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The use of the resistivity piezocone (RCPTU) for the geoenvironmental characterization of sulphide bearing… Boyd, Timothy John 1996

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THE USE OF THE RESISTIVITY PIEZOCONE (RCPTU) FOR THE GEOENVIRONMENTAL CHARACTERIZATION OF SULPHIDE BEARING TAILINGS A N D NATIVE SOILS by TIMOTHY JOHN BOYD B.Eng., Technical University of Nova Scotia, 1992 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of Civil Engineering We accept this as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1996 © Timothy John Boyd^ In presenting this thesis in partial fulfilment 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. The University of British Columbia Vancouver, Canada Date DE-6 (2/88) ABSTRACT Recent advances in the in-situ testing of sulphide bearing mine tailings have included the development of a resistivity piezocone (RCPTU) and improved water sampling technologies. The RCPTU measures the bulk resistivity of the soil, in addition to all other standard piezocone (CPTU) measurements. The bulk resistivity profile permits assessment of pore water chemistry with correlation to pore water samples and the standard CPTU measurements give accurate estimates of stratigraphy and key geotechnical parameters and hydrogeological characteristics. Also, use of the RCPTU in combination with discrete pore water sampling technologies can permit the development of relationships between bulk resistivity measurements and specific pore water constituents. The technology is repeatable, rapid and economical when compared to traditional drilling and sampling site investigation techniques. A significant area of concern in the mining industry is acid rock drainage (ARD). A R D is the contaminant drainage which results from oxidation of sulphide minerals and it can represent a serious hazard to surrounding surhcial and groundwater systems. The evolution of A R D creates elevated electrical conductivity of tailings pore water which can be readily detected by the RCPTU bulk resistivity measurements. In addition to environmental issues, there are significant geotechnical considerations in the construction of large dams for tailings storage. One fundamental consideration is the potential for a flow failure of the tailings impoundment due to liquefaction of the tailings under both static and dynamic loading conditions. There is a significant challenge in adequately characterizing these impoundments for their geochemical, hydrogeological and geotechnical nature. The potential to use a single procedure for determining many varied engineering design parameters is highly attractive. Ill Results of a field testing program carried out at sulphide bearing tailings impoundments of three Canadian mines are presented with respect to environmental and geotechnical characterization issues. Site-specific relationships between bulk resistivity measurements and pore water chemistry are developed. CPTU data is used to assess hydrogeological characteristics at specific sites and estimate movement of A R D contaminated pore water. CPTU-based methods are used to assess the susceptibility of liquefaction of tailings, considering both static and dynamic load conditions. Finally, recommendations are made with regard to the use of the RCPTU as a component of an overall geoenvironmental characterization plan for the evaluation of sulphide bearing tailings impoundments. iv TABLE OF CONTENTS ABSTRACT ii TABLE OF CONTENTS iv LIST OF TABLES . .vii LIST OF FIGURES. viii LIST OF SYMBOLS xii ACKNOWLEDGEMENTS xiv 1.0 INTRODUCTION 1 2.0 EVALUATION OF SULPHIDE BEARING TAILINGS IMPOUNDMENTS 4 2.1 GENERAL 4 2.2 PORE WATER CHEMISTRY 6 2.2.1 Acid Rock Drainage (ARD) 8 2.2.1.1 Generation of ARD 9 2.2.1.2 Generation of ARD in Sulphide Bearing Tailings 11 2.3 SOIL LIQUEFACTION 14 2.3.1 Flow Liquefaction 14 2.3.2 Cyclic Liquefaction 16 3.0 IN-SITU TESTING METHODS 18 3.1 RESISTIVITY CONE PENETRATION TEST (RCPTU) 18 3.1.1 Resistivity Measurement In Soils 19 3.1.1.1 Influence of Pore Water Affected by ARD Contamination on Bulk 21 3.1.1.2 Influence of Soil Type on Bulk Resistivity Measurements 23 . 3.1.2 Description of UBC Resistivity Module 23 3.1.3 Calibration of UBC Resistivity Module 28 3.1.4 Application of RCPTU for Assessment of ARD Contamination 30 3.2 BAT PORE WATER SAMPLING TECHNOLOGY 35 3.3 CONE PENETRATION TEST (CPTU) 37 3.3.1 Application of CPTU for Assessment of Static Stability 45 3.3.2 Application of CPTU for Assessment of Flow Liquefaction Susceptibility 46 3.3.3 Application of CPT for Assessment of Cyclic Liquefaction Potential 47 V 4.0 SITE DESCRIPTIONS AND TESTING PROGRAMS 53 4.1 INCO COPPER CLIFF TAILINGS AREA 53 4.1.1 Site Description 53 4.1.2 Tailings Mineralogy 53 4.1.3 Test Program 55 4.2 FALCONBRIDGE TAILINGS IMPOUNDMENT 57 4.2.1 Site Description 57 4.2.2 Tailings Mineralogy 57 4.2.3 Test Program 59 4.3 GIBRALTAR MINES TAILINGS IMPOUNDMENT. 59 4.3.1 Site Description : 59 4.3.2 Tailings Mineralogy 61 4.3.3 Test Program 61 5.0 DISCUSSION OF TEST RESULTS 63 5.1 TYPICAL RCPTU TEST RESULTS 63 5.1.1 Pistol Tailings Impoundment (INCO) 63 5.1.2 Base of Pistol Dam (INCO) : 65 5.1.3 Fault Lake Tailings Impoundment (Falconbridge) 67 5.1.4 Gibraltar Tailings Impoundment (Gibraltar) 69 5.2 REPEATABILITY OF RCPTU TEST RESULTS 71 5.3 CHARACTERIZATION OF PORE WATER CHEMISTRY 71 5.3.1 Pore Water Sampling Practices and Chemical Analyses 74 5.3.2 RCPTU Bulk Resistivity Measurements in Unsaturated Sulphide Bearing Tailings (INCO and Falconbridge Failings) 76 5.3.3 Comparisons Between RCPTU Bulk Resistivity Measurements and Pore Water Chemistry in Sulphide Bearing Tailings and Surrounding Saturated Native Soils (All Test Sites) 81 5.3.3.1 Comparison of RCPTU Bulk Resistivity and Pore Water Resistivity 82 5.3.3.2 Comparions of Pore Water Sulphate Concentration and RCPTU Bulk Conductivity 87 5.3.3.3 Comparison of Pore Water p H and RCPTU Bulk Conductivity. 95 vi 5.3.3.4 Comparison of Pore Water Heavy Metals Concentrations and RCPTU Bulk Conductivity 99 5.3.3.5 Summary. 105 5.4 CHARACTERIZATION OF HYDROGEOLOGICAL CHARACTERISTICS 108 5.4.1 Base of Pistol Dam (INCO) 108 5.4.2 Fault Lake Tailings Impoundment (Falconbridge) I l l 5.5 PHYSICAL CHARACTERIZATION 113 5.5.1 General 113 5.5.2 Preliminary Assessment of FlowLiquefaction Susceptibility 118 5.5.3 Preliminary Assessment of Cyclic Liquefaction Susceptibility 118 6.0 COMPARISON OF THE RCPTU AND CONVENTIONAL TESTING METHODS 123 7.0 RECOMMENDED PROCEDURE FOR USING IN-SITU TESTING METHODS FOR THE GEOENVIRONMENTAL CHARACTERIZATION OF SULPHIDE BEARING TAILINGS IMPOUNDMENTS 125 8.0 SUMMARY AND CONCLUSIONS 128 9.0 RECOMMENDATIONS FOR FUTURE RESEARCH 132 REFERENCES 135 APPENDIX A: RCPTU CONEPLOTS. 141 APPENDIX B: RCPTU INTERPRETATIONS (CPTINT 5.0). 150 APPENDIX O RCPTU PORE PRESSURE DISSIPATIONS 165 APPENDIX D: PORE WATER CHEMISTRY 202 VII LIST OF TABLES TABLE PAGE 2.1 Authorized Levels of Deleterious Substances Prescribed 7 in the Metal Mining and Effluent Regulations (After Environment Canada, 1992) 2.2 Examples of Water Quality Affected by A R D Processes 9 (After Frytas et a l , 1992) 2.3 Stages in the Formation of A R D (Adapted from Broughton et al., 11 1992) 2.4 Summary of Tailings Flow Failures (Adapted 15 from Vick, 1991) 3.1 Summary of Typical Resistivity (Conductivity) Measurements 33 of Bulk Soil Mixtures and Pore Fluid (UBC Experience) 4.1 Summary:1993 Field Investigation Program at INCO Central 53 Tailings Area 4.2 Summary.1993 Field Investigation Program at Falconbridge 59 Fault Lake Tailings Site 4.3 Summary:1994 Field Investigation Program at Gibraltar 62 Tailings Impoundment 5.1 Summary of Estimated Hydrogeological Characteristics at the Base 109 of Pistol Dam 6.1 RCPT Testing Versus Conventional Testing Methods With Respect to 124' Data Procurement and Cost VIII LIST OF FIGURES FIGURE TITLE PAGE 2.1 Tailings Dam Construction Methods (After Klohn, 1980) 5 2.2 One-Dimensional Water Quality Model For a Tailings 13 Impoundment (After A.Robertson, 1987) 2.3 Undrained Behaviour of Sand 16 2.4 Undrained Cyclic Behaviour of Sand 17 3.1 Comparison of Bulk Resistivity and Friction Ratio 24 (After Kokan, 1992) 3.2 UBC Resistivity Piezocone (RCPTU) 26 3.3a RES1 Resistivity Module Calibration Curve - Low Excitation 29 3.3b RES1 Resistivity Module Calibration Curve - High Excitation 29 3.4a RES2 Resistivity Module Calibration Curve - Low Excitation 31 3.4b RES2 Resistivity Module Calibration Curve - High Excitation 31 3.5 Observed Relationship Between Total Dissolved Solids and 35 Bulk Resistivity (After Ebraheem et al., 1990) 3.6 UBC Modified BAT Pore Water Sampler 37 3.7 Standard Piezocone (CPTU 38 3.8 Typical RCPTU Profile in Sulphide Bearing Tailings 40 3.9 Soil Behaviour Type Classification Chart (After Robertson 42 and Campanella, 1988) 3.10 Typical Pore Pressure Dissipation in Fine-Grained 44 Sulphide Bearing Tailings 3.11 CPTU-Based Screening Chart For Estimating the State 47 Parameter of Soils (After Plewes et al., 1992) 3.12 Comparison Between Robertson and Campanella (1985) 49 CPT-Based Method For Estimating CRR of Clean Sands and Recent Field Performance Data (After Robertson and Fear, 1995) IX FIGURE TITLE PAGE 3.13 Variation of Fines Content With Friction Ratio 51 (After Suzuki, 1995) 4.1 Schematic of INCO Copper Cliff Central Tailings Area 54 (After Coggans, 1991) 4.2 Schematic of Falconbridge Fault Lake Tailings Impoundment 58 (After St. Arnaud et al., 1994) 4.3 Schematic of Gibraltar Tailings Impoundment 60 (After Gibraltar Mines Ltd., 1992) 5.1 RCPTU Profile - Crest of Pistol Dam 64 5.2 RCPTU Profile - Base of Pistol Dam 66 5.3 RCPTU Profile - Falconbridge Fault Lake Tailings Impoundment 68 5.4 RCPTU Profile - Gibraltar Tailings Impoundment 70 5.5 Repeatability of CPTU Measurements 72 5.6a Comparison of RCPTU Bulk Resistivity Measurements at 73 Cecchetto Dam (INCO) 5.6b Comparison of RCPTU Bulk Resistivity Measurements at 73 A-Area (INCO) 5.7a RCPTU Bulk Resistivity Measurements in Unsaturated 77 Sulphide Bearing Tailings at the Crest of Pistol Dam 5.7b RCPTU Bulk Resistivity Measurements in Unsaturated 77 Tailings at the Fault Lake Tailings Impoundment 5.8a Comparison Between RCPTU Bulk Resistivity 80 Measurements and Pore Water p H in Unsaturated Sulphide Bearing Tailings 5.8b Comparison Between RCPTU Bulk Resistivity 80 Measurements and Pore Water Fe Concentrations in Unsaturated Sulphide Bearing Tailings 5.8c Comparison Between RCPTU Bulk Resistivity 80 Measurements and Pore Water N i Concentrations in Unsaturated Sulphide Bearing Tailings 5.8d Comparison Between RCPTU Bulk Resistivity 80 Measurements and Pore Water M g Concentrations in Unsaturated Sulphide Bearing Tailings X FIGURE TITLE PAGE 5.9a Comparison Between RCPTU Bulk Resistivity 83 Measurements and Pore Water Resistivity -INCO Saturated Tailings 5.9b Comparison Between RCPTU Bulk Resistivity 84 Measurements and Pore Water Resistivity -Saturated Falconbridge Tailings 5.9c Comparison Between RCPTU Bulk Resistivity 85 Measurements and Pore Water Resistivity -Saturated Gibraltar Tailings 5.9d Comparison Between RCPTU Bulk Resistivity 86 Measurements and Pore Water Resistivity -Saturated INCO Tailings 5.10a Comparison Between RCPTU Bulk Resistivity 88 Measurements and Pore Water Sulphate Concentrations - Saturated INCO Soils 5.10b Comparison Between RCPTU Bulk Resistivity 89 Measurements and Pore Water Sulphate Concentrations - Saturated INCO Soils 5.10c Comparison Between RCPTU Bulk Resistivity 90 Measurements and Pore Water Sulphate Concentrations - Saturated INCO Soils 5.10d Comparison Between RCPTU Bulk Resistivity 91 Measurements and Pore Water Sulphate Concentrations - Saturated INCO Soils 5.11 Comparison Between Pore Water Sulphate 94 Concentration in Saturated Sulphide Bearing Tailings and Native Soils 5.12a Comparison Between RCPTU Bulk Resistivity 96 Measurements and Pore Water p H - Saturated INCO Tailings 5.12b Comparison Between RCPTU Bulk Resistivity 97 Measurements and Pore Water p H - Saturated Falconbridge Tailings 5.12c Comparison Between RCPTU Bulk Resistivity 98 Measurements and Pore Water p H - Saturated INCO Native Soils 5.13a Comparison Between RCPTU Bulk Resistivity 100 Measurements and Pore Water Fe Concentrations in Saturated Sulphide Bearing Tailings XI FIGURE TITLE PAGE 5.13b Comparison Between RCPTU Bulk Resistivity 101 Measurements and Pore Water N i Concentrations in Saturated Sulphide Bearing Tailings and Native Soils 5.13c Comparison Between RCPTU Bulk Resistivity 102 Measurements and Pore Water M g Concentrations in Saturated Sulphide Bearing Tailings and Native Soils 5.14 Estimate of Hydraulic Gradient in Native Soils at the 110 Base of Pistol Dam 5.15 Estimate of Hydraulic Gradient in Sulphide Bearing Tailings 112 at the Fault Lake Tailings Impoundment 5.16 Estimate of Geotechnical Strength Parameters For RCPTU 114 Sounding at the Crest Of Pistol Dam 5.17a CPTU-Based Method of Estimating State Parameter 117 C¥) For RCPTU Sounding at the Crest of Pistol Dam 5.17b State Parameter QV) Versus Depth For RCPTU Sounding 117 at the Crest of Pistol Dam 5.18a q c Versus Depth For RCPTU Sounding at the 119 Crest of Pistol Dam 5.18b q c i Versus Depth For RCPTU Sounding at the 119 Crest of Pistol Dam 5.19a Estimated Fines Content (FC) Versus Depth For 121 RCPTU Sounding at the Crest of Pistol Dam 5.19b A q c i Versus Depth For RCPTU Sounding at 121 the Crest of Pistol Dam 5.19c (qci)ecs Versus Depth For RCPTU Sounding at 121 the Crest of Pistol Dam 5.20 Seismic Stress Ratio Versus Depth For RCPTU Sounding 122 at the Crest of Pistol Dam 7.1 Proposed Methodology For the Application of In-Situ 126 Testing Methods For the Geoenvironmental Characterization of Sulphide Bearing Tailings Impoundments LIST OF SYMBOLS A - Cross-Sectional Area a m a x - Maximum Earthquake Acceleration at Ground Surface A R D Acid Rock Drainage A P L Aqueous Phase Liquid B q Dynamic Pore Pressure Ratio Cv,h Coefficient of Consolidation CEC Cation Exchange Capacity CRR Cyclic Resistance Ratio CSR Cyclic Stress Ratio CPTU Standard Piezocone; Cone Penetration Test D r Relative Density e Void Ratio ec Critical Void Ratio fs CPT Friction Sleeve F Stress Normalized Rf F Formation Factor FC Fines Content FS Factor of Safety g Gravity i Hydraulic Gradient I Current Ic Soil Behaviour Type Index IP Induced Polarization k Resistivity Module Calibration Factor K Hydraulic Conductivity 1 Path Length of Flow M Molar M Earthquake Magnitude m Shape Factor mV/h Coefficient of Compressibility M C E Maximum Credible Earthquake n Porosity N Standard Penetration Test Resistance xiii (Ni)6o - SPT N Value Corrected For Overburden Stress and Rod Energy N A P L - Non-Aqueous Phase Liquid Pa - Atmospheric Pressure (101.3 kPa) q c - CPT Penetration Resistance q c i - Stress Normalized q t (qci)ecs - q c i Corrected For Fines Content q t - q c Corrected For In-Situ Water Pressures Q - Stress Normalized q t Q p - Normalized Q p R - Resistance RCPTU - Resistivity Piezocone; Resistivity Cone Penetration Test Rf - CPT Friction Ratio SH - Strain Hardening SPT - Standard Penetration Test SS - Strain Softening Su - Undrained Shear Strength U - CPTU Dynamic Pore Pressure Uo - Equilibrium Pore Pressure U l - U Measured at the Cone Tip U2 - U Measured Behind the Cone Tip U3 - U Measured Behind the Cone Friction Sleeve V - Voltage v - Groundwater Velocity o\,o - Total Overburden Stress a v o ' - Effective Overburden Stress <t>' - Peak Friction Angle Pb - Bulk Soil Resistivity pf - Pore Water Resistivity Q-m - Measure of Resistivity uS/cm - Measure of Conductivity VP - State Parameter y w - Unit Weight of Water (9.81 k N / m 3 ) xiv ACKNOWLEDGEMENTS I would like to thank Dr. R.G. Campanella for his guidance and direction throughout the process of writing this thesis. I would also like to express my sincere thanks to Michael Davies for his support both during the field testing portion of this work and for his advice and guidance during my tenure at UBC. INCO Ltd., Falconbridge Ltd., Gibraltar Mines Ltd. and the Federal M E N D (Mine Environment Neutral Drainage) are recognized for their financial support without which this work could not have been done. In addition, I thank the different mines for allowing access to their sites for carrying out the field work, and for the help of on-site mining personnel who provided valuable support as required. I also thank the Federal Natural Sciences and Engineering Research Council (NSERC) for their financial support in the form of a research grant. I also thank my employer David Woeller of Conetec Investigations Ltd. for providing me with the support and time required to complete this thesis. Finally, I thank my family (Mom, Dad, Stephen, Mike, Chris, David, Peter and Ian) and friends (you know who you are) for their love and support in the course of completing this thesis. 1 1.0 INTRODUCTION Site characterization is the key component of any subsurface investigation of the prevailing physical and geochemical conditions. The overall framework for characterizing the prevailing physical and geochemical conditions is termed geoenvironmental characterization. The University of British Columbia In-Situ Testing Group (UBC ISTG) has been developing and documenting in-situ tools for site characterization for over 15 years. The standard piezocone (CPTU) has been a principle focus of research and development. The CPTU has proven to be an excellent means of logging stratigraphy for most soils and provides accurate estimates of key geotechnical parameters and hydrogeological characteristics. The primary geotechnical applications of CPTU technology were expanded to include environmental engineering with the development of a resistivity piezocone (RCPTU) in 1988 (Campanella and Weemees, 1990). The RCPTU measures the bulk resistivity of the soil and pore water, which can be used to infer pore water quality. In addition, use of the RCPTU in combination with discrete pore water sampling technologies can facilitate the development of site-specific relationships between bulk resistivity measurements and pore water chemistry. Mine tailings represent a significant challenge for adequate geoenvironmental characterization. Some mine tailings, particularly from large ore operations that contain sulphide minerals, pose significant environmental problems due to processes such as acid rock drainage (ARD). A R D is the contaminant drainage, often containing high concentrations of sulphates, heavy metals and acidity, which results from the oxidation of sulphide minerals. Additionally, there are inherent geotechnical stability considerations in large tailings impoundments, as many of these are hydraulically constructed entirely with tailings. One fundamental consideration is the potential for a flow failure of the tailings impoundment due to liquefaction of the tailings, under both static and dynamic loading conditions. There can be 2 a significant challenge in adequately characterizing these impoundments for their geochemical, hydrogeological and geotechnical nature. Traditional methods of drilling and discrete sampling followed by laboratory analysis are expensive, time intensive, and provide a small statistical sample of the subsurface. The RCPTU, which provides a near-continuous log of requisite engineering parameters, can provide a rapid, technically sound and cost-effective alternative for adequate geoenvironmental characterization of sulphide bearing tailings impoundments. A geoenvironmental site characterization program using RCPTU in conjunction with discrete depth pore water sampling was carried out at sulphide bearing tailings impoundments of three Canadian mines. The objective of this work was to develop a technical understanding of the environmental and geotechnical considerations which confront safe storage of sulphide bearing tailings, and to assess the capability of the RCPTU for characterization of sulphide bearing tailings with respect to both environmental and geotechnical parameters. More specifically, the environmental component of this work focused on the application of the RCPTU to evaluate A R D processes in sulphide bearing tailings, whereas the primary geotechnical component was the evaluation of liquefaction susceptibility of tailings using CPTU-based methods. Field test data are presented to demonstrate specific applications of the RCPTU, and recommendations are made with respect to the use of the RCPTU as a component of an overall geoenvironmental characterization plan for the evaluation of sulphide bearing tailings impoundments. To meet the stated objective of this thesis a research program was formulated and is summarized as follows: • Gather available literature and consult acknowledged experts on the following subjects: 3 (a) , environmental and geotechnical issues confronting safe storage of sulphide bearing tailings, particularly A R D processes affecting tailings pore water chemistry and soil liquefaction. (b) . geoenvironmental site characterization methods, including in-situ testing techniques and conventional drilling and sampling techniques. (c) . electrical conduction in soil and water, and the application of resistivity techniques for the delineation of A R D contamination. (d) .CPTU-based techniques for evaluating the liquefaction susceptibility of soils, considering both static and dynamic loading conditions. • Design, implement and interpret results from relevant field and lab testing programs. • Provide a thorough evaluation of the geoenvironmental characterization site investigation techniques upon completion of the testing programs. 4 2.0 EVALUATION OF SULPHIDE BEARING TAILINGS IMPOUNDMENTS 2.1 GENERAL Tailings may be defined as crushed rock particles that are either produced or deposited in a slurry form as a result of mineral extraction processes. Sulphide bearing tailings are tailings that contain sulphide minerals. The properties of tailings are dependent upon the characteristics of the host rock and the procedures employed for mineral extraction. Currently, the most common method for tailings disposal is on-land impoundments. In 1993, of the 150 operating mines in Canada, almost all mines practised on-land disposal, with the exception of three operations which have unconfined disposal on an ocean or lake bottom (Giancola, 1993). Generally the tailings impoundment is constructed by building a dyke at the downstream end of the tailings area, or entirely surrounding the planned impoundment area if the topography is flat. The tailings are deposited hydraulically behind the dam and the process water is either decanted, evaporated, recycled to the mill for reuse or some combination thereof. This results in a tailings beach and a zone of fines associated with the ponded decant water. As the level of the tailings rises, the height of the impoundment is raised to increase the impoundment volume. There are three general methods of constructing new raises on tailings dams, namely upstream, downstream and centerline construction (Vick, 1983). Historically upstream construction methods were used extensively. The upstream method (Figure 2.1a), in which dykes used for successive raises are constructed on settled tailings, is subject to instability due to high seepage rates, excessive settlement and liquefaction susceptibility. Modern tailings dams are generally constructed by the downstream or centerline methods, Figures 2.1b and 5 2.1c. These methods incorporate the principles of conventional water retention dams to produce a physically more stable design. a) Upstream Method Dikes. Mailings b] Downs team Method Tailings or Water Raises, \ lmpervious Core c] Centerline Method Tailings Raises. Imperv. Core Figure 2.1: Tailings Dam Construction Methods (After Klohn, 1980) 6 2.2 PORE WATER CHEMISTRY Pore water chemistry is controlled by the influence of pore water contaminants, which strictly speaking include all substances other than H2O. Types of pore water contaminants can be broken down into two categories: aqueous phase liquids (APL's) and non-aqueous phase liquids (NAPL's). APL's are those contaminants which occur as dissolved species (ions) in the pore water, whereas NAPL's have low solubilities in water and include organic substances such as gasoline and PCB's. N A P L contaminants would not be expected to be an environmental issue at a sulphide bearing tailings impoundment, unless localized dumping of such substances had occurred. The pore water of sulphide bearing tailings contains a variety of dissolved ionic species, and these dissolved constituents may be classified as A P L contaminants. The pore water chemistry of a specific pore water sample is influenced by a number of factors, which are listed below: • water chemistry of the effluent with which the tailings are discharged to the impoundment; • tailings mineralogy; • water chemistry of external sources (such as surface waters and precipitation) which infiltrate the tailings impoundment; • pore water transport processes; and • chemical and biological reactions. Of the above factors governing pore water chemistry of sulphide bearing tailings, it is chemical and biological reactions which often have the largest influence. The oxidation of sulphide minerals by means of chemical and biological reactions can pose a serious detriment 7 to pore water quality through a process referred to as acid rock drainage (ARD). The evolution and potential implications of this process are discussed in Section 2.2.1. The designation of dissolved constituents contained in tailings pore water as A P L contaminants does not give a measure as to the potential impact the pore water may have on a receiving environment. The potential impact of the tailings pore water is dependent upon the type and concentration of the dissolved ionic species. In Canada discharge from tailings impoundments must meet the criteria laid out in the Metal Mining Liquid Effluent Regulations and Guidelines under the federal Fisheries Act. The present limits are shown in Table 2.1 (Environment Canada, 1992). In addition, many mines are subject to more stringent requirements on discharge by provincial regulations. Table 2.1: Authorized Levels of Deleterious Substances Prescribed i n the Metal Mining and Liquid Effluent Regulations (After Environment Canada, 1992) Parameter Max. Authorized Monthly Arithmetic Mean Max. Authorized Composite Sample Maximum Authorized Grab Sample PH 6.0 5.5 5.0 Arsenic 0.5 mg/L 0.75 mg/L 1.0 mg/L Copper 0.3 mg/L 0.45 mg/L 0.6 mg/L Lead 0.2 mg/L 0.3 mg/L 0.4 mg/L Nickel 0.5 mg/L 0.75 mg/L 1.0 mg/L Zinc 0.5 mg/L 0.75 mg/L 1.0 mg/L Total Suspended Matter (TSM) 25.0 mg/L 37.5 mg/L 50.0 mg/L Radium-226 10.0 pCi/L 20.0 pCi/L 30.0 pCi/L 8 2.2.1 ACID ROCK DRAINAGE (ARD) Acid rock drainage (ARD) is the single largest environmental concern currently facing the Canadian mining industry (Filion and Ferguson, 1989). A R D is the contaminated drainage that occurs as a result of the natural chemical and biological oxidation of reactive sulphide minerals when exposed to air and water. The primary sources of A R D at a mine site involve sulphide bearing mine rock which has been disturbed and for which the exposed surface area has been increased. These sources include: • underground mine workings; • open pits; • mine waste dumps • tailings impoundments • roads, dams etc. constructed from mine waste; and • exposed rock faces in rock cuts for roads etc. After oxidation of the sulphide minerals has occurred, water flushes the oxidation sites and flows along the drainage paths, reacting with the surrounding soil and rock material. This results in changes in p H and contaminant concentrations of the drainage. Acidic drainage may be neutralized by alkaline material in the flow paths. Thus, the drainage in the initial stages of A R D development may be of neutral p H , but contain significant concentrations of dissolved ionic constituents (typically sulphates and heavy metals) from the oxidation process and reactions along the flow paths. This drainage can cause a detrimental effect on water quality in the receiving environment. Table 2.2 presents typical examples of water quality affected by A R D processes. The discrepancies between the water quality data and federal restrictions shown in Table 2.1 are readily apparent. 