3 Rotational slides (Slumps) 7 2.1.4 Translational Slides 9 2.1.5 Compound Slides 10 2.2 Landslides in Glacio-lacustrine Clay 12 2.2.1 Rotational Failures2.2.2 Translational Failures 3 2.2.3 Compound Slides 15 2.2.4 Sudden Spreading Failures 12.2.5 EarthFlows 6 2.2.6 Mudflows 7 2.2.7 Flow Slides 12.3 Examples of Landslides from the Canadian Prairies 19 2.3.1 Shale2.3.2 Glacio-lacustrine Clay 22 3.0 Regional Setting 5 3.1 Physiography 23.2 Climate 6 3.3 Quaternary History 7 3.4 Local and Regional Infrastructure 29 4.0 Bedrock Geology and Geotechnique 30 4.1 Outcrop Location 34.2 Description of Formations 2 4.4 Geotechnical Properties 7 4.4.1 Shaftesbury Shale4.4.2 Dunvegan Sandstone 43 4.5 Comparison with Other Prairie Shales 44 5.0 Surficial Geology and Geotechnique 6 iii 5.1 Location 46 5.2 Late-Quaternary Materials 47 5.2.1 Gravels5.2.2 Pre-glacial Silt, Sand, and Clay 8 5.2.3 Late Wisconsinan Till 9 5.2.4 Glacial Lake Peace Clay 45.3 Geotechnical Properties 50 5.3.1 Bulk Properties ; 51 6.0 Landslide Inventory Mapping System 52 6.1 Slide Types in the Study AreaSlide Type 1: Raveling 53 Slide Type 2: Retrogressed Rotational Failure 54 Slide Type 3: Rotational Failure 55 Slide Type 4: Mobile Flow 6 Slide Type 5: Earth FlowSlide Type 6: Multi-level Failures 7 Slide Type 7: Compound Failure 58 Slide Type 8: Shallow Retrogressive Failure 56.2 Activity Classifications 63 6.3 Morphological Symbols for the Inventory Map 70 7.0 Landslide Inventory 75 7.1 Objective7.2 Referencing System7.3 Methodology 80 7.4 Database 2 7.5 Results 5 7.5.1 Distribution7.5.2 Activity 7 7.5.3 Failure Type 90 7.5.4 Material Involved 3 7.5.5 Slide Aspect 5 8.0 Detailed Investigation of Selected Landslides Areas 98 8.1 Slide Area 1 100 8.1.1 Location8.1.2 Local Stratigraphy 108.1.3 Landslides 4 8.1.4 Area Model 117 8.2 Slide Area 2 9 8.2.1 Location8.2.2 Local Stratigraphy 121 8.2.3 Landslides 122 8.2.4 Area Model 148.3 Slide Area 3 6 iv 8.3.1 Location 146 8.3.2 Local Stratigraphy 148 8.3.3 Landslides 9 8.3.4 Area Model 178.4 Slide Area 4 188.4.1 Location 6 8.4.2 Local Stratigraphy 188.4.3 Landslides 189 9.0 Discussion 200 9.1 Landslide Mechanisms and Distribution 209.2 Generalized Geologic Model 203 10.0 Conclusions 205 References 9 v LIST OF FIGURES Figure 1.1 Site Location Map 4 Figure 2.1 Rotational Slide Failure Modes 8 Figure 2.2 Generalized cross-section, Brilliant Cut 9 Figure 2.3 Compound Slide Modes 11 Figure 2.4 Translational Failure Types 4 Figure 2.5 Stratigraphic profile of the Little Smoky landslide 21 Figure 2.6 Stratigraphy of the WID landslide 2Figure 2.7 Cross section after 1939 Montagneuse landslide 24 Figure 2.8 Section through Rycroft landslideFigure 2.9 Stratigraphy of the Attachie landslide 2Figure 3.1 Quaternary Valley Fill Materials Location 8 Figure 4.1 Bedrock Geology Map 31 Figure 4.2. Dunvegan Sandstone within the Beatton River Canyon 36 Figure 4.3 Valley Rebound with resultant deformation 38 Figure 4.4 Site C Damsite Schmetic with discontinuities 9 Figure 4.5 Typical sampling area of sheared shale and gouge 41 Figure 4.6 Tested Sample Location Map 42 Figure 5.1 Plasticity Chart (Unified System) - Peace River Samples 51 Figure 6.1 Slide Type 1: Raveling 59 Figure 6.2 Slide Type 2: Retrogressive Rotational Failure 5Figure 6.3 Slide Type 3: Rotational Failure 60 Figure 6.4 Slide Type 4: Mobile FlowFigure 6.5 Slide Type 5: Earth Flow 1 Figure 6.6 Slide Type 6: Multi-level Failure 6Figure 6.7 Slide Type 7: Compound Failure 2 Figure 6.8 Slide Type 8: Shallow Retrogressive Failure 6Figure 6.9 Very Active Landslide (Photo) 68 Figure 6.10 Active Landslide (photo)Figure 6.11 Low Activity - Dormant Slide (Photo) 69 Figure 6.12 Low Activity - Abandoned Slides (Photo)Figure 6.13 Modified Slide (Photo) 6Figure 6.14 Morphological Classification 73 Figure 6.15 Landslide Type Examples using Morphological Classification 74 Figure 7.1 Reference Areas for Landslide Inventory 76 Figure 7.2 Landslide Outlines on Enlarged Photographs 84 Figure 7.3 Landslide Outlines on TRIM Map 8Figure 7.4 Digitized Landslide OutlineFigure 8.1 Detailed Landslide Study Areas 99 Figure 8.2 Landslide Area 1 101 Figure 8.3 Area 1 - Stratigraphic Profile (not to scale) 103 Figure 8.4 Intact Pre-glacial Stratigraphy (Slide 1-1) 5 Figure 8.5 Former Big Bam Ski Hill Tower Line (Slide 1-2) 106 Figure 8.6 Bison Vertebrae found in place (Slide 1-6) 110 Figure 8.7 Landslide Profile 1-1 Ill vi Figure 8.8 Landslide Profile 1-2 112 Figure 8.9 Landslide Profile 1-3 3 Figure 8.10 Landslide Profile 1-4 4 Figure 8.11 Landslide Profile 1-5 115 Figure 8.12 Landslide Profile 1-6 6 Figure 8.13 Landslide Area 1 - Geologic Model 118 Figure 8.14 Landslide Area 2 120 Figure 8.15 Area 2 - Stratigraphic Profile (not to scale) 122 Figure 8.16 Shear Plane found and sampled (Slide 2-4) 5 Figure 8.17 Landslide Profile 2-1 131 Figure 8.18 Landslide Profile 2-2Figure 8.19 Landslide Profile 2-3 3 Figure 8.20 Landslide Profile 2-4 134 Figure 8.21 Landslide Profile 2-5 5 Figure 8.22 Landslide Profile 2-6 6 Figure 8.23 Landslide Profile 2-7 137 Figure 8.24 Landslide Profile 2-8 8 Figure 8.25 Landslide Profile 2-9 9 Figure 8.26 Landslide Profile 2-10 140 Figure 8.27 Landslide Profile 2-11 1 Figure 8.28 Landslide Area 2 - Geologic Model 145 Figure 8.29 Landslide Area 3 147 Figure 8.30 Area 3 - Stratigraphic Profile - North and East Valley Walls 150 Figure 8.31 Area 3 - Stratigraphic Profile - South Valley Wall 15Figure 8.32 Area 3 - Stratigraphic Profile - Stoddart & St. John Creeks 151 Figure 8.33 Cross-Tilting of trees on Landslide Profile 3-4 154 Figure 8.34 Landslide Profile 3-1 165 Figure 8.35 Landslide Profile 3-2 6 Figure 8.36 Landslide Profile 3-3 7 Figure 8.37 Landslide Profile 3-4 168 Figure 8.38 Landslide Profile 3-5 9 Figure 8.39 Landslide Profile 3-6 170 Figure 8.40 Landslide Profile 3-7 1 Figure 8.41 Landslide Profile 3-8 2 Figure 8.42 Landslide Profile 3-10 173 Figure 8.43 Landslide Profile 3-11 4 Figure 8.44 Landslide Profile 3-12 5 Figure 8.45 Landslide Profile 3-13 176 Figure 8.46 Landslide Profile 3-14 7 Figure 8.47 Landslide Profile 3-15 8 Figure 8.48 Landslide Area 3 - Model 1 184 Figure 8.49 Landslide Area 3 - Model 2 5 Figure 8.51 Deltaic Sequence 18Figure 8.52 Area 4 - Stratigraphic Profile 189 Figure 8.53 Intact Section Photo (Slide 4-1) 190 Figure 8.54 Complex Stratigraphy (Slide 4-4) 3 vii Figure 8.55 Landslide Profile 4-1 194 Figure 8.56 Landslide Profile 4-2 5 Figure 8.57 Landslide Profile 4-3 6 Figure 8.58 Landslide Profile 4-4 197 Figure 8.59 Landslide Area 4 - Geologic Model 199 viii LIST OF TABLES Table 4.1. Summary of classification test results, shale and gouge 43 Table 4.2. Geotechnical Properties of Prairie Shales 46 Table 5.1. Summary of classification test results for surficial materials 52 Table 7.1 Measured Distance within Slope Segment Districts 78 Table 7.2. River Identifies within Charlie Lake Map Sheet 80 ix LIST OF APPENDICES Appendi Appendi Appendi Appendi Appendi iixl iix II iix III iix IV iix V Appendix VI Geotechnical Lab Results - Shale and Clay Air Photograph List Landslide Maps - Overall and Each TRIM Landslide Inventory Inventory Analysis Results Rosette Diagrams x ACKNOWLEDGEMENTS A thesis can be referred to as a work of art full of passion and beauty, the pinnacle of ones knowledge and enthusiasm. It can also be referred to as a pain in the neck. I think all theses belong somewhere in between these extremes. I wish to thank my advisor, Dr. Oldrich Hungr for making my experience closer to the former than the latter. His excellent advice and imparted knowledge will be with me always. He has installed a thirst for knowledge and eagerness to experience all facets of life. I also wish to thank the members of my committee. Thanks to Dr. S. Evans from the Geological Survey of Canada, Dr. M. Bovis of the UBC Department of Geography, and Dr. J. Clague of the SFU Department of Earth Sciences. Dr Evans also provided financial support, documentation, and some great advice on landslides and life. During my summers in the Peace River Region, I have met some interesting characters. None more so than those who have helped me in the field. I would like to thank Adrian "The Hulk" Hansen for his tireless effort through the brambles and roses in the area and nicotine withdrawal. I would also like to thank Greg "G-Man" Hartman who conducted a sister project on the Quaternary history of the area. I also wish to thank Ina Adams for allowing us such lovely accommodations while in the area. I would also like to thank the 3 black bears that I saw, and the grizzly that I did not, for not making me a casualty of the Peace. There are others that I am grateful for, Mr. B. Gerath of Thurber Associates and Mr. D. Cavers of AMEC Earth & Environmental for their help and access to files. I wish to extend my gratitude to Dr. L. Dyke of the Geological Survey of Canada who has helped, not only with funding but also with advice and support. I would also like to thank the EOS Men's hockey team for making my time in Vancouver that much more enjoyable. One person does not write a thesis. They are surrounded by support and in fact driven by it. Without the friendship and inspiration from Scott McDougall, Brooke Smith, Allistar McClymont, John Macklin, and Joshua Caulkins, I would not have succeeded. As the other half of the Landslide Research Team at UBC, Scott McDougall was essential to my success and I count it one of my highest honors, not only to know him, but also to be present when he married his lovely wife Samantha. Finally, I would like to acknowledge the love and support I received from my lovely partner, Naomi Ellis. Without her, not only would this thesis not have been finished, and it would not have mattered if it hadn't. xi 1.0 INTRODUCTION The Peace River Area of northeastern British Columbia and northwestern Alberta is one of the most important oil and gas production districts in Canada. The vast amount of hydrocarbon extraction has created the need for an extensive system of pipelines, railways, and roads to be built that traverse the unstable riverbanks of the region. Many large, deep-seated landslides have occurred within the Peace River Valley and its steep-sided tributary valleys. A better understanding of landslides in the region, type, activity, and failure mechanisms will be beneficial to the management of current and future regional infrastructure. This thesis summarizes a research project devoted to the investigation, mapping, and classification of landslides in the Fort St. John area, which is the centre of the present petrochemical extraction activity. The project was a component in a wider study of landslides in the region conducted by the Geological Survey of Canada and headed by Dr. L. Dyke. The landslides mostly occur within the Lower Cretaceous Shaftesbury Formation, a horizontally bedded marine shale and the pre-glacial silt and clay beds within the Quaternary sequence. Many landslides occur near critical pipeline crossings and several failures have resulted in pipeline rupture. In other cases, wellheads are threatened by head-ward retrogression of landslides. Landslides in Cretaceous bedrock involve slow sliding along geological defects in horizontal strata. These defects are a result of primary deposition and valley rebound (Matheson and Thomson, 1973). Landslides in the fine-grained Quaternary sediments may be rapid catastrophic flowslides, as at Attachie and Flatrock, or more commonly, slow moving slides. Failure is 1 related to the existence of highly plastic horizons, glaciotectonic shears, valley rebound, and syn-erosional slumping. Pioneering observations on Peace River landslides were made by Mathews (1963, 1978) with further work being undertaken by Evans et al. (1996), Bobrowsky et al. (1991) and Fletcher et al. (1998, 2002). The relationship between pipeline performance and moving slopes in the area has been illustrated by McClarty and Cavers (1998). Geotechnical aspects of the Cretaceous bedrock in the Peace River have been reported by B.C. Hydro in the geotechnical engineering literature (Hannah and Little, 1992; Imrie, 1991; Cornish and Moore, 1985; Sargent and Cornish, 1985; Maber and Stewart, 1976) and a number of unpublished reports. The failure of the Peace River Bridge at Taylor has been reported by Hardy (1963), Hardy et al. (1962), and Brooker and Peck (1993). 1.1 Objectives The primary objective of this research was to establish the relations between landslides and geologic conditions in the northeastern B.C. region and to produce a landslide inventory map and database for the Charlie Lake Map sheet (NTS 94A). This was done using air photo interpretation; previously written geotechnical reports; and site-selected fieldwork. This map is to be produced in digital form with locations of landslides denoted by symbols distinguishing bedrock or surficial slides. Although landslides are very wide spread in the region, very little has been published on the relationship between the geology and geotechnics of landslides in the region and no comprehensive or systematic study of the distribution and behaviour of landslides in the Peace area has 2 been undertaken. The inventory will also be used to analyse landslide activity after 1948 and in prehistoric time for selected focus areas. A further objective was to use selected fieldwork to characterize the materials and landslides in the area in order to determine typical failure mechanisms. Investigation of selected slides included detailed mapping, regional landslide models, and materials testing. Fieldwork was necessary to develop type landslide cases in the two main units, find marker horizons, and to form a better understanding of the area. Using the landslide inventory and site descriptions, the final result is a synthesis of a geological-geotechnical model of slope behaviour. This will hopefully provide the oil and gas transmission industry with a geotechnical framework for understanding the behaviour of slopes in the study area. 1.2 Area Introduction The study area is defined by the NTS map sheet 94A - Charlie Lake, which encompasses the city of Fort St. John as well as the towns of Hudson Hope, Taylor, and Charlie Lake (Figure 1.1). The study area boundaries are defined by the Alberta boundary to the east (120° W), the town of Hudson Hope to the west (1220 W), and by the 56° N and 57° N parallels of latitude. 3 Figure 1.1 Site Location Map 2.0 LITERATURE REVIEW 2.1 Landslides in Shale The body of literature available on landslides in shale is quite extensive, as they represent a unique problem in the field of engineering geology and geological engineering around the world. The Prairie shales of western North America have required a broad amount of investigation and research on the subject (Mollard, 1977; Thomson and Morgenstern, 1978, Locker, 1969; Scott and Brooker, 1968; Sauer et al., 1990; Cruden, 1996). The following types of mass movements have been noted as important in shale failures within the Peace River Area; 1) Falls, 2) Topples, 3) Rotational Failures, 4) Translational Failures, 5) Compound Failures, and 6) Block Slides. A brief description of each and case histories are provided. 2.1.1 Falls Rock falls are rapid to extremely rapid (Varnes, 1978) free descents of masses of rock. This type of failure occurs typically at a small scale in shale; however, a few large-scale cases are known (Gray et al, 1978). Few reports of shale falls are documented, as shales do not tend to support large cliffs, therefore, shale falls are generally thought of as insignificant owing to the small volumes involved and small hazards that they present. A shale fall originates from a steep slope; the mass then descends down the slope by a combination of free fall, rolling, and bouncing depending on the angle of the original slope. 5 Minor falls are commonly observed in natural slopes and excavations. Shale slopes are usually at a shallow enough angle to allow for detritus to accumulate instead of free falling. Vertical or near vertical slopes in shale do commonly occur along river valleys, especially in the Peace River area, however these generally allow the rock to fall directly into the river or creek. Slopes of shallower angles will accumulate colluvial aprons because of the low impact resistance of shale. Pieces of shale are usually tabular and break on contact with a harder surface. The disaggregation of shale releases much of the kinetic energy accumulated during the fall and the smaller pieces will not roll as far as a stronger material. The high plasticity of shale allows small clay flakes or blocks to break down quickly to the properties of clay. A clay talus cone will absorb much of the energy of falling rock instead of allowing the rock to bounce or roll down the slope. Gray et al (1978) produce an example of shale failure near Ambridge, Pennsylvania. A 15m high nearly vertical cut was made of soft shale, claystone, and sandy silt shale. In this case the shale was compact enough to fall as a single 115-m3 block, which unfortunately killed 22 persons. 2.1.2 Topples A shale topple typically involves detachment of a slab of material, defined by near-vertical fissures, followed by forward rotation out of the slope. This rotation takes place about a point or axis below the center of gravity of the displaced mass when an external force is applied, or when softening and ductile deformation of the base causes slight forward rotation of the mass. The motive force is usually supplied by the block's weight or by water or ice pressure exerted in a previously developed tension crack. 6 Shale can be susceptible to simple or flexural toppling if the bedding planes have been displaced. On a small scale, block toppling can occur although in horizontally bedded shale, however, is rare as the discontinuities are generally horizontal along the bedding plane, not vertical. If the shale has gone through advanced diagenesis the shale may contain fissures or vertical joints, however, a majority of horizontally bedded clay shales are poorly indurated. 2.1.3 Rotational slides (Slumps) Rotational slides are those in which the movement of a mass is roughly rotational about an axis running parallel to the slope crest (Varnes, 1978). The term 'roughly' is used to allow for a condition where the basal shear surface is partly developed along a horizontal weak layer, which causes truncation of the normally curved or listric shear surface. The weak horizontal basal layer has to play a minor role so that the movement can still be considered rotational and little internal deformation of the sliding body occurs. A rotational movement will show downward displacement of the head of the mass, which commonly tilts backward toward the slope, and upward displacement at the toe. Rotational failures in shale occur on fresh steep scarps, as seen in highway road cuts or eroded riverbanks, or when there is a resistant cap rock. This is because the long-term equilibrium state of shale is at angles too shallow to form rotational failures. Rotational failures occur mostly in deep, homogenous formations, i.e. London Clay (Hutchinson, 1988). In the Western Canadian Prairies where poorly indurated shales are predominant, rotational failures are rare. Poorly indurated shales, or clay shales, are highly anisotropic having weak-bedding planes that modify the rotational movement. 7 This type of failure may occur if it is small enough that it can take place between weak layers. Hutchinson (1988) identified three modes of rotational slides: single, successive, and multiple rotational slides (Figure 2.1). Single rotational slides contain a single concave slip surface and the moving mass acts as a coherent unit. Successive rotational slides refer to many shallow rotational slips that are aligned head to toe up the failing slope. Often this type of failure will produce regular step-like terraces, which can easily be reactivated. Each of the failures can be described as a shallow to moderately deep-seated rotational slip. Multiple rotational slides occur from the retrogression of a single rotational slip with a curved, generally deep-seated failure surface. The retrogression of the slide forms two or more slipped blocks with slip surfaces tangential to a common slip base. Figure 2.1 Rotational Slide Failure Modes (Hutchinson, 1988). Gray et al (1978) presented a case history in which a rotational failure did occur within shale. The Brilliant Cut failure in the northern Appalachian Plateau occurred within a sequence of interbedded shale, sandstone, and limestone. A railway cut was made at 45° to a height of 50 metres in the early 1930's and within 10 years the slope was severely unstable. Over 70% of the failure surface was located within the soft clay shale 8 (Figure 2.2). The movement was marked with a rapid drop in the head of the slide, 5m within 90 seconds and was triggered by elevated pore pressures within the slope. The slide had a total volume of roughly 160,000 m3. Figure 2.2 Generalized cross-section, Brilliant Cut (Gray et al., 1978) 999 AFTER ai^vera Wt n n. r.'xcuir T r.KB EK.LS.htriTr, 0»EN JOIMT SIUW 5JU)05T0ME Cimn(I.N*C*ijgi; 39 5H.H.IJ 000 Off SET. FEET 50 15 IE3 OFFSET, MCTXIti ISO An open pit mine in Wyoming (Clough et al, 1978) displayed several rotational slides, which took place during excavation. Two of these rotational failures had volumes of 1.4M m3, and were largely confined to the shale strata. 2.1.4 Translational Slides Translational slides are a common type of failure in bedded shales. The failed mass progresses along a more or less planar shear surface running sub-parallel to the bedding, with several well-defined blocks separated by oblique shears. Generally, the proximal segment of the rupture surface of the slide is a downward extension of the main 9 Extensional features and a low angle of movement dominate surface morphology. Horst and graben features within the debris mass may or may not be accompanied by back tilting. The upper blocks are the last to begin moving due to the removal of material near the toe. Other blocks may become detached, pushing material forward to a river or another erosional agent. If unimpeded, the displaced mass will run parallel to the slope, starting out as a coherent unit, but as sliding continues, the mass may become more distorted. The entire shear plane is active within a translational failure and the shear plane must be at a sufficient angle to horizontal to allow for movement in the downslope direction. Within the Western Canadian Prairies, such failures can occur in Upper Cretaceous marine clay shales and develop retrogressively (Mollard, 1977) providing that the bedding is at a sufficient angle to allow movement. Failures may occur along bentonitic-rich layers within the shale, along weaker layers caused by softening, along interbed slip planes caused by the lateral release of valley rebound or glaciotectonic stresses, or release of residual tectonic forces caused by the mountain building processes to the west. Examples of this type of failure are found in Section 2.3 Examples of Landslides from the Canadian Prairies. 2.1.5 Compound Slides Compound slides are a form of translational slide in which the head of the slide mass may rotate backward due to a curved proximal segment or subside to form a graben. They differ from translational slides in that sections along the shear plane are passive and 10 They differ from translational slides in that sections along the shear plane are passive and are simply pushed downslope by the upslope action. The failure plane typically occurs at a much lower angle than required for translational failures. These are a very common type of landslide in horizontally bedded shales within the Canadian Prairies. The failure plane is slightly deeper than the typical translational failure and the debris is normally extremely distorted. Surface morphology of this type of landslide will have both horst and graben type features, possibly combined with back tilting near the head scarp. These failures can also occur at very low angles, 5° to 11°. Hutchinson (1988) classified compound slides into two categories: progressive compound slides and compound slides released by internal shearing (Figure 2.3). Progressive compound slides are those in which there is a rotational failure at the rear of the slide and the remaining basal slip surface is planar. Compound slides released by internal shearing are those that have a weak basal surface and have undergone internal shearing, to accommodate curvature at the intersection of the basal surface and the back scarp. Sliding will occur once the cohesion within the mass is removed. Figure 2.3 Compound Slide Modes (Hutchinson, 1988) Examples of this type of failure can also be found in section 2.3 Examples of Landslides from the Canadian Prairies. 11 2.2 Landslides in Glacio-lacustrine Clay Landslides in clay and silt have been investigated more than any other material within the body of landslide literature (Hardy et al, 1962; Skempton, 1964; Skempton and Hutchinson, 1969; Varnes, 1978; Hutchinson, 1988; and Cruden and Varnes, 1996;). Glacio-lacustrine clay has unique properties, which have to be considered in slope stability analysis (Townsend et al, 1965; Kenney, 1975; Evans, 1982; and Giraud et al, 1991). Evans (1982) suggests that within British Columbia, two distinct types of glacio-lacustrine clay are present. Type A (Southern Interior) has more silt than clay layers and is more likely to reflect the properties of the silt. Type B (Northern Interior) has a greater thickness of clay than silt and the properties are thought to reflect the properties of clay. Townsend et al. (1965) quantified the importance of material grain size within glacial varves with laboratory experiments. The following types of mass movement have been noted as important within glacio-lacustrine materials in the Peace River area; 1) Rotational Slides, 2) Translational Slides, 3) Compound Slides, 4) Sudden Spreading Failures, 5) Earthflows, 6) Flowslides, 7) Mudflows, and 8) Complex Slope Movements. A brief description of each and case histories are provided. 2.2.1 Rotational Failures Rotational failures in clay show the same mechanisms as rotational slides in shale, although they are more common in these deposits than in shale. Rupture takes place along an identifiable plane that approximates a listric or cylindrical surface. Again we see a degree of backward rotation to the slipped mass accompanied by sinking at the head of 12 the slide and heaving at the toe. Hutchinson (1988) identifies three modes of rotational slides; single, successive, and multiple rotational slides, as described earlier in Section 2.13 (Figure 2.1). Glaciolacustrine clay is normally varved, which imparts an anisotropic nature to the material, rendering true rotational failures rare, though shearing across laminae can occur in some glaciolacustrine clays (Giraud, et al., 1991). Slides in varved clay deposits may also be approximately circular providing that the pore water pressure in the silt layers is low (Terzaghi and Peck, 1948). Retrogression of a single rotational slip is more common in these deposits than in shale. An example of retrogression of a rotational failure has been documented near Quesnel, B.C. (Evans, 1982). An active slope movement is taking place in a 150 m thick sequence of varved Quaternary glacio-lacustrine clays and silt. Retrogression at the main scarp takes place by multiple rotational slumping and produces backward tilted slump blocks, which move down the slope and undergo progressive disintegration and remolding. 2.2.2 Translational Failures This is a common type of failure in glacio-lacustrine clay. The clay body needs an exceptionally weak layer at sufficient angle top allow movement to fail along without disturbing most of the overlying debris. Within glaciolacustrine clay, highly plastic varves can serve as the weak layer. In some cases, translational failure can occur due to liquefaction of the basal slip surface. This is normally seen in quick clays in Eastern Canada and Norway, which are glacio-marine clays. Skempton and Hutchinson (1969) 13 Canada and Norway, which are glacio-marine clays. Skempton and Hutchinson (1969) note that a shallower depth to the weak layer increases the amount of translational movement that the slide will experience. Two types of translational slides identified by Skempton and Hutchinson (1969) that arise in clays are block slides and slab slides (Figure 2.4). A block slide arises when a hard, jointed block of clay disconnects from the parent mass at a joint or weakness. Then the clay block slides along the plane of weakness with the clay mass. Slab slides take place on more weathered clay slopes when the mantle or crust of a residual soil or sensitive clay is disturbed. The broken crust or slab moves along the slope, with little distortion, as a single unit. This implies that the weak surface is sloping at a steep enough angle top allow for movement. Figure 2.4 Translational Failure Types (Skempton and Hutchinson, 1969) TRANSLATIONAL SLIDES A translational slide in glacio-lacustrine sediments occurred in 1977 near the town of McBride, British Columbia (Thomson and Mekechuk, 1982). The failure plane was located within a thick bed of varved clay and silt deposited during the retreat of Cordilleran ice. The clay was medium to high plasticity and dipped slightly toward the river. 14 2.2.3 Compound Slides Compound slides are a far more common failure type in glaciolacustrine clay and silt than are translational failures. This is due to the low strength of clay and relative ease with which shear can occur through varves and the horizontal bedding. This allows for a steep or circular head scarp to form in situations in which they could not occur in shale. For the most part, these failures are the same as in shale. Examples of compound failures in glacio-lacustrine are given in Section 2.3 Examples of Landslides from the Canadian Prairies. 2.2.4 Sudden Spreading Failures Clay spreading involves extension of a cohesive mass combined with a general subsidence into a softer underlying material (Cruden and Varnes, 1996) making it a category of translational failure (Hutchinson, 1988). It commonly displays horst and graben structures where lateral extension has occurred accommodated by shear or tensile fractures. Movement is very rapid even over low gradients (Hutchinson, 1988). This type of failure is most described in soft, sensitive clay; however, Terzaghi and Peck (1948) note that this style of movement can occur in varved clays having high pore water pressures developed in silt or sand layers. Varnes (1978) identifies two types of spreading failure. The first is due to an overall extension of material without a recognizable basal shear surface or zone of plastic flow. This type is predominantly a bedrock feature so will not be discussed here. The second type of failure, called earth lateral spreads, involves fracturing and extension of a coherent material, in this case, a solid clay mass, due to a 15 plastic or liquefied basal layer. The upper unit blocks may move by any mechanism, such as subsidence, translation, or rotation. Skempton and Hutchinson (1969) described these failures as a particular type of retrogressive compound slide. Gentle slopes, broad fronts, rapidity of movements, and the succession of horst and graben structures characterized them. The retrogressive nature of the slide comes from the subsidence, which drives the displaced mass forward. As the mass subsides, the lateral support acting on the new back scarp is insufficient to hold it in place; thus a new wedge will subside pushing the previous wedge forward. Mitchell (1978) reports lateral spreading in fresh water varved clays at Wawbewawa and at Beattie Mine, Quebec. 2.2.5 EarthFlows Earth flows are defined as rapid or slower, intermittent flows of plastic clayey earth (Hungr et al 2001). They involve spatially continuous movement in which surfaces of shear are short lived, closely spaced, and usually not preserved (Cruden and Varnes, 1996), with a distinct boundary between the moving mass and the intact material. This type of failure generally arises from a large influx of water either through an increase of precipitation or by the melting of ice or frozen ground. They are relatively shallow failures that resemble the flow of a viscous fluid and depend on the water content, movement, and mobility of the mass. The disturbed mass is thoroughly broken up and keeps little of its previous structural integrity. Over-consolidated and varved or laminated clays are most susceptible to earth flows. 16 "Earth flows are commonly tongue or teardrop-like in shape. They have rounded, bulging toes and sinusoidal longitudinal profiles, concave upward near the head of the earth flow and convex upward near the toe" Keefer and Johnson (1983). The Thistle slide in Utah (Duncan et al., 1986) is an example of an earth flow involving silty, sandy, and gravelly clays of medium plasticity (average LL = 40, PI = 18). The landslide mass is roughly 1800 m long and an elevation difference of 305m from the crest to the toe of the slide debris. 2.2.6 Mudflows Mudflows are very rapid to extremely rapid flows of saturated plastic debris in a channel, involving significantly greater water content relative to that of the source material (Hungr, 2001). Rainstorms can sometimes cause clayey colluvium to become diluted beyond its Liquid Limit in desiccated, especially dispersive clays. The triggering hillslope failures are usually shallow seated (< 5m thick). In areas of low relief, clay flows are generally restricted to oversteepened slopes, such as gully sidewalls and undercut river bluff slopes. 2.2.7 Flow Slides Hungr et al (2001) describe flow slides as very rapid to extremely rapid movements of sorted fine-grained sediment, involving liquefaction. Clay flow slides occur in association with quick clays and form due to a collapse of an internal structure and the build up of high water pressures. If significant disintegration of the failed mass has occurred it may be difficult to identify the failure mechanism. 17 The material liquefies when the metastable structure of the clay collapses. The loss of strength gives the failing clay a semi-fluid character, which allows the flow to develop. The result is a high velocity movement that travels a long distance. Mitchell and Markell (1974) completed an investigation of flow sliding in the sensitive clays of eastern Canada. Their studies conclude that undrained failure in sensitive clays will not occur if the stability number for the clay is greater than 6. The stability number is defined as: Ns = yH/ Cu where y is the bulk unit weight of the soil, H is the slope height, and Cu is the undrained strength of the soil. In this study, three proposed phases of the development of flow slides were introduced. First, an initial slide is caused by the long-term instability of the slope. After the initial slope failure, the slope undergoes a retrogressive failure caused by the undrained short-term instability of the successive slices. The third phase is an earth flow involving the extrusion and flow of the soft underlying materials. Hutchinson (1988) refers to this type of failure as a flow slide, while others (Varnes, 1978) often group it in with the above category. Skempton and Hutchinson (1969) add a section in their category of multiple and complex landslides, quick clay slides. Here they present a failure peculiar to quick clays, the 'bottle-neck' type of retrogressive, multiple rotational failures. It initially begins with a rotational slip, then the disturbed mass is remolded to a liquid, which runs off, leaving the near scarp unsupported. This new scarp is then attacked; it fails, and flows out like the previous. This continues until a new back scarp is supported by other means. 18 The Thompson River experienced a flow slide in 1880 that involved approximately 15 Mm3 of normally consolidated Early Holocene or Late Pleistocene glaciolacustrine sediments (Evans, 1984). The sediments were characterized by varves and laminations within the debris that dammed the Thompson River for approximately 44 hours. The cause of the landslide is speculated to be due to the irrigation of the bench in the area of the failure (Stanton, 1898). 2.3 Examples of Landslides from the Canadian Prairies As the Peace River area is located with in the Interior Plains, the geotechnical literature from Alberta is more relevant than that from British Columbia. Both shale and glacio-lacustrine examples are given. 2.3.1 Shale The Little Smoky landslide is an excellent example of a retrogressive compound rotational failure in shale (Thomson and Hayley, 1975). The slide affects a bridge over the Little Smoky River near the town of Valleyview, Alberta. The basal failure plane is nearly horizontal and occurs within clay-shale the Lower Smoky Formation (Figure 2.5). In the Peace River Area this formation is known as the Kaskapau Formation, and crops out to the east of the Kiskatinaw River. The slide occurs within a pre-glacial valley plugged with till and associated glacial deposits. The failure is reported to move at a slow creep toward the river, with each slice acting as a separate entity. The Lesueur landslide (Thompson, 1971 & Cruden et al., 1998) is on the North Saskatchewan River on the northern outskirts of the city of Edmonton. It is an example of 19 a translational failure within the bentonite-rich Cretaceous shale. The landslide scarp was reported to be 50m wide, with a depth of rupture of 32m deep, and a volume 0.76 Mm3. The cause was river erosion, ice-blocked drainage, and weakening of the strata due to interbed slip from valley rebound of Upper Cretaceous Mudstone with bentonitic seams. It shows continued differential movement along the shale failure plane. This paper comments on Hutchinson's (1973) cycle of landsliding, which will be considered later in this thesis. Dewar and Cruden (1998) report a landslide on the MacKay River that shows deep, translational movement (35m) along weak, sheared clay in Lower Cretaceous Clearwater Formation. The failure has a residual angle of 6° and the probable cause of shearing is valley rebound and swelling. It has a volume of 0.14 Mm3 with 1 basal shear plane and a large graben at the head of the failure. The presence of bentonite was noted at this site. A compound failure occurred in Cretaceous shale within the city of Calgary near the Western Irrigation District (WID) (Krahn and Weimer, 1984). The sliding surface was within the Paskapoo Fm, an interbedded mudstone, siltstone, and sandstone (Figure 2.6). The basal deep-seated horizontal movement occurred along a weak clay seam with a residual angle of the slope was 9°. The head scarp is interpreted as a rotational failure truncated by the same weak layer. 