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Slope stability of Nemo and Wee Sandy Creek basins near Slocan Lake, British Columbia Pack, Robert Taylor 1982

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SLOPE  STABILITY OF NEMO AND  WEE  SANDY CREEK  BASINS  NEAR SLOCAN LAKE, BRITISH COLUMBIA by ROBERT TAYLOR PACK B.S., B r i g h a m Young U n i v e r s i t y ,  1980  A THESIS SUBMITTED IN PARTIAL FULFILMENT THE REQUIREMENTS FOR  THE DEGREE OF  MASTER OF APPLIED  SCIENCE  in THE FACULTY  OF GRADUATE  STUDIES  DEPARTMENT OF GEOLOGICAL -(Programme  of G e o l o g i c a l  SCIENCES Engineering)  c  We  accept  this  t h e s i s as conforming  to the r e q u i r e d  THE UNIVERSITY  OF BRITISH COLUMBIA  July  © Robert  standard  1982  Taylor  Pack,  1982  OF  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of  requirements f o r an advanced degree at the  the  University  o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make it  f r e e l y a v a i l a b l e f o r reference  and  study.  I further  agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying of t h i s t h e s i s f o r s c h o l a r l y purposes may  be granted by the head of  department or by h i s or her  representatives.  my  It is  understood t h a t copying or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l gain  s h a l l not be allowed without my  permission.  Department O f  Geological  Sciences  The U n i v e r s i t y of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date  DE-6  n/sn  30 July  1982  written  ABSTRACT  In  order  engineering basins are  to on  near  determine landslide  Slocan  evaluated  scheme b a s e d  Lake,  geotechnical wasting  processes  debris  avalanches,  involve  complex  grained factors  currently  plutonic  include  slope  past  and  colluvial  high  soil  g r o u n d w a t e r , and  shear  plane  model can  only  be  surficial  m a t e r i a l b e c a u s e of  estimated  friction, to  soil  shear  soil  s l o p e a n g l e . From t h e distribution  surrounding  region  probability  of  actually  predict  particular  to  i n t e r m s of  nor  the  in  and  coarse  bedrock.  Primary  the  region  slopes  geotechnical mantled  i n h e r e n t a s s u m p t i o n s and  it  shallow  rockfalls,  for of  broad  angle  of  is  possible  internal  landslides  to  i n the  factor  the  likelihood  units. soil  p i e z o m e t r i c head,  expected  However,  with  requires  slope  d e n s i t y , tree surcharge  t h e number of  slope,  uniform  of many l a n d s l i d e s  failure.  and  Mass  strength, tree root strength,  values  model  stochastic  include  occurrence  root cohesion, bulk  a  deposits overlying  parameters  for  cohesion,  plane,  observed  of  classification  geometry. A s t o c h a s t i c  applied  Ranges  are  shear  slopes  experience.  grade metamorphic  angle,  estimates  hazard  rockslides  forest  Columbia,  i n the a r e a  influence landslide  quantitative  British  engineering  d e b r i s flows,  of  eastward-draining  subdivisions,  a t work  and  impacts  in four  a landslide  terrain  and  glacial  known t o  occurrence  to  natural  model,  possible  southeastern  according on  the  weight,  and  explain  the  study of  area  safety  probabilities likely  depth  to occur  and and  cannot on  a  of a l a n d s l i d e o c c u r r i n g  ii  within of  a certain  landslide  are  less  time  period. Accurate, quantitative  occurrence  can  subjectively  calibrated  and  determined,  compared  quantitatively  be made o n l y where  with  determined  indices  stability  of  that  responded  unfavorably  a r e a s . From s u c h hazard  of use  areas  where  In  the  to f o r e s t the  events.  stability  s l o p e s i n the  comparisons  classes  of  model  variables  where p r o b a b i l i t i e s  observed  compare t h e have  and  predictions  study  to forest  semi-  are best  area  used  with  to  slopes  engineering in other  i n d i c e s can  be  managers and  geotechnical  These  are  grouped  to  form  engineers.  model  d o e s not  apply,  hazards  are assigned according to past  engineering experience  natural  terrain  i n the  units rocky  units  similar  include c o l l u v i a l terrain.  include  Slopes  those  indicated  to those  f a n s and  classed  i n the  by  gravity  processes.  group i n c l u d e c o l l u v i a l  fans,  and  slopes  probabilities  of  failure  'moderate h a z a r d ' slopes  mantled  failure  less  'Low slopes  factors  of  group with  than  10%  hazard' mantled safety  classification road alignments  mantled  fans, with  high  i n c l u d e lower  surficial but  10%.  expected  surficial  greater  than  practical  logging  systems.  material 1.6.  The  terrain  i n the  'high debris  material  having  classed  p a r t s of d e b r i s  f a c t o r s of  as  of  Slopes  i n the  fans  and  probabilities  safety  slopes include gently sloping with  rocky  parts  m a t e r i a l having  group  landsliding  classed  upper  steep  hazard'  steep  surficial  g r e a t e r than  scheme has and  Slopes  These  d e b r i s f a n s , and  s l o p e s w h i c h show s i g n s of a c t i v e  hazard'  and  'very  by m o r p h o l o g y or v e g e t a t i o n , and  dominated  1.6.  aprons,  study a r e a .  in  less  exposed having  landslide  m e r i t s f o r use  in  of  than  bedrock expected hazard planning  iii  TABLE OF  CONTENTS  ABSTRACT  1  ACKNOWLEDGEMENTS  9  CHAPTER  1  1 Introduction  1.1 The L a n d s l i d e P r o b l e m  1  1 .2 Scope Of S t u d y  3  1.3 P r e v i o u s Work In The S t u d y A r e a  6  CHAPTER  2 Study Area  Description  2.1 P h y s i o g r a p h y  8 8  2.2 B e d r o c k G e o l o g y  10  2.3 S u r f i c i a l  13  Geology  2.3.1 M o r a i n a l D e p o s i t s  14  2.3.2 G l a c i o f l u v i a l  17  2.3.3 F l u v i a l  Deposits  Deposits  2.3.4 C o l l u v i a l  18  Deposits  2.3.5 W e a t h e r i n g 2.4 G e o m o r p h i c  19  Processes  2.4.1 D e b r i s A v a l a n c h e  18  20 - D e b r i s Flows  20  2.4.2 R o c k s l i d e s  27  2.4.3 R o c k f a l l s  28  2.4.4 E r o s i o n  29  2.4.5 S o i l  29  Creep  2.4.6 Snow A v a l a n c h i n g  30  2.5  Climate  31  2.6  Vegetation  33  CHAPTER  3 Slope  Stability  In The S t u d y A r e a  36  iv  3.1  Approaches  3.2  The  3.3  Soil  To  Slope S t a b i l i t y  Stochastic Shear  Estimation  3.3.2  Range Of  Root  G e o t e c h n i c a l Model  Of  Soil  Soil  Shear  Shear  Strength  54  3.4.2  Range Of  Cohesion Values  Root  Strength  56 59  Estimation  3.5.2  Estimated E f f e c t s  Of  Piezometric Pressures Of G r o u n d w a t e r  61  In S t u d y  Area  ..  Slope Angle Measurement Of  3.6.2  Distribution  Slope Angle  Of  Miscellaneous Factors  3.8  Slope E q u i l i b r i u m  CHAPTER 4 L a n d s l i d e On  4.1.2  Hazard  4.1.3  Preventative  Area  76 79  Surficial  Material  ...  Near S t u d y A r e a  And  79  Remedial  Engineering Techniques  S t e e p Rocky S l o p e s  4.2.2  Hazard  4.2.3  Preventative  Colluvial  Near The  Study  Area  90 91  Remedial Aprons  4.3.1  E n g i n e e r i n g Problems  4.3.2  Hazard  Class  87 89  Classes And  79  83  E n g i n e e r i n g Problems  On  70  Classes  4.2.1  Hazards  Study  Slopes Mantled With  E n g i n e e r i n g Problems  On  Area  Classification  4.1.1  Hazards  In Study  74  In The  Hazard  70  Slope Angles  3.7  Hazards  65 69  3.6.1  4.3  55  Groundwater  3.5.1  4.2  51  Strength Root  4.1  47  Strength Values  E s t i m a t i o n Of  3.6  39 47  3.4.1  3.5  36  Strength  3.3.1  3.4  Assessment  Engineering Techniques  And  Fans  Near The  Study  92 93  Area  93 94  V  4.3.3 P r e v e n t a t i v e  And R e m e d i a l E n g i n e e r i n g  4.4 H a z a r d s On D e b r i s 4.4.1  Engineering  Techniques  Fans  Problems  94 In O t h e r R e g i o n s  95  4.4.2 H a z a r d C l a s s  96  4.4.3 P r e v e n t a t i v e And R e m e d i a l E n g i n e e r i n g 4.5 H a z a r d s On T e r r a c e s 4.5.1  Engineering  Techniques  And G u l l i e s  P r o b l e m s Near  4.6 Summary  The S t u d y A r e a  CHAPTER  97 99  And R e m e d i a l E n g i n e e r i n g  Techniques  Of The H a z a r d C l a s s i f i c a t i o n System  4.7 D i s t r i b u t i o n  96 97  4.5.2 H a z a r d C l a s s 4.5.3 P r e v e n t a t i v e  94  Of H a z a r d C l a s s e s  5 Road C o r r i d o r A s s e s s m e n t s  99 100 101 104  5.1 G e n e r a l  104  5.2 Nemo C r e e k Road O p t i o n s  104  5.3 Wee  108  CHAPTER  Sandy C r e e k Road O p t i o n s  6 Summary  And C o n c l u s i o n s  111  BIBLIOGRAPHY  116  APPENDIX A  124  APPENDIX B  1 26  APPENDIX C  130  APPENDIX D  132  APPENDIX E  1 34  APPENDIX F  1 36  vi  L I S T OF FIGURES  1.1  I ndex Map  3  2.1  Upper  2.2  G e o l o g y Of The S t u d y A r e a  10  2.3  Receeding G l a c i e r  13  2.4  Grain-size  2.5  Debris Avalanche  2.6  Debris Avalanche - d e b r i s  Nemo C r e e k  Basin  8  In A l a s k a  Distributions  F o r SM S o i l s  In Lower Nemo C r e e k Flow  15 Basin  Path  21  In  Nemo  Creek  Basin  22  2.7  D e b r i s Flow  2.8  Bifurcated  2.9  Profile  System  In Lower Wee Sandy C r e e k  D e b r i s Flow  Of  A  Debris  I n Upper Flow  Nemo C r e e k  Basin.  ... 24  Basin  P a t h I n Upper  25  Nemo C r e e k  Basin  25  2.10  Toppling  Rock F a i l u r e  2.11  Buttressing  Effect  In Lower Nemo C r e e k Of  Tree  Roots  Basin  27  Resisting  Soil  Creep  29  2.12  Index Map Showing  2.13  Mean T o t a l M o n t h l y  2.14  T w e n t y - f o u r Hour Extreme  2.15  Fourty-eight  Hour  Weather S t a t i o n Precipitation  Locations Near  Precipitation  Precipitation  31  The S t u d y A r e a Data  Extremes  31 For  New  Denver  32  3.1  Definitions  Of Model  3.2  Sensitivity  Of FS To V a r i a t i o n s  Input V a r i a b l e s  40  In The V a l u e s Of  Model  Variables 3.3  Alterations  31  42 To S l o p e E q u i l i b r i u m  Following  Deglaciation  vii  43 0 Values  3.4  Range Of  3.5  L a n d s l i d e A n a l y s e d F o r Root C o h e s i o n  Determination  3.6  Variation  Rainfall  3.7  Typical  3.8  S l o p e C l a s s I n t e r v a l s U s e d F o r The  3.9  Three  3.10  Of M W i t h  Profile  Of  Respect An  To  24 Hr  Idealized  Profile  52 ....  56 65  Hillslope Study  Maps Showing S l o p e D e l i n e a t i o n  Slope  Slope  For V a r i o u s S u r f i c i a l M a t e r i a l s  Showing R e l a t i v e  66 Area  71  Methodology  Stability  Of  72 Various  Segments  76  4.1  Cutslope Failures  C a u s e d By  4.2  D e b r i s Avalanche  4.3  Fill  4.4  Rock F a i l u r e  4.5  Landslide Initiated  4.6  H y p o t h e t i c a l Slope  Seepage  - D e b r i s Flow On  80  Wragge C r e e k  Road  ...  82  S l o p e E r o s i o n From C u l v e r t  Classification 5.1  Hazards  Map  A —  Map  B -- T e r r a i n  Map  C —  Slope  Map  D —  Slope  On  Lower Shannon C r e e k By  L o s s Of  Road  90  Root C o h e s i o n  Illustrating  The  Landslide  System  T r a v e r s e d By  Foot  82  98 Hazard 100  Proposed  t r a v e r s e s and  sample  Road C o r r i d o r s sites  106  ~~1  LifU-W Stability  J  vi i i  LIST  S l o p e s F a c t o r s On  TABLES  3.1  Effects  3.2  Estimated  3.3  Definitions  3.4  Maximum V a l u e s Of M F o r V a r i o u s M o i s t u r e Regimes  69  3.5  Average Bulk D e n s i t i e s  74  3.6  In-situ  4.1  Of  OF  <t> V a l u e s  Model V a r i a b l e s  For C o h e s i o n l e s s S o i l s  Engineering  49  Of M o i s t u r e Regimes  Indices Failures  62  For D i f f e r e n t  Bulk D e n s i t i e s Determined  Stability  42  Calculated  Soil  In The For  Classes Study  Area  Slopes  ...  74  Near 83  ix  ACKNOWLEDEGMENTS  The British need  author  wishes  to  for this  adverse  study  and a r r a n g i n g  conditions;  mapping and f i e l d Mathews, reviews; patience of  this  and  L.M.  financial  Utzig  for assistance  R.E.  Kucera,  the  a s s i s t a n c e ; H.T.  a s s i s t a n c e i n the f i e l d ,  M.J.  and f i n a l l y he wishes t o thank h i s wife and  suggesting  sometimes with  field  Bovis,  W.H.  L a v k u l i c h for c o n t i n u a l advice and c r i t i c a l  encouragment helped  Shelley  whose  s u s t a i n him during the course  study.  Council  of  f o r l i v i n g expenses was provided British  Research i n Engineering and  G.  logistics;  F i n a n c i a l support Science  and T. Baker of the  Columbia M i n i s t r y of F o r e s t s f o r f i r s t  Smith f o r p r o v i d i n g f a i t h f u l in  thank G. S t i l l  research  expenses  by the  Columbia i n the form of a Graduate  and Technology Award. Support f o r was  provided  M i n i s t r y of F o r e s t s , Research D i v i s i o n .  by  the B r i t i s h  field  Columbia  1  CHAPTER  1.1  The  Landslide  Landsliding process  in  1 INTRODUCTION  Problem  i n i t s v a r i o u s forms  r e m o v i n g and  steep mountainous  is  a  dominant  transporting soil  s l o p e s of t h e w e s t e r n  and  the  developed.  Various  from  such  evaluated  that  understood  landslide 1979,  Froehlich,  with  marked  erosion.  Sedimentation  p o p u l a t i o n s and  has  1977,  and  Columbia, sediment  soil  i n s t r e a m s has  Slocan Valley  on  the  resulting  channels  be  local  may  indicates have  marked  1974,  Zeimer  1981,  Takeda  1976).  the  focus  from . r o a d  In  of  l o a d have been  and  Jeffrey  disturbance  from  landsliding  a negative  the this  linked  1968). Such  and  effect  skidder surface on  fish  m u n i c i p a l water s u p p l i e s .  of t h e West K o o t e n a y R e g i o n ,  (Slocan V a l l e y  being  resulting  world  building  w h i c h have l e d t o b o t h  occasionally  are  impacts  documented numerous e x a m p l e s of b o t h  degradation stream  of  (Chamberlain to  British  watersheds  (Swanston  James  attributed  r e s o u r c e s of  development.  road  of B r i t i s h  systems  study  and  and  operations  are  the  to  occurrence  logging  In  prior  larger  demanding t h a t s l o p e h a z a r d s  i n c r e a s e s i n stream  logging  increases  now  from  As  environmental  in various parts  Dale  West K o o t e n a y R e g i o n study,  are  deforestation  on  difficult  economic and  experience  both  impacts  more  development and  Past  steeper,  debris  Cordillera.  demands a r e p l a c e d upon t h e v a l u a b l e f o r e s t Columbia,  rock  erosional  building  Community  on  s l o p e and steep  1974). Such  a  local stream  slopes  near  occurrences  2  are  not  unique  Vancouver, are  to t h i s  B.C.,  responsible  region.  O'Loughlin for  up  directly  into  fact  i n most a r e a s  that  stream  In  the  Coast Mountains  (1973) e s t i m a t e d  to  47%  of  channels.  of  logging  landslides  T h i s can  main a c c e s s  that  north  roads  be  of  roads  which  run  a t t r i b u t e d to  are  close  the  to  major  i n d i c a t e that  severe  effect  forest  streams. Studies soil  to  disturbance  productivity, 1975).  litter,  A  Slocan  have  an  at high  is buried  and  mineral  long-term in  elevations are  by  British  B-horizon  are  of  the are  of  soil forest  removed;  debris;  or  s e v e r e l y compacted.  landsliding  Columbia  Herring  where  (1)  m or more  horizons  effects  greatest  the  .25  on  ( U t z i g and  i s , where  a p o r t i o n of  surface  productivity  adverse  or deep, t h a t  and  B  Valley  reductions  i s 'severe'  the  of  particularly  soil  the  date,  may  A-horizon,  the  (3)  east  Productivity  disturbance  (2)  the  have  not  on been  To  forest assessed  quantitatively. Road damage c a u s e d by environment,  but  may  m a i n t e n a n c e c o s t s and companies  are  construction though c o s t l y financially As problem Columbia,  now on  landslides  the  comprehensive  c o s t s - i n c u r r e d by  the  not  only  or is  damage  increase  transport delays. either  engineering often  to  the road  Forest  avoiding  road  roads  f o r them ,  their  advantage  1979). are  financially land  that  slopes  outset,  may  significantly  realizing  (Gardner  both  also  unstable  at  landsliding  becoming and  manager  understanding  of  an  increasingly  environmentally i s faced with the  nature  the and  widespread in  need  British f o r a more  extent  of  the  3  problem.  