9 Table 2.2: Examples of Water Quality Affected by ARD Processes (After Frytas et al, 1992) Water Quality Seepage From Waste Rock Dump Mine Water From Parameter Abandoned Seepage From Active Underground Uranium Mine Mine in B.C. Copper Mine in B.C. Tailings Pond in Ontario P H 2.0 2.8 3.5 Sulphate (mg/1) 7440 7650 1500 Acidity (mg/1) 14600 43000 _ M n (mg/1) 5.6 78.3 6.4 Cu(mg/1) 3.6 89.8 16.5 Al(mg/1) 588 359 _ Pb (mg/1) 0.67 2.0 0.1 Cd(mg/1) 0.05 0.5 0.14 Zn(mg/1) 11.4 53.2 28.5 As (mg/1) 0.74 25 0.05 Ni(mg/1) 3.2 8.0 0.06 2.2.1.1 Generation of ARD There exists a variety of sulphide minerals which are susceptible to oxidation processes and subsequent generation of ARD. Some common sulphide minerals include pyrite (FeS2), pyrrhotite (Fe7Ss), pentlandite (Fe, Ni^Ss and galena (PbS). By means of example, the chemical reaction for oxidation of the sulphide mineral pyrite can be expressed as follows: [2.1] FeS2 + -^0 2 +-H 2 0-> Fe(OH) 3 + 2SO*" +4H + 10 As shown in equation [2.1] oxidation of sulphide minerals requires sulphide minerals, oxygen and pore water. The implication of this with respect to A R D in tailings is that oxidation of sulphide minerals and subsequent acid generation generally occurs in the unsaturated zone of tailings. In the saturated tailings the low diffusion coefficient of oxygen through water [Steffen Robertson and Kirsten, 1990] prevents significant oxidation of sulphide minerals. However, ionic constituents produced in the unsaturated zone may be transported to the saturated tailings, and any remaining acidity may result in additional dissolution of ionic constituents in the saturated tailings. The net result of the A R D process is that hydrogen ions are produced resulting in an increase in acidity and subsequent dissolution of ionic constituents. Drainage water p H is an indication of the development of ARD: over time, p H drops in stages. In the near neutral p H range, most of the oxidation is chemical (by oxygen) and the acidity that is released is quickly neutralized by alkalinity contained in the mine waste. As this alkalinity is consumed, the p H drops (in stages depending upon the alkali minerals). Generally at this stage, while sulphate, acidity, and later iron concentrations increase, the concentrations of other metals (such as copper) are limited by pH-solubility controls. At p H values of approximately 4.5, the much more rapid biologically catalyzed oxidation predominates, increasing the rate of acid production. Solution p H values are acidic and elevated sulphate, acidity and heavy metals concentrations are present in the drainage. The evolution of A R D can be separated into three stages as shown in Table 2.3 and summarized below: • chemical oxidation with minimal acidity; • biological oxidation becomes significant with acidity increasing and ultimately • oxidation is very rapid and the solution becomes acidic. 11 Table 2.3: Stages in the Formation of Acid Rock Drainage (After Broughton et al., 1992) Unsaturated (Vadose) Zone Saturated Zone STAGE I (Onset of Sulphide Mineral Oxidation) •chemical oxidation buffered •sulphate levels elevated •ferric hydroxide precipitates •neutral seepage •sulphate levels elevated STAGE II (Acidic Conditions Occurring •biochemical oxidation •acid runoff •highFe3+, SO42-•elevated heavy metals •neutral seepage high Fe3 +, S04 2" high acidity low heavy metals STAGE III (Buffering Agents Depleted) •biochemical oxidation •acid runoff •highFe3+, SO42-•high heavy metals •acid seepage •high Fe3 +, S0 4 2" •high acidity •high heavy metals It is important to note that elevated levels of sulphate (S042-) are characteristic of all three stages of A R D formation. Sulphate concentration, which is not restricted under water quality regulations, can be used to assess sulphide oxidation processes. Elevated sulphate concentrations, in the absence of elevated heavy metals concentrations and acidic conditions, are likely indicative of Stage I A R D formation. Identification of sulphide oxidation processes prior to the onset of acidic conditions permits the implementation of appropriate abatement strategies to mitigate the effects of ARD. 2.2.1.2 Generation of ARD in Sulphide Bearing Tailings The development and progression of A R D in sulphide bearing tailings is relatively well-understood. Blowes et al. (1994), Blowes et al. (1988), Coggans et al. (1991) and Dubrovsky et al. (1984) each provide details with respect to the evolution and effects of A R D processes in sulphide bearing tailings for specific sites. 12 A R D generation in sulphide bearing tailings impoundments generally occurs when the impoundment is inactive or after closure. In operating tailings impoundments the tailings are usually saturated. The pore water inhibits movement of oxygen through the tailings which limits acid generation. However, after termination of active discharge into the impoundment the water levels within the tailings drop, and air is permitted to fill the voids. Infiltration of surface water reacts with the oxygen and sulphide minerals resulting in acid generation in the unsaturated tailings and subsequent generation of A R D . A one-dimensional model showing the vertical progression of oxidation and the resulting contaminant migration is shown in Figure 2.2. Surface water infiltrating through the tailings enters a zone of partial saturation, Z l . The water progresses from this zone to the saturated zone (Z2) below the water table. Progression into Z2 causes the original process water to move downwards into the underlying soil where it mixes with the groundwater. The zone of oxidation, Z3, indicates the depth to which oxidation of the sulphide tailings has taken place, and correspondingly the depth to which acid generation has occurred. Water becomes acidic as it infiltrates through Z3 and dissolves ionic constituents until it reaches Z4 where it may be neutralized by alkalies if present in the tailings. Consumption of the sulphides in the oxidation zone allows oxygen to progress to a greater depth in the tailings, resulting in a progression of A R D contamination. This process advances with time and Z4 eventually penetrates the foundation soils, where A R D mixes with the groundwater. In addition to movement of A R D downward through the tailings, transport in the horizontal direction is often more pronounced. The manner in which tailings are deposited produces a layered effect which results in much higher values of hydraulic conductivity (K) in the horizontal direction. The ratio of horizontal to vertical hydraulic conductivity (K h /K v ) can range from 10-1000 for many tailings impoundments (Davies, 1996). 13 Acid generation in tailings impoundments is a long process (Lawrence, 1994). Even after acid generation is initiated a period of time (possible tens of years) wi l l transpire before A R D is released into the groundwater. Thus, tailings at a mine site may appear to be innocuous for a long time, when in fact they represent a significant environmental liability. AIR TAILINGS S U R F A C E ZONE OF OXIDATION Z 3 Z l P A R T I A L L Y SATURATED ZONE Z O N E OF NEUTRALIZATION Z 4 T ' Z 2 INFILTRATION INTERSTITIAL W A T E R PROCESS INTERSTIT IAL WATER TAILINGS A L L U V I U M MIXED GROUNDWATER AND SEEPAGE WATER Figure 2.2 One-Dimensional Water Quality Model For a Tailings Impoundment (After A. Robertson, 1987) 14 2.3 SOIL LIQUEFACTION Static and transient load stability considerations are usually the primary geotechnical engineering concern with respect to design, construction and operation of a tailings impoundment. Table 2.4 provides a summary of historical tailings dam failures, which in many cases caused significant economic and environmental damage as well as human injury and loss of life. Common features of each of the tailings dam failures presented in Table 2.4 are the use of upstream construction methods and the significant flow movement of tailings due to liquefaction of the tailings. The term liquefaction encompasses two distinct phenomena: flow liquefaction and cyclic liquefaction (Robertson, 1994), each of which are discussed in the following two sections. 2.3.1 FLOW LIQUEFACTION Flow liquefaction is synonymous with strain softening (SS) of sand in undrained shear, as illustrated in Curve 1 in Figure 2.3. Straining beyond the peak undrained shear strength results in a drop in strength to an ultimate condition referred to as steady state (equivalent to the residual strength of the soil). Steady state conditions imply increasing deformations under constant effective stress. A soil can also exhibit limited strain softening (LSS) behaviour to a quasi-steady state, as shown in Curve 2. This behaviour may result in significant deformations due to the level of strain required to mobilize increased strength. Finally, Curve 3 is an example of a strain hardening (SH) soil in which shear strength increases with increasing strain, and subsequently liquefaction is not a consideration. There is the potential for a flow liquefaction failure of a tailings dam if the tailings dam is entirely or partially composed of a SS soil. If a tailings dam is entirely composed of SS soil and 15 Table 2.4: Summary of Tailings Flow Failures (adapted from Vick, 1991) Tailings Dam Failure Cause Volume Displaced M El Cobre, Old seismic 1.4 x 106 El Cobre, New seismic 355 000 Hierro Viejo seismic 850 Los Maquis seismic 21000 La Patangua seismic 36 000 Bellavista seismic 71000 Ramayana seismic 140 Cerro Negro 3 seismic 86 000 Barahona seismic 2.8 x 106 Veta de Agua seismic 280 000 Cerro Negro 4 seismic 500 000 Mochikoshi 1 seismic 80 000 Mochikoshi 2 seismic 3000 Churchrock piping 76 000 Bafokeng piping 3 x10s Southwest US stability -Texas seepage 100 000 Mike Horse overtop 150 000 Western Nuc. overtop 40 Union Carbide overtop 11 000 Kimberly stability 1.5 x 106 Stava stability 200 000 Bilbao stability 140 000 Deneen overtop 38 000 Blackpool stability 11000 Cholwich stability 18 000 Tyrone stability 2.1 x 106 United Nuc. pipeline 36 000 Union Carbide - 360 Edgemont - 140 Grootvlei stability -Captains Flat - 40 000 the in-situ gravitational shear stresses are greater than the steady state strength of the soil a catastrophic flow slide can occur if a triggering mechanism causes flow liquefaction. If a tailings dam is partially composed of SS and SH soil a flow failure can occur if the SS soil is triggered to strain soften and the SH soil cannot support the gravitational shear stresses. Triggering mechanisms include both cyclic and monotonic undrained loading. In addition, 16 Sasitharan et al. (1994) have shown that flow liquefaction can be triggered by certain types of drained monotonic loading (e.g. a slow rise in the water table). Si Figure 2.3: Undrained Behaviour of Sand 2.3.2 CYCLIC LIQUEFACTION The principle concerns with respect to dynamic loading of a tailings dam are cyclic liquefaction under earthquake loading and the potential for a resultant flow liquefaction failure. During cyclic undrained loading almost all granular soils develop positive pore pressures due to the contractant response of the-soil at small strains. If there is shear stress reversal, the effective stress can progress to the point of zero effective stress, as illustrated in 17 Figure 2.4. When a soil element reaches the condition of essentially zero effective stress, the soil has very little stiffness and large deformations can occur during cyclic loading. When cyclic loading stops, the deformations due to cyclic liquefaction essentially stop, except for those due to local pore pressure redistribution (Robertson, 1994). However, the reduction in shear strength (to residual values) of soils that experienced cyclic liquefaction can produce conditions favourable for flow liquefaction. Therefore, deformations of tailings dams under cyclic loading may be attributed to the effects of both cyclic liquefaction and flow liquefaction. Figure 2.4: Undrained Cyclic Behaviour of Sand 18 3.0 IN-SITU TESTING METHODS In-situ testing, and more specifically CPT technology, can provide an accurate and cost-effective method for geoenvironmental characterization in appropriate ground conditions. Appropriate ground conditions include sands, silts, clays and some sands and gravels. Mine tailings, consisting of predominately sand to clay-sized materials, are highly amenable to CPT technology. Campanella et al. (1984), Woeller et al. (1989) and each demonstrate the use of the CPTU for geotechnical and hydrogeological characterization of tailings with specific case examples. The CPTU is effective in identifying the physical regime, but geoenvironmental characterization also requires assessment of geochemical conditions. The recent development of a resistivity piezocone (RCPTU) and improved water sampling technologies provide a means of assessing the geochemical properties of sulphide bearing tailings. Campanella et al. (1994) provided an overview of the use of the RCPTU for environmental characterization of sulphide bearing tailings, and used some of the field data presented in this thesis. The following sections provide details concerning the CPT technology used in this study. 3.1 RESISTIVITY CONE PENETRATION TEST (RCPTU) The resistivity cone penetration test (RCPTU) records the same measurements as the cone penetration test (CPTU) (which is described in Section 3.3), and in addition measures the bulk resistivity of the soil. Bulk resistivity measurements are made by a module (referred to as a resistivity module) which resides behind the standard cone. This section describes the theoretical basis and operation of the resistivity module for bulk resistivity measurement of soils, and focuses on the application of the resistivity module for assessment of A R D contamination in sulphide bearing tailings. 19 3.1.1 RESISTIVITY MEASUREMENT IN SOILS The term bulk resistivity is used to describe resistivity measurements of the soil, pore water and gas phase. Bulk resistivity measurements are affected by the following factors (Urish, 1981): • degree of saturation • ionic composition of the pore water • porosity • temperature • shape of pore size • cation exchange capacity (CEC) of matrix materials In saturated soils, the bulk resistivity is primarily influenced by electrical conduction through the pore water, which is a function of the ionic composition of the pore water and the pore volume. In the unsaturated zone the effect of the soil matrix resistivity (which is much larger than that of the pore fluid) increases relative to the electrical conduction of the pore water (Frolich and Parke, 1990). This, coupled with the fact that air in the voids acts as an insulator, generally results in much higher values of bulk resistivity in the unsaturated zone. Interpretation of bulk resistivity measurements in the unsaturated zone is complicated by the difficulty of discerning the relative influence of pore water saturation and pore water chemistry on the measurements. For the case of saturated soils, the bulk resistivity can be related to the pore water resistivity through application of Archie's Equation (Archie, 1942, Telford et al., 1976). This empirical formula assumes that bulk resistivity is directly related to pore water resistivity and the geometry of the pore spaces in the soil. A term commonly used to relate soil resistivity to pore 20 water resistivity is the formation factor (F), which is a function of the pore geometry. Archie's Equation can be expressed as follows: [3.1] F = ^ = n - m Pf where, F = Apparent Formation Factor p b = Bulk Resistivity Pf = Pore Water Resistivity n = Porosity m = Constant related to soil behaviour type For sands the value of m is approximately 1.5, and for various clays m has been found to range from approximately 1.8 - 3.0 (Jackson et al., 1978) The term apparent formation factor implies that surface conduction effects and other intergranular pore water effects may contribute to the measured bulk resistivity. The intrinsic formation factor of a soil is function of only the pore geometry, which has been found to be a function of particle shape (Jackson et al., 1978). Archie's Equation is recognized to be an over-simplification of the relationship between bulk resistivity and pore water resistivity, but is still valid under the condition that the pore water is highly conductive and the soil particles are non-conductive relative to the pore water (Urish, 1981). Based upon the discussion in Section 2.2.1, A R D contamination can result in significant ionic loading of the pore water, which results in a corresponding increase in the electrical conductivity of the pore water. Also, the relative electrical conductivity of the generally non-21 plastic tailings is negligible in comparison with that of the pore water. Thus, for the case of saturated sulphide tailings affected by A R D processes, it appears that Archie's Equation is likely valid. 3.1.1.1 Influence of Pore Water Affected by ARD Contamination on Bulk Resistivity Measurements At low frequencies, similar to that employed by the UBC resistivity module, conduction in pore water takes place by electrolytic conduction . A current is produced when the ions migrate due to the application of an electric field. In general, the more ions present in the pore water the greater the electrical conductivity, and subsequently the lower the bulk resistivity (as resistivity is the direct inverse of conductivity). However, the relationship between the electrical conductivity of an electrolyte and the ionic constituents is complicated by the effect of viscous drag (Keller, 1982). Viscous drag opposes the mobility of individual ions, which limits the electrical conductivity of the pore water. The main factors affecting viscous drag include the following: (a) .Temperature - fluid viscosity is a function of temperature and therefore conductivity of a particular ion wil l increase with an increase in temperature. (b) .Ionic concentration - conductivity increases with increased ionic concentration, but there also is an increased tendency towards collisions which retard migration of the ions. (c) .Ion Size - the tendency for smaller ions to have a higher mobility due to a decreased incidence of collisions is complicated by the tendency of charged ions to attract a layer of water molecules, and thus increase overall size. 22 (d).Ion Valence - the greater the valence the more charge transferred per ion, which results in higher electrical conductivity of the pore water. As was discussed in Section 2.2.1, pore water affected by A R D contamination contains a variety of ionic constituents, which act to increase the electrical conductivity of the pore water. Assuming the temperature of a given pore water sample remains constant, changes in pore water electrical conductivity can be attributed to factors (b) through (d). As the A R D process advances from Stage 1 - Stage 3 the concentration and type of ionic constituents in the pore water increases significantly. The relative activity of some common pore water ions are shown in Table 3.1. The high mobility and correspondingly high relative activity of the hydrogen ion (H + ) is readily apparent. Initially, in Stage 1 A R D the principle contributor to elevated electrical conductivity of the pore water is due to increased sulphate concentrations. As ARD progresses to Stage 2 and Stage 3 development, increases in types and concentrations of heavy metal ions and increases in acidity result in significant increases in pore water electrical conductivity. Table 3.1: Relative Electrical Activity of Common Ionic Species (After King and Sartorelli, 1991) Major Cations Specific Conductance Major Anions Specific Conductance H + 34.8 OH- 19.7 K + 7.5 so 4 2 - 8.0 NH4+ 7.5 ci- 7.7 Ca 2 + 6.1 NO3- 7.1 Na + 5.0 HCO3" 4.6 23 3.1.1.2 Influence of Soil Type on Bulk Resistivity Measurements Changes in soil stratigraphy are generally less influential on bulk resistivity measurements than pore water chemistry. Changes in stratigraphy are often marked by changes in bulk resistivity, but the influence of these changes is often limited by changes in electrical conductivity of the pore water. However, under amenable soil conditions and relatively low pore water conductivity, changes in stratigraphy can be linked directly to changes in bulk resistivity, as evidenced in Figure 3.1. Kokan (1992) found that the peaks in friction ratio (Rf) (indicative of changes in soil lithology) corresponded with changes in bulk resistivity. From 3-12 m the peaks in Rf corresponded with increased organic content, from 12-15 m the peaks in Rf were representative of organic-rich soil with increased clay content and beneath a depth of 15 m the peaks in friction ratio were indicative of clayey-silt layers. The decrease in bulk resistivity in the organic and clay soils can be attributed to surface conduction effects of the soils. The observed influence of soil type on bulk resistivity is largely recognizable due to the relatively low pore water conductivity at the site (as evidenced by the majority of bulk resistivity measurements of > 30 Q-m). For the case of sulphide bearing tailings, it is unlikely that soil type would have a significant influence on bulk resistivity measurements. Stratigraphic variations in the tailings would likely be minimal considering the relative uniformity of the tailings and surface conduction effects of the generally non-plastic tailings would be negligable in comparison with the electrical conductivity of tailings pore water affected by A R D processes. 3.1.2 DESCRIPTION OF UBC RESISTIVITY MODULE The description contained herein of developments in UBC resistivity module design includes developments to 1994, and more recent changes to the equipment are not described. The 24 RESISTIVITY ( o h m - m ) 0 10 .20 30 40 50 FRICTION RATIO (%) Figure 3.1: Comparison of Bulk Resistivity and Friction Ratio (After Kokan, 1992) 25 measurement of resistance to electrical current flow in soils is a relatively new development in penetration technology (Weemees, 1990). Resistivity cone penetrometers are available on a limited but increasing commercial basis (Van de Graff and Zuidberg, 1985, Horsnell, 1988, Woeller et al., 1993, and Rossabi, 1993). The RCPTU consists of a resistivity module which resides behind a standard cone. The addition of the resistivity module permits assessment of pore water quality by measuring bulk resistivity, while still providing all other standard CPTU measurements. A schematic of one of the UBC resistivity modules (RES1) used in this study is shown in Figure 3.2. The diameter of the resistivity module is 44 mm. Three different sets of brass electrode spacings of 10, 25, and 75 mm are used for measurement. Smaller distances between the electrodes allow for possible detection of thinner layers of contrasting resistivity. Wider spacing provides a greater penetration of the electric field into undisturbed soil and provides a more averaged resistivity response. The performance of the module is related to the thickness, width, and composition of the electrodes (Kokan, 1992). The electrodes should have stable and linear conductive properties at varying current levels. Brass electrodes have been found to offer the best compromise between conduction and wear characteristics (Weemees, 1990). The two outer electrodes have widths of 5.0 mm while the three inner electrodes have widths of 2.5 mm. Delrin, a plastic, is used as the insulator separating the electrodes. The outer electrode spacing also acts to supply a constant peak excitation current of 1000 Hz to the resistivity module. Research by Weemees (1990) found that this frequency eliminates polarization of the current supply electrodes. Polarization is the process where ions accumulate at the electrodes thus increasing the measured resistance. The applied frequency is also within the range of 25-3000 Hz suggested by the American Society for Testing and Materials (1982) for conductivity testing of water. 26 ~ 350 mm Resistivity Module 15 cm 2 p a I 75 mm standard cone rods plastic insulation current electrode 110 mm grounded electrode ~ 650 mm V Standard Piezocone 10 cm 2 Figure 3.2 Schematic of Resistivity Piezocone (RCPTU) 27 A signal generator was used to apply an excitation voltage at 1000 Hz. This excitation voltage controls the amount of current supplied to the electrodes. The required excitation current depends on how conductive the soil is, so that lower resistivity soils require a higher excitation current. The resistivity module does not directly measure resistivity, but rather measures resistance. For a given excitation current, measured voltages across the different electrode spacings are converted to resistance through Ohm's Law: [3.2] V = IR where, V = Potential Difference (V) I = Excitation Current (A) R = Resistance (ft) Resistance is not a fundamental material property, but rather is a function of resistivity and geometry (specifically length (L) and cross-sectional area (A)) of the different electrical conducting material being measured. Resistance is related to resistivity, p, through the following relationship: [3.3] R = Weemees (1990) proposed a calibration factor, k, to account for the influence of the electrode configuration on measured resistance. Assuming that (1) the soil acts as a homogeneous, isotropic media, (2) the electrodes act as perfect conductors and (3) the electronic circuitry of 28 the resistivity module acts as a perfect current supply source, the geometry factor (A/L) would be constant, k, and equation [3.3] would reduce to the following equation: [3.4] p b =R * k Laboratory calibrations were carried out to determine this relationship for the different electrode configurations. 