20 Figure 2.5 Little Smoky landslide (Thomson and Tweedie, 1975) * FltiOMIteie HVtt PAHUK KAMI » ">*• S3 m «a js» ton TOO (MMM| HORIZONTAL DISTANCE LEGEND | [ PLEISTOCENE (MAIMLT "MLO _|_ UPPER CBtrTACECXJS CO-fW SHAI_£> • uf>#es SHEAR r>ut,m mewrwmv m mamamiMm Figure 2.6 Western Irrigation District landslide (Krahn and Weimer, 1984). 21 2.3.2 Glacio-lacustrine Clay The Montagneuse slide occurred in 1939 on west wall of the Montagneuse River Valley (Cruden et al 1997). It is a large compound failure noted to be the largest historic rapid landslide on the Interior Plains with a volume of 76 Mm (Figure 2.7). The horizontal failure plane occurs within pre-glacial lacustrine sediments, with the mass subdivided into two main blocks, with the upper block breaking into many smaller blocks with oblique shears. There is little to no tilting of the debris masses and the rupture surface is relatively deep seated. This failure in this valley coincides with Shaftesbury pre-glacial channel of Peace River in common with many of the older, dormant landslides along this valley. Nasmith (1964) describes 2 different stages of retrogressive rotational slides within the Meikle River Valley in northwestern Alberta. The basal failure plane occurs within pre-glacial lacustrine deposits beneath clay-rich till. The volumes of these are not given but assumed to be quite large as they were hard to view from the ground (Nasmith, 1964). The south facing slopes were noted to be stable at slightly steeper angles, giving rise to a slight asymmetry of the valley. Till is observed within the debris confirming the location of the failure plane below the glacial deposit. A compound failure, 12 km northeast of the town of Rycroft, Alberta (Cruden et al, 1993), dammed the Saddle River. There is one deep-seated failure plane within a pre-glacial clay unit underneath a thick till unit on which the translational failure occurred (Figure 2.8). The trigger to this slide was lateral vertical and horizontal erosion as a result 22 of a severe rainstorm and it's resultant flood. The landslide was quite large with a volume of roughly 40 Mm3. The Attachie slide (Figure 2.9) is a flow slide occurring 50 km west of Fort St. John along the Peace River near the town of Attachie (Evans et al, 1996; Fletcher et al, 2001). This was a catastrophic event involving the glacio-lacustrine unit seen through out the Charlie Lake map sheet. The total volume of the slide was 12.4 Mm3, similar size to the case above. The clay is pre-sheared parallel to the bedding caused by glaciotectonism and postglacial landsliding. This was a rapid event that dammed the Peace River for approximately 12 hours. 23 Figure 2.8. 1939 Montagneuse landslide (Cruden et al., 1997) B 950-1 000 H 400 H 350 MN-1A • Pre landslide topography 288 'Hypothetical surfaces of rupture m —j , _. BOO SCO metres 1060 1200 1400 Figure 2.9. Rycroft landslide (Cruden et al., 1993) Figure 2.10. Attachie landslide (Fletcher et al., 2001) « JSO-i -500 1 Unpersfaps BIB Unit 6 CoHmiuni g__ Units pMt-zl»ciaJlamiiatal ctov Unit 4 Till Unit 3 S»nd Unit 2 Pre-glacial laminated clay and silt Eggl Unit I Cohhl*.'|rs*e! Stale Iwiwck — — Rupta* surface —*R> •-MSI--55..I JOO-J | | | | j | | | | | j | | | | f | j 1 1 1 1 1 1 1 1 1-I) io 100 130 3» MO m J» *» *50 500 JSO 6(0 «N 700 730 24 3.0 REGIONAL SETTING 3.1 Physiography The Charlie Lake Map Sheet lies on the western edge of the Alberta Plateau sub-province of the Great Plains (Bostock 1948, Holland 1964). The topography is subdued, reflecting the underlying Cretaceous bedrock, and includes northwesterly trending belts of rolling terrain with northeasterly directed drainage (Stott, 1982). The region is dissected by a deeply incised, integrated dendritic drainage system tributary to the Peace River, flowing through the area from west to east and draining the entire area. The Peace River flows within a broad, flat-floored trench that averages 3.2 km wide and 210 meters deep (Mathews, 1978). The walls of the Peace River and its tributaries rise sharply at angles close to 35° where the banks are cut into bedrock (Mathews, 1978), however the wall slope can be as low as 8° where failures have occurred. The upper platform above the river trench that connects the upland area to the river valley has a low continuous slope of about 1/4° to 2°, although it bears a significant amount of micro-relief of mounds and swampy hollows (Mathews, 1978). The current Peace River Valley, cut in post glacial time, mostly follows an interglacial valley of the Peace, which contains a dissected, complex Pleistocene fill (Mathews, 1978). Where the post-glacial channel follows the interglacial valley, the floor of the present trench is cut into the bedrock floor of the interglacial valley and is therefore lower (Evans, 1996). The significance of this is that the toe and basal shear plane of the landslides in the Pleistocene sediments lie above the present river valley (Evans, 1996). The downcutting also exposes steep sections of Cretaceous bedrock, allowing for failure along weak bedding planes. River elevations from Bobrowsky et al. (1991) at Hudson Hope (520 m) in the west and at the mouth of 25 the Kiskatinaw River (450 m) give an average gradient of the river over the 129 km section of 0.54m/km. 3.2 Climate The present climate of the Fort St. John area is continental boreal, marked by cold winters (January mean temperature -14°C), warm, humid summers (July mean temperature 15°C), and moderate annual precipitation, 465mm (of which 185 mm as snow). The summer maximum of precipitation includes frequent, intense thunderstorms. These values are averages from the last 30 years and categorize the area as sub-humid (Drinkwater et al., 1969). Annual precipitation in the region is unlike much of British Columbia, with peak monthly precipitation in July and drier in the winter months, however, it mirrors the style seen in most of Alberta. The cold winters are due to rolling uplands and prairies allowing Arctic air to flow unobstructed. With westerly-dominated winds, the nearby Rocky Mountain Range may act as a barrier, placing Fort St. John in a rain shadow. The Peace River region is within the Boreal White and Black Spruce biogeoclimatic zone (B.C. Ministry of Forests, 1988). On some south facing slopes, warmer plants such as the prickly pear cactus can be found locally in relative abundance. The south facing slopes are often covered with grass and scattered tree cover, while the north facing slopes are generally densely tree covered with few natural clearings. 26 3.3 Quaternary History The Laurentide Ice Sheet advanced over the Peace River area on at least three separate occasions during the Quaternary (Mathews, 1978). Cordilleran ice from the Rocky Mountains also reached the area to an unknown extent, and is thought to be contemporaneous with the last Laurentide advance. A bed of gravels represents the first glaciation with typical Canadian Shield gneiss within it. These gravels are found in one location within the map sheet, near Golata Creek. The second glaciation is represented by a small deposit of till above the aforementioned gravels and a thick bed of silt above the Peace River near Old Fort. These beds are localized and play little to no part in the stabilization of the river valley slopes. These deposits are represented by the light blue colour in Figure 3.1. This glacial episode was followed by a well-defined erosional interval, widening the valley to 6.5 km - 8 km wide and 30 m above the present level. During this event well-graded gravel was being deposited under aggrading conditions while the valley widening process occurred. The last, Late Pleistocene Laurentide advance from the east terminated this event. The ice-dammed Peace River likely began ponding early within the advance due to the size of the valley. This initiated a notable period of sedimentation of bedded sands, silts, and clays within a glacio-lacustrine environment. Because the lacustrine materials predate the maximum of the last glaciation, they are commonly referred to in the region as "Interglacial Clays and Silts", or ICS. There are local occurrences of ice rafted pebbles within silt and clay suggesting a close proximity of glacial ice front. These deposits are represented by the light red colour in Figure 3.1. 27 Figure 3.1 Quaternary Valley Fill Materials Location (based on Mathews, 1978) The last ice advance is marked by till and glacial grooves from the Laurentide sheet from the east and the Cordilleran from the west. It is thought that the two sheets met between Bear Flat and the town of Attachie (Mathews, 1978). The ice retreat was slow, and at stages allowed the level of glacial lake Peace to drop, creating smaller ice-damned lakes, ages 13,500 and 9,960 BP (Mathews, 1978). After the ice had retreated, the drainage of the lake occurred. This drainage caused rapid erosion of the present river valley, cutting through all of the sediments and into shale bedrock. 3.4 Local and Regional Infrastructure Two major highways run through the Charlie Lake map sheet. B.C. Provincial Highway 97, known as the Alaska Highway, stretches from the southeast section of the region through Fort St. John and continues toward the northwest on its way to the Yukon boundary. The Alaska Highway only crosses the Peace River once, however, its significance lies in the fact that many Canadian and American motorists use this roadway on travels toward Alaska. B.C. Provincial Highway 29 runs from Charlie Lake to the town of Hudson Hope at the southwestern corner of the map sheet. This road follows the Peace River Valley for most of its length crossing the valley slope 3 times. There are several smaller roads created for access to homesteads, logging areas, and petroleum exploration sites. Due to the considerable amount of petroleum exploration and extraction activities, an extensive system of oil and gas pipelines runs through the area. 29 4.0 BEDROCK GEOLOGY AND GEOTECHNIQUE 4.1 Outcrop Location The flat lying succession of transgressive-regressive marine to near-marine formations of the late Cretaceous are generally covered by a thick succession of Quaternary sediments masking much of the bedrock topography, resulting in very few natural bedrock exposures. Most bedrock exposures occur along deeply dissected river and creek valleys within the Charlie Lake map sheet (NTS 94A) (Figure 4.1). On the western border of the study area, near the town of Hudson Hope, the Peace River Valley exposes the Lower Cretaceous Moosebar, Gates, Hulcross, and Boulder Creek Formations, over a distance of approximately 17 kilometers. These formations are also well exposed along the entire length of Maurice Creek on the south bank of the Peace River; however, these locations are the only exposures in the map sheet. Stratigraphically above the Hulcross Formation lies the Shaftesbury Shale, which crops out along the rest of the Peace River Valley walls to the Alberta border. The Beatton River Valley also displays Shaftesbury Shale outcrops along its walls for much of its length to the town of Rose Prairie located approximately at 56° 30'. The Shaftesbury also crops out along the valleys of the Pine, Moberly, and Halfway Rivers within the map area. Other steep tributary channels within the Shaftesbury Formation include the Farrell, Septimus, Red, and Cache Creeks along with the mouth of the Alces and Kiskatinaw Rivers. The Sully group in the western section of the map sheet crops out only along the upper Halfway and the Cameron Rivers. 30 Figure 4.1 Bedrock Geology Map (based on Stott, 1982) E E o 5 3 co q. CO CO E £ E a> LL. O CO CO LT CO •go <_ » £ 8 2 « c £ W 3 _ co —: Q co co m co • • 1 • • O o OQ CO E CD CO O O At the Peace River and Cache Creek confluence, outcropping of the Upper Cretaceous Dunvegan Sandstone appears above the Shaftesbury Shale on the north bank of the Peace River Valley. This outcropping continues for 5 km where it recedes off the river valley at Wilder Creek. The Dunvegan sandstone appears on the Peace River Valley again near Golata Creek and continues to the Alberta border. West of Cache Creek, the Dunvegan Sandstone trends to the west-northwest toward Cameron River making an escarpment throughout the map sheet. On the southern bank of the Peace River Valley, the Dunvegan Sandstone outcrops near the confluence of the Pine River at the head scarp of a large landslide and within the Kiskatinaw and Alces River Valleys. The Smoky Group appears north-east of the Peace and Beatton River confluence to the Alberta border and extends to the top of the map sheet. It does not outcrop on either river (Figure 4.1). The Kaskapau shale, a formation with in the Smoky Group, is differentiated along the south walls of the Peace, Alces, and Kiskatinaw River valley walls near the Alberta border. 4.2 Description of Formations The Moosebar Formation, as mapped by Stott (1982), is part of the Fort St. John Group and consists of marine shales and siltstones. It has a maximum thickness of 290 metres in the Peace River Valley and lies conformably on the Gething Formation within the Bullhead Group and the Gates Formation. The shale of the Moosebar Formation is dark grey, rubbly to blocky, and contains reddish brown sideritic concretions. The basal shale grades upward into mudstone and siltstone until it comes in contact with a thick, continuous sandstone, which is the base of the Gates Formation. The shale beds have a 32 banded appearance with continuous and uniform layers from 1.5 to 10 cm. Stott (1967) reports thin bentonitic layers of up to 1 inch think, however, it is believed that these may in fact be weathered gouge layers created along bedding plane shears caused by valley rebound (Matheson and Thomson, 1973). This unit extends for the first 12 of 17 kilometres covered by the lower Cretaceous unit along the Peace River at the western border of the map sheet. The Gates Formation (Stott, 1967 and 1982) is a massive to thick bedded, fine grained, well-sorted sandstone lying stratigraphically above the Moosebar shale and is marked by a thick, continuous sandstone bed. The unit is roughly 18 metres thick at the 'Gates' on the Peace River, a resistant island of rock, but over 61 metres at Steamboat Island. The Gates sandstone represents a complete marine succession with a sequence of sandstone, shale, and conglomerate layers with the on lap sandstones getting coarser upwards within the sequence. The sandstones of the Gates Formation are brownish-grey, slightly rusty, and fine-grained with fine laminations and uniform beds. The beds are dominantly quartz and chert with minor amounts of rock fragments, carbonate detritus, and feldspar. There are often thin beds of platy sandstone and shale, and the sandstone beds grade laterally into shale to the north. Flow rolls are fairly common within the Gates Formation on the Peace River as well as ripple marks and mud cracks within the bedding planes. The upper boundary with the Hulcross Formation shows a distinct change from sandstone to dark, marine shale Stott (1982) mapped the Hulcross Formation as blocky to rubbly, silty, dark grey to black marine shale with sideritic concretions with no real bedding planes. The Hulcross shale thins to the south due to decreased sedimentation. The formation is stained 33 with limestone or a yellow powdery efflorescence caused by sulphur and iron weathering within the unit. The silt content of the unit increases upward within the unit and even becomes sandy to the top. The thickness and the number of sandstone beds increase upwards until the shale disappears. The shale is dense and structure-less with micro-granular carbonate with quartz, clay, and pyrite. Irish (1955) mapped the shale unit as being up to 113 metres thick east of the Gates Formation along the Peace River. The contact with the coarser Boulder Creek Formation above is also gradational and appears as a succession of siltstone and shale beds. The Boulder Creek Formation is a succession of conglomerate beds (Stott, 1982), however, along the Peace River, the beds have graded into flaggy, silty marine siltstone with interbedded sandstone. It is almost indistinguishable from the Gates Formation, except for a lower percentage of carbonate detritus. The sandstones are mostly made up of quartz and chert with some rock fragments and matrix. Irish (1955) estimated the thickness of the Boulder Creek Formation as 22 metres. The sandstones are thickly bedded, laminated, and have abundant ripples on the bedding planes with abundant ironstone concretions. Within the map sheet, the Gates Formation, Hulcross Formation, and the Boulder Creek Formation are mapped as one indistinguishable unit. The Shaftesbury Formation is a dark grey, flaky to fissile, rusty shale to mudstone, equivalent to the Hasler Formation and the Cruiser Formation to the south. The Goodrich sandstone, between the Hasler shale and Cruiser shale, grades into very silty shale within the Peace River Valley making the three formations undifferentiable. The unit contains abundant fish-scale layers, one of which is quite widespread and serves as a regional boundary unit between the Upper and Lower Cretaceous units. The lower 34 boundary of the Shaftesbury shale with the Boulder Creek Formation is distinct as the sandstone layers are directly overlain by dark marine shale, likely marking a hiatus. The upper boundary is gradational showing interbeds of shale and sandstone with the number of beds and their thickness increasing upwards. The beds of the Shaftesbury shale show a rhythmic development; flaky and fissile at the base to silty and blocky near the top. Stott (1982) was not able to give a thickness for the Shaftesbury Formation; however, it must be appreciable as the unit covers the entire Peace River from the Gates to at least the Alberta border. Stott (1982) maps several thin bentonitic layers, which may in fact be weathered clay within valley rebound bedding plane shears. In sections seen during the landslide investigations, there is appreciable degradation of the shale to a flaky texture with iron rich partings between the beds of shale. These partings are likely from alteration of bedding planes that have been disturbed during the valley rebound process. Along much of the Peace River Valley, the Shaftesbury shale represents the only bedrock unit exposed, as many of the Pleistocene sediments are deposited directly on the shale. This is due to the present river valley following the pre-glacial river valley, therefore, only exposing the lower units. The Sully Formation, generally recognized in the Sikanni Chief region, is seen in the western most area of the Charlie Lake map sheet. It underlies the vicinity west of the Cameron River and is roughly equivalent to the Shaftesbury Shale. The Sully Shale are dark grey to black, silty, rubbly, and contains sideritic concretions as well as the same 'fish scale' marker seen in the Shaftesbury Formation. The formation is conformable to the older sandstones to the west and the Dunvegan Sandstone to the east. 35 The Upper Cretaceous Dunvegan Formation is a prominent sequence of fluvial and deltaic sandstones and conglomerates, with minor shale, which form distinct escarpments along many river valley walls throughout the map area. This formation is quite large, having been mapped from the Smoky River in Alberta to the Liard River in northern British Columbia. In the Fort St. John area it has been mapped by Crickmay (1944), Russel (1943), and Jones (1968) and is estimated to be of a thickness near 305 meters (Stott, 1982). Although the type section is near Fort Dunvegan, there are well-exposed sections near Bear Flat on the Peace River near Cache Creek and within the canyons on the Beatton River (Figure 4.2). In the Peace River area it is generally a fine grained sandstone interbedded with shale. The sandstone is dominated by quartz and chert, with minor amounts of lithic fragments. Stott (1982) has done microscopic analyses of the unit, describing quartz grain boundaries and grain deformation. The Dunvegan Sandstone is conformable between the Shaftesbury Shale below marked by a well-bedded fine-grained sandstone that grades downward. South of the Peace River, the Kaskapau shale of the Smoky Group overlies the Dunvegan Sandstone conformably, with the contact being above a coaly horizon. Figure 4.2. Dunvegan Sandstone within the Beatton River Canyon 36 The Kaskapau Formation is the youngest of the beds in the area. The beds are thick, over 700 meters, and consist of dark grey, marine shales, separated into members by calcareous or sideritic content and concretions. The basal unit, the Sunkay Member, seen in the Peace River area, contains much siltstone and sandstone. It is part of the Upper Cretaceous Smoky Group, seen undifferentiated north of the Peace River due to lack of outcrop exposure. In terms of paleo-geography, the marine and near-marine sequence of sandstones, siltstones, and shales represents four transgressive - regressive cycles in the Western Interior Cretaceous Seaway during the Albian and Cenomanian periods (Plint, 1988). 4.4 Geotechnical Properties 4.4.1 Shaftesbury Shale During the 1970's and 1980's, several investigations were conducted on behalf of British Columbia Hydro to determine the geotechnical properties of the Shaftesbury shale (Cornish and Moore 1985, Sargent and Moore 1985, Imrie 1991). A proposed dam site, Site C, was investigated in order to establish the feasibility of constructing an earthfill hydroelectric dam on the Peace River, 6 kilometres southwest of Fort St. John. The Shaftesbury Shale is a compaction shale, heavily overconsolidated by Quaternary glaciations, that outcrops with slopes seldom steeper than 1H: IV along most of the Peace River valley within the 94A map sheet. The regional dip is 1° to 5° to the northwest with small amounts of localized thrust faulting. The shale is poorly consolidated and therefore is prone to rapid weathering and breakdown as it is conducive to decomposition and swelling. The bedrock has been identified as a soft shale based on 37 the Morgenstern and Eigenbrod (1974) classification. According to Cornish and Moore (1985) the content of clay sized material ranges from 35 to 49%, with Atterberg limits of 40 - 50 % for Liquid Limit (LL) and 21 - 25 % for the Plastic Limit (PL). The Shaftesbury Shale was found to be mainly quartz (27 - 52 %), interlayered illite / smectite (34 - 52 %), illite (0-11 %), and kaolinite (3-10 %). The rock shows swelling pressures ranging form 20 to 50 KPa. The intact rock is moderately strong showing a range of compressive strength of 6 - 28 MPa (Irnrie, 1991). The samples tested by Imrie (1991) show an average shear strength of <j)p = 45° and §T = 20°. After the removal of late-Wisconsinan ice loads, post-glacial rebound and erosional unloading with associated river valley cutting have caused a bulging of valley floor materials and stress-relief deformation of valley side materials known as valley rebound (Matheson and Thoomson, 1973). This caused an inward relaxation of the valley walls and possible shearing displacements as well as local cross cutting shear zones (Figure 4.3). Figure 4.3 Valley Rebound with deformation (Matheson and Thomson, 1973) 38 The outcrop examined in detail at Site C, was found to have three types of major discontinuities (Irnrie, 1991); 1) bedding plane failures, 2) cross-cutting shears, and 3) relaxation joints (Figure 4.4). These discontinuities are thought to persist throughout much of the Peace River Valley. Figure 4.4 Site C Damsite Schmetic with discontinuities (Imrie, 1991). The changes in stress regimes, vertical unloading, caused arching within the central valley floor, which is accompanied by limited shearing and fracturing along the bedding planes in the river valley walls. These bedding plane shear zones often act as slide surfaces for deep-seated failures within the bedrock even though they appear as tightly interlocked hairline partings. These partings can range up to 1 centimetre thick, allowing for shale softening and the development of gouge filling. These fillings generally have mineralogy similar to the rock, indicating the rock as a parent material. They appear white or yellow and can be confused with seems of bentonite and are laterally discontinuous as they pinch out away from the valley wall. The weak bedding planes also control the foundation strength of the Shaftesbury shale within the Peace River valley (Imrie, 1991). The cross-cutting shears occur with in the bed of the Peace River mostly dipping south with the remainder dipping to the north, causing the right bank to be more intensely 39 sheared compared to the left bank. They are generally thrust faults in nature and have a maximum thickness of 5 cm, infilled with gouge, breccia, infilling, and distorted bedding. Imrie (1985) found vertical offsets of 0.2 m to 3 m with a dip movement of 7.6 m and vertical offset always less than 3 metres. The south-dipping shears form a complex pattern striking 80° to 150° and dipping 15° to 30° away from the river. The residual friction angle was found to vary from (}>r = 12° to 20° with additional strength being provided by plane waviness at (|)i = 5°. Imrie (1991) discounts the remnant orogenic stresses as being a factor in their creation but rather suggests these features are valley rebound structures. The final structures observed due to valley rebound are rock relaxation joints due to inward movement of the valley walls. These are near-vertical fractures that parallel the river, observed in adits during the investigation of site C. Imrie (1991) reports relaxation joints as far as 35m in from the ground surface. These are at least partially infilled by broken rock and clay. Through rising and falling head tests, the permeability range was found to be 10"7 to 10"10 cm/sec with a downward head gradient. This is explained by the presence of the shear zones allowing water to saturate the upper beds of the shale while the lower beds remain out of equilibrium, therefore causing a downward gradient. During the summer of 2003, samples were collected to determine the bulk properties of the materials found in association with landsliding. The locations of the tested samples can be found on Figure 4.6. The samples consisted of slickenensided, remolded shale (8) and a disturbed gouge material (4) which appears in conjunction with the rupture surface (Figure 4.5). The samples were collected by locating the shear plane 40 and removing the slicked material with a knife. The samples were tested for Atterberg Limits and Grain Size analysis, using both sieve and Hydrometer methods, at the Fort St. John field office of AMEC Earth & Environmental Ltd. The test sheets can be found in Appendix I. A summary of classification results for the samples collected is given in Table 4.1. The sheared shale was found to have an average Liquid Limit of 49% and Plastic Limit of 20%. This indicates shale of moderate plasticity and not indicative of sheared material (Figure 5.1). The shale was dominated by silt with a mean of 70%, with minor amounts of clay, 20%, and sand, 10%. Hardy et al. (1962) suggest that the propensity of the shale to fail is determined more by bonding agents and pore water chemistry than by grain size alone. The test results of these failed shale samples would agree with their findings. Figure 4.5 Typical sampling area of sheared shale and gouge. 41 Figure 4.5 Tested Sample Location Map 42 Table 4.1. Summary of classification test results, shale and gouge Property Sheared Shale Gouge n = 8 n = 4 Liquid Limit (%) 49.1 50.7 {40-80} {45-56} Plastic Limit (%) 19.9 26.4 {16-30} {23 -30} Plasticity Index (%) 29.2 24.3 {20-51} {20-29} Clay Content (%) 20 11 {3-36} {4-22} Silt Content (%) 70 58 {50-85} {40-68} Sand Content (%) 10 31 {1-22} {23-38} n = number of samples tested The gouge material found in relation with the sheared shale displayed a higher Liquid Limit, 51%, however, the Plasticity Index proved to be lower, suggesting a higher concentration of coarser material. From the grain size analysis done on the samples, the sand component, 31%, appears to be higher than the shale and both clay and silt were lower, 11% and 58%, respectively. 4.4.2 Dunvegan Sandstone The Dunvegan Formation is very competent and acts as a cap rock for the weaker shale below. This allows the valley wall to achieve steeper slopes seen near Bear Flat on the Peace River, within the lower Beatton River, and at the Cameron and Halfway River confluence. In situations where the underlying shale is exposed, large bedrock failures occur as the static load of the Dunvegan Sandstone causes plastic deformation of the ductile shales below. Where the lower shale is not exposed in the upper Beatton, 43 Kiskatinaw, and Alces Rivers, deep canyons with stable walls are produced while the bedrock is exposed. The Dunvegan sandstone does produce large blocks that fall in the canyons, as there are discontinuities along bedding planes and minor amount of vertical jointing. Saint Simon et al. (1979) had investigated the Peace River Valley near the town of Dunvegan, Alberta, which also shows the Shaftesbury, Dunvegan, and Kaskapau Formations. At this site, stress relief jointing and horizontal bedding joints of the Dunvegan were observed, indicating that the valley rebound process is likely wide spread throughout the prairie environment, not localized to the Peace River. The claystone investigated at this site was found to be moderate to highly plastic and the shear strength of both siltstone and claystone were found to decrease with increased moisture content. The clay stone also shows residual angles of 13°. 4.5 Comparison with Other Prairie Shales The geotechnical properties of the Shaftesbury Shale were compared to those of other prairie shales located in Canada and the northwest of the United States. Data for this section was collected from published geotechnical papers (Cornish and Moore, 1985; Scott and Brooker, 1967; Haug et al.,1977; Peterson et al, 1960; Thompson and Hayley, 1975; Thompson and Tweedie, 1971; Thompson & Yacyschyn, (1977); and Beene (1967). Table 4.2 summarizes the Atterberg limits, peak and residual shear angle, and clay percentage are compared between the Shaftesbury Shale and the other shales. The Shaftesbury Shale has a plastic limit roughly equal to that of other prairie shales allowing plastic deformation at similar moisture content. Deformation occurs 44 without cracking with the consistency of stiff putty to soft butter (Conduto, 1998). This low plastic limit also allows a pre-sheared surface to remain within a plastic state at natural moisture content. The liquid limit of the Shaftesbury Shale is lower than most of the other prairie shales, permitting it to be at a liquid state at lower moisture content. The Shaftesbury Shale has a low plasticity index (29.2%) suggesting that it is of moderate plasticity (Sowers, 1979). The Kaskapau and Pepper Formations also show a medium plasticity, however, the Bear Paw, Belly River, and Edmonton Formations all have high plasticity indexes making them highly plastic shales. The Shaftesbury Shale was sampled using a rotary drill during an investigation for diversion tunnels within the left bank. The rotary drill probably did not allow for the bentonitic-rich layers to be sampled alone. This contamination makes the samples appear to be less plastic than they really are. The Shaftesbury Shale also has lower clay content than many of the other materials sampled. The residual friction angle of the Shaftesbury Shale at 20° appears to be much higher than the other materials listed below in Table 4.2. However, the listed value of 20° is thought to represent a bentonitic-poor zone within the formation, and therefore should not be used as a practical lower limit for strength within the formation as a whole. A lower value would be more practical to use for the shale of this area. The difference between the two values found for the Bear Paw Formation (Haug et al., 1977 and Peterson et al., 1960) was found to 14°. A similar difference should exist for the Shaftesbury Formation when testing bentonitic-rich and bentonitic-poor zones. Most of the prairie shales have residual angles within the range of 5° to 15°; therefore, a practical value for the residual angle for the Shaftesbury Shale would lie within this range. 45 Table 4.2. Geotechnical Properties of Prairie Shales Formation Liquid Limit Plastic Limit Peak Shear <t>P Residual Shear (j>r Clay % Source Shaftesbury 40-50 % 21-25% 45° 20° 35^9 % Cornish & Moore (1985) Bear Paw 65-100 % 20-25 % - 8U (Haug, 1977) 30-60 % Scott & Brooker (1967) Bear Paw 120% 25% 28° 22° Peterson et al (1960) Kaskapau 55% 31 % 34° 14° 38-43 % Thompson & Hayley (1975) Belly River 102-149 % 20-30 % - 8° 76% Thompson & Tweedie (1971) Edmonton-Bentonitic Shale 125-220% 30-45 % 14° 8°-10° -Thompson & Yacyshyn (1977) Edmonton -Bentonite 80-400 % 50-60 % 14° 5°-10° -Thompson & Yacyshyn (1977) Pepper 58% 26% 14° 9° - Beene (1967) 5.0 SURFICIAL GEOLOGY AND GEOTECHNIQUE The surficial geology of the Peace River area has developed primarily from glacial episodes during the Quaternary (Mathews, 1978), as described briefly above. The last two of these episodes left deposits in the region while the evidence of any older glaciations have not been found. Geomorphic processes have altered the glaciated landscape slightly to produce the modern topography. 5.1 Location Like the Cretaceous bedrock, the best exposures of Pleistocene sediments occur along the deeply dissected valley of the Peace River and its tributaries. Much of the valley exposures are so disturbed that a complete section is difficult to find, therefore, the stratigraphy has to be pieced together using head scarps and slump blocks of the landslides. The glacio-fluvial and glacio-lacustrine deposits are confined to pre-glacial valleys; however, till and post-glacial deposits are more can been observed widespread throughout the map area. The upland area is usually covered in blankets of till and glacial lake sediments with little to no exposure. The middle and north parts of the map sheet are 46 covered in an extensive bog land and muskeg. Much of the area that is not along the river valleys is covered in forest cover. Another important source of Pleistocene stratigraphy are the many road cuts made throughout the area as the local infrastructure is well developed. Road cuts may also be highly disturbed due to small-scale slumping and disturbance from construction. From oldest to youngest, the typical sequence of Late Quaternary materials within the Peace River Valley and environs consists of basal fluvial gravel, a thick sequence of interglacial silts, sands, and clays (ICS), a widespread blanket of basal till, and post glacial lacustrine clay. Within the Beatton River Valley, the sequence is often like Peace to the south, however, around the area of North Pine, a deltaic sequence begins to occur. Sands with minor beds of silt and clay dominate this deltaic sequence. The Halfway River is mostly filled with glacio-fluvial sands and gravels except for in the south where the river enters the pre-glacial valley. 5.2 Late-Quaternary Materials 5.2.1 Gravels The pre-glacial gravels are seen along the Peace River for most of its length, as well as some parts of the Beatton, Halfway, Pine, and Moberly Rivers. These are confined to the pre-glacial river valleys (Mathews, 1978), and are noticeably missing near Old Fort. The gravels have a rusted colour due to prolonged oxidation, well-rounded clasts up to 15 cm in size, and are partially cemented. The thickness of this unit varies from lm to 30m. It may act as an aquifer in some slopes. The unit is clean, gap-graded, and contains a sand matrix with pebbles and cobbles. There are a few sand beds up to 25 47 to 30 cm thick. Quartzite clasts dominate the unit with well-cemented sandstones, gray granites, and volcanics. Shield rocks are present but rare. The gravel has sharp contacts, top and bottom, with the bedrock always underneath. The unit has a fairly constant elevation above river level. Evans et al. (1996) suggest that the gravel unit does not play a part in the instability of the slope. 