The  three  managers a b o u t (1980), can  be  "(1)  analyses:  (1)  areas,  and  broad  (4)  stability  If is  intensity, terrain is  collection  they?,  of  slope  land  Burroughs and  (3)What  t o the  of  1979,  landslide  is difficult  are  engineering  that  a  and  in  these  stability  inadequate is  overcome as  to  t o be  relative  factors  inaccessible  involved  assumptions  of  in  in large  processes  assignment  1980  controlling  o f t e n b a s e d on  limitations  of  potential  Swanston  uncertainties  the  ratings  stability  several limitations  i n t e r p r e t a t i o n s are  quality  hazard  Rice  are  leads to  these  and  by  to  are  methods  and  There  determinable,  leads  these  (Foggin  knowledge of  incomplete.  questions  for evaluating landslide  the h e t e r o g e n i e t y  (2) d a t a  (3)  (2)How bad  several  1978).  natural setting  analysis,  data,  they?,  years,  al.  asked  landslides are, according  have been d e v e l o p e d  et  the  commonly  them?  f o r e s t e d watersheds  Simons  in  Where a r e  recent'  analysis in  potential  done a b o u t  In  most  usually  and  slope  the  imposed  kind, upon  the  hazard  ratings.  It  t o the  are  of  interest  to e v a l u a t e  the  stability  land  manager.  1.2  Scope Of This  four  Study  t h e s i s attempts  eastward-draining  Slocan  Lake,  54'-50° 01'N; basins  of  Wee  basins  southeastern see F i g u r e Sandy  Slocan  British  1.1). Creek  b a s i n s of Hoben C r e e k and facing  i n the V a l h a l l a  Lakefront  Sharp  Columbia  It includes and  between  (117° the  the  which two  slopes in  M o u n t a i n s west 22'-38'W;  major  Nemo C r e e k and  Creek  of  the  drain  of 49°  drainage two the  minor east-  major d r a i n a g e s .  The  4  Figure area  encompasses some  harvestable many s t e e p , value  to  recreational are  of  timber.  160 km This  potentially the  forest  values.  1.1 2  Index  map.  o f w h i c h 66 km  area  unstable  2  have  was c h o s e n b e c a u s e slopes, merchantable  industry,  and  some  high  P o t e n t i a l land-use c o n f l i c t s  in  potentially i t includes timber  of  aestheticthis  area  p u b l i c c o n c e r n and s t u d i e s a r e needed t o d e t e r m i n e what  5  impact, No  i f any,  logging operations  l o g g i n g or d e v e l o p m e n t  least  30  has  will  have on  occurred  i n the  first  describe  the  slopes  in  study  of  two  objectives  fundamental the  is  factors controlling  study  area.  The  the  factors  properties,  root  conditions,  slide  geometry  slope angle.  in  assessing  stability  the  analyses  i n c l u d e s the  second  controlling practices  stability  strength,  reliability  of  of  geologic  groundwater  This  i s the  first  conventional  slope  hazard  ratings. This objective  examination  factor  interactions leading  are  objective  of  to  produce activities  method of  stability  a n a l y s i s , the  quality  areas, of  study  and  on  with  slopes  hazard  rating  how  to  landslide  particular  engineering  Landslides  similar  engineering  certain  The  determine  caused  to those  system  of  i n the  by  the  study  study  area.  l a n d s l i d e p r e d i c t i o n i s t h e r e f o r e based  engineering  area.  to  landslides.  a b a s i s f o r the  other  is  interact  A rational  the  and  and  in determining  factors  engineering  in  at  instability.  The  area  for  include  soil  natural  area  t o d e t e r m i n e , map,  structure,  also  environment.  years.  The  step  the  assumptions  alterations  final  behaviour  result  as  t o be  is a  of to  the  imposed  map  of  similar  slopes  type  upon s l o p e s  slope  on  and in  stability  hazards. This  study  occurrences  of  does  which are  In  cases,  particularly  attempt  l a n d s l i d e s and  rate areas some  not  where  likely  failed they  predict  i s designed  to produce slopes are  to  are  only  slope  to d e l i n e a t e  stability  described  critical  site-specific  to  and  problems.  individually, the  watershed  6  development  scheme.  Potential  problem  roads, as w e l l  as  slopes  emphasized. Primary are  not  divides but  less  landsliding,  1.3  1964)  such  as  to  land-use  are  examined b u t engineering  constitute  conflicts,  of g r a v i t y  agencies  will  be  will  be  such  largely  the  mapping  and  are,  as  soil  independent  of  a s f l o w i n g water o r wind  considered.  used  an  Other  geomorphic  n o t be d i s c u s s e d . The equivalent  to  'mass-  o r ' s o i l mass-movement' f o r t h w i t h , f o r s i m p l i c i t y .  P r e v i o u s Work In The S t u d y soil  Forest District  Forests  descriptions regimes  which  snow a v a l a n c h i n g , w i l l  Reconnaissance  of  logged  relevant to forest  timberline  the influence  'landsliding'  Castlegar  be  i . e . t h e d o w n s l o p e movement o f r o c k ,  f o r c e s from  (Leopold et a l .  wasting'  will  highways a r e a l s o  as  above  or  forest  not c o n s i d e r e d i n d e t a i l .  contributing  term  be  important  d e b r i s under  hazards,  have  low-volume  between w a t e r s h e d s a r e i n c l u d e d i n t h e l a n d f o r m  therefore,  and  to  A l l areas  are  Only  that  and s e c o n d a r y  considered  problems.  areas a s s o c i a t e d with  surveys  Their  of  geologic  encountered  environment  s k e t c h y and of l i t t l e  not  ground checked  were e s t a b l i s h e d  in  1980 by t h e  of F o r e s t s report and  (Ministry  includes brief soil  moisture  d u r i n g a two-day t r a v e r s e a l o n g Nemo  are  road  begun  preliminary  Remarks r e g a r d i n g s l o p e s t a b i l i t y  Tentative  were  o f B.C. M i n i s t r y  1981a). the  Area  and road b u i l d i n g  use t o t h i s  Creek.  a r e made b u t  s t u d y . Wee Sandy C r e e k was  by t h e s u r v e y . locations  i n b o t h Nemo a n d Wee Sandy  i n 1980 by t h e N e l s o n  Regional Engineer  Creeks o f B.C.  7  Ministry  of  potential  slope  alignments  Forests.  A  stability  report  contains  problems  ( M i n i s t r y of F o r e s t s  along  1981b).  brief the  d e s c r i p t i o n s of proposed  road  8  CHAPTER 2 STUDY AREA DESCRIPTION  >  2.1  Physiography  The  study  east-west  trending  southeastern 1350  area  lies  i n the high,  ridges of  British  range  a t Mount Denver The  upper  northern  Columbia. L o c a l  meters, but the t o t a l  elevations  the  steep-walled,  relief  Valhalla  relief  varies  i s about  2200  from 535 m e t e r s a t S l o c a n Lake  6 kilometers  serrated, Range  from 900 t o meters  t o 2743  floors  t o t h e west.  end o f Nemo C r e e k  Nemo C r e e k  at  i s flanked  some 1060 m e t e r s small  elevations  i s dominated  between  by Mount Meers  that  enter  bottom. from  triburaries  from t h e s t r a i g h t ,  lower v a l l e y . V a l l e y  geometry  upper  cirque  the  feed  Creek  2.1  illustrates  basins  valley  istypically  r e a c h e s b u t becomes d o m i n a t e l y V - s h a p e d Figure  basins  t h e U-shaped  which  rise  Nemo C r e e k h a s numerous  n o r t h and s o u t h s i d e s o f which  to  1850 and 2150 m e t e r s . Lower  t o t h e n o r t h by r u g g e d c l i f f s ,  from t h e v a l l e y  tributaries  and  meters  t h e n o r t h , H e l a Peak t o t h e s o u t h , a n d a s e r i e s o f c i r q u e with  of  and  a  few  minor  steep slopes of the  U-shaped  in  on b o t h t h e  the  geometry  i n t h e upper  lower  valley.  of t h e upper Nemo  Basin. The  that  p h y s i o g r a p h y o f Wee Sandy C r e e k  of  Nemo  Creek.  The  upper  valley  section  b u t , r e m a r k a b l y , h a s no t r i b u t a r y  north.  Wee  Sandy  Creek  originates  occupies a north-south trending  at  Basin  is  similar  i s U-shaped cirque Wee  in cross-  basins  to the  Sandy Lake  hanging t r i b u t a r y  to  valley  which  at the  9  Figure 2,1. A e r i a l view of upper Nemo Creek  head  of  the b a s i n .  Basin.  The lower v a l l e y again assumes a V-shaped  c r o s s - s e c t i o n , as does Nemo Creek, at the 1370 meter l e v e l . steepest northern  slopes  and  cliff  The  faces a r e c o n s i s t e n t l y found on the  sides of both v a l l e y s .  Both Nemo and Wee Sandy Creek have r e l a t i v e l y gentle stream g r a d i e n t s i n the upper abruptly average  at m i d - v a l l e y  valley  which  then  steepen  to descend v i a r a p i d s and cascades at an  15% g r a d i e n t to Slocan  cascade 1 kilometer  portions,  t o Slocan  Lake below. One notable  long occurs approximately 5 km up Wee  Sandy  Creek and has an average g r a d i e n t of 27%. Hoben drain  and Sharp Creeks occupy hanging c i r q u e v a l l e y s which  i n t o Slocan Lake between Nemo and Wee  Creeks descend a s e r i e s of g l a c i a l l y  Sandy  Creek.  Both  formed steps, some of which  10  are  occupied  main S l o c a n into  by  small  t a r n s , and then  V a l l e y . Neither  bedrock  stream  t h e head o f S h a r p C r e e k B a s i n  once e x t e n s i v e  2.2  Bedrock The  valley  area  Valhalla  Gneiss  Complex  i s centered  the  see  canyons  i s perched  representative  half  Figure  surrounding  the  between two d i s t i n c t  t o "the s o u t h .  at  of  the  core  of  the study  are  The  geologic  Valhalla  the V a l h a l l a  15 km t o t h e s o u t h , area  2.2). F o l i a t i o n s  and  which r i s e  reflected  (Parrish  of  the  gently  Dome n e a r  and  includes  1982 a n d R e e s o r  gneiss  by a s e r i e s  Gneiss  dome d i p  of inward  steeply  to  curving  ridges  central  g n e i s s c o r e . The h i g h c l i f f s  of lower  of northward d i p p i n g  the  by e r o s i o n . The n o r t h - f a c i n g  Valhalla  Dome  s l o p e s o f Nemo  between the the  Creek  incised Basin  more  and a r e c o n s e q u e n t l y  less  closely  15° a n d 25° t o t h e NNE t h r o u g h o u t  study  area  and c a n be c l e a r l y  foliations  approach  steep. Gneiss  of  valley  dip-slope  foliations dip  the southern  observed  facing  entirely  Nemo C r e e k a r e an e x p r e s s i o n  geometry  of  s y n c l i n e t o t h e n o r t h a n d (2) t h e domal  Complex  quaquaversally cliffs  V-shaped  New Denver G l a c i e r  i s the only  i s situated  Peak, a p p r o x i m a t e l y  southern  1965,  significantly  glaciers.  (1) t h e S l o c a n  Gladsheim  incised  into the  Geology  study  features:  has  and t h e r e f o r e have n o t d e v e l o p e d  as have Nemo a n d Wee Sandy C r e e k s . at  drop a b r u p t l y  half  of  on t h e h e a d w a l l o f  upper Hoben C r e e k c i r q u e b a s i n . At  intrudes plutonic  t h e head o f Nemo C r e e k , the  gneiss  complex.  rocks c o n s t i t u t e  a  the monzonitic A  zone  mixture of  Nemo  of  "mixed  Lake  Stock  metamorphic and gneiss"  at the  '  ;  7 PLUTONICi"*  i  ' Mk<<<:\ o>y', --v-i)-,N(»>'v-x6 LEGEND PLUTONIC  granodiorite , l e u c o q u a r t z monzonite, quartz diorite, quartz monzonite monzonite, granite  HIGH GRADE MET AMORPHICS  leucogranite gneiss  granite gneiss, g r a n o d i o r i t e - a u g e n gneiss  MEDIUM GRADE METAMORPHICS  amphibolite ,  pelitic s c h i s t , c a l c - s i l i c a t e metasediments ultramafics  LOW GRADE METAMORPHICS  argillite , quartzite ,  slate , pelitic phyllite  Figure  2.2  Geology  of  the  study  area.  KM -v-  1 2 i n t r u s i o n boundary (Reesor  rocks  are  1965) Both  consistently  the g r a n i t i c  coarse-grained  and  and  gneissic  are  of  similar  composition. North grade  of the study  metamorphic  Syncline  Dome.  weaker r o c k s A  The  drainage  belt  o f medium g r a d e  grade  and  leucogranite uncertain  on  that  found  is  exposed  drainage  from  the  Slocan  Batholith  these  mechanically  farther  t o the rocks,  principally  pelitic  and  i n the rocks  p h y l l i t e s and to  the  south  the  Nemo  somewhere  Lakes  Belt  and the  Complex o f t h e s o u t h i s  within  the  Sharp  Creek  area.  The  Wragge  immediately strong,  Creek  and t h u s  of  Stock  and  the  granitic  rocks  precludes  Cariboo  basin.  The  Snowslide  t o t h e Wragge C r e e k S t o c k ,  S l o c a n Lake F a u l t the  correlation  have  mechnically  resisted basins  Creek  Stock,  occurs  to  glacial on  that  similar in  the  west  and  (see F i g u r e 2 . 2 ) .  bounds t h e s t u d y  area  t o t h e e a s t and  of r o c k s a c r o s s S l o c a n Lake  1982). The g r a n i t e s (some p o r p h y r i t i c ) immediately  stock l i e  These  e x p l a i n the absence of c i r q u e  o f upper Wee Sandy C r e e k B a s i n The  East  t o t h e n o r t h of Wee Sandy C r e e k .  coarse-grained  composition  lie  complex  o f t h e c o n t a c t between t h e p e l i t i c  the V a l h a l l a  occurs  medium  t o t h e west. These  gneisses  of  to  i n t e r m e d i a t e metamorphic  of  is  Nelson  formed  amphibolites  but  low  to the l e u c o g r a n i t e gneisses  1982). The p o s i t i o n  schists  south  Belt,  continuously  to the north  (Parrish  side  boundary of t h e  topography  Lakes  of  the s t r u c t u r a l l y  o f Wee Sandy C r e e k a n d f a r t h e r  possibly  erosion  form  i s more subdued t h a n  termed t h e Nemo  slates  rocks  on t h e n o r t h e r n  Valhalla  south.  a r e a , an a s s e m b l a g e  of the  t o the east of the V a l h a l l a  Nelson  Gneiss  (Parrish Batholith  Dome a s does  13  the  Slocan Group  2.3  Surficial The  (Little  Geology  West K o o t e n a y  (Holland  1976)  materials  giving  the  flutes  by  once o c c u p i e d level  glaciers  Basins  as  a similar  occupying  probably of  seen  the  the  valley  in Alaska  d o m i n a t e d by  deposits  tributary  Sandy  during  to  and  t h e main t r u n k  and  trunk  and  Wee  final  glacier  tributary  as  The  Sandy  prior  with  glacial  at  glacial  to  the  ablation stages  F l u t e d knobs t o  Creek  Lower  area.  east-facing slopes.  ( F i g u r e 2.3).  Sandy C r e e k B a s i n . both  study  glaciation  up-valley  glacier  of Wee  t h a t a r e e n t r a n t of Wee  last  Nemo, S h a r p , Hoben  trunk  ablation),  i n a modern example of t h e d e g l a c i a t i o n  of t h e c o n f l u e n c e  lower  and  genetic  the S l o c a n V a l l e y  during  receeded  glaciations of  d e p o s i t s i n the  S h a r p C r e e k on  suggest the  meter  colluvial  between Hoben and  stages,  south  and  (basal  glaciofluvial  disapperarance  of  t o complex d i s t r i b u t i o n s morainal  glacier  1200  undergone m u l t i p l e  ice-marginal  tributary Creek  rise  fluvial  A main t r u n k  evidenced  r e g i o n has  including  glaciofluvial,  least  1952).  the  Slocan  Lake  entered  into  valleys  are  deposits.  14  F i g u r e 2.3 Salmon G l a c i e r , near Stewart, B.C. showing the r e t r e a t of a t r i b u t a r y g l a c i e r p r i o r to the disappearance of the main trunk g l a c i e r . The t r i b u t a r y valley occupies a v a l l e y s i m i l a r i n geometry to that of both Nemo and Wee Sandy Creeks. (Photo taken by W.H. Mathews).  