3.1.3 CALIBRATION OF UBC RESISTIVITY MODULE Calibration procedures require submerging the resistivity module in constant temperature solutions of known resistivity. Typically calibration work is carried out by starting with de-ionized water and then potassium chloride (KC1) is added to the water in small quantities. This permits calibration of the resistivity module over a wide range of resistivities. The resistivity of the solution was recorded using a hand-held conductivity meter (Omega model CDH-30). The conductivity meter was calibrated with a 0.01 Molar (M) solution of KC1 and then checked with a 0.10 M solution. The submerged resistivity module measures potential difference across the three electrode spacings for the different solution resistivities. Given that the excitation current remains constant, the potential difference measurements can be directly related to solution resistivity using equation [3.4] to determine calibration factors for each electrode spacing. Figure 3.3 presents calibration data for the resistivity module used during field testing at INCO and Falconbridge mine sites (referred to as RES1). RES1 is a non-isolated resistivity module, in which the power supply to the resistivity module is not completely separate from that of the cone. This results in non-linear calibrations due to grounding and impedance effects (Kokan, 1992). The calibration for an excitation voltage of 0.1 V (Figure 3.3a) is highly 29 1 1 1 1 1 1 1 1 1 0 100 200 300 400 Resistivity (Q-m) Figure 3.3a: RES1 Resistivity Module Calibration Curve - Low Excitation Resistivity (n -m) Figure 3.3b: RES1 Resistivity Module Calibration Curve - High Excitation 30 non-linear, particularly for the 10 mm and 25 mm electrode spacings. However, the calibration for a higher excitation voltage of 1.0 V (Figure 3.3b), required for measurement of lower resistivity, exhibits a more linear response for resistivities up to 100 Q-m. The calibration data for each electrode spacing for the 1.0 V excitation can be approximated by two linear relationships; the first from 0-60 Q-m and the second from 60-100 Q-m. As the purpose of this study was to delineate low resistivity A R D , it was anticipated that the resistivity module would be operated at an excitation voltage of 1.0 V. Recent improvements in resistivity module design have eliminated the non-linear calibrations. A n isolated resistivity module (referred to as RES2) has a power supply totally independent of the cone power supply, which prevents grounding losses to the cone body. Figure 3.4 presents calibration data for the improved resistivity module (referred to as RES2), which was used during testing at the Gibraltar mine site. For the low excitation voltage (0.5 V) the calibrations are linear for resistivities up to 350 Q-m and have a lower boundary of approximately 1 Q-m, as shown in Figure 3.4a. For the higher excitation voltage (5.0 V) the calibrations are linear to 40 Q-m and have a lower boundary of approximately 0.01 Q-m, as shown in Figure 3.4b. This represents a significant improvement over previous resistivity module performance. 3.1.4 APPLICATION OF RCPTU FOR ASSESSMENT OF ARD CONTAMINATION The application of resistivity techniques for delineation of contamination requires that there be a contrast between the natural resistivity of the subsurface (background values) and the resistivity of contaminated zones. Contaminants can provide this contrast and influence the bulk resistivity measurements by changing the resistivity of the pore water. Dissolved aqueous phase liquids (APL's) typically act to decrease the resistivity 31 Excitation Voltage - 0.50 V Temperature ° 10 degrees C -4.00 200 400 600 Resistivity (fi-m) Figure 3.4: RES2 Resistivity Module Calibration Curve - Low Excitation 6.00 —i 4.00 2.00 0.00 -2.00 -4.00 Excitation Voltage = S.O V Temperature = 10 degrees C 20 40 60 Resistivity (n -m) 80 100 Figure 3.4b: RES2 Resistivity Module Calibration Curve - High Excitation 32 of the pore water (i.e. A R D leachate from mine tailings) and insulating organic non-aqueous phase liquids (NAPL's) increase bulk resistivity by blocking paths of conduction through the pore space of the soil (i.e. organic contaminants). The UBC ISTG has carried out RCPTU tests at a variety of sites since 1988. Results to date clearly demonstrate the capability of the RCPTU to produce repeatable and accurate profiles of resistivity. A summary of typical resistivity measurements of fluids and bulk soil-fluid mixtures is shown in Table 3.2. Values of conductivity, which are simply the reciprocal of resistivity values, are also shown due to the widespread convention of using conductivity in the environmental sciences. The conversion between resistivity and conductivity is as follows: [3.5] Conductivity (uS/cm) = 10000 / Resistivity (Q-m) As can be seen in Table 3.2, the RCPTU is capable of delineating highly conductive pore water. Based on this experience, it was believed that the RCPTU would be effective in identifying highly conductive pore water associated with A R D contamination. The use of resistivity measurements to delineate zones where A R D is developing or occurring is relatively well-documented. For example, Ebraheem et al. (1990) and King and Sartorelli (1991) show how high ionic loading of both early stage and low p H , fully developed A R D is well defined by surface geophysics. However, the ability to carry out resistivity soundings and avoid the non-unique solution interpretation of surface geophysics is a large advantage of the RCPTU. The use of the RCPTU for assessment of A R D contamination requires consideration of bulk resistivity measurements in both the unsaturated and saturated zones. In the unsaturated zone the effects of conductive pore water affected by A R D contamination are countered by the insulative effects of air also contained in the voids, making interpretation of bulk resistivity measurements difficult. It is reasonable to expect that bulk resistivity measurements in the 33 Table 3.2: Summary of Typical Resistivity (Conductivity) Measurements of Bulk Soil Mixtures and Pore Fluid (Campanella et al., 1994) Material Bulk Resistivity pb, Q-m Fluid Resistivity pf, Q-m Bulk Conductivity uS/cm Fluid Conductivity uS/cm Sea Water _ 0.2 - 50000 Drinking Water _ >15 - <665 McDonald Farm Site Clay 1.5 0.3 6700 33300 Laing Bridge Site Clay 20 7 500 1430 Colebrook Site Clay 25 18.2 400 550 232 Ave. Clay 8 - 1250 -Strong Pit Clay 35 - 285 -Kidd 2 Site Clay 14 12.5 715 800 McDonald Farm Site Sand 5-20 1.5-6 2000-500 6700-1670 Laing Bridge Site Sand 5-40 1.5-10 2000-250 6700-1000 Colebrook Site Sand 70 143 Strong Pit Site Sand 115 89 Kidd 2 Site Sand 1.5-40 0.5-21 6700-225 20000-475 Typical Landfill Leachate 1-30 0.5-10 10000-330 20000-1000 Industrial Site- Inorganic Contaminants in Sand 0.5-1.5 0.3-0.5 20000-6500 33000-20000 100 % Ethylene Dichloride (ED) - 20400 - 0.5 50% ED/50% Water in Sand 700 - 14 -17% ED/83% Water in Sand 275 - 36 -Industrial Site - Organic 125 - 80 -Contaminants in Sand BC Place Parcel 2, PAH's (Coal 200-300 - 50-33 -Gas Plant) BC Place Parcel (Wood Waste) 300-600 - 33-66 -unsaturated zone would be highly variable, owing to the effects of changing pore water chemistry and variable saturated conditions. Therefore, interpretation of bulk resistivity measurements in the unsaturated zone requires a qualitative approach, as one must attempt to decipher the influences of these countering factors. However, this qualitative approach can be strengthened if pore water samples can be collected and subsequent chemical analyses carried out. For the field test work carried out at INCO and Falconbridge mine sites pore water samples were collected in the unsaturated zone using a modification of the immiscible displacement technique developed by Patterson et al., (1978). 34 In the saturated zone the interpretation of bulk resistivity measurements is more straightforward. For the case of sulphide bearing tailings changes in bulk resistivity are predominately due to changes in pore water chemistry. The influence of changes in soil type are not as significant, due to the relatively uniform nature of the tailings and the generally low plasticity (and hence low surface conduction effects) of the tailings. As was discussed in Section 3.1.1.1, under constant temperature conditions the factors affecting electrical conductivity of the pore water are ion concentration, ion size and ion valence. Of primary importance in mapping A R D contamination as it progresses from Stage 1 - Stage 3 A R D , is monitoring increases in concentrations of specific ionic constituents (sulphate, specific metals, H + ) . Research by Ebraheem et al. (1990) demonstrates a direct relationship between total dissolved solids (TDS) (a measure of the total dissolved ionic loading of the pore water) and bulk resistivity, as shown in Figure 3.5. Therefore, it appears reasonable that the development of A R D and its characteristic increase in ionic loading of the pore water can be linked directly to bulk resistivity measurements. Moreover, based upon relative values of bulk resistivity measurements and identification and quantification of specific ionic constituents from pore water samples, the approximate stage of A R D can likely be identified. For instance, bulk resistivity measurements which correspond to water samples having elevated sulphate concentrations, but with low heavy metals and acidity, are likely indicative of Stage 1 ARD. However, bulk resistivity measurements which correspond to pore water samples having elevated concentrations of sulphates, metals and acidity are likely characteristic of more advanced Stage 2 and/or Stage 3 A R D processes. While it is acknowledged that ion size and ion valence also influence electrical conductivity of the pore water, consideration of these factors appears less critical to the evaluation of A R D processes than the overall increase in ionic loading with A R D progression. 35 1E+6 0.1 1.0 10.0 100.0 Bulk Resistivity (ohm-m) Figure 3.5: Observed Relationships Between Total Dissolved Solids and Bulk Resistivity (After Ebraheem et al., 1990)) 3.2 BAT PORE WATER SAMPLING TECHNOLOGY The BAT pore water sampler, named after its inventor (B.A. Torstennson, 1984), was used to collect pore water samples during the field investigation program for this study. The system consists of a sampling tip that is accessed through sterile evacuated glass sample tubes (volume = 35 ml) and a double-ended hypodermic needle set-up. The tube sampler is lowered by a cable through standard A W water sampling rods. The BAT sampler is pushed into the ground in the same manner as the piezocone. The UBC modified BAT sampling tip consists of a probe slightly larger in diameter than the resistivity module (50 mm vs. 44 mm). This permits undisturbed sampling down the same alignment as a previous CPTU sounding, or the sampling tip may be pushed on its own. Everard (1995) demonstrated that there is no 36 difference in sample integrity in pore water samples collected from sampling down a previous CPTU sounding versus pore water samples collected from the BAT pushed on its own. A schematic of the UBC modified BAT pore water sampler is shown in Figure 3.6. Recent modifications to the design of the UBC modified BAT pore water sampler were made following completion of field work for this thesis. Campanella (1995) gives a detailed description of these recent changes. The first pore water sample at a depth is generally purged and after the second pore water sample is retrieved to the ground surface preliminary chemical tests can be carried out on site (e.g. p H , conductivity and temperature) and the samples stored for future chemical analyses. After sampling is carried out at.a specific depth, the probe is then pushed to the next depth and the procedure repeated. There is no limit to the number of samples that can be taken at one location. The time to retrieve a sample is dependent upon the hydraulic conductivity of the soil unit being investigated. The United States Environmental Protection Agency (US EPA) have conducted many field trials and comparisons of existing water sampling technologies (Blegen et al., 1988). They have recognized the BAT technology as being superior in obtaining high quality pore water samples for geoenvironmental characterizations. BAT groundwater sampling can be used to significantly enhance the application of the RCPTU. RCPTU logs can be used to target potential areas of contamination and identify permeable soil strata, which facilitates cost-effective pore water sampling. After pore water samples have been collected, comparisons between bulk resistivity logs and specific chemical properties of the samples can potentially enable the formation of site-specific relationships. Such relationships can improve the interpretation of any future RCPTU soundings at a site, which makes the technology attractive for monitoring water quality changes over time. 37 44 mm O.D. AWL casing septum wire line weight sample container septum double ended hypodermic needle fluid channel water sample filter 50 mm O.D. solid steel previous RCPT hole (44 mm O.D.) Figure 3.6: Schematic of UBC-Modified BAT Pore Water Sampler 3.3 CONE PENETRATION TEST (CPTU) The cone penetration test represents a repeatable means of delineating soil stratigraphy and determining physical geotechnical parameters. The designation of the U in CPTU implies pore pressure measurements are recorded, as compared to a CPT test which is not equipped to measure pore pressure. A schematic of the standard cone is shown in Figure 3.7. The cone has a standard (ASTM D-3441) 10 cm 2, 60° conical tip, a 150 cm 2 friction sleeve and pore pressure transducers which allow the CPTU to measure tip resistance (qc), friction sleeve stress 38 STRAIN GAUGES FOR FRICTION LOAD CELL TEMPERATURE SENSOR PORE PRESSURE TRANSDUCER POROUS PLASTIC FILTER MATERIAL CONE CABLE SEISMOMETER SLOPE SENSOR ~ 50 cm FRICTION SLEEVE (150 sq. cm) STRAIN GAUGE FOR CONE BEARING LOAD TEST CELL 60 CONE 35.68mm O.D. (10 sq. cm) Figure 3.7: Schematic of Standard Piezocone (fs), and pore pressure response at up to three locations (typically referred to as U l , U2, and U3). U l is located in front of the cone tip, U2 is located behind the cone tip and U3 is located behind the friction sleeve. U2 is the most common location for measurement of pore pressure response. A l l measurements are made by calibrated strain gauges and /or pore pressure 39 transducers that are highly linear and non-hysteretic. Temperature (t) and inclination (i) are also measured simultaneously as the CPTU is advanced into the ground. In addition, a cone capable of recording seismic wave velocities has been developed (Campanella and Robertson, 1984). From seismic wave velocities (V8 and V P) low strain moduli can be computed directly. The cone is pushed into the ground at a rate of about one metre every 50 seconds as per the A S T M Standard by a hydraulic pushing source. The specialty built UBC in-situ research vehicle was used for all field testing in this study. A detailed description of this vehicle and its capabilities is given by Campanella and Robertson (1981). A l l cone channels are continuously monitored and are typically digitally reported at 25 mm intervals, thus providing essentially continuous in-situ data sampling. Data are acquired in clear format ASCII files which allow the user to carry out straightforward post-investigation analyses with any number of proprietary and commercial CPTU data evaluation software packages. Figure 3.8 is an example of a typical graphical data output, referred to as a cone plot, from a CPTU sounding carried out in sulphide bearing tailings. The first data column contains friction ratio (Rf), which can be used to estimate soil behaviour type. Rf is not directly f measured, but rather is defined as — * 100%,with fs and q t plotted in the second and third If columns, respectively, qt, is q c corrected for the effects of in-situ water pressures on the mechanical design of the cone, which is only significant in soft cohesive soils (Robertson and Campanella, 1988). Column 4 contains the dynamic pore pressure response, and as denoted on the figure, the U2 pore pressure location was used for this sounding. Column 5 contains the bulk resistivity measurements recorded by the resistivity module. The interpteted stratigraphy for the sounding is shown in column 6. 40 TJ a a CM CM n cr. i CD o o z h-t > P! z o z o z * C m o -) . RESISI (ohm-m) H o i ° t h (/) SSURE if wat u n in RE PRE in m c 0 h n O ' D . O CM — • I O D 2 H (/) Z H Q: I n •> o x u z o o u CO J CL LL. CC O U J CC Q « O t> 0) S.-D 2 P c o t ra o o uj J O > _ z w C8 w 3 »-OS ( s j a^ao j ) H ld3Q 41 Extensive empirical correlations have been developed between the various C P T U channels, and combinations thereof, that provide soil behavior type (equivalent to stratigraphy) and geotechnical strength parameters (e.g. (j)' ,1)^ SPT-N and Su). These extensive correlations have been incorporated into the PC-based software program CPTINT (CPTINT 5.0, 1994). CPTINT was used to process data collected during field investigation programs for this study. CPTINT utilizes soil interpretation charts developed by Robertson and Campanella (1988) for the estimation of soil behavior type. These charts are presented in Figure 3.9. The upper chart in Figure 3.9 estimates soil behavior type using the cone bearing (qt) and the friction ratio (Rf) In general, as the proportion of fines and plastic characteristics increases, the bearing decreases and the friction ratio increases. In the case of a clean sand the cone bearing wil l be generally greater than 40 bar (where 1 bar = 100 kPa) and the friction ratio wi l l be less than 0.75 %. Values of friction ratio greater than 2 % are generally representative of silty and/ or clayey soils, whereas values greater than 5 % usually indicate high organic content. This is readily apparent on Figure 3.8, where the Rf in the sandy tailings was approximately 0.7% and was in excess of 2% in the clayey-silt native soil. It is not always possible to accurately estimate soil behavior type using q t and Rf, particularly in fine-grained materials (Campanella and Robertson, 1992). In these materials, the lower chart in Figure 3.9, which incorporates pore pressure measurements, provides more definitive interpretation. During penetration, pore pressures above or below equilibrium values (e.g. dependent upon a materials propensity to contract or dilate during shearing) are termed excess pore pressures. The excess pore pressure (Au) measured during penetration provides an excellent means of detecting details in soil behavior type. For clean sandy soils excess pore pressures dissipate almost immediately (as seen in Figure 3.8 for the sandy tailings), while for finer-grained silts and clays significant excess pore pressures can be generated. Excess pore pressures can be either positive or negative depending upon pore pressure measurement 42 woo CO a o z < UJ o Ul Z 8 100 10 1000 •J, v—1—1 / 1 / V 1 2 / — r i It 7 / /jy/h -3 — — i — * i i • " 2 • i 0 ) i I T T 2 4 FRICTION RATIO 1 1 1 r 6 8 ( % ) i i O z c < UJ a ui z o o 10r-0 0.4 0.8 1.2 PORE PRESSURE RATIO. Bq lac Oc/N SOIL eouviou* TYPE 2 soon IVI M * OUIKD t 1 ORSiXIC KATEAIAL 1 1 CLAY 4 1.S SILTY CLAY io CLAY s 2 CLAYEY SILT '0 SILTY CLAY s 2.5 SAMJY SILT io CLAYEY SILT » 3 SILTY SAM) TO SAM)Y SILT • 4 SAM) TO SILTY SAW • • S SAM) 10 6 GRAVELLY SAX) TO SAM) II 1 VERY STIFF n« OUIHED <«l u 2 SAM) TO CLAYEY SAM) (•) (•) OvtrtenMllstttd or cwwitii Figure 3.9 Soil Behaviour Type Classification Chart (After Robertson and Campanella, 1988) 43 location and soil behavior (Gillespie, 1990). Normally consolidated silts and clays tend to develop positive excess pore pressures, whereas overconsolidated silts and clays tend to develop smaller positive or even negative excess pore pressures in the U2 measurement location. The negative pore pressure response observed in Figure 3.8 for the native soil would suggest that the clayey-silt soils are overconsolidated. The net effect of incorporating excess pore pressure measurements in the identification of soil behavior type is to improve the interpretation of fine-grained soils, while leaving the interpretation in sands unchanged. The lower chart in Figure 3.9 is based on the U2 location for pore pressure measurement. Excess pore pressure measurements also provide valuable insight into the consolidation and hydraulic characteristics of the different soil strata. When penetration ceases, typically after each 1 m rod push, the excess pore pressures decay with time. Figure 3.10 is an example of a CPTU pore pressure dissipation from a sounding carried out in sulphide bearing tailings. The amount of time required for the pore pressure to decay to the equilibrium value (denoted as Uo on Figure 3.10) depends on the coefficient of consolidation, which is a function of the compressibility and hydraulic conductivity of the soil. Conversely, the dissipation time can be used to estimate the coefficient of consolidation, Q, (or (where v and h are vertical and horizontal coefficients, respectively), through the use of cavity expansion theory. Robertson and Campanella (1988) provide a detailed discussion concerning the estimation of coefficient of consolidation from pore pressure dissipation data. Knowing cv / l v the hydraulic conductivity (K) can be estimated using: [3.6] K v / h = cv,h * iriv,,, * y w where m v h is the coefficient of volume compressibility in either the vertical or horizontal plane, which can be estimated from C P T U data, and y w is the unit weight of water. In addition, in-44 45 situ equilibrium pressure head distribution and the identification of vertical gradients within the saturated zone can be determined based on the equilibrium pore pressure data for all soil types. Estimates of horizontal gradients can be made based on the depth of the water table at different CPTU locations. 3.3.1 APPLICATION OF CPTU FOR ASSESSMENT OF STATIC STABILITY The CPTU offers an excellent method of delineating the information required for a static stability analysis of a tailings dam. Analysis of tailings dam stability, notwithstanding the form of the stability assessment being carried out, generally requires the following information: • geometric configuration of the tailings dam; • stratigraphic profiles within the dam and foundation materials; • strength parameters for each stratigraphic unit within the dam and foundation materials and • pore pressure distribution within the dam The CPTU is unparalleled in its ability to identify soil stratigraphy (Campanella and Robertson, 1988). After distinct stratigraphic zones have been identified, the CPTU can give estimates of key geotechnical strength parameters for each stratigraphic zone. Established correlations exist for estimating (J)', D„ SPT-N and Su (References for each correlation are included in the CPTINT 5.0 documentation contained in Appendix B). In addition, the CPTU can measure the in-situ equilibrium pressure head distribution and identify any gradients. Depending upon the scope of the project, more detailed geotechnical and hydrogeological information may be required. The CPTU data can be used to delineate critical zones for soil sampling and/ or piezometer installation. 46 3.3.2 APPLICATION OF CPTU FOR ASSESSMENT OF FLOW LIQUEFACTION SUSCEPTIBILITY Plewes et al. (1992) proposed a screening procedure for evaluating the susceptibility for flow liquefaction of soils using the CPTU. The screening procedure was developed on the basis of the state parameter Q¥) and critical state theory. The state parameter, originally proposed by Been and Jefferies (1985), is defined as the difference between the current void ratio (e) and the critical void ratio (ec) at the same stress level: [3.7] ¥ = e - ec A positive 4* value is representative of a SS (contractive) soil, whereas a negative *F value is representative of a SH (dilative) soil. The relative distribution of SS and SH soils can be used to assess the potential for flow liquefaction, given the SS soil is triggered to strain soften. Plewes et al. (1992) applied the theoretical framework of critical state soil mechanics to laboratory and in-situ field data and derived a methodology for estimating the state parameter of a broad range of soils directly from the CPTU. Figure 3.11 presents the essence of this screening procedure. The parameters incorporated in Figure 3.11 are defined as follows: 4* = state parameter Qp = normalized CPT resistance = Qp(l-B<,) Qp = stress-normalized qt = —— 47 U 2 - U 0 B, = dynamic pore pressure ratio = ^ _ ^ vO stress normalized friction ratio = 2 (100%) q t _ c r v o ZONE 2 ORGANIC SOILS-PEAT J CLAYS—CLAY TO SILTY CLAT 4 SILT MIXTURES-CLAYEY SILT TO SILTY CLAY 5 SANO UIXTURES-SILTY SAND TO SANDY SILT 6 SANDS-CLEAN SWO TO SILTY SAND ATTER JEfFERIES AND DAMES. I M l . Figure 3.11: CPTU-Based Screening Chart For Estimating the State Parameter of Sands (After Plewes et al., 1992) 3.3.3 APPLICATION OF CPT FOR ASSESSMENT OF CYCLIC LIQUEFACTION SUSCEPTIBILITY Currently, the most popular method for estimating liquefaction potential under dynamic loading conditions, referred to as cyclic liquefaction potential, makes use of the penetration 48 resistance (N value) from the Standard Penetration Test (SPT). Seed et al. (1985) proposed a methodology for evaluating liquefaction potential based upon a back analysis of historical records (referred to as the Berkeley records) at sites which were known to have liquefied or not liquefied under earthquake loading. Liquefaction was assumed to have occurred based on the presence of observable surface features such as sand boils and ground cracks. In the Seed methodology the soil conditions are defined by the normalized standard penetration resistance (Ni)«) (normalized to one tsf and 60 % energy). Seed et al. (1985) give a comprehensive explanation of the methodology employed to relate (Ni)oo values to cyclic liquefaction potential. However, due to the poor repeatability associated with the SPT and the discrete nature of the test, CPTU-based methods of assessing cyclic liquefaction potential of soils are becoming increasingly popular. Robertson and Campanella (1985) proposed a chart, for estimating cyclic resistance ratio (CRR) for clean sands and silty sands using normalized CPT resistance. The normalized CPT resistance, q c i , is defined as follows: [3.8] qcl=qc*(^r OvO where, q c = cone penetration resistance Pa = 101.3 kPa ovo' = effective overburden stress (kPa) The purpose of the normalization procedure is to remove the effect of stress level from the measured CPT tip resistance. It is recognized that q c i does not represent true normalization, as q c i is not unitless. Not withstanding this fact, q c i can be effective in evaluating the cyclic 49 liquefaction susceptibility of soils. SPT-CPT conversions, as detailed by Robertson et al. (1983), were used to develop the CPT-based chart from the Seed SPT chart (Seed et al., 1985). Recent comprehensive databases compiled by Stark and Olson (1995) and Suzuki et al. (1995) are in excellent agreement with the work of Robertson and Campanella (1985). Figure 3.12 compares the results of the recent CFT field performance data and the correlation developed by Robertson and Campanella (1985) for clean sands. 