5.2.2 Pre-glacial Silt, Sand, and Clay The pre-glacial sand, silt, and clay lies above the gravels with sharp contact along the valley of the Peace River, much of the Beatton River, and the Pine, Moberly, and Halfway Rivers. It is roughly 100 to 150 m thick with silt or sand found at the base. For the most part, silt dominates sequence, except near the pre-glacial lake boundaries, where sand prevails. Sand can occur at any level (up to 35 m thick) and indicates aggrading fluvial condition. The beds are all well sorted, however, there can be extremely complex structures within this unit. Scattered pebbles are observed within the clay indicating the proximity to the glacial ice. Clay layers within the unit can be moderately to highly plastic, and can provide loci for landslides in the area (Mathews, 1978). This pre-glacial sedimentary package is not cemented but acts as a poor drainage element within most slopes on account of the interspersed, low conductivity clay beds. The upper contact with the till is sharp, although some intact rip-up blocks of silt and clay can be found within the till. Several samples were taken of this unit during the investigation of several of the landslides in order to help characterize the beds. 48 5.2.3 Late Wisconsinan Till The unit described in this section is from the final ice advance in this region as it is the only one that is preserved over the area. Mathews (1978) maps the till unit as two separate units from contemporaneous glacial advances from the Laurentian Ice Sheet in the East and Cordilleran Ice in the west. The two sheets coalesce near the town of Attachie. Even though the two tills are different, they are not distinct so will be considered one unit. Both tills rest on the interglacial river and lake deposits and act as an impermeable cap for surface recharge. Both are geotechnically more competent than the deposits below making them analogous to the sandstone above shale in the role that it plays in slope stability. The only difference seen between the two tills is that in the east the deposit has more gneissic clasts from the Canadian Shield and in the west, the deposit has more schist from the Rocky Mountain Trench. The basal till is clay-rich, massive, and shows a gradation of drop stones near the top as the ice receded above it. The unit has an average thickness of 15 m and a maximum thickness of max 28 m, being slightly thicker in the eastern part of the map area. 5.2.4 Glacial Lake Peace Clay The upper most unit within a typical section of the Late Pleistocene sequence is clay deposited from Glacial Lake Peace. It formed as water built up behind a glacier slowly retreating down the pre-glacial valley. The duration of deposition is a minimum of 220 years determined from counting varves within the deposit. The silt in the deposit forms distinct layers (fraction of an inch to feet thick) within clay, particularly in the 49 west. The unit acts as an impermeable cap controlling most of the surface morphology over all of the platform and upland areas. The clay has played role in initial drainage pattern in area after the retreat of the area. The most abundant material within the unit is clay with few or no stones on platforms to east, however, there is clay with scattered pebbles that may look like the till below. Sand and gravel is found within this unit, although it is limited to the former lake limits. The clay is firm when dry, and slick and sticky when wet due to its high plasticity. There are shallow failures contained within this unit on the Beatton and Halfway Rivers, however, it has no importance for deep-seated failures. The thickness of the clay unit shows greater isostatic rebound to west, suggesting that it has been ice-free for a longer period of time. 5.3 Geotechnical Properties Several samples of sheared and intact pre-glacial clay were collected during the field investigation of the selected landslides. The location of the tested samples is found on Figure 4.6. These samples were then tested for Atterburg Limits and grain size analysis at AMEC Earth & Environmental Ltd in Fort St. John. Tests to obtain material properties were conducted on the principle units involved in the slide movement and materials resultant from the movement. A summary of classification test is given in Table 5.1. The test sheets can be found in Appendix I. 50 5.3.1 Bulk Properties The pre-glacial lake clay deposits are generally classified as inorganic clay of low to medium plasticity (CL/CH) using the Modified Unified Classification System (Figure 5.1). Grain size analyses indicate that most of the samples originally described as clay are actually clayey silt with an average clay fraction of 30%. Few samples were relatively rich in clay, up to 57%. The clay fraction is not an indicator of failure potential as sheared clay beds had as few as 10% clay and intact beds had a high of 57%. Sand content is also a non-factor in stability as intact beds actually showed a lower average fraction of sand at 2%, than the sheared beds at 6% with a high of 25%. Many non-plastic silt beds were witnessed during the slide investigations beneath the sheared beds. These beds were rarely sampled and were not be analyzed. Figure 5.1 Plasticity Chart (Unified System) - Peace River Samples XShale - Sheared +Gouge AlntactClay •ICS-Sheared 60 50 10 < > A X * • X X A . 0 10 20 30 40 50 60 70 80 90 100 Liquid Limit 51 Table 5.1. Summary of classification test results for surficial materials Property Pre-glacial lake sediments Intact Sheared n = 4 n= 12 Liquid Limit (%) 47 50 {28-69} {39-73} Plastic Limit (%) 20 20 {17-21} {15-23} Plasticity Index (%) 28 30 {8-48} {18-53} Clay Content (%) 29 30 {1-57} {10-50} Silt Content (%) 70 63 {43 - 97} {49-86} Sand Content (%) 2 6 {0-4} {0-25} n = number of samples tested The Atterberg Limits of the clay indicate an average liquid limit is near 50 for both intact and sheared materials, bordering between high- and low-plasticity clay. The plasticity index for the sheared materials is only slightly higher at 30.3, making the clay highly plastic. The Atterberg Limits classify the material as medium to highly plastic clay while the grain size analysis suggests that the material is clayey silt. The till is classified as well graded, medium plastic silty clay (CL) by Fletcher (2001). 6.0 LANDSLIDE INVENTORY MAPPING SYSTEM 6.1 Slide Types in the Study Area To properly catalogue all of the landslides in the study area, two classification systems were created, based on activity and morphology of the landslides. Taking into 52 account previous classifications already in place (Hungr, Hutchinson, Skempton, etc), new classifications were developed for the activity and the morphology of the landslides. These classifications, as well as previously developed ones are discussed here. Slide types were defined in the order in which they were noted during the initial photo interpretation and desk study phases of the landslide inventory. Slide Type 1: Raveling The first type of slide identified in the Peace River region of British Columbia was simple raveling of the shale, sandstone, and cohesive surficial material (Figure 6.1). The scarps are generally clean as the process affecting them is active. The scarp height can vary although the debris apron will normally only accumulate on slopes with a height of at least 5m. There is no unique mechanism indicated here, as the process could be a simple fall, small scale slumping, or flaking of the material. The Shaftesbury Shale is easily slaked so the intact scarp tends to produce a weathered rind along the exposed face. Both the shale and the local clays and silts have very low impact strength so when the material strikes the intact ground or debris below it will accumulate producing an apron of undistinguishable debris. Often the scarp will be directly above the river so no accumulation can occur, however accumulations are common in the smaller creeks. The fissile nature of the shale and the steep relaxation joints and bedding plane discontinuities produced from the valley rebound process allows for small pieces to constantly break off. Often the shale breaks in paper-thin partings. This shale paper will flake off and slides down the shale face. The pre-glacial lacustrine deposits tend to break apart along silt interbeds and vertical jointing, also causing blocks of materials to fall. 53 Slide Type 2: Retrogressed Rotational Failure The heterogeneity of both the Shaftesbury shale and the Pleistocene sediments generally does not favour single rotational failures. Instead the rupture surface will extend along a weak layer within the slope. Multiple rotational slides in the Peace River occur from upslope progression of a single rotational slip with a more or less planar basal shear surface, which terminates as a curved back scarp. Retrogression of the slide forms two or more slipped blocks with slip surfaces tangential to a common slip sole (Hutchinson, 1988). After an initial small failure, the intact scarp behind the failed mass becomes unstable, since toe support has been removed. This unstable scarp fails and now removes support for the next failure. In the Peace Region, the new failure can occur along the same plane or on a nearby weaker layer within the slope that can now be utilized. If the curved back scarp has a weak layer within it, a new failure will often occur along that discontinuity, as the toe has now been unloaded. These failures will retrogress further as successive slices become unstable from the removal of lateral support. The slope eventually self-stabilizes when the build up of debris downslope provides sufficient buttress support for materials further upslope (Figure 6.2). When the debris is removed, the intact section will become unstable again. These failures can progress a long distance into the slope as both the shale and the clay can fail at low angles and there are many weak layers with in both that can be mobilized. During air photo interpretation, it can be very hard to distinguish these failures from compound failures. Often the difference is the lack of extensional features and the presence of back tilted blocks both near the head of the failure and within the debris mass. These features are often difficult to locate and the interpretation must by supplemented with a field examination. On older, dormant or 54 abandoned slopes, the ability to distinguish these features is reduced remarkably as the features are overgrown and weathered. A majority of these failures occur within the Pleistocene sequence, although they are not exclusively to it. When the failures occur within the upper portion of a section, removed from the erosive force of the river, they generally become stabilized and difficult to recognize. Slide Type 3: Rotational Failure The third type of failure recognized in the study area was a single rotational failure (Figure 6.3). These failures occur mostly within pre-glacial sediments, although they can also occur at a very small scale within Cretaceous shale. A majority of these failures occur on the south-facing slopes, although there are a few cases on north-facing slopes as well. As mentioned, single rotational failures rarely occur in earth materials that are heterogeneous and anisotropic, however, if the basal shear plane truncates the curvilinear failure plane deep within the failed mass, the movement will remain mostly rotational. The Peace River area has many rotational failures, even though the horizontally bedded materials are not a favorable material for such a movement. These rotational failures occur within the pre-glacial sediments at locations were the heterogeneity is at a minimum. The Pleistocene sequence is more favorable than the shale because of the weaker compressive strength of the material and a smaller discrepancy between the plastic and non-plastic materials. Many of the non-plastic clay layers actually act to hold the unconsolidated materials together, allowing for the curved back scarp to occur. As most of the failures within this region occur above river level, the debris of the rotational failure is often disturbed and does not appear as a slumped block but rather broken up debris covering the slope. Pre-sheared surfaces allow the initial 55 movement to occur and in most cases will allow the material behind to mobilize. These failures are important to recognize because many of the larger failures may actually begin as a rotational slide, which unloads the toe and lets a larger mass to fail. Generally, rotational failures in this area are of small size and occur either within Pleistocene materials or within the landslide debris of larger failures. Such failures may involve either intact or remobilized material. The small size of these failures makes their identification difficult using high-level photographs. Slide Type 4: Mobile Flow Several highly mobile flows, likely mudflows within the colluvium derived from the pre-glacial sand, silt, and clay or the post-glacial clay (Figure 6.4), were identified during the air photo investigation. These failures generally occur within gullies cut into river bluffs and show the typical fan shape at the exit point of the gully. Hungr et al (2001) classifies these failures as mud flows, which are extremely rapid or slower, fine grained flows of liquid clayey soil. They are shallow failures occurring during heavy rainfall and snowmelt seasons. These are small, continuing processes that build up to form gentle fans near the mouth of the gullies. They occur in a range of sizes from 5,000 m3 to 500,000 m3; however, they are often very small and shallow. These failures were identified and noted within the air photos and database but not examined in detail in the field. Slide Type 5: Earth Flow A few slopes were identified as containing earth flows or earth flow complexes (Figure 6.5). These failures occur within the colluvium derived from the underlying 56 Pleistocene materials. They generally occur in the far western section of the study area around the town of Hudson Hope. Hungr et al. (2001) defines these movements as earth flows that are slow movements of earth near its plastic limit, sliding as a plug-like mass. They mostly occur within the gullies although they can also happen along the main valley walls as well. These failures occur exclusively within the pre-glacial valley boundaries. This type of failure was not examined in the field, only recognized during the air photo interpretation. Slide Type 6: Multi-level Failures The majority of the failures within the Peace River area utilize several weak shear planes at different levels. These are considered multi-level failures (Figure 6.6). The compound failures can involve any combination of the other slide types mentioned. The presence of two very weak materials, shale and pre-glacial clay, in which many shear planes can exist at different elevations, make this a dominant type of slide. There are two types of multi-level failures occurring within the study area: those in which the failures are independent of each other and those that appear to have failed together. If the failures are independent of each other, then there is an intact scarp between the two failures that is not covered by debris or colluvium. The debris from the upper failure may play a role in the stability of the lower failure(s) but the shear planes are not connected and distinct form each other and the failures occurred at different times. These failures are generally shallower and can occur in either material. Shear planes that have failed simultaneously, are generally deeper within the slope. The debris mass that has failed is large enough to cause the other failure too occur roughly at the same time. If the mass is not large enough to move a second mass, the disturbed material can either fail by itself or be buttressed and 57 supported by the stable material. When the stable material fails, debris from both shear planes will be mobilized. This also occurs in both materials. Slide Type 7: Compound Failure The Shaftesbury shale contains bentonitic-rich layers that are widespread, which allows a sheared surface to propagate deep into the slope leading to the development of large, low-angle compound failures (Figure 6.7). Many of these failures are dormant, so the original morphology of grabens and horsts is not recognizable on air photographs. These failures are prevalent on the north-facing slopes, although not exclusively. Most of these failures are older, making the features difficult to recognize both on the air photos and on the ground. Within the shale, the failures are thought to occur on pre-sheared surfaces at many different elevations above 420 meters a.s.l. Below this, no shear planes were witnessed or inferred. This type of failure also occurs within the pre-glacial sequence with the largest failures occurring near the base of the sequence. These failures can be large, up to 60 Mm3. Extensional features within the debris, such as horst and grabens, as well as the low angle at which debris can be found, distinguish these failures from all others. At very low angles of slip, a Compound failure is more likely than a rotational failure. Slide Type 8: Shallow Retrogressive Failure Shallow retrogressive failures (Figure 6.8) occur exclusively within the Glacial Lake Peace clay. These were only witnessed along the Halfway River (Bobrowsky, 1991) and near the canyons on the Beatton River. The till below acts as a stable base below, which the failure plane cannot penetrate. The basal shear plane normally coincides with 58 Figure 6.1 Slide Type 1: Raveling - Photo and Schematic Diagram (inset) Figure 6.2 Slide Type 2: Retrogressive Rotational Failure - Photo and Schematic Diagram (inset) 59 Figure 6.3 Slide Type 3: Rotational Failure - Photo and Schematic Diagram (inset) 60 Figure 6.5 Slide Type 5: Earth Flow - Photo and Schematic Diagram (inset) 61 Figure 6.7 Slide Type 7: Compound Failure - Photo and Schematic Diagram (inset) the surface of the Wisconsinan till. The sediment involved remobilizes and flows over a stable bench. The debris mass is thought to undergo quick disintegration and flow in a fluid-like manner. The retrogression occurs quickly and can extend for a slope angle of 3.5°. The mandate of this report was to focus on deep-seated failures, so this type of failure was not surveyed during fieldwork, only recognized during air photo interpretation. 6.2 Activity Classifications Many attempts to create a system in which to map landslides in terms of activity (Cruden and Varnes, 1996), intensity (Hungr, 1997), and morphology (Sissakian et al., 1983 and Yanez, 1979) have been made, however, as of yet none have been fully recognized. This is partly due to the highly variable nature of slope movements around the world and the complexity of the mapping systems needed in order to map them. The landslide mapping system used for this project is a hybrid of previous classifications and unique features used for the Canadian Prairies. Cruden and Varnes (1996) describe 6 states, Active, Suspended, Reactivated, Dormant, Stabilized, and Relict to describe the activity of a landslide. Active failures are those that are currently moving and reactivated failures are those which are currently active after being inactive. Suspended failures were defined as failures, which have been recently active, within the last annual cycle of seasons but not moving at present. Dormant movements include inactive landslides in which the cause of the movement remains apparent. Failures in which the toe has been protected against erosion are described as being stabilized, and those in which the failure occurred under different geomorphic or climatic conditions are described as Relict. This system is not practical for 63 use in the Peace River Area, as almost all of the slopes within the river valley are actively moving. The rate of the movement is the main difference. The failure planes on which the failures occur extend into the slope further than the current failure boundaries, therefore new movements can occur. This makes an otherwise "stabilized" slope still susceptible to failure, therefore, categorizing it as stable would be misleading. Another issue is that much of the debris of the initial failure remains on the slope due to the low angles of the failure planes. This debris moves very slowly, therefore, it is currently moving but to classify it as active would also be misleading. The contention is that there are very few stable slopes and that the classification has to reflect the relative activity of the failure. Hungr (1998) describes a method of mapping landslides in terms of intensity. Hungr (1988) defines intensity as the set of quantitative or qualitative spatially distributed parameters, which determine the potential of a given landslide phenomenon to cause damage. If this inventory is to develop into a risk map, then the intensity of the failures should be considered. A map of this nature could not be undertaken at this time due to the lack of full knowledge of the elements of risk. Due to the preliminary and broad nature of this map, only the recognition of a hazard and the estimate of size could be undertaken. Hungr (1988) uses an incremental classification system based on the return period of a landslide to create a system of mapping failures relatively. This method was deemed unfeasible for this project, as the failures are not discrete movements in which a return period can be calculated, but rather constant slow moving failures, which seemingly randomly fail catastrophically. A hazard map would be difficult to produce in this area as all of the slopes are failing. Generally (the Attachie Slide being an exception), once a slope is failed it is 64 known and can fail again, but it actually reduces the hazard as the slope is at a shallower angle and is closer to stabilizing itself. It is the slopes that have not failed catastrophically in recent times but have known failure planes that are of a high hazard. An activity classification was developed to distinguish landslides and landslide areas, according to their degree of recent movement activity. This may allow for possible landslide triggers to be identified. As landslides are ubiquitous within in the area, the most active areas were identified to distinguish areas of higher hazard. In this way, a determination of the most active areas can be made for practical purposes. Although the active areas are distinguished, other slopes should not be thought as safe and stable, as dormant slopes have been known to fail catastrophically as in the Minias Creek Slide (Thurber, 1982). Another important reason for developing an activity classification was to help determine whether or not different types of slides had different activities. This may allow for a temporal analysis of mechanism or mode of failure. Cruden and Varnes (1996) discuss activity under three separate headings; State of Activity, Distribution of Activity, and Style of Activity. Within the classification used for this project, only the state of activity is considered, which is defined as what is known about the timing of the movements. Activity levels were defined from dated air photographs taken between 1997 and 1945, and by site investigation during the summers of 2002 and 2003. Photos used for this purpose are noted in Appendix A. Due to the size of the area, not all river segments were visited in detail and therefore the index may show them as less active than they really are. Also, due to the small scale of the air photos, not all active features may have 65 been recognized. The activity levels created for this project are: 1) Very Active, 2) Active, 3) Low Activity - Dormant, 4) Low Activity - Abandoned, and 5) Modified. Very Active slides are those that have failed within the last 5 years, in this case since 1997. They show up as a red colour within the inventory and had a very fresh appearance during the investigation (Figure 6.9). These slides were classed by field investigations done by the author and from reports from practicing engineers and geologists in the region. The river valleys were flown over during the summers of 2002 and 2003. The five year cut off for very active slide grouping was chosen because smaller features tend to begin to be muted after this time period and young trees begin to appear. It also allows practioners in the area enough time to add observed slides to the database. Active slides are those that have failed within the last 50 years, in this case since 1953, excluding the above Very Active cases. In the inventory they appear with a light blue colour. In the field they can range from looking fairly fresh with no vegetation cover to grass covered with smaller trees (Figure 6.10). This activity can be hard to define in the field, as aspen grows at a very fast rate. Landslides with this activity were determined by studying air photos from 1985 and 1945 along with geological and geotechnical reports from practicing professionals within the area. The ground generally looks disturbed with stands of younger trees; however, after about 50 years the slide can become indistinguishable from the rest of the slope. This classification exists because the investigation of these landslides may still be useful for understanding slide mechanics within the area. With a separate classification, they can be selected and visited. After approximately 50 years, the features of the slide can become distorted and muted by weathering, leading to false interpretations. Also the work that has been done in the area 66 within the past 50 years can be added to the inventory in order not to lose a valuable resource. Low Activity - Dormant landslides (Figure 6.11) are those, in which movements are probably older than 50 years, yet they still have active erosion near the toe (e.g., fluvial undercutting). Within the inventory they appear as a green colour. These failures are mainly determined through air photo interpretation with some selected field studies. This is an important classification because even though some of the river slopes appear to be stable, they still contain one or more pre-sheared layers within them. These pre-sheared planes allow the slope to fail easily with even a small trigger. The probability of failure is higher due to the active erosion as it can either undermine intact material at the toe of the landslide making it more susceptible to failure or transport debris of older sliding movements so that it can not act as support for the toe. Low Activity - Abandoned landslides are those that are older than 50 years and do not currently have active erosion at the toe (Figure 6.12). They appear as the colour purple in the inventory. For this classification, an understanding of river morphology must be incorporated to deduce where past river erosion has taken place. These slopes are marked as they have failed since glacial times and therefore also likely contain sheared clay layers within the slope. For practical purposes, they are mapped due to the possibility of remobilization along the shear plane if the slopes are disturbed, either naturally or anthropogenically. As river erosion is a major trigger within the area, slides situated away from the river are less likely to fail and therefore of a lower hazard. The final class of landslide defined within the area is Modified. These are landslides that have been stabilized by artificial earth works after failure (Figure 6.13). They are 67 Figure 6.9 Very Active Landslide (Photo) 68 Figure 6.11 Low Activity - Dormant Slide (Photo) 69 almost always along a part of the infrastructure, including roadways, railways, or pipelines. In order to be part of this grouping, the slide features have to be disturbed enough to be unrecognizable. These are important slides to note because in the years to come, the slope will be weathered and all traces of a failure will be erased. These slides must be noted so that the presence of the shear plane is not lost to other investigators. One of the problems encountered using this classification is that some slides show different activities within different sections of the slide. A slide with an active toe and a dormant top must be defined as one or the other. In this case, the activity which best describes the majority of the slide will be used. 6.3 Morphological Symbols for the Inventory Map A set of morphological symbols was designed for use on the landslides in the Peace River Area during this project. The features used for this inventory are seen in Figure 6.14. This is based upon Yanez (1979). Figure 6.14a is the first symbol defined and is used to denote a large scarp within intact material. Intact material is defined as any large mass of material that has not previously failed, whether it is bedrock or Quaternary material. A large intact slump block is, therefore, mapped as debris rather than intact material. A large scarp is defined as any scarp that measures over 1.0 mm in plan width on the air photos used. The air photo sets (BC 86047, BC 86074, BC 86075, and BC 86099) are flown at a high altitude with a resultant scale of 1:60,000. The large scarp therefore corresponds to 60 meters in horizontal length. The same symbol is also used for large, nearly vertical cliff scarps whose length is not represented properly on air photos. 70 Figure 6.146 is used for large scarps within defined debris masses. This includes any materials that have incurred any movement including creep and intact blocks that have moved. Large scarps within the debris mass are rare but do occur on the larger failures. The symbol has the same shape as the intact material in order to allow the large slopes to be easily picked out. Often the determination of intact or debris material is difficult, therefore, when the material is in question, the conservative approach was taken and the material is assumed to be debris. Figures 6.14c and 6.14 identify symbols used to denote small scarps within the study area, in intact material (rock or soil) and debris respectively. The latter symbol was created with a similar appearance to the small scarp in order that all small scarps could easily be identified. The definition of a small scarp includes any scarp with a down slope plan length less than 60 meters. This symbol is also used for a small vertical scarp. This is a very common symbol often used to denote a cliff. It was chosen to represent a small scarp due to the practical smaller size. An arrow attached to any of the above symbols, indicates a movement in the direction of the arrow. The arrow by itself does not indicate a type of slide but rather the direction itself. A failure with this symbol is usually a rotational failure with no obvious back tilt or an older translational or compound failure. Other symbols within the failure can determine the type of slide. Figure 6.14e is a symbol that represents back tilting within the debris mass. The arrows from the head scarp and the arrows from the debris meet at the base of the head scarp. The symbol used for the head scarp depends on if the material is intact or in debris and the size. 71 Figure 6.14/*represents the extensional feature of a graben and is usually used in conjunction with Figure 6.14g, which represents a horst. These symbols are not dependent on size and because these features only occur in debris, the intact version was not considered. In the case where a horst is at the base of a head scarp, the two features coalesce at the base of the head scarp. This symbol is used exclusively on compound and compoundfeatures. The symbol for a debris apron is represented by Figure 6.14/?, which can be used in conjunction with any of the other symbols to represent the debris of the slide. It can also be used by itself if a debris apron is observed at the base of a slope with no clear features. An example of this would be the base of a raveling slope. The above symbols can by combined in order to define most of the landslide types defined in Section 6, however, two unique symbols were created to describe specific conditions. A highly mobile flow is indicated by Figure 6.14/. The scarp at the head of the failure depends on the size and material. The body of the displaced material is outlined with an arrow outlining the suspected path of flow. A less mobile earth flow is represented by Figure 6.14/ with the head scarp symbol defined by the size and material found. The body of the debris is outlined. The area in which debris has been removed is represented by a concave curve, the center of the mass is a straight line, and the accumulation area is represented by a convex curve. When an earth flow complex covers the whole slope, then the symbol represented by Figure 7.7e is used. The scarp symbol depends on the material and size. The use of the morphological symbols in describing the eight landslide types described in Section 6.1 is shown in Figure 6.15. 72 Figure 6.14 Morphological Classification Symbol Description Large Scarp (Intact Material) A large scarp is defined as any scarp that measures over 1.0 mm in plan width on 1:60,000 scale air photos, corresponding to 60 meters in length. This symbol is also used for large, nearly vertical scarps whose length is not properly represented on air photos. Intact material is defined as any large mass of material that has not previously failed, whether it is bedrock or Quaternary material. Large Scarp (in Debris) A large scarp, defined above to be over 60 meters in length in plan view, within a defined debris mass.This includes any materials that have incurred any movement including creep and intact blocks that have moved. The symbol has the same shape as the intact material in order to allow the large scarps to be easily picked out. The arrow indicates that movement in that direction has occurred. Small Scarp (Intact Material) A small scarps is defined as any scarp mesaureing less than 1.0 mm in plan width on 1:60,000 scale photos, corresponding to less than 60 meters in length. The scarp may be within any intact material, Cretaceous bedrock or Quaternary sediments. It was chosen to represent a small scarp due to the practical smaller size. Small Scarp (in Debris) A small scarp, defined above to be less than 60 meters in length in plan view, within a defined debris mass.This includes any materials that have incurred any movement including creep and intact blocks that have moved. The symbol has the same shape as the intact material in order to allow the small scarps to be easily picked out. The arrow indicates that movement in that direction has occurred. e • • • Backtilt This symbol represents back tilting within the debris mass. The arrows from the head scarp and the arrows from the debris meet at the base of the head scarp. The symbol used for the head scarp depends on if the material is intact or in debris and the size f 1 l 1 1 l • ••ii Graben This symbol represents the extensional feature of a graben, usually used in conjunction with Figure 7.6g. This symbol is not dependent on size and only occurs in debris, therefore the intact version was not considered. This symbol is used exclusively on translational and rotational-translational features. g Horst This symbol represents the extensional feature of a horst, usually used in conjunction with Figure 7.6/ This symbol is not dependent on size and only occurs in debris, therefore the intact version was not considered. This symbol is used exclusively on translational and rotational-translational features. h ^^^^ » J Debris Apron A debris apron is an accumulation of debris. This symbol can be used in conjunction with any of the other symbols to represent the debris of the slide. It can also be used by itself if a debris apron is observed at the base of a slope with no clear features. Mobile Flow (Mud Flow) Mobile Flow is a highly saturated mass of fines moving in a fluidized manner. The scarp at the head of the failure depends on the size and material. The body of the displaced material is outlined with an arrow outlining the suspected path of flow. Earth Flow Earth Flow is an intermittent flow of plastic clayey earth moving in plug-like manner. The head scarp symbol defined by the size and material found. The body of the debris is outlined. The area in which debris has been removed is represented by a concave curve, the center of the mass is a straight line, and the accumulation area is represented by a convex curve 73 Figure 6.15 Landslide Type Examples using Morphological Classification a Ravelling b Retrogressive Rotational Failure c Rotational Failure d Mobile Flow e Earth Flow (Complex) d Multi-level Rotational Failure — 1 u^v. f Compound Failure g Shallow Retrogressive Failure 74 7.0 LANDSLIDE INVENTORY 7.1 Objective The primary focus of this thesis was to create a landslide inventory that could be used by practicing geologists and engineers working in the Peace River area. The hope is that this thesis will form the basis of the most detailed inventory of landslides in Canada, to be continuously added to and updated as more information is collected. The inventory will be implanted into a geographic information system (GIS) that is tied to a database that has been compiled during the inventory. This will hopefully become available through an open file from the Geological Survey of Canada - Terrain Sciences Division webpage. This inventory is not to be used for design purposes; however, it may give an insight to a prospective or practicing landslide investigator. Further detailed fieldwork is necessary in order for the inventory to be more reliable. The inventory is entirely based on air photo interpretation and the relatively limited field experience of two summers. The inventory and models are to provide a basis of ideas, to be added to and argued with. Due to the large size of the study area, small features on individual landslides may have been misinterpreted or missed. These features may help determine or completely change landslide type. 7.2 Referencing System Before an inventory can be attempted, a referencing system must be in place in order to know where the slides have occurred. The landslide inventory is a linear inventory as almost all of the region's landslides occur within the current river valleys. The linear nature of the inventory requires a linear referencing system, in this case the river valleys had to be referenced. The size of the study area forced the referencing 75 system to be detailed and ordered in a way that is easy to reference. The system breaks down the entire area into 6 smaller, more manageable areas (Figure 7.1); 1) Peace River, 2) Beatton River, 3) Southern Tributaries, 4) Beatton River East, 5) Halfway River West, and 6) Halfway River to Beatton River. Each of these six areas was then broken down into individual rivers or large creeks. Smaller creeks are simply incorporated as tributaries to the larger creek or river numbering system. The total distance covered by this referencing system was 1292 kilometers (Table 7.1). Figure 7.1 Reference Areas for Landslide Inventory 76 The Peace River division includes the Peace River and the Peace River Valley and covers 276 kilometers. The distinction is made because the current river level has created its own slope segments within the larger, Peace River Valley. No other rivers were added to this division because of the quantity of landslides and river segments within the Peace River valley. It is a large enough division without adding any other rivers as the river traverses the entire map sheet. The Beatton River division is another that only has a single river within it. The Beatton River runs for almost the entire map sheet from the north to the south, incorporating 265 kilometers worth of river valleys. The number of tributaries to the Beatton River would make the division unmanageable. The third division, Southern Tributaries, includes the Pine, Moberly, and Kiskatinaw Rivers. It also includes Maurice and Septimus Creeks. The bottom of the map sheet truncates all of the above-mentioned waterways except Septimus Creek. The rivers and creeks are tied together by the geographic boundary of the Peace River and were an easy target to group. The number of river segments was limited by the map sheet boundary limiting the total amount of distance covered to manageable size of 200 kilometers. The fourth division established is Beatton River East, which incorporates the Doig, Alces, and Osborn Rivers as well as Milligan Creek. The Beatton River in the west and the Peace River to the south act as the boundaries of the area. The section encompasses 194 kilometers of river valleys, which is 15% of the whole area. Milligan and Osborn Rivers to the north, have only a few slides that are large enough to be 77 recognized, however, if a slide occurs, they will be able to be placed within the referencing system. The area from the Halfway River west is the fifth area to be defined. It includes the Halfway and Cameron Rivers as well as Ground Birch and Farrell Creeks. There is 263 kilometers of River Valley within this section. This area is mostly outside of the pre-glacial valley and is underlain by the Sully Formation and not the Shaftesbury Shale (Stott, 1982). The Pleistocene sediments here are outwash sands and gravels (Mathews, 1978) so the number of failures and their types should vary in this division. It is also very easy to separate this western section as a separate unit. The final division is made up of the rivers and creeks between the Halfway River in the west and the Beatton River in the east and north of the Peace River. The waterways include the Blueberry River and St. John, Red, and Cache Creeks. This area is upon the upper plateau and underlain by the competent Dunvegan Sandstone, so a majority of the activity in this section occurs within the pre-glacial valley boundary near the Peace and Beatton Rivers. There is only 94 kilometers (8%) of referenced river slope within this section. Table 7.1 Measured Distance within Slope Segment Districts Division Peace Beatton S. Tributaries Halfway Beatton Halfway River River West East to Beatton Kilometers 276 265 200 263 194 94 measured % of Total 21.4 20.5 15.5 20.4 14.9 7.3 The individual rivers within the divisions were then broken up into separate river segments. This was done by examining the topographic map and breaking the slope up 78 into subjectively defined segments that appear homogeneous in terms of slope dimensions, stratigraphy, morphology, and activity. There were no maximum length criteria used as an entire valley wall could be classified as one slope segment as long as there were no large breaks in the wall (i.e. gullies) or distinct changes in direction or average slope angle. After both banks of each river were broken into these dissimilar slope segments, the segments were then numbered. The banks were numbered independently of each other, starting with the segments nearest to the mouth of that river. In the case of the Peace River, the numbering began in the east at the Alberta border and finished in the west at the Peace Canyon Dam. If a small creek, located along the valley wall, was made of more than two segments, it was labeled independently, with the number scheme matching that of the rivers. The left and right banks were numbered independently starting where that creek meets the larger river valley. In this manner, all slope segments within the study area were numbered independently of each other. For this exercise, the left bank is defined as the bank on the left hand side of the viewer while viewing in a downstream direction. Each river and creek was then given an identifier so that the river and the segment could easily be recognized (Table 7.2). For example, the eleventh segment on the left bank of the Beatton River is labeled as BL-11. Smaller tributaries that were large enough to be labeled separately but not large enough to have their own identifier were given a tributary identifier based on the larger river. The tributaries were also numbered starting at the mouth of the river with the left and right banks labeled separately. For example, the third segment of the right side of the sixth tributary found on the left hand side of the Peace River is labeled as PL-T6R 3. 