2.3.1  Morainal Ablation  Deposits morainal  blankets  and  veneers  1  are  abundant  throughout the study area. Comminution of coarse g r a i n e d bedrock in  Nemo, Hoben and p o r t i o n s of Sharp and Wee Sandy Creek  has produced g r a v e l l y  to  sandy  morainal  deposits  with  Basins silt  'The term 'ablation' refers to the wastage of g l a c i a l i c e by melting and evaporation l e a d i n g t o depostion of e n g l a c i a l l y and/or supraglacially transported d e b r i s , the term 'blanket' means a mantle of unconsolidated m a t e r i a l s t h i c k enough to mask minor irregularities i n the u n d e r l y i n g u n i t , but which s t i l l conforms to the general u n d e r l y i n g topography ( g e n e r a l l y greater than 1 m t h i c k ) , and the term 'veneer' means a l a y e r of unconsolidated materials too thin to mask the minor i r r e g u l a r i t i e s of the u n d e r l y i n g u n i t s u r f a c e (between 10 cm and 1 m thick).  15  fractions morainal sand  generally deposits  components  schists.  Figure  less  i n Wee  than  Sandy C r e e k b a s i n  resulting 2.4  20% and o n l y  form  tend  comminution  i l l u s t r a t e s the obvious  Gravel  minor c l a y . to  Ablation  have  of f i n e r  difference  finer grained between  Sand Coarse to medium  Fine  Silt  Clay  U.S. standard sieve sizes  £ 6 d  d  o  Grain diameter, mm  Figure  2.4 G r a i n - s i z e d i s t r i b u t i o n s f o r m o r a i n a l SM sampled i n Nemo and Wee Sandy C r e e k B a s i n s .  the  grain-size  in  the  distributions  Unified  of m o r a i n a l  Soil Classification)  silty  soils  sand d e p o s i t s  s a m p l e d i n Wee  (SM  Sandy C r e e k  1 6  Basin  versus  Nemo Creek  Basin . 1  These m a t e r i a l s , a l t h o u g h observed  in  widely  distributed,  cross-section in gullies  study  area.  Consequently, observations  soil  pits  where  the l a t e r a l  i s not observable.  Englacial  within  ablation  are  o r on s t r e a m banks i n t h e were  mostly  complex  and  King  I n one i n s t a n c e , a marked v a r i a t i o n  within  exposing  underlying  glaciofluvial Such  1 meter  pocket  complexities  moraine  laterally ablation  where a  areas  tree  moraine  of a  include  (Embleton  and  i n t e x t u r e was had  overturned  associated  with  a  ( s e e samples N l 9 - 1 a n d N19-2 i n A p p e n d i x A ) . make  problematic  i n other  to  materials  frequently  l e n s e s and pockets  observed  limited  and s u p r a g l a c i a l  glaciofluvial 1968).  seldom  c o n t i n u i t y or s t r a t i f i c a t i o n  deposit  moraine  were  as  positive most  identification  observations  of  ablation  are limited  to s o i l  pits. Morainal elevations in  places  come  deposits a s s o c i a t e d with  are exhibit  cases,  typically  blocky  t e r m i n a l of  cirque  1  in  Nemo  rock  fewer  higher  f i n e s and  morphology.  exists  Creek B a s i n . L a t e r a l  deposits  at  In  i n t o a b l a t i o n moraine  glacier  i n t h e lower v a l l e y s ,  basal morainal  with  moraine  t a l u s aprons grade g r a d u a l l y  moraines a r e r a r e • Compact  or rubbly  lateral  near c i r q u e b a s i n w a l l s . A l o b a t e north-facing  cirque basins  i n one  or terminal  a s a r e kame t e r r a c e s .  are  observed  only  where  The p e r c e n t a g e s of c o a r s e fragments g r e a t e r than a p p r o x i m a t e l y 2 cm were e s t i m a t e d i n t h e f i e l d a n d d i s c a r d e d from t h e sample. Samples were t h e n a i r - d r i e d a n d s i e v e d w i t h U.S. s t a n d a r d mesh s i e v e s a c c o r d i n g t o ASTM D1140-54 s p e c i f i c a t i o n s . S i z e f r a c t i o n s l e s s t h a n .425 mm (# 40 s i e v e ) were d e t e r m i n e d by t h e s t a n d a r d hydrometer method (Bowles 1978). Sample l o c a t i o n s a r e shown on Map A ( f i l e d s e p a r a t e l y ) .  1 7  morainal  blankets  associated  deeply  incised  lower  Nemo C r e e k y i e l d s  12%  deposits  In  p e r c e n t a g e s of s i l t  ablation  underlying  surprising  a b l a t i o n moraine  can i n p l a c e s  general,  blanket'  t h e main t r u n k  glacier are  by s t r e a m e r o s i o n . Sample N-0+80 t a k e n  respectively. Unlike  compact  with  of  near  a n d c l a y o f 43% and  in  the  area,  these  i n c l u d e p o c k e t s of pure c l a y .  m o r a i n e and g l a c i o f l u v i a l  basal  absence  from  moraine.  observable  This  may  basal  materials  explain  moraine  the  i n the study  area.  2.3.2  Glaciofluvial Glaciofluvial  subangular, clay.  well  Deposits deposits sorted  These d e p o s i t s  particularly Valley. include  characterized  Morphologic small  throughout  area  the  study  associated  terraces, ridges, blankets,  ablation  morainal  rounded  little  features  deposits  by  sands and g r a v e l s w i t h  common on t h e e a s t - f a c i n g s l o p e s  Glaciofluvial with,  occur  are  s i l t or but a r e  o f t h e main  with  to  these  Slocan  deposits  and v e n e e r s .  in places  grade  into,  materials  of  similar  or  are  mixed  texture  and  angularity,  and c a n be d i s t i n g u i s h e d o n l y  by t h e a b s e n c e o f s i l t  and  Relatively  distances  clay.  tributary  basins  short  frequently  gravels  associated with  glacial  meltwater.  transport result  ice-marginal  within  the  i n subangular c o b b l e s and or  englacial  sorting  by  18  2.3.3  Fluvial  Deposits  Fluvial well and  sorted  deposits s a n d s and  s t r e a m s on  deposits fans  are  within  2.3.4  50  flat  blocky  to  movement. dominate mostly  on  usually  confined  t o narrow  deposits  are  materials  or a t  the  base  bedrock. is  composition  competence of  the  steep  occurs terrain  aprons  e s c a r p m e n t s a t any the  moraine or  creeks  fans.  These small  limited.  poorly  sorted,  o v e r l y i n g bedrock by  or  gravity-induced  the  area  and  e l e v a t i o n s where t h e y  are  blocky,  strongly  study  rubbly  texture  influenced  granites, gneisses  by  and  the  schists  i t is derived.  Colluvium  along  and  by  throughout  The  colluvium  and  present-day  areally  slopes  of h i g h e r  of  fans  are  slopes  of  occur  terrain  from  steep  characteristic  mantling  moderately  f l o o d p l a i n s and  characterized on  deposits  derived  from w h i c h  to  Deposits  steeper  and  well  floodplains  m of a c t i v e s t r e a m s and  These the  g r a v e l s a s s o c i a t e d with terraced  rubbly  accumulated  c h a r a c t e r i z e d by  or  Colluvial Colluvial  are  are  most  f r e q u e n t l y as  veneers and/or  i n e x c e s s of  30°  on  common a l o n g  the  toe  elevation.  u p p e r p a r t s of v a l l e y glaciofluvial  Colluvium sides  deposits.  upper  slopes.  slopes  derived  in places  blankets  of  Thick  steep  from  rock  bedrock  overlie ablation  19  2.3.5  Weathering Weathering  only  slightly  materials. area  Committee  typically  to  forest  has  p r o p e r t i e s of  altered  surficial  a r e common t h r o u g h o u t allow  soil  t o medium  or h e a t h  the  development.  textured,  acid  vegetation in cool  climates  were n e v e r  development  characteristics  materials  in coarse  perhumid  Podzols  Mechanical  where  occur  agents  (Canada  Soil  to  Survey  1978).  soil  physical  Podzolic soils  under  humid  Humo-ferric Podzolic  physical  geomorphic p r o c e s s e s  materials, cold  and  the n e a r - s u r f a c e p h y s i c a l  inactive  These s o i l s  very  biological  Humo-ferric  where  parent  by  was  weathering  preferentially  had  observed  schists  t o more g n e i s s i c  m a t e r i a l s have not  than  effect  on  m a t e r i a l s i n the lithic  in  have  deeper  little  surficial of c o a r s e  occasionally  mica-rich  surficial  of  has  observed  fragments  Wee  Sandy  broken  rock  the  bulk  in  glacial Basin  i n - places  However,  been s i g n i f i c a n t l y  and  area.  Creek  down,  fragments.  1 m  most  weathered s i n c e  deposition.  2.4  Geomorphic  Processes  Geomorphic p r o c e s s e s  including  flows,  rockslides,  rock  erosion  and  are a c t i v e  glaciated played  flooding terrain  a role  glaciation. processes  in The  of  falls,  the  debris snow  slope  following  discussion  affect  the  morphology  or a r e  will  be  recently  of p r o c e s s  since limited  themselves  debris  water-born  steep,  a r e a . Each type  modifying  which d i r e c t l y  avalanches,  throughout  study  avalanches,  has  the  last  to  those  affected  by  20  the  activities  2.4.1  Debris  Avalanche  Debris slopes  o f man.  avalanches  strong  material  bedrock  1980).  saturated  at  debris  flowage  slurry  of  along  o r compact  Burroughs  1  When  saturation initial  debris  of  shear  surface  the  surficial debris  mechanically  (Swanston  material  avalanching  steep  cohesionless  impermeable,  till  and o r g a n i c  term  'debris  avalanches  and almost  with  material,  1979  is  and  nearly  may r e v e r t t o of  a  debris  directly  t o stream  avalanche  - debris  flow'  are  immediately  initiated  revert  by p a r t i a l  to debris  avalanches occur  blankets  surface  flows  slopes  where  for transport. Figure on  a  of  is soil  after  north-facing  surficial  of  example slope  debris  terrace  avalanches  supplies  2.5 i s an  uniform  by r e c u r r e n t  o r on s t e e p  largest  ample  on l o n g  veneers  undercut  erosion,  t o s t r e a m c h a n n e l s . The  avalanche  or  g u l l y side walls  continuous  uniform  available  debris  continuous  on s t e e p  or  adjacent  1  a relatively  rocks,  the study area,  slopes  debris  bouncing and r o l l i n g  from  failure.  In  long  failures  r e s u l t i n g i n t h e r a p i d downslope t r a n s p o r t  soil,  where  Flows  r a p i d , shallow  time of f a i l u r e ,  c h a n n e l s . The combined  flows  are  involving sliding,  surficial  used  - Debris  faces  occur  material of  with  a a  on are  major smooth  This d e f i n i t i o n of d e b r i s avalanche i n c l u d e s the l a n d s l i d e type commonly r e f e r e d t o a s ' d e b r i s s l i d e ' by V a r n e s ( 1 9 5 8 , 1 9 7 8 ) . The d i s t i n c t i o n i s p r o b l e m a t i c a s t h e two p r o c e s s e s are c l o s e l y related and v i r t u a l l y indistinguishable i n many e n v i r o n m e n t s ( B l o n g 1973).  21  unweathered g r a n i t e gneiss shear  surface  inclined  at  30° i n  lower Nemo Creek Basin.  F i g u r e 2.5. Debris avalanche on a n o r t h - f a c i n g slope of the lower Nemo Creek Basin.  Many  debris  avalanche - d e b r i s  g u l l i e s and a r e subsequently channel.  With  significant mobilized  time,  flows  confined to  numerous  by  a  major  adjacent to  previously  scoured  small l a n d s l i d e s may accumulate  amounts of d e b r i s i n the g u l l y later  a  occur  debris  bottoms  flow  from  only above  to be or by  22  excessive  storm  Debris avalanches planar  flow  flows in  during  initiated  linear  inclined  avalanche  distinguished  transported These g u l l i e s develop  as  in  avalanche  (2)  (3)  gradient  the  momentum gully  mouth  lower  Wee  derived  1  the  and  show  by  given  the  mouth  w a l l s or  Sandy  evidence  chutes  avalanche  had  debris  forest  Figure  dormancy the  area  stability of  (4)  the  the  (Eisbacher Sandy  largely  side as  l o w e r Wee  some t i m e ,  gully  simple  of  rise  to  can  be  presence  of  and/or i n the  paths  large  channel.  when  they  path  flows  stands  2.6  for at  least  g r o w i n g on  i s an  levee  example o f an  subsequently  150  reforested  old in  Basin.  (1)  gully,  40°  These  the  o l d growth  gullies.  relative  d e t e r m i n e d by  not  - d e b r i s flow  l o w e r Nemo C r e e k The  serve  have  i n d i c a t e d by and  and  of  erosional gullies  gully  debris  areas.  gullies  deposits debris  also  in alpine  Many years  may  on  1  spoon-shaped  slopes  flows.  d e b r i s fans at  boulders  event.  a r e more common t h a n  which have, a t  - debris  on  small  between . 30°  from o r d i n a r y  levee deposits  by  storm  South-facing  numerous V - n o t c h g u l l i e s debris  extreme  depressions  debris avalanches.  Creek B a s i n  an  or  of c a t c h m e n t of  gully  size  and  1982).  Creek,  activity  slopes  of  basin  i n the  where t h e  a debris feeding  flow  gains  of  On  north-facing  source  from g l a c i o f l u v i a l  materials and  into  d e b r i s source  gradient the  flow  the  the area,  destructive fan at  the  slopes  of  for d e b r i s flows  are  morainal  debris  is  blankets.  Figure  S u c h an o c c u r r e n c e i s r e f e r e d t o by many a u t h o r s as a 'debris torrent' ( W i l f o r d and Schwab 1982 and M i l e s and K e l l e r h a l s 1981).  23  F i g u r e 2.6 Debris avalanche - d e b r i s flow path subsequently r e f o r e s t e d on the n o r t h - f a c i n g slope of lower Wee Sandy Creek Basin.  2.7 a  i s the plan view of a p a r t i c u l a r g u l l y network i n c i s e d g l a c i o f l u v i a l blanket  that serves as a d e b r i s source  a r e c u r r e n t d e b r i s flow system. The the  base  suggests  s l i g h t l y a c t i v e since evidence  the  last  glaciation.  area f o r  debris  t h i s d e b r i s flow system has  of f l u v i a l e r o s i o n at the toe of the  Debris of  that  s i z e of the  There  fan  is  little  fan.  Sandy Creek Basins are r e l a t i v e l y  r e l a t i o n to the fans on the s o u t h - f a c i n g  at  been only  fans at the mouths of g u l l i e s on n o r t h - f a c i n g  both Nemo and Wee  into  slopes.  These  slopes  small in larger  24  fans  develop  long,  linear,  steep  from  more  frequent  rock-walled  rock  cliffs  gullies  and  debris  inclined  benches  flows  originating in  i n excess  where  of  colluvial  40° on  materials  F i g u r e 2.7 D e b r i s f l o w s y s t e m on t h e n o r t h - f a c i n g s l o p e o f t h e lower Wee Sandy C r e e k B a s i n showing t h e d e b r i s s o u r c e , t h e main g u l l y , and the d e b r i s f a n .  accumulate.  Heavy  rainfalls,  snowmelt, p e r i o d i c a l l y resulting on  in  flush  perhaps  the accumulated d e b r i s  d e p o s i t i o n on t h e d e b r i s  the south-facing  slopes  as  recent  c o l l u v i a l l y derived debris This  slopes Figure flow  excellent  are  serve  fan.  debris  particular  a s low a s 6° i n t o 2.9  path  flow  source  areas.  flow  of the l a r g e s t  the  fan'. D e b r i s  rapid  from  gullies  to  at  the  materials  accumulating Figure  bifurcated  continued  and  2.8 shows a  on  a  debris  t r a n s p o r t d e b r i s on toe  of  the f a n .  showing a t y p i c a l p r o f i l e o f a d e b r i s  measured on t h e s o u t h - f a c i n g  the size  with  fan. C o l l u v i a l  continuously  Nemo C r e e k  i s a diagram  and  coupled  boulder  s l o p e o f Nemo C r e e k  deposited  Basin  on e a c h segment o f  f a n s may have t o e s l o p e s a s low a s 5° o r a s h i g h  25  Figure 2.8  Debris  flow that has b i f u r c a t e d on a d e b r i s fan of upper Nemo Creek B a s i n .  as 20° depending on the width of the v a l l e y descends.  The  texture  c o l l u v i a l apron or f a n .  i n t o which the  flow  of a d e b r i s fan i s s i m i l a r to that of a  26  DEBRIS FLOW CHUTE  BOULDERS »1 BOULDERS  (erosion)  m  DIAMETER  >1 m BOULDERS  SMALL  LARGE  1 m  COBBLES  DIAMETER  1  30° ^  3  DIAMETER 24° 20°  COBBLES 17° 12° 6°  .HAZARD CLASSIFICATION  HAZARD CLASSIFICATION  Fl  F2  F i g u r e 2.9 P r o f i l e o f a d e b r i s Nemo C r e e k B a s i n showing t h e s i z e s d e p o s i t e d as l e v e e s along t h e flow s u b d i v i s i o n s f o r d e b r i s fans  2.4.2  Rockslides A rockslide  as  f l o w on a d e b r i s f a n i n upper of t h e l a r g e s t rock fragments path. Included a r e the hazard d i s c u s s e d i n C h a p t e r 5.  