0.6 M=7.5 0.5 + n 0.4 u 0.2 + CO 0.1 0.25 < Dso (mm) < 2.0 FC (%) £ 5 Robertson & Campanella (1985) A A No liquefaction O CQ-A AO Field Performance Liq. No Uq. Stark & Olson (1995) • O Suzuki el al. (1995) A A 5 10 15 20 25 Corrected CPT tip resistance, qcl (MPa) 30 Figure 3.12: Comparison Between Robertson and Campanella (1985) CPT-Based Method For Estimating CRR of Clean Sands and Recent Field Performance Data (After Robertson and Fear, 1995) Robertson and Fear (1995) proposed corrections to the normalized penetration resistance (qci) to obtain equivalent clean sand normalized penetration resistance (qci)ecs, based on fines 50 content and grain size. Fines Content (FC) is defined as soil particles having a mean diameter less than 68 um. The proposed corrections are defined as follows: [3.9] Aq ci = 5 M P a ifFC>35% Aq c i = 0 i fFC<5% Aq c i = (FC-5)/6 MPa if 5% < FC < 35% One shortcoming of using the CPTU instead of the SPT for cyclic liquefaction assessments is the inability to collect a soil sample and subsequently estimate fines content. However, over the past decade charts have been developed to estimate soil behaviour type from CPTU data (Robertson and Campanella, 1988; Robertson, 1990; Jefferies and Davies, 1993). A fundamental feature of each of the soil behaviour type charts is an increase in fines content with an increase in friction ratio (Rf), as demonstrated in Figure 3.13 by the recent work of Suzuki (1995). Also shown in Figure 3.13 are recent data collected by the UBC ISTG (Kokan, 1992). There is a fair degree of scatter about Figure 3.13, with fines content ranging approximately an order of magnitude when Rf is greater than 1%. This may be largely attributed to the fact that the CPT is not solely influenced by fines content in responding to soil behaviour, but is also influenced by factors such as soil plasticity and mineralogy. A fundamental difficulty with Figure 3.13 is that a loose clean sand falling in Zone 1 on Figure 3.9 could be confused with a denser sand containing fines. Caution should be exercised in using the relationship in Figure 3.13, and it is recommended that fines content be determined from soil sampling prior to its application to specific sites. > Robertson and Fear (1995) proposed a methodology for estimating fines content directly from CPT data by means of the soil behaviour type index, Ic, which they defined as: [3.10] I c =[(3.47-logQ) 2 +(logF + 1.22)2]05 51 100 F u c <u c o CJ CL) C 10 0.1 "T I i i I i r~T~ "* B «* • * • • • A U B C ISTG 0 Af ter S u z u k i et a l . (1995) -1 I I I I I I ! ' • • • • ' 10 Friction Ratio, R f (%) Figure 3.13: Variation of Fines Content With Friction Ratio (Adapted From Suzuki et al., 1995) where, Q = normalized penetration resistance, dimensionless = (qc-Ovo)/Ovo' F = normalized friction ratio, in % [(f./(q«rOvo)]*100% q c = CPT penetration resistance fs = CPT sleeve friction ovo = total overburden stress avo' = effective overburden stress 52 The premise of I 0 which was originally proposed by Jefferies and Davies (1993), is that soil behaviour type is a function of the radius of a concentric circle about a common point for a stress-normalized soil behaviour type chart. Jefferies and Davies (1993) provide a detailed explanation of the theoretical development of Ic. Robertson and Fear (1995) proposed that the soil behaviour type index and the relationship between Rf and fines content proposed by Suzuki et al. (1995) could be used to directly estimate fines content from Ic according to the following relationship: [3.11] Fines Content, FC (%) = 1.375 Ic3-3.5 The above expression to determine fines content can be coupled with the corrections recommended in [3.9] to determine corrections to q c i for fines content. Subsequently, this correction can be applied to q c i to determine the equivalent normalized penetration resistance for clean sand, (qci)ecs, from which the CRR of the soil profile can be determined according to Figure 3.12. The CRR for the soil profile can then be compared to the cyclic stress ratio (CSR), which is computed similarly to the Seed method (Seed et al., 1985) to determine the cyclic liquefaction susceptibility of the soil. Given that the methodology proposed by Robertson and Fear (1995) for estimating cyclic liquefaction susceptibility incorporates the relationship shown in Figure 3.13, it should be used with caution. As was previously stated there is a fair degree of scatter associated with Figure 3.13, and there is a danger of confusing loose sands with denser sands containing fines. In the absence of fines content determination from soil sampling at specific sites, the methodology proposed by Robertson and Fear (1995) should be treated as a preliminary assessment of cyclic liquefaction potential. 53 4.0 SITE DESCRIPTIONS AND TESTING PROGRAMS 4.1 INCO COPPER CLIFF TAILINGS AREA 4.1.1 SITE DESCRIPTION INCO's Central Tailings Area is located near the town of Copper Cliff, Ontario, just west of the city of Sudbury. The Central Tailings Area consists of five inactive impoundments (designated as A , CD, M , P and Q) where tailings deposition occurred from 1937-1988, and the adjacent R area where tailings are actively being deposited. A schematic of INCO's Central Tailings Area is shown in Figure 4.1. In addition a smaller inactive tailings impoundment exists in the Upper Pond area to the north of the smelter complex. Tailings dam construction at the Central Tailings Area has been and continues to be carried out using the upstream construction method. Martin and Tissington (1996) provide a detailed summary of the evolution of tailings dam design at the Central Tailings Area. The tailings occupy an area in excess of 20 k m 2 and the depth of the tailings ranges from less than 1 m, where they lie directly on a bedrock ridge, to greater than 45 m overlying the Pleistocene sediment cover in the centre of the main tailings area (Coggans, 1991). 4.1.2 TAILINGS MINERALOGY Tailings in INCO's Central Tailings Area were produced from processing of ore extracted from the Sudbury sublayer. The ore mineralogy of the sublayer is generally well understood but many minor phases are present (Hawley, 1962). The majority of the Sudbury ore consists of varying proportions of pyrrhotite, pentlandite and chalcopyrite. Other sulphide minerals of local importance include pyrite, cubanite and millerite (Pattison, 1979). 54 Figure 4.1: Schematic of INCO Copper Cliff Central Tailings Area (After Coggans, 1991) It is difficult to give absolute values for the mineralogical constituents of the tailings due to variations in the host rocks, ore grades and extraction practices over time. However, an approximate estimate of tailings mineralogy is as follows (Peters, 1984): 55 Feldspar 50% Magnetite 0.6% Amphiboles 20% Pentlandite 0.5% Quartz 10% Chalcopyrite 0.3% Pyroxenes 7% Biotite 7% Pyrrhotite 5.6% From the above list it is apparent that pyrrhotite is the principle contributor to the overall sulphide content of the tailings. Oxidation of sulphide minerals and subsequent development of A R D is well-documented for the various impoundments contained in the INCO Central Tailings Area. W.D. Robertson et al. (1991), Coggans. (1991) and De Vos (1992) each give details concerning contamination of tailings pore water due to A R D processes. 4.1.3 TEST P R O G R A M A geoenvironmental field investigation was carried out by the UBC ISTG at INCO's Copper Cliff Central Tailings Area in October of 1993. In addition to acting as a test site for the purposes of this thesis, the site investigation program formed the basis of a demonstration project carried out for INCO and the Federal government M E N D (Mine Environment Neutral Drainage) initiative for the purpose of evaluating the applicability of the RCPTU for the geoenvironmental characterization of sulphide bearing tailings. The findings of this demonstration project are included in Campanella et al., (1994). A summary of the testing program is given in Table 4.1. A l l test work was carried out using the UBC In-Situ Research Vehicle, which was shipped by railway to Sudbury, Ontario and subsequently driven to the mine site. The field testing program was carried out over a span of approximately 2 weeks, and included 6 CPTU and 26 RCPTU tests at 11 different tailings impoundments within the Central Tailings Area. 56 TABLE 4.1: Summary: 1993 Field Investigation Program at INCO Central Tailings Area L o c a t i o n o f S o u n d i n g F i l e N a m e Test Date ( m o n / d a y ) Test P e r f o r m e d S o u n d i n g ; D e p t h (m) S p e c i f i c C o m m e n t s M - A r e a 103-9301 10-1-93 R C P T U 9.62 B A T water samples were recovered at 5.60 a n d 6.00 m . 102-9304 10-3-93 R C P T U 4 2 3 0 A - A r e a 106-9302 10-2-93 R C P T U 1830 106-9303 10-2-93 R C P T U 18.20 106-9321 10-10-93 R C P T U 19.12 B A T water samples were recovered at 4.0, 5.0, 6.0, 7.0, a n d 8.0 m . C - D Area 104-9305 10-3-93 C P T U 7.72 Pistol A r e a -Pistol D a m 111-9308 10-4-93 C P T U 13.78 S o u n d i n g was at crest of d a m . 111-9309 10-5-93 R C P T U 40.20 S o u n d i n g was at crest of d a m . 118-9322 10-11-93 R C P T U 36.40 S o u n d i n g was at first bench of d a m (Sla. 386 o n existing L P . line) 119-9323 10-11-93 R C P T U 6 5 2 S o u n d i n g was at base of d a m (4m equidistant from Waterloo piezometer nests IN82 . I N 2 1 , and IN23). 120-9324 10-11-93 R C P T U 5.20 S o u n d i n g was at base of d a m (10m N o r t h of Waterloo piezometer nest IN23). 121-9325 10-11-93 R C P T U 4.95 S o u n d i n g was at base of d a m (adjacent to Waterloo piezometer nestTN23). 122-9326 10-12-93 R C P T U 3.88 S o u n d i n g was o n service road at the base of d a m (adjacent to Waterloo piezometer nest IN32). 123-9327 10-12-93 R C P T U 14.48 S o u n d i n g was o n service road at base of d a m (adjacent to Waterloo piezometer nest IN22). 124-9328 10-12-93 R C P T U 3.42 S o u n d i n g was o n service road at base of d a m (adjacent to Water loo piezometer nest IN27). 111-9330 10-13-93 R C P T U 43.28 S o u n d i n g was at crest of d a m 125-9331 10-14-93 R C P T U 3.85 S o u n d i n g was o n service road at base of d a m (adjacent to Waterloo piezometer nestIN33) . 126-9332 10-14-93 R C P T U 10.08 S o u n d i n g was o n service road at base of d a m (adjacent to Waterloo piezometer nest IN34). Whisse l D a m 112-9306 10-4-93 R C P T U 15.05 112-9307 10-4-93 C P T U 28.43 Cecchetto D a m 110-9313 10-6-93 R C P T U 1838 110-9314 10-6-93 R C P T U 22.50 Q - A r e a 113-9310 10-5-93 R C P T U 7.75 117-9311 10-6-93 R C P T U 13.70 114-9312 10-6-93 R C P T U 8.48 R 3 -D a m 15 109-9315 10-7-93 C P T U 10.58 109-9316 10-7-93 C P T U 10.40 R 2 -D a m 14 108-9317 10-7-93 R C P T U 2.08 S o u n d i n g was stopped due to extremely dense material. 108-9318 10-7-93 C P T U 8.45 U p p e r P o n d 115-9319 10-8-93 R C P T U 19.68 116-9320 10-9-93 R C P T U 19.25 B A T water samples were recovered at 4.0,5.0, a n d 6.0 m . Pyrrhotite . D a m 101-9329 10-13-93 R C P T U 41.62 The locations of all tests were designated by INCO personnel, with the exception of test work at the base of Pistol Dam. In this area testing was carried out in close proximity to existing 57 University of Waterloo piezometer nests to optimize geochemical data. deVos (1992) gives details concerning University of Waterloo piezometer installations. A l l tests were carried out in sulphide-bearing tailings, with the exception of the test work in the native soils at the base of Pistol Dam. 4.2 F A L C O N B R I D G E FAULT L A K E TAILINGS I M P O U N D M E N T 4.2.1 SITE DESCRIPTION The Fault Lake tailings impoundment is located near the town of Falconbridge, Ontario, and approximately 0.5 km east of the Sudbury Airport. A schematic of the Fault Lake tailings impoundment is shown in Figure 4.2. The creation of the Fault Lake tailings impoundment consisted of filling in several glacial kettle lakes, between 1965 and 1978, whose remnant deposits form the basal layers for the tailings. The tailings are contained by dams to the northeast and southwest of the site. The tailings encompass an area of approximately 22 hectares, and the tailings have a maximum depth of approximately 30 m (St. Arnaud et al., 1994). 4.2.2 TAILINGS M I N E R A L O G Y Similarly to the tailings at INCO, the Fault Lake tailings were produced from the milling of ores extracted from the Sudbury sublayer. The complete details of the mineralogical make-up of the Fault Lake Tailings site are not documented, but it is estimated that the tailings contain as much as 50 % pyrrhotite (St. Arnaud et al., 1994), which is approximately ten times the pyrrhotite content of the INCO Central Tailings Area. The very high pyrrhotite content of the tailings indicates the tailings are highly susceptible to A R D processes, and this was confirmed by previous site investigations at the site (St. Arnaud et al., 1994). 58 59 4.2.3 TEST P R O G R A M Two RCPTU soundings were carried out near the centre of the impoundment at Falconbridge's Fault Lake Tailings site in October, 1993. The UBC In-Situ Research Vehicle was used for the test work, and was driven to the test site as it was in close proximity to the INCO Copper Cliff site (<30 km). In addition to acting as a research site for this thesis, Falconbridge personnel were interested in locating the phreatic surface in the tailings. The locations of the tests were designated by Falconbridge personnel. Details concerning the two tests are presented in Table 4.2. T A B L E 4.2: Summary: 1993 Fie ld Investigation Program at Falconbridge Fault Lake Tai l ings Impoundment L o c a t i o n of S o u n d i n g F i l e N a m e Test Date ( m o n / d a y ) Test Per formed S o u n d i n g D e p t h (m) Spec i f i c C o m m e n t s Fault Lake F01-9333 10-14-93 R C P T U 41.10 Falconbridge Piezometers FS-15A a n d FS-15B installed adjacent to R C P T U location to depths of 35m a n d 24 m , respectively F02-9334 10-14-93 R C P T U 22.70 4.3 GIBRALTAR MINES TAILINGS I M P O U N D M E N T 4.3.1 SITE DESCRIPTION The Gibraltar Mines tailings impoundment is located approximately 160 km south of Prince George, British Columbia, near McLeese Lake. A schematic of the Gibraltar Mines tailings impoundment is shown in Figure 4.3. The tailings impoundment is currently active and has been in operation since 1977. The impoundment area is a natural valley with a small saddle 60 Figure 4.3: Schematic of Gibraltar Mines Tailings Impoundment (After Gibraltar Mines Ltd.) 61 dam located at the east end and a tailings dam under construction at the west end. Cycloning of the tailings produces a sand used in the centreline method of dam construction. 4.3.2 TAILINGS MINERALOGY The Gibraltar Mines tailings were produced from processing of ore obtained from the quartz diorite of the Granite Mountain pluton (Gibraltar Mines Ltd., 1992). This rock is composed of quartz (25-30%), a mixture of albite-epidote-zoisite-muscovite (50-55%), chlorite (20%) and biotite (1%). The sulphide content of the tailings is estimated to be less than 1% pyrite, based on acid-based accounting tests of tailings samples (Gibraltar Mines Ltd., 1992). The sulphide mineral content is significantly less than that found in the tailings at the INCO and Falconbridge sites. This would indicate that A R D development in the Gibraltar tailings would be of a lesser extent than that experienced at the other sites. 4.3.3 TEST PROGRAM A geoenvironmental field investigation program was carried out by the UBC ISTG at the Gibraltar Mines tailings impoundment in late summer 1994. The UBC In-Situ Research Vehicle, which was transported to the site by truck, was used for all test work. The location of all tests were designated by Gibraltar Mines Ltd. personnel. A summary of the field investigation program is presented in Table 4.3. The purpose of the field work was to further evaluate the RCPTU for geoenvironmental assessment of sulphide bearing tailings, and more specifically to increase the database of bulk resistivity measurements and accompanying pore water chemistry for sites affected by A R D contamination. It was hoped that further data would permit more detailed comparisons 62 between the different sites, and provide better insight into the applicability of the RCPTU for evaluating A R D processes. Table 4.3: Summary 1994 Field Investigation Program at Gibraltar Mines Tailings Impoundment L o c a t i o n o f F i l e N a m e Test D a t e Test S o u n d i n g S p e c i f i c C o m m e n t s S o u n d i n g ( m o n / d a y ) P e r f o r m e d D e p t h (m) Tai l ings CB-T9403 8-30-94 R C P T U 10.20 GB-T9404 8-30-94 R C P T U 3.28 GB-T9405 8-31-94 R C P T U 3.92 GB-T9406 8-31-94 R C P T U 6.15 GB-T9407 8-31-94 R C P T U 12.02 GB-T9409 9-1-94 R C P T U 30.68 GB-T9410 9-3-94 R C P T U 12.65 GB-T9411 9-3-94 R C P T U 18.33 2 Bat samples at both 16.5 m and 17.1 m 63 5.0 DISCUSSION OF TEST RESULTS The intention of Section 5.1 is to demonstrate the interpretation of RCPTU data for the range of materials encountered in the field investigation programs. Also, the RCPTU soundings presented in Section 5.1 wi l l be discussed in greater detail with respect to characterization of tailings pore water chemistry, hydrogeological properties and geotechnical parameters in later sections of this chapter. Graphical and tabular data for all RCPTU soundings discussed in Chapter 5 are included in the appropriate appendices following the text of this thesis. 5.1 TYPICAL R C P T U TEST RESULTS 5.1.1 PISTOL TAILINGS I M P O U N D M E N T (INCO) A graphical representation, known as a coneplot, for an RCPTU sounding (111-9330) carried out at the crest of Pistol Dam located in the INCO Central Tailings Area is shown in Figure 5.1. Briefly reviewing the stratigraphy, there is a very dense oxidized layer evident from the surface to a depth of approximately 3 m. Below this depth, a fine sandy tailings is present that shows a slight fining downward trend. Based upon the pore pressure and bulk resistivity response, the phreatic surface was determined to be located at 15 m. The pore pressure profile from 15 m to 37 m in the tailings shows interlayered positive and negative excess pore pressure response. This CPTU signature is consistent with beached tailings that periodically are allowed to establish a desiccated and oxidized layer during the period following deposition and prior to further dam construction. The sounding exited from the tailings at a depth of about 37 metres into a very stiff silty clay deposit. In this fine-grained native material, excess pore pressures of over 100 m of water pressure were measured during penetration, attesting to the stiff nature, low hydraulic conductivity and high stress levels present in this material. 64 65 It is interesting to note that some lower resistivity values (higher conductivity) do exist above the phreatic surface. The moisture retention capabilities of tailings are well-documented (Vick, 1983) and it is apparent that the unsaturated tailings in this area may have a high degree of saturation and that the pore water present has elevated levels of ionic constituents. Below the phreatic surface, the bulk resistivity values were quite constant at approximately 10 Q-m, indicating that elevated levels of ionic loading are present in the pore water. The resistivity values in the native materials rose sharply to values of about 30 Q-m which indicates a reduction in ionic loading of the pore water. 5.1.2 BASE OF PISTOL D A M (INCO) Eight RCPTU soundings were carried out in native soils at the base of Pistol Dam and a typical RCPTU profile (123-9327) is shown in Figure 5.2. A review of the coneplot indicates that the upper 1.3 m is a relatively firm silty clay soil, which is well demonstrated by the peak in friction ratio values above 3% to 5% and the negative response of the pore pressure. This upper layer is underlain by a fine silty sand to a depth of approximately 3.4 m, where the cone encountered a soft sensitive fine-grained soil to a depth of approximately 6 m. From 6 m to approximately 14.3 m is a compact sand with interbedded silt layers, below which is a large boulder or bedrock. The phreatic surface was estimated to be at the ground surface based on pore pressure dissipation data and bulk resistivity response. The bulk resistivity measurements exhibited interesting variability in this sounding. The bulk resistivities generally ranged from 10 -20 Q-m in the upper 3 m, increased to greater than 50 Q - m from 5 - 10 m and then decreased to approximately 20 Q-m from 11m - refusal. The lower bulk resistivity measurements in the upper and lower depths of the sounding indicated elevated levels of ionic loading of the pore water, whereas the higher bulk resistivity measurements in the middle portion of the sounding indicate significantly lower levels of pore 66 0) <u Q C Q. •> I f OS £ 0 m 1 lo. u >>l I TJ C re (0 >. CO <D c > «5 si I I I I I I TJ P T J L J o C 0) <•> (/) S W • i i i i i i i i i i i i i i — 0) CO -> O o HI T 1 I 1 I 1 I I I I I I I I I I s * I I I I I I Q Q) Q. *- £ E 67 water ionic loading. The trends in bulk resistivity observed in this sounding are in agreement with the findings of de Vos (1992), who carried out chemical analyses of pore water samples from an adjacent University of Waterloo piezometer installation (IN22). Data from de Vos (1992) are included in Appendix D. 5.1.3 F A U L T L A K E TAILINGS I M P O U N D M E N T (FALCONBRIDGE) A coneplot for an RCPTU sounding (F01-9333) carried out near the centre of the Fault Lake tailings impoundment is shown in Figure 5.3. The tailings to a depth of approximately 4.6 m consist of a compact silty sand, as indicated by the cone bearing and friction ratio. From 4.6 m to 28 m the tailings are interbedded layers of loose silty sand and clayey silt. The fine-grained nature of the tailings made it difficult to discern the boundary between the tailings and the underlying lacustrine native soil. The more uniform response of the cone channels below a depth of approximately 28 m is indicative of the relatively homogeneous native soil, rather than the highly layered tailings. The phreatic surface was estimated to be at a depth of approximately 10.5 m based upon the dynamic pore pressure response and this was confirmed from pore pressure dissipation data. There is no discernable decrease in the bulk resistivity at 10.5 m, which suggests a high degree of tension saturation and significant ionic loading of the pore water. The RCPTU met refusal at a depth of 41 m in what was considered to be a very dense gravely till material. Similarly to the RCPTU bulk resistivity measurements at Pistol Dam, the Fault Lake tailings exhibited low bulk resistivity measurements above the phreatic surface, This indicates a high degree of saturation and significant ionic loading of the pore water. Very low bulk resistivity measurements of between 1-2 Q-m were recorded in the upper 4 m, suggesting ionic loading of the pore water was most severe in the upper tailings. The bulk resistivity profile remained 68 TJ £ — 11 i i TJ o c a co 0.(0 o £ Oft I I I I I I • Til I I I I I I I I -So ? £ J 8 8 5 n -M —i irt C 0) l l CO CO 3 •5 0£ a 4-* (Q a a s " 5 ' l§ to co U - JQ I i i i i i I I I I I I I I I I I I ' ' ' 1 T3 o Oh S in 60 co H .8 cS I—1 3 (0 Uh I a o CL, D CO in 2 Q o a « r E 69 relatively constant near 15 Q-m in the saturated zone and showed an increasing trend in the native material. 5.1.4 GIBRALTAR TAILINGS IMPOUNDMENT (GIBRALTAR) A coneplot for an RCPTU sounding (GB-T9411) carried out on the northern crest of the tailings impoundment is shown in Figure 5.4. The upper tailings consist of a dense sand to a depth of approximately 1.6 m. This upper crust is underlain by a compact sand to a depth of approximately 8.2 m. From 8.2 m to a depth of approximately 17.2 m the tailings ranged from a loose to compact sand. The phreatic surface was determined to be at a depth of 16.5 m, as evidenced by both pore pressure response and bulk resistivity measurements. The native soil, consisting of a clayey silt soil, is encountered at a depth of approximately 17.2 m, and the RCPTU met refusal at a depth of 18.3 m. Bulk resistivity measurements in the unsaturated zone generally remained between 50 and 200 Q-m. The much higher bulk resistivity measurements at this site in comparison with those observed at the crest of Pistol Dam at the INCO site and at the Falconbridge site, can be explained by lesser saturation of the tailings and/or lesser ionic loading of the tailings pore water. Given the lower sulphide mineral content of the Gibraltar tailings in comparison with the other sites, it is likely based upon this limited data that A R D processes are less developed. The lower values of bulk resistivity measured in the unsaturated zone (between 50 - 75 Q-m) are likely due to higher levels of saturation of the tailings. Bulk resistivity measurements below the phreatic surface decreased to values of approximately 20 Q-m, which indicates elevated levels of ionic loading of the pore water. 70 71 5.2 REPEATABILITY OF RCPTU TEST RESULTS One of the key concerns to the user of any characterization technology is the repeatability of the data produced. The repeatability of the CPTU is well-established (Gillespie, 1990). To demonstrate the full nature of the data repeatability, three soundings were carried out within a total distance of 5 metres in the A-Area of the INCO Central Tailings Area. Figure 5.5 shows the three soundings plotted with respect to their cone tip resistance, friction and pore pressure values. The repeatability of the CPTU data is excellent, and any differences can be attributed to stratigraphic variations in the tailings themselves. As the purpose of this study was in part to demonstrate the ability of the RCPTU to delineate A R D contamination, it was essential to demonstrate the repeatability of the bulk resistivity measurements. Figure 5.6 shows comparisons between two sets of RCPTU soundings carried out in two different tailings impoundments at INCO. In each case, the RCPTU soundings were carried out within a distance of 5 metres. The repeatability of the RCPTU measurements is very good for both comparisons, particularly for measurements below the phreatic surface. Bulk resistivity measurements above the phreatic surface show similar trends, and differences can largely be attributed to the effects of variable saturated conditions. 5.3 CHARACTERIZATION OF PORE WATER CHEMISTRY One of the main purposes of this thesis was to evaluate the ability of the RCPTU to assess the pore water chemistry of sulphide bearing tailings and adjacent native soils affected by A R D contamination. To evaluate relationships between bulk resistivity measurements and pore water chemistry in a straightforward manner, reference to Table 2.3 in Section 2.2.1.2 was used as the basis for evaluating A R D processes. From Table 2.3, increasing oxidation of sulphide minerals results in a corresponding increase in ionic loading of the tailings pore water. This 72 CM CM CO CM 1 1 1 1 1 1 1 1 1 1 - * l i i | -1 _ 1 -! 