79 Table 7.2. River Identifies within Charlie Lake Map Sheet River Identifier River Identifier River Identifier Alces A Ground Birch GB Peace P Beatton B Halfway H Peace Valley Pv Blueberry BB Kiskatinaw K Pine Pi Cache Creek Cc Moberly M Red Creek Rc Cameron C Milligan Creek Mc Septimus Creek Sc Doig D Osborn 0 St. John Creek SJc Farrell Creek Fc North Cache Creek NCc 7.3 Methodology Once a referencing system was in place, a database of landslides could be compiled. Before any landslides were identified and catalogued, a referencing system for the landslides themselves was created. This system is to be used in combination with the river slope segment referencing system, in order to locate a particular slide. The landslide format is set up similarly to the segment system and uses the same identifiers (Table 7.2). The main difference is that the numbering scheme is different. The landslides are numbered in order of their identification and not geographically oriented. This was done to allow for new slides to be placed within the inventory without using further qualifiers (e.g. BRlb). A new failure would appear as a higher number in the same slope segment. An example of this full labeling system is given for slide PiR-23 located on slope segment PiR-8 PiR-23 - PiR-8 Slide Identifier <*"7 ^ Slope Identifier 80 With a system of referencing the slides and their location in place, the identification of individual slides and slide complexes above a minimum size of 10,000 m2 could be properly undertaken. Within the 6 previously defined divisions (Peace, Beatton, Southern Tributaries, Halfway West, East of Beatton, and Halfway to Beatton), the valley slope of each waterway was studied using high level air photographs with a scale of 1:60,000. These photos were used because they matched the 1986 Trim data, for which a complete set of maps is available at 1:20,000 scale. The photos were of good quality with only a small amount of cloud cover and good contrast between tones. High-level photos were used in this initial interpretation to cover the large study area efficiently. Black and white photos were used to minimize the amount of noise witnessed through the stereoscope. Enlarged laser quality photocopies of the air photocopies were made and used to record the observed features. These copies were enlarged to a scale of 1:30,000, allowing for many of the smaller features to be identified. The enlarged copies were bound together and used for interpretation. The copies were useful during the analysis as they could be marked on. As features were recognized, they were marked on the copied photos with one of four coloured markers, blue, green, orange, and purple (Figure 7.2). These colours corresponded to the defined activity levels of Active, Dormant, Abandoned, and Modified. Active failures were defined by the relative freshness of the failures, marked by a distinct tone change due to the difference in vegetation. Dormant slides were those that were older with toes currently being eroded and abandoned were those that did not appear to be currently eroded. Many modified slopes were previously defined by geotechnical reports. Very Active slides were not defined using the 1986 air photos, as they had not occurred yet. Very Active slides were 81 defined outlined by fieldwork during the summers of 2002 and 2003. As the features were delineated on the photocopies, slide types were recognized and defined (Section 6). All failures outlined to that point were then classified and the same classification applied to all future failures outlined. 7.4 Database During the interpretation, a set of information was developed and then recorded in a database for every failure. This information set includes: Failure Identity, Slope Segment Identity, Activity Level, Failure Type, Waterway of Occurrence, Air Photo Identity, Probable Material of Basal Shear Plane, Length, Width, Area, Aspect, and Additional Information (Appendix IV). This information was placed within a database of all failures. The waterway of occurrence is simply the river or creek on which the failure occurred. The air photo on which the failure occurred was also recorded so that the photos could be easily retrieved. The probable material of the basal shear plane was identified on the basis of the bedrock geology map created by Stott (1982), the surficial geology map created by Mathews (1978), and by field observations. Both the bedrock and the Pleistocene sequence are made of materials that are horizontally bedded within highly plastic layers. This leads to a similar morphology in landslides within both materials. The similar morphology can make the determination of the materials involved very difficult. Only the basal shear plane material was inferred, as many of the failures have multiple shear planes and only the basal plane can be estimated. The length and the width were estimated from the air photos and the area was calculated from these values. The aspect of the failures was also measured off the air photos in order to help analyze 82 slide type trends. The additional information category incorporates any other pertinent information. Once the initial inventory was completed using the air photos from 1986, the data was checked against air photos from two other time periods, 1945 and 1997 at a scale of approximately 1:10,000. This allowed the slides marked as "Active" to be cross-checked against the older photos and the "Very Active" slides to be cross-checked by the younger photos. The larger scale photos also allowed for selected sites to be examined in more detail. Unfortunately, the entire area was not checked and only partial cross-checking could be accomplished. The activity of some of the landslides was very hard to determine as the slopes have all experienced failure since deglaciation. Some of the failures appear to have undergone a slow deformation with periodic larger movements. It is possible that many of the failures are actually younger than they appear on the photographs, with small movements remaining undetected. After the database had been updated and cross-checked by the secondary photographs, the slide outlines and features were transferred from the photocopies to the hardcopy 1986 TRIM maps (Figure 7.3). This was done manually, drawing the features on the map as they appear on the photocopied air photographs using coloured pencils corresponding to the colours of the activity classification. Once the landslides were transferred to the map sheets, they were digitized in order to create a digital version of the landslide inventory. The landslides were digitized at a 1:20,000 scale using a Summagraphics ® SummaSketch ® II Professional Tablet (Model: MM II1812) into AutoCAD ® 2002. This 83 Figure 8.2 Landslide Outlines on Enlarged Photographs Figure 8.3 Landslide Outlines on TRIM map Figure 8.4 Digitized Landslide Outlines produced a digitized version of the landslide inventory within a single file. All features and outlines were reproduced as they appear on the map sheet (Figure 7.4). The landslide locations were normalized by the Universal Transverse Mercator Projection (UTM) using North American Datum - NAD 83. Within the AutoCAD program, normalizing with UTM allows the slides exact location to be given only in UTM co-ordinates. Map boundaries and labels were also reproduced to serve as a locating device. Only the map sheets in which failures have been found to exist were included. The water way(s) in contact with the landslide were digitized as well. 7.5 Results 7.5.1 Distribution The total number of slides identified during this inventory is 1610. The analysis of all of the slope failures is done with respect to the divisions defined during the initial stages of the inventory and as an entire area. All results are summarized in Appendices IV and V. The divisions that contain the largest number of slides are the Peace River Valley containing 465 slides, roughly 28.9% of all slides, and the Beatton River Valley containing 407, approximately 25.3%. The higher values for these two rivers are due to the length in which they occur within the pre-glacial valley limits. Within these boundaries, the presence of valley fill and rebound features within the shale bedrock are more prominent than outside of the boundaries. The rest of the slides are allocated as follows, Southern Tributaries contains 255 failures (15.9%), Halfway River West contains 216 failures (13.4%), Beatton River East contains 137 failures (8.5%), and Halfway River to Beatton River contains 130 failures (8.1%) (Table V-3; Appendix V). 85 As the total number of kilometers was measured during the initial investigation, an average ratio of slide per kilometer was determined for each division (Table V-3). The highest ratios of slide per kilometer are 1.82 occurring within the Peace River Valley and 1.60 within the Beatton River Valley. This ratio for the Peace River Valley is slightly underestimated as the were many slides coalescing and indistinguishable becoming long slide complexes, often persisting longer than several kilometers, especially along the south valley wall. The Beatton River ratio is also somewhat misleading as the ratio is skewed by large tracts of valley walls in the northern part of the river and bedrock canyons within the middle of the river that do not show many failures. The southern section of the river alone would have a much higher ratio. The remaining sections have the following ratios, Southern Tributaries (1.28), Halfway River West (0.82), Beatton River East (0.71) and Halfway River to Beatton River (1.38). The total failed area was also calculated for each division as well as the ratio of area per slide (Table V-3). Even though the Peace River Valley and the Beatton River Valley have a similar number of failures, the area covered by the Peace River (258.92 km2) failures far exceeds that of the Beatton River (151.98 km2) (Table V-3). This suggests larger failures on the Peace River (0.56 km2/slide) than the Beatton River (0.37 km2/slide); likely due to pre-sheared bedding planes protruding further into the valley wall. These longer pre-sheared surfaces are likely due to the size of the post-glacial river and the relatively quicker rate of excavation. There are also a larger number of rock falls identified within the Beatton Canyons, which generally have small volumes. The Southern Tributaries division has a 0.59 km2/slide ratio with an overall area covered of 151.62 km2. The failures within the Halfway River West section cover a total area of 116.79 km with an average size of 0.54 86 km2. The Beatton River East sector covers a total of 33.01 km2 with failures and an average of 0.25 km2 per slide. Sandstone bedrock canyons along the Doig and Alces Rivers control this small average failure size. The Halfway to Beatton River section has a 2 2 total area of 53.13 km , which is covered by failures with an average size of 0.49 km . 7.5.2 Activity An activity value was assigned to each slide during the investigation. This allows for the activity to be divided with respect to area, failure type, aspect, and material involved. The results are given as percentages with respect to the respective divisions and as an average through out the entire area (Table V-l; Appendix V). This relative comparison allows for separate divisions to be compared to the whole study area. The dominant activity throughout the entire map sheet is "Low Activity-Dormant" with 61.0% of all failures. This activity has a high in the Halfway to Beatton River division with 80.8%. "Very Active" failures comprise of 1.9% of all failures, or 30 landslides. The area with the highest activity is the Beatton River Valley with 4.2% of all failures in the division being "Very Active" and over half of all of the "Very Active" failures in the region. "Active" failures comprise 12.9% of all failures, with the Beatton River East (16.8%), Halfway to Beatton River (15.4%), and Beatton River Valley (15.2%) with higher than average active failures. Combining "Active" and "Very Active" failures together, allows for the analysis of every slide that has failed within the past 50 years. These activities together comprise 14.7% of all failures in the area, making the Peace Region one of the most active areas in British Columbia, over that time period with 237 landslides. "Low Activity-Abandoned" failures include 22.9% of the areas landslides, 87 with a high of 40.7% in the Halfway River West division. There are 23 "Modified" slides over the area with a majority of that (12) with the Peace River Valley. The area for each activity level was calculated and compared within the division and throughout the entire study area (Table V-7; Appendix V). The area distribution of the landslides is similar to the location of the slides with respect to activity with Activity 3, "Low Activity-Dormant" dominating with 58.6% and "Low Activity-Abandoned" with 30.7%. The increase with respect to "Low Activity-Abandoned" suggests that the average size of failures is decreasing. This is supported by the "Active" and "Very Active" failures representing smaller areas as a percentage than in number as a percentage. This indicates that the active failures are smaller than the failures with a lower activity. "Modified" slides are represented by a similar percentage in size and number, 1.5%. The failure type for each activity was determined and compared within the division and throughout the entire study area (Table V-9; Appendix V). "Very Active" slides are dominantly multi-leveled failures, which consist of 73.3% of that activity level. The number of type 6 failures along the Beatton and Peace River Valleys heavily influences this number. "Active" failures are also dominated by multi-leveled failures, 43.0%, however, there is a larger component of rotational, 20.8%, and retrogressive rotational failures, 23.7%, which resembles the values for the overall type values. The values slightly change when analyzing "Low Activity-Dormant" failures as the percentage of retrogressive failures actually falls to 12.6%, and Compound failures rises to 7.3%. Multi-leveled failures and rotational failures consistently comprise of a large percentage of the failures at 48.8% and 25.8%. "Low Activity-Abandoned" failures show a similar distribution of failure types with 44.0% being multi-rotational landslides, and 88 33.4% being rotational. The value for rotational failures is likely inflated by the conservative classification of a deep-shear plane. A large majority of multi-level failures exists within the activity 5 grouping, "Modified" with a total of 17 failures, which represents 73.9% of this activity. There are no strong trends within this analysis, therefore, it cannot be said that failure type is changing with time. It can however be said that retrogressive rotational failures and multi-level failures are harder to recognize as the features become muted, thus being classified as a rotational failure. The slope aspect for each activity level was determined and compared within the division and throughout the entire study area (Table V-l 1; Appendix V) using the groupings described in 8.4.5. 30% of all "Very Active" landslides had a northern aspect, which is twice the average and corresponds to 9 failures. This is opposite to the over all trend of landslides with respect to aspect, which showed a higher number of failures on the south-facing slopes. "Active" slides are fairly evenly distributed with slightly higher values of south-facing, 17.9%, and east-facing, 18.4%, slopes. "Low Activity-Dormant" failures and "Low Activity-Abandoned" failures follow the overall trend displaying a higher proportion of south-facing slopes with both activity levels displaying 19.3% of their landslides having a southern aspect. "Modified" failures are generally on the south-facing valley walls, 26.1%, as a majority of the infrastructure runs along south-facing slopes. This value is influenced far more by location of infrastructure than landslide activity. The material, suspected or known, containing the basal shear plane for each activity level was determined by geologic maps and field investigations. The values were then compared within the division and throughout the entire study area (Table V-10, 89 Appendix V). "Very Active" slides are predominantly within the Quaternary sediments, with 73.3% of failures of this activity. Most of these failures, 63.6%, occur within the Beatton River Valley, north of the Sandstone canyons. "Active" failures are more evenly distributed between the materials, with 43.5% of the slides within the shale bedrock, and 56.5% in the pre-glacial sediments. The dominant activity, "Low Activity-Dormant", displays an even distribution of materials, with 47.2% of failures in shale and 52.8% in the Quaternary materials. Two exceptions to this average are the Southern Tributaries, with 66.4% of failures in shale, and Beatton River East, with 64.9% of failures in shale. Of the "Low Activity-Abandoned" failures, 62.8% of the failures are within the Pleistocene sequence, while only 37.2% are in the shale bedrock. The same divisions, Southern Tributaries and Beatton River East, show a dominance of bedrock failures. "Modified" failures occur evenly within the shale, 43.5%, and the silt, sand, and clay, 56.5%. 7.5.3 Failure Type The failure type of each slide was assigned during the investigation. Each failure type was then divided with respect to area, activity, aspect, and material involved. The results are given as percentages with respect to the respective divisions and as an average through out the entire area (Table V-2, Appendix V). This relative comparison allows for separate divisions to be compared to the whole study area. The dominant failure type within the Charlie Lake map sheet (NTS 94A) is the multi-level failure with 47.8% of all landslides, which corresponds to 769 slides. The Peace River and Beatton River Valleys display higher values than average for this type of failure. This number may be slightly underestimated as slides in which the mode of failure is uncertain are conservatively 90 designated as a deep-seated failure, either single rotational or retrogressive rotational landslide. Conversely, the values of the deep-seated single rotational and retrogressive failures may be bolstered by this conservatism with values of 26.3% and 13.0% respectively. The Halfway River West division has a very high component of single rotational failures, 44.9%, due to the homogenous nature of the pre-glacial material in the area. Compound slides with one shear plane are fairly uncommon in the Peace Region due to the low number of weak shear planes available for failure. Compound failures comprise 6.5% of all failures with a high of 15.4% within the Halfway to Beatton River section. The remaining failures make up a total of 6.4%, with raveling at 0.6%, mudflows at 2.1%, earth flows at 2.4%, and shallow retrogressive failures at 1.4%. The area for each failure type was also calculated and compared within the division and throughout the entire study area (Table V-8; Appendix V). As expected from above, the failure type, which covers the most area, is the multi-leveled failure with 53.1%. Even though compound failures do not represent many failures in terms of number, they do represent a larger number in terms of area, 13.8%. This suggests that compound failures are larger than other failures, which is supported by the average size calculated for each type of failure. The average size for a compound failure is 1.0 km2/slide, whereas the average size of the next largest type slides, earth flows, is 0.61 km2, and multi-leveled failures with an average size of 0.53 km2. The activity levels for each failure type was determined and compared within the division and throughout the entire study area (Table V-l2, Appendix V). Most retrogressive rotational failures are "Low Activity-Dormant" representing 59.1%, of all slides of this type, while 23.3% are "Active". Rotational failures are also have a dominant 91 activity of "Low Activity-Dormant" at 59.8% with the "Low Activity-Abandoned" activity representing 29.1%. Multi-level failures have a higher than average amount of "Very Active" failures at 2.9%, however, the failure type is also dominated by the "Low Activity-Dormant" activity level, 62.3%. Compound failures have a very high component of the "Low Activity-Dormant" activity level at 68.8%, with 21.0% represented by "Low Activity-Abandoned" failures. There are very few active compound failures. The slope aspect for each failure type was determined and compared within the division and throughout the entire study area (Table V-14; Appendix V) using the groupings described previously. Raveling occurs with all aspects, although more have been identified on south-facing scarps, 30.0%, then other aspect groups. Of the aspect groups analyzed, retrogressive rotational failures occur at a higher frequency on the east-facing slopes, 19.5%, and west-facing slopes, 19.5%, than on the north-facing slopes and south-facing slopes. Rotational failures occur more often on south-facing slopes, 20.8%, than on the other aspect groups examined. Both mobile mudflows and earth flows are also dominantly on the south facing slopes, with 27.7% and 21.1% respectively. South-facing slopes have more multi-leveled failures, 19.9%, than the other aspect groups. Of the compound failures within the study area, 31.4% of them occur on north-facing slopes, with only 6.7% occur on north-facing slopes. This may in fact be due to the regional dip of the bedrock towards the northeast. 31/8% of all shallow retrogressive failures occur on west-facing slopes, mostly within the western portion of the map sheet. The material suspected or known to contain the basal shear plane for each failure type was determined by geologic maps and field investigations and compared within the division and throughout the entire study area (Table V-13, Appendix V). Mobile 92 mudflows, earth flows, and shallow retrogressive failures are all completely within the Quaternary materials or colluvium derived from these sediments. The dominant failure type, multi-leveled failures, is evenly distributed between the shale, 51.9% and the silt, sand, and clay, 48.1%. The Southern Tributaries and Beatton River East divisions heavily influence the overall average, with values of 90.7% and 82.1% respectively. Compound failures are dominantly within the shale bedrock, 61.9%, especially within the Peace River Valley, 79.3%, and the Halfway to Beatton River section, 75.0%. Single rotational failures are mainly found within the Quaternary sequence, 64.8%, heavily influenced by the Peace and Beatton River Valleys. Retrogressive rotational failures have basal shear planes with in both materials evenly with shale containing 41.4% and silt, sand, and clay with 58.6%. 7.5.4 Material Involved Each slide was assigned a material suspected or known to be involved with the basal shear plane during the desk study using geologic and surficial maps and field investigation. This allows for the materials to be divided with respect to activity, failure type, and aspect. The results are given as percentages with respect to the respective divisions and as an average through out the entire area (Table V-4, Appendix V). This relative comparison allows for separate divisions to be compared to the whole study area. Both the consolidated shale bedrock and the pre-glacial sediments have a propensity for failure as observed by the distribution of materials involved in failure. Shale represents 43.7% of material in which the basal shear plane is located, while the Pleistocene sequence represents 56.3%. This equal distribution is one of the reasons why landslide investigation is so difficult in the Peace River Region. The material in which the failures 93 shear plane is not witnessed can be difficult to determine. During this investigation, surficial geology maps and bedrock maps were consulted along with field investigation, but often what is needed is geotechnical drilling. Divisions that have a higher precentage of shale failures are Southern Tributaries with 65.3% and Beatton River East with 60.6%. Quaternary failures dominate the Beatton River Valley, 65.1%, particularly in the northern section, Peace River Valley, 60.4%, Halfway River West, 65.7%, and Halfway to Beatton River, 56.9%. The activity for each basal shear plane material was determined and compared within the division and throughout the entire study area (Table -15, Appendix V). Mirroring the overall activity, both the shale and the Quaternary sequence are dominated by "Low Activity-Dormant" failures. The value for shale failures that are dormant is slightly higher, with 65.9% than the silts, sand, and clay at 57.5%. Shale and Quaternary failures show similar amounts of "Active" and "Modified" failures, and Quaternary failures have a higher percentage of active failures at 2.4% compared to 1.1% within the shale. The failure type for each material involved was determined and compared within the division and throughout the entire study area (Table V-16, Appendix V). Multi-rotational failures make up 56.5% of all shale failures, with rotational failures and retrogressed rotational failures comprising 21.1% and 12.4% respectively. Failures in shale have a much higher component of compound failures with 9.3%, over double of the amount within the Pleistocene sediments, 4.4%. The distribution of failures in the silt, sand, and clay is more widely distributed as mudflows, earth flows, and shallow retrogressive failures occur within the sequence. The dominant failure type within the 94 surficial material is multi-leveled failures as well, with 40.7%. The unconsolidated sediments have a higher percentage of rotational failures, 30.3%, and retrogressed rotational failures, 13.6%. The Halfway River West division shows a large component of rotational failures within both of the bedrock, 48.6%, and the surficial materials, 43.0%. The slope aspect for shale and surficial failures was determined and compared within the division and throughout the entire study area (Table V-l7; Appendix V) using the above groupings. This was done primarily to observe the difference between aspects in the Cretaceous bedrock, as it has a slight regional dip towards the northeast. The shale bedrock does show slightly more failures in the south facing and west facing slopes with 18.3% and 17.9% respectively. Conversely, the north-facing and east-facing slopes have below average values at 13.8% and 14.9%, respectively. To understand this, the analysis of type and aspect has to be revisited, as there were a large number of compound failures on the north and east facing slopes. Also, if the analysis of area and type is re-examined, then it can be seen that the average size of compound slides is much larger than others. Therefore, the lower number of shale failures facing the north and east is due to larger compound failures that occur in that direction. Overall, there appear to more failures on the south and east facing slopes, likely related to the size of failures. 7.5.5 Slide Aspect A slide aspect was determined for each slide using maps and field investigation during the inventory. These aspects were then grouped into north-facing slopes (330°-30°), east-facing slopes (60°-120°), south-facing slopes (150°-210°), and west-facing slopes (240°-300°). This allows for the aspect to be divided with respect to activity, failure type, and material involved. The results are given as percentages with respect to 95 the respective divisions and as an average through out the entire area (Table V-5, -6; Appendix V). This relative comparison allows for separate divisions to be compared to the whole study area. If landslides occurred in every direction equally, the average value of occurrence would be 16.7% as the aspects were assembled into 60° groups. Therefore, aspect groupings greater than this average have a higher density of failures. These grouping are the east, south, and south-east facing slopes, the highest of which is the south-facing group at 19.1%. The north-facing slopes have a smaller percentage due to the number of failures that coalesce to form complexes. The activity levels for the aspect groupings were established and compared within the division and throughout the entire study area (Table V-18; Appendix V). Of the north-facing failures, 56.6% are "Low Activity-Dormant", 26.1% are "Low Activity-Abandoned", 12.4% are "Active" and 4.0% are "Very Active". This aspect grouping has a relatively high percentage of "Very Active" failures, when compared to other aspects. East-facing slopes have a higher percentage of "Low Activity-Dormant" slides, with 66.5%, as well as a higher percentage of "Active" failures at 15.3%. South-facing failures also have a high component of "Low Activity-Dormant" failures with 62.4% as well as a high percentage of "Low Activity-Abandoned" failures at 23.4%. West-facing slopes have a similar distribution with respect to activity with 63.6% of the failures being "Low Activity-Dormant" and 20.1% being "Low Activity-Abandoned". No obvious trends of the slide aspect exist with respect to activity. Failure types for each of the aspect groupings were established and compared within the division and throughout the entire study area (Table V-19; Appendix V). For north-facing slopes, the majority of the failures are multi-leveled failures making up 96 48.1%, with the conservative value of 19.5% for rotational failures. Compound failures comprise 14.3%> of the north-facing slopes, while they only make up 2.2% of the south-facing slopes. Multi-leveled failures account for 47.3% of the south-facing slopes with rotational failures making up 27.8%. East-facing failures have a high percentage of shallow retrogressive failures, 13.2% and conversely a relatively very low percentage of multi-leveled failures, 37.5%. West-facing slopes have a high number of multi-leveled failures, 45.1%, and rotational failures, 27.8%. The trend seen from this analysis is that there are more compound failures on north-facing slopes, whereas all other aspects seem to be fairly evenly distributed between types with higher values belonging to multi-leveled failures. The material suspected or known to contain the basal shear plane for each aspect grouping was determined by geologic maps and field investigations and compared within the division and throughout the entire study area (Table V-20; Appendix V). All of the aspect groupings have a fairly even distribution of materials, with the Quaternary materials being slightly higher in each case. This mirrors the overall allocation of materials involved in basal shear planes. 55.8% of all north-facing failures are within the Quaternary materials, dominated by the Beatton River Valley, 72.3%, and the Halfway River West division with 91.7%. South-facing failures are similarly distributed with 58.0% of all failures within the silt, sand, and clay. East-facing failures have the Pleistocene sequence involved in 57.3%, while west-facing failures are slightly lower at 51.9%. There are no distinct trends involving the material with respect to the aspect of the slide. 97 8.0 DETAILED INVESTIGATION OF SELECTED LANDSLIDES AREAS For a directed field study, four areas were chosen to be investigated in detail (Figure 8.1). These area were named : 1) Big Bam Ski Area, 2) Old Fort, 3) Beatton -Big Bend, and 4) Christian Camp. These areas were chosen due to their importance to the area, both sociologically and scientifically, the variety of materials within these sites, the variety of landslide types, their accessibility, and their proximity to the city of Fort St. John. Each area is described in detail including location, stratigraphy, and profiled landslides. A generalized stratigraphy was created from exposures mapped during the field season and published geologic information on the area. Each slide was investigated in detail with a description and a interpretation within this section. Profiles were conducted using an inclinometer, a range finder, and a 50m measuring tape during the summer of 2003. Given the stratigraphy and the interpreted mechanisms of the landslides, a generalized geologic model was produced to better explain slope movements within that area. These models were then considered at the scale of the map sheet in an attempt to explain landsliding in the Fort St. John area. 98 Figure 8.1 Detailed Landslide Study Areas 99 8.1 Slide Area 1 8.1.1 Location Six slopes were profiled near the old Big Bam Ski Hill approximately 4 kilometers south west of the town of Taylor on the south bank of the Pine River at the confluence with the Peace River (Figure 8.2). The area extends for 3.5 km along the north-facing slope and encompasses the ski hill, part of Septimus Creek, and an abandoned residential area. At the upper elevations, the head scarps of these slides border on a farm field. Much of the area is overgrown except for where the younger landslides have a disturbed surface and where the vegetation has been cleared for the ski hill paths. The ski hill was in operation as late as mid-1996 (Zandbergen, 1999). The area was chosen due to the relative easy accessibility and it's proximity to a highly active, much-discussed area (Hardy, 1952; Maber and Stewart, 1976). The area is also a very distinct landmark with in the Peace River area as many local residents still use the area for recreation purposes such as horseback and ATV riding. 