an i n c o h e r e n t  bedrock,  and  i s a rapid  d o w n s l o p e movement o f  mass o r a s a l a r g e u n b r o k e n b l o c k  may  have  either  surface,  d e p e n d i n g on t h e n a t u r e  joints,  bedding,  Several  large,  identified Creek arcuate  planes,  a  and o r i e n t a t i o n  foliations  deep-seated,  curvilinear  or other  rotational  on t h e n o r t h - f a c i n g s l o p e s o f b o t h  Basins. headwall  These  slides  scarp areas  rock, detached  or p l a n a r of  either from shear  controlling  discontinuities. rockslides  were  Nemo a n d Wee Sandy  a r e c h a r a c t e r i z e d by w e l l d e f i n e d associated with altered  valley-side  27  forms  below.  rotational  Near rock  lower slide  Nemo  Creek,  the toe of  i s undergoing  toppling  evidenced by deep cracks shown i n F i g u r e 2.10.  F i g u r e 2.10  that  T o p p l i n g rock f a i l u r e  northward  oversteepened  dipping  a  large  failure  It  as  i s supposed  i n lower Nemo Creek B a s i n .  foliations,  coupled  with  glacially  slopes are c o n t r i b u t i n g t o these s l i d e s . They a r e  l a r g e enough t o c o n s t i t u t e mappable rock u n i t s , but because they either  ( 1 ) r e t a i n t h e i r mantle of o r i g i n a l  or ( 2 ) form blocky c o l l u v i a l  s u r f i c i a l materials  slopes s i m i l a r t o other n o n - s l i d i n g  areas, they have not been mapped i n d i v i d u a l l y . Small are  rockslides  c o n f i n e d t o areas of steep rock and c o l l u v i u m where f a i l u r e  i s c o n t r o l l e d by e x f o l i a t i o n  j o i n t i n g and perhaps  frost-wedging or seismic a c t i v i t y .  initiated  by  28  2.4.3  Rockfalls Colluvial  aprons  steep  rock  cliffs  study  a r e a . The.wide  metamorphic blocks  and  attest  plutonic  several  freeze-thaw  p e r i o d s . No  in  frequent  at  t h e base of v i r t u a l l y a l l  frequency  spacings  rocks  meters  most  fans  to the  joint  known t o be  this  and  and  result  of  in  h i g h competence of  i n the detachment  diameter.  of  the these large  In g e n e r a l , r o c k f a l l s  d u r i n g earthquake  falls  rockfalls  were o b s e r v e d  events  and  are  during  d u r i n g the course  of  study.  2.4.4  Erosion Erosional  wasting may  processes  produce  instability eroded.  processes both  local  which,  Gullies  occasionally  as  soils areas.  closely  are mutually  slope  associated  with  interdependent.  oversteepening  which  in turn, c o n t r i b u t e s m a t e r i a l to formed  occur  blankets.  solely  throughout  commonly a s s o c i a t e d w i t h morainal  are  by  area  Erosion increases  be  surface erosional  the , study  but  further processes are  sandy g l a c i o f l u v i a l - t e r r a c e s and  Gravelly-to-rubbly,  have r e t a r d e d n a t u r a l e r o s i o n a l  shallow,  processes  in  mass-  most deeper  well-drained most  other  29  2.4.5  Soil  Creep  Trees  t i p p e d o r bowed a l o n g  of  incipient  the  study  soils  landsliding  or s o i l  a r e a . The n o n - v i s c o u s  have l i m i t e d  soil  tree  r o o t i n g and t r e e o v e r t h r o w .  subject  2.4.6  Linear  s c a r s and  that  the v a l l e y  both  commonly in  chutes  sharp  f r e q u e n t l y occur  Nemo start  of s o i l  creep  indicative observed i n  to  gravelly  a s s o c i a t e d with a c c e l e r a t e d by  slopes  inclined  observed.  Figure  patterns trimlines  i n the area.  sloughing.  on  steep  indicate Many  forested that  avalanche  rocky  terrain,  Colluvial  serve as run-out  then  become  aprons or v e n e e r s ,  zones.  snow paths  on t h e s o u t h - f a c i n g s l o p e s  a n d Wee Sandy C r e e k B a s i n s . Snow a v a l a n c h e s i n steep  in  o f a t r e e on a 40° s l o p e  some minor  bottom, p a r t i c u l a r l y  or g u l l i e s .  fans u s u a l l y  on  effects  vegetation  display  were r a r e l y  particles  Only  c r e e p and p e r h a p s  Avalanching  length,  t o those  of d i s c r e t e  buttressing  Snow  avalanches  of  the  to s o i l  slopes  reach  movement  o f 35° was s t r o n g e v i d e n c e shows  creep,  creep processes  incremental  2.11  entire  p r o p e r t i e s o f sandy  the  excess  their  most  concentrated and/or d e b r i s  30  Figure  2.5  2.11  Buttressing  e f f e c t of t r e e roots creep.  resisting  soil  Climate The  maritime  southern and  predominately Fauquier  continental moist  (elev.  elevations,  Selkirk  472  at  mountains air  lower  m),  and  are  masses.  elevations, increases  e.g. 1055 mm/yr at Sandon  terrain  of  the study  The  by both  climate  is  e.g. 574 mm/yr at to  wet  at  upper  ( e l e v . 1067 m). L o c a l i z e d  v a r i a t i o n s i n r e g i o n a l weather p a t t e r n s mountainous  influenced  are s i g n i f i c a n t  i n the  area and a r e i n f l u e n c e d by  l o c a l aspect, e l e v a t i o n , r e l a t i v e topographic p o s i t i o n , and the  31  effects  of l o c a l b o d i e s o f w a t e r o r i c e .  The  seasonal  5 l o c a l weather station  Figure  2.12  Sandon  intensities Denver,  i n t o t a l monthly p r e c i p i t a t i o n  for  1941  for  that  proper are s i m i l a r of  (see  between  the  1941  and  precipitation  and  2 . 1 3 ) . Extreme  in  the  24-hour  At  in  weather  to station  at  the  precipitation New  Denver  -  precipitation  a r e shown i n F i g u r e  Sandon.  2.12  patterns  of p r i n c i p a l  b o t t o m and t h a t  elevation  1970  (see F i g u r e  from s t a t i o n  valley  with  Figure  Fauquier  t o 1970  showing l o c a t i o n s stat ions.  significantly area  from  indicate  Index map  elevations  increases  New  stations  locations)  Slocan Valley lower  variations  a l l stations,  2.14  for  t h e most  32  200 CRESCENT VALLEY SOUTH SLOCAN NEW DENVER SANDON  150  e l e v . 564 m  e l e v . 1067 m  FAUQUIER  25 O M H < 100  e l e v . 450 m  e l e v . 457 m  e l e v . 472 ra  i  50  0  -I  J  J  MONTH  F i g u r e 2.13 Mean t o t a l m o n t h l y p r e c i p i t a t i o n f o r s e l e c t e d w e a t h e r s t a t i o n s n e a r t h e s t u d y a r e a ( A i r S t u d i e s B r a n c h , B.C M i n i s t r y of Environment).  intense with air  storms o c c u r r e d d u r i n g  intensities  ranging  t h e months o f J u n e a n d  between  41 and 56 mm/day. The u n s t a b l e  p a t t e r n s w h i c h d o m i n a t e t h e summer s e a s o n g i v e  thunder c e l l s nature areal  of these  affect  storm  distribution  summer upper  that  localized  events  areas  precludes  p a t t e r n . However,  extremes  (Utzig  f o r New  1978).  Denver  are  given  to large  The  the determination  i t h a s been  The  rise  only.  t h u n d e r s t o r m s may i n c r e a s e i n f r e q u e n c y elevations  September  suggested  random o f any that  and i n t e n s i t y a t  48-hour  precipitation  in Figure  2.15 showing a  maximum o f 77 mm p e r 48-hour p e r i o d . Rainfall snowfall  occurs  i s limited  temperature data  during  every  t o November  i savailable  month  through  of  April.  the  year  while  U n f o r t u n a t e l y , no  f o r t h e New Denver  - Sandon  area.  75 SANDON  T  T  F  M  —  NEW DENVER  - —  FAUQUIER  1  1  1  1  A M J J MONTH OF L A S T DAY OF  1  1  ,  1  A S PERIOD  O  N  4  D  F i g u r e 2.14 T w e n t y - f o u r hour p r e c i p i t a t i o n e x t r e m e s f o r New D e n v e r , Sandon and F a u q u i e r from 1924 to-1979 ( A i r S t u d i e s B r a n c h , B.C. M i n i s t r y of E n v i r o n m e n t ) .  25  H J  1 F  1 M  1  1  1  1  A M J J MONTH OF L A S T DAY OF  1 A S PERIOD  1 O  1 N  1  f  D  F i g u r e 2..15 F o u r t y - e i g h t hour p r e c i p i t a t i o n e x t r e m e s f o r New D e n v e r , B.C. from 1924 t o 1979 ( A i r S t u d i e s B r a n c h , B.C. M i n i s t r y of E n v i r o n m e n t ) .  34  2.6  Vegetation  The  study  area  is  dominated  t h e Engelmann S p r u c e  S u b a l p i n e F i r (ESSF)  and  W e s t e r n Hemlock  B i o g e o c l i m a t i c Zones a c c o r d i n g t o  and  Brooke  level The  on  zone  Lake.  Plant climatic to  a  (1969).  t h e upper  ICH  Slocan  and  s l o p e s of a l l b a s i n s w i t h i n  habitat  betulifolia  Clintonia  ,  soils ,  uniflora  , ,  rapidly,  Gaultheria  chlorantha  ,  and  soil  In  ,  during Ribes  amplexifolius  and  certain  lacustre  disperma  plant  associations i s found  are  more found  in Utzig  ,  removed  times  A  t h e ICH  near  certain  restricted range  study area  include Spiraea ,  ,  ,  Fragaria  the  vesca  . In soil  table the  somewhat quite  as  , Pyrola  become  year,  complete ESSF  , more  approaches  }  Equisetum  and  of on  Cornus c a n a d e n s i s  of  ,  area.  occurring  Rubus p a r v i f l o r u s  et a l (1978).  of  membranaceum  ,  meter  those  a broad  S m i l a c i n a racemosa  abundant.  1400  Mahonia a q u i f o l i u m  from  , Vaccinium  filix-femina  within  are  oblongifolia  unifoliata  ,  , Athyrium  Carex  zones  Goodyera  a r e a s where t h e g r o u n d w a t e r  surface  horridus  borealis  -  Krajina  membranaceum, ,  -  meters.  indicative  the  Cedar  study  species  canadensis  i s not  Tiarella  shrub  throughout  ovatifolia  Gymnocarpium d r y o p t e r i s prevelant.  and  Linnaea  a r e a s where water  1700  Some s p e c i e s  Vaccinium  Shepherdia  umbellata  the  w h i l e o t h e r s occupy  dominant p l a n t  myrsinites  Red  slopes, p a r t i c u l a r l y  shrub communities are o f t e n  well-drained  Chimaphila  lower  hydrologic variables.  The  Paxistima  Western  ESSF zone o c c u r s above t h e  dominates  particular  drier,  The  Interior  T i m b e r l i n e i s at approximately  and  habitats.  wetter  (ICH)  the  by  the  Oplopanax Streptopus  arvense  and  description  of  biogeoclimatic  In a r e a s where t h e  forest  35  canopy  in  particularly  dense,  understory  vegetation  can  be  sparse. Geomorphic vegetation and  play  a  major  c o v e r . Those s l o p e s i n f l u e n c e d  colluvial  those  processes  activity  support  s u b j e c t to only p e r i o d i c  shrub  role by  in determining  snow  communities  disturbances permit  is  limitations,  o r g e o m o r p h i c p r o c e s s e s do  tree by  soils,  growth. V a r i a t i o n climate  contorta fir) lower  and  available  (lodgepole  stands  temperature  pine)  were f o u n d  elevations.  in forest  moisture. and  to p r e f e r  Otherwise,  - moisture  cover  dense  type In  Pseudotsuga  type  where  certain  forest  not  inhibit governed  areas  menziesii  Pinus  (Douglas  south aspects at  varies  changes a s s o c i a t e d w i t h  while  elevation  is largely  sunnier, d r i e r forest  only,  mature  development. F o r e s t cover thin  typically  avalanching  largely  elevation.  with  36  CHAPTER 3 SLOPE STABILITY  3.1  A p p r o a c h e s To  Despite knowledge  Slope  Stability  recent advances  of  soil  heterogeniety  and  of  determination understanding  of  rock  most  of  in  theory,  stability,  is  of  relationships  in  a  demonstrated  that  the  slopes  conditions failure  applied  accurate  stability  properties,  natural  causes  STUDY AREA  Assessment  slope  stability  mechanics  IN THE  to  in  complete  site  assessing  small  area.  this  technique  the  However, p a s t  groundwater h y d r o l o g y  at a s i t e .  costly  and  impractical.  analysing  factors  reconnaissance  level  being  controlling  been  landslide approach  used hazards  characteristics  can  second approach,  involving  statistical  analyses  be  of  the  engineering  knowledge Where t h e such  slopes  of  stability by  various  at  the  researchers. techniques  for features d i s t i n c t i v e  photographed  measurable  the  to  and  hazards  empirical  of  a number of a p p r o a c h e s  (Foggin  i f landslide  has  considerable  with p a t t e r n r e c o g n i t i o n  i n many a r e a s  is effective  experience  are  slope  t o examine t e r r a i n  of  techniques  have been d e v e l o p e d  Remote s e n s i n g c o u p l e d have  analysed,  Consequently,  analysis  requires  a specific  are  Soil  strength-stress  i n v o l v e d , and  watershed  1981).  specific  soils  entire  a  (O'Loughlin  properties  an  and  and  measurement of  and  complexity  accurate  expertise, accurate  geology  and  prevent  geotechnical of  analysis  Rice  1979).  manifested  or otherwise models field  This  in surface detected.  developed and  of  A  through  photogrammetric  37  data,  attempts  (Furbish  to provide  1981  discriminant  and  such  stability  factor  occurrence  Pillsbury  function  developing  are  factor  combinations  that  so  hazard  that  factor  maps  hazards  (VanDriel  gross  number o f  are  about  often  dependent  wrong  strength very  be  coincident  Computer  techniques  and w e i g h t i n g  quickly  the  produced  operation  interpreting  in  to  the  of  from  now  factors digitized  makes  of the p h y s i c a l  system  rigorous  stability) the  physical  studies,  the  analysis. This  can  be  difficulties  classification  Beven  evaluation....whenever •well-defined  are  necessarily  in s t a t i s t i c a l l y  Evaluations  expected  indices. If  points  structure  analysis,  we  success  the  to  be  weighting  eg. l o s s of root  out t h a t ,  may  be  "Without  some  on w h i c h t o base t h i s  type  may or  p o s s i b l e , we s h o u l d principles,  has a  i n weighting the  the r e s u l t i n g evaluation  (1981)  p h y s i c a l l y based  (slope  with  assigned  following harvesting,  underlying of  on s e p a r a t e maps t h e n  or i f c e r t a i n f a c t o r s a r e neglected,  inaccurate.  landslide  a r e a s on t h e map a r e t h e n  implicit  due  importance of v a r i o u s is  i s the  1980).  consequences.  operator  to  for  Identical  be  t o l a n d s l i d i n g . Even  assumptions  approach  related  each of these approaches  assumptions  leading  techniques  t h e map a r e i d e n t i f i e d .  manipulation  can  stability  r e g r e s s i o n and  more common  found t o  rating.  maps  common  delineated  on  i n other  facilitate  Unfortunately,  A  combinations  hazard  available  are  slope  Multiple  Factors  individually  landslide  appropriate  analyses  technique.  known  index of  1976).  relationships.  superimposed. Factor  an  a numerical  rather  be  very  failure base than  wrong of  our on  models  in our on  empirical  38  relationships  that,  to a l a r g e  extent,  o b s c u r e c a u s e and  models  that  effect  relationships." Recently, variability been  geotechnical  of  soil  developed  stability 1978  to  and  order  and  in  'probability involved  in  either This  transferred  from one  other  for  opens  the  A  way  measurement  or  region  the to  assumptions  method may  where  the  that  model has  studies  like  involve i t as  al.  can  be and  of  b e i n g more  slope easily  the  its  may  of  uncertainty  estimation  outset  render  et  safety'  amount of  limiting  actually  man  further  of  but  have  principles {Simons  a d v a n t a g e of another,  account  equilibrium  factor the  physical  for  systems Slope  into  conditions  physical  on  model v a r i a b l e s  recognizing  the  depending  M o r e o v e r , what a t  approach.  basis  1980).  'expected  several  objective  e s t i m a t e s of  groundwater  extend  a p p r o a c h has  has  applicability.  of  failure',  properties.  completely  to  Swanston  terms  of  in  approaches,  and  l a n d s l i d e h a z a r d mapping  Wu  determined  properties  take  other  universal  seem many  like  a  subjective as  any  d o e s , however, p r o v i d e  the  least  subjective  understanding  w h i c h can  strengthen  and model  weaknesses. This based is  study  model t o  hoped t h a t ,  useful  in other  is a  first  attempt  at  l a n d s l i d e h a z a r d mapping if  proven  parts  of  successful, the  province.  