1 1 1 i i 1 i is l J3 c cu s in « D u 0 RS 01 a, DC in in* & IX, ( U J ) M i d e g 73 (UJ ) Ml deg 74 increased ionic loading takes the form of increased sulphate levels, increased hydrogen ion concentration (resulting in a decrease in pH) and increased heavy metals concentrations. Correspondingly, increased ionic loading results in decreased pore water resistivity (or increased electrical conductivity) and subsequently decreased bulk resistivity measurements below background values. It should be noted that all data collected for the respective sites represent relatively small samples of site conditions, and all discussions contained herein with respect to A R D processes and contamination are restricted to the specific locations where test work was carried out. Appendix D provides a summary of locations at which both RCPTU testing and chemical analyses of pore water samples were carried out. The large size of the sulphide bearing tailings impoundments at which test work were carried out precludes any overall assessments with respect to A R D development and contamination. Interpretations of test results with respect to A R D contamination in the native soils at the base of INCO's Pistol Dam may be more definitive due to the relatively small size of the site. 5.3.1 PORE WATER S A M P L I N G PRACTICES A N D C H E M I C A L A N A L Y S E S Pore water sampling and subsequent chemical analyses were carried out at all test sites to facilitate the interpretation of RCPTU bulk resistivity measurements. At INCO, pore water chemistry data were collected from three different sources: BAT pore water samples, pore water extractions from tailings samples and pore water samples from existing University of Waterloo piezometer nests. The BAT pore water sampling was carried out by the UBC ISTG and the pore water extractions from tailings samples were done by INCO using a modification of the immiscible displacement technique developed by Patterson et al. (1978). INCO conducted all chemical analyses for both the BAT samples and samples extracted from tailings solids, with the exception of the p H and conductivity of BAT samples which were carried out 75 in the field by the UBC ISTG using portable meters. Metals were analyzed by means of an Inductively Coupled Plasma - Atomic Emission Spectrophotometer (ICP-AES) and sulphate concentrations were determined through use of a High Performance Liquid Chromotograph (HPLC). The University of Waterloo carried out all sampling and chemical analyses for pore water samples collected from the University of Waterloo piezometer nests, de Vos (1992) provides details concerning piezometer specifications, sampling protocol and chemical analyses. Pore water analyses and sampling at the Fault Lake tailings site were conducted by the Noranda Technology Centre under the direction of Falconbridge Ltd. Two piezometers, FS15A and FS15B, were installed immediately adjacent to RCPTU sounding F01-9333 to depths of 35 m and 24 m, respectively. The piezometers consist of a 1.9 cm ID, schedule 80 PVC pipe with a 0.30 m PVC screened tip. Continuous tailings samples were recovered from borehole FS15A with a 1.5 m split spoon sampler. Subsequently, pore water samples were collected by squeezing tailings using a pneumatic squeezing device (Noranda Technology Centre, 1994). Chemical analyses were carried out on the pore water samples extracted from tailings solids using an ICP - AES. In addition, p H and conductivity measurements were recorded for each pore water sample. Limited pore water sampling, comprised of four BAT samples, was conducted at the Gibraltar Mines tailings impoundment. The BAT pore water samples were collected by the UBC ISTG, and conductivity measurements were recorded for each sample in the field using a portable meter (Omega model CDH-30). Gibraltar Mines Ltd. determined sulphate concentrations for each sample by HPLC. Appendix D contains a summary of pore water chemistry data from all test sites. 76 5.3.2 RCPTU BULK RESISTIVITY MEASUREMENTS IN UNSATURATED SULPHIDE BEARING TAILINGS (INCO AND FALCONBRIDGE TAILINGS) Bulk resistivity measurements above the phreatic surface were generally much higher and showed more variability than bulk resistivity measurements in fully-saturated conditions. This is readily apparent by examination of the bulk resistivity profiles shown in Figure 5.6. The relatively uniform nature of many tailings deposits facilitates the interpretation of the factors affecting bulk resistivity response in tailings. Section 3.1.1 reviewed the various factors which can affect bulk resistivity response in soils. In a uniform tailings deposit the porosity, temperature, shape of pore size and cation exchange capacity of matrix materials are likely similar and their influence on changes in bulk resistivity response may be considered negligible. Therefore, the remaining two factors: (1) degree of saturation and (2) ionic composition of the pore water predominately control changes in bulk resistivity response. The moisture retention capabilities of tailings can result in variable saturated conditions above the phreatic surface and subsequent variability in bulk resistivity response. Variabilities in saturation make it difficult to discern the influence of the ionic composition of the pore water on bulk resistivity response. There were two RCPTU soundings which exhibited very low bulk resistivity measurements above the phreatic surface. Coneplots of the RCPTU data for the soundings at INCO's Pistol Dam (Figure 5.1) and Falconbridge's Fault Lake Tailings impoundment (Figure 5.3) were provided in Section 5.1 and general interpretations were given for each test. Figure 5.7a and Figure 5.7b present bulk resistivity profiles for the unsaturated portion of each sounding and the location of the phreatic surface is noted for the respective soundings. Also shown on each figure are pore water sulphate concentrations which were derived from pore water sampling at the depths shown and subsequent chemical analyses. The purpose of the pore water 77 OJ 3 Li, «s OJ « > g> .a in CO H (tu) indarj LfS §> o Oh E 60 CO o o CM CM i i > w '55 o o fc 3 m oj U *"' OJ 3 (0 OJ > •J3 •i2 'in OJ OS 3 CO to 00 1 (0 H T3 ii RJ 2 (0 C D CO I N in OJ u E « Q o ( L U ) qjdaQ 78 sampling was to evaluate the influence of pore water ionic composition on the low bulk resistivity measurements above the phreatic surface observed for each sounding. The elevated sulphate concentrations above the phreatic surface for the two soundings confirmed that the low bulk resistivity measurements in the unsaturated tailings are not only a function of variable saturated conditions, but are also affected by significant ionic loading of the pore water. The elevated sulphate concentrations are consistent with pore water affected by A R D processes, as discussed in Section 2.2.1. The elevated sulphate concentrations for the sounding at Pistol Dam are relatively uniform and vary from approximately 2000 - 5000 mg/L, indicating significant ionic loading of the tailings pore water. Based upon the relative uniformity of the pore water sulphate concentrations, the variability noted in the bulk resistivity measurements is likely more a function of variable saturated conditions. The spikes in the bulk resistivity measurements (such as near the surface and at a depth of approximately 11.5 m where bulk resistivity measurements exceeded 100 Q-m) are indicative of poorly saturated conditions. The lower boundary of bulk resistivity measurements (values of approximately 10 Q-m) are indicative of nearly-saturated tailings where the influence of the conductive pore water is readily apparent. Sulphate concentrations of the tailings pore water in the unsaturated zone for the sounding at the Fault Lake tailings impoundment were more variable than those observed at INCO's Pistol Dam. Sulphate concentrations were very high in the upper 4 m (values > 10 000 mg/L) and were lower and more uniform below this depth (values of approximately 2000 mg/L). The much higher sulphate concentrations measured in the near surface tailings pore water at the Falconbridge site in comparison with those measured at INCO's Pistol Dam, suggests that sulphide oxidation processes are more severe in the upper 4 m of the unsaturated tailings at the Falconbridge site. This can largely be explained by the much higher sulphide mineral content contained in the Falconbridge tailings. Bulk resistivity measurements in the upper 4 79 m at the Falconbridge site varied from approximately 1 Q-m - 20 Q-m. The very low bulk resistivity measurements are reflective of very high ionic loading of the tailings pore water, whereas the upper boundary of these measurements indicate lesser saturation of the tailings. From a depth of approximately 4 m to the phreatic surface depth at 11.5 m the bulk resistivity measurements were generally higher than those found in the upper 4 m, which corresponds with the reduction in tailings pore water sulphate concentration. The higher spikes of bulk resistivity measurements recorded between approximately 6 m and 8 m are most likely due to a lower degree of tailings saturation. More detailed pore water chemistry data were available from pore water sampling carried out adjacent to the RCPTU sounding (F01-9333) at the Fault Lake tailings impoundment. Figures 5.8a - 5.8d present pore water p H , iron (Fe) concentrations, magnesium (Mg) concentrations and nickel (Ni) concentrations respectively for the upper 20 m of tailings. The increased acidity (pH less than 4) and elevated heavy metals concentrations in the upper 4 m of tailings are consistent with Stage 3 ARD processes, as discussed in Section 2.2.1. The extremely high sulphate concentrations, shown in Figure 5.6, also support this finding. Below the depth of 4 m, the p H is relatively neutral due to alkalinity in the tailings which acts as a buffering agent. The heavy metals concentrations of the tailings pore water below 4 m depth are significantly lower, with the exception of M g which showed a smaller decrease. The pore water chemistry below the depth of 4 m indicates that A R D processes are less severe than that experienced in the upper 4 m of tailings, and are consistent with Stage 2 A R D processes. The evolution of A R D development at the Fault Lake tailings impoundment can be explained in terms of the one-dimensional model presented in Section 2.2.1.2. The upper 10.5 m of the tailings are not fully-saturated (denoted as Z l in Figure 2.2). The zone of oxidation (Z3) comprises the upper 4 m of the tailings and the zone of neutralization (Z4) extends below a 80 S i B-B. S I S i r ' a (ui) mdea 8 E q o TO & C o S ° 5 ; -T 1 r (ui) qidea C c e o a, c 88 to bO —, .5 u § tS in m 3 bO CO in £ 3 bO CO "3 pa D c «t2 ^ H > bo OJ c *r* «° B CU c (3 in C E I 3 '8 S3 E •-O 0) U K 5.8 r-a. ^ "3 I u T3 > 3 v/ 0) CO u 01 (8 3 « 1 ? ^ 3 C •? « .2 <» O B i bO S > S 5? p.<2 U H S ? bo S (ui) mdoQ 8 (8 00 in 3 bO (ui) ifldea in £ 81 depth of 4 m. The interface between the zone of neutralization and the original tailings process water (Z2) could not be determined from the available data. Based upon the data presented in this section, the RCPTU can be used to qualitatively assess A R D contamination in the unsaturated zone. Interpretation of the countering effects of variable saturated conditions and changing pore water chemistry on bulk resistivity measurements are enhanced if tailings pore water chemistry data are available. A measure which would further enhance interpretation of bulk resistivity measurements in the unsaturated zone would be the collection of tailings samples, and subsequent measurement of tailings saturation. The measurement of tailings saturation would permit better interpretation of the relative influence of tailings saturation and pore water chemistry on bulk resistivity measurements. 5.3.3 COMPARISONS BETWEEN RCPTU B U L K RESISTIVITY M E A S U R E M E N T S A N D PORE WATER CHEMISTRY I N S A T U R A T E D SULPHIDE B E A R I N G TAILINGS A N D S U R R O U N D I N G SATURATED N A T I V E SOILS (ALL TEST SITES) The data presented in this section were collected in saturated sulphide bearing tailings, with the exception of some INCO data from the saturated native soils at the base of Pistol Dam. With the influence of variable saturation removed, the bulk resistivity response is largely governed by the ionic composition of the pore water. The ability of the RCPTU to assess A R D contamination of pore water is evaluated through comparisons between bulk resistivity (and bulk conductivity) measurements and specific properties and dissolved ionic constituents of pore water samples. 82 5.3.3.1 Comparison of RCPTU Bulk Resistivity and Pore Water Resistivity Plots of RCPTU bulk resistivity in relation to pore water resistivity for saturated INCO tailings, Falconbridge tailings, Gibraltar tailings and INCO native soils are shown in Figures 5.9a through 5.9d, respectively. Estimates of average apparent formation factor (F) (F = ^-=nm) are shown on each plot. By defining F for a given site, estimates of pore water Pf resistivity can be made directly from the RCPTU bulk resistivity measurements, which reduces the need for more expensive pore water sampling practices. While recognizing that there is a fair degree of scatter about the linear trends of the respective plots and the relatively small data sets (particularly for the Gibraltar data), the average F is approximately 3.6 for the INCO tailings, 5.4 for the Falconbridge tailings and 3.6 for the Gibraltar tailings. Estimates of F in the INCO native soils (shown in Figure 5.9d) demonstrated a bilinear realtionship. The average F for pore water resistivities below 20 Q-m was approximately 4.0, and the average F was approximately 1.75 for pore water resistivities above 20 Q-m. Considering that the data were collected in similar sandy soils at the base of INCO's Pistol dam, differences in soil type and porosity are likely not responsible for the variations in F. The differences in F for the higher pore water resistivities can be explained by the fact that Archie's Equation may not be valid for the less conductive pore water due to the influence of the soil matrix on the bulk resistivity measurements. The average F was the same for the INCO and Gibraltar tailings from which the data were collected, indicating similarities in soil behaviour types for the two sites. This is in agreement with the generally sandy nature of the tailings previously noted for the INCO and Gibraltar tailings in Section 5.1. However, the small size of the data sets precludes any definitive comparisons between the two sites. 83 20 16 —\ a 1 2 > co o CD 8 H / / Average F = 3.6 Estimate of m for n=0.45 F=n-m 3.6 = (0.45)-m m « 1.6 1 1 1 1 I ' I 2 4 6 8 Pore Water Resistivity (o -m) 10 Figure5.9a: Comparison of RCPTU Bulk Resistivity and Pore Water Resistivity - Saturated INCO Tailings 84 40 30 / / / / 7 0 Average F = 5.4 20 —I o ^ oo Estimate of m for n=0.45 / o I F = i r m i o - l .1 I I lo 5.4 = (0.45)-m m « 2 . 1 2 4 6 Pore Water Resistivity (o -m) 10 5.9b: Comparison Between RCPTU Bulk Resistivity and Pore Water Resistivity -Saturated Falconbridge Tailings 85 2 0 — i 1 6 H A A I Average F = 3.6 < £ , 1 2 > % (0 1 8 CO. 4 H 1 1 — i — 1 — i — 1 r 2 4 6 8 Pore Water Resistivity (ft -m) 1 0 Figure 5.9c: Comparison Between RCPTU Bulk Resistivity and Pore Water Resistivity -Saturated Gibraltar Tailings 86 100 — i 80 —\ Average F = 1.75 + -+ + i i ~ 60-4 / + 40 —\ + i Average F = 4.0 20 + / + + 20 40 Pore Water Resistivity (n -m) 60 Figure 5.9d: Comparison Between RCPTU Bulk Resistivity and Pore Water Resistivity -Saturated INCO Native Soils 87 The differences in F observed between the different sites can largely be explained by differences in soil behaviour type, as F is an intrinsic property of the soil. The relative influence of soil behaviour type on F is reflected in the soil behaviour type constant, m. Estimates of m are shown in Figures 5.9a and 5.9b for the INCO and Falconbridge tailings, respectively. A n average porosity (n) of 0.45 was used in these estimates for both sites, which was based on literature values from previous investigations at each site (Coggans, 1991 and St Arnaud et al., 1994). The estimate of m for the INCO tailings was approximately 1.6, and for the Falconbridge tailings was approximately 2.1. The estimates of m for each site are consistent with literature values (Jackson et al., 1978) for the soil behaviour types exhibited by the INCO and Falconbridge tailings. The Falconbridge tailings were much finer-grained and more cohesive than the INCO tailings, and this is reflected in the higher m value for the Falconbridge tailings. Estimates of m were not made for the Gibraltar tailings and the INCO native soils due to the absence of estimates of porosity, but given the generally sandy nature of the soils at both sites from which the data were collected, it is likely that m values would be similar to the estimate for the INCO tailings. 5.3.3.2 Comparison of Pore Water Sulphate Concentration and R C P T U Bulk Conductivity The observed relationships between pore water sulphate concentrations and bulk conductivity measurements are shown for the saturated INCO tailings, Falconbridge tailings, Gibraltar tailings and INCO native soils in Figures 5.10a through 5.10d, respectively. Bulk conductivity is used instead of bulk resistivity, due to the accepted use of bulk conductivity in the environmental sciences. The relationship between pore water sulphate concentration and bulk conductivity is especially important due to the fact that sulphate concentration is an excellent indicator of A R D development. Elevated sulphate concentrations generally occur in tailings pore water prior to increased heavy metals concentrations and increased acidity. Identification of elevated sulphate concentrations during Stage 1 A R D can enable the 88 6000 — i O) >E 4000 c o •4-1 2 € o o c o o (0 2000 —\ a CO n 1 1 1 r 400 800 1200 Bulk Conductivity (MS/cm) 1600 Figure 5.10a: Comparison Between Pore Water Sulphate Concentration and RCPTU Bulk Conductivity - Saturated INCO Tailings 89 6000 — i 4000 • • - ' 1 2000 T T 400 800 1200 Bulk Conductivity (MS/cm) 1600 Figure 5.10b: Comparison Between Pore Water Sulphate Concentration and RCPTU Bulk Conductivity - Saturated Falconbridge Tailings 90 2000 — i 1600 —H .2 1200 800 400 —\ 200 400 600 800 Bulk Conductivity (MS/cm) 1000 Figure 5.10c: Comparison Between Pore Water Sulphate Concentration and RCPTU Bulk Conductivity - Saturated Gibraltar Tailings 91 2500 — i 2000 .2 1500 —\ 1000 —\ + / s s 500 H + / s s 1—1—I—1—I 1 r 200 400 600 800 Bulk Conductivity (/* S/cm) 1000 Figure 5.10d: Comparison Between Pore Water Sulphate Concentration and RCPTU Bulk Conductivity - Saturated INCO Native Soils 92 enactment of appropriate mitigation and abatement strategies prior to the development of more contaminated Stage 2 and Stage 3 ARD. For the INCO tailings, sulphate concentrations generally increased with bulk conductivity, and an approximate curvilinear relationship is shown in Figure 5.10a. The pore water sulphate concentrations ranged from approximately 1500 - 5100 m g / L and the corresponding bulk conductivity measurements ranged from approximately 380 - 1250 uS/cm. Sulphate concentrations in the Falconbridge tailings generally increased with bulk conductivity (Figure 5.10b) and demonstrated a more linear trend than that for the INCO tailings. Pore water sulphate concentrations ranged from approximately 1400 - 3600 m g / L and bulk conductivity measurements ranged from approximately 400 - 1100 uS/cm. The data set for the Gibraltar tailings consisted of only three data points (Figure 5.10c), with sulphate concentrations of approximately 800 - 1100 m g / L and corresponding bulk conductivity measurements of approximately 600 - 700 uS/cm. Pore water sulphate concentrations in the INCO native soils demonstrated a linear relationship with bulk conductivity measurements (Figure 5.10d). Pore water sulphate concentrations and corresponding bulk conductivity measurements varied significantly for the INCO native soils. Pore water sulphate concentrations varied from very low values of approximately 20 m g / L to a peak of approximately 2000 mg/L, and bulk conductivities similarly ranged from approximately 100 - 1000 uS/cm. The lower values of pore water sulphate concentrations and bulk conductivity measurements are likely reflective of baseline values (i.e. not affected by A R D contamination) for the site, whereas elevated pore water sulphate concentrations and bulk conductivity measurements indicate the influence of A R D contamination. de Vos (1992) gives details concerning the transport of ARD contamination from the adjacent INCO sulphide bearing tailings, and also gives a detailed assessment of the extent of A R D contamination at the site. 93 The much higher sulphate concentrations and higher bulk conductivities in the saturated INCO and Falconbridge tailings indicate that A R D processes are more pronounced than for the saturated Gibraltar tailings and INCO native soils. Correspondingly, the greater linearity observed between pore water sulphate concentrations and bulk conductivities for the INCO native soils in comparison with the INCO and Falconbridge tailings is likely due to a lesser degree of A R D contamination at the site. The generally low pore water sulphate concentrations measured in the INCO native soils are indicative of Stage 1 A R D processes, and therefore the pore water likely contains low heavy metals and acidity. With the absence of significant heavy metals and acidity contained in the pore water, bulk conductivity measurements are largely influenced by pore water sulphate concentrations. It is interesting to note that the data collected in the Gibraltar tailings plots very close to the relationship derived between pore water sulphate concentrations and bulk conductivity for the INCO native soils. Figure 5.11 shows a plot of pore water sulphate concentration and bulk conductivity for all test sites, and also shown are data from Merkel (1972). Merkel carried out surface resistivity testing in combination with discrete pore water sampling in native soils adjacent to sulphide bearing mine waste. As can be seen in Figure 5.11, the data from this study were in reasonably good agreement with the findings of Merkel. High bulk conductivity measurements correspond with elevated pore water concentrations, which are indicative of A R D contamination. The linear trend shown in Figure 5.11 is very valuable for the characterization of A R D processes in saturated sulphide bearing tailings and adjacent native soils, as it enables a direct estimate of pore water sulphate concentration from RCPTU bulk conductivity measurements. Given that the data set from which Figure 5.11 was developed is relatively small, its application is likely limited to the sites studied in this thesis. The agreement between the data from this.study and the data of Merkel suggests that Figure 5.11 94 may have more global applications to other sites, but this requires corroboration from further field studies at different sites. 10000 -=i 1000 — Ui E c o 2 t= o o c o o o (0 Q. 3 100 - d 10 —J • INCO Tailings Data + INCO Native Soils Data Falconbridge Data A Gibraltar Data • After Merkel, 1972 o %o o • • •«. • • • 1—I I I 11 III 1—I I I 11 III 1—I I 111 III 10 100 1000 Bulk Conductivity (/* S/cm) i—i i i 11iij 10000 Figure 5.11: Comparison Between Pore Water Sulphate Concentration and Bulk Conductivity in Saturated Sulphide Bearing Tailings and Native Soils 95 5.3.3.3 Comparison of Pore Water pH and RCPTU Bulk Conductivity Pore water p H is an important indicator of the progression of A R D development. Decreases in p H (or increases in acidity) are associated with more developed Stage 2 and Stage 3 A R D processes. Subsequently, it would be expected that decreases in p H would be accompanied by increases in bulk conductivity. Plots of pore water p H and bulk conductivity measurements for the saturated INCO tailings, Falconbridge tailings and INCO native soils are shown in Figures 5.12a through 5.12c, respectively. No pore water p H data were measured for the saturated Gibraltar tailings. Pore water p H showed no discernable trend with respect to bulk conductivity for the INCO tailings, as shown in Figure 5.12a. However, p H measurements were slightly acidic and ranged from approximately 5 - 6 . Corresponding bulk conductivity measurements in the INCO tailings ranged from approximately 800 - 1400 uS/cm. For the Falconbridge tailings, pore water p H followed the expected trend and decreased with increased bulk conductivity (Figure 5.12b). p H measurements were essentially neutral and ranged from approximately 6.4 - 7.6 and bulk conductivities ranged from 400 - 1000 uS/cm. Pore water p H measurements in the INCO native soils showed a decreasing trend with bulk conductivity (Figure 5.12c), similar to that observed in the Falconbridge tailings. p H values were neutral and generally higher than at the other sites and ranged from approximately 6.5 - 8.3, although a p H low of approximately 6 and a p H high of 10 were measured. Correseponding bulk conductivities ranged from approximately 100 - 1000 uS/cm in the INCO native soils. The slightly acidic p H measurements in the saturated INCO tailings pore water suggests that alkaline materials in the tailings are not sufficient to neutralize acid generated from oxidation of sulphide minerals. The small number of samples precludes any definitive conclusions, but it appears that acidic conditions (later Stage 2 ARD processes) are developing for the tailings 96 12 — i 8 —\ X a. 4 —\ 400 800 1200 Bulk Conductivity ( MS/CITI) 1600 Figure 5.12a: Comparison Between Pore Water p H and RCPTU Bulk Conductivity -Saturated INCO Tailings 97 12 — i 8 H • • X Q. 4 H T T 400 800 1200 Bulk Conductivity (/< S/cm) 1600 Figure 5.12b: Comparison Between Pore Water p H and RCPTU Bulk Conductivity -Saturated Falconbridge Tailings 98 12 8 H + + n 1 1 1 r 400 800 1200 Bulk Conductivity (/* S/cm) 1600 Figure 5.12c: Comparison Between Pore Water p H and RCPTU Bulk Conductivity -Saturated INCO Native Soils 99 from which the samples were collected. The neutral p H values for the saturated Falconbridge tailings and INCO native soils indicate that alkaline materials are sufficient at both sites to neutralize any acidity associated with A R D processes. 