8.1.2 Local Stratigraphy This site is within the pre-glacial valley (Mathews, 1978) and is underlain by Shaftesbury Shale. The shale bedrock elevation has been noted at three slides (Slides 1-1, 1-5, 1-6) at a constant elevation of approximately 397 meters a.s.l. with a small variation of 0.3 meters. Bedrock was seen in near vertical exposures mirroring the steep sided bedrock exposure on the opposite side of the Pine River. This angle likely persists to the depth of the current river. 100 Figure 8.2 Landslide Area 1 Above the bedrock lies a bed of Pleistocene sand and gravel with a fairly constant thickness of 8.5 meters with a variation of approximately meter to an elevation of 405 meters a.s.l. The sand and gravels were noted at three of the six profiles completed (Slides 1-1, 1-5, 1-6). The unit was lightly cemented and iron stained and the well-rounded gravel ranged in size from 4 cm to 12 cm and contained small lenses of sand 20 cm thick. A fossil was found intact within these gravels on Slide 1-6 at 402.5 a.s.l. (Figure 8.6). Above the gravels lies a thin bed of sand seen in 2 of the profiles. In the west (Slide 1-1), the bed has a thickness 0.2 m and in the east (Slide 1-6) the bed is 0.1m thick. In the two profiles where this unit was seen directly above the gravels, the beds do not show the same facies suggesting the pre-glacial sand, silt, and clay unit is variable at the base. A different section of this unit was seen in Slide 1-4 at 446 m a.s.l. The section was completely dominated by weakly bedded sand with a thickness of 15 m. No shear plane could be found at this locale above the sand although one is inferred to be at approximately 457 m a.s.l. Another intact section of weakly bedded sand was observed in the same profile (Slide 1-4) at 489 m a.s.l. The sand unit was 16.5 m thick extending to an elevation of 505.5 m a.s.l. Above the sand is a 4 cm bed of massive clay (sample 1-4B) followed by a 4 cm bed of laminated silt and clay. Directly above the clay and silt beds is a 1 mm thick softened clay shear plane (sample 1 -4A) in which highly polished shear surfaces were observed. Above the shear plane was massive debris made mostly of sand with some silt and clay; These same beds of sand-rich deposits were observed to the west (Slide 1-3) at 493.6 meters a.s.l. This exposure became silt rich near the top (522.6 m a.s.l.) with frequent interbeds of clay. At the top of this unit is a bed of silt with drop 102 stones that resembles till seen at an elevation of 543 m a.s.l. Lake Peace clay and till were not witnessed at this location; however, the silt near the top of Slide 1-2 and Slide 1-3 appears heavily disturbed and could be near the upper limit of the pre-glacial unit. The presence of drop stones suggests a close proximity of ice when deposited. The top 10 metres very well may be till, however, it was difficult to tell the till from the underlying strata. An approximate stratigraphic column is produced (Figure 8.3). Figure 8.3 Area 1 - Stratigraphic Profile (not to scale) -543 m a.s.l »•••+•»»»••••• -506 m a.s.l -457 m a.s.l -406 m a.s.l -405 m a.s.l -397 m a.s.l Till - grades below with drop stones Laminated Silt, Sand, and Clay - contains at least 2 shear planes, sand-rich near bottom Found or Inferred Shear Planes Sand and Gravel - Intact fossil found at 402.5 m a.s.l Shale Bedrock - extends to depth 103 8.1.3 Landslides Slide 1-1 Slide 1-1 is on a northwest-facing slope, within the Septimus Creek valley (Figure 8.7). The profile starts within a field and continues down slope at an azimuth of 290°. Using the previously defined activity classification, the upper section is active showing some fresh features, the middle section is dormant, and the toe is very active. The slide contains three failure plains. The upper two planes were both covered with debris and interpreted from surface morphology. Near the head scarp, the features are generally small suggesting that the failure planes are shallow instead of one deep plane. There are minor amounts of back tilt suggesting that the failures are compound. Small mobilized debris flows occurred near the head of the slide, obliquely cutting the profile. A rounded diapiric structure was observed 50 meters off the profile to the east for which an explanation is still not clear. Then there is a lengthy section with a disturbed hummocky surface with a small overall gradient. The area is thought to be a compound section because of the muted horst and graben features witnessed during the traverse. At the end of this section a remobilization of the debris has occurred which is expressed by major scarp in debris. A shear plane was examined at 407 m a.s.l., 20 m to the northwest. This is thought to be the same failure surface controlling the profiled failure. A sample of this shear plane was sampled and found to be a clayey silt of low plasticity with a silt fraction of 61. Figure 8.4 shows the pre-glacial stratigraphy directly below the shear plane. Below the debris, intact rubbly shale was observed. The bedrock surface likely drops at a steep angle to the level of the current creak elevation, as this was likely a cut bank before the slope above it 104 failed. The debris at the creek level is remobilized debris activated by erosion from the present creek. Downstream of this failure on the opposite bank, a failure within the shale mass was witnessed at 10 metres above the creek bed. Figure 8.4 Intact Pre-glacial Stratigraphy (Slide 1-1) Slide 1-2 The second profile in the area was done along the tower line of the Big Bam Ski Hill that failed in 1997 closing operations permanently (Figure 8.5). The profile started near a farmer's field and continued down the north-feeing slope on an azimuth of 345°. There were no exposures of shear planes or intact materials found during the traverse, however, many of the features can be interpreted from surface morphology and comparisons with nearby slopes. The slide is understood as having three failure planes, all within the pre-glacial sand, silt, and clay unit (Figure 8.8). During the upper part of the failure, the features were small indicating that the failure planes were relatively shallow. 105 There was enough displacement in the upper portion of the failure to force many of the ski towers to fall over or tilt, however, the movement appeared to have been compound with little rotational component. Further down slope, a large horst was observed, suggesting a new failure surface much deeper with little or no rotational displacement being observed. The bedrock is suspected to underlie the deep compound failure and then sharply dropping off causing debris to slide over and producing a steeper slope within the debris. The toe of the slide is remobilized debris. Figure 8.5 Former Big Bam Ski Hill Tower Line (Slide 1-2) This active slide is at the western edge of the Big Bam ski area and has a north-facing slope. The profile starts on a ridge caused by an abutting failure on Septimus Creek. The profile goes down slope at an azimuth of 7°. The failure consists of two successive compound slides within the pre-glacial sand, silt, and clay unit (Figure 8.9). I^^.-.UA lii-kfliA Slide 1-3 106 No shear planes or intact sections were observed as they were covered by debris, but rather inferred by slope morphology. Both failures show a definite component of back tilting and the resultant ponding of water as well as horst and graben structures. Intact slopes underneath the debris are expressed as steeper slopes within the profile. The start of the profile is at the exposed head scarp of till above bedded silt-rich pre-glacial silts of a rotational component of the failure. The two failure plane hypothesis is supported by the small nature of most of the features seen on the slide. Locally, the bedrock is inferred from neighbouring slides, bedrock elevation across the Pine River, and that the site is completely within the pre-glacial valley (Mathews, 1978). The toe is made of remobilized debris that is heavily treed and shows small-scale back tilting and compound features. Slide 1-4 Slide 1-4 is an active failure consisting of three failure planes within the pre-glacial sand, silt, and clay unit (Figure 8.10). It is located in between Slides 1-2 and 1-3 and also has a north-facing slope. The profile started on an undisturbed surface near a field at the top of the failure and traversed at an azimuth of 0° to the toe. The head scarp of the slide is made entirely of till and the debris near the top was slightly back tilted suggesting a rotational component to the failure. The upper shear plane was observed and sampled (1-4A) during the traverse, however, the lower two failures are an interpretation. The upper failure plane lies directly above a massive intact sand bed with minor interbeds of silt and clay . The shear plane has a clay fraction of 38 with a liquid limit of 51% and a plasticity index of 33%. The middle failure shows back tilting and ponding so it is also considered a compound failure. The debris of this failure had small features suggesting the failure 107 surface is shallow. Below this debris, another intact section of sand with clay beds was observed, however the shear surface above it could not be found. One of the intact beds of clay was determined to be mostly silt at 72%, with a liquid limit of 41% and a plasticity index of 24%. The horst and graben features within the debris mass of the lowest failure below the second intact bed of sand were also small so a third, shallow failure plane is inferred here. The bedrock surface is again assumed from other profiles to be below this failure plane forcing the debris to slide and remobilize below. An interesting element of this slide was a series of laterally extending ridges within the remobilized debris, which appeared to be compressional features as if the debris is being loaded on to and pushed toward the river. Slide 1-5 This failure is at the eastern end of the area and has a north-facing slope. The slide is dormant with three shear planes within the pre-glacial unit (Figure 8.11). The upper shear planes are interpreted from slide morphology and the lower shear was seen although not accessible. The profile starts in a farmer's field at an azimuth of 323° and continues down slope to an abandoned property. Within the field, a small crack was observed which might be a tension crack, however with the amount of seasonal modification caused by plowing of the field, features within a field can be deceptive. The head scarp for the upper failure is shallow at 23.5 and all the features are overgrown and muted. This is likely a compound failure with a shallow failure plane with little to no rotational movement. The trees on the slope are J-shaped and have an estimated age of 60 to 80 years. Wide scale ponding marks the head of the next compound failure and represents subsidence of a graben. Several large horst and graben structures were 108 observed representing a deep compound failure. The third failure plane is at a very low angle and is quite long, roughly 9000 meters, and is represented by large-scale horst and graben features and hummocky terrain. The toe of this section is remobilized and shows a rotational failure. The shear plane was covered along the traverse but it was detected in a ravine next to the profile, making sampling impossible. Gravel was also seen at this section as well as the intact shale below. Elevations were taken obliquely off the profile. The bedrock surface dips steeply toward the current river level. The debris below is remobilized and highly disturbed. The slide surface was modified at the toe due to the development of a residence. Slide 1-6 Slide 1-6 is located just west of Slide 1-5 and is very similar to it (Figure 8.12). It is dormant near the top of the slide and active at the toe and within the debris apron. The profile starts within the same farmers' field and goes down slope at an azimuth of 330° towards an abandoned property. There are three shear planes within the pre-glacial sand, silt, and clay. The two upper failure surfaces are inferred from Slide 1-6 and surface morphology. These are shallow compound slides in a successive manner with small horst and graben features along with shallow head scarps. There is little to no back tilt, however, trees with ages up 60 years are J-shaped suggesting that this failure is a continuous slow movement. The lower failure is a long, deep compound failure interpreted from the large horst and graben features. The toe is actually failing with fresh scarps in a rotational manner. The toe is very hummocky and disturbed with a gully obliquely cutting the profile exposing the lower gravels. In the bank of the gully, a fossil was found intact within the gravels, location marked in Figure 8.6. The fossil has 109 tentatively been identified as a Pleistocene bison's 4th cervical vertebra and was dated as being 26,530 + 320 years BP (Hartman, In Progress). Off the debris on the other side of the gully, intact gravels and sands were found, however, no shear plane could be located. A smaller bone fragment was also found at this location. Below the gravels, intact rubbly shale was detected to dip steeply into the slope, likely to the present river level. The toe was made of remobilized debris. Previous development caused the slope to be modified. This property was to be later abandoned due to landslide hazard. Figure 8.6 Bison Vertebrae found in place (Slide 1-6) 110 Figure 8.7 Landslide Profile 1-1 ("I'S'X) U) UO!q.TJA313 Note" Stratigraphic details Inferred from surface observations nay not be accurate Drawn By: J. Severln SCALE As Shown Landslide Profile 1-1 Figure No. 8.7 111 Figure 8.8 Landslide Profile 1-2 i—i—i—T o o so o o CO o o CU o o o in o o CO \_/ CU u c -p LTj n Notei Stratigraphic details Inferred from surface observations nay not be accurate Drawn By: J. Severln Landslide Profile 1-2 SCALE As Shown Figure No. 8.8 112 Figure 8.9 Landslide Profile 1-3 o o r--I I I I I I No-tei Lo g Lo § Lo § Stratigraphic tn in co oo details Inferred from surface CU) UOI1XJA3H observations nay N ' ' ' 1 —' not be accurate Drawn By: J, Severln Landslide Profile 1-3 SCALE As Shown Figure No. 8.9 113 Figure 8.10 Landslide Profile 1-4 o o Notei Stratigraphic details Inferred from surface observations x ' '~ '-1 accurate Drawn By; J. Severln Landslide Profile 1-4 SCALE As Shown Figure No. 8.10 114 8.1.4 Area Model This area is located completely (Figure 8.13) within the pre-glacial valley (1), which has undergone glaciation (2), re-established its drainage (3) and eroded to a lower elevation (4) (397 metres a.s.l). During this erosional event several landslides likely occurred, starting the valley widening process. The slides that occur in this area are completely within the Pleistocene sediments with at least two failure planes and sometimes three. The rapid downcutting into the soft sediments of the Pine River and Septimus Creek has exposed weak clay layers (4), on which the slides occur. The clay layers are pre-sheared surfaces, although the cause of the shearing is not obvious. The pre-shearing could have occurred due to glacial loading, syn-erosional slumping, or the release of lateral stresses during valley rebound. The valley expanded with a migrating river constantly eroding the resultant debris. As the river cut down into the bedrock, this abandons the basal shear surface (5). The first-time failures in this area are likely due to erosion from the river, however, reactivation of failures can occur if the debris mass is eroded and the river once again attacks the intact slope (6). Most continued failures are likely due to increased pore pressure from precipitation, softening of the clay layers, and simple creep along these pre-sheared failures (7 and 8). In this area, there seems to be one major shear surface within a meter of the gravel contact, which was sheared in all the landslides. At the eastern edge of this area the plane is extended for quite a distance, allowing for a more translational movement. Several planes appear to extend over a few slides but not the whole area. These are smaller localized beds with limited area. There is another failure plane near the top of the 117 Figure 8.13 Landslide Area 1 - Geologic Model 1) Broad, stable pre-glacial bedrock channel; 2) Aggregating deltaic environment into encroaching ice-damned lake followed by glaciation; 3) Drainage re-establishes; 4) Post-glacial river erodes down into till leaving steep banks, once softer, laminated sediments below are reached, initial failures occur; 5 & 6) Failures continue to N occur, on older, upper lower bedding planes and lower planes once exposed; 7) Debris at base acts as a berm for debris on slope; 8) Erosion of debris and intact bank and increases in pore pressure in pre-glacial units cause 118 sequence, which appears in all slides that reach this elevation. Bedrock plays little or no part in these failures except to provide an intact ledge for the debris to slide over. In general, this area has a few clay beds within the Pleistocene sequence that seem to be more apt to failure; however, failure is not confined to these beds. As the lowest failure plane usually contains the largest slide, it seems unlikely that the failures are successive, but rather retrogressive. The lower slide would fail, unloading the toe for the next failure in sequence. 8.2 Slide Area 2 8.2.1 Location Eleven slopes were profiled near Old Fort, approximately 2 kilometers south of the City of Fort St. John, on the north bank of the Peace River (Figure 8.14). The area extends for 5 km along the south-facing slope and encompasses the settlement of Old Fort, several coulees, and the Peace River Valley. At the upper elevations, the head scarps of these slides border on a bison farm owned by Mr. Bouffioux, a sewage treatment plant, a gravel pit, and a garbage dump. Most of the slopes are south-facing. Much of the area is developed and only has localized tree cover at the base of the slope. The area was chosen due to the relative easy accessibility, the location of a human settlement, the location of a pipeline crossing and a few oil wells, and its distinct geologic setting. The area is also a very important historical landmark with in the Peace River region as it is the location of an original location of Fort. St. John. Residents and tourists alike visit this location to view the scenic Peace River Valley. 119 8.2.2 Local Stratigraphy The local stratigraphy at this site is very complex and poorly understood. Most of the section is outside of the pre-glacial valley so there is a distinct lack of pre-glacial sediments at these locals. Shaftesbury shale, observed in 9 of the 12 slides, underlies the area, outcropping quite high in the profiles. The actual height of the Shaftesbury shale is hard to determine as in most sections the top was not actually seen, but rather a shear surface and not actually representative of the maximum shale height. The highest elevation at which the shale was seen at was 636 metres a.s.l (Slide 2-3). The top of the shale unit is irregular as intact till and clay are seen below this elevation. The material directly above the shale was seen intact once (Slide 2-5) where rip-up clasts of shale were observed within till. The debris directly above the shear plane is thought to be disturbed till which contains clay, silt, and minor amounts of sand and gravel. The till unit was seen at varying elevations but never lower than 568 metres a.s.l (Slide 2-11). The till has a maximum thickness of 44 meters (Slide 2-7), which may actually contain till from the previous glacial advance. The locations of the till are controlled by the pre-glacial bedrock topography. Above the till unit lies a blanket of post-glacial clay seen at most locations at approximately 660 meters a.s.l., with an average thickness of 3 meters. The pre-glacial sediments are seen again at Slide 2-8 in the east, marking the extent of the pre-glacial valley. An approximate stratigraphic column is produced (Figure 8.15). 121 Figure 8.15 Area 2 - Stratigraphic Profile (not to scale) <636 m a.s.l 660 m a.s.l Till - not below 586 m a.s.l, rip-up clasts near base(~1.0m) Post Glacial Clay - approximate thickness 3 m Shale Bedrock - contains bentonitic-rich layers and structural discontinuities 8.2.3 Landslides Slide 2-1 Slide 2-1 is located on a west-facing slope within Bouffioux Coulee. The profile starts at the top within a field and continues down slope at an azimuth of 262°. The failure is currently dormant except near the toe where some of the debris has remobilized. The failure is interpreted as having three failure planes within shale (Figure 8.17). The lowest failure plane was the only one observed, however it could not be sampled. The upper two failure planes are simply inferred due to surface morphology and neighbouring slides. A vertical face of post-glacial clay was seen near the top at an elevation of 663 meters a.s.l, within the head scarp of a small compound failure. The profile goes down a covered intact scarp. The scarp is likely intact because the slope is likely too steep for the debris to maintain. Large horst and graben structures appear along the next failure plane. The depth of this failure plane is interpreted from the size of the features. The toe of this failure slides over another intact scarp where a large compound failure occurs. Back tilting and ponding occur within the slide mass at this point, suggesting a rotational 122 component. At the base of this failure, intact shale is seen overlain by debris within a ravine. There is no sign of the pre-glacial sand, silt, and clay so they bedrock surface in the area must be controlled by failure surfaces. Slide 2-2 Slide 2-2 has a south facing profile down the Peace River Valley at an azimuth of 138 . The profile begins at a common sight seeing location directly above Old Fort (Figure 8.14) where there has been a great amount of modification in order to incorporate parking. Garbage within the landslide debris, including several automobile bodies, suggests that this may have been a trash disposal site in the past. Several shear planes, four or five, all of which are in the shale bedrock, control the dormant landslide (Figure 8.18). At the head scarp of the slide, a 10m intact section of Quaternary materials was found to have 4 m of glacial Lake Peace clay and 6 m of till. The upper most shear plane was observed within the shale and sampled (sample 2-2A). The shear plane had undergone some alteration and shale clasts were seen within the debris. The shear plane consisted mainly of silt, 70%, and has a liquid limit of 40% and a plasticity index of 20%. A sample of the shear plane within the debris was also sampled and found to have the exact composition but with a slightly higher liquid limit, 43%, and plasticity index, 24%. Below the shear plane a displaced slump block with a heavy concentration of garbage was encountered. No controlling shear plane was observed beneath this failure, however, below the debris, intact but rubbly shale was found allowing the shear plane to be inferred within a certain elevation range. A third shear plane is also inferred below based on surface morphology and thought to be in shale as well. This part of the failure may be interpreted as two failure planes. Below this, the slide has a large translational 123 component, made up largely of remobilized debris with a few large-scale horst and graben features. Along the profile, ponding and highly disturbed terrain was encountered. At the toe, the debris is remobilized in a rotational slump, thought to represent the edge of the underlying intact shale. Slide 2-3 This slide is on a south-facing slope within the Peace River Valley. The profile starts at a fence line near the sewage lagoon and heads down slope at an azimuth of 192 . Even though this slide has an active upper section, overall it would be classified as a dormant slide. This slide has multiple failure planes, four or five, all thought to be within the shale bedrock (Figure 8.19). The depth of the failures planes are inferred from surface morphology and the material is inferred from neighbouring slide reports. The upper most failure is interpreted as a compound failure with till and glacial Lake Peace clay within the head scarp. This was the only section of unconsolidated sediments found during the profile. There was one intact section of shale seen during the profile below the upper failure. Further down in the profile, the debris is very hummocky with small-scale features. The location of the sewage lagoon makes this an important failure to study as further movement could cause rupture of the lagoon leading to a higher risk in failure. Slide 2-4 Slide 2-4 is a dormant slide on the south-facing slope of the Peace River Valley, with an active upper most section. The profile starts on the fence of the sewage lagoon 50 meters east of the beginning of profile 2-3 and continues down slope at an approximate azimuth of 160 . The top of the profile is within a plowed field so some features may 124 have been disturbed. The intact section at the head scarp of this upper failure shows glacial Lake Peace clay above till within an 8-meter section. The upper most failure plane is within shale so the failure planes lower in the slide are also thought to be within the shale unit. The upper failure is a retrogressed rotational slide with large, tilted slump blocks. The shale failure plane was located about 30 meters off the profile (Figure 8.16) and sampled (sample 2-4 A and B). Sample 2-4B consisted of 32% clay, 49% silt, and 19% sand. The shear plane has a liquid limit of 47% with a plasticity index of 28%. The failure plane was partially altered to a gouge that was also sampled (sample 2-4 C and I) and tested. The gouge had an average of 67% silt and 27% sand; it has a high liquid limit Figure 8.16 Shear Plane found and sampled (Slide 2-4) of 53% and a low plasticity index of 23%. Below the gouge, a sheared surface in the shale was observed and found to consist mostly of silt, 85%, with a liquid limit of 41% and a plasticity index of 22%. Another intact section was beneath the upper failure made of weather shale. The rest of the slope is made of 2 inferred failure planes, both showing small, muted compound features (Figure 8.20). This slide shows 2 interesting features not seen elsewhere. The first is a large amount of cobbles near the base of a gully at the top 125 of the slide. This is simply a collection of weathered cobbles that have been released from the till unit. The second, a banded diamicton found near the top of the slide within the debris, is thought to represent several surges of debris that have been deposited and then broken up by a later failure. Slide 2-5 Slide 2-5 is on a southeast-facing slope within the Peace River Valley. The profile starts at the edge of a field, same field as Slide 2-1, and continues down slope at an azimuth of 132 . The slide is mostly dormant and contains three failure planes all with in the Shaftesbury Shale (Figure 8.21). The head scarp of the slide shows a thick layer of glacial Lake Peace clay of 9.5 meters above a till unit of 25 meters in thickness. At the base of the till unit is the contact with the shale below. This contact is a zone of shale rip-up clast dominated till with a clay-rich matrix of about a meter in thickness. Below this contact is a 2.5-meter vertical section of intact shale above the talus of the slope. At the base of this intact section is a large slump block of a rotational failure. The failure plane was not observed, however, below the failure another section of intact shale was found suggesting that the failure is in shale. The intact section of shale is approximately 50 meters thick and below this is two compound failures interpreted from surface morphology with several small horst and graben features. The toe of this failure is a modified river terrace that has since been farmed that shows no natural features. Slide 2-6 This slide is dormant with a south-facing aspect in the Peace River Valley and an azimuth of 154 . The profile starts on a knife-edge with Bouffioux Coulee, so a stable top 126 section in not possible to attain. The head scarp is completely grassed so no intact section was observed, although the small flake slides within the head scarp and the neighbouring slide suggest that the head is made of till and post-glacial clay. The slide is composed of two independent failure planes within the slope (Figure 8.22). The upper failure plane is abandoned and currently stable and represented by a small dip in the profile. No failure surface was observed, but rather interpreted from surface morphology and neighbouring slides to be within the shale. At the base of the main scarp, a small, rotated block was found with shear planes (sample 2-6 A), was observed. The shear plane has a clay fraction of 34 and a silt fraction of 57. The liquid limit of the sample is 48% with a plasticity index of 28%. Below this, a layer of gouge within the shale, which does not look sheared, was located (sample 2-6 B). This sample consisted of 38% sand, 40% silt, and 22% clay. The sample displayed a liquid limit of 45% and a plasticity index of 22%. The second failure is a retrogressed rotational failure that has been weathered and the features are now muted, although ponding is still prevalent in the debris mass. No intact sections or failure planes were observed during this profile. The toe of the slide has been modified by a river terrace and subsequent farming activity. Slide 2-7 Slide 2-7 is south-facing with an aspect of 188 in the Peace River Valley. The profile begins on a hummocky, plowed field within a Bison Ranch belonging to Mr. Bouffioux. This is an active failure with three shear planes within the shale (Figure 8.23). The head scarp of the failure shows an anomalous section of Quaternary sediments. This section is at least 56 meters thick and dominated by a unit of till. The top of the section displays a 10-meter unit of glacial clay underlain by 44 meter thick of till and at least 2 127 meters of sand and gravels at the base. The till displays glaciotectonic shears near the base, however, these shears don't seem to control the stability of the vertical till face. There is a rotational failure below the intact face with a shear plane in the shale. Below this failure, an intact shale face was encountered that leads to the debris mass of the middle failure on the slope. This failure is also a rotational failure with shale found directly below in a nearby gully. A third rotational failure exists below this intact face. The debris of this lower failure flows over an intact shale bed below, with the toe being remobilized debris. This slide has three failure planes allowing for independent rotational failures. All failure planes are inferred as none were witnessed during the profile. Slide 2-8 This slide represents the edge of the pre-glacial valley of the Peace River and is on the eastern edge of the slide area. The profile has a western aspect with an azimuth of 252 and starts upon a flat where several pump jacks and a field exists. The slide is active and contains three failure planes, however, only one is in shale (Figure 8.24). There is a small rise within the field and back tilted trees, which may be a filled tension crack. The main head scarp is dominated by till with a thin layer of glacial clay near the surface. The displaced debris is slightly back-tilted from a rotational movement. The shear plane for this failure was located within a clay bed above a thick unit of silt. Both the failed clay bed and intact clay beds below were sampled (sample 2-8A and 2-8B). The failed clay consisted of 57% clay and 43% silt, whereas the intact clay below consisted of 32% clay and 68% silt. The Liquid Llimit for the failed clay was 47% with the Plasticity Index at 28%. The intact clay showed a higher Liquid Limit of 69% and a Plasticity Index of 48%. The silt unit has some smaller beds of clay, up to 3 cm in thickness, and lenses of sand, 128 up to 45 cm thick. The failure below this intact section is a rotational failure moving along a clay layer within the pre-glacial sediments (sample 2-8 D). This surface occurs 0.1 meters above the gravel contact and is composed of 36% clay and 63% silt. The Plasticity Index of the failed clay is 26% and a Liquid Limit of 48%. A bed of intact clay below the slide plane was sampled (sample 2-8 AA) and found to be 57% clay with 43% silt. The intact bed has a Liquid Limit of 51% and a Plasticity Index of 31%. The gravel unit is anomalously thick in this section at 36 meters with an over steepened angle of 45°. Below this intact section, highly disturbed debris with ponding and minor back tilting suggests another failure plane within the shale. The steeper slope within this debris is likely caused by the presence of an intact scarp below. The toe along the river's edge is very active, failing within the last 5 years. Slide 2-9 The profile of slide 2-9 begins in a field near many bent, twisted, and tilted trees and heads down slope at an azimuth of 104 . The slide occurs within Crawfords Coulee near the eastern edge of the area with an eastern aspect. The 6-meter vertical head scarp shows glaciolacustrine clay for most of the face with till composing the bottom 0.2 meters. The head scarp shows distinct pinnacles of till and clay 3 to 5 meters high that have moved several meters. The failure is a retrogressed rotational failure with a slide surface that daylights in the scarp below (Figure 8.25). There is a large amount of back tilting and small scarps within the debris. The failure plane occurs within a clay bed of the pre-glacial sediments (sample 2-9 A). Below the shear plane, the quaternary sediment sequence is dominated by silt with minor amounts of sand and discreet clay beds. The lower failure is a compound failure displaying steps within the debris and extends the rest 129 of the slope. The toe of the failure is very active with fresh features and disturbed material. A lower shear plane within in the shale was located within the ravine that the debris mass is sliding on. Slide 2-10 This small slide has an eastern aspect, occurring within a coulee east of Crawfords Coulee. The profile begins on a knife-edge between two coulees and continues down slope at an azimuth of 96 . The profile goes down into a large tension crack and back to a vertical face of a diamicton, which may be disturbed till. The failure is active and has one failure plane within the shale (Figure 8.26). The head scarp is steep and the debris below exhibits major back tilt within several steps. The slide is interpreted as a retrogressed rotational failure within the shale bedrock. The debris steps are large suggesting that there is a deep failure plane. The toe of the slide has been reactivated with a disturbed surface and small pockets of ponding. No shear surfaces or intact sections were observed in the slide mass, however, a shale scarp was witnessed nearby extending above the elevation that the shear plane is interpreted to be at. Slide 2-11 This short failure occurs within the Peace River Valley on a south-facing slope. The profile begins on a ridge between coulees and follows along it and down slope on an azimuth of a 192 . The failure is very active and has two failure planes within the Shaftesbury Shale (Figure 8.27). The head scarp is composed of 9 meters of glaciolacustrine clay above 5 meters of exposed till. Pre-glacial sediments were not 130 Figure 8.17 Landslide Profile 2-1 E U c5 -P in (U) uo|q_x)Aa]3 Notei Stratigraphic details Inferred from surface observations nay not be accurate Drawn By: J. Severln Landslide Profile 2-1 SCALE As Shown Figure No. 8.17 131 Elevation (m) 3 OQ*' n CT oo GO cn o o o cn CD ui o o ai cn o o o ai o o <+ <+ P <+ (D "5 P X) ;x n Q. fD <+ P 3 a> "5 "5 ro QL -r> -5 O 3 w c "5 -r> P n 03 o in < P <+ O 3 Ul 3 P *< 3 O (T> P n n c 3 P <+ <D in oo I 3" O s 3 3 0) < 3 3" oo 00 ro i ro o I P 3 Q_ ro CD CD c Y fl) in" T £.-, f3 | *>> • >? *.'•» '5 i ! •j» J- Ir TJ —1 O 3" Ul P <+ I ro" (D_ rxl P fl) n Q_ pj O n n P ^< CJ CD O in" P n 4v o o cn o o cr. o CD ^1 o o CO CD CD CD CD Cu Cu CT O BJ to I to CD CD CD to Figure 8.21 Landslide Profile 2-5 £ OJ U c5 -P in Notei Stratigraphic details Inferred from surface observations nay not be accurate Drawn By: J. Severln Landslide Profile 2-5 SCALE As Shown Figure No. 8.21 135 Figure 8.23 Landslide Profile 2-7 o o o o in o o o o co o o OJ o o o in o o o in in o o in o in o o o in ro E v/ u cS -P in PI (U) UO|^X)A3]3 Note' Stratigraphic details Inferred from surface observations nay not be accurate Drawn By: J. Severln Landslide Profile 2-7 SCALE As Shown Figure No. 8.23 137 o o CD LO LO CD CD LO CD O LO o CD LO CO (id) uojq.rjAai3 Notei Stratigraphic details Inferred from surface observations nay not be accurate Drown By; J. Severln SCALE As ShOWn Figure No. Landslide Profile 8-8 8.24 138 Figure 8.25 Landslide Profile 2-9 o LO CO >> a u a _ -I "3 - w -S x S o _ 10 hi H u o i. "D Or O O CO o LO CU o o cu o LO OJ U C5 -P 10 n o o o LO o o in sO o LO SO LO OJ SO o o sD in LO o LO LO (U) uo!q.x)Aa)3 Notei Stratigraphic details Inferred from surface observations may not be accurate Drawn By: J. Severln Landslide Profile 2-9 SCALE As Shown Figure No. 8,25 139 Figure 8.26 Landslide Profile 2-10 w L Cu f=> cu 73 o o CO CD OJ O CD OJ O in o o o in £ OJ U in CD LD O in o in CD in CD ID CO o 00 in CO CD OD MD \D MD in in in in (U) uo!q.