applying  a  in B r i t i s h the  physicallyColumbia.  technique  will  It be  39  3.2  The  Stochastic Geotechnical  In acting  simplest on  terms, a l a n d s l i d e  slope  strength  or  internal  resistance  material.  The  factor  s a f e t y (FS) of t h e  the  strength  shear  is  greater  of  (s) t o s h e a r  In  traditional  represented  by  soil  stress, in  is effective and  Sheu  version  s = C  for  y  weight 1975  of  + Cr  the  and  be  of  f o r e s t e d s l o p e s as  [qo/H  stress  slope  of  the  i s the  shear  slope  ratio  of  strength  is  (3.2) .  e'  is  included i n equation  formulated  r  by  lead  represented  (ysat- wet)M  normal  friction.  root cohesion  1973). T h i s has  +  effective  internal  including  strength equation  2  shear  tan.*'  angle  factors  O'Loughlin  + H cos £  the  to  ( T ) , SO t h a t  soil  cohesion,  should a s l o  shear  stress  (3.1)  + a'  is effective  f o r e s t e d watersheds,  surcharge and  <t>  stress  shear  equation  soil  1  equal  to shear  mechanics,  t h e Coulomb  or  i f the  = S/T  s = C  where c'  than  occurs  the  FS  1  Model  However, and  3.2  t o an  (Brown  expanded  by  + y(l-M)] tan*'  Simons  The term "effective" refers to measurements account pore water p r e s s u r e e f f e c t s .  et  tree  al.  (3.3)  (1978).  t h a t take  into  40  Symbols a r e  defined  Similarly, tangential  Figure  zone o f  according  the  simple  component  3.1.  sliding  of  to Figure  3.1.  v e r s i o n of  shear  gravitational  stress  s t r e s s due along  6  =  slope  0  =  range of angles  C  =  soil  cohesion  Cr  =  root  cohesion  qo  =  t r e e surcharge  load  ywet  =  u n i t weight of  soil  ysat  =  u n i t weight o f s a t u r a t e d  Y  =  u n i t weight o f water  H  =  h e i g h t o f s o i l mantle above shear  surface  Hw  =  h e i g h t o f water t a b l e above shear  surface  M  =  to  the  the  basal  inclination of i n t e r n a l f r i c t i o n o f  soil  soil  Hw/H  D e f i n i t i o n s of i n p u t v a r i a b l e s u s e d d e t e r m i n i s t i c g e o t e c h n i c a l model.  i s expressed  in  the  as  T = W.sinp  (3.4)  41  0  where the  is  slope  shear plane;  surcharge  angle  and  W  with  the  a d d i t i o n of  but  l o a d and  groundwater,  i s weight  the  of  the  the  equation  soil  mass above  effects expands  T = H(qo/H + r s a t ( M ) + r ( 1 - M ) ) s i n *  of  tree  to  cos* (3.5)  It  i s assumed  isotropic, surface,  in t h i s  the  and  equation  piezometric  that  the  surface  effects  3.5  are  the  soil  i s homogeneous  is parallel  to a planar  of wind s t r e s s a r e  equations  3.3  of  i t i s a l s o assumed t h a t  safety,  and  that  divided directly the  slope  shear  negligible.  to determine i s planar  and  If  factor  and  semi-  has  only  infinite. As thin type  discussed  deposits failures  generally  1  in Chapter  of on  surficial a bedrock  confined  to  shear  narrow  the  slopes  assumptions  of  the  infinite  the  slope  model  much of  materials  s l o p e s . Many of  infinite  2,  the  subject  surface  and  gullies  generally  area  to shallow debris  that cross  satisfy  slope model.  i s expressed  study  1  In  the  planar-  flows the  are  broader  geometrical  i t s expanded  form,  as  It may be noted that g l a c i a l d e p o s i t s i n the study a r e a are g e n e r a l l y inhomogeneous. T h i s d i f f i c u l t y i s p a r t i a l l y addressed by Lumb(l970) who f o u n d t h a t an inhomogeneous, m u l t i l a y e r s o i l can o f t e n be r e p r e s e n t e d as a homogeneous soil i f the soil p r o p e r t i e s are averaged p r o p e r l y .  42  c' FS  + C r + H cos *?  [qo/H + ( s a t - ywet)M + (1-M)] t a n * '  2  r  = H(qo/H + r s a t  (M) + y ( l - M ) )  cos?  sinp  (3.6)  The  model  (Cr,  i n c l u d e s terms f o r s o i l  ( C , rsat,  ( p ) and g r o u n d w a t e r  q o ) , topography  r , #'),  vegetation  (M) a s shown i n F i g u r e  3.1. As  with  sensitivity collected  a l l mathematical helps  define  models,  which  and w h i c h c a n be r o u g h l y  of  values  for  each v a l u e  one  variable  a t a time  across  i n FS c a n be c a l c u l a t e d .  shown  in  Figure  equilibrium  load  coincide  is  with  associated  with  carefully ranges  and t h e m i d p o i n t the  value  of the a n a l y s i s  i t i s evident  to slope  angle,  surface, s o i l  such  obviously  general  be  model  Realistic  selected  The r e s u l t s  piezometric of f a c t o r s  of  of  i t s range of v a l u e s , the p e r c e n t  i s highly sensitive  cohesion. Variation surcharge  estimated.  3,2. From t h e f i g u r e  relative  must  t o compute F S . By a l t e r i n g  change  friction,  values  f o r FS v a r i a b l e s a r e f i r s t i s used  analysis  as  less  soil  soil  cohesion density  important.  observations  that  that  These  are slope  internal and r o o t and  results  landslides  s t e e p s l o p e s , s e e p a g e , and s o i l s  with  tree  are  low s h e a r  strength. It  h a s been a r g u e d  that the i n f i n i t e  account  f o r many e n v i r o n m e n t a l  location  (Blong  1981).  Many  the  values  of  influence (Table  such  geotechnical  3.1  to  factors,  however,  directly  variables  i n t h e model  of the cause e f f e c t  relationships  i s the source  approach.  fails  known t o i n f l u e n c e s l i d e  fundamental  3 . 1 ) . The d e t e r m i n a t i o n  shown i n T a b l e  factors  s l o p e model  of  much  subjectivity  i n the  43  +«AFS  +%AX  100%  -%AF8  100%  F i g u r e 3.2 Diagram showing the s e n s i t i v i t y of the f a c t o r of s a f e t y FS to v a r i a t i o n s i n model v a r i a b l e s .  Many  of  the  factors  influencing  time dependent. F i g u r e 3.3 i l l u s t r a t e s reaching  slope  evolutionary term the  equilibrium.  path within  the model v a r i a b l e s are the  cycle  involved  in  Slopes can c o n c e i v e a b l y follow  any  the c y c l e , the end r e s u l t  being  long-  s t a b i l i t y . The values of model v a r i a b l e s a r e determined by severity  and  number  of  cycles  a  particular  slope  has  undergone since g l a c i a t i o n . For example, one slope may have been continuously  subjected  to l o c a l steepening by g u l l y a c t i o n and  subsequently burned by a f o r e s t rainfall  fire.  A  particularly  intense  two years l a t e r then t r i g g e r s a l a n d s l i d e . An adjacent  slope may have escaped any or a l l of the above events  and  thus  44  FUNDAMENTAL VARIABLES IN MODEL FS  FACTOR INCREASE  M  Cr  B  REFERENCES  qo  RAINFALL  0  PREVIOUS LANDSLIDE  0  Cleveland 1973 Terzaghi and Peck 1967|  DEFORESTATION  -  Brown and Sheu 1975 P r e l l w i t z 1975  ROAD BUILDING TREE CANOPY DENSITY  +  L i 1974  PROXIMITY TO DRAINAGE DEPRESSION  0  O'Loughlin 1973  WET CLIMATE  ±  Schumm 1968 Megahan 1972  SLOPE FLOODING  0  EARTHQUAKE  0  Youd 1973  SHADED ASPECT  ±  Lee 1963  Table  3.1 E f f e c t s o f v a r i o u s f a c t o r s on t h e v a r i a b l e s fundamental t o the i n f i n i t e s l o p e model.  remained  stable.  building  From  Figure  3.3  i s t h e most s i g n i f i c a n t  factor  model v a r i a b l e s <t>, C, C r , M, and p A  stochastic  version  model has been d e v e l o p e d range o f v a l u e s statistical  i t  distributions  of  input v a r i a b l e s r e s u l t  FS,  and t h a t  f o r the input  of these  t h a t assumed u n i f o r m  values  b e c a u s e an upper and l o w e r  geotechnical The  uniform  i s best  convenient  without  deviations.  The  the  alter  the  testing  of v a r i o u s  by Ward e t a l . (1978)  first  distribution  need  limit  distributions  involves  is  estimates of as  Gaussian  particularly  (or d i s c r e t e  for statistically of  in detail  slope  realistic  described  derivation  model i s d e s c r i b e d  methodology  road  a  (rectangular)  The  assigned  of  i n t h e most c o n s e r v a t i v e  t h e FS d i s t r i b u t i o n assumed  that  simultaneously.  (normal).  standard  i t can  f o r 0 , C, and C r . Monte C a r l o  determined  be  as  apparent  of the d e t e r m i n i s t i c i n f i n i t e  to allow  has  can  is  the  i n Appendix  the  range) derived  stochastic B.  determination  of a  45  Figure  realistic  3 . 3 A l t e r a t i o n s t o s l o p e e q u i l i b r i u m subsequent t o g l a c i a t i o n leading to long-term stability.  range of v a l u e s  f o r <p, C r and C o v e r  unit.  S i n g l e v a l u e s of p, M,  either  average  variables  0  resulting  value  o r 'worst  and  M  of  This d i f f i c u l t y  will  at t h i s  assumptions an  series  values  probably  an e n t i r e  point to  method  assigned  to  of e q u a t i o n s  slope,  slope  estimated  as  f o r t h e s l o p e . Whereas t h e  the  most  critical  of a s i n g l e  value,  to  the  assumed  i s sometimes p r o b l e m a t i c a l .  be d i s c u s s e d i n s e c t i o n s 3 . 5 and 3 . 6 . I t i s  are s a t i s f i e d  alternative  values  are  r , and qo a r e t h e n  o f FS, t h e a s s i g n m e n t  representative  important  case'  H,  the e n t i r e  decide  whether  or  f o r the slope being  of s t a b i l i t y  analysis  not  analysed. is  t h e model v a r i a b l e s a r e t h e n  which  result  i n the output  a l l model  of  If not,  required.  The  run t h r o u g h an  a  expected  46  distribution the  o f FS f o r t h e s l o p e . The v a l u e  frequency  distribution  is  the  factor  of s a f e t y ' E [ F S ] .  The a r e a  under  curve  with  FS < 1.0  yields  failure'  values  P, so t h a t  of  failure  P  Values of E[FS] equilibrium model,  though  factor the  combinations. intuitive  researchers hazard  the  of  the  'probability  of  (3.7)  be u s e d t o d e s c r i b e units  throughout  simplified, behaviour  It explains  judgements  and p r o v i d e s  portion  the  area.  demonstrates of  in real  made  the s t a t e s of  a slope  The  i n a semi-  having  certain  p h y s i c a l t e r m s some  qualitatively  a framework on w h i c h t o  by  base  of  various relative  classification.  The  following  delineation area.  slope  the  1  that  = p[FS<1.0].  extremely  sense ,  'expected value of  P so t h a t  and P c a n t h e n  of various  quantiative  sections  of the fundamental  Slopes  application  1  curve  o f FS a t t h e peak o f  with  deal"  with  variables  characteristics  o f t h e model a r e t r e a t e d  which  the found do  measurement in not  the allow  and study the  separately.  The term ' s e m i - q u a n t i t a t i v e ' s u g g e s t s t h a t many v a r i a b l e s a r e somewhat s u b j e c t i v e l y d e t e r m i n e d .  of  the  input  47  3.3  Soil  Shear  Soil  Strength  shear  internal  strength i s a function  friction  effective  stress  <f> d e p e n d s on  (*')  grain  interlocking, associated The  between  fine  soil  soil  v a l u e o f c'  density  pore  The  3.3.1  soils  in  shear  testing  been  developed  use  types  Shear  the  v a l u e of  values  particle  of  <t> a r e  materials  (Rahn  so  a  forces  function  of  that  - u  Shear  (3.8)  Strength <t> and  mechanical  equipment, d e s i g n e d f o r use  of  C are determined  shear for  by O ' L o u g h l i n costly,  in-situ  and  and  of  the  by  apparatus. Large soil-root  (1973) and  time  apparatuses  directly in-situ  networks, Gray  consuming.  has  (1970) but These  and  are a l s o very d i f f i c u l t roads  are  required  to for  installation.  boxes o r t r i a x i a l  laboratory  size  The  shape,  is  w a t e r p r e s s u r e u,  v a l u e s of a  transportation  the  the  of t h e a t t r a c t i v e  v a l u e of  i n r e c o n n a i s s a n c e surveys because  their  in  Soil  somewhat u n r e l i a b l e ,  other  and  2  Traditionally,  is  of  yHcos £.  E s t i m a t i o n Of  testing  3.2.  angular  is a reflection  particles. y and  Larger  angle  (C)  particle  graded,  tf' = e  where c =  equation  density.  well  effective  cohesion  size distribution,  and  soil  effective  as d e s c r i b e d by  w i t h dense,  1969).  the  (*'),  of  shear  as a s e c o n d apparatus,  testing  alternative. <t> and  equipment can  be  used  However, d e p e n d i n g  on  C v a l u e s o b t a i n e d can  be  48  inaccurate tested. soils  when g r a v e l l y s o i l s  Moreover,  a r e t o be  difficult of  with  and s o i l s  represented.  either  the  are  methods  inference  for of  testing, account  shear  strength  reasonable  o f 0 and C from  ranges  Although  such  s u b j e c t i v e and much l e s s  accurate  variability  than  the advantage of being <t> and  variations in  of  glacial  are  determination  classification.  for local  grained  o f a l a r g e number  with  t h e methods o f f e r  are  logistics  experience  engineering  highly  clasts  problematic.  s l o p e m o r p h o l o g y o r from p a s t  identical  Where  are g r a v e l l y , the t e s t i n g  r e p r e s e n t a t i v e s a m p l e s c a n be  include  coarse  l a r g e samples a r e r e q u i r e d i f c o a r s e  accurately  Alternative  large  and  C  soils  o f an  inferences actual  shear  better able to  resulting  fluvioglacial  from  the  depositional  conditions. Erosional the  slopes  <t> p a r a m e t e r  pressures Judd  according  cohesion.  Slopes  subject  soils  These  1976).  with  <t> v a l u e s  avalanching  are extremely  harvesting  therefore,  = tan*,  for  of l i m i t e d  ravel  stability  water  (Krynine  and  behave  the i n f e r e n c e of  densities  of  road  erosional  and  cuts  or  no  slopes  fills clearly  groundwater, or  i n the study  necessarily  utility.  and p o r e  generally  allowing  of v e g e t a t i o n , rare  reflect  loose materials are e s p e c i a l l y  t o be c r i t i c a l l y are  mechanics  relative  Unfortunately,  by t h e e f f e c t s  forest  dry  'loose'  uninfluenced  of slopes  to  tan*  when p r e d i c t i n g t h e  (Wilson  sometimes  i f f a c t o r s such as r o o t c o h e s i o n  to the equation  <t> v a l u e s - f o r  majority  soils  have no i n f l u e n c e on t h e s o i l  1957).  useful  on c o h e s i o n l e s s  snow  a r e a . Moreover, the  evaluated forested!  for  impacts  of  T h i s method i s ,  49  If  a surficial  genesis,  alteration,  be  similar  the  same g e n e s i s ,  et  strength,  (USC)  purposes  of  the  fine  to  Table  Unfortunately,  USC  soil  classes  distributed It  is  compile  according  therefore  materials typical  (i.e.  USC  mappable  with  and wide  the  difficult to g e n e s i s , to  and  Wilson  not  shear  basis  and  Classification  for  engineering  definitions).  Engineering  the of  world  has  allowed  <t> and  C as  shown i n  areal distribution  because d e p o s i t s are grain  size  characterize  moraine,  etc.)  units  experience  in  of  problems  the  distribution.  mappable  according  genetic  to  i n c l u d e the r a n g e s of  area.  their  t o t h e USC from t h e  reported  accurately and  C of  or  lack  in  the  classifying  genesis,  identification  W i l s o n and h i s c o - a u t h o r s d e v e l o p t h i s c o n c e p t to the areal a s s e s s m e n t of s o i l e n g i n e e r i n g 'pedotechnical engineering . 1  C  the  <t> and  Sources  unreliability  <t> and  involved with  resulting  in determining  study  of  generally  Such a c h a r a c t e r i z a t i o n p r o v i d e s  t h i s method  of v a l u e s  this  ranges  mapping m a t e r i a l s a c c o r d i n g range  having  distribution  Unified  d e l i n e a t i n g the  universal applicability  literature,  the  for  engineering  soil  1976  its  should  deposit  (Wilson  grainsize  on  expected  classification.  