5.3.3.4 Comparison of Pore Water Heavy Metals Concentrations and R C P T U Bulk Conductivity Pore water heavy metals concentrations are commonly the most harmful contaminants contained in A R D contamination to the receiving environments. This is reflected in the Federal restrictions on effluent quality from mine sites (shown in Table 2.1 in Section 2.1), which largely contains restrictions on pore water heavy metals concentrations. Elevated pore water heavy metals concentrations are symptomatic of more developed Stage 2 and Stage 3 A R D processes. Acidity generated in the sulphide bearing tailings causes the dissolution of heavy metals contained in the tailings. The type and concentrations of heavy metals contained in A R D contamination from sulphide bearing tailings impoundments are dependent upon the mineralogy of the tailings and the surrounding native soils. It would be expected that increased heavy metals concentrations in the tailings pore water would correspond with increased bulk conductivity of the tailings, due to the overall increase in concentration of ionic constituents. However, due to the variability in the mineralogy of the tailings and the surrounding native soils for a large impoundment structure, it is reasonable to expect that relationships between specific heavy metals concentrations and bulk conductivity measurements would be highly site-specific and show a high degree of scatter. Figures 5.13a through 5.13c present comparisons between pore water iron (Fe) concentration, nickel (Ni) concentration and magnesium (Mg) concentration and bulk conductivity measurements for the saturated INCO tailings, Falconbridge tailings and INCO native soils. No pore water heavy metals concentrations were measured for the Gibraltar tailings. The 100 10000.0 -=> 1000.0 - d O) E w 100.0 - d c o 5 c o o c o o o 10.0 - d 1.0 - d 0.1 + + + 0 INCO Tailings Data ^ Falconbridge Tailings Data + INCO Native Soils Data n 1 i «—i—•—r 400 800 1200 1600 Bulk Conductivity (n S/cm) 2000 Figure 5.13a: Comparison Between Pore Water Fe Concentration and RCPTU Bulk Conductivity in Saturated Sulphide Bearing Tailings and Native Soils 101 100.0 B) 1 0 0 -J E, c o 5 c 0> o c O 2 u - l 0 INCO Tailings Data ^ Falconbridge Tailings Data + INCO Native Soils Data 0.1 -a—t-400 800 1200 1600 Bulk Conductivity (M S/cm) 2000 Figure 5.13b: Comparison Between Pore Water N i Concentration and RCPTU Bulk Conductivity in Saturated Sulphide Bearing Tailings and Native Soils 102 1000 100 -A B c 0 1 10 ^ o o c o o Ui + + 0 INCO Tailings Data <^  Falconbridge Tailings Data + INCO Native Soils Data n 1 r 1 i 1 r 400 800 1200 1600 Bulk Conductivity (M S/cm) 2000 Figure 5.13c: Comparison Between Pore Water M g Concentration and RCPTU Bulk Conductivity in Saturated Sulphide Bearing Tailings and Native Soils 103 selection of Fe, N i and M g pore water concentrations for these comparisons was based on careful consideration of multi-element chemical analyses on pore water samples from the different sites. Fe, N i , and M g generally had higher concentrations than other dissolved heavy metals and had a wider range of magnitudes which facilitated comparisons with bulk conductivity data. Figure 5.13a shows a plot of iron (Fe) concentration versus bulk conductivity measurements for the saturated INCO tailings, Falconbridge tailings and INCO native soils. Data from each site showed a trend of increased pore water Fe concentration with bulk conductivity, and this trend was more pronounced for the INCO data. Pore water Fe concentrations ranged from approximately 100 - 1000 m g / L for the INCO tailings, from approximately 0.1 - 70 m g / L for the Falconbridge tailings and from approximately 0.5 - 20 m g / L for the INCO native soils. The corresponding bulk conductivity measurements ranged from approximately 800 - 1500 uS/cm for the INCO tailings, 400 - 1100 uS/cm for the Falconbridge tailings and 100 - 500 uS/cm for the INCO tailings. The same data set of bulk conductivity measurements is used in comparisons with Fe, N i and M g concentrations, as heavy metals concentrations were determined from multi-element analyses of a constant set of pore water samples. The much higher pore water Fe concentrations and higher bulk conductivities measured in the INCO tailings are indicative of more severe A R D contamination at the site in comparison with the Falconbridge tailings and INCO native soils. Figure 5.13b shows a plot of pore water N i concentrations with respect to measured bulk conductivities for the saturated soils at the different test sites. N i pore water concentrations generally increased with bulk conductivity measurements for the INCO tailings and Falconbridge tailings, while pore water N i concentrations in the INCO native soils were below testing limits (< 0.05 mg/L). Similarly for pore water Fe concentrations, pore water N i concentrations were much higher for the INCO tailings and ranged from approximately 1.5 -104 60 mg/L . The upper bound of 60 m g / L is significantly greater than the maximum "grab sample" N i concentration of 1 mg/L , as specified in the Federal restrictions governing effluent from mine sites (Table 2.1). N i concentrations in the Falconbridge tailings pore water ranged from approximately 2 - 7 mg/L, which are also higher than the Federal restrictions. The much higher N i concentrations measured in the INCO tailings pore water samples further supports the premise that A R D processes are more developed in the saturated INCO tailings than for the saturated Falconbridge tailings and INCO native soils. Pore water M g concentrations are plotted in relation to bulk conductivity measurements for the saturated soils of the different test sites in Figure 5.13c. M g concentrations measured in the pore water of INCO tailings were generally much greater than pore water M g concentrations in Falconbridge tailings and INCO native soils. In the INCO tailings pore water M g concentrations generally increased with bulk conductivity and ranged from approximately 50 - 500 mg/L. Similarly, M g pore water concentrations in the INCO native soils tended to increase with bulk conductivity and ranged from approximately 10 - 100 mg/L. M g pore water concentrations in the Falconbridge tailings showed no discernable trend with bulk conductivity and ranged from a low concentration of 0.5 m g / L to a peak concentration of 60 mg/L. The generally much higher M g concentrations in the pore water of the saturated INCO tailings in comparison with data from the other sites are consistent with the findings for pore water Fe and N i concentrations. Moreover, it provides further evidence of more significant A R D contamination affecting the saturated INCO tailings than at the other sites. Copper (Cu), arsenic (As), lead (Pb) and zinc (Zn) concentrations for INCO and Falconbridge pore water samples were below federal restrictions, as specified in Table 2.1 in Section 2.2, and in many cases were below the detection limits of the testing equipment. 105 5.3.3.5 Summary Of the relationships presented in Section 5.3.3 between RCPTU bulk resistivity (or bulk conductivity) measurements and pore water chemistry, those between bulk resistivity and pore water resistivity and bulk conductivity and pore water sulphate concentration appear strongest. The strength of the relationship between RCPTU bulk resistivity and pore water resistivity lies in the fact that a fundamental characteristic of A R D development is increased ionic loading of the pore water with A R D development. Increased ionic loading of the pore water results in a corresponding increase in pore water conductivity, which largely governs the bulk resistivity response of the soil. Similarly, the strength of the relationship between RCPTU bulk conductivity and pore water sulphate concentration can be attributed to the fact that increased pore water sulphate concentration with A R D progression is a principle contributor to overall increased ionic loading of the pore water. The relationships between RCPTU bulk conductivity measurements and pore water p H and heavy metals concentrations are clouded by the influences of soil mineralogy. The p H of the pore water is a function of acid generated by sulphide oxidation and alkalinity contained in the tailings and native soils. The net effect is that pore water samples of similar p H can have widely varying pore water ionic concentrations (which directly influence bulk conductivity measurements), due to the effects of alkalinity. Thus, it is difficult to infer pore water p H directly from RCPTU bulk conductivity measurements. Similarly, pore water heavy metals concentrations are dependent upon soil mineralogy. For a large tailings impoundment it is reasonable to expect significant variations in tailings mineralogy, which results in a fair degree of scatter between RCPTU bulk conductivity measurements and pore water concentrations of specific heavy metals. The data presented in Section 5.3.3 gives insight into the relative stage of A R D development for the test locations from which test data were collected. It must be stressed that 106 interpretation of the data should be restricted to the specific testing locations for the respective sites. The results of testing indicate that A R D contamination is more severe for the saturated INCO tailings than for the saturated Falconbridge tailings and INCO native soils. In general higher RCPTU bulk conductivity (or lower bulk resistivity) measurements and higher pore water concentrations of acidity and heavy metals were measured for the INCO saturated tailings in comparison with the other test sites. In the saturated INCO tailings, high pore water sulphate concentrations in combination with the slightly acidic pore water p H and elevated heavy metals concentrations of the pore water indicates later Stage 2 development. In the saturated Falconbridge tailings, the fact that elevated heavy metals are contained in the pore water is indicative of Stage 2 ARD development. However, the significantly lower pore water heavy metals concentrations and generally lower sulphate concentrations and bulk conductivity measurements in comparison with the saturated INCO tailings data indicates that ARD processes are less developed for the saturated Falconbridge tailings. Further evidence of this fact, was the neutral p H of the Falconbridge tailings pore water in comparison with the slightly acidic INCO tailings pore water. In the saturated INCO native soils, lower pore water sulphate concentrations and bulk conductivity measurements were measured in comparison with the saturated INCO and Falconbridge tailings. Significantly lower pore water heavy metals concentrations and higher p H were measured in the saturated native INCO soils in comparison with the saturated INCO tailings, while these values were approximately similar to those measured in the saturated Falconbridge tailings (with the exception of pore water N i concentration, which was much lower). A R D contamination is significantly lower for the INCO native soils than for the INCO tailings, and based upon pore water sulphate concentrations and bulk conductivity measurements is less severe than that in the Falconbridge tailings. However, based upon the peaks in pore water sulphate concentrations and heavy metals concentrations and peaks in bulk conductivity measurements at specific 107 locations at the base of INCO's Pistol dam it is apparent that A R D contamination is impacting the site from the adjacent INCO tailings. This is in agreement with the findings of de Vos (1992) who provides more definitive information with respect to the impact of ARD contamination at the site. The small quantity of data from the saturated Gibraltar tailings prevents any meaningful comparisons with the site, although based on limited bulk conductivity and pore water sulphate concentration data it appears A R D processes are less developed than those for the saturated INCO and Falconbridge tailings. It is important to note that the findings with respect to A R D development in the saturated INCO tailings and Falconbridge tailings is the opposite of the findings for the unsaturated tailings at each site. In the unsaturated Falconbridge tailings higher pore water sulphate concentrations and higher bulk conductivity measurements were measured in comparison with the unsaturated INCO tailings, which indicates that A R D processes are more developed in the unsaturated Falconbridge tailings. By contrast, based upon the data presented in Section 5.3.3, it appears that A R D processes are more developed for the saturated INCO tailings in comparison with the saturated Falconbridge tailings. This can likely be explained by the fact that the INCO tailings are much older than the Falconbridge tailings. Deposition of tailings in the INCO Central Tailings Area occurred from 1937-1988, whereas deposition of tailings at the Falconbridge Fault Lake site took place from 1964-1978. A R D is a time-dependent process, as discussed in Section 2.2.1, and the pore water of the saturated INCO tailings has had a longer time to accumulate ionic constituents from acid generation in the unsaturated zone (as shown in Figure 2.2) in comparison with the saturated Falconbridge tailings. Based upon the much higher sulphide mineral content and the more severe A R D development in the unsaturated Falconbridge tailings, it is reasonable to project that A R D development in the saturated Falconbridge tailings could exceed that found in the saturated INCO tailings with the progression of time. 108 5.4 C H A R A C T E R I Z A T I O N OF H Y D R O G E O L O G I C A L CHARACTERISTICS 5.4.1 BASE OF PISTOL D A M (INCO) A summary of estimated hydrogeological characteristics for the base of Pistol Dam is presented in Table 5.1. Pore pressure dissipations carried out during CPTU soundings were used to measure equilibrium pore pressures and estimate hydraulic conductivity for each depth shown. The CPTU data are in excellent agreement with data obtained from University of Waterloo piezometer installations, which are also shown in Table 5.1. Of particular interest was sounding 123-9327, which confirmed the existence of an upward gradient, i , (characteristic of an Artesian condition) by University of Waterloo piezometer installation IN22. Figure 5.14 shows the measured equilibrium pore pressures versus theoretical hydrostatic pore pressures for both the CPTU and the University of Waterloo piezometer. The agreement between the two data sets is excellent, and the magnitude of the upward gradient is approximately 0.10 -0.15. As shown in Figure 5.14, hydraulic gradient is defined as the ratio between the excess pore pressure (Au), which is the difference between the measured equilibrium pore pressure and the estimated hydrostatic pore pressure, and the vertical depth (Al) over which the excess pore pressure was recorded. As both Au and Al have units of metres, hydraulic gradient measurements are dimensionless. The CPTU estimates of hydraulic conductivity show good consistency and range from 10"*6 -10"7 cm/s. This is consistent with University of Waterloo piezometer data and with the literature (Freeze and Cherry, 1979) for the observed soil stratigraphy (clay - fine sand). W.D. Robertson et al. (1991), on the basis of sulphate measurements from University of Waterloo piezometer nests, estimated an upward migration (v) of seepage from Pistol Dam of 109 Table 5.1: Summary of Estimated Hydrogeological Characteristics at the Base of Fistol Dam CPTU Depth Equilibrium Hydraulic U. of W. Depth Equilibrium Hydraulic Sounding (m) Pore Conductivity Piezometer (m) Pore Pressure Conductivity Pressure (cm/sec) Installation (mofH20) (cm/sec) (mofH20) 119-9323 1.2 1.5 4.1 x 10"7 2.2 2.5 8.8 x lO"6 3.2 3.4 3.4 x 10"* 4.2 4.2 120-934 2.2 2.0 7.3 x 10"7 3.2 3.1 3.5 x 10"7 4.2 4.2 1.6x10* 121-9325 2.2 0.9 4.7 xlO"7 4.2 2.7 3.4 x 10"7 4.9 3.4 8.1 x 10"7 122-9326 3.9 4.1 6.7 x 10"7 IN32 2.1 2.1 4.1 43 123-9327 43 4.2 IN22 2.2 2.0 2.Ox NT7 9.3 10.6 8.1 x 10"7 6.9 4.0 x 10-8 10.3 11.6 1.4 x VT6 7.0 8.5 123 13.6 4.0x10* 8.8 10.4 133 14.8 10.0 11.6 143 15.7 14.4 15.9 9.0 xlO"5 14.5 15.9 126-9332 6.2 6.2 2.7 x 10* IN34 5.5 5.5 8.2 8.2 2.8 x 10* 9.5 9.6 9.2 9.2 12.5 12.6 10.2 10.2 110 Pore Pressure (m of water) o 4 8 12 16 20 — 1 Figure 5.14: Estimate of Hydraulic Gradient in Native Soils at the Base of Pistol Dam approximately 20 cm/year in the vicinity of piezometer IN22. The rate of upward migration is equivalent to the groundwater velocity and is defined as follows: [5.1] v=K*i The rate of upward migration of seepage from Pistol Dam in the native soils in the vicinity of piezometer IN22 can be calculated from [5.1] using the estimates of upward gradient and hydraulic conductivity derived from the CPTU data. Assuming an average gradient magnitude of 0.125 and an average hydraulic conductivity of 2.5 x 10"6 cm/sec for the native soils, the upward rate of migration of the seepage is estimated to be 10 cm/ yr. Considering 111 the strong dependence of equation [5.1] on hydraulic conductivity, which can show a broad range of values, the agreement between the W.D. Robertson et al. (1991) estimate for upward migration and that derived from CPTU data is considered excellent. 5.4.2 FAULT LAKE TAILINGS IMPOUNDMENT (FALCONBRIDGE) Hydrogeological parameters for this site were based on extensive pore pressure dissipation tests carried out during sounding F01-9333. Determination of the depth of the phreatic surface was a primary concern of Falconbridge personnel. The location of the phreatic surface was found by measurement of the equilibrium pore pressure for each dissipation test depth, and this indicated a significant downward gradient in the tailings. Figure 5.15 shows a comparison between the equilibrium pore pressures measured in the tailings and the hydrostatic pore pressures based on the estimated location of the phreatic surface. The difference between the measured pore pressures in the tailings and the hydrostatic pore pressures translates to a downward gradient of magnitude 0.4, as shown in 5.15. It should be noted that the magnitude of the gradient has been estimated based on only one day of testing and that the magnitude of the gradient may be subject to seasonal variation. The existence of the downward gradient is due to the difference in pore water pressures between the tailings impoundment and the regional groundwater system. During active deposition of the tailings into the impoundment the tailings were kept saturated. The process water discharged with the tailings and infiltration from precipitation maintained the local groundwater table at the surface of the impoundment. After deposition of tailings into the impoundment ceased in 1978, the position of the phreatic surface gradually started to decline. Currently, the phreatic surface is estimated to be at a depth of 10.5 m. The downward gradient is acting to lower the phreatic surface in the tailings until it coincides with the 112 Figure 5.15: Estimate of Hydraulic Gradient in Sulphide Bearing Tailings at the Fault Lake Tailings Impoundment elevation of the regional groundwater table. The rate at which this decline is occurring is very slow, and this can be attributed to the low hydraulic conductivity of the tailings. Estimates of hydraulic conductivity were also made based on pore pressure dissipations at different depths. Estimates of hydraulic conductivity in the tailings ranged from lO'MO" 6 113 cm/s which are representative of the fine-grained nature of the tailings and in agreement with previous studies (Noranda Technology Centre, 1994). The hydraulic conductivity in the lacustrine foundation material were in the same range as the tailings, which is typical of the clayey-silt soil. Based upon the estimates of average gradient magnitude of 0.4 and average hydraulic conductivity of the tailings of 5.0 x 10'6 cm/s, the average downward migration of tailings pore water is estimated to be 60 cm/year from equation [5.1]. This estimate of pore water migration should be considered preliminary as it is dependent upon the magnitude of the gradient estimated from CPTU data, which was not corroborated due to a lack of other field data. 5.5 PHYSICAL C H A R A C T E R I Z A T I O N 5.5.1 G E N E R A L Figure 5.16 presents estimates of geotechnical strength parameters and interpreted stratigraphy for an RCPT sounding carried out at the crest of Pistol Dam (111-9330). Relative Density (Dr) and peak friction angle (cj)') are drained strength parameters, and therefore estimates of these parameters were restricted to sandy tailings and native soils. Contrastingly, estimates of undrained strength (Su) were restricted to the silty clay native soils. Estimates of SPT ( N i ) « ) were made for all soil types. Details concerning the empirical correlations used in the estimation of each parameter are included in the references for CPTINT 5.0, which are included in Appendix B. Relative Density (Dr) is an index parameter that can be used to provide an indication of the stress-strain behaviour of a cohesionless soil. D r is a ratio used to express the relationship 115 between the actual void ratio and the minimum and maximum void ratios of a soil. D , in the upper tailings crust (above 1.6 m depth) was above 90 % indicating a very dense soil. Below the upper crust of tailings, D r of the tailings generally ranged from 35-60 %, with occasional looser and denser layers falling outside this range. Peak friction angle (<J>') is essentially the stress-dependent component of the shear strength for the soil. It is not an inherent value but depends on many things, most predominately the density and distribution and angularity of grain size. rj>' was estimated to be greater than 45° in the dense upper crust of tailings. Below this layer, tj>' showed a decreasing trend and ranged from approximately 31 - 41° in the tailings. The correlation used to estimate (J)', proposed by Robertson and Campanella (1983), was developed for incompressible sands. The stratigraphic profile shown in Figure 5.16, which was inferred from the CPTU data, indicates a higher silt content of the tailings below a depth of approximately 22 m. This increase in silt content results in a corresponding increase in soil compressibility. For more compressible soils, the correlation typically results in lower (and conservative) estimates of (j)'. Below a depth of approximately 27 m, estimates of (j)' were not made as the more compressible nature of the tailings was beyond the scope of the correlation. SPT (Ni)6o values are considered an index of soil density. Predicted (Ni)6o values were very high (> 45 blows/ft.) in the dense upper crust of the tailings, ranged from approximately 15 -20 blows/ft. in the tailings from 1.6 m - 6.4 m and ranged from approximately 8-15 blows/ft. for the remaining depth of tailings. Estimates of (Ni)«) values in the native silty clay soil ranged from 4 -12. Undrained shear strength is the shear strength of the soil measured during shearing under undrained loading conditions. S„ is not a unique parameter and depends significantly on the type of test used, rate of strain and the orientation of the failure planes. Estimates of S„ in the 116 native silty clay soil ranged from approximately 110 - 200 kPa. This corresponds to a — ^ ° v 0 0.2 - 0.4, which is indicative of a lightly overconsolidated fine-grained soil. 5.5.2 PRELIMINARY ASSESSMENT OF FLOW LIQUEFACTION SUSCEPTIBILITY CPTU data from a RCPTU sounding at the crest of INCO's Pistol Dam (111-9330) is plotted in Figure 5.17 with respect to state parameter in accordance with the framework of Plewes et al. (1992) presented in Section 3.3.2. Negative values of \j/ are representative of essentially dilative (SH) soils, whereas positive values of \j/ are representative of essentially contractive (SS) soils. Figure 5.17a is a plot of all CPTU data points for the sounding (collected every 0.025 m) with respect to Most of the data points for the sounding plot as a negative \\i value, but a significant portion of the data has a \j/ value between 0 - -0.05. Considering the screening nature of this methodology, soils with vj/ values between 0 - -0.05 can be conservatively viewed as potentially contractive. Figure 5.17b is a plot of \\i versus depth, which facilitates the interpretation of the data presented in Figure 5.17a with respect to specific depths. The phreatic surface for this sounding was located at a depth of 15 m, and the discussion of soil behaviour and the susceptibility for flow liquefaction is focused on saturated soils. Upon review of Figure 5.17b, it is apparent that there is potential for contractive behaviour of the tailings. If the boundary of contractive/ dilative soil behaviour is conservatively assumed to be y = -0.05, then the saturated tailings are potentially contractive from 15 m - 27 m and from 31 m - 32.5 m. Saturated zones that show stronger tendencies for contractive behaviour include the tailings between 15 - 17.5 m, 22.5 m - 24 m and 31m - 32 m. The interface between the tailings and the native soils is approximately located at a depth of 37 m. The native silty clay soil is interpreted to be strongly contractive, with v|/ values generally greater than 0.10. s However, the relatively stiff nature of the silty clay soil ( as evidenced by —— » 0.2 - 0.4) (ba-k) do 118 indicates that the native soils may not exhibit a strain softening response and subsequently may not be susceptible to flow liquefaction. 5.5.3 PRELIMINARY ASSESSMENT OF CYCLIC LIQUEFACTION SUSCEPTIBILITY A n assessment of the susceptibility for cyclic liquefaction of soils requires consideration of site seismicity. The maximum credible earthquake (MCE) represents the most severe earthquake that could be reasonably expected to occur at a given site, and is generally considered the \ appropriate design event for closure of tailings impoundments. The INCO Central Tailings Area lies in a zone of low seismicity that includes northeast and southeast Ontario, Southern Quebec and northeast Newfoundland. There are no known events larger than M = 4.3 since records were initially compiled in the 1930's (Basham et al., 1982). For the INCO Central Tailings Area, a peak ground acceleration (amax) of O.lg is estimated for a M C E of M=5.0, occurring at a distance of 20 km for the site (Martin and Tissington, 1996). Section 3.3.3 described a methodology proposed by Robertson and Fear (1995) for evaluating the cyclic liquefaction susceptibility of soils from CPT data. Figure 5.18 through Figure 5.20 provide a summary of this procedure for a RCPTU sounding at the crest of INCO's Pistol Dam (111-9330). The CPT tip resistance (qc) is normalized with respect to effective overburden stress according to equation [3.8]. The effect of the normalization procedure is readily apparent, as shown in Figure 5.18. The plot of non-normalized q c (Figure 5.18a) shows an increasing trend with depth, whereas the plot of normalized q c i (Figure 5.18b) shows a slight decreasing trend with depth. The differences between q c and q c i can be attributed to stress-level effects. By elimination of these effects, q c i gives a more meaningful measure of soil behaviour. 119 120 Figure 5.19 details the steps followed in correcting q c i for the effects of the fines content (FQ in the tailings and native soils. The fines content was estimated according to equation [3.11], and was found to increase with depth (Figure 5.19a). The increase in FC with depth is consistent with the previous observations noted for this sounding, as discussed in Section 5.1.1. Of particular interest were the estimated FC for the tailings from a depth of approximately 22.5 m - 24 m. The large increase in FC in this zone (25 < FC < 50) is in agreement with the previously denoted sandy silt soil behaviour type. The interface of the tailings and the fine-grained native soils at a depth of approximately 37 m is readily apparent by the large increase in FC. Corrections to q c i for FC, referred to as A q c i were made according to equation [3.9], and are shown with respect to depth in Figure 5.19b. The A q c i values mirror the changes in FC, with increases in FC resulting in increases to A q c i values. Figure 5.19c is a plot of normalized CPT tip resistance (qci) corrected for fines content to an equivalent clean sand, referred to as (qci)ecs/ with respect to depth. The (qci)ecs values are simply the sum of q c i and Aq c i values. The net effect of correcting q c i for FC is to reduce the susceptibility for cyclic liquefaction of finer-grained soils, which is similar to the recommendations of Seed et al. (1985) for the SPT. It should be noted that the estimates for FC shown in Figure 5.19b were not compared with FC determined from soil samples due to a lack of available data. Given the discussion in Section 3.3.3 concerning the correlation from which the FC estimates were derived, and the fact that FC acts to reduce cyclic liquefaction susceptibility, this procedure for estimating cyclic liquefaction susceptibility should be considered preliminary. Figure 5.20 presents the results of a preliminary assessment of cyclic liquefaction susceptibility for the tailings and native soils at the crest of INCO's Pistol Dam. The cyclic resistance ratio (CRR) of the soils were estimated from (qci)ecs values using the chart shown in Figure 3.12. 