*0Aai3 Notei Stratigraphic details Inferred from surface observations nay not be accurate Drawn By: J. Severln Landslide Profile 2-10 SCALE As Shown Figure No. 8.26 140 ure 8.27 Landslide Profile 2-11 o o o o LO in o o in o LO o o Drawn By; Note" Stratigraphic details Inferred from surface observations nay not be accurate J, Severln SCALE As Shown Landslide Profile 2-11 Figure No. 8.27 141 detected during the profile. Behind the head scarp is a large crack thought to be a tension crack connecting with the failure plane used for the upper failure. It is likely that this whole section is unstable. The talus below the vertical section is till-like and ends at a bench within the slide. The upper failure is a rotational failure completely separated from the lower failure. The failure plane was observed in the shale but could not be sampled. Below this shear plane, an intact section of weathered shale was found and extends until a debris bench overlying a stable bedrock layer likely containing another shear plane within the shale. 8.2.4 Area Model This area occurs completely within the Shaftesbury Shale boundaries making the more resistant Dunvegan Sandstone irrelevant to slope stability studies (Figure 8.28). The highest intact elevation that the shale was observed at was 636 meters a.s.l.; however, in most cases the exposures were truncated by a shear plane. This area is unique within the map sheet because it represents a location in which the present river valley does not follow the pre-glacial valley (1), shown by the high shale elevation and distinct lack of pre-glacial sediments. Only one slide to the east is within the boundaries of the pre-glacial valley. The area was then glaciated (2), represented by till and glaciolacustrine clay in the headscarp and debris through out the slide profiles. Drainage re-established itself within the pre-glacial valley (3) and eventually migrated to erode the bedrock shale, exposing the weak strata (4). As the site is outside of the pre-glacial valley, the shale is found at a high elevation and the shear planes are located within the bedrock. The shale, being a marine deposit, has much less variability than the pre-glacial sand, silt, and clay. 142 With this in mind, the shear planes are more likely to be correlated over a small area as the lithology plays a role in the slope stability. As the river migrated throughout its channel, proven by current terraces, it also eroded into the bedrock valley wall exposing older weak planes and creating new ones through valley rebound (5). Eventually the river became smaller and controlled by the upstream dam, the lower shear planes were abandoned. Near the bottom of the river valley, there is a 14-meter thick zone, between the elevations of 420 meters a.s.l and 433 meters a.s.l., in which all profiles that extend to that elevation show a failure. This widespread failure zone is likely a bentonite-rich section of the Shaftesbury Shale reported by others (Sargent and Moore, 1988; Imrie, 1991). Another failure zone exists between 465 meters a.s.l and 478 meters a.s.l. in which 6 of the 9 profiles that are at that depth show a failure plane. Within this study site, there are four more such groupings that can be made that correlate failure planes from at least three profiles. These groupings occur near 522 meters, 555 meters, 585 meters, and 633 meters a.s.l. These shear plane groupings are expected in a material within such a uniform depositional environment. The amount of groupings suggests that bentonite is quite prevalent within the formation, confirmed by other reports on the Shaftesbury Shale and other Cretaceous shales. This bentonite-rich shale occurs in discreet zones roughly correlatable because of the sporadic nature of deep-sea deposition. The shale will fail along the weakest of these zones given the proper setting or else it will fail along the next weakest layer. The bentonite does not occur in discrete beds but rather dispersed within a larger zone. The slides occur along planes that have been sheared due to one of many causes. These planes may be pre-sheared due to relaxation along bedding planes due to 143 valley rebound, over steepening of valley walls during erosion causing syn-erosional slumping, and larger horizontal stresses cause by the orogenic events to the west. The Peace River area is close enough to the mountains that horizontal stresses cannot be ruled out. With the amount of weak zones within the unit and the number of possible causes for pre-shearing, it is no surprise to see individual slides with multiple shear planes. The slides occurring within the coulees generally only have one to three failure planes, simply because the lower failure zones have not been reached by the downcutting of the small streams. One interesting feature of this area is the asymmetry of the coulee slopes. The coulees are generally aligned north-south, however the asymmetry is not consistent. In some of the coulees, the shallower slope is to the east, and in others, to the west. The failures not occurring in the shale show a similar morphology to the slide area around Big Bam Ski Area. A weak clay layer less than a meter above the gravel contact and another failure plane occurring higher in the pre-glacial succession. In general, there are several weak layers within the shale due to the inclusion of bentonite allowing the shale to fail at many elevations. All of these failures occurred post-glacially as the current valley wall did not exist and as scouring action of the glaciers eroded previous landslide deposits. Therefore, the rapid erosion of the current Peace River Valley, caused relaxation of the valley walls along bedding planes, pre-sheared surfaces caused by tectonic forces, and perhaps glacio-tectonics. As the river level dropped, many of the slides became abandoned and some debris features were destroyed by river erosion. 144 Figure 8.28 Landslide Area 2 - Geologic Model 1) Bedrock dominated plain near edge of pre-glacial river valley; 2) Aggregating deltaic environment into encroaching ice-damned lake followed by glaciation; 3) Drainage re-establishes in pre-glacial river valley; 4) Migrating river allows intact material to be eroded and failures to occur exposing weak strata; 5) Migrating river continues to expose weak strata allowing failures to occur; 6) Debris from failures acts as a stabilizing berm of unstable material, although erosion of debris may cause reactivation of failure plane. 145 8.3 Slide Area 3 8.3.1 Location The third area chosen was approximately 12 kilometers long and located near the confluence of the Beatton River and St John Creek (Figure 8.29). The area encompasses the large bend in the river where general course changes from the south to the east, roughly 7 km to the northeast of the City of Fort St. John. It also includes most of the lower St. John Creek, Stoddart Creek, and some sites further downstream on the Beatton River. Within the area, 15 slides were profiled within the study site encompassing 5 kilometers of valleys. The area was chosen because of the extensive infrastructure located within it. It contains Cecil Lake Road 103, which has two bridges crossing the Beatton River and St. John Creek, a pump station owned and operated by Devon Gas Services, approximately 15 operating pump jacks, and several pipelines crossing the river valleys. One bridge crossing the Beatton River has been rendered inactive due to the failures making the approach unstable. The area constantly undergoes movements that affect the roadway and pipelines and is currently undergoing slope stabilization project. The area was also very accessible because of the amount of infrastructure. The south-facing slopes show little to no vegetation and steeper slopes while the north-facing slopes are heavily vegetated and generally much gentler slopes producing a distinct asymmetry to the riverbanks. 146 Figure 8.29 Landslide Area 3 8.3.2 Local Stratigraphy As in many cases, when the study area is larger, the complexity of the stratigraphy is increased. The stratigraphy of Slide Area 3 is best described by dividing the area into three sections, the north and east walls of the Beatton River, the south and west walls of the Beatton River, and the valley walls of St. John and Stoddart Creeks. The first section is the north and east valley walls and incorporates the left-hand side of the valley wall, facing the down stream direction. Six profiles were completed within this section. This section contains both Shaftesbury Shale and Dunvegan Sandstone (Stott, 1988) and is interpreted as being the boundary of the pre-glacial valley (Mathews, 1978). The Shaftesbury Shale extends to an elevation of approximately 560 meters a.s.l; however, because the contact is gradational and exact elevation is hard to determine. The Dunvegan Sandstone reaches to an elevation of approximately 590 meters a.s.l with a local high of 621 meters a.s.l. on landslide profile 3-13. Above the sandstone is a silt-rich unit of the pre-glacial sequence. This unit contains interbedded clay and sand on which the upper failures occur. This unit was not witnessed intact but rather inferred from the material within the colluvium and within the debris. This unit is capped by a till blanket which extends to an approximate elevation of 710 meters a.s.l. The post-glacial clay was not observed at this site. An approximate stratigraphic column is produced (Figure 8.30). Four slide profiles were completed in the second section, the south and west valley walls, which is the right hand side of the valley when looking down stream. This section is within the pre-glacial valley (Mathews, 1978) and therefore the sandstone unit is missing and the shale unit has been eroded down to an elevation of 460 meters a.s.l. 148 Above the shale is a thin unit of gravels with a thickness of 2 meters. The gravels are clean, uncemented and has a reddish colour. Above the gravels are the pre-glacial bedded sand, silt, and clay beds observed to extend to an elevation of approximately 592 meters a.s.l. At this elevation, the unit becomes clay-rich and contains drop stones with the bedded material to an elevation of approximately 609 meters a.s.l. An approximate stratigraphic column is produced (Figure 8.31). The third section has five profiles and encompasses the valley walls of St. John and Stoddart Creeks. This section has a similar stratigraphy to the south wall of the Beatton River. The shale was found at an elevation of 487 meters a.s.l on the north side of the valley and lower at 455 meters a.s.l on the south walls. This section is also thought be within the pre-glacial valley (Mathews, 1978) and is therefore missing the Dunvegan Sandstone in all sections except the north wall of Stoddart Creek. The gravel unit is located above the shale with a thickness of 4 meters. The gravels are partially cemented and contain cross bedding indicating an aggrading condition during deposition. Above the gravels, with a gradational contact, is the pre-glacial sequence, dominated here by silt and clay. The sequence continues to an estimated elevation of 650 meters a.s.l. A till blanket of unknown thickness is located at the top of the plateau. An approximate stratigraphic column is produced (Figure 8.32). 8.3.3 Landslides Slide 3-1 The first slide studied within this area was a multi-leveled failure on a south-facing slope with an azimuth of 198 .The profile began on the upper plateau and 149 Figure 8.30 Area 3 - Stratigraphic Profile - North and East Valley Walls (not to scale) 710ma.s.l. -650 m a.s.l. 590ma.s.l. 560 m.a.s.l. , ••••••••••••< Till - extends to top of plataeu Laminated Silt, Sand and Clay - silt-rich with clay, upper contact inferred from St. John Creek Dunvegan Sandstone - gradational contact Shaftesburv Shale Figure 8.31 Area 3 - Stratigraphic Profile - South Valley Wall (not to scale) 609 m a.s.l 592 m a.s.l Clay with dropstones Laminated Silt, Sand and Clay - Silt-rich 462 m a.s.l 460 m a.s.l Sand and Gravels - slightly cemented Shaftesbury Shale - top contact represents hiatus 150 Figure 8.32 Area 3 - Stratigraphic Profile - Stoddart & St. John Creeks -700 m a.s.l 650 m a.s.l 459 m a.s.l 455 m a.s.l - " ' '."1 1 " . •' Till - upper limit inferred by North Valley Wall of Beatton River Laminated Silt, Sand and Clay - Silt-rich Sand and Gravels - slightly cemented Shaftesbury Shale - top contact represents hiatus headed down slope towards St. John Creek, near its confluence with Stoddart Creek (Figure 8.29). The slide has two failure planes both within the pre-glacial sequence (Figure 8.34). The top failure is abandoned and completely independent of the lower, very active bottom failure. The head scarp is completely grassed over and appears stable, though morphology indicates that this part of the slope was previously active. The upper failure plane was not observed but rather inferred from the terrain. The lower failure has fresh features even though the main scarp is grassy and appears stable. The lower failure is rotational with many scarps within the debris mass. The failure plane was observed with the vertical face visible from the roadway and sampled (sample 3-1A). Slickensided surfaces were located near the bottom of the pre-glacial unit, 3 meters above the gravel. The debris mass protruded up to 7 cm from the intact section. The shear plane consisted of 47% clay and 52% silt. The liquid limit of the layer is 54% and a plasticity index of 151 34%. The gravel unit extends for 5 meters until the shale was reached. The toe of the slide, on which a roadway is located, is remobilized debris. This toe has been armored at the creek level in order to stop the remobilization of the debris and to add stability to small slumps that threaten the roadway. Slide 3-2 Slide 3-2 is multi-level failure located on an east-facing slope on Stoddart Creek near its confluence with St. John Creek (Figure 8.29). The profile begins along a knife-edge and continues down slope at an azimuth of 100 . This slide is a very active part of a larger, south-facing slide complex extending further to the west. The slide incorporates two failure planes, both within the pre-glacial sequence above the bedrock (Figure 8.35). Neither shear plane was observed, but rather their location is inferred from slide morphology. The failure planes are thought to be in the unconsolidated sediments because of the low elevation that the shale is found around the area. The shale outcrops only 2.5 meters above the creek level. The material within head scarp of the upper failure appears to have been disturbed from the abutting slide to the north. Even though the material is disturbed, it can still be noted that it is dominated by silt and sand with minor clay. The upper failure is a retrogressed rotational failure displaying back tilt of a slump block and scarps within the debris. This failure appears to be independent of a lower failure, which is more of a compound failure with the typical horst and graben extensional features. The toe of the failure had failed earlier in the summer of 2003 in as a rotational slump. 152 Slide 3-3 Even though this large landslide has two distinct failure planes, it is best classified as a compound failure (Figure 8.36). The failure occurs within the Beatton River Valley on a slope that has a western aspect (Figure 8.29). The profile begins within a field on the upper plateau and continues down slope at an azimuth of 262 . The failure is dormant with a few sections that are active to very active. The upper failure is a small rotational slump within a silt-dominated sequence of the pre-glacial unit that appears abandoned. This failure is above a steep face controlled by the Dunvegan Sandstone, which acts as a head scarp for the lower compound failure. The large pond at the base of the scarp abuts against a large horst block with smaller scale hummocky terrain within in. Other large-scale horst and graben features are seen further down slope including a second pond near the road, which services a pump jack within the debris. Sandstone blocks were seen through out much of the failure up to the location of the second pond. The toe of the failure is at a low angle and drops near the current river level. This is interpreted as the edge of the stable bedrock below. The failure is thought to be deep as the size of the features are quite large and must be in shale due to the presence of the sandstone strata. This type of failure is common along the Beatton River Valley within this section of the river. Slide 3-4 This failure profile begins at the fence of a bison ranch south of Stoddart Creek (Figure 8.29) and continues down slope at an azimuth of 336 . The ranch is within the flat, stable plateau above the river valley underlain by the Dunvegan Sandstone. The profile follows along a seismic line that has cut through the dense vegetation on the 153 north-facing slope. The slide has some small active sections, although in general it would be classified as dormant. The slide is interpreted conservatively as having one dominant basal shear plane within the shale bedrock allowing for a large compound failure (Figure 8.37). This surface was not seen, but rather inferred from the slide terrain. No intact sections or failure planes were seen along this profile, however the bedrock elevation is projected from neighbouring intact sections. Much of the morphology of this slide is interpreted from the tree cover, as there was several sections within this slide that displayed a distinct cross tilting of the trees (Figure 8.33). The cross tilting is interpreted as an extensional feature where discrete blocks are separating from each other. Several muted horst and graben features were encountered during this profile supporting the compound interpretation. Figure 8.33 Cross-Tilting of trees on Landslide Profile 3-4 154 Slide 3-5 The profile of Slide 3-5 on the south-facing slope occurs opposite of Slide 3-4 on Stoddart Creek (Figure 8.29). The profile starts upon the stable plateau above the creek near a cluster of pump jacks and continues down slope at an azimuth of 129 . This multi level slide has three distinct failure planes independent of each other with the upper failure being abandoned and the lower failures being very active (Figure 8.38). The upper failure has no distinct features, however, from the shape of the slope the failure might have been a compound failure. The sandstone face below the failure indicates that the failure plane is within the pre-glacial sediments. The second failure, below the sandstone face, is a small rotational failure with a shear plane that is within the shale bedrock. The active debris shows minor back tilt although the features are fairly muted. There were sandstone blocks scattered throughout the debris of this section from the bedrock above and below. The shear plane for this failure was not found here although debris was observed directly above intact shale. The failure plane was located deep within the slope and could be sampled with a shovel; however, the same plane was sampled (sample 3-5A) approximately 200 meters giving enough field evidence to support that the failure plane was located at this level. This shear plane was found to consist mostly of silt, 68%, with minor clay, 19%. The Liquid Limit of the shear was found to be 53% with a Plasticity Index of 35%. The intact shale below the failure plane was heavily weathered and produces a large talus cone of raveled shale. A gouge layer within the shale was sampled (sample 3-5B) and tested. The gouge consisted of 32% sand, 58% silt, and 10% clay. The layer has a Liquid Limit of 52% and a Plasticity Index of 29%. Below this section, distinct horst and graben features were observed indicating a translational 155 movement of the debris. Near the river, intact shale was observed again signifying that the lowest shear plane is also within the shale and not simply remobilized debris. Slide 3-6 Slide 3-6 is a multi-level failure occurring on a southwest-facing slope within the valley created by St. John Creek (Figure. 8.29). The profile begins at the base of a pump jack within a field on the stable plateau and continues down slope at an azimuth of 206 . The slide is classified as dormant although the upper sections are likely to be abandoned. The slide has three distinct failure planes independent of each other (Figure 8.39). The upper most failure is abandoned and has muted features making the failure type hard to distinguish. It likely a compound failure based on the slope morphology, however, no shear plane was found. A steeper section of the slope is interpreted as being a stable back scarp for a lower compound failure. The debris within this section shows large-scale horst and graben features with little to no back tilt observed. The slope in this section has a low angle until a large scarp is reached. This large scarp was vegetated with grass and shrubs and thought to be the head scarp for the third ad lowest failure. Originally it was thought that the debris below this scarp was remobilized debris from the failure above, however, a failure plane was located within the shale near a vertical section by the creek. This lower failure is a retrogressed rotational failure displaying back tilt and scarps within the debris. As most of the slide had no exposure, the shale elevation was inferred by projecting near by elevations found. The inferred shale elevation leads to the conclusion that the upper two failures occur within the pre-glacial material while the lower most failure occurs within the shale. 156 Slide 3-7 This is an active, multi-level failure on the north-facing slope along the Beatton River (Figure 8.40). The profile begins along a ridge between a gully towards the west and a large bowl-shaped failure to the east, and continues down slope at an azimuth of 350 (Figure 8.29). This failure has partially destroyed a road that approached a now decommissioned bridge making it impassable. This occurred some years ago and has now been partially reclaimed. There is still danger associated with this slope as there are still a few residents serviced by this road further upslope. The failure incorporates three failure planes all within the pre-glacial sediments. The upper most failure is an independent, dormant rotational slide. It is heavily modified as heavy equipment is in the process of moving earth and really can only be recognized by the hummocky terrain and the existence of shear planes found in the scarp of the next failure. The vertical face of the next failure is of intact clay-rich material with drop stones through the mass. A distinct shear plane was observed and sampled (sample 3-7A) for a slide that occurs next to the one profiled. A similar failure plane likely exists for the above failure, however was not actually observed. The second failure shows back tilting and scarps within the debris indicating a retrogressed rotational failure. The failure plane for this section was not observed either, although because the section is active, it can be inferred due to the fresh features and the total lack of shale within the debris. An intact scarp below the debris is interpreted from a small scarp within the debris that begins a steeper section of the slope. It is unknown whether this failure is within the Quaternary sequence or within the bedrock, however it is believed to be within the pre-glacial progression as little to no shale was found within the debris. This is the approximate location of the intact road 157 section on the slope. The toe of the failure is interpreted as being remobilized debris from the above failures. This failure is located on an outlying section of pre-glacial material, as failures have retrogressed the slopes on either side of this section. Slide 3-8 Slide 3-8 is compound failure on a north-facing slope along the Beatton River (Figure 8.41). The slide profile starts on the plateau above the river and mostly follows the edge of a pipeline right of way down slope at an azimuth of 340 . The failure is dormant and many of the slide features are small and muted. The profile was taken 20 meters off the right of way so that disturbance from the pipeline would not be added to the data. The slope is interpreted as having one major basal shear plane within the shale and another near the top within the unconsolidated material. The upper shear plane was not actually observed, although the surface expression of the slope would indicate that a failure had occurred in that location. The only section of intact material observed was at the bottom of the slope within a ravine less than 10 meters of the profile. The ravine revealed a section of intact shale that was rubbly and slaked. Near the bottom of the shale section, more intact shale was found. Within this more competent shale, several shear planes were located suggesting that the shale was undergoing creep within this section. This suggesting the presence of a deep-seated shear plane on which the shale mass is moving, albeit, very slowly. Above the shale was a slightly disturbed bed of sands and gravels, common to this side of the river valley. The material was loose and easily excavated. The controlling shear plane of the failure is thought to occur below this and movement along it must be very slow as not to cause the gravel bed to be disturbed more 158 than it was. The material above the gravel was bedded silt with plumes of gravel intruding from below. Slide 3-9 This is a multi-leveled failure with three distinct failure areas (Figure 8.42) on an east-facing slope across from Slide 3-11 within the Beatton River valley. The profile for the slide starts upon the stable plateau on an access road and heads down slope at an azimuth of 80 (Figure 8.29). This slide is entirely dormant and is currently used by recreational vehicles. None of the shear planes were observed, however their location was inferred from surface morphology. The upper two shear planes are thought to be within the Quaternary materials while the lower failure is thought to be in shale. The lower shear plane was placed in the shale due to the amount of shale within in the debris near the base of the slope. Shale was not witnessed in other sections of the slide. The upper most failure is dormant and many of the features were either to muted or disturbed to make a decision on what type of failure it may have been. The debris of the middle failure displayed back tilting with little to no extensional features so it was likely a rotational failure. The lowest compound failure was longer than the upper two and did show horst and graben features with little rotation. The debris at the toe of the slide was vegetated and appeared to be stabilized debris from the above failures. The elevation of the shale is low in this area due to the pre-glacial valley so many of the shear planes in this area are within the Pleistocene sequence. 159 Slide 3-11 Slide 3-11 is a large compound failure occurring on a southwest-facing slope within the large bend of the Beatton River Valley (Figure 8.29). The profile begins on the corner of the upper plateau above the river and heads down slope at an azimuth of 241 . The failure is dormant and is controlled by one dominant failure plane (Figure 8.43). The slope morphology suggests a second failure plane that may be in the intact material or within the debris. The main head scarp is covered in grass and colluvium and shows signs of minor shallow slumping. The debris close to the head scarp shows decided back tilting and translational horst and graben features further down the profile. The toe of the failure is modified for the right of way of a pipeline. If the debris remobilized along the shear plane, this pipeline would be under extreme hazard. Near the river, a series of scarps within the debris show that the debris has moved in the past and may move again in the future. Slide 3-12 This slide profile is on a south-facing slope at the large bend within the Beatton River Valley on an azimuth of 184 (Figure 8.29). The profile begins within a field and continues along a pipeline right of way down slope and ends at the gas plant fence line. The slide, like others around it, has one dominant basal shear plane and a smaller, independent failure above the bedrock face (Figure 8.44). The failure is dormant with no recent deep-seated movements, although there are some shallow failures within the colluvium cover forced at an unstable angle due to the underlying bedrock. The upper shear plane was not observed as the slope had a thin cover of colluvium but the slope morphology suggests an abandoned slide. Several reflectors were set up on the slope to 160 monitor movement by an unknown party. An intact sandstone scarp was encountered, beneath which debris from the deep-seated failure within the shale begins. The bottom part of this failure mirrors that of Slide 3-13, although the features along this profile were much more muted than the neighbouring slide. The roadway also crosses this profile increasing the risk of this failure but more importantly, the gas plant is located on the debris of this old failure. The profile was truncated by the presence of the plant and finished from topographical data. Slide 3-13 Slide 3-13 is a large failure on a south-facing slope along the Beatton River near a pump house for a pipeline that transects the area (Figure 8.45). The profile starts near a pump jack up on the stable plateau within a field and continues down slope at an azimuth of 344 . The failure resembles Slide 3-3, in that it should be classified as a multi-level failure but because a majority of the movement occurs along one shear plane, it can be considered a compound failure. The upper two failures that occur within the Pleistocene unit are dormant and covered in light vegetation. They are compound failures and neither shear plane was witnessed but rather inferred from surface morphology. They are believed to occur within the Pleistocene sequence, as the vertical face below is composed of Dunvegan Sandstone and not likely to failure. The dominant lower failure is a compound failure occurring along within the Shaftesbury Shale. The debris has recently become active, failing along the same deep-seated shear plan. A sample of the remolded shale was collected (sample 3-13A) and found to be 78% silt and 19% sand. The Liquid Limit of the shale is 42% with a Plasticity Index of 24%. The debris is very hummocky with major ponding occurs where is an intact scarp beneath the debris. The toe of the 161 slide has been disturbed as the debris that blocked the roadway was removed and used as fill in another location. The landslide also damaged a transmission line and forced one of the wells offline. Slide 3-14 Slide 3-14 is on a south-facing slope of the Beatton River approximately 7 kilometers down stream of the St. John Creek confluence (Figure 8.29). The profile begins on the stable plateau near the edge of the slide and continues down slope at an azimuth of 180 . This is a multi-level failure with three shear planes with the upper section being abandoned and lower two being active (Figure 8.46). The upper most failure is distinct and should be considered of a special type. It is bowl-shaped failure with a very low angle, somewhat resembling quick clay failures occurring within the Leda Clay in Eastern Ontario and Quebec (Mitchell, 1977). The failure has the appearance of an abandoned meander scar, however there is a distinct set of sub-parallel ridges, thought to be debris scarps. The interpretation of the upper failure is that it is a shallow retrogressed rotational failure that has receded for an extensive distance with highly mobile debris. The failure has occurred within the pre-glacial unit, which makes it unique. Most of the failures that have this morphology within the map sheet occur within the post-glacial clay. The middle failure is a retrogressed rotational slide that occurs within the shale unit. The failure plane was sampled (sample 3-14 A, B, C) and a thin unit of remobilized shale was found above the bottom shear plane. Both the shear plane found in the shale (sample 3-14A) and the remobilized material (sample 3-14B) consisted dominantly of silt 77% and 74%, respectively and minor clay, 22% and 25%. Both materials have a Liquid Limit of 41% and a Plasticity Index of 21%. The debris contains 162 till, sand, silt, and pockets of weathered shale. Near the edge of the slide, an intact layer of cemented gravel was found above the location of the shear also supporting the location of the failure plane within the shale. Below the middle failure, an intact scarp in which the failure plane daylights, is made of bedded shale. At the base of this scarp is a large, intact, rotated block of shale indicating that a compound failure below the scarp. This bottom failure plane was not observed, however it can be placed with confidence within the shale. The debris mass is very disturbed and is mostly made-up of shale with minor a minor amount of till and sandstone. The underlying intact shale bed abruptly stops where the debris thins toward the toe. Slide 3-15 Slide 3-15 is on a south-facing slope of the Beatton River less than 1 kilometer up stream from Slide 3-14 (Figure 8.29). The profile starts at the river level and continues up to the plateau at an azimuth of 350 . This is a multi-level slide incorporating two independent failures, with the upper section being abandoned and the lower section being active (Figure 8.47). The upper failure has a steep, grassy head scarp with a disturbed and back tilted debris mass. The failure by itself could be described as a single rotational failure. The shear plane of this failure was not observed as it likely daylights behind the lower grassed scarp below the ledge. The total lack of sandstone and shale within the debris, allows the assumption that the failure is within the pre-glacial unit to be made. The grassed scarp below the first failure is the head scarp of the active lower failure. The lower failure is a compound slide with a shear plane with in the shale. This shear plane was located and sampled (sample 3-15A) in the vertical face below the second debris mass. The shear plane consists of 22% sand, 57% silt, and 21% clay. The Liquid Limit of 163 the sheared layer is 55% with a Plasticity Index of 40%. A distinct layer of remolded shale was also observed and sampled (sample 3-15B). This layer had high plasticity with a plasticity index of 51% and a liquid limit of 80% and contained fragments of intact shale. Above this layer, a disturbed layer of gravels, often found in pockets or included was found within the debris above suggesting that the movement was slow enough not to completely disturb the pre-slide stratigraphy. The failure occurred near the top of the shale unit with the section of disturbed shale being mostly transported out of the slope. Secondary shears also occurred within the Pleistocene sequence, however these were not the controlling structures within the slope. 