with  of  on  throughout  ablation  between p a s t  surficial  texture  C  necessary  link  uncertainty  is  to  i t s r a n g e of p r o p e r t i e s  fraction,  USC  engineers  according  physical properties, including  Appendix  with  3.2.  and  dependent  the  classified  i n another  been d e v e l o p e d  (see  experience  found  alteration  largely  has  is  texture,  Whereas s o i l  1  are  and  those  plasticity  System  1  to  a l . 1982).  the  deposit  and  the  of more  i n t o an approach p r o p e r t i e s termed  50 CLASSIFICATION  AVERAGE  use  LOOSE  DENSE  36-40  40-45  SUBGROUP  GW  GW-GC  * VALUE  RANGES  REFERENCES  BA,BO,M  31--38  SANDY GB  BA,M  33-36  36-42  BA,H,M  34-36  36-38  BO,M  GM  34 e s t .  M  GC  31 e s t .  M  sw  SP  33-36  36-41  BA,H,M  DRY  COARSE  32-35  35-38  BA,BO,M  WET  COARSE  31-34  34-37  BA,M  MEDIUM  31-34  34-39  BA,BO,M  FINE  28-32  32-37  BA,BO,M,H  MOIST  29-33  30-34  BA,BO,M  SATURATED  25-29  29-32  BA,BO,M  SM SC 2  28-34  M  B A = BAZANT(1979) BO = BOWLES(1979) H = HOUGH(1957) M == MOORE(1969) Table  than  3.2  Estimated angles of i n t e r n a l cohesionless soils  one USC c l a s s Values  density  (1975), C  within a single  o f 0 and C  encountered  with a r e i n f o r c i n g  and  2  also  vary  i n the f i e l d .  r o d and hammer,  complex  friction  genetic m a t e r i a l .  according  to  (see  Appendix  D  the  T h i s c a n be c r u d e l y  for  complete  3  relative estimated  a method d e v i s e d by t h e  a n d s h o u l d be c o n s i d e r e d when d e t e r m i n i n g values  (*) f o r  USDA  a p p r o p r i a t e <t>  description  of  methodology). 3  T h i s i s n e c e s s a r i l y t h e c a s e w i t h complex g l a c i a l m a t e r i a l s t h a t have <t> a n d C v a l u e s w h i c h v a r y o v e r a b r o a d r a n g e .  51  3.3.2  Range Of In o r d e r  and  hence  System  was  C  employed  genetic  as Map  B  the  Province especially  (terrain  map  terminology  and  i n Appendix  E.  the  study  requiring  area  map are  composite  are  criteria.  complex  symbols. During  was  found  from  soil  classes  inferring  knowledge of  are  very  the  USC.  inferred  USC  with  characteristic  by mode  s i z e and  explanation  surficial  c l a s s e s were e s t i m a t e d  similar  course  Where i n the  that of  are of map,  materials map  the  units  mapping,  materials  and  was  not  according  to  USC  deposition  the  the  sampling  the  requirements to  of  field  and  of  many  genetic  texture  gradation  the  t h e mapping p r o j e c t  the  to a l a r g e extent  particle  of  demonstrates that  to  modifying  Columbia,  s e p a r a t e l y ) . An  governed  the  and  of  useful in recently glaciated  found  extremely  It  British  basis  legend  according  standard  the  the  later  USC  on  Classification  on  of t h e  possible,  of  results  filed  samples were t a k e n classified  Terrain  expression  symbols and  in  the  surface  1976). The  terrain  area,  material,  the  The  study  of g e n e t i c m a t e r i a l s  units  t o be  (E.L.U.C.  distribution  mapping  system  i s designed  the  Values  in  by  found  Strength  i n the  process. Developed  terrain  c l a s s e s are and  genesis.  1  of c o a r s e  criteria  can  be  Indeed, grained  applied  in  genesis.  Terrain  1  Shear  to determine  <t> and  (TCS)  texture,  Soil  units recognised  Unfortunately, d i r e c t l y to the  the texture USC.  i n the  field  were f o u n d  d e s i g n a t i o n of TCS  to  d o e s not  include  relate  52  a p r e d i c t a b l e number o f U n i f i e d in  genetic  materials  soils  silt of  genetic occur  significant to  and  <t> v a l u e s w i t h  of l e s s  than  20% by w e i g h t ,  types. S i l t y  as pockets  within  deposits,  homogeneous  for  complex  to  fluvial  'firm'  probable  <t> v a l u e s  Surficial the  surface  determined possible  of  the  the  firm  decline  1  o f low p l a s t i c i t y  have  morainal  enough t o add a ranges  deposits.  <t>  of  of  hand, have <t>  soil  is  Thus t h e c o m p l e x i t y  reflected  in  always  materials  in soil  exhibit  planar  or  t h e range of  firm  within  relative  with a r e i n f o r c i n g  a r e denser  failures  pits  by r o a d b u i l d i n g  may  1 meter  of  d e n s i t i e s as rod.  It i s  deeper w i t h i n the d e p o s i t .  blankets  or  i n the study  veneers,  area,  $ v a l u e s a r e most a p p l i c a b l e t o s t a b i l i t y  in  and  d e p o s i t s , on t h e o t h e r  by m u l t i p l e p r o b i n g s  Disturbance  variety  i n F i g u r e 3.4.  almost  to shallow  with  Relatively  However, t h e p r e d o m i n a n c e o f t h i n rise  sandy  1  d e p o s i t s observed  that  in a  ablation  soils  v a l u e s w h i c h may v a r y w i t h i n a 5° r a n g e . unpredictibility  occur  (ML) s o i l s  silty  (SM) s o i l s ,  but a r e not c o n t i n u o u s  'loose'  sandy  sandy  to  and m o r a i n a l  range than  deposits. Silty  for various  according  colluvial  a greater  weak component. M o r a i n a l  16°  ranked  As one would e x p e c t ,  material  fluvioglacial  up  calculated  and f l u v i o g l a c i a l  percentages  rarely  were  strength.  have h i g h e r  fluvial  c l a s s e s and a r e a c c o r d i n g l y  F i g u r e 3.4. The range o f <t> and C v a l u e s  grouped  relative  Soil  giving  suggest  that  calculations.  l o o s e n t h e m a t e r i a l and c a u s e a  The l o o s e <t> v a l u e s c a n be u s e d  in calculations  of  In a r e a s where compact t i l l s a r e common, t h e r a n g e o f p o s s i b l e <t> values c a n be much h i g h e r t h a n 1 6 ° . I n - s i t u compact t i l l s a r e much s t r o n g e r t h a n r e m o l d e d o r d i s t u r b e d m a t e r i a l s .  53  I STRENGTH]  25  s*sF .sM  FIRM  LOOSE d> VALUES  use  TCS  CLASS  A5°  45°/25°  c  27°  u  <(> VALUES  29°  32°  34  c  SM  4gT  27 fgF frM fgM ^rM  34  c  29°  c  36°  SM  G  GM  SP G gkF^ g F  GP  36  27°  38°  29°  c  SM  kgF^  GM  * ** * ** * * *  sF SP SM  sF  30° sF  SP  ksF kF eF  GP  32°  34°  30°  31°  35°  36°  37°  SP  SW rM gM bM srM  27  40°  e  29  43  c  SM GW  ***  GM  35°  aC rC arC  *  38°  40°  43°  GW  * *  **  Figure 3.4. R a n g e s o f <t> v a l u e s f o r b o t h l o o s e a n d f i r m surficial materials i n the s t u d y a r e a . The a s t e r i s k s represent p l o t s o f 0 v a l u e s i n f e r r e d f r o m a n g l e s o f r e p o s e on r o a d c u t s and f i l l s near the study a r e a .  possible  road  The reasonable  cut  or  estimated when  road  f i l l  ranges  compared  with  stability.  of the  <t> g i v e n  in  repose  angles  Figure of  cut  3.4 and  appear f i l l  54  slopes study  on  roads  area.  In a l l but  <t> v a l u e s  the these work  in similar one  inferred  measurements a r e  test  data  Estimates the  and of  field.  soil  in  cohesion  characteristics  results  from  (1970)  who  deposit,  3.4  Root  this  zone  contribute particles,  to  the  exhibited tests by  silt  or c l a y soils  in  with  actual  to  In (GM)  determine on  all and  almost  all  d i d not  have  cohesion.  Similar  been r e p o r t e d by  Swanston  cohesion  of compact  area  values  from a b l a t i o n m o r a i n e  morainal  study  Further  the p l a s t i c i t y  little  derived  a  of  3.4.  performed  gravels  exception in  plots  in similar materials.  testing  soils  the  ranges  fraction.  have  shear  lens  Figure  were  silty  the  or  are  till  and  the  glaciofluvial assumed t o have  cohesion.  Strength  on  laterally  and  s l o p e s . The  determine  fine  and  A l a s k a . With the  Cohesion effect  (SM)  0 for silty-loam  all  negligible  to  of  encompasses  a r e more d i f f i c u l t tests  of t h e  Atterberg  southeast  occasional  measured  limit  determined  approaching  angles  south  range  on  assumed  order  sands  measurable p l a s t i c i t y  assumed  the  cohesion  Atterberg  silty  the  from t h e measured  repose  collected  cases,  m a t e r i a l s t o the  shown as a s t e r i s k s  samples  in  case,  i s needed t o c r o s s - c h e c k  shear  in  built  soil is  imparted  to s o i l s  by  s t r e n g t h w i t h i n the confined  s t r e n g t h to the anchoring to adjacent  substratum,  and  to  to  the  t r e e r o o t s has root  z o n e . In t h e  upper meter of  soil  by  b i n d i n g and  the  underlying  root networks,  important study  soil.  area,  Roots  reinforcing  bedrock  transfering  inducing negative  an  soil  surface  surcharge  pore pressures  by  can  or  loads root  55  capillary Cr  tension  (O'Loughlin  i s a term which d e s c r i b e s  soil  strength  geotechnical  3.4.1  possible  model t o a c c u r a t e l y  Of Root  and  Sheu  of  .stress-field  root  cohesive  failure;  individual  modelling  2 i s i m p r a c t i c a l and c a n  soils  having  such a computation overturning leading  strength  testing  the  and  inaccessibility Method of  error  1, l i k e  analysis are strength, strength.  tree  Method  as  only  failures  Method  in-situ  (5)  tensile  applied  the other many  soil-  strengths.  to  cohesive  i m p r a c t i c a l as  requires  in-situ  because  of the study  the  to  values  studies  accurately  (see O'Loughlin  determine  1973  failures root  strength  versus  on r o o t  T h i s may p r o v e t o be an e x t r e m e l y  by  as  useful  root  or s o i l  different values f o r  Morton  tensile  sources  i n a back  a t time of f a i l u r e  produced c o n f l i c t i n g  the  area.  assumed c o r r e c t  of slope  shear  of  methods, h a s many p o s s i b l e  input  difficult  4  impractical  5 c a n be employed when d a t a  available.  (4)  the p o s s i b l e presence of r o o t - r o t  deemed  Consequently, have  creep;  ( 1 9 7 3 ) ; and  be  five  soil  overthrows;  known r o o t  s u c h a s seepage c o n d i t i o n s  researchers identical  overthrow.  o f many p a r t s  because  i n the  r e q u i r e s a known wind v e l o c i t y i m p a r t i n g  was  on  i n c l u d i n g (1)  of  b e h a v i o u r . Method 3 i s a l s o  moment and i g n o r e s  to  roots  parameters  (2) a n a l y s i s  with  Method  viscous  of  determine.  measurements s u c h a s t h o s e by O ' L o u g h l i n root  effects  cohesion  (1975) and Wu e t a l . (1979) d e s c r i b e  of a slope  analysis  root  Strength  ways o f e s t i m a t i n g  back-analysis (3)  t h e combined  and i s one of t h e most d i f f i c u l t  Estimation Brown  1973). The a p p a r e n t  1975).  strength are method  as  56  research species  into  the  s t r e n g t h and r o o t i n g h a b i t s o f v a r i o u s t r e e  develops.  3.4.2 Range Of Root C o h e s i o n Forest  cover  maps c o m p i l e d  when  supplemented  basis  f o r determining  influenced forest size. the  by  type,  Values  with  root  data  Ministry  aerial  tree  estimated  from  provide the to  be  according to  density  and  tree  for accurately delineating  of Cr v a l u e s . A c e r t a i n from  Forests,  likely  of Cr v a r y  depth,  exists  of  photos,  of s l o p e s  Values  soil  v a l u e s c a n o n l y be c a l c u l a t e d or  from  cohesion.  No m e t h o d o l o g y c u r r e n t l y  analyses,  B.C.  the d i s t r i b u t i o n  r o o t i n g depth,  distribution  by  realistic  site-specific  range of Cr  landslide  p r e v i o u s work i n s i m i l a r  back  forests  elsewhere. A d e b r i s avalanche fits  the  analysis. a planar water  criteria  found  for  root  shear  diverted  the  and  has  i n a shallow  that the f a i l u r e  a l e n g t h t o depth  C = 0  and  slope  <t> = 38°-43° a r e t a k e n from  the l o c a l  forest,  study  determination  by a l o g g i n g r o a d c o m p l e t e l y  the use of the i n f i n i t e  estimated  of  area  by b a c k -  colluvial  surface at the colluvium-bedrock  allows  is  1  slope  10 km  cohesion  L a n d s l i d e D-14 o c c u r r e d  ( s e e F i g u r e 3 . 5 ) . The f a c t planar  within  interface  soil  on  where  saturated the slope occurs  ratio  model.  from  Table  rsat  =  on a  uniform  g r e a t e r than  Input  values  10 of  3.3, qo = 250 kg/m  1960  kg/m  3  can  be  The v a l u e s qo and r s a t , t h o u g h somewhat i n a c c u r a t e l y e s t i m a t e d , should not i n t r o d u c e t o o much error, a s FS i s much less s e n s i t i v e t o t h e s e than the o t h e r parameters (see F i g u r e 3.2).  2  57  estimated  for firm  GW s o i l  1  , H = 1.0 meters and * = 35° were  d i r e c t l y measured and rw = 1000 kg/m  3  Firsthand  observations  of  water  is a  physical  issuing  constant.  from the head scarp  F i g u r e 3.5. L a n d s l i d e D-14 showing the f a i l u r e of a t h i n of s o i l on a planar bedrock shear s u r f a c e .  s t r o n g l y suggest failure,  that the s o i l was  saturated  kg/m  2  root  cohesion  failure,  time  of  back-analysis  values ranging between 301 kg/m  2  and 409  f o r <f> values of between 38° and 43°. I n - s i t u shear t e s t i n g by Endo and Tsuruta  f o r e s t s produced 1200  the  i . e . M = 1.0 ( r e f e r to F i g u r e 3 . 1 ) . Assuming that the  f a c t o r of s a f e t y was 1.0 at the time of yields  at  veneer  kg/m .  produced  2  (1968)  in  birch  values of root cohesion ranging between 200 and  Using  lower values  a  similar ranging  technique, between  8  O'Loughlin and  186  (1973)  kg/m  2  for  58  selected tests  sites  were  similar  in  southwestern  conducted  to  O'Loughlin's  encountered  shear  tests  3 t o 4 cm,  root  cohesion.  (1973)  realistically  found  fall  soils  These  of  ranging  though  provide  reinforcement  trees could that  conceivably  have  depending  the  rooting forests  on  zone.  available,  assume t h a t  value  orientation and  estimate  of  Cr.  of  the  the  between plane  1200  unique  kg/m  2  their  m a g n i t u d e of  value  to  i n the  the  could  450  kg/m , 2  to  for  to  area  the birch  forests.  delineate  study  Cr  r e g i o n of  kg/m . In n o n - f o r e s t e d 0.  in  relative  t o hardwood  values  of 2  mountain technique.  0 and  It i s t h e r e f o r e necessary  i s assumed t o be  same  the  Swanston  in  2  foregoing,  shear  impossible  450  range.  more  soils.  of  in a l l f o r e s t e d areas  overall  values  kg/m  less  techniques,  assumptions  Tsuruta's being  2  u s i n g the  where  of  kg/m  t o 450  with  1 d a t a p o i n t f o r Cr  r a n g e between 0 and of Cr  350  view any  i t is virtually  distribution  will  in  the  analysis  t o 300  to  diameters  cohesion  Alaska  impart  i s d i s r e g a r d e d as  With only  from  some  values  Endo  160  fraught  do  appears  root  w i t h i n the  calculation,  It  that  back  soils  area. Unfortunately,  contribute to  with  southeastern  values,  study  O'Loughlin's forest  included roots with  work  (1970) d e r i v e d v a l u e s till  i n the  only  Columbia.  cedar-hemlock  which o n l y p a r t i a l l y  further  O'Loughlin  coastal  those  than  Doing  in  British  any  study areal  subjectively v a l u e s of areas,  Cr the  59  3.5  Groundwater Piezometric  effective  normal  strength. erosion,  pressures  In  s t r e s s on  addition,  subsurface  seepage p r e s s u r e ,  flow  pecolation  transmitted  horizon is  water  (duff  via  layer)  then conveyed  basal  zone  bedrock  or  hydraulic  compact  root  surface  allow  the  c h a n n e l s . The Chamberlain  relative factors  of  till.  to  soil  with  matted The  to  open s o i l  will  transmitted  to  to  soil  root  soil  at  to the  first  develop; the  soil  further suggests that most  important  'openness'  impermeable if  less  not,  of  water to  r a p i d l y with  a  with high  watertable  or  'open' as i t  matrix  between  network. root  development  the  soil  a  soil.  water  matrix  forming  If  layer, i t is likely  soil  organic  interface  of  infiltrating  permeable  water  conduits  i s termed  a natural drainage  i s the  and  surface  a true  by  sufficiently  rainfall,  the  soil  depth  the  caused  c h a n n e l s . The  s a t u r a t i o n of  has  of  infiltration  permeable  The  of  typical  intense  allow  model  surface  zone d r a i n s  does n o t form.  (1972)  the  an  roots  basal  surface  model d e s c r i b e s  complete  respect  penetrate  soils  these h i g h l y conductive  c o n d u c t i v i t y and  piezometric d o e s not  through  composed  the  individual tree  soil  strength,  'interflow'  vertical  extremely  to  the  earthquakes.  impermeable b e d r o c k ,  t a b l e . During  to  reduce  cohesive  forest  normal  the  of  an  to  lower  contribute  C o l u m b i a . The  s u c h as  to the  thereby  can  during  to  in B r i t i s h  prevent  and  introduced  applicable  to  groundwater  reduction  liquifaction  conditions,  restrictive  is  slope  of w a t e r movement p a r a l l e l  boundary  by  groundwater  (1972)  mountainous t e r r a i n process  a  piping,  or  Chamberlain groundwater  induced  roots that  will  between  an be  root  60  conduits  and  conductivity  in  groundwater  1 meter  mantle of bouldery  monitored  illustrates  with  10  through  cm.  full  rapidly  the  It  is  soils,  important  sandy  hydraulic Depending  loam  inferred  other  to  that  than  table  base  position of  is  the  slope more  rainfall  coupled  more l i k e l y  with  surface  to r i s e  seepage  also  concentrate in  steep  a  in  of p i e z o m e t r i c  head  drainage  did  of  o f water  not  compact  root  allow  soil  below  reach  where  from the  temporary  pressures are areas.  piezometric  drainage  in  the  cause  surfaces  depressions  s t u d i e s by O ' L o u g h l i n  depressions  zone.  input  and c r e a t e  or elevated  the  steady-state  can  i n these  by  site,  groundwater  infiltration  case,  root  the  is  but i s  In t h i s  the  1980). P i e z o m e t r i c  soils  Water  largely  of  to  tills,  zone  path.  governed  stability  seepage  open  flow  position  interflow. Piezometric linear  was  the  t o ..the s u r f a c e  to influence slope  occur  of  slope,  (Freeze  A r e a s o f permanent can  with a  till  surface  likely  upslope  permanent  compact  impermeable  is  of  or  slope  and m i n i m a l mat f o r m a t i o n .  relative  table  till  tough  e q u i l i b r i u m . At the t o e  piezometric  O'Loughlin's  rapid conduction  i n t o a deeper  conductivity  groundwater  over  the  significantly.  the  incorporated  on t h e  hydraulic  predicting  convex  Measurements  to rise  transmitted  groundwater  in  t h i s p o i n t . A steep  root penetration  subsequently  lower  of up t o 80 mm/day i n d i c a t e d a maximum r i s e  pressures  Deeper allow  are  t h e r o o t mat a t t h e compact  piezometric  of  1978).  piezometers.  rainfalls  soil  p o s i t i o n s on a s l o p e . Some o f  work  only  closed  considerations  (1973)  during  a  ( d e V r i e s a n d Chow  These probable  result  shallow  (1973) soils  61  approximately piezometric Likewise, study  head  meter  indicated  80  mm/day  depressions  occasionally  indicating  complete  though not a r e a l l y occurrence  O'Loughlin  1973).  traditional  piezometers surface  was  indicators  conditions. areas,  indicate  Mottled  a periodic  Where more d i r e c t vegetation with  types  some  have  success  s p e c i e s may  occupy a broad  restricted  to,  conditions. areas  and  When  are observed  table  localized  and  slopes  with  monitoring  is  a r e a . Where  subsurface  at  or  with  on s t e e p  possible,  groundwater  near  observed  discharge  the  in soil  indicators  a r e not  groundwater  ground  pits  of a n e a r - s u r f a c e water  also  table. available, conditions  S a t t e r l u n d 1978). C e r t a i n p l a n t  indicative  plants  seepage  S t e v e n s 1967  range of h a b i t a t s w h i l e  thus  runoff  ( B i s h o p and  used t o i n f e r and  ephemeral  s e e p s were mapped as  groundwater  (Pole  of t h e  to  or f r e e water  been  soils  significant  i n the study  attainment  input.  been  of  s p r i n g s and  soils  rainfall  These  are used t o d e c i p h e r  Swamps,  rises in  Pressures  method  i . e . where t h e water  surface.  of  e x t e n s i v e , have  not f e a s i b l e  90 cm  permeable  signs  i n many a r e a s  to  maximum  saturation.  E s t i m a t i o n Of P i e z o m e t r i c The  70  in shallow  show  soil  landslide  3.5.1  deep  g i v e n an  linear  area  areas,  1  of,  habitats  slopes,  slope  o t h e r s may  specific restricted  be  moisture to  instability  seepage can  be  suspected. The moisture scheme  use  of  plant  indicators  r e g i m e s r e q u i r e s an e x i s t i n g for  for  assessing  vegetation  the b i o g e o c l i m a t i c subzone  ecological  classification  under c o n s i d e r a t i o n o r a  62  reconnaissance vegetation  indicators  conditions. Columbia  Such  a  and  Ministry  of  the  area,  study  exists  each  and  each  the subzones  Interior  for  Engelmann  Spruce-Subalpine  guarantee  sometime d u r i n g  regime  a  precipiation  (iCHal)  subzone  on  a subzonal  precipitation  and  F i r Subzone  similar  are given  soil  Moist  the  Moist  (ESSFc).  Plant  i n t h e subzone c a n site  then  be  i n the study  i n T a b l e 3.3. does n o t g u a r a n t e e  saturation.  On  the  of w a t e r - l o v i n g p l a n t a s s o c i a t i o n s can table  i s near-surface at  mesic  sites  are i n a state  i n p u t and s u b s u r f a c e  least  biogeoclimatic input than  subzone  a mesic  site  and must be s c r u t i n i z e d basis. inputs  The  ICHal  ranging  of e q u i l i b r i u m  outflow. A  recieves  a  mesic much  i n a d r y subzone.  regimes a r e t h e r e f o r e not q u a n t i t a t i v e l y to  of  into  the year.  definition,  wet  determine  a number o f s u b z o n e s . In  at a p a r t i c u l a r  t h a t t h e water  between p r e c i t a t i o n in  i s to  areas  wet-site plant indicators  hand, t h e p r e s e n c e  By  British  i n c l u d e the Kootenay-Columbia  the absence of o c c a s i o n a l n e a r - s u r f a c e  usually  and n u t r i e n t  B.C. h a s been d i v i d e d  including  regime d e f i n i t i o n s  absence.of  step  encompassing  with p l a n t s observed  area. Moisture  other  between  southeastern  the f i r s t  Cedar-Hemlock Subzone  f o r a given moisture  The  range of m o i s t u r e  Southeastern  regions,  patterns  compared  relationships  t o b i o g e o c l i m a t i c maps p u b l i s h e d by B.C.  Forests.  climatic  species  the  using plant indicators,  three c l i m a t i c  Southern  establish  scheme  subzone by r e f e r i n g  Southern  tp  (Comeau e t a l . 1982).  When the  of the area  and  higher Moisture  e q u i v a l e n t from  with  subzone  r e s p e c t t o groundwater  ESSFc  between  site  subzones 70  and  150  average cm/yr  63  Table  VERY XERIC  Water removed extremely r a p i d l y i n r e l a t i o n to supply; s o i l i s moist f o r a n e g l i g i b l e time a f t e r ppt.  XERIC  Water removed v e r y r a p i d l y i n r e l a t i o n t o supply; s o i l i s moist f o r b r i e f p e r i o d s following ppt.  SUBXERIC  Water removed r a p i d l y i n r e l a t i o n to supply; s o i l i s moist f o r s h o r t p e r i o d s following ppt.  SUBMESIC  Water removed r e a d i l y i n r e l a t i o n t o supply; water a v a i l a b l e f o r moderately short periods f o l l o w i n g ppt.  MESIC  Water removed somewhat s l o w l y i n r e l a t i o n t o supply; soil may remain moist f o r a s m a l l , but s i g n i f i c a n t p e r i o d o f the year.  SUBHYGRIC  Water removed s l o w l y enough to keep the s o i l wet f o r a s i g n i f i c a n t p a r t of the growing season; some temperary seepage and p o s s i b l y m o t t l i n g below 20 cm.  HYGRIC  Water removed s l o w l y enough t o keep the s o i l wet f o r most of the growing season; permanent seepage and m o t t l i n g p r e s e n t ; p o s s i b l y weak g l e y i n g .  SUBHYDRIC  Water removed s l o w l y enough to keep the water t a b l e a t or near the s u r f a c e f o r most o f the year; gleyed m i n e r a l or o r g a n i c s o i l s ; permanent seepage l e s s than 30 cm below the s u r f a c e .  3.3. D e f i n i t i o n s  of m o i s t u r e  regimes (from  Walmsley e t a l .  1980) .  respectively.  Whereas p l a n t s do n o t  piezometric  head  caused  depressions  with  piezometric  s u r f a c e s a t or near  time  during  slope  stability  subxeric  by  intense  t o mesic p l a n t  the the year. and i n t h e s e 1  reflect  rapid  changes  rainfall,  drainage  could  have  t h e g r o u n d s u r f a c e a t some  brief  Dynamic areas,  indicators  in  fluctuations are c r i t i c a l to plants  fail  to  accurately  64  indicate  critical  Examination opportunity using  plant  table  just  indicated  placed  these  of s o i l  to verify  though  below  may  by o t h e r use  examination  of p l a n t  primary  regimes,  interest  t a b l e to the v e r t i c a l  is  This  important  distance  ratio  only  more e m p h a s i s  the s o i l ,  as  sites  completely  by  should  many  of  o r may be Even  tool for  replace  the  slope  stability  a n a l y s i s i s the  between  the shear  surface  soil M  to  do  the  study  in  delineating  moisture  o f M.  water  (Walmsley e t a l . 1980).  thickness  can  this, area  as  above  be g e n e r a l i z e d  i f the depth t o f a i l u r e  groundwater  values  detected  disturbed  i t cannot  to  water  regimes  may have a  materials.  of the v e r t i c a l  moisture  r e g i m e made  i s , t h e r e f o r e , not  be  sites,  o f f e r s an  i n d i c a t o r s c a n be a v a l u a b l e  ratio  plane.  that  by e x a m i n i n g  species  soil  can  drier,  profiles  of m o i s t u r e  zone  which  invade  invader  of s o i l  soil  textured  rooting  gained  recognizing moisture  shear  or exposed  p i t . On d i s t u r b e d  on r e s u l t s  conditions.  the determination  the  a soil  the  Of  pits  i n d i c a t o r s . A coarse  indicators  displaced  groundwater  by t h e v e g e t a t i o n ,  excavating be  subsurface  plane  best  regime d i s t r i b u t i o n s  potential  for different  i s estimated.  reconnaissance is  the  and t h e  mapping  accomplished and r e l a t i n g  It of by  them t o  65  3.5.2  Estimated Surface  evident  drainage  in g u l l i e s  permeable  sandy  conductive rainfall Such  sites,  elsewhere  M  respect  approximately 3.6  assumed  1  1972,  to  be  at  Figure  3.6  appreciable  have  behave  the  precipitation  in  precipitation These  trends observed  in  soils  mesic  where  mesic moisture  the  slopes,  other  the or  t o between  can  be  at  gullies, soils and  parameter  steep  soils  i s shown i n  shear  surface  soil-compact  than  slopes  is till  do  not  50 mm  of  rainfall.  extreme r e c o r d e d  at  Fauquier  assuming hand,  receiving  rise  soils  Patric  the  B.C.  shedding  less  t o 0.04,  concave  of  similar  data,  areas.  in similar 1978,  high  0.4  and  study  given  area  soils  the  same  s l o p e s , the v a r i a b l e 0.9  with  the  given  input.  frequently shallow  On  M  highly  toe  Chow  on  soil-bedrock  in M with  with  allows  southwestern  these  Highly  of h a n d l i n g  variation  input  only  area.  only  been o b s e r v e d  shows t h a t convex  e x t r e m e on  M could conceivably  interlaced  is  s a t u r a t i o n i n most  1967). The  raised  similarly.  study  d e V r i e s and  deep  rises  only  i n the  depressions,  r e c o r d 56 mm/day p r e c i p i t a t i o n  would  rainfall  behaviour  rainfall  meter  full  has  f o r comparison. For  interface.  The  hydrologic  to  heavy  soils,  reaching  Swanston  Area  e v i d e n t l y capable  i . e . drainage  and  from  gravelly  (Chamberlain 1968  have  to  In S t u d y  t o bedrock  s a t u r a t i o n as  Swanston  Figure  scoured  soil  to reach  with  resulting  inputs without  receiving  Groundwater  root networks are  'open'  etc.,  E f f e c t s Of  are  soils  i n the  correlated study  area. Planar  generally subxeric deepen or on  with  moisture to  convex  t o s u b m e s i c and  steeper  slopes grade  to  subxeric  to  s l o p e s where o n l y  a  s h a d e d a s p e c t s . The  regimes dominate the  regimes  66  Swanston O'Loughlin  1.0 2  (1967) (1973)  5  0.8  ii O t  c o n c a v e receiiving  slopes;  0.6  U J Q OL OL  UJUJ  0  4  convex  0.2  UJ  <0C  10  20  30  shedding  40  slopes  50  PRECIPITATION  60  70  90  80  mm/day  F i g u r e 3.6. V a r i a t i o n of t h e r e l a t i v e p i e z o m e t r i c head M w i t h r e s p e c t t o 24 hr r a i n f a l l i n p u t s as d e t e r m i n e d by Swanston (1967) and O ' L o u g h l i n (1973).  slight  rise  rainstorm. gullies to  in piezometric On  the  observed  other  on  the  hygric vegetation,  slope.  In t h e s e  likely  to  head can hygric allow  areas,  reach  a l s o be  particularly relative  expected  p l a n t s as m o i s t u r e  On thicker  lower and  to  slopes  on  the  piezometric  lower head  in g u l l i e s  not  be  too  heavy  subhygric  p o r t i o n s of is  much  in  supporting  f l u c t u a t i o n s may  a  and'subdued  sometimes s u p p o r t  A rapid rise  surficial  subhygric  3.7  typical  study  i n the  during  depressions  above 0.4.  where  flatter,  expected  the more  piezometric subhygric  to  short-lived  to  develop.  more common. F i g u r e slope  hand, d r a i n a g e  same s l o p e s  values  phreatophytes  head w o u l d be  is  a  area  and  deposits  are  hygric moisture  schematic showing  the  generally regimes  cross^section relationship  of  are a  between  67  slope, sites  soil  -depth,  are almost  evident  at  the  t e r r a i n c l a s s , and m o i s t u r e  e n t i r e l y confined base  of  to  locally  areas  regime.  where  steepened  Hygric  seepage  terrace  faces  is and  F i g u r e 3.7 T y p i c a l p r o f i l e of an i d e a l i z e d h i l l s l o p e i n t h e s t u d y a r e a showing m o i s t u r e r e g i m e s , p r o b a b l e g r o u n d w a t e r t a b l e p o s i t i o n s and s u r f i c i a l m a t e r i a l t y p e s .  floodplains Using  near  streams.  both  surface  distribution traversed delineated of  of  during on  and  groundwater the course the basis  plant was  of  t h i s work was done c o n c u r r e n t l y  plant  ecologist  also  working  the  roughly delineated.  the  of slope  indicators,  survey  position  were  Areas not  subjectively  and m o r p h o l o g y . Much  w i t h Greg U t z i g ,  i n the study  areal  area.  a soils  and  68  The be  results  included in  the  Classification Utzig,  of  Office.  file  and  report the  with  B.C.  study  area  and  of  Forest,  Arrow  regime d e l i n e a t i o n s o f t e n c o r r e s p o n d of  linear  gullies,  drainage  to  Ecological  Mountains Study Area"  Ministry  of g r o u n d w a t e r  regimes a d j a c e n t  where  "Terrain  are  by  G.F.  District to  terrain  depressions  fronts.  Observations  cuts  r e g i m e mapping p r o j e c t  entitled  Valhalla  the e x c e p t i o n  terrace  moisture  the m o i s t u r e  of  Moisture  units with  of  possible. and  t o the  This,  table study  positions a r e a were  coupled  for  both  ICHal  made  at  with observations  p r e v i o u s l y published data  generalizations  in relation  and  lead  to  ESSFc  the  to  road i n the  following  biogeoclimatic  subzones: (1) X e r i c t o m e s i c s i t e s on v e n e e r s and thin blankets surficial m a t e r i a l g e n e r a l l y e x h i b i t i n t e r f l o w at bedrock i n t e r f a c e . T h i s flow i s sometimes rapid drainage d e p r e s s i o n s a f t e r storms.  