121 122 SEISMIC SHEAR STRESS RATIO 0.00 0.10 0.20 0.30 0.40 50 —1 Figure 5.20: Seismic Shear Stress Ratio Versus Depth For RCPTU Sounding at the Crest of Pistol Dam The cyclic stress ratio (CSR) induced by the M C E was calculated using the relationship proposed by Seed at al. (1985). A scaling factor of 1.5 was used to account for the earthquake M=5.0, in accordance with the recommendations of Seed et al. (1985). As shown in Figure 5.20, the CRR of the penetrated soils are substantially greater than the CSR induced by the M C E for both unsaturated and saturated conditions. Thus, cyclic liquefaction of the saturated tailings and native soils does not appear to be a possibility based on this preliminary assessment. This finding is not surprising considering the low seismicity of the site. 123 6.0 COMPARISON OF THE RCPTU AND CONVENTIONAL TESTING METHODS Table 6.1 presents a summary comparison of the RCPTU and conventional testing methods with respect to data procurement and cost for geoenvironmental characterization of sulphide bearing tailings. The quality of data procurement for each test is rated from A - C for the various geoenvironmental criterion shown in Table 6.1, with A being the highest rating. Factors considered in rating quality of data procurement include data continuity (e.g. continuous data collection versus discrete sampling) and the overall preference of test data for engineering design. N / A indicates that a test method is not applicable for evaluating a particular geoenvironmental criteria. The costs shown for each test method are approximate and exclusive of mobilization/demobilization costs, which are likely similar for all test methods. Based on the comparison shown in Table 6.1, the RCPTU can provide a technically sound cost-effective alternative to conventional testing methods. To match the data accumulated by the RCPTU, conventional technology would require a combination of (2) to (5) inclusive from Table 6.1. The likely per-metre costs for a combination of these methods would exceed $100/m, although not all sites require such a comprehensive characterization and consequently costs would be lower for less detailed characterizations. However, even the cost of carrying out drilling with just SPT testing is still more costly than the RCPTU, which provides (2) to (5) inclusive. The economic benefit gained by expanded use of RCPTU in comparison with conventional methods can be used to strengthen site investigation programs. For a given site, the cost savings realized through application of RCPTU testing could be used to carry out a larger number of RCPTU tests in comparison with standard drilling methods, which would result in a more detailed characterization of subsurface conditions. The cost savings from using RCPTU testing could also be used for collection of pore water samples by means of BAT technology, which would significantly enhance interpretation of bulk resistivity 124 measurements. The comparison presented in Table 6.1 underscores the ability of the RCPTU to provide comprehensive geoenvironmental site characterization at reasonable cost in sulphide bearing tailings impoundments. Table 6.1: R C P T U Testing Versus Conventional Testing Methods With Respect to Data Procurement and Cost Stratigraphy Bulk Resistivity Geotechnical Parameters Hydrogeological Characteristics Cost (S/m) (1). RCPTU A A B B 25-30 (Woeller, 1994) (2).Drilling with 5' SPT B N / A C N / A 50 (Dijwle, 1994) (3).Drilling with continuous sampling A N / A A (with lab testing) N / A 100 + lab costs (Diggle, 1994) (4).Drilling with resistivity well logging C A N / A N / A 45 (King, 1994) (5).Drillingwith nested piezometers c N / A N / A A 100 (Diggle, 1994) 125 7.0 RECOMMENDED PROCEDURES FOR USING IN-SITU TESTING METHODS FOR THE GEOENVIRONMENTAL CHARACTERIZATION OF SULPHIDE BEARING TAILINGS IMPOUNDMENTS Based on the experience and results from the field work carried out for this thesis, Figure 7.1 provides a framework for the application of in-situ testing methods for the geoenvironmental characterization of sulphide bearing tailings impoundments. The RCPTU and CPTU can rapidly provide a comprehensive and economical assessment of environmental and geotechnical site conditions. The RCPTU provides a direct measure of the bulk resistivity of the soil and pore water, which can be used to infer pore water contamination due to oxidation of sulphide minerals and subsequent ARD processes. In addition, discrete pore water sampling (i.e. BAT sampling) and subsequent chemical analyses can be used to augment RCPTU testing by assisting the interpretation of the effects of pore water chemistry on bulk resistivity measurement. The CPTU provides valuable insight into the geotechnical and hydrogeological properties of tailings. The CPTU effectively delineates stratigraphic variations in tailings, gives estimates of key geotechnical strength parameters and can measure pore pressure distribution within the tailings. This information is, at a minimum, required for any stability analysis of a tailings impoundment. Additionally, the CPTU data can be used to carry out preliminary assessments of liquefaction susceptibility, considering both static and dynamic loading conditions. The ability to examine liquefaction susceptibility directly from CPTU data is a significant attraction of the technology, considering the preponderance of historical tailings dam failures which have been attributed to liquefaction of the tailings. Finally, estimates of hydraulic conductivity of tailings and the identification of hydraulic gradients in the tailings can be used to assess transport of A R D contamination in sulphide bearing tailings. 126 CT p I = J i i <D T3 O Q) o 0 Q . £ CO O *r O CT C = O 0) I-(0 N 3 & CO • c o 2 CO O CO o E o o CD O "co o CT O O 0) CT O i_ •o >» X "co o 'E o o O < m 06 i -Q_ O a : 0) Q) 2 ro a. CO "D 3 2 ng I ring/sampli if required nitoi ons o ;= E * Specific instal Q_ O cs 1 tratigraphy, conditions, its and characteristi Determine s piezometric gradier hydrogeologic Determine s piezometric gradier hydrogeologic I I 3 o tn a c c o 2 *= E J2 U CO E 1A o c o> — Q. CO r -o 0> . C <-> Q_ O) n c « w 2 « 4>rf CO (A U a 'E 9 E _ 2 co « ro Q. E <» 0) o CO -£ ° re O (A o ° 0J0) Q O) d> "2 '5 CO m O) C Si E v§ CS CA (A O o -r o o s is Q. 2 10 o .Q 5> 127 Depending upon the complexity of the site being investigated, the in-situ testing data may be sufficient. However, the in-situ testing results may indicate environmental and geotechnical conditions which require further assessment. In general, it would be expected that the results of an in-situ field testing program at a sulphide bearing tailings impoundment would be supplemented by some form of conventional drilling program. The results of the in-situ testing program could be used to direct additional site investigation activity, which may include discrete soil sampling and lab testing, installation of monitoring/sampling stations and discrete pore water sampling and chemical analyses. A n initial site investigation program may include a wide variety of conventional testing methods to supplement the in-situ testing program. However, if strong correlations can be developed between the results of the RCPTU data and the results of the conventional drilling-based testing methods then future geoenvironmental characterizations at the site can be focused on the more cost-effective in-situ testing technology. 128 8.0 S U M M A R Y A N D CONCLUSIONS The results from site investigations carried out at three Canadian mine sites demonstrate that in situ testing, and more specifically the resistivity piezocone (RCPTU), can provide a technically sound and cost-effective technique for the geoenvironmental characterization of sulphide bearing tailings impoundments. Based on the results from the in situ field testing program the following can be concluded: (1). RCPTU bulk resistivity measurements in the unsaturated zone of sulphide bearing tailings and native soils affected by acid rock drainage (ARD) processes can provide a qualitative measure of pore water chemistry. Bulk resistivity measurements are influenced by the countering effects of changing saturation and pore water chemistry which causes measured bulk resistivities to be highly variable. However, the assessment of A R D processes in sulphide bearing tailings by the RCPTU is aided by the moisture retention capabilities of tailings and the highly conductive pore water symptomatic of A R D contamination. As evidenced by RCPTU soundings at INCO and Falconbridge mine sites, very low bulk resistivity measurements (< 10 Q-m) can be measured in the unsaturated tailings. These low bulk resistivity measurements are a function of high saturation and high pore water conductivity. The low bulk resistivity measurements corresponded with high pore water sulphate concentrations, obtained from chemical analyses of discrete pore water samples, which are indicative of A R D contamination. Discrete pore water sampling in combination with RCPTU testing enhances the qualitative interpretation of the relative influence of saturation and pore water chemistry on bulk resistivity measurements in the unsaturated zone of sulphide bearing tailings and native soils. Based on the results of RCPTU testing and chemical analyses of discrete pore water samples, A R D processes were more severe in the unsaturated Falconbridge tailings than in the 129 unsaturated INCO tailings, for the specific test locations. Lower bulk resistivity measurements (indicative of higher pore water conductivity and corresponding ionic loading) and significantly higher pore water sulphate concentrations were measured in the Falconbridge unsaturated tailings in comparison with the INCO unsaturated tailings. (2). RCPTU bulk resistivity measurements in the saturated zone of sulphide bearing tailings and native soils provide a more definitive measure of pore water chemistry than measurements in the unsaturated zone, due to the removal of the influence of variable saturation on bulk resistivity measurements. RCPTU bulk resistivity measurements corresponded with pore water chemistry of discrete pore water samples, demonstrating the ability of the tool to map low resistivity pore water. Of particular interest were relationships developed between pore water resistivity and RCPTU bulk resistivity and pore water sulphate concentration and RCPTU bulk conductivity for all test sites. Estimates of apparent formation factor (F) based on the relationship between bulk resistivity and pore water resistivity were made for all test sites. The estimates of F enable estimation of pore water resistivity directly from RCPTU bulk resistivity measurements, from which increases in ionic loading of the pore water due to A R D contamination can be inferred. RCPTU bulk conductivity measurements showed good agreement with pore water sulphate concentrations for all test sites. Pore water sulphate concentration is a key indicator of A R D processes, as elevated sulphate concentrations occur prior to the development of more developed A R D processes (i.e. increased acidity and heavy metals concentrations). The results from this study indicate that the detection of elevated pore water sulphate concentrations in sulphide bearing tailings and native soils is feasible with the RCPTU. Therefore, the RCPTU appears to be well-suited for the long-term monitoring of sulphide bearing tailings impoundments, where contamination can take place over tens of years. 130 The data presented in this study for saturated sulphide bearing tailings and saturated native soils give insight into the relative stage of A R D development for the test locations from which test data were collected. It must be stressed that interpretation of the data should be restricted to the specific testing locations for the respective sites. The results of testing indicate that A R D contamination is more severe for the saturated INCO tailings than for the saturated Falconbridge tailings and INCO native soils. In general higher RCPTU bulk conductivity (or lower bulk resistivity) measurements and higher pore water concentrations of acidity and heavy metals were measured for the INCO saturated tailings in comparison with the other test sites. In the saturated INCO tailings, high pore water sulphate concentrations in combination with the slightly acidic pore water p H and elevated heavy metals concentrations of the pore water indicates later Stage 2 development. In the saturated Falconbridge tailings, the fact that elevated metals are contained in the pore water is indicative of Stage 2 A R D development. However, the significantly lower pore water heavy metals concentrations and generally lower sulphate concentrations and bulk conductivity measurements in comparison with the saturated INCO tailings data indicates that A R D processes are less developed for the saturated Falconbridge tailings. Further evidence of this fact, was the neutral p H of the Falconbridge tailings pore water in comparison with the slightly acidic INCO tailings pore water. In the saturated INCO native soils, lower pore water sulphate concentrations and bulk conductivity measurements were measured in comparison with the saturated INCO and Falconbridge tailings. Significantly lower pore water heavy metals concentrations and higher p H were measured in the saturated native INCO soils in comparison with the saturated INCO tailings, while these values were approximately similar to those measured in the saturated Falconbridge tailings (with the exception of pore water N i concentration, which was much lower). A R D contamination is significantly lower for the INCO native soils than for the INCO tailings, and based upon pore water sulphate concentrations and bulk conductivity measurements is less severe than that in the 131 Falconbridge tailings. However, based upon the peaks in pore water sulphate concentrations and heavy metals concentrations and peaks in bulk conductivity measurements at specific locations at the base of INCO's Pistol dam it is apparent that A R D contamination is impacting the site from the adjacent INCO tailings. The small quantity of data from the saturated Gibraltar tailings prevents any meaningful comparisons with the site, although based on limited bulk conductivity and pore water sulphate concentration data it appears A R D processes are less developed than those for the saturated INCO and Falconbridge tailings. (3) . CPTU pore pressure dissipation data can provide reasonable estimates of hydrogeological characteristics which can be used for modeling transport of A R D contamination. A n estimate of the migration of A R D contamination at the base of Pistol Dam was in reasonable agreement with an estimate based on pore water sulphate concentration. (4) . CPTU-based methods can provide an initial assessment of the potential for liquefaction of tailings, under both static and dynamic loading conditions. Methodologies proposed by Plewes et al. (1992) and Robertson and Fear (1995) were used to assess flow liquefaction and cyclic liquefaction susceptibility, respectively, of tailings at the crest of INCO's Pistol Dam. Results indicate that zones of tailings are potentially contractive, and therefore could be susceptible to flow liquefaction if a viable triggering mechanism exists. Results of the preliminary assessment of cyclic liquefaction susceptibility indicate that the tailings would not liquefy under the design earthquake event. 132 9.0 RECOMMENDATIONS FOR FUTURE RESEARCH In order to improve the application of the RCPT and discrete pore water sampling technologies for the geoenvironmental characterization of sulphide bearing tailings the following recommendations are proposed: (1) . Improved Physical Design of the Resistivity Module: The length (350 mm) and the diameter (15 cm2) of the resistivity module can inhibit penetration in dense soils due to excessive friction on the resistivity module. Although this occurred seldomly during the course of the field investigation program, it is recognized that the size of the resistivity module could be problematic at other sites. The UBC ISTG has recently reduced the diameter of the resistivity module from 15 cm 2 to 10.5 cm 2. The smaller diameter of the new module should significantly reduce potential problems with pushing in dense soils. (2) . Improved BAT Water Sampling Technology: The hypodermic needle system employed by the BAT system used in this study became blocked several times by rubber after it punctured the septum. Notwithstanding the problems experienced with blocking of the hypodermic needle, the hypodermic needle system often requires a long period of time for sample recovery. Methods based on BAT-type technology, but not employing a hypodermic needle should be investigated. Campanella et al. (1995) modified the BAT system by replacing the hypodermic needle and septum system with a 9.5 mm swagelock fitting in a study of in situ measurement of hydraulic conductivity in sands. This system permits much higher flow rates than the hypodermic needle, which reduces the length of sampling time. The use of the swagelock fitting may be appropriate for 133 environmental sampling, but issues of sample integrity and cross-contamination require further research. (3) . More Comparisons of RCPTU Bulk Resistivity Measurements and Pore Water Chemistry in Sulphide Bearing Tailings: It would be beneficial to conduct further studies at the INCO Central Tailings Area, Falconbridge Fault Lake tailings impoundment and Gibraltar tailings impoundment to strengthen the relationships developed between RCPTU bulk resistivity measurements and pore water chemistry for these sites. Also, more site investigations at other sulphide bearing tailings impoundments would provide data for evaluation of potential global relationships between bulk resistivity measurements and pore water chemistry, particularly for the relationship between bulk resistivity and pore water sulphate concentration. (4) . Development of a Resistivity Module Capable of Measuring the Induced Polarization Response of Sulphide Bearing Tailings: Induced polarization (IP) is a current stimulated electrical phenomena observed as a delayed voltage response in earth materials (Sumner, 1976). Surface resistivity methods have been used in mineral exploration for identifying disseminated sulphide minerals, which exhibit a characteristic IP response (Sumner, 1976). Research is currently being carried out by the UBC ISTG for modification of the resistivity module to enable measurement of the IP response of penetrated soils. The ability to measure IP response with the resistivity module would enable estimation of sulphide content in sulphide bearing tailings. Thus, the RCPTU would be capable of assessing the current state of A R D processes through bulk resistivity measurements, and also give insight into the future potential for sulphide oxidation by estimating the sulphide content of the tailings. 134 (5). Use of a pH Module in Combination With the Resistivity Module For Geoenvironmental Characterization of Sulphide Bearing Tailings: A p H module, capable of measuring pore water p H , could be used in combination with the resistivity module for assessing A R D contamination in sulphide bearing tailings. As the pore water acidity is indicative of the stage of A R D development, the p H module would provide valuable insight into A R D contamination of sulphide bearing tailings. 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Department of Mining and Mineral Processing, University of British Columbia, Vancouver, B.C. Martin, T.E. and Tissington, I. (1996). Design Evolution of Tailings Dams at INCO Sudbury. Proceedings of the Third International Conference on Tailings and Mine Waste '96, Fort Collins, Colorado. Merkel, R.H. (1972). The Use of Resistivity Techniques to Delineate Acid Mine Drainage in Groundwater. Ground Water, V.10, No.5, pp.38-42. Noranda Technology Centre (1993). Hydrogeological Investigation of the Fault Lake Tailings Site. Draft report submitted to Falconbridge Ltd. Unpublished. Patterson, R.J., Frape, S.K., Dykes, L.S. and MacLeod, R.A. (1978). A Coring and Squeezing Technique For The Detailed Study of Subsurface Chemistry. Can. J. Earth Sci., 15, pp. 162-169. Pattison, E.F. (1979)," The Sudbury Sublayer", Canadian Mineralogist, Vol . 17, pp. 257-274. Peters, T .H. (1984), "Rehabilitation of Mine Tailings: A Case of Complete Ecosystem Reconstruction and Revegetation of Industrial Stressed Lands in the Sudbury Area, Ontario, Canada", in Effects of Pollutants at the Ecosystem Level, Edited by P.J. Sheehan, D.R. Miller, G.C. Butler and P.H. Bourdeau, John Wiley and Sons, pp. 403-421. Plewes, H.D., Davies, M.P. and Jefferies, M.G. (1992). CPT Based Screening Procedure For Evaluating Liquefaction Susceptibility. Proceedings of 45th Annual Canadian Geotechnical Conference, Toronto, pp. 4-1 - 4-9. Robertson, W.D., Blowes, D.W., Cherry, J.A., Coggans, C , and McGregor, R.J. (1991). Hydrogeology and Geochemistry of the INCO Copper Cliff Mine Tailings Impoundment, Draft. Waterloo Centre For Groundwater Research. Unpublished. Robertson, A . Alternative Acid Mine Drainage Abatement Measures. Proceedings of the 11th Annual B.C. Mine Reclamation Symposium. Campbell River, British Columbia. Apri l , 1987. Robertson, P.K. and Campanella, R.G. (1983). Interpretation of Cone Penetration Tests - Part 1 (Sand), Canadian Geotechnical Journal, Vol. 20, No.4. Robertson, P.K. and Campanella, R.G. (1988). Guidelines For Use, Interpretation and Application of the CPT and CPTU. University of British Columbia Soil Mechanics Series No. 105, University of British Columbia, 187 pgs. 139 Robertson, P.K. and Campanella, R.G. (1985). Liquefaction Potential of Sands Using the Cone Penetration Test. Journal of Geotechnical Engineering. ASCE, March, 1985, 22(3):298-307. Robertson, P.K. (1994). Suggested Terminology For Liquefaction. Proceedings of the 47th Canadian Geotechnical Conference, Halifax, Nova Scotia, 277-286. Robertson, P.K. and Fear, C.E., (1995). Liquefaction of Sands and its Evaluation. Proceedings of First International Conference on Earthquake Engineering. Tokyo, December, 1995. Robertson, P.K., Campanella, R.G., Gillespie, D. and Greig, J. (1986). Use of In-Situ Testing in Geotechnical Engineering. In Situ '86 ASCE Specialty Conference, Blacksburg, West Virginia. Rossabi, J. (1993), "The Savannah River Technology Centre for Environmental Monitoring Field Test Platform", in Proceedings of the U.S. E P A / A & W M A International Symposium on Field Screening Methods for Hazardous Wastes and Toxic Chemicals, Volume 2, pp. 749-761. Sasitharan, S., Robertson, P.K., Sego, D.C. and Morganstern, N.R. (1994). State Boundary Surface For Very Loose Sand and its Practical Implications. Canadian Geotechnical Journal, 31(3):321-334. Seed, H.B., Tokimatsu,K., Harder, L.F., and Chung, R. (1985). Influence of SPT Procedures in Soil Liquefaction Resistance Evaluations. Journal of Geotechnical Engineering. Division, ASCE, 111(12):1425-1445. St. Arnaud, L.C., Aube, B.C., Wiseman, M.E. and Aiken, S. R. (1994). Proceedings of Third International Conference on the Abatement of Acidic Drainage. Pittsburgh, PA., Apri l , 1994. Stark, T.D. and Olson, S.M. (1995). Liquefaction Resistance Using CPT and Field Case Histories. Accepted for publication in ASCE Journal of Geotechnical Engineering. Sumner, J.S. (1976). Principles of Induced Polarization For Geophysical Exploration. Elsevier Scientific Publications, Colorado. Suzuki, Y., Tokumatsu, K. Taye, Y., Kubota, Y. (1995). Correlation between CPT Data and Dynamic Properties of In Situ Frozen Samples. Proceedings of the Third International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics, 1, St. Louis, U.S.A. Telford, W . M . , Geldart, L.P., Sheriff, R.E., and Keys, D.A., (1976). Applied Geophysics. Cambridge University Press. Cambridge, pp. 442-457. Torstensson, B.A. (1984), "A New System for Groundwater Monitoring", Ground Water Monitoring Review, Fall 1984, pp. 131-138. Urish, D.W. (1981). Electrical Resistivity-Hydraulic Conductivity Relationships in Glacial Outwash Aquifers. Water Resource Research. Vol. 17, No.5, pp.1401-1408. 140 Van de Graff, H.C. and Zuidberg, H . M . (1985). Chapter 2, Field Investigations, The Netherlands Commemorative Volume, ED. de Leeuw, 11th International Conference on Soil Mechanics and Foundation Engineering, pg. 35. Vick, S.G. (1983). Planning, Design, and Analysis of Tailings Dams. BiTech Publishers Ltd. Vancouver, British Columbia, Canada. 369 pgs. (2nd Ed. 1990). Vick, S.G. (1991). Inundation Risk From Tailings Dam Flow Failures. Poceedings of Ninth Panamerican Conference on Soil Mechanics and Foundation Engineering, Vol 3, pp. 1137-1158. Weemees, I.A., (1990). Development of an Electrical Resistivity Cone for Groundwater Contamination Studies. M.A.Sc. Thesis, Department of Civi l Engineering, University of British Columbia, Vancouver, B.C. Woeller, D.J., M.P. Davies, and P.K. Robertson (1989). Use of Recent Cone Penetration Test Technology In Evaluating Geotechnical Properties Of Mine Waste. In proceedings 1989 Vancouver Geotechnical Society Symposium - Geotechnical Aspects of Tailings Disposal and Acid Mine Drainage. Woeller, D.J., I. Weemes, M . Kokan, G. Jolly, and P.K. Robertson (1992)," Penetration Testing for Groundwater Contaminants", in ASCE Engineering Congress, pp. 76-87. Woeller, D.J. (1994). (Conetec Investigations Ltd., Vancouver, B.C.). Personal Communication APPENDIX A - RCPT CONEPLOTS 142 0 z H h (/] TJ a a +> w ~a n CM CM n * Oi i a n u oi z a * z H m a a Z T 3 a w D h H (/) Z i H 0 CD a a> UJ i a oi I n I C3 a a Ul Ul < a a a ui en < CD m T _i i- a H • U a. M z a a z ui a ui H z i-H < 13 U z a Ul -J 0 a I I Pre-Bore | Silty Clay . Silty Sand ' Sensitive Fine-Grained. Compact Qanri With OallU Willi Interbedded-Silt Layers | Refusal | a ih o i / t I • • h •ri 6 I - M P i i i i 143 144 TJ a a CM 3 o n n CP 0 — z a H1 h (/] D 2 UI I Q H (/] z H UI cc i n 0 1 ui z o o CO UI a o 10 D < o o ( s j a^au j ) H ld3Q 145 TJ a a v CM TJ o -n — n * 0 — in / H CD o e O 1 t O £ U J £ z -> H ° ct o o h " T o (/] U i •*-» ce ro 3 X to t O H -LU ^ C L E U J c | ro (/) CD ' C L C\J O D I h H if) Z H 0 00 D < o o u V) UI a o a co a . M z a or z u i o UI t-H Z I -< C3 O Z O UI _ l V a Q 146 ra TJ n n n o> i TJ a a CM 0 IH i 2 O O < u. 1/1 f-(/) u h D 2 h i H (/) z H 0 CO n ui < a »-> a. u o I — i - 7 1 1 1 1 1 1 1 1 "8 >> a Compact Silty San Compact Silty San Interbe Layers Loose: Sand a Clayey o m in ;LEEVE FRICTION Fs (bar) i 2. o in o in FRICTION RATIO Rf=Fs/Qt (X) ) 5 a <u o ( s j a^au j ) H ld3Q 147 148 ra V n n TJ a a CM 0 H | il/) h O < co o n to D 2 |h H (/) z H u CO D n CD 0 1 z ui < CO _ l < ( s j s ^ a u j ) H ld3Q 149 I CD Z H h (/) bJ i h D h H i(/) Z H u CD D TJ a. c a O CM 0 D i i XI CO 0) o 1/1 0 - CM — D T O a* co 1 D n CM o 1/1 i ui o\ or o u UJ H z < o o o < i -z CO o z o •d — 1 i San ipact nd ase to mpact and o CO o usal 0) E co ase to mpact and > Ref (A C 01 o w u o o w -J u ra z Ref Q-( s j 3 } a w ) H ld3Q APPENDIX B - RCPT INTERPRETATIONS CPTINT 5.0 - List of reference sources Originally from the Reference section of the f i l e INTRT2.TXT for the program CPTINTR1 version 3.05, written by JAMES GREIG. This section was extracted, revised and new information was added for the program: Program: CPTINT - CPT Cone Interpretation Program Version: 5.0 Written by: Thomas Wong and R. G. Campanella University of British Columbia Department of Civil Engineering REFERENCES 1) Bellotti , R., Crippa, V. , Pedroni, S. , Baldi, G., Fretti, C , Ostricati, D., Ghionna, V., Jamiolkowski, M., Pasqalini, E . , 1985, "Laboratory Validation Of In-Situ Tests", Italian Geotechnical Society Jubilee Volume for the XI ICSHFE, San Francisco, Cal. 2) Ourgunoglu, H.T. and Mitchell, J .K. , 1975, "Static Penetration Resistance of Soils: I-Analysis", Proceedings of the ASCE Specialty Conference on In-Situ Measurement of Soil Properties, Raleigh, North Carolina, Vol. I. 3) "Earthquake Design in the Fraser Delta - Geotechnical Aspects" Task Force Report, May 1991 - Co-chair: Dr. P. M. Byrne, Univ. of British Columbia, Dept. of Civil Engineering, Vancouver, B.C., V6T 1Z4. 