164 Figure 8.34 Landslide Profile 3-1 CD CD LO o CD CD CD CO O CD OJ OJ U c5 -P o o o LO CD O CD LO LO o o LO o LO CD O "ST (ui) uo|j_x)Aa]3 Notei Stratigraphic details Inferred fron surface observations nay not be accurate Drawn By: J. Severln Landslide Profile 3-1 SCALE As Shown Figure No. 8.34 165 Figure 8.35 Landslide Profile 3-2 \s Hi U c5 -P in o o o LO LO o o ID o (ui) uoj^tjAa^ Note" Stratigraphic details Inferred from surface observations nay not be accurate Drawn By: J. Severln LandsOda Profile 3-2 SCALE As Shown Ratim No. 8.35 | 166 Figure 8.36 Landslide Profile 3-3 w E 75 -o dC = JAM Si 3 o LO |v o o r-. o m o o sO o in in o o in o in (U) uo|q.x)A3]3 o o 00 o o rv o o so o LO o o o o cu o o £ U d +> in n Note' Stratigraphic details Inferred from surface observations nay not be accurate Drawn By: J. Severln Landslide Profile 3-3 SCALE As Shown Figure No. 8.36 167 Figure 8.38 Landslide Profile 3-5 o o LO o o o o CO o o OJ o o £ OJ U -P (U) uo!u_rjAa]3 Notei Stratigraphic details Inferred from surface observations nay not be accurate Drawn By: J. Severln Landslide Profile 3-5 SCALE As Shown Figure No. 8.38 169 Figure 8.40 Landslide Profile 3-7 o o O O O O O O in o in o in o so in in M- NOTE, Stratigraphic details Inferred (U) UOjq.X)Aa,)3 from surface observations nay not be accurate Drawn By: J. Severln Landslide Profile 3-7 SCALE As Shown Figure No. 8.40 171 Figure 8.43 Landslide Profile 3-11 o o O If) in -t (U) uoiq_x)Aa]3 Notei Stratigraphic details Inferred fron surface observations nay not be accurate Drawn By: J. Severln Landslide Profile 3-11 SCALE As Shown Figure No. 8,43 174 Figure 8.44 Landslide Profile 3-12 (U) UOjq.X)Aai3 o Notei ro Stratigraphic details Inferred fron surface observations nay not be accurate Drawn By: J, Severln Landslide Profile 3-12 SCALE As Shown Figure No. 8.44 175 Figure 8.45 Landslide Profile 3-13 o • o SO o • o oo o • o CVJ £ CH u c a -p LO i—i—r o o IT) o o vO in m o o ID ^ o in ro (U) uo|arx)A8]3 Note' Stratigraphic details Inferred from surface observations nay not be accurate Drawn By: J, Severln Landslide Profile 3-13 SCALE As Shown Figure No. 8,45 | 176 gure 8.47 Landslide Profile 3-15 o o o o CO o o cu OJ u d -P o o (U) U0!D.rjAa]3 Notei Stratigraphic details Inferred from surface observations nay not be accurate Drawn By: J. Severln Landslide Profile 3-15 SCALE As Shown Figure No. 8.47 178 8.3.4 Area Model The most interesting feature of this slide area is the marked asymmetry of all the river valley walls. Three models are presented to explain both the landslides in the area and the valley wall asymmetry. The three models presented are for; 1) south-facing slopes, 2) north-facing slopes, and 3) slopes that are at an oblique angle to the previous two. South-facing Slopes (Model 1) There are six profiles within the area that have south-facing slopes, four on the Beatton River, and a single profile on each of St. John and Stoddart Creeks. Common features seen in all of these slopes are that the all contain multiple failure planes, have steep overall angles, and are only lightly vegetated. When the north wall is outside of the pre-glacial valley boundary, the failures show a dominant basal failure plane in the shale and smaller failures within the Quaternary sequence. Since the shale has very weak and often pre-sheared bedding planes, a long compound failure would be expected. This does not occur in the south-facing slopes of the Beatton River because of the regional dip of the strata and the presence of the overlying sandstone. The Cretaceous bedrock dips gently to the northeast, (into the slope) at a value of 5 .If the slope were made entirely of shale, then there would be several short failure surfaces utilizing the bedding planes even with the bedrock dip into the slope. This insignificant angle provides enough friction to make a long compound failure impossible, but would still allow for a steeper failure. The sandstone cap and sandstone interbeds within the shale acts as a stabilizing factor allowing for a much steeper angle and to act as a cohesive agent to keep the material above a weak 179 plane from failing. Lower in the slope, where the sandstone interbeds occur less frequently, the weak bedding planes are mobilized making deep failures with steep head scarps possible (Figure 8.48). The initial river valley (1) was filled with ice-damned pre-glacial sediments and eventually glaciated (2). The formation of the failures occurs by an initial stage of river erosion near the edge of the pre-glacial valley (3) causing the nearby pre-glacial sediments to fail (4). Eventually the river erodes to a weak layer that can be mobilized (5). The slide may utilize a slip surface caused by horizontal stress relief during the valley rebound process (Matheson and Thomson, 1973). After the slope fails, the river adjusts its course around the debris and active erosion takes place (6). After enough erosion has occurred, a remobilization of the debris will occur (7). Eventually the failure plane will be allowed to fail again after the buttressing debris is removed (8). The local dip and the sandstone layers allow the south-facing slopes to stand at much steeper angles than their north-facing counterparts and only allow for short failure planes. When the north wall is inside the boundary of the pre-glacial valley, a number of situations could occur. If the shale is stable and the failure planes are only within the silt and clay, then the failures can occur at any level and often several failure planes are mobilized. The failure planes still appear to be much shorter and there is an absence of the long compound failures. When the basal failure is in shale, the shear surface is short due to the local dip making a forced rotational failure. If the dip were not present, the failure plane would retrogress further into the slope. 180 North-facing Slopes (Model 2) There are three slide profiles on south-facing slopes within the area, two within the Beatton River and one within Stoddart Creek. This section is wholly within the pre-glacial valley (Mathews, 1978) and is also affected by the process of valley rebound. In general, the south facing slopes are gentle and highly vegetated and contain mostly ancient compound failures (Figure 8.49). These slopes have a dominant shear surface affected by bedrock creep within the shale. The post-glacial valley down cutting and pre-glacial valley down cutting affects these slopes. The process of valley rebound is well-defined (Matheson and Thomson, 1973) and in this area, two cycles of valley rebound may affect the stability of the slope. The initial valley formation eroded to the top of the Shaftesbury Shale. In this location, crosscutting shears and vertical relaxation joints are of minor importance because of the competence of the Dunvegan Sandstone. The most important feature created during this first down cutting is the upward arching of the riverbed within the shale. The north-facing slopes within the valley are currently above the pre-glacial riverbed. The discontinuities created by upward arching now affect the shale slope allowing for creep to occur along the horizontal planes. Upward arching affects a large area under the riverbed, allowing a large failure to occur along the shale bedding. The second series of valley down cutting exposed this riverbed and also allows for horizontal bedding plane joints to shear. These horizontal bedding plane joints allow the arching to be mobilized within the slope. The pre-glacial valley existed with steep valley walls due to the competency of the sandstone bedrock (1). The area became filled with ice-damed, pre-glacial valley fill sediments and eventually became glaciated (2). Drainage re-established itself near the 181 north end of the pre-glacial valley (3) and eroded down until a layer of weak material could be mobilised (4). These layers were very weak and had only a small amount of time to consolidate under the load of the glacial ice. As the river continued to erode down, more weak layers were sheared and mobilized (5) until eventually the river channel was confined by the shale bedrock. The overlying weight has allowed movement along the pre-sheared layers within the shale allowing for a bedrock creep to occur forcing the slope to move slowly toward the river (6). Failure in the shale likely occurs along weak bedding planes; therefore the structural properties of the rock control the slope angle and movement. Oblique Slopes (Model 3) Within this area, there are six slide profiles where the slides are at oblique angles to the regional dip, three east facing and three west facing. Of the west facing slopes, two of these are outside of the pre-glacial valley. These failures show the same mechanism and morphology as the south facing slopes outside of the valley. They are deep-seated failures within the shale with slightly longer failure planes. The other west-facing slope has a basal shear plane within the shale and upper shear planes within pre-glacial sequence. The shear plane within the shale is of an intermediate length, however, the failure planes within the pre-glacial materials are longer as they do not correspond to the bedrock geology. The west facing slopes are all within the pre-glacial valley and therefore the shear planes are mostly within the Pleistocene sequence. The failure planes within the shale also have an intermediate length and those within the surficial material are variable. 182 In general, if the slopes are at an oblique angle to the north and south, the failure planes within the shale are longer than those on south-facing slopes and shorter than those on north-facing slopes. Failure planes within the Pleistocene sequence are variable and do not correspond to any trends. 183 Figure 8.48 Landslide Area 3 - Model 1 V ,' ' ' ' •!'*... 1) Broad, stable pre-glacial bedrock channel; 2) Aggregating deltaic environment into encroaching ice-damned lake followed by glaciation; 3) Drainage re-establishes; 4) Post-glacial river erodes down into till and sandstone leaving steep banks; 5) Once softer shale is reached, initial failures occur along near-horizontal surface unloading slope; 6) Failures continue to occur, on older, upper bedding planes and lower planes once exposed; 7) Debris at base acts as a berm for debris on slope, internal deformation of debris occurs; 8) Erosion of debris and intact bank cause failure. 184 gure 8.49 Landslide Area 3 - Model 2 1) Broad, stable pre-glacial bedrock channel; 2) Aggregating deltaic environment into encroaching ice-damned lake followed by glaciation; 3) Drainage re-establishes; 4) Post-glacial river erodes down into till and sandstone leaving steep banks, once softer, laminated sediments below are reached, initial failures occur; 5) Failures continue to occur, on older, upper lower bedding planes and lower planes once exposed, debris at base acts as a berm for debris on slope; 8) Erosion of debris and intact bank and increases in pore pressure in pre-glacial units cause failure. 185 8.4 Slide Area 4 8.4.1 Location The fourth area chosen to study was along the Beatton River, north of the town of North Pine (Figure 8.50). The area was chosen due to its accessibility and because all of the landslides are completely within the Pleistocene sequence. In fact, the shale bedrock is at or beneath the river level and does not play a role in slope stability in the area. Both sides of the river are easily reached as there is a bridge in the immediate area and the approach to the bridge has undergone recent failure, undermining the foundation of the road. The road services a petroleum extraction area to the north east of the site. This locale was also selected due to the high number of very active and active slides in the area. Four slides were profiled in this area. The area encompasses both banks along an 8-kilometer stretch of the Beatton River. This region is also home to 'Kings Valley Christian Camp" which provide valuable assistance in accessing areas and providing witnessed accounts of some of the local failures. 8.4.2 Local Stratigraphy This area is located within the boundaries of the pre-glacial valley near its northern end (Mathews, 1978). The local stratigraphy is pieced together from the four slides in the area (Slide 4-1, 4-2, 4-3, and 4-3). The bedrock extends to an elevation of 531 meters a.s.l if the slide is located near the edge of the pre-glacial valley; otherwise, the bedrock is not present. This location is within the Dunvegan Formation as the regional dip places the Shaftesbury Shale at an elevation not yet reached by the river. Above the bedrock occurs a thin unit of gravel (<lm) within two of the profiles. All of 186 Figure 8.50 Landslide Area 4 the slides show good intact sequences within some of the scarps, where all the detailed stratigraphy is noted. Unfortunately, the stratigraphy of the Quaternary deposits is complex and cannot be correlated from one section to another. The pre-glacial unit is variable, laterally and vertically, within these separate sections so it is not likely that beds match up over longer distance. This area is interpreted as being part of a deltaic sequence due to the silt and sand cross beds observed and the variability of the materials over a small distance. The intact section neighbouring Slide 4-3 shows a detailed deltaic sequence supporting this interpretation (Figure 8.51). A till cap was witnessed at an elevation of 640 meters a.s.l. A hypothetical stratigraphic column is produced (Figure 8.52). Figure 8.51 Deltaic Sequence (Slide 4-3, * G.Hartman-notes) 5' 573 if. Bt-g^nrTTtfl" SSV-S SW5 -5 37 SM,5. o~'-r fir . 1 * S - Lo^t,^ tfa-r^tf t~OAd% ^C-f if. jC'Vw, t<^i 188 Figure 8.52 Area 4 - Stratigraphic Profile 650 m a.s.l 640 m a.s.l 532 m a.s.l 531 m a.s.l Clay with dropstones Laminated Silt, Sand and Clay - stratigraphy variable, unit thought to represent deltaic sequence Sand and Gravels - slightly cemented Dunvegan Sandstone - top contact represents hiatus 8.4.3 Landslides Slide 4-1 Slide 4-1 is an active, multi-leveled failure with two slide planes within the pre-glacial unit (Figure 8.55). The slide occurs on a west-facing slope along the Beatton River directly across the river from the Christian Campground (Figure 8.50). The profile begins on a knife-edge with a larger dormant slide with an aspect that is opposite of the 256° azimuth of this slide. The head scarp is made of a disturbed material likely caused by the older abutting failure. The upper shear zone was observed to be within silt dominated facies of the pre-glacial unit at an elevation of 595.65 meters a.s.l. A slickensided surface was not found within this degraded and modified shear zone, however, a sample of the clay zone was taken (sample 4-1 A). An intact section of the facies was found 30 meters to the north (Figure. 8.53) and was found to be sand dominated with larger cross beds and few clay layers. The fine-grained beds below the 189 shear surface have smaller-scale cross beds with a higher percentage of clay. The second failed mass shows some back tilt and horst and graben structures although the shear plane was not observed. The morphology of the slope suggests that the debris slides over an intact section and the toe appears to be remobilized debris. A bedrock elevation was found at an outcrop near the toe of the failure with a thin (< 1 m) intact unit of gravel above along with a sand-dominated pre-glacial section. Figure 8.53 Intact Section Photo (Slide 4-1) Slide 4-2 This failure is a very active multi-level failure within the Pleistocene sequence on a north facing slope on the Beatton River (Figure 8.56). The failure is located approximately 500 meters upstream from the bridge within the area. The profile begins upon a stable plateau underlain by till and heads down slope at an azimuth of 26°. The failure contains three failure planes all within the sand-dominated pre-glacial sediments. Most of the upper section of the slope is covered in colluvium and the shear planes are 190 Most of the upper section of the slope is covered in colluvium and the shear planes are not visible. The upper failures are interpreted from slope morphology to have rotational and translational failure mechanisms. Most of the features are muted and older than the toe. Below the upper failures is an intact section of massive sand with small interbeds of silt and clay. The lower failure is fresh with a shear surface (sample 4-2 A) within a silt-rich package within the sequence (sample 4-2 B). The shear plane is composed mostly of silt (77%) with some clay (18%). The plasticity of the sheared material is fairly low, with a liquid limit of 39% and a plasticity index of 24%. The intact clay bed sampled is actually 97% silt, which has low plasticity with a liquid limit of 28% and a plasticity index of 8%. Below the intact section where the shear plane was found, is a toe of remobilized debris. Slide 4-3 Slide 4-3 is a small, very active, rotational failure on a south-facing slope on the Beatton River (Figure 8.57). The profile begins mid-slope on a stable bench and heads down towards the river level at an azimuth of 147 pgure 8.50). The slope above this failure is likely part of a separate failure. It could not be profiled, as the roadway that bisects the slope was heavy with traffic. The debris surface is fresh with ponding and intact slump blocks within the debris mass. The head scarp has a complex stratigraphy with silt, gravel, and massive clay. The single failure plane for this slide is within the pre-glacial unit with the bedrock missing at this section. The basal shear plane was not found but is interpreted as being slightly below the river level. The slump blocks within the debris have matching stratigraphy found in the head scarp and in an intact section near the slide. 191 Slide 4-4 Slide 4-4 occurs on a north-facing slope on the Beatton River roughly 3 kilometers south of the Christian Camp (Figure 8.50). The profile begins on a stable section of the slope. It is presumed stable due to the lack of any landslide features and the low angle of the slope (1 ). The profile continues down the slope at an azimuth of 330 . The slide has two failure planes, both within the pre-glacial sediments (Figure 8.58). The upper failure is a deep, compound failure approximately 700 meters long and 50 meters deep. The debris mass exhibits dormant, translational features, i.e. horst, grabens, and cross-tilted trees. A rotational failure occurs behind the toe of the upper slide because of an intact scarp in which the shear plane for the compound failure was located (sample 4-4 A). The shear plane is made of silt, 76%, and clay, 13% and has a medium plasticity with a liquid limit of 58% and a plasticity index of 35%. Below the main shear, smaller shear planes were found and sampled (sample 4-4 B). These shear planes are also mostly made up of silt, 86%, with minor clay, 10%. The secondary shears are much more plastic with a Liquid Limit of 73% and a Plasticity Index of 53%. The intact face shows a complex stratigraphy (Figure 8.54) with several shear planes and massive clay unit with drop stones and gravel lenses. Below this intact face exists a second debris mass with rotational slide features, including ponding and back tilted slump blocks and trees. This lower failure has fresh features and is very active as it occurred 2 years ago. The toe of the slide is assembled of remobilized debris. 192 Figure 8.54 Complex Stratigraphy (Slide 4-4) > Figure 8.55 Landslide Profile 4-1 o o Notei Stratigraphic U) UOI4.T0A811 details inferred from ' '~ '—1 surface observations nay not be accurate Drawn By. J. Severln Landslide Profile 4-1 SCALE As Shown Figure No. 8.55 194 Figure 8.57 Landslide Profile 4-3 e: OJ U sz -P in o o in o in o in f\ in OJ o rv in LO in in ^-Drawn By? Note" Stratigraphic details Inferred fron surface observations nay not be accurate J. Severln LandaMa Profit* 4-3 SCALE As Shown Figure No. 9.57 196 8.4.4 Area Model This area represents a deltaic sequence within the pre-glacial materials above a stable bedrock channel of sandstone (1). The materials of this sequence are variable and therefore the failure planes cannot be correlated over a longer distance (Figure 8.59). The pre-glacial unit represents a deltaic environment as the Beatton River continued to transport sediment into an expanding ice-damned lake within the river valley (2). The area then became glaciated (3) as evidenced by the till and post-glacial lake sediments. Drainage became re-established (4) and eventually cut into the deltaic silts, sands, and clays. The river channel at this time likely had steep walls, as the till in this area is mostly competent. Once the river eroded down into the pre-glacial sediments, layers of weaker, more plastic materials were exposed and failures occurred along them. The debris mass likely acted as a protection berm until it was eroded. As the river continued to cut downward, new layers were exposed and failures occurred along several failure planes as the intact material weakened and softened. This process is still occurring, shown by the high activity of landslides found on this river. Several of the failure planes occur at similar elevations, so there may be larger beds which can extend over a large area, but for the most part, failures that occur at similar levels at this site do so by coincidence. The failures at this location are generally rotational with shorter shear planes than in other areas. The variability of the materials is directly responsible for the shorter shear planes. The valley was created by rapid erosion and down cutting. This process has exposed the plastic layers and allowed them to fail. The clay beds within the sequence may have been pre-sheared by glaciotectonics and by horizontal relaxation during the valley rebound. During valley rebound, the weakest layers undergo the most deformation; in this case, the 198 Figure 8.59 Landslide Area 4 - Geologic Model 1) Stable pre-glacial bedrock channel; 2) Aggregating deltaic environment into encroaching ice-damned lake; 3) Glaciation; 4) Drainage re-establishes; 5) Post-glacial river erodes down into till leaving steep banks, once softer, laminated sediments below are reached, initial failures occur; 6) Failures continue to occur, on older, upper lower bedding planes and lower planes once exposed. Debris at base acts as a berm for debris on slope. 199 plastic clay layers are the victims. As downcutting occurs, these failure planes are exposed and allowed to fail. Often the upper sections of the slope contain older, dormant failures, suggesting that toe erosion is the major trigger of landslides in this area. 9.0 DISCUSSION 9.1 Landslide Mechanisms and Distribution This study of slope movements in the Peace River area has led to the formation of several interesting discussion points. The most important one is the understanding of the river valley slope morphology in shale and unconsolidated valley fill sediments. This project also helps to characterize the geotechnical properties of the sediments located within the Peace River Valley and associated tributary valleys. This project is also the first attempt to systematically map and take inventory of landslides within the Peace River Valley, one of the many valleys in the Canadian Prairies, which shows ubiquitous landsliding throughout its length. The first major result of this project is that a majority of the failures contain more than one shear plane on which the landslides mobilize. These multiple failure planes are located both within the Cretaceous shale and the Pleistocene laminated silts, sands, and clay. Further, there are several elevations within the shale that are apt to fail, that is to say that there is no one unique elevation at which all failures occur within the shale. There are several bentonite-rich layers within the shale that are weak enough to fail. No pure bentonite layers were found within this extensive field-based project, however, as there are numerous failures, most of which with covered shear planes, it is possible that such bentonite layers exist. Many slides, especially those that occur outside the preglacial 200 valley, noted in the "Old Fort" area, have multiple shear planes within the shale. In other areas, located within the pre-glacial valley, there are often failure surfaces within both the Cretaceous bedrock and Pleistocene sediments, or often exclusively within the unconsolidated silts, sands, and clay. Another result from this project is the recognition that morphology can rarely be used to determine the material in which the shear plane is located. Failures in both Cretaceous shale and Pleistocene sediments are morphologically similar with comparable features and sizes. Even though the materials are geologically different from each other, their engineering properties, which control the stability of the slopes and the failure mechanisms, can be similar. During this investigation, the location of the failure surface was often inferred by an understanding of material distribution and deposit geometry as understood by past geologic investigations of the area (Stott, 1982, and Mathews, 1978). From the detailed landslide map and resultant inventory, a number of trends can be noticed. As mentioned in Section 8.4, a total of 1610 slope failures covering 1262 km were analyzed in terms of their distribution, activity, type, material involved, and aspect. The Peace river contained nearly a third (28.9%) of all failures catalogued and together with the Beatton River, contains over a half of all failures, 54.2%. The average slide per kilometer ratio is 1.28 slide/km, with the Peace and Beatton Rivers showing the highest values of 1.82 and 1.60 respectively. The overall area covered by all failures was 765.5 km2 with an average area per slide of 0.48 km2. The dominant activity level throughout the entire map sheet is "Low Activity -Dormant" with 61.0% of all failures classified as this level. "Very Active" and "Active" failures comprise 1.9% and 12.9% of all failures, respectively. "Very Active" and 201 "Active" slides are also both dominantly multi-leveled failures, 73.3% and 43.0%, respectively. Approximately 30.0% of all "Very Active" failures had a northern aspect, twice the average percentage and are dominantly in the Quaternary sedimentary sequence (73.3%). The dominant failure type within the study area is the multi-leveled failure comprising nearly half of all failures, 47.8%, or over 769 failures. This value is thought to be conservatively low as the worst-case scenario, or deeper failure plane was assigned if doubt existed as to its location. Multi-rotational failures are the most active with 2.9%, which is to be expected due to the distribution of landslide types. Compound failures occur mostly on north-facing slopes, likely a reflection of the regional dip in the bedrock towards the northeast. East and west-facing slopes are dominated by retrogressive rotational failures each with 19.5% on slopes of those aspects. South facing slopes are dominated by multi-level failures, with 19.9 %. The dominant failure type, multi-leveled failures, is evenly distributed between the shale, 51.9%, and the Pleistocene sequences, 48.1%. Compound failures occur mostly within the shale bedrock (61.9%). This is probably due to the relative ease with which the overlying Quaternary sand, silt and clay can be sheared through in order to produce a curved head scarp. The higher number of single rotational failures occurring in the unconsolidated sediments, 64.8%, supports this fact. Shale is the basal material in 43.7% of all failures, while the Pleistocene sequence represents 56.3%. This equal distribution is one of the reasons why landslide investigation is so difficult in the Peace River Region. The value for shale failures is 202 slightly higher in north-facing failures as the regional dip of the bedrock is more favorable for failure. 9.2 Generalized Geologic Model A series of generalized geologic models depicting the occurrence of landslides in the Peace River Region has been produced. Each investigated site fits into an aspect of this model depending on local conditions. The model starts with the deposition of the low energy sediments into an inland sea during the Cretaceous Period. During this time, several volcanic events occurred, associated with the orogenic activity to the west, depositing ash in the deep sea environment. This was followed by continued deposition, which allowed the sediments to compact into shale incorporating the weathered ash, or bentonite, into laminations of the shale. During the Tertiary and Quaternary Periods, a long period of erosion allowed broad valleys to form in to a mature drainage system. It is possible that these broad valleys developed by extensive landsliding that developed along the weak layers within the shale to retrogress back from the river and become stable at a very low angle. During the ice advances of recent geologic time, the valleys have been plugged with valley fill sediments, such as silt, sand, and clay followed by a glacial diamicton unit that overlies the sedimentary sequence. The weight and movement of the glaciers may have caused further failure in the shale and shearing within the unconsolidated sediments below. Upon retreat of the glaciers, a post-glacial lake occurred, and another unit was deposited of normally consolidated clays. Once the ice or sediment dam, which retained the post-glacial lake, was breached, a rapid downcutting through the Pleistocene sequence occurred, uncovering the sheared planes and allowing 203 syn-erosional slumping to occur. The rapid downcutting may have also caused some new shear planes to develop as riverbanks became too steep to be supported. Valley rebound features occurred within both the horizontal shale bedrock along the bentonitic-rich layers and within the Quaternary sedimentary package along the plastic clay layers. As further erosion occurred, the current river valley began to take shape with slow moving failures along the pre-defined shear planes. The valley developed as a series of landslide cycles, in which the valleys walls retrogress back, stabilize, are eroded, and retrogress back again. A similar sequence involving the London Clay and wave erosion was noted near the Thames estuary in England (Hutchinson, 1975) and has been postulated to occur in Alberta (Cruden et al., 1998). Of course, several (of the) parameters would have to be taken into account; however, the same type of cycle could be responsible for the development of the pre-glacial and current Peace River Valleys. A secondary conclusion, based on air photograph interpretation and field investigation, is that the river morphology of the Peace River is completely dependent on the slope morphology of the river valley slopes. Several of the large islands within the Peace River are at the base of failed slopes. The large slide at Attachie in 1973, allows us to examine the effects of failures on the river morphology. Smaller areas of the slide debris have stabilized within the riverbed, making islands at the edges of the river. Conversely, the islands themselves can help the investigation of slopes as well. The islands may indicate that a large amount of debris has been deposited denoting the presence of a large landslide. In the Peace River, it can then be said that the slope was unstable and may still be. The slope may consist of several shear planes and can then be 204 marked as an abandoned failure even though the slide morphology has been completely destroyed. 10.0 CONCLUSIONS One of the main objectives of this research project was to complete a comprehensive landslide inventory and map to be used in future engineering and geological work done in the Peace River region. The landslide map, containing over 1600 slope movements, is one of the main products of this project. The detail contained within the map, including activity and morphological features, make it a valuable document to be included in any desk or field study with respect to the Peace River region. The detailed inventory database, created to accompany the map, includes: River Segment, Activity, Failure Type, Slide Aspect, Likely basal shear material, Length, Width, Area, and Morphological features (Appendix II). This inventory, based on air photo interpretation and field proofing, was used to analyze the landslides with respect to these characteristics, in order to make some basic conclusions about landslides in the Charlie Lake map sheet. The most important conclusion derived from an analysis of this data was that a majority of the failures were multi-leveled, containing at least two shear planes. Almost 48% (769) of all failures were multi-level. This number is thought to be conservative as many of the failures are now dormant and their features obscured. In this case, the worst case scenario was used, i.e., a single large failure, therefore, the number of multi-level failures is likely to be higher and the number of rotational, retrogressive rotational, and compound failures would be lower than shown. A corollary to this conclusion is that 205 instead of having one single weak layer within the region, there are many relatively weak horizons both in the unconsolidated material and in the bedrock. Based on laboratory testing of both failed and intact materials, there was little difference in bulk properties between the two types of material tested and the failed materials were not highly plastic. Of the 28 samples collected, four were a gouge material, eight were of sheared or disturbed shale, and 16 were of clay, sheared and intact. The average value of the Liquid Limit of the intact clay beds was 47.4%, while the sheared beds had a Liquid Limit of 49.8%. The Plasticity Indices of the intact and sheared beds are 30.3% and 27.9%, respectively. The sheared beds are silt dominated, 70% and 63%, respectively. The shale has a slightly higher Liquid Limit of 49.1% and a Plastic Index of 29.2%. Thus, the physical differences between weaker and stronger horizonz is subtle. The preferences for failure occurring on certain horizons is probably due to pre-shearing as a result of flexural slip. Another important result was that the Beatton River seems to be the most active of all areas. Over half of all the Very Active failures were found within the Beatton River Valley. This thought to be because the rate of erosion is slightly higher that the Peace River, with the same weak materials. The higher rate of erosion is due to the steeper gradient of the river. The third conclusion is that north-facing slopes appear to be more active than their south facing counterparts. 226 failures (14%) occurred on north-facing slopes as opposed to the 113 (7%) on south-facing slopes. The reason is thought to be the gentle northeastern dip of the underlying bedrock. The dip of the shale bedrock in to the valley allows for more failures to occur than would otherwise be allowed at such shallow 206 angles. This gentle dip can also dramatically affect the type of slide observed in the river valleys. On the north-facing slopes, a distinct majority of long, compound failures were found. These failures are thought often to utilize weak layers in the Cretaceous shale rather than the Quaternary sequence above. Unfortunately, this is not always the case, therefore it can not be a rule, but rather a generality. Often, morphology alone can be a deciding factor in determining which type of material has failed. This can occur only if the preferred failure mechanism it is known for a material in that situation. This study presents the opposite situation in which knowing the type of failure can not really help determine which material had failed. This is due to the similarities in the failure setting for both the shale and the pre-glacial clays. The Peace River region provides an example where making assumptions on failed material based on morphology could prove incorrect. The final conclusion to be made from this work is derived from field work completed during the summers of 2002/2003, when a total of 40 landslides were profiled within the Peace River Area. These profiles were completed in four landslide investigation areas; Big Bam Ski Hill, Old Fort, Beatton Big Bend, and Beatton Christian camp. These areas were investigated in greater detail in the field with profiles of individual slides and several samples being collected and tested. From this work, geologic models were created for each of the areas and then combined to produce a generalized model for failures in the Peace River region. The generalized model is discussed in Section 9.2. 207 The results of the research indicate how a landslide inventory can be compiled, the necessary steps that must be taken in order to make it valid and useful, and what types of information can be harvested from such an inventory. 208 REFERENCES Barton, M.E. 1984. The preferred path of landslide shear surfaces in over-consolidated clays and soft clays. In 4th International Symposium on Landslides, Vol. 3., pp75-79. Beene, R.R.W. 1967. Waco Dam slide. ASCE Journal of the Soil Mechanics and Foundations Divisions, Vol. 93 (SM4). pp. 35-44. Bobrowsky, P.T. and Smith, CP. 1991. Quaternary studies in the Peace River District, 1990: stratigraphy, mass movements and glaciation limits (94P). In Geological Fieldwork 1990, B.C. 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Retrogressive slope behaviour at Beaver Creek, south of Saskatoon, Saskatchewan, Canada. Canadian Geotechnical Journal, Vol. 14. pp. 288-301. Holland, S.S 1964. Landforms of British Columbia, a physiographic outline. B.C. Department of Mines and Petroleum Resources. Bulletin 48, 138 p. Hungr, O. 1997. Some methods of landslide hazard intensity mapping. In Landslide Risk Assessment. Ed. Cruden, D.M. and Fell, R. pp. 215-226. Hungr, O., Evans, S.G., Bovis, M., and Hutchinson, J.N. 2001. Review of the classification of the landslide of the flow type. Environmental and Engineering Geoscience, Vol. VII, No. 3, pp. 221-238. Hutchinson, J.N. 1973. The response of London Clay cliffs to differing rates of toe erosion. Geologia Applicata e Idrogeologia, Vol. 8, Part 1, pp. 28-301. Hutchinson, J.N. 1988. General Report: Morphological and geotechnical parameters of landslides in relation to geology and hydrogeology. In. Proceedings, 5th International Symposium on Landslides, Lausanne, Vol. 1, pp. 3-35. Imrie, A.S. 1991. Stress-induced response from both natural and construction-related processes in the deepening of the Peace River Valley, B.C. Canadian Geotechnical Journal, Vol. 28, pp. 719-728. Irish, E.J.W. 1958. Charlie Lake, British Columbia. Geological Survey of Canada, Map 17-1958. 211 Jones, J.F. 1968. Geology and groundwater resources, of the Peace River District, Northwestern Alberta. Alberta Research Council, Bulletin 16. 143 p. Keefer, D.K. and Johnson, A.M. 1983. Earthflows: Morphology, mobilization and movement. U.S. Geological Survey Professional Paper 1264. 56 p. Kenney, T.C. 1975. Formation and geotechnical characteristics of glacial-lake varved soils. Laurits Bjerrum Memorial Lecture, Oslo. pp. 15-39. Krahn, J. and Weimer, N.F. 1984. The W.I.D. Landslide. In Proc. 37th Canadian Geotechnical Conference. Canadian Geotechnical Society of Canada, pp. 209-215. Locker, J.G. 1973. Petrographic and engineering properties of fine-grained rocks in central Alberta: Research Council Alberta Bulletin. 30, 144 p. Lu, Z-Y, Cruden, D.M., and Thomson, S. Landslides and Pre-glacial channels in the Western Peace River Lowland, Alberta. In Proc. 51st Canadian Geotechnical Conference. Geotechnical Society of Canada, pp. 267'-21'4. Maber, CT. and Stewart, P. 1976. The Peace River Hill Landslide. Proc. 29th Canadian Geotechnical Conference, Canadian Geotechnical Society, pp. 35-47. Matheson, D.S. and Thomson, S. 1973. Geological implications of valley rebound. Canadian Journal of Earth Sciences. Vol. 10, pp. 961-978 Mathews, W.H. 1978. Quaternary stratigraphy and geomorphology of Charlie Lake (94A) map-area, British Columbia. Geological Survey of Canada Paper 76-20, 25 p. McClarty, E.A. and Cavers, D.S. 1998. Surface-Pipeline segments solve slide problems in B.C. gasline. Oil &Gas Journal, Dec. 14. pp. 43-52. Mitchell, R.J. 1978. Earthflow terrain evaluation in Ontario. Ontario Ministry of Transportation and Communications, RR 213. 