4) Janbu, N. and Senneset, K., 1974,. "Effective Stress Interpretation of In Situ Static Penetratuion Tests", Proceedings of the European Symposium on Penetration Testing, Stockholm Sweden, Vol. 2.2. 5) Jamiolkowski, M., Ladd, C.C., Germaine, J .T . , Lancellotta, R., 1985, "New Developments in Field and Laboratory Testing of Soils", State of the Art Address for XIth ICSMFE, San Francisco. 6) Robertson, P.K. and Campanella, R.G., 1983, "Interpretation of Cone Penetration Tests -PART I (SAND) and PART II (CLAY)", Canadian Geotechnical Journal, Vol. 20, No. 4. 7) Robertson, P.K., Campanella, R.G., and Wightman, A., 1983, "SPT - CPT Correlations", Journal of the Geotechnical Division, ASCE, Vol. 109, Nov. 8) Robertson, P.K. and Campanella, R.G., 1989 "Guidelines for Geotechnical Design using CPT and CPTU", Soil Mechanics Series NO. 120, Civil Eng. Dept., Univ. of B.C., Vancouver, B.C., V6T 1Z4, Sept 1989. 9) Robertson, P.K., 1990, Soil Classification using the CPT, Canadian Geotechnical Journal, Vol. 27, No.1, Feb, 151-158. 10) Schmertmann, J .H. , 1976, "An updated Correlation between Relative Density, Dr and Fugro-type Electric Cone Bearing, qc" Department of Civil Engineering Report, University of Florida, July. 11) Seed, H.B., Idriss, I.M. and Arango, I., 1983, "Evaluation of Liquefaction Potential Using Field Performance Data", Journal of Geotechnical Engineering Division, ASCE, Vol. 109, No. 3, March 1983, pp. 458-482. 12) Seed, H.B. and Idriss, I.M., 1971, "Simplified procedure for Evaluation Soil Liquefaction Potential", Journal of Soil Mechanics and Foundations, ASCE, SM9, Vol. 97, Sept. 152 I I O II • II i n II n t— C M < O H O ~ - II • in II N . t- II rsi 4 ) II ro > II o» II • i n m II <M h- II — as II ^ « II 4-> II c II •— II § : : II n 01 II •• —• II U J • ~ II _ J H - II ~ " 311 >-CL II 3 U II V H - II U c o a >-o CO 3 o u * J II 3 II O II 01. U 3 2 ' to "0 c < u I/) < co o o o o o o CO o • +-• • CTO> ^ <\l O o o co z « - z CI c n c V o «-» CO (D *-» II I— »~ co co L U «j IO CD O 3 ° 4-> —< 0> C C •- Q. O » U . O U >-Of < ° a TJ O 2 "o • • <fl a « i 6X1 c. CO C C 3 • - o in co +-< v o a o • -OIJ3 ••- 4-» *-» C I I V C ID - I- '~ OI--(0 •— 3 10 L VI 01 U at to 2 — 3 w _ a o to u o "in 3 ci ' c c o <- c 3 o o o H-I- H- ISl cn o c - o H - CI TJ • - O 3— in J = - —< i/j * J CO tQ tD 01 - > > X X to •• l_ u 01 o *^ go to to . . i_ o •• V* to 01 j<: a . t- —< z o cn TJ H - c « C _ < c to >. to co « c — o 10 I c o — w 0 * - J3 U U »0 </l «-01 U) u. J Z 01 01 f C c. 0 a o 01 U TJ oi c o 3 « - - g J : ta oi to oi > o co x "8 c * •jo-g cn ra <o oi c >. 10 (0 to <0 to </) H • —' (0 *v ••-•*- fO C 01 CD CO u- CO O > CO II II II II II II O « - CM 01 01 01 0) 01 01 c c c c c c _ O O O O O O TJ N N N N N N O "8 u c u o to ^ l_ "5 Ol—• c to CO 0) — C c •p 01 oi H- * J 9 ' 4-* CO oi e (0 — —' > —' «0 — W-— o o t o - ; >. O • - c >. 01 >. to Vi to >-Tl C C OI to w n c o 01 u • . — • ro u CO O CJ CO U CO c II II II II II II 01 « - (M 8 ~r m o > % % % « : « O 01 01 01 01 Oi 01 « c c c c c c o o o o o o N N N N N N _ 3 O 153 a a. 3 . * Ui w *N o 4-* —» Q..O (/> w •M 0 —• ui w at 01 c O I — GJ - C T J a. w <-»« c O V N C o CO w O H - N a: w ? 10 w (D </> a . O UJ w K l f ' e >» z IS o E I to - C — U J o Of V < t-O U J > Ul _ i a l. M W ffi U . X) a ~ o . z » L. f 01 4-> 4-* — a . oi • 01 e 2 £ ( \ i ^ c o ^ ^ i n i n c \ j < \ i ^ C » e o i / > i n i n i n i f t i n i n i n i n i n o o e o ^ o ^ w i c o c o e o c o o o c o o o - o - o -o o i n « - < \ j o o O " - r \ j « - » - « - » - o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o c > 154 "8 c « 2 "8 CO CO I i ! O II • II m II II i— C II < O II o • - II • CO II o t- II to w II to > II o • - II — H II C H- II U II  II II II II II II II II OJ II —• II U J — II - J «*. II — II u . w II 2 II i -Q . 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O UJ w • o E I ( O f — u i o < o 0> o- C M E w u o t » o > o > o > c o e o c o o o c o c o e o e o c o c o a c o c > o > o < o t O > c * o > c * i c o c o c o c o c o o o o o o o o o o o o o o o o o o o o o o o c o c o o o c u i u j i n ^ 0 3 c > o « — r n » 4 " i n ^ c o o * o « — t O x t i n > o o o c > o « — r o > » i / ^ ^ o o o » o « — t o ^ r i n o » c > « » i o c M ^ ^ o c > c o N . « o i / > > » > * f O r u « - o o > c o r v . t x . > o i n > * f O C M » - o ' " ' ^ < l ^ * d ^ ^ ^ ^ ) ^ ^ ^ l A O U 1 0 l f l O l A O l / 1 0 i n O . J C * ^ C ^ < C * > J C > ^ C * ^ t C O I O C O M O O M ( O O T C O M C O N N N K N M M < f . * i n t n < l ^ S N C O c o c ^ C ^ o o ^ T - ( y N M M ^ ^ ^ u i i n « < ) S S c o c o C > C ^ o o « - * - r j p j n M ^ ^ i n i n < ) ^-v-CMCMCMCMCMCMCMCMCMCMCMCMCMfMCM c\i rv. 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Z ^> M [_ J C 0) fe* fe* — a oi • at E • o ^ o>e>o^ o>e^ o>e>CK<^ o>.c><>o>o»e»»c>o><^ eKCKt>c^  U J U J U J U J I J J U J U J I J J I J J I J J I J J U J U J U J U J U J U J I J J U ^ o * c > c > c > c > c > c > c > c > c > c > c > o * c > « - o i * i i - c o v i t > * - o > ' - » > t o « - ' 0 ^ o K i < < » i n O x * ru oo Iv. t> u-> C M » - «\J « - CM C M C M C M C M C M » - M «— C M « - « - « - • - • - . r - ^ - T - ^ - ^ ^ | M I M I M O O O O O M C > O M C M C M B a K s ^ s s s s s S c M a c M , ^ ^ 33358333333^^ O » C K C K C K 0 * 0 » O ! C K I > C > C > C > C > C > C > C > C > O > O > C ^ «— « - o ^ ^ ^ r - ^ ^ « - O O O O O O O O ^ O r - « - ^ 0 « - ^ ^ ^ ^ ^ « - » - K t t N I « — « - 0 « - 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 158 C o M II o> it II c o II II m II <J II 1- i CO c II < • 01 o II O • *-* II 0) II to • c c II to I o a 01 II to I u. >-> II O I o II 1 CD 1 II II o • 01 • t— II U . 1 lit ~3 Z II 0" 1 c II *-» t 3 z t- II c • O o . 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W ID "8 C t-o CO •>» CO CO 01 •— C u TJ 01 01 W *-* 4-* a >—• «rf to oi 6 co •— —• "o > in — — •— O O B) —' " — >- o c >• oi >> ui CO > .w >-TJ C O) CO —> CO c o c/l —' CO in o o co c j co ii II ii ii ii ii « - to jo xt in *o O 01 01 01 01 01 0> * c c c c c c o o o o o o N N N N N N o • • I VI U l • I- 1 t-o • o 01 oi c 3 O in c CO o UJ o OJ o 159 CO CL in w z 4-» —' O.J3 CO V *>• —' Q.J3 CO w 4) 4) c CO — 41 J = T ) a. w • - » < a w ^> 4 1 * O C T N ca w 4) * 0 41 1X1 C O **— N CC w 01 > a w (D co a . o LU w ro <s'e g »%. E z CO Jjf I C ? • O E • co j z LU O l— • c IO 41 ro «v 1 => w o u -c a<«-»t U O C v y U • • Ol<"N LU > CO J I L — CO u . J3 a v i — a. z L-_C 4) — a « • 4i e i O w I I 0 * C * L n r O C > 0 * C * O ^ C > C > 0 ^ ( > C > C > C > 0 ^ •JJ IJJO^xa-UJLUIJJ iJJUJIJJLULUUJUJUJIJJU^ o ^ o ^ c o i o o ^ c ^ o ^ o « c > a c > o ^ & c > a c ^ cNjrv! i n t - » - <o co co co r^ - o m « — *o r\j o ro > O N f O v t o g o - j i n T - r o N cviro co o CM so o o a O s r o j * i N j i n f \ i CM O CM O CM i n <o co a CM O r>- <o « * V— r- •— «— »— «— «— V— *— *— *— *— •— CM «— Xf » -^ c > ^ ^ c M P d C M v * o a 3 i n « — ^ o « — o * c o c o i n < ) * O x f x 3 - u ^ r ^ r x - L n > o c o r ^ i r o i M o i Os Ov cjt Q> tjt Cjt O* O* 0 s o» Cj\ cj* Cj\ O* CJs cj* o» o Cj\ Cjx ox o» o* o* o* o» O* O» O* u j i ^ i i j i u * - « - f - ^ « - < - « ^ O X r x N N N i n n n i u u j i u u m u j i n f - L U f - i A i o « - m m u c > < i < > c ^ s r x r % f ' * % t * » < i i o i o r o i o r o r o m r o o * O ^ C > c ^ M J O* O * 0« C3* C3* 0« ©» O* O* O* cj* o* CJ * Cjt CJ* C?* O * O» O * O * o « ^ u i i i J O * r o c o i x - c > c > i n i y i x f * 4 - i o u ^ c > r o c M L ^ ^ M j c > c > r o u i x j s j N j i n i n s s - r o t o r o c M * — * — « — O O O O O O C M * - C > C M * - t > o o o o o o o i o o o o o o o o o o o o o * *o *o *o m i n ^ i f i O | n o < ' « 0 ' ' - * < ) 0 > ' - ^ < o i n o i n o i f i o i n o i n » i \ i N N ' O O i n o i n o i n o i n o i n o r o x » ^ r x - o ^ o * - c M x * u ^ ^ o r x . c > o ^ f o > * > o r x - c > o c M r / o i n v o r ^ C K 0 * r x - x T « - « r x . N O L n x * r o C M ^ o o o ^ K - v j T - c o i n r O o r ^ N S N N i - < o V x ) V i a ^ < i ' - > ) o i n o i n ( > ^ a > } a — j - o c o r - r o u i N o r j s j s r > » - s j v O • " i - N i \ i n r o < r M i n i n < ) > ) N N c o a 3 c o o > o > o o i - ^ N f « r o i O v f x r i n ^ • - • - « - » - ^ » - « - ^ « - « - . - « - « - « - « - « - T - « - « - > - C M C M C M C M C M C M C M C M C M C M C M t M C M C M C M C M o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o • 0 ^ s o ^ u ^ i n i n i n i n i n i n i n i n i n * O ^ M 3 * 0 ^ 0 ^ 0 > o ^ x D N O L ^ c o c c c o c o < ) ^ o ^ x O s o < > s 3 N O ^ x ^ a 3 c o c o a 3 c o c o c o c o c o c O H O c o o o c a O s c o c o c o c o o s O s C > > o * c > ( > c > c > c > c > c o c o c o c o c o c o c o r a • - f k o o e o m i n S o i - c O N N K i c o s o i D r - o o . " — * r > - « » e o o c M i n t v < o r v c o r o c o r x . < r o > o c M ^ o * f c M O > O r ^ i n r - i - B N M O ' i n M - 0 % » r O M < ) O C O n o N i n N O C k N M m » - ' O N O > 0 ^ r > m « ) < - C A c o N o k c > o i n i n » S ' ^ o i n a i \ i O f - i n ^ < - c > N S S N < > x r a r x - c M > ^ « - » - c o c M i n « * C M C M ^ i n c o r O i N . ^ M j | x . < o S - < o c > ^ r x - r o ^ i n «— T - T— C\J «— «— « - « - CM CM CM « - CM « - CM « - » - * - « - CM CM « - « - CM « - « - « - « - « - « - « - • - « - CM « - CM O O O C M O O O O O O O O O O O O O O O O O O O O O O O O O O O O O t - O r r N i - N N r - i - r - i - r - i - i - i - ^ N N N ^ ^ r r - ^ ^ N N t - i - ' - ' - ' - N i - ^ ' - N ' - N i - i - r r o - S S t S K S R r o K S S K r o R ^ o o o o « - « - ^ * - C M r M C M r j M M M i o * * N * N * s r i n i n i n i n 160 a. 4-* **-o 4-* —' O..Q CO w Z 3 o 4-> —' CO w OP OP c D) — V -£= TJ a. w a w a** O 4) IM C O cr N CO w ^% aj« o OP rvi c o H - N DC w ^x O) > 10 ^x w CO co a. o LLl W IO I E 6 *-» E z CO ^ CO w : i c E • O E I CO - C — u i o Of w t -< 0 • f-tO 01 to to 01 O N E 1 3 x> o C * J ^x O O C v u ^% • • D l ^ UJ > » —J CO C LLT * J 5 a w i— 3 o. z •—• l_ f 01 — a j) • oi E m o i » » i > - i n ^ o < » > 0 0 3 > 0 i n o * e g ^ 0 v ^ x » e o t n i n o i n c 0 f n > o i > < r - i v * t c M f 0 ^ i > - x * f x . f x . t x . \ o o ^ o * O f O O ^ ^ c > ^ i n r x . o i n r x . x r ™ ^ K x i ' C M ^ ^ x » v t c > » f r i ^ < o ^ o » i o ^ ^ r v i x * i v c > « - i V c M ^ t o > * i n i n i o c > c ^ od co >o «^ <o «^ 6* <o s f CM v t m i n o> C M CNJ O i n « - CM s f >o to to >o ~t m . » c o c o - * t o - o c M i V t o > » C M » - CM « - >o co co co o » . O >C CM xt tO CM tO xt v» «0 » - i n tO ^ IV O* O 00 xt >0 CM CO « - (V CM CO IN. * - O *0 m tO •— m O 00 O r O O O I A I M t - ^ O N l O C O i - o S e o o c ^ c O { > c ^ t - N ( > o w £ > ^ o c > ^ o o » - S M O O ( > c > r - o f \ i n n M O r - i / i ^ r o r o > j r o c > f \ J i n » - ' 0 ^ r g f y N > j r o f O M i n i r i ' oj O; 00 oj O; 00 oj 00 00 « o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o C O f v i > » ^ c O i ^ r ^ r ^ f > ^ r o > O r ^ N ^ i y ^ c o t n ( \ J C \ i ^ c \ i f \ j ( N J ^ r O N * i n ^ c \ i t o r ^ > t M > * i n r o M 5 N « - ^ o ^ o p ^ t f \ i n > * M M ^ ^ ^ f N J O t n o ^ c > * - * o e o ( > o > w h O ^ C O r O C \ J > 4 - S - i ^ r v J i ^ C O ( ^ r ^ r ^ r ^ t - > 0 ^ i n > t i V > r O N r - 0 ( > O l O « - O N N O > t i r \ > 0 ( > W ^ 0 « - ^ ^ K M O « - s » 0 0 > t * - l f t N ( > M ) ^ * O N T - t > N » - ^ i - O U ^ > 0 ^ « - > 0 > o ^ < > C h o o O N ^ o ^ o o o o s t r > o o o < > « - N « - s o N * o S r - » - e o M ^ N f O ( a t > ( > ^ i n t > > O i n o ^ i n o » c o o > O r ^ r v J i n c x ) N j o N N l o o o o e o o e o o o * - N ( \ i o * - « N J C o i n M « — * c ^ ^ c o i ^ c > o r o « c o ^ > x f c o f O CM f\j «— ( \ J CNJ «— C\J c \ J C U ^ ^ r A i ^ « - ( \ i r u « - r j ^ o j ^ t % j ^ T - c j c ^ o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o i/^oinOLnOLnoinoinoi/^ou^oinoLn > J > t i ^ i n u ^ i 7 > > 0 > 0 > 0 < ) N S N N C O C O C O W T - i - T - r - T - r - T - r - » - r - * - i - f ^ i - r - i - i - T - T - ^ r - r - r \ I P J < \ J { \ J ( \ J N N r J N A J 161 CD o. 3 (/> «- ^ Z 3 O *•» —' Q..Q H -z ^ 0 4-* —' m a CO w 4) L-01 '•- 01 J=TJ a . w g * o oi IM C O cr N CO ^ ^x 0 1 * c O 01 IM C o oe CO CO c/i a . o LU V to J B ' E E E z CO J * C9 w I • c n E : O E I CO JZ LU O I— < • c-ro oi to to o O CM E *N Q . H - » < O K U X * U • • O l A LU > CO J • L •—i \^ (D U. 4-> J 3 a ^ i -a . z t_ j= oi 4-» +-» CL 01 • 01 E I Q x^ c o t ^ c > i > - © ^ i n K t i n i n ^ i n f M i n c > t w i n i v i i N . c o ^ N i o r « < » s t S S i o c > o « - i - ^ 0 > N ' O r » i n i n N m > - c \ i < - r » c > o c ^ r M C M i n o o < M i n t n K ) c o ^ ^ ^ N > i V i n c > r J t O M j c > r - ^ o > o c > c > i n K ) > o » » ^ C > C O ^ i n t ^ ^ M i p J ^ M N t ^ l ^ l ^ O C O I O x » M o c o c o r o c o K ^ a c M O ^ o i S - c o ^ ^ c M r o i o i n c M r o i n r o o o i M < o r » - « - « o m - * « - » - c M f O O ) «-CM * - s t s t » - i A w i o » - m K i N O f o o N O « - 0 ' - o o o a c o c o o o o ^ » - o « - o r > * - « o * -— *— *— i— *—«— «— «—«— »— •— •— •— «—«— •—»— •— «— « - •— »— xf 0^C>»C^O^C>C>C>«C^C>C>>C>C>C>O^C>>O'0*C>C>C>'C>C> H I i t tit til til I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 111 til I I I I I I I I I 111 111 I I I I I I i n U J 111 U J U J U J I1J uj C>C>C^CJ*CJ\C>C>tC>C>C>C>C>C>C>C>C>C>C>C>C>C> tit ti it til H I H I H I H I H I I I I I I I I I I 111 til lit I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 111 U J 111 I I I 11J U J I U U J U J U J U J %n CM C > O t ( > C > 0 > > 0 « 0 * 0 ' C > C > C K C > C > C > C > C > C > C > C > C > C > C > C > C > C > C ^ e o c > c > c o O ' O t O t c a c > o c d c o c o c > c > c > c > c > "8 c « II 01 II •• —' II U l '— II —I >*- II — II u -* J II 2 II i-Q . I I D 4-< II IX 3 II Z O II -01 c 8-CO u >. c o 111 CD Q. II c O II • II J C in II u II co C II 01 O II *-* — II 01 II C l — II O 01 II U -> II Of • II o • • II CJ I II 01 1- II CO Z II (_ — II •* i I - II o • o a. II i— i (J CJ II CO I CJ EJ II C3 • CO O 11 y i 3 c II •4- 11 CO • U TJ uiTJ c < 01 u o o o o in oo • . 4 J . • <0 0 ~ » J C I M O O •— CO «— z«— z o o o II o >-o CO CM s t- o CJ CO CO - J 3 9! 1— CM E • 00 CO Q U l a. ocr 1— • • 3Z UJ I— 1— UJ 01 4 J . . 01 00 01 L. a l _ 3 o >« >-a. z * J i— DC c_ CO < 01 01 1- 01 3Z * J 01 c SZ c ••— a. o 3 •-• u . O CJ 00 o Q. TJ 01 ft TJ • CO oija c co CO t-_ . 41 O CO o H— 01 3 CO •• C u 3 f « O l / K O J C O . — Z ^ O OI TJ D P C P L 0 ' - C O 4-» *-» CO 00 H - £ O P •— CD—• C/l t_ 01 •— 3 C O II « l ) 0 4 -CO 3 —• O —' ra so U V U II £ 01 U C L V C C 3 O O O **-**- M N OI O C TJ 01 O I I c •— CO J= 3 •— —' CO 4-> —' H -C0"— 0) CO 01 > Z Z > Q ""8 CO O 2? CD CO CO 01 c >-CO CD U) N ' <t- O —• *J o —' CO -M >» 01 01 TJ > >«TJ — C C CO L . c ••- co t- ai co 00 U - 00 CO > C/l II II II II II II O r - I M » - 00 C * « - « - <r-CO c VI CO o o o o o o ISJ ISI CM CM CM ISI "8 ID e u -ro 01 C I— 01 CO ' *-» ID 01 E CO •— —• TJ > VI — • - O U V) —• * *« - >. o — C >. 01 > » CO to co > .« >.-n c C OI 10 —< 10 c o 01 C —. •— —• ID O CO O CJ 00 CJ 00 t_ II II II II II II 0> «- rufo ~t m>o > % % % % % % o 01 01 01 OI 01 01 * c c c c c c o o o o o o IM ISI IM ISI INJ IM 01 OI c ID Of Ul c CD 01 E o U J o 163 a a. CO V Q.J3 CO ="3 JO T ) a . v c O 41 IM C o triM CO 01 % o a CO > CO w CO cn a . ec (M E O 2 v CJ u c c w m • • CO LU > CO _i a c M w CD a w — a. eu • ai E l O w i— f\j f\j x— f\j p j »— o o o o* *o *o o o o* o» 0* CO CO CO CO CO CO CO CO CO CO CO CO CO CO CO M N N M ^ r - S S i n i f l « f I O M M ^ O * % l ^ N N < - t - l > I N ' - N N ^ O : - 0 0 C M f O « M « M C M C M « - « - « - « - » - « - » - ' - « - C M < ^ « - « - « - « - » - « - « - « - « - ' - ' - « - « - ' - ' ^ ' ^ i n ^ 0 0 i n » * N » ^ ^ O O C > C > C > O ^ t » . r v . i n t 0 C M C M C M C M » * » * » » i n ^ l ^ 2iujijjVininro<-~^<*o>e>o»rv..-^c>c>r«»r^ S » S 3 3 i 3 > » * < * l o M f i n i o * < f n n i o n n M n n i o n )0>o>c»coeocoeooocococococor>-coooo3coooeooocoooooooeoeooocoooo3aacooooOM e o r > e o e o e o o o e o o o e o e o r v . c x . r v . i x . r « . c o e o c o o o o o c o o o c o c o c o o o c o c o a j e o c ^ o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o 8 3 3 8 3 8 3 3 3 S S S S v e ) « S « » c i ^ * o * > ^ ^ ^ ' O N O o o CO UI e g >st CM XT o o •O m O E CO JO ro ro UI CM u i o co co Of V CM CM CM CM c8 in § ro m CO • * o o r -ro co xT O ro o «— 3 m o >» «» r -o CM co o m CO CM co o CO ro i n o r«! o ro CO i o NO o o NO m f> m CM i n CM «o .— O O <o • - CM CM CM ro CM i n CM CM ro o ON VO ro CO CO CM CO O ro .— o i~ CM .— i— ro CM IN- oo ro «— r-ro CO * - ro m «» ro r- CM CM CM CM CM CM o o o o o O o o o o o> N . vO m ro m m *— m ro m m s in fSS8 •* co CM > » «* CM xT 00 CM «*• o r-«* •>0 r-. vO CM r~ r--m xf CM in -* .397 .403 in o m CM ro ro .362 .373 o o o o o o O d d o O o o o o o o o o o o o o o o r x . r N - r x - 0 * i n t o i n r o r - r > - O C * r O i n r x - - £ C M 0 3 ^ C M c o c o » O M O ^ i - o c o S i n r o N o n o i o o r - t - N M O i n ^ s s M Pi ^ v— «— ^ O O O O O O O O O O O O O O O * 0 O O O O O O O O O O O O O O O O O O O O > « - o c M o o « * « o « - r o N . v t m » » m S . > o c o o o c M * s O C M r o i n N O i n r o r o c o c > * - i n i n r o * v t r o c M r o r o i r o r o r o r O M r o r o r o r o M « * r o r o « * > » « * « » > » » » to = 2! (/> w «. •M H-5 ^ o CO w ^ % * * H -z ^ 0 *-» —< c o . CO w V 01 L . CO « - eu J= T J O . X* -^x Q X^ ^X c O 01 i x l c o C T N m w o>% O 01 CXI C o CD > CO ^ x x ^ CO CO O -O Ul xrf ^ x K l S ' E g ^ x E Z CO 13 w ^ x fx. I O E CO J= uj o C£ C M O => u «~ «— x » 0 I— 1 *"X C O H - X U U C x . CO ^ x . . C D ^ x UJ > CO _ I CO L . Lu 4 J J j or x ^ t— => C L Z ^ x —• L . J= 01 *-» *-» CL «J • 01 £ I Q X^ O x C S C x C > C > ' C S C ) * C > C ^ O » C > * C > * 0 O C > * O * O * U J U I U J U I U J U J U J U J U J U J U J U J I A U l UJ UJ O * O * 0 s O * O . O . 0 * O * O c*» CJ* Ox c o < > o > c o c o c o c o e o c o t x . x O m x i ' t n > O L n CM K l M K I M M M m n s l g g x ; SSR:CM!MCMCMK5SS^ CIS^ O1 o o c o c o c o c o c o c o c o c o c o c o r x . x 0 t x . c o o C s ^ x * x O C > T - x t x O r x . f x . r x . c o « - K » i n i y j i n h x c o t > o c M K i x r o O x j - o x o r o c > i n » -x O U 1 x » M t O C M » - O x t 0 . x J - r x . O C M x O C M | v r j r x . ( M r x . c M i > - C M i n r x . o c M i n r x ^ c s i > j c o c s t > o o » - » - c M C M C M r O i O r O M i y > x j -o o o o o o o o o o o o o o o o i n m i / i i n i n i n i n i / i i n i r i i n x ) x ) x } i n x t x O O O x O - O O O x O x O x O O C O c O o O x O x r c > c s c > c s c s o > c s o > o « c > c > c o o o o o o > o « - « - « - « - « - T - « - « - » - . ^ » - « - « - « - « - C M • y i o i n x O x g x ) - r x . r o o i o c o o o o o o O O ^ C M N 0 m « - 0 0 C M x J - O C \ J O O O O 0 0 < O M O O x O O O r x . | / » O C M C M O O O O E j - x * x O x * r o m M M C M « - x i - o o o o C 0 r x . L n r O i M t M C M C M C M C M C M < -g i i x i s i p . s i s i s s p O O O O O O ^ i - ^ t - r - O O i n « N O O O O O O O O O O O O C M C M C M O sssKSsss ' sSx iP i tSx?^ 165 APPENDIX C - RCPT PORE PRESSURE DISSIPATION PROFILES FILE: 119-9323 DISSIPATION AT DEPTH : 1.2 m U2mH20 0 5 10 15 20 25 SQUARE ROOT OF TIME (sec.) 167 FILE: I19-9323.DIS DISSIPATION AT DEPTH : 2.2 m U2 mH20 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 -3.0' -3.5 -4.0' -4.5' -5.0' + + ^  f + + + SQUARE ROOT OF TIME (sec.) FILE: I19-9323.DIS DISSIPATION AT DEPTH = 3.2 m U2mH20 6.0" 4.5" 3.0" 1.5" 0.0 -1.5" -3.0" -4.5 -6.0+ -7.5-1--9.0 -10.5 -12.0 + -13.5 -\5.0J-f + + H ++ + ++++ 10 SQUARE ROOT OF TIME (sec.) FILE: I19-9323.DIS DISSIPATION AT DEPTH = 4.2m U2mH20 5.0T 4.5 4.0 3.5-3.0-2.5 2.0-1.5-1.0 0.5f 0.0 0 SQUARE ROOT OF TIME (sec.) FILE: I19-9323.DIS DISSIPATION A T DEPTH = 5.2 m U2mH20 20-18-16" 14-12" 10-8-6-4 -2" 0 0 10 15 20 SQUARE ROOT OF TIME (sec.) FILE: 119-9323.DIS DISSIPATION A T DEPTH = 6.5 m 7.0T U2mH20 SQUARE ROOT OF TIME (sec.) 172 FILE: I20-9324.DIS DISSIPATION A T DEPTH = 2.2 m SQUARE ROOT OF TIME (sec.) FILE : I20-9324.DIS DISSIPATION AT DEPTH = 3.2 m SQUARE ROOT OF TIME (sec.) FILE: I20-9324.DIS DISSIPATION A T DEPTH = 4.2 m 5 -4--3--2--1 0 -1--U2mH20 -2 --3---4 -5 -6 -7+ -8 -9 -10-1-f 1 + 5 10 15 SQUARE ROOT OF TIME (sec.) FILE: I21-9325.DIS DISSIPATION A T DEPTH = 2.2 m U2 mH20 SQUARE ROOT OF TIME (sec.) FILE: I21-9325.DIS DISSIPATION A T DEPTH = 4.2 m U2 mH20 6.0 T ,4.5 3.0 1.5 0.0 -1.5 -3.0 -4.5---6.0---7.5---9.0 -10.5---12.0---13.5 -15.0 10 15 SQUARE ROOT OF TIME (sec.) FILE: I21-9325.DIS DISSIPATION A T DEPTH = 4.95 m U2mH20 6.0-5.5-5.0 4.5 4.0" 3.5" 3.0 2.5 2.0 1.5t 1.0 T T 0 10 15 SQUARE ROOT OF TIME (sec.) 178 FILE: I22-9326.DIS DISSIPATION A T DEPTH = 3.9 m U2mH20 10T 9 8-7"-6f 5 4 3" 2-T -0 0 -f-10 15 SQUARE ROOT OF TIME (sec.) 179 FILE: I23-9327.DIS DISSIPATION A T DEPTH = 4.3 m U2mH20 5.0-4.8-4.6" 4.4" 4.2" 4.0 3.8 3.6 3.4 3.2 3.0 0 + -I- ++++ + + + + f + 2 4 6 8 10 SQUARE ROOT OF TIME (sec.) FILE: I23-9327.dis DISSIPATION A T 9.3 U2mH20 25-r 23--21--19-17-15-13-11-9--7---f-+ ++ ++4 R"H-H+ 0 5 10 SQUARE ROOT OF TIME (sec.) FILE: I23-9327.dis DISSIPATION A T 10.3 m U2mH20 25" 23" 21" 19" 17" 15 131 11 9 7t 5 0 H-10 15 SQUARE ROOT OF TIME (sec.) 182 20 r FILE: I23-9327.dis DISSIPATION A T 12.3 m 154- +• U2mH20 10f 0- + 0 5 10 SQUARE ROOT OF TIME (sec.) 15 FILE: I23-9327.dis DISSIPATION A T 13.3 m U2 mH20 20T 19 18t 17 16t 15 14 13-12-11 10 0 + + • { - + , . .++4-, whw 10 15 SQUARE ROOT OF TIME (sec.) 184 FILE: I23-9327.dis DISSIPATION A T 14.3 m U2mH20 20-19-18-17--16--15? 14-13-12-f 11 10 0 r - H - H-10 15 SQUARE ROOT OF TIME (sec.) 185 FILE: I23-9327.dis DISSIPATION A T 14.5 m U2mH20 20-r 19--18--17--16--15--14--13--12--11--10 0 +• +• + +• "r-r--f-"r-t--t-"T" 4- 4- +-4 6 SQUARE ROOT OF TIME (sec.) 10 FILE: I26-9332.dis DISSIPATION A T 6.2 m 6+ 4+ U2mH20 0 -4+ - 6 X T SQUARE ROOT OF TIME (sec.) 187 FILE: I26-9332.dis DISSIPATION A T 8.2 m 10T 6* U2mH20 4+ 2+ 0 •f-fH-"1" # o SQUARE ROOT OF TIME (sec.) 188 FILE: I26-9332.dis DISSIPATION A T 9.2 m U2mH20 10.0-r 9.5--9.0--8.5--8.0--7.5 7.0 f 6.5 6.0-5.5--5.0 0 + .-t H T - +• H-K--W-11 III .111111. .11 lUl ,,111,111111,11111-t — J t SQUARE ROOT OF TIME (sec.) 10 189 FILE: I26-9332.dis DISSIPATION A T 10.2 m U2mH20 15 13 4-12 11--10--9 -8 -7--6--5 0 4. ++4-T-H- + 1 11111 III L-i-J 11 i~*T L]_L 11111 LjX^ r^hTll^ IJ^ lj^ |XLi|jj! IT^1J]X!^11JTJJi 2 4 6 8 SQUARE ROOT OF TIME (sec.) 10 190 CO I CM E CM 6 CO CO CO CD c _o CO a. "co CO Q a »_ 3 CO CO 0) k> Q. 0) t_ O Q . d < </> cj cu j/> 00 uj 2 r— I-a CO CO to CO o> c 'io I-0) CO 3 (0 CM o CO LO CM o CNI LO O LO 191 192 o oo E IN CO CO CO CO CO c _o "•3 CO CL " 5 5 CO Q CD k. 3 CO co 0) + CO LO LO © < CO u to in 0) E F r-CC O CO CO CO CD c 'Jo r-(I) 3 CO CO O a. CO o CO LO CM O CM LO LO ( J31BM J O UJ) Zft 193 195 196 LO CN 197 198 - r - 1 0 CO E CM CM CM CO CO CO CO c o "•3 CO a. "co CO Q CD 3 GO CO CD 1— Q . CD O CL cn LO d < in o v in oj E cc a CO CO (0 CO c a> ro 3 CO LO CO o CO o o co o o LO o o CO CM (jaie/w jo iu) zn 199 ( J 3 ; B M JO ui) z(] 200 + cn (J9JB/W JO u i ) zn 201 ( J 3 1 G M J O U l ) Z(] APPENDIX D - PORE WATER CHEMISTRY C O CO CO 00 00 203 E SI U i <u 0 a. 1 O u z 204 i f CO e <or |£ E o l e t CO . " | Q cT *-* in E CD j C CJ •a c CO c E 0) t_ 3 10 co > '55 . «> 15 3 m t o cc 11 CO g o co CO t o < I-o cc Li. CO CJ < cc r -X UJ g LU DC o CL co E I E I f o LU 1-< I a . _ i co o CM CO x* co IS < a h-Q. CJ CC LO r-x CO LU CC i n l CN O CO o co LU cc i n q 00 CM CO CO i n i n Ico co 00 CO CM I CM i n |cn CM •xf co co i n oo CO CD l o o CM i n i n r» I co I co 31 IS CO CO I co o CO CO CO CO LU cc CO a o co co E o CJ) c '1 ici co CM a . LU a i n O oo i n CO O CO co co o o CO CO CO i n «— CO CM CO CM CO CO CO o r» CM CO ,— CM CM CO CO CO I 01 f U 1 cu V . o Cu O U 2 co 205 </> E a> j= U 0) +-< I o a. O cj 206 CO 00 e CD J= CJ CD w 0 o. 1 o u 2 207 C3 co 1 CD JZ CJ tw <v tQ £ o o 208 13 E o> JZ u t _ <U «-» CO OJ o a. t O u 209 i f 131 '•a < < Q CC LU E x: o C L E . ™ *-» JO E o O E <D JZ U •o c ro E o> 3 OJ <° OJ to . «> 12 3 CO t u cc c o CO ro o. E |3 a c a T J c CJ 3 c o o CO U o M U J D_ o o —I cc LU r— < O > CO cc LU > z < r -< Q c-CL CJ CC LU < I a . _ j co £ CO 3 co E CM co to 1 a> J C O v_ 0J *-» ro o 0 . O U LO r~-O CO LU cc LO CM O CO LU cc o CO LU CC r*-q CN CN O. O d CM cn E lo a . o C N c 5 (ma/I) > CT i "<i r-ir <r : u CN > cc ) c ! ir > oc IIN22 1 z (mo/I) IT o Q IX c a if c c If c c ir a o j CD U. (mg/l) CO o CN «-«ct CO a 00 PIEZOMETER DATA: RES (ohm-m) 3.79 44.44 52.63 44.44 14.71 CD CC r> 5.81 00 PIEZOMETER DATA: COND. (uS/cm) 2640 in CM CM o CD LO CN CN o 00 CO 1300 1720 ( ts and Chemistry Data From Pore Water Samples / OF WATERb ISULPHATE 1 (mg/l) 17.7 29.91 If) CO CN CO •<* m o ts and Chemistry Data From Pore Water Samples UNIVERSIP I a 1 6.89| I 8.311 I 8.23I 1 8.071 I 7.94I L 7.37 I 6.96I ts and Chemistry Data From Pore Water Samples ts and Chemistry Data From Pore Water Samples |RES075 1 (ohm-m) 1 17.571 I 81.72| I 80.56I 76.04| 57.101 42.95II 20.38H Measuremen < RES025 (ohm-m) 16.30 74.35 74.47 69.07 55.65 43.40 20.46 Resistivity I RCPT DAT, RES010 (ohm-m) 16.98 78.04 77.51 83.01 58.52 43.40 18.94 i of RCPT Bulk T CN HOG3RES E6/ZL/0L 0.0 m uomparisor < bounding: Lone iu: mate: II r a. . XI 3 . 1 o IN o j) £ o q v.' o o o 6 O LO 6 o IN •o r— 211 Q E u r: U w <U i £ i o u 212 CO in E cu $ OJ k. o Q. • O u z 213 |C0 w CD <0 i£ l o l Icj C a <a c o E CD L_ 3 vt to \i o 00 LO CO ro CO a> CO O) <* CO CO tr- CM q CO CN to ro to i n o> i n q _ 03 CO CO X* cn r » **-CM i n ro' i n "<t ro co CO co' co 0) o •<* co' t t •NT' r o r -CO t CO CO CM O T— o i I t o CM lO o CN CO* t CN o> o CM d CN •*' o> o> •cr' o d O r o co CO i n CM a 1 o ro CM CD q i n o> CO co ro i - q CO q 00 o> r o co LO CO CM q 6 6 Q «t 00 6 *— CM CM d r— CM' CN to' *~ •-' co' CM co' d CM CO* CM d d co* co* 2 (mg/1) CM CO CM o O CM q CM CO q T™ i n CO CO CO q CO i n 00 CM r o o CO 00 i t o |(mg/l) 1 8008 1 12500 6 CM CD oo' o" d CM m* co' CO co' CM d d d d d d d CM d d ro CO CO O) CO CO ro i n CO ro CO CO q CM CM CM O ro CO i n CO o i n i n i n q ro q o> o> CO CO CO 00 00 CD i n ro CM ro ro CO Tt CM CO CO E 6 «~ CM' co' co' CM co' co' co' co' co* *t* co' CO CM CM CM co' » t •<t" t ' * t •vt* •«*' <st RES |(ohm o E 10270 5040 3730 2800 2680 4300 3320| 3110| 2490| 2520| 2850| 2560| 2480| 28201 32801 3750 3340| 3530| 3020| 2050| 2180 2110 2120| 2290 2360| 20701 CONI (uS/c ISULPHATE |(mg/l) | 36600 | 27840 | 17130 | 3300 I 2751] | 3720J | 3060| I 3210| | 22851 | 22901 | 20671 | 1862| | 23081 | 2590| | 2805| | 3060| | 2433| 2552| 2775| 15921 14521 14011 15721 1704| 15921 23291 o> CO 00 ro CM o i n CO i n ro CM q i n i n •st CO CO CO 00 * t CN <* CO * r i n 00 00 o ro i n i n t i n CD CO CN I t i n CM i n CO i n CO LO o ro. CO co' CO* co' co' ro ro co' CO* CO* CO' co' CO* co' CO co' ro.' ro co' ro ro ro to* CO* ro CO* I a CN CM 15 3 CO r-0. O CC U J cc , CO § CN d a c •1 3 O o i n CM i n LO o o CN ro o CN o ro * t CO co CO CO q i n CO q i n CM o CO d co' co' co' oo' CO CN co' * t <6 CN CN CM CN CM CM CM CM CO CO CO CO CO 214 V) CD f CD t o w 0) i CD o 0-E o \L co CO Q 'E CD J= O X) c co c CD E CD w 3 CO co 1 *^ V) 'co CD OC J* 3 m t u oc in in E CD JZ U k. <L) •-» I CD O a. • co *-> co w X) i5 215 CM CD I* CO c o c v o ic! •4 i . 10 0) l l (0 3 > '55 15 O CO . w IQ CO *c o CO IX CN LO CM CM CD CD CO 

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