23p. Mitchell, R.J. and Markell, A.R. 1973. Flow sliding in sensitive soils. Canadian Geotechnical Journal, Vol. 11, pp. 11-31. Mollard, J.D. 1977. Regional landslide types in Canada. In. Reviews of Engineering Geology, 3. Geological Society of America, pp. 29-56. Morgenstern, N.R. and Eigenbrod, K.D. 1974. Classification of argillaceous soils and rocks. Am. Soc. Civil engineers Proc, Journal of Soil Mechanics and Foundations Division, Vol. 100, No. GtlO, pp. 1137-1156. Naismith, H. 1964. Landslides and Pleistocene deposits in the Meikle River valley of northern Alberta. Canadian Geotechnical Journal, Vol. 1, pp. 155-166. 212 Peterson, R., Jaspar, J.L., Rivard, P.J., and Iverson, N.L. 1960. Limitations of laboratory shear strength in evaluating stability of highly plastic clays. American Society of Civil Engineers Conference of Shear Strength of Cohesive Soils, Boulder, Colorado. Pp. 765-791. Plint, A.G. 1988. Sharp-based shoreface sequences and "offshore bars" in the Cardium Formation of Alberta: their relationship to relative changes in sea level. In: Sea-level Changes: An Integrated Approach. C.K. Wilgus, B.S. Hastings, C.G.St.C. Kendall, H.W. Posamentier, CA. Ross, and J.C Van Wagoner (eds.). Society of Economic Paleontologists and Mineralogists, Special Publication 42, p. 357-370. Russell, L.S. 1943. Sexsmith-Bison Lake, preliminary map. Geological Survey of Canada, internal report. Saint Simon, P.G.R, Solymar, Z.V., and Thompson, W.J. 1979. Damsite Investigation in soft rocks of Peace River Valley, Alberta. In Proc. International Congress on Rock Mechanics, Suisse, pp. 553-560. Sargent,, D.W. and Cornish, L.J. 1985. Water susceptibility of Shaftesbury Shale. Proc. 38th Canadian Geotechnical Conference. Canadian Geotechnical Society, pp. 197-206. Sauer, E.K., Gareau, L.F., and Christiansen, E.A. 1990. Softening of Cretaceous clay by glacial erosion. Quaterly Journal of Engineering Geology, London. Vol. 23, pp. 307-324. Scott, J.S. and Brooker, E.W. 1968. Geological and engineering aspects of Upper Cretaceous shales in western Canada. Canada Geological survey Paper 66-37. 75 p. Skempton, A.W. 1964. Long-term stability of clay slopes. Geotechnique, 14. pp. 77-101. Skempton, A.W. and Hutchinson, J.N. 1969. Stability of natural slopes and embankment foundations. In Proc. 7th International Conference on Soil Mechanics and Foundation Engineering, Mexico. State of the Art Vol., pp. 291-340. Sissakian, V., Soeter, R., and Rengers, N. 1983. Engineering Geological Mapping from Aerial Photographs: The Influence of Photoscale on Map Quality and the Use of Stereo-Orthophotographs. ITC Journal, No. 2, pp. 109-118. Sowers, G.F. 1979. Application of results of exploratory borings and index properties to soil engineering problems. In Simposio Internacional de Mecanica de Suelos. pp. 3-16. Stanton, R.B. 1898. The great landslides on the Canadian Pacific Railway in British Columbia. In Minutes of the Proc. of the Institution of Civil Engineers, London, Vol. 132, pp. 1-20. 213 Stott, D.F. 1982. Lower Cretaceous Fort St. John Group and Upper Cretaceous Dunvegan Formation of the Foothills and Plains of Alberta, British Columbia, District of Mackenzie, and Yukon Territory. Geological Survey of Canada, Bulletin 328, 124 p. Stott, D.F. 1967. Jurassic and Cretaceous stratigraphy between Peace and Tetsa Rivers, northeastern British Columbia. Geological Survey of Canada, Bulletin 66-7, 73 p. Terzaghi, K. and Peck, R.B. 1948. Soil Mechanics in engineering practice. 1st ed. John Wiley and sons, New York. Thurber Consultants Ltd., 1981. A report on field inspection of overburden landslides. Report to B.C. Hydro & Power Authority. File 15-2-169A Thurber Consultants Ltd., 1982. Feasibility of stabilizing the Attachie Slide and adjacent areas, Site C Reservoir. Report to B.C. Hydro & Power Authority. File 15-2-169 Thomson, S. 1958. Collapse of the Peace River Bridge. In B.C. Professional Engineer, May 1958. Thomson, S. 1971. The Lesueur Landslide, a failure in Upper Cretaceous clay shale. In Proc. 8th International Conference on Soil Mechanics and Foundation Engineering. Moscow, Vol. 4.3, pp. 330-343. Thomson, S. and Hayley, D.W. 1975. The Little Smoky landslide. Canadian Geotechnical Journal, Vol.12, pp. 379-392. Thomson, S. and Mekechuk, J. 1982. A landslide in glacial lake clays in central British Columbia. Canadian Geotechnical Journal, Vol. 14, pp. 508-523. Thomson, S. and Morgenstern, N.R. 1978. Landslides in argillaceous rock, Prairie Provinces, Canada. In Rock slides and avalanches, Vol. 2, Edited by B.Voight. Elsevier Press, Amsterdam, The Netherlands, pp. 515-540. Thomson, S. and Tweedie, R.W. 1978. The Edgerton landslide. Canadian Geotechnical Journal, Vol. 15. pp. 510-521. Thomson, S. and Yacyshyn, R. 1975. Slope Instability in the city of Edmonton. 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Thesis, University of British Columbia. 70p. 215 APPENDIX I Geotechnical Lab Results Grain Size Analysis Atterberg Limits SUMMARY OF HYDROMETERS TO: Geological Survey of Canada 601 Booth Street Ottawa ON K1A0E8 ATTENTION: Mr. Larry Dyke PROJECT: Peace & Beatton Rivers ame OFFICE: Fort St. John PROJECT NO: GX04091 CLIENT: Geological Survey of Canada COPIES TO: Mr. Jordan Severin SAMPLE NO. 1-1C 1-4A 1-4B 2-2A DATE July 20/03 June 21/03 July 23/03 2-2B 2-4B 2-4C 2-4D 2-4I 2-6A 2-6B 2-8A 2-8AA 2-8B 2-8D June 26/03 June 27/03 June 29/03 June 29/03 June 29/03 July 23/03 June 30/03 SOIL DESCRIPTION Shale Failure Plane Shear Surface #1 ICS Massive Clay Shale/Shear? Debris/shear Debris Shear Plane Gouge Shale Shear Plane June 30/03 July 3/03 July 23/03 3-1A 3-5A 3-5B 3-13A 3-14A 3-14B 3-15A 3-15B 4-2A 4-2B 4-4A 4-4B July 3/03 July 3/03 July 6/03 Shear Gouge Failed Clay Shear Gouge in Shale Upper Shear Plane Sand 25% 3% 4% 7% 7% 19% 30% 4% 23% 9% 38% Intact Clay II Intact Clay Beneath Shear f5cm) Lower Slide Plane July 8/03 July 8/03 July 12/03 July 13/03 July 13/03 July 13/03 July 13/03 July 19/03 July 19/03 July 22/03 PMA July 22/03 Shear Plane ICS Adjacent Shear Gouge Remolded Shale Shale Shear Remolded Clay? Middle Material Shale Shear Remolded Shale 0% 0% Silt 61% 59% 72% 70% 70% 49% 66% 85% 68% Clay 14% 38% 24% 23% 23% D30 mm .0054 .0011 .0029 .0032 32% 4% 11% 57% 40% 50% 0% 1% 1% 13% 32% 19% 1% 1% ICS Shear Intact Clay Shear Upper ICS June 24/03 Shear ICS Shear Plane 22% 14% 5% 2% 11% 4% 4% 43% 68% 63% 52% 68% 58% 78% 77% 74% 57% 50% 77% 97% 76% 86% 57% 34% 22% 50% 57% 32% 36% 47% 19% 10% 3% 22% 25% 21% 36% 18% 1% 13% 10% 39% .0030 .0018 D60 mm .023 .0086 .018 .046 .027 .021 .0066 .014 .0015 .0042 .0010 .00082 .0018 .0014 .00088 .0056 .016 .045 .0035 .0026 .0038 .0012 .0063 .016 .028 .0031 .0012 .026 .061 .033 .054 .011 .070 .0032 .0025 .051 .013 .0037 .030 .055 .063 .027 .0088 .044 .023 .038 .031 .060 .0059 .0055 ^ AGRA GRAIN SIZE ANALYSIS 1.3 1 PROJECT • — SAMPLE PHA 3*t34 1 Sh ^f\n n r [LAB ORDER ' • ~—'—: • 1 tST HOLE DEPTH ' f " — . sieve A TECHNICIAN ' [ ' SlALYSIS " TOTAL SAMPLE total wt. ret. on #10 — wt. pass. #10 1 pan — wt. pan _ wt. passing #10 total wt. _ hydrometer sample tare no. : wt. tare &. wet soil — _ wt. tare — wt. wet soil — 50'tO, water content , — wt. dry soil ' — START TIME - ,**)', CPO TIME "K" FACTOR TIME INTERVAL j SIEVE SIZE WT. RETAINED PERCENT PASS. 1" •w r 4 10 20 40 60 O. 2s" 100 ( 200 ( -WATER CONTENT tare no.' wt. tare & wet soil — 2QrS3) wt. tare & dry soil wt. tare wt. water wt. dry soil | water content % — "a"factor diameter HBLT 70 - 68 /09 ['"<^seryice^,y.tnSineer,nn interpretation valuation of tnt, test results is provided only on written request. GRAIN SIZE ANALYSIS SAMPLE f-. • DATE Is provided cn/yon wri„an request. ©AGRA ^__^2!l^nvironmenial | PROJECT ~ ~ ~ _ LAS ORDER GRAIN SIZE ANALYSIS 2L>._ .;• ' DPPTu *~ TOTAL SAMPLE TQTAl'wT RFT OrJ«m— A^MQ ~ WT. PASS. #10 & PAN — _ WT. PAN - Y I ' 7 • WT. PASSING #10 TOTAL WT. -—-|rgC^rfclAN _S!EVE ANALYSIS DEPTH "• DATE [3A5 HYDROMETER SAMPLE TARE NO. • | WT. TARE & WET SOIL — '. WT. TARE — WT. WET SOIL — — WATER CONTENT — I WT. DRY SOIL !i<lFACTOR INTERVAL | RDG SIEVE WT. DETAINED PERCENT PASS. WATER CONTENT TARE NO. I WT. TARE & WET SOIL - 2"},& •— ' WT. TARE & DRY SOIL - "Z-7.3 S %" ~~~ WT. TARE ^2.^ . 4 WT. WATER _ • io WT. DRY SOIL 20 WATER CONTENT % _ 40 ' 60 l\ 100 — 200 ( HYDR ^ZZT 3METER TES r _J Zio / §AGRA / Eartn & Enviroritnental !-^Z__^0_tWT^ ~ LAB ORDER ' ; GRAIN SIZE ANALYSIS TEST HOLE ! " TECHNICIAN DEPTH TOTAL SAMPLE TOTAL WT. RET. ON #10 — . WT. PASS. # 10 & PAN —. WT. PAN — . WT; PASSING #10 — TOTAL WT. — HYDROMETER SAMPLE . TARE NO. WT. TARE St WET SOIL — — WT. TARE — — WT. WET SOIL ———— WATER CONTENT — WT. DRY SOIL ' — START VME^JjPJ^/P TEMP •c SIEVE SIZE WT. j RETAINED PERCENT PASS. 1-y<" Vi"' X" 4 10 | 40 60 . 100 °- 9/ j 200 ( WATER CONTENT TARE NO.' JzHL WT. TARE & WET SOIL —. WT. TARE & DRY SOIL — _/ 7 • ^6 WT. TARE ——L= (— WT. WATER — — WT. DRY SOIL — ——-WATER CONTENT % — HYDROMETER TEST les,'results is provide only on written request. an This page intentionally left blank 222 ^ AGRA . 7R0JECT^ . • — f-AB ORDER ^_____^GRAIN SIZE ANALYSIS ""7 ' 7 : ; —: nppTu -L^CHNIOAN , I PERCENT f^ETA/NED ' 1 ^ " " ' " ' " prc""d<K' °"ly°n written truest. ^AGRA . GRAIN SIZE ANALYSIS 7 ? DEPTH ^~^-L^^~^ . 1V\ GRAIN SIZE ANALYSIS WT. PASS. #,0 4^- 91/. £6 - u-^r • — | WT. PASSING #10 _ TOTAL WT. WATER CONTENT (TARE NO.' | WT. TARE & WET SOIL — 3Z*0? WT. TARE & DRY SOIL - » • j WT. TARE — ! — WT. WATER — — WT. DRY SOIL — — WATER CONTENT % — ™<*!tonor,Y,/u,llon on written request. Earth & Environmental J GRAIN SIZE ANALYSIS XJS (PROJECT — __ (LAB ORDER " ~ " TEST HOLE J OETT^T^^-r ' ~ . SIEVE AJ TECHNICIAN '. "oATF : uirsis" ~ TOTAL SAMPLE. cast TOTAL WT. RET. ON #10 — . WT.'PASS. #10 4 PAN — . WT. PAN • • — BQ\T."T WT. PASSING #10 TOTAL WT. — HYDROMETER SAMPLE TARE NO. f WT. TARE 4. WET SOIL — . WT. TARE — : <1 IS WT. WET SOIL — — WATER CONTENT — WT. DRY SOIL — START TIME— / H> '.r>,-> TEMP SIEVE SIZE WT. RETAINED 1 PERCENT PASS. 1" 4 10 20 40 60 ( 100 200 j WATER CONTENT TARE NO. Zj~^C WT. TARE 4 W£TSOIL -WT. TARE 4 DRY SOIL WT. TARE — -J-^-S— WT. WATER — — WT. DRY SOIL — — WATER CONTENT V. — pAGRA Earth & Environmental HYDROMETER SAMPLE TARE NO. WT. TARE & WET SOIL — '. WT. TARE — WT. WET SOIL — _~EjE!ljV5'~ WATER CONTENT — WT. DRY SOIL r 4 -— 40 60 TARE NO. ' WT. TARE & WET SOIL — JZ^J^LHL WT. TARE & DRY SOIL — _jL^bJl / WT. TARE WT. WATER WT. DRY SOIL WATER CONTENT % — St oik provided only or, written request. f& AGRA fr PROJECT iwAS ORDEfl I-TOTAL SAMF TlTTA! WT RFT ON #10 — \?>.ar%>~ WT. PASS. #10 & PAN • WT. PAN — HJ\l • ^-WT. PASSING #10 TOTAL WT. • — HYDROMETER'SAMPLE TARE NO. < WT. TARE & WET-SOU —. ;WTIAHt~ WT. WET SOIL ' WATER CONTENT — -WT. DRY SOIL ' ' — f'WTIME -i :— "K' r •. GRAIN SIZE ANALYSIS ^7 -7 ; — TEST HOLE -. DEPTH LI!EL™L___T~ o^ri —-.SIEVE ANALYSIS • °'^VT WT. PERCENT 1 SIZE j RETAINED f PASS • WATER CONTENT 1"' TARE NO.' . >/<"' IwT.'MnC k WET SOIL - 23^ <T WT. TARE & DRY SOIL — —.— ' X" —• WT. TARE. _ | .2>j 4 WT. WATER _ 10 WT. DRY SOIL _ 20 ••— WATER CONTENT % — 40 60 iqo • 206 _ 2-1$ r___J=arth & Environmental '.PROJECT ; ~ ~—~ : LAB ORDER GRAIN SIZE ANALYSIS ^ZJ^ TEST HOLE TECHNICIAN DEPTH f DATE TOTAL SAMPLE ' TOTAL WT. RET. ON #10-WT. PASS. #10 & PAN — WT. PAN __ WT. PASSING #10 _ TOTAL WT. _ HYDROMETER SAMPLE TARE NO. : WT. TARE & WET SOIL — '• WT. TARE — — WT. WET SOIL — ..^Q'ft^. WATER CONTENT — WT. DRY SOIL ' — • SIEVE SIZE WT. RETAINED PERCENT PASS. 1" >/<" Vi" r 4 10" —-20. ' 40 60 100 200 Loo WATER CONTENT TARE NO. • 'P*T ^ -WT. TARE & WET SOIL —. ,^§A\ WT. TARE 4 DRY SOIL - ^LzJll-L--WT. TARE — , WT. WATER — — WT. DRY SOIL — . WATER CONTENTVo — - / "H- >"< consoles , testing H8LT TO - 88/09 servh, only. Engineering interpretation orevtluetion of th, i„, nsM, is provided only on written request. ^?™&Envlronmental :r>r'' . . —: TARE NO. WT. TARE & WET SOIL — WT. TARE — WT. WET SOIL ' WATER CONTENT — WT. DRY SOIL • ' — S iRT TIME — • 1Q0 200 3.0 'WT. TARE & WET SOIL —. WT. TARE & DRY SOIL — WT. TARE WT. WATER WT. DRY SOIL WATER CONTENT % — PERCENT PASSING 230 ^ AGRA Earth & Environmental .TOJECT GRAIN SIZE ANALYSIS *3><fD TEST HOLE ^ ~ •HBLT 70 - 88 /09 23>\ AGRA GRAIN SIZE ANALYSIS '3( .•ROJECT /„Yy^| • .... " ~ JLAB ORDER" ' • ' ~ •—;— IfcST HOLE DEPTH 0 : SIEVE A TECHNICIAN ' 0AT£^ ^ ^ YALYSIS ' v ~^ 1 Reporting of these test results constitutes a HBLT 70 - 68/09 testing service only. Engineers Interpret,,,™ or evaluation of the test results is provided only on written r in Garth jtTt?' * f AGRA Earth & Environmental GRAIN SIZE ANALYSIS "3j3 HBLT 70 - 88/09 LZIL- r""°""'E"~*'T on written request. 2*>f @AGRA Earth & Environmental •< Engineering & Environmental Services * GRAIN SIZE ANALYSIS PROJECT " SAMPLE 3 - IAsJul^t/Mf3h^r-piw/-jr LA8 ORDER TEST HOLE DEPTH TECHNICIAN DATE TOTAL SAMPLE TOTAL WT. RET. ON #10 — WT. PASS. # 10 & PAN — WT.PAN • • -_BMM WT. PASSING #10 — 4o\- f TOTAL WT. — .ao HYDROMETER SAMPLE \ _3_ TARE NO. WT. TARE &. WET SOIL — WT. TARE " — WT. WET SOIL — 'S'Q'lft-WATER CONTENT • — WT. DRY SOIL — J SIEVE 1 SI2E WT. RETAINED PERCENT PASS. 1" V." W Y," 4 10 G,o f 40 o.lr-60 0.13 100 c 200 ( WATER CONTENT TARE NO. WT. TARE 4 WET SOIL — 2-5"^ WT. TARE & DRY SOIL — 7~^* ^ WT. TARE — -LIS WT. WATER — WT. DRY SOIL — WATER CONTENT % — 235" ^AGRA GRAIN SIZE ANALYSIS *3> PROJECT R ~ • _ SAMPLE 3^5k tjti.lv ILAB ORDER • ~ " :—: TEST HOLE .' DEPTH . .' : : : SIEVE A TECHNICIAN *JAI VSI«. • DATE H&LT 70 - 88/09 Earth & Environmental GRAIN SIZE ANALYSIS 3^ PROJECT Gyioio^i SAMPLE 3 LAB ORDER • : ' ' TEST HOLE DEPTH SIFVP A TECHNICIAN •JALYSIS DATE TOTAL SAMPLE TOTAL WT. RET. ON #10 — . WT. PASS. #10 4 PAN — . WT. PAN —. WT. PASSING #10 — TOTAL WT. — '.HYDROMETER SAMPLE TARE NO. - ~^—^£> WT. TARE 4 WET SOIL — '. WT. TARE — WT. WET SOIL WATER CONTENT WT. DRY SOIL ' SIEVE SIZE WT. RETAINED PERCENT PASS. 1" V." V4". X" 4 10 20 40 m 60 100 : 200 . i *8W WATER CONTENT TARE NO. WT. TARE & WET SOIL WT. TARE & DRY SOIL WT. TARE WT. WATER WT. DRY SOIL WATER CONTENT % -^ AGRA Earth & Environmental GRAIN SIZE ANALYSIS 3"S POJECT ' ~ ~ ~' " — -'• .- SAMPLE Shcd£ [LAB ORDER : • TEST HOLE • DEPTH — : _____ SIEVE Al TECHNICIAN • DATF ^ALYSIS ' TOTAL SAMPLE, . TOTAL WT. RFTON»m— WT. PASS. #10 & PAN WT. PAN — §A& i£> WT. PASSING #10 TOTAL WT. — 33 HYDROMETER SAMPLE ,' TARE NO. " ...^'^ WT, TARE & WET SOIL — _i • . . — WT. TARE — — WT. WET SOIL' • -_____JL3rZ-WATER CONTENT — ,WT. DRY SOIL ' — SIEVE SIZE WT. RETAINED PERCENT PASS. 1" VS" Vi" 4 10 20 ' .40 , 60 I,Of 100 200 LCZ WATER CONTENT TARE NO.' WT. TARE & WET SOIL 3 ~/3 fa WT. TARE & DRY SOIL —. WT. TARE — —I' ' WT. WATER — -WT. DRY SOIL — WATER CONTENT % — _!_f_2____^^^^ :_ • HBLT 70 - 88/09 o'lhe tut results Is provided only on written r a*>8 GRAIN SIZE ANALYSIS . r, ^ 2l°l Earth & Environmental 'PROJECT (j>K0H0°\ rf-.LAB ORDER ...>' GRAIN SIZE ANALYSIS TO SAMPLE ^ ly 13 -/V B ft,J, f i. .7 TEST HOLE DEPTH Affcjj I ZMJJ^JJ TECHNICIAN DATE SIEVE ANALYSIS TOTAL SAMPLE TOTAL WT. RET. ON #10 — . WT. PASS. #10 & PAN —. WT. PAN —. WT. PASSING #10 — TOTAL WT. — HYDROMETER SAMPLE TARE NO. WT. TARE i^BT^oiT —. JVJ^rARE —. WT. WET SOIL — . WATER CONTENT — WT. DRY SOIL ' — SIEVE SIZE WT. RETAINED PERCENT PASS. V v<" Vi" X" 4 . 10 20 40 60 100 O. t o . 200 Q.ll WATER CONTENT TARE NO.' WT. TARE & WET SOIL — "Z- %* Z-Z_ WT. TARE & DRY SOIL — WT. TARE — -WT. WATER — WT. DRY SOIL — — WATER CONTENT % — • HR ^^w^*^^^^«^«*o~ar^^^ ^ MBLT 70 - 88/09 W AGRA Earth & Environmental ,-iAB ORDER GRAIN SIZE ANALYSIS ^f-J DEPTH TECHNICIAN TOTAL SAMPLE TOTAL WT. RET. ON #10 -~ JTKK\_ WT.PASS.#10 4J5A^^__' WT. PAN-SIEVE ANALYSIS DATE SIEVE WT. SIZE RETAINED WT. PASSING V^>ry -TOTAL WT. _ " PERCENT PASS. • WATER CONTENT TARE NO.' WT. TARE & WET SOIL —. WT. TARE & DRY SOIL 1__Z_ WT. TARE — ^'"^"7 WT. WATER — WT. DRY SOIL — WATER CONTENT % — Reporting cdhe^e test results constitutes , HBLT 70 - 88/09 !"<">9 service only, engtneerinn interprets. Ilonorenluetbnof the last results is provided only on written request. Earth & Environmental Reporting of these test results KBLT 70 - 88 /09 institutes.,esting service oniv. ^..^ 'on or ey.lu.thn of the test results is provided only on written request. GRAIN SIZE ANALYSIS V3 | PROJECT f^jLC<4j°IJ : SAMPLE Q-~2.fr- TCS £^r^ iLAB ORDER • ! •— TEST H.OLE . DEPTH ': : . SIEVE A" TECHNICIAN YAI VBIC DATE Tulv/^y^l TOTAL SAMPLE TOTAL WT. RET. ON #10 — . WT. PASS. #10 4 PAN — . WT. PAN —. WT. PASSING #10 — TOTAL WT. — HYDROMETER SAMPLE" TARE NO. •• V-"2-^. WT. TARE 4 WET SOIL — — WT. TARE — WT. WET SOIL WATER CONTENT WT. DRY SOIL ' _• . — -So.(7 SIEVE SIZE WT. • RETAINED PERCENT PASS. V «/«••• . i VV r 4 10 20 40 60 100 .. 200 : L 35-WATER CONTENT TARE NO. WT. TARE 4 WET SOIL. . WT. TARE & DRY SOIL — J. ' " 1 WT. TARE — —-— WT. WATER — — WT. DRY SOIL — _ • WATER CONTENT V. — HBLT 70 - 86/09 AURA Earth & Environmental GRAIN SIZE ANALYSIS .LAS ORDER TEST HOLE r^T 9^ Reporting o[thKa las! mu/(s HBLT 70 - 88 / 09 constitutes, testing ssnha on^^_ Mgrpi reteUonoreveluetiono, the lest results is provided only on written request. f AGRA Earth & Environmental GRAIN SIZE ANALYSIS LT<y ROJECT- . ' SAMPLE L|. 4 A T,,, 22/03 ShPart,rn.f .r< LAB ORDER TEST HOLE ' DEPTH. ' TECHNICIAN .DATE TOTAL SAMPLE TOTAL WT. RET. ON #10 — . WT. PASS. #1Q & PAN — iFfS-Cg WT. PAN — 3o>p-C> WT. PASSING #10 . — L|7o\^ TOTAL WT; — SIEVE ANALYSIS HYDROMETER SAMPLE TARE NO. ff-^rf WT. TARE & WET SOIL — J WT. TARE — '-WT.'WET SOIL • WATER CONTENT .WT. DRY SOIL' SIEVE ~ SIZE WT. RETAINED PERCENT PASS. 1" • Vt" • .'/;• 4 10 • 20 40 60 LU 100 200 L 7/ • WATER CONTENT TARE NO.' V-'Vff WT. TARE & WET SOIL — ^ ^6 WT. TARE & DRY SOIL — . - I.Z3 WT. TARE ' WT. WATER WT. DRY SOIL WATER CONTENT % — Reporting ol these test results c0„slilutas , Ufy/ct mly £ng. HBLT 70 - 88/09 •inuring interpretation or Mixtion otthe test results I, provide* only on written request. 2^5" BAGRA GRAIN SIZE ANALYSIS SAMPLE LI ~Ufi 1UAB ORDER " " • TEST HOLE DEPTH SIEVE A TECHNICIAN YALYSIS DATE TOTAL SAMPLE TOTAL WT. RET. ON #10 — , WT. PASS. #10 & PAN ' —. WT. PAN —-. WT. PASSING #10 — TOTAL WT. — SIEVE SIZE WT. RETAINED 1" - v<" HYDROMETER.SAMPLE TARE NO. ... .- Lf-Li^— WT. TARE & WET SOIL — '. WT. TARE — WT. WET SOIL — jffi* ^ ff-WATER CONTENT — WT. DRY SOIL ' • — PERCENT PASS. 10 20 40 60 WATER CONTENT ' TARE NO. ZZLELSL-WT. TARE & WET SOIL — -3~ ^ ' WT. TARE & DRY SOIL — —_ _ WT. TARE — •* ~- '-WT. WATER — — WT. DRY SOIL — — WATER CONTENT % — 'A" FACTOR PERCENT PASSING Reporting olthese ten results KBLT 70., 88/09 constitutes . testing serylce only. Engineering interpret. "Hon predion olthe test results Is proy,^ only on written request '=>}]+• ATTERBERG LIMITS TO: Geological Survey of Canada 601 Booth Street Ottawa ON K1A0E8 . ATTENTION: Mr. Larry Dyke . PROJECT: Peace & Beatton Rivers ame OFFICE: Fort St. John PROJECT NO: GX04091 CLIENT: Geological Survey of Canada COPIES TO: Mr. Jordan Severin SAMPLE NO. 1-1C 1-4A 1-4B 2-2A 2-2B 2-4B 2-4C 2-4D 2-41 2-6A 2-6B 2-8A 2-8AA 2-8B 2-8D 3-1A 3-5A 3-5B 3-13A L3-14A I 3-14B 3-15A I.3-15B I4-2A L4-2B . 4-4A 4-4B PMA LL PL = PI MUSC = DATE July 20/03 June 21/03 July 23/03 June 26/03 June 27/03 June 29/03 June 29/03 SOIL DESCRIPTioKT Shale Failure Plans Shear Surface #1 ins Massive Cfav Shale/Shear? Debris/shear June 29/03 July 23/03 June 30/03 June 30/03 July 3/03 July 23/03 July 3/03 Debris Shear Plans Gouge Shale Shear Plans Shear Gouge Failed Clay Shear Gouge in Shale Upper Shear Plane July 3/03 July 6/03 July 8/03 July 8/03 July 12/03 July 13/03 Intact Clay II LL 39.4 50.9 41.2 40.0 43.1 47.4 PL 21.1 17.8 17.4 19.6 19.5 49.8 40.9 55.7 47.6 44.9 47.4 19.0 29.6 19.0 30.4 PI 18.3 33.1 23.8 20.4 23.6 28.4 20.2 MUSC Cl CH Cl Cl Cl CI/CH 21.9 19.6 22.7 Intact Clav Beneath Shear (fir.m) Lower Slide Plane 50.9 69.4 Shear Plane ICS Adjacent Shear Gauge Remolded Shale July 13/03 July 13/03 July 13/03 July 19/03 July 19/03 July 22/03 July 22/03 Shale Shear Remolded Clav? Middle Material CkrtU r>L. —• Shale Shear 47.6 53.7 52.9 52.3 41.9 19.4 19.6 21.2 21.2 25.3 CI/CH Cl 28.0 22.2 28.0 31.3 48.2 26.4 19.9 18.2 18.0 40.6 40.6 Remolded Shale ICS Shear Intact Clav June 24/03 Shear Upper ICS Shear ICS Shear Plane 55.4 80.4 38.8 28.1 57.5 73.2 51.1 19.9 19.2 15.9 29.6-14.6 19.9 22.7. 20.7 18.1 33.8 34.7 CH CI/CH Cl CI/CH CI/CH CH CI/CH CI/CH 29.4 23.9 20.7 21.4 39.5 50.8 24.2 8.2 34.8 52.5 33:Q CI/CH CI/CH Cl Cl CH CH Cl CL CH CH CI/CH Liquid Limit Plastic Limit Plasticity Index Modified Unified Classification System 24? A.TTER8ERQ LIMITS DETERMINATION Project Location of Project Description ol Soil <JW*W r%fr< Depth o( Sample Li-- Teste'3'By Flow index F, • Liquid limit =_39V^ Plastic limit = _ctA/ '' Plasticity index /, ==•__,^ No. of blows. A/ 80 100 Can no. ATTERBeRQ '-"""TS DETERMINATION Project Location of Project Oascrlpt/on ol Soil DePln of Sample °ala Sheet 3 No. of blows, A/ 50 « M 100 Can no. '<a (/mi lift ameer ATTERBERQ UMITS DETERMINATION Project location of Pro/acl Description of Soil -/^k$Sn/£, °eplh of Sample °ata Sheet 3 Can no. No. of blows. rV 60 IOO 750 dme ATTERBERQ LIMITS DETERMINATION Project Job No. _J____"_3 H-dq / ?) ^rr. -—— Sample No. Oata Sheel 3 Location of Project 7) Ascription of Soil SE^ZJI_W1 ^ ^ DeP'h of Sample * Tested'By V No. of blows, /V 60 eo ioo £f_!_fj__^«en„l,,_Hnil Can no. Wt. of wet soil + can 231 ATTERBERO LIMITS DETERMINATION Project Location ol Project Descriplion ol Soil Oepth of Sampl Liquid Li'mil Oclcrnu'nad'on °ala Sheel 3 Flow index F, =. ,32 Plastic limit =_1£2<5> L'quid limit =-^j_j£_-J P'asticily index lr = ATTEHBERQ LIMITS OETE dmecy RMINATION Project Location ol Project Description of Soil E^VvS Oepth of Sample Liquid Limit Dc/crnifnad'oit ~~ IE • Job NO. jla2^HQfU_ °ata Sheet 3 •— Boring No. Sample No. 7 -Plow index F, = Liquid limit =. ^ Plastic limit =_[?iP Plasticity index /, R-. "Z'S.^ No. of blows, W 80 (00 253 ATTERBERO LIMITS DETERMINATION Project Location ol Project Description ol Soil Q)6cVT Oeplh ol Sample Liquid Liinir D;(crm{iia(((iu Oata Sheet 3 Date ,s 20 2S Can no. Wt. of wet soil + can *> 50 eo w Too No. of blows, N \ 154 ATTERBeR° L,M1" DETERMINATION Projecl Location of Project Ascription 0f Soil 0eP'h of Sample °aU Sheel 3 Flow, index F, = Liquid limit = J&2_J Plastic limit =J_9_C Plasticity index /, CJZ <0 SO 60 (4 n» Ho. of blows, fV ATTERBERO LIMITS 0 ^TERMINATION Pro/eel . Localion of Projecl Ascripilon of Soj( °epth of Sample Job No. °ala Sheet 3 30 <o so No. of blows, fV 60 M loo Can no. ATTMB6RQ LIMITS DETERMINATION Project . location of Project _ Description of Soil vSZZZZSl^ 0ePlh of Sample ~ Tested'By Job No. Boring No. Data Sheet 3 Sample No. t!Hl'!d U"'« Oelcrmluaii,,,, Can no Wl- of wet soil + can 20 2S *> <o so so" No. of blows, /V £f^!lii«"0«len,,J,,aH(,ll Can no. ?.3 3 • wet soil + can Wt. of dry soil + run " * «*^n T can Wl. ol can Wt. of dry soil Wl. of moisture Water content, wy. = lBr ATTERBERO LIMIT3 DETERMINATION Project 0a'a Sheet 3 Location of pro/BCt ~ :— Job N°-Plow index F, =. Liquid fimi( = Ji£frVp' PJ«tic limit «jZ_3-_7 Plasticity index /, ^^-Z.2_ 20 25 no 7; 1 L 30 <0 SO 60 No. of blows, /v 60 100 r/dJlic Limit Detenu Can no Wt. of wet Wt. of dry soil Wt. o( can Wt. of dry soil Wt. of moisture Water content, u>' Z58 ATTERBERO LIMITS 0 ^TERMINATION Pro/eel Location of Project °9scripti0n of So DeP(h of Sample Uquid Li Can no Wt. of we Job No. '09/ 0aU Sheet 3 Tested 8 5! 3 Plow index F, = Liquid limit = Plastic limit = Plasticity index I, 25 30 N°. of blows, N SO 60 . 100 Can no ATTERBERO LIMITS DETERMINATION Project Location ol Project Description of Soil Depth of Sampt Liquid Limit Dcterniiiiat 0ata Sheet 3 Job No. _. S°-rin9 No. ^Lz2$$ ATTERBERG LIMITS DETERMINATION Project Location ol.Project . ameer • Job No. ^ ~p\ " Data Sheet 3 .w. \lt,\r / ' Boring No. -^=g£Samp|e Ho Depth o( Sample J ~ Tested By . , „ ' " - Data Uuuid Limit Determinate Can no. M. of wet soil + can to IS 20 « 30 4 0 50 60 No. ol blows, tf Flow index F, = Liquid limit = . . -Plastic limit = . PC I. Plasticity index /, *~/^.r ^ SO 100 ""'tic Limit Determinate •Wt. of moisture Water content. wV. - „, — m ATTERBERG UMITS DETERMINATION Data Sheel 3 Proiect' Job No. . 6M_1L Location o( Project ._ : Boring No. . Sample No. %• — Description ol Soil Si f .cJVvt , ?) V..^ Oepth of Sample Tested' By '. O&te ", °1 Q6^ LitViiii Limit Oclermfii-tioii Can no Wt. o( wet soil Wl. of dry soil Wt. of can Wt. of dry soil Wt. of moisture. Water content,-yi No. ol blows. No. of blows, N 60 K too nation Can no. '/ ISA-ArTERBERQ LIMITS DETERMINATI Project ____ ON 0a'a Sheet 3 Location of Project " ~ Tested' By 0ePlh of Sample Can no P'asticily index /, =,_33_,T ZS 30 N°. of blows, H 50 SO 80 too. Can no ATTERBERQ LIMIT3 DETERMINATION Projecl Data Sheet 3 Location of Proj9C1 —^ -*•«.«« ^ssz^^ Depth of Sample ' • Tested'By Liquid Liuut Determinant,,, " °ata Sample No. Can no. Wt. of wet soil + can Wt. of dry soil + can Wt. of can cz^~ 10 £!!^_L________^ Can no. 20 » M <0 50 so" No. of blows, rV Flow index F, =. Liquid limit = _ Plastic limit Plasticity index lr M tOO 4? ATTERBERG LIMITS OETE RMINATIOIW Pro/eel Location of Pro/ocl Description of Soil _J___0^£ 0ePth of Sampl °ala Sheet 3 ^ " SO SO N°- of blows, /V eo IOO ATTERBERQ LI"'TS DHTERM.NAT.OrV Project . Location ol Pro/act Oesorip,ion o' son ^SmJSISEIk Depth of Sample Boring No. 3 ~f3$ e :—Sample No. 20 J5» ^~S0~6O No. of blows, JV eo too Can no. ~ H,S~L W.l. of wet soil + clrT" " Wt. of dry soil + can ~~ Wt. of can Wt. of dry soil Wt. of moisture Water content %7 ~" v-unieni, twv» — to. ATTERBERQ UM1T3 DETERMINATION Project TT?—7 7~ '-— Job No. • :—L-L-~ Sample No. Dala Sheet 3 Description of Soil Depth of Sample _ liquid U„tit Determination Can no. Wl- °f wet soil + can »S 20 2S ao <0 so 60 No. of blows, ry 60 tOO Can no. ATTERBERG LIMITS DETERMINATION Project Data Sheet 3 Job No. Location ol Project -°eplh of Sample <^ Tested'By W « 30 «0 SO^ No. of blows, N 80 100 ^li^D^rmlu^lo,, Can no. • 2-^8 ATTERBER0 LI«'T3 DETERMINATION Pro)ect Location o( Projecl , . -Description ol Soil -Depth of Sample Liquid Llmil Determinant Can no. Job No. Boring No. -SjLf^f °ala Sheel 3 <22/ Sample No. '5 20 25 M <0 No. of blows, fV BO 100 £lf^lf^«.0«l«r..,j,,a,toll Can no 2J/I ATTERBERQ LIMITS DETERMINATION Project Job No. Data Sheet 3 Location ol Project - • _-, - / Oascripiion ol Soil i^^2^ZlS^2MZlf~ Tested'By Depth of Sample _W Limff Dctcrminath,, Can no Date ^^U^03 30 « 50 60 60 (00 No. of blows, N [^ifUmlt Determination Can no. ATTERBERQ LIMITS DETE amed-* RMINATION Pro/eel location of p reject Job No. °»U Sheel 3 Description of Soil ~-/{!SlSAl Depth of Sampli ____^m<< Dctcrn„„allan Can no. ATTERBERQ LIMITS DETERMINATION Project ______ Location of Project Description of Soil Depth of Sample Job No. Data Sheet 3 Wt. of dry soil Wt. of moisture Water content, wV. No. of blows, N M 25 30 <0 SO 60 No. of blows, N M 100 Wattle Limit Determination ATTERBERQ LIMITS DETERMINATION Project Location of Project _ Description of Soil SJ}Qa^JA^U_ J^__ Depth of Sample ' • Tested'By Boring No. _L~ T/T c • , . /\ z**1 ~*—- ' r - Sample No. Data Sheel 3 Liquid LUnU Dclcrmtnatl,,,, SS 30 No. of blows, N 50 60 "«*lic Limit Determinate Can no. WI. of wet soil + can WLof dry soil + can ATTERBERQ UM.TS DETERMINATION Pro|ect location ol Project Description o( Soil Depth of Sample _ Liquid Limit Dclernilnatian /*7 0flta J - *<> NO. ~-^2^2^L09/ B°rin9 ^ ^^^amp^T7^ Oata Sheet 3 1V3 yi>A 20 25 JO No. of blows, W Flow index: F,= • Liquid limit =___5//^ Plastic limit = J____] Plasticity index /, <0 »'M to too ^cU»,lt Determinate Can no Wt. of wet soil + can ATTERBERO LIMITS DETERMINATION • Job No, Project — Location o( Project . _ Boring No. fl'IP Sample No. Description of Soil Depth of Sample — Tested' By Liquid Oiiriff Determination Can no. Data Sheet 3 Date No. of blows,NfV riastic Limit Determine! Can no. APPENDIX II Air Photograph List c o '~> 03 (/) > c 7_ +_ V .Q 03 c "C • 3 •u >< ed c D Ci CO a. a. <D < CO _c Q. 03 i_ O) o o SZ a. i o x: a o c • D) (0 a> o c 0J OS m (D > br c o ro a> m CO in co LU > or c o CO CD CO o m CM OT "t CM CO 1 CO co CM CO 1 CM CO cn CM • o" 00 CM T-T 1 CD 00 T— CM in in CD CD T— 00 T— 1 CM i 1 CO i T— CO IO CD in N-T— in TJ- r-- in a> in •<* i— r-o o o o o o o o CD CD CO CD CD CD CO CD oo 00 00 00 00 CO 00 OO O o O o a o O o ca CO CQ ca CQ CQ CQ CQ CO > a: >» CO 1 CO X <- <D CD > >» O ro & S co £ o) ro CQ X 277 Appendix II - Table 2 Air Photograph Sets Used during Activity Determination Date Flight Line No. Photograph No. 1997 1945 30BCC 97159 A 7904 A 8000 A 8001 A 8002 A 8050 A 8101 A 8103 A 8104 A 8105 A 8108 A 8109 A 8109 A 8141 A 8145 A 8146 A 8148 A 8149 A 8150 A8151 A 8153 A 8155 A 8156 A 8288 A 8291 A 8292 A 8294 A 8296 A 8302 A 8305 A 8349 A 8350 A 8353 A 8402 A 8403 |A 8404 |A 8407 A 8410 A 8411 A 8440 A 8450 A 8504 A 8507 A 8514 A 8528 A 8531 A 8532 A 8537 A 8540 A 8541 A 8542 A 8543 A 8544 A 8577 A 8580 A 8587 A 8597 |A 8598 A 8600 A 9111 A 9137 A 10429 A 10431 A 10434 A 10457 A 10461 1 -290 71 -75 30 - 55, 60 - 66, 68 - 72, 74 - 97 1 -6 100-106 1 - 6, 38 -55, 70 - 84 1 - 10 57-66 1 -34,61 -70, 77-108 5 - 26, 37 - 44 80-101 17-30 20 - 30, 44 - 47, 56 - 78, 80 - 92 16-35 8 -16, 28 - 38, 45 - 59, 69 - 79, 88 - 97 9-14,24-29,56-73 10. 18-35,49-53, 65-77 30, 43 - 48, 58 - 67, 73 - 75, 77 - 80, 82 - 84, 89 - 92 - 26, 40 - 50, 80 - 88 15, 27-55,61 -71 -21,25-33, 37-39,81 -86 25, 40 - 57, 60 - 80 29, 34 - 44 14, 17-29, 43-47, 53-64, 88-96 25, 29 - 32, 38 - 41, 52 - 54, 58 - 60, 85 - 95 56 15, 25-40,57-70,74-78 10 23, 80 - 89 20, 65 - 76 47 60 -75 10,20-43, 53-59 26, 40 - 54 - 23, 47 - 52, 57 - 72 -15,74-80 -33 64 18 45 - 77, 80 - 85 12 10 60, 65 - 74 36, 46 - 56 45, 76 - 80 68 67 81 72 69-74 •24 •15 -83 -23 -70 -45 15-J_ 10-76-17-67-39-11 J5-5_-33 - 37, 51 -55 56-65-1 -10,24-31 I - 17 i- 18 •12 5-67 -69 278 APPENDIX III Landslide Maps Region Individual TRIM Sheets 2£0 0-091 0.092 0.033 0.094 0.095 0.096 0.097 0.098 0.099 0.100 j 0.081 0.082 0.083 0.084 0.085 0.086 J 0.087 0.088 0.089 0.090 •mS 0.071 o.o72 0.073 0.074 0.075 _ Ckfl^ 0.077 0.078 0.079 0.080 0.061 0.062 0.063- 0.064 0.065 0.066 0^67 0.068 0.069 0.070 0.051^ 0.052 0.053 0.054 0.055 0.056 0.C&7 0.0J58 0.059 0.060 nru4 0.045 0.046 0.047^ 0.048 0,049 C 0.041 J.O^U 0.043 0.044 0.045 0.046 0.^0.048 0.049 0.050 •^V:X nw| 003V 0.035 0.036 0.fc7" 0.038 0.039 V 0.040 0.029 / 0'030 i 0.031 0.0^ 0.033J ^ 0.021 0.022-; J,^3 ^ * < V ? ;5 -iK ... ..-•b^ig>'<b.oi6~ M 1,014/ O'O^p^ o.oiev^ o>oi7^ ^0.018/^0.019^ o^aoj 0.006/ 0.007 O.OJDB Q.009 , JMJIO 0.011 0/12^13 — ^jr 7 f ^ ' CTS< - - V / nnn? 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CD .C S fe oj ro co ~' c aj ro ro o f2 2 "55 S d •D CO ? O ro fQ —I o 3« Landslides in the Charlie Lake Mapsheet UBC MSc. Thesis. Jordan Severin Appendix V - Inventory Analysis Results Basal Failure Plane Material ISheet TaA£Pv "fl,7" ,nventorV Analysis Results Table V - 4 Basal Failure Plane Material (Divisions) Total Slides Peace River 465 Beatton River 407 Southern Tributaries 255 Beatton River East 137 Halfway River West 216 Halfway River to Beatton Rivpr ' 130 Shale 184 39.6% 142 34.9% 164 64.3% 83 60.6% 74 34.3% 56 43.1% Quaternary 281 60.4% 265 65.1% 91 35.7% 54 39.4% 142 65.7% 74 56.9% 3^8 Landslides in the Charlie Lake Mapsheet UBC MSc. Thesis. Jordan Severin Appendix V - Inventory Analysis Results Slide Aspect Total Appendix V - Inventory Analysis Results Table V - 5 Slide Aspect (Divisions) 3^ Landslides in the Charlie Lake Mapsheet UBC MSc. Thesis. Jordan Severin Appendix V - Inventory Analysis Results Generalized Slide Aspect Appendix V - Inventory Analysis Results Table V - 6 Generalized Slide Aspect (Divisions) JBeatton River Jsouthem Tributaries I tseatton River East [Halfway River West i-iaiiway River to Beatton" River 3^0 <2 = % s < .2 >> O ro < c < o c OJ > c > X TD C OJ CL Q. < OJ OJ CO CL .5 ro co -1 c 0 ro 1 -ro o f-£ 0 8 6 "O CO ro CD CO +J 3 (/) ^ O co * § .12 » — Q CO ^ C « o > c > •5 5 c « CD t— a a < 1 CM 1 O E 1 co * 1 1 n •<*• 1 & 1 > 1 Act 1 00 &> S? 3? O is. iri Tt CM CN CN 1 °! °? E | 1 T— CO M 1 j in CD CO I & 1 •'- 1 " 1 1 •*! CD < 1 1 •* •* CO o 1 ^~ 1 T— 1 c> N-%9' N? o N." 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O S CD -J O 3^3 > < U o £ § Ul |o|o|S? jf gl ° ° " O O °! <° " - H CN CNN-N- • o > ro CO -1 c a> ro ^ ~2 ro o 8 d •a co E O ro CO _l D saltan 1 CQ o > > if it >, ?, >. Hall 3 > T rr 3=H 31Q> Landslides in the Charlie Lake Mapsheet UBC MSc. Thesis. Jordan Severin Appendix V - Inventory Analysis Results Table V -12 Landslide Type - Activity Appendix V - Inventory Analysis Results Landslide Type - Activity Peace River Beatton River Southern Tributaries Beatton River - East Halfway River - West Halfway River to Beatton River Total 3^ Landslides in the Charlie Lake Mapsheet UBC MSc. Thesis. Jordan Severin Appendix V - Inventory Analysis Results Landslide Type - Activity S § SI (/) , 0) Q. CO >. O O O < SSS! 1 II Hie o c olo o < < bi 5 S S i Id dole 2 IS I JJ co .5 S 5 ° u ? o> .5! i= a) X! CO C O S m to > III i I § II 88 .It Bl I llll a rr a: g I lllll • eg X X 0 Landslides in the Charlie Lake Mapsheet UBC MSc. Thesis. Jordan Severin Appendix V - Inventory Analysis Results Landslide Type - Aspect Appendix V - Inventory Analysis Results Table V -14 Landslide Type - Aspect 38o Landslides in the Charlie Lake Mapsheet UBC MSc. Thesis. Jordan Severin Appendix V - Inventory Analysis Results Landslide Type - Aspect Sheet Peace River Beatton River Southern Tributaries Beatton River - East Halfway River - West Halfway River to Beatton River Total 3 1 3 1 14 1 North Faci 1 0 2 0 2 0 ng (330-30) 33.3% 0.0% 66.7% 0.0% 0.0% 0.0% L East Facit 0 1 0 0 4 0 ig (60-120) 0.0% 100.0% 3.0% 0.0% 0.0% 0.0% >5 South Faci 1 0 0 1 6 0 ig (150-210) 33.3% 0.0% 0.0% 100.0% 0.0% 0.0% West Faclr 1 0 1 0 2 1 g (240-300) 33.3% 0.0% 33.3% 0.0% 0.0% 100.0% total 23 5 21.7% 5 21.7% 8 34.8% 5 21.7% Sheet Peace River Total 177 North Fac 36 ng (330-30) 20.3% L East Facii 40 ig (60-120) 22.6% )6 South Faci 65 ig (150-210) 36.7% West Facir 36 g (240-300) 20.3% Beatton River Southern Tributaries Beatton River - East Halfway River - West Halfway River to Beatton River Total 128 73 38 35 41 492 27 28 8 6 6 111 21.1% 38.4% 21.1% 17.1% 14.6% 22"6% 35 12 . 8 6 7 108 27.3% 16.4% 21.1% 17.1% 17.1% 22.0% 30 25 9 8 16 153 23.4% 34.2% 23.7% 22.9% 39.0% 31.1% 36 8 13 15 12 120 28.1% 11.0% 34.2% 42.9% 29.3% 24.4% Sheet Peace River Beatton River Southern Tributaries Beatton River - East Halfway River - West Halfway River to Beatton River Total 16 16 12 3 4 15 North Fac 8 9 7 1 1 7 ng (330-30) 50.0% 56.3% 58.3% 33.3% 25.0% 46.7% L East Faci 1 5 2 1 1 5 ng (60-120) 6.3% 31.3% 16.7% 33.3% 25.0% 33.3% 3 7 South Faci 4 1 0 0 0 2 ng (150-210) 25.0% 6.3% 0.0% 0.0% 0.0% 13.3% West Facir 3 1 3 1 2 1 ig (240-300) 18.8% 6.3% 25.0% 33.3% 50.0% 6.7% Total Sheet Peace River 66 Total 2 33 North Faci 1 50.0% ng (330-30) 50.0% 15 L; East Facir 1 22.7% g (60-120) 50.0% 7 8 South Faclr 0 10.6% ig (150-210) 0.0% 11 West Facin 0 16.7% g (240-300) 0.0% Beatton River Southern Tributaries Beatton River - East Halfway River - West Halfway River to Beatton River Total | 1 4 0 7 0 14 0 0 0 0 0 1 I 0.0% 0.0% 0.0% 0.0% 0.0% 7.1% 0 1 0 1 0 3 I 0.0% 25.0% 0.0% 14.3% 0.0% 21.4% 0 3 0 0 0 3 I 0.0% 75.0% 0.0% 0.0% 0.0% 21.4% 1 0 0 6 0 - 7 I 100.0% 0.0% 0.0% 85.7% 0.0% 50.0% 38! Landslides in the Charlie Lake Mapsheet UBC MSc. Thesis. Jordan Severin Appendix V - Inventory Analysis Results Table V -15 Material - Activity Appendix V - Inventory Analysis results Material - Activity 382 Landslides in the Charlie Lake Mapsheet UBC MSc. Thesis. Jordan Severin Appendix V - Inventory Analysis Results Material - Type Appendix V - Inventory Analysis Results Table V -16 Material - Landslide Type 383 Landslides in the Charlie Lake Mapsheet UBC MSc. Thesis. Jordan Sevrin Appendix V - Inventory Analysis Results Material - Aspect Appendix V - Inventory Analysis Results Table V -17 Material - Aspect 381 Landslides in the Charlie Lake Mapsheet UBC MSc. Thesis. Jordan Severin Appendix V - Inventory Analysis Results Table V -18 Aspect - Activity Appendix V - Inventory Analysis Results Aspect - Activity Peace River Beatton River Southern Tributaries Beatton River - East Halfway River - West Halfway River to Beatton River Total S H QC » cn — TO ro <^ £••3 o 0 f < Ii co -o •a 5 CO TJ C C < J O u C a > < c — o> X a) 'o 3 c £ q, r-a a < o CQ CD CJ d CN co cn '• 3s oo o> CO CO CN CN 35 I CN|CO CO| ' 5 ^ 8? 3* olo Ol do d 13 1 | a. m I>I> > > 8? IO O N d ^ 3? Ico o CO O'lcO s » C CO 1*1= 1 I1 sis I CO CO 3 CO 0)1 0) O CD a. co </i CD 2r <= 111 38k ~ 1 —5 I— CO » CO 1 <3 o c CD > X T3 C CD CL CL < tf) 3 tf) O t£ w CO 'tn CD >> CQ co c • < -<—» 0 CD Q_ O <w < C O O > CM 1 > > ble x cs TJ C O OL Q. < CD CD .C CO 8-.E ^ co J! co CO CO -1 c co ro 1 -ro o • •s £ 0 0 O •o CO 1 0 ro co s CC cn co ro tu m Q 2 >. ro ro > X CC sP sP sP sP sP s? 3s OS 5s 5s OS OS Tt CO CO CM CM CD in CO CO CD 1— & in in CO CO CD Tt LO ro c ai ro a CD CO 0 Tt |s- CD O CO CN T-Tt CO 0 0 CO 0 Tt CM sP sp sP sp sP sp c> <> os OS 5s 5s 5s a CO CD fs- T- co oq CO c Tf CM CD Tt CO CO 00 Ti Tt Tt CO rs- CO in Tt Fa< ale est MS CD O Tt 0 CD Tt CD CN CM CO T— CN r-tai in O T— rs- CD CD 00 m CM To CD is- CM CM Tt CN sP sP sP sP sP sP sP c> OS OS tfs 5s 5s 5s T— CM CD CD r~- eo 0 CO CD CO in CD° CD 00 & co CD CO in CD in in ro c JS ro O 00 in CO CD 0 CO 00 CD Tt f- CN T— 0 CM O in .8 sp sp sP sP ^p sP 5^ tfs 5s OS 0 t> 5S 01 CD 00 T— Tt CO cq O c CD CO CD Tt d co CM 0 CO CO CD Tt CO Tt •st 1 Fa ale ^ JC 3 CO 0 CO 00 CM rs- co 0 Tt CD CM co CM CO T— 3 CO in CD co TO CM rs-To 0 CD in CO CO co c 0 CO "co ro CO 10 CD CD utarii -Ea 1 m 0 i_ CD JD CD 1 0) i_ CD :ivei Riv lTr Riv Riv Riv rr 4- c >. >^ 0 CD ace attoi Uttl€ attoi Ifwa Ifwa ro XI CD <D 0 CD ro ro 0 CO 0. CQ CO CQ X X CC H 38^ APPENDIX VI Slide Aspect Rosette Diagrams !(#[0 Rx'Jor^s IBo° 38^ "Peace "R\v<_c "DtVis/o«\ LarsAslide Asptof (2^ ,^ciOi Hie^ Fcx\\urtS La^aslide *\sp«x-f (2"^,ACO MO? PoaWeS 3<ii Z^"5~ FcxvWe^ Landslide flsfet-f C2%> irtc/.") o 3f3 1 SO f^cxv^ores ZICP Failures 

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