of the in  (2) X e r i c to m e s i c s i t e s on t h i c k e r b l a n k e t s of s u r f i c i a l m a t e r i a l may have wate^r t a b l e s a p p r o a c h i n g t h e s u r f a c e i n d r a i n a g e d e p r e s s i o n s but a r e u s u a l l y d e e p e r t h a n 1 meter. (3) S u b h y g r i c to hygric s i t e s a r e most commonly f o u n d i n s o i l s deeper than 1 meter and usually have water t a b l e s w i t h i n 1 meter of t h e s u r f a c e (4) O c c a s i o n a l l y s u b h y g r i c t o h y g r i c p l a n t i n d i c a t o r s o c c u r on shallow w e l l - d r a i n e d s l o p e s where p l a n t r o o t s a r e a b l e t o t a p permanent i n t e r f l o w i n m i n o r d e p r e s s i o n s . (5) S u b h y d r i c t o h y d r i c s i t e s a l w a y s the s u r f a c e .  On  straight  slopes  where  groundwater  have  watertables  at  i s not  concentrated  and  69  where p o t e n t i a l t h e maximum to  be  planar debris s l i d e s  value  those  are less  of M f o r v a r i o u s m o i s t u r e  shown  i n Table  than  regimes  m  thick,  i s estimated  3.4. These v a l u e s do n o t a p p l y t o  MOISTURE REGIME  M  MOISTURE REGIME  Very  0  Subhygric  Xeric  2  M .5  Xeric  .1  Hygric  1.0  Subxeric  .1  Subhydric  1.0  Submesic  .1  Hydric  1.0  Mesic  .2  T a b l e 3.4. Maximum v a l u e s o f M f o r v a r i o u s m o i s t u r e regimes, i n E S S F a l and ICHal s u b z o n e s where s h e a r p l a n e s a r e l e s s t h a n 2 m deep.  deep  rotational  hydrology treating  3.6 S l o p e  The  of  variety, of  large  locallized  nor  slopes  to must  drainage not  be  depressions.  The  g e n e r a l i z e d without  c o n c e n t r a t i o n s of groundwater s e p e r a t e l y .  Angle  geotechnical  inclination potential  slides  model  of the shear slides  to  be  the slope angle  t h e shear  plane.  plane  is  highly  sensitive  to  the  p a s shown i n F i g u r e 3.2. Whereas  analysed  are  of  the shallow  i s assumed t o be i d e n t i c a l  planar  t o the slope  70  3.6.1  Measurement Of  Slope  Maps d e l i n e a t i n g certain  interval  topographic  be p r o d u c e d  and  classes  Slope are  by  aerial  best  slope  between  found  33°  and  processes,  i n the 35°  that  study  is,  to  more  In S t u d y  a r e a . One  originating concave,  from  are  steeper  flatter  Area into  intervals  cliffs  slope  profiles  (Caine  soil  cover,  rock outcrops  upper  limit  uniform  forested  inclined  at  typical  of  falling found Valley Though  less  than  glaciated  either or on  on  15°  either  this  serve  of p r i m a r y limit.  valleys t o 35°  s c a r s i n the 30°  interest  Concave  till  range.  Slopes  of  are  run-out  U-shaped  gravity  to  36°.  to t h i s  zones  for  snow  and the Most  study  mantled  are  slopes  inclinations than  valley  processes,  by  1969). Young  15°  t h e e a s t - f a c i n g s l o p e s of t h e main and  of  altered  r o o t mat,  less  at  gravity  vegetation  g e n e r a l l y have s l o p e  not d o m i n a t e d by as  or  is typically  cirque basin floors  usually  sometimes  slope angle slopes  w i t h i n the  breaks  affected  s l o p e s above and  for a slope with continuous  of t h e  which,  with pockets  sometimes  (1972) m e n t i o n s t h a t without  or  n a t u r a l break o c c u r s  f a n s and  fans  of  measurements.  c o i n c i d e n t with n a t u r a l  colluvial  a (1)  surveys  above w h i c h s l o p e s a r e d o m i n a t e d by  c o l l u v i u m . However c o l l u v i a l avalanches  within  (2) a n a l y s i s  ground  subdivided  when d e l i n e a t e d , have b o u n d a r i e s in  photos;  by  field  Angles  occurring  t h r e e methods i n c l u d i n g :  either  (3) a c t u a l  Of  slopes  of  produced  3.'6.2 D i s t r i b u t i o n Slope  with  measurement  maps  photogrammetry;  units  can  photogrammetric  Angle  are  Slocan  bottoms.  these  slopes  avalanches  and  71  landslides debris  in  the  steeper  particularly  on t h e lower  fans.  On t h e b a s i s o f t h e s e the  valleys,  study  classes  area  shown  are  general  somewhat  in Figure  observations,  arbitrarily  the  slopes  grouped  into  - --  - •-  of  the 4  3.8.  HORIZONTAL DISTANCE  - -  -  F i g u r e 3.8. S l o p e showing t h e t y p e s  Wherever  ---  not a l l o w  area; to  possible,  a complete  therefore aerial  slopes  survey  were  interval)  of  1:50,000  method o f Chapman  during  ground  photos. Study area  of a l l s l o p e a n g l e s  p h o t o s and t o p o g r a p h i c  t o 1:20,000 p e r m i t t e d  bar-template  measured  on a e r i a l  i n t e r p o l a t e from known t o unknown Enlargement  -e  c l a s s i n t e r v a l s used f o r the study area of s l o p e s o c c u r r i n g w i t h i n each c l a s s .  t r a v e r s e s and p l o t t e d d i r e c t l y did  - ----  size  i n the study  maps were employed  slopes.  topographic slope (1952).  maps (100 f t c o n t o u r  u n i t s t o be d e f i n e d by t h e I t was f o u n d  that  10°  to  72  15°  slope  class  cartographically topography Map  C  and for  to  error  variations  indicate  photos  slope  1:50,000 map  be  used  boundaries  indicated  that breaks  in slope are  eg. a t a l u s  colluvial  s l o p e below a  moraine.  By  seen appear,  decision  made as  t o be  possible,  the  results  m e a s u r e m e n t s . An  the to  of t h i s  In  s l o p e map units  map  account truth  artificial  final  from  mantled with  the  with  slope  changes steep  ablation many  Where  major  photos enables  a  i s most a c c u r a t e . Where  resembles  when compared w i t h  the  s l o p e map,  with  Nemo C r e e k B a s i n  map  and  mapping  face or a  a r e compared  and  inclination  with multimodal  slope  Terrain  with a e r i a l  lower  s l o p e map  slope  with  correspond.  process  topographically derived  derived  bench  to which boundary  and  of  not  often associated with  roughly  3.9.  representation  coupled  discussed.  terrain  Figure the  method;  t o d e l i n e a t e more n a t u r a l  comparison  example  The  by:  then e n l a r g i n g  are  s l o p e below a r o c k  flatter  comparing  discrepancies  are  u n i t . Ground  boundaries  when  previously  are  boundaries  i n many a r e a s .  maps  boundaries  is  introduced  and  w i t h i n t h e map  complex  survey  s l o p e c l a s s e s w h i c h do  unit  m a t e r i a l type,  unit  inaccuracies  terrain  in  of t h i s  that slope unit  can  slope c l a s s  result  i n u s i n g the b a r - t e m p l a t e  i n topography  somewhat e r r o n e o u s  accurate  of  delineate  extremely  the  error  to  i n v i e w of t h e  subject to  effect  required  s e p a r a t e l y ) . The  in producing  the a v e r a g i n g  Aerial  end  filed and  were  units  The  1:20,000; o p e r a t o r  measurements and  map  artificial  machine it  readable  encountered.  (slope  largely  intervals  both is  than  a  the  ground  i s shown i n terrain  more  map  accurate  the t o p o g r a p h i c a l l y  ground  measurements.  class  distributions,  e.g.  73  (a) slope map derived from 1:50,000 topographic contours  (b)  (c)  terrain map  slope map Interpreted from maps (a) and (b)  F i g u r e 3 . 9 T h r e e maps o f a p o r t i o n o f l o w e r Nemo C r e e k B a s i n s h o w i n g (a) t h e o r i g i n a l s l o p e map d e r i v e d f r o m . a t o p o g r a p h i c map; (b) t h e o r i g i n a l t e r r a i n map; a n d ( c ) t h e more a c c u r a t e s l o p e map r e s e m b l i n g t h e f i r s t two m a p s .  74 t e r r a c e d or hummocky t e r r a i n , the s t e e p e s t mode i s assumed to be  the  most  slope  class  larger This  critical  i s , consequently,  d e s i g n a t i o n . Map  area  covered  i s because  steepest)  and  by  class  class;  Miscellaneous Tree  two  weight  variables  and  which  and  they  detail  the  other v a r i a b l e s .  density  between t h e  the  will,  bulk  access  limited  upper  to  dense  values  can  different  limits  of  relative be  map  (a).  to  critical  (or  the  sections  such  as  ignored.  the  Table  assumed  to  these  i n as  soils  in  the  to  considered  given are  in  sensitive  be  last  much  in  the  3.5.  lie  Bulk  midway  values. in-situ  and  ranges  densities,  combined  are  1  consideration  cohesionless  soils  (Utzig  expected  density  less  are  Those v a l u e s  volume measure t e c h n i q u e the  somewhat  than  bulk  is  of  System  dense  area.  soil  t h e r e f o r e , not  densities  l o o s e and  study  a  4 slopes  necessarily  model  porosity for firm  Time and in  The  Classification and  basis for  has  flatter  require  variables  Unified  assigned  are  model.  Expected  1  unit  geotechnical  as  class  3.9  the  Factors  surcharge  factor  3 and  unmappable  benches, e t c . w i t h i n the  3.7  (c) of F i g u r e  slope u n i t s are  slope  u s e d as  and  bulk  determined, Herring  was  determinations  using a  1975),  are  done  given of  in Table  rwet and  f o r <f> v a l u e s  modified  fall  for gravelly soils  to d e r i v e values  g e n e t i c m a t e r i a l s as  density  within  with 3.6.  rsat in  firm These  for  the  section  T h i s t e r m i s not e q u i v a l e n t t o ' u n i t w e i g h t ' u s e d i n some t e x t s . B u l k d e n s i t y i s mass p e r u n i t volume (kg/m ) w h i l e unit weight i s f o r c e p e r u n i t volume ( k N / m ) . 3  3  75  3.3.2. Brown forests  and  Sheu  are t y p i c a l l y  USC  dry*  GP GW GM GC SP SW SM SC  1400 1425 1600 1600 1330 1360 1390 1390  (1975)  found  250 kg/m  LOOSE sat 1420 1440 2000 2000 1345 1380 1410 1410  n .46 .41 .50 .75 .47 .47  2  that  with  extremes  FIRM dry s a t 1860 1880 1985 1985 1610 1740 1710 1710  surcharge  1940 1960 2250 2250 1760 1875 1840 1840  as  l o a d s due t o high  n  dry  DENSE sat  ;—  2320 2340 2370 2370 1890 2115 2035 2035  2460 2480 2500 2500 2180 2370 2275 2275  .29 .26 .26 .40 .55 .35 .35  as  500  n .12 .11 .11 .29 .35 .23 .23  kg/m'  T a b l e 3.5. A v e r a g e b u l k d e n s i t i e s f o r d i f f e r e n t U n i f i e d S o i l C l a s s e s ( f r o m Bowles 1979, Sowers 1979 a n d Hough 1957).  kg/m . 2  These  t r e e s and can available. fail value  surcharge  be  Forest  to provide of  values  250  vary  derived cover  enough d a t a kg/m  2  is  according from  t o t h e s p a c i n g and s i z e o f  forest  maps do e x i s t f o r surcharge assumed  load for forested slopes  mensuration f o r the study  data,  a r e a , but  load determination.  as a estimate i n the study  if  A  of the average  area.  76  3.8  Slope  It  E q u i l i b r i u m In The S t u d y  i s now  NO.  important  REL . DENS.  D-l Nl+100 R-1 N-0 Nl+100-2 Nl+55  Table  variables slope area  i s shown  3.3,  SW SM SM SM SM SM  bulk  forested  35.1 38.5 42.6 20.0 20.4 14.3  11.6 9.0 17.2 9.3 8.8 7.7  The p r o f i l e  various  in-situ  dry  the  flatter  (kg A O (kg/m ) (kg/m ) 3  1921 1781 1790 2327 2304 2455  1720 1630 1520 2120 2110 2270  2324 2257 2158 2544 2540 2594  i n the study  compensate  for  v a l u e s . The e x c e p t i o n where  probabilities critical  Some  for  slope  usually  other to this  in  both  wetter.  study  forested  and  and non-  interrelationships  These  two  and  variables  e x t r e m e FS and P  course,  the  terrace  t o produce  of root cohesion  on t h e s t e e p e r  to  Figure  E[FS]  s l o p e s combine  o f 100%. Second, t h e e f f e c t s stability  to  safety  in less  i s , of  wet c o n d i t i o n s and s t e e p  to  the  slopes are usually d r i e r  and r e s u l t rule  of  interesting  the steeper  are  each  area.  s e c t i o n s combine t o a f f e c t  factors  P shown,  segments.  slopes  sat  3  of a t y p i c a l  expected  of f a i l u r e  slope  model  3.10. M o d e l p a r a m e t e r s , when a s s i g n e d  become a p p a r e n t . F i r s t ,  more  w%  the  d e n s i t i e s determined  in Figure  yield  front  n%  how  segments o f t h e s l o p e and combined a c c o r d i n g  probabilities  the  examine  d e l i n e a t e d i n the p r e v i o u s  stability.  various  use  FIRM FIRM FIRM DENSE DENSE DENSE  3.6. I n - s i t u  to  Area  slopes. This  are point  77  agrees with loss  observed  of root  strength  increases after  i n l a n d s l i d e occurrence  logging  on s i m i l a r  slopes  following in  Alaska  Figure 3.10. P r o f i l e of a typical slope i n the study area showing the relative stability resulting from various combinations of quantified variables of the s t o c h a s t i c g e o t e c h n i c a l model.  and  S.W.  Third, low  British  slopes  the  quantitative is  inclined  probabilities From  the  Columbia  (Swanston  at less  than  1974 and O ' L o u g h l i n  20° have h i g h  somewhat u n c l e a r  FS v a l u e s  and  of f a i l u r e . model  it  is  possible  to  terms t h e o b s e r v e d d i s t r i b u t i o n  study  1973).  area  and  surrounding  explain o f many  region.  a s t o what t h e s t a b i l i t y  values  in  semi-  landslides  However, really  i t  mean  is in  78  terms  of  forest  probabilities landslides  model  cannot  likely  likelihood period.  of  values  such  of  comparisons,  classes  of use  Many  do  cliffs  little  and  polygons; fans  with  than  experience  develop  slope equilibrium the  behaviour  words, similar  f o r these  is  i n the case  with  be  the  They  when  events. indices  compare  slopes in other  i n c l u d e : rocky  flow  or  the  that  have  areas.  From  form  hazard  be  and  the  slopes  and  d e l i n e a t e d as  minor also  of  site-specific  processes;  and  map  talus  rockslides.  The  predicted  by  be  slopes elsewhere.  However,  schemes f o r t h e d e t e r m i n a t i o n  slope classes, throughout  of s t e e p r o c k y  slopes,  problems  and  assumptions  which cannot  similar  time  made where  relative  grouped to  homogeneous  engineering  certain  engineers.  s l o p e s must on  the  to  material; linear  individual  anywhere w i t h i n t h e u n i t ; fans.  can  rockfall  of t h e s e  s l o p e , nor  o n l y be  used  engineering  model.  fronts  of  a  as  The  number  determined  be  satisfy  discrete  behaviour  comparison rather  by  can  used  area  d e b r i s f a n s d o m i n a t e d by  formed  probable  study  surficial  terrace  within  best  managers and  not  geotechnical  particular  can  indices  stochastic  gullies  P are  to f o r e s t  the  compared w i t h o b s e r v e d  indices  to f o r e s t  slopes  with  and  and  the  a  subjectively  s l o p e s i n the  unfavorably  on  engineering.  predict  predictions  calibrated  These  proposed  occurring  less  of E [ F S ]  stability.  responded  occur  are  are  and  to a c t u a l l y  landslide  variables  equilibrium  used  quantitative  probabilities  of  be to  a  Such  The  management  are  l i k e w i s e on  likely  it  is  the it to  assumed unit.  is  of  that  In  other  assumed  that  be  terrace fronts  encountered and  debris  79  CHAPTER  4.1  Hazards  A  Slopes Mantled  reconnaissance  forest was  On  engineering  conducted  existing  likely  impacts, to  stratify  certain  in  to  be  Landslides either  slides  are  caused  by  area  and  the  study  kind,  i m p o s e d on  the  slope.  associated  with  forest  road  downslope, by  and  or  retrogressively in  values  with  cuts  loosening  loading  the  slope  sidecast  material,  by  root  most  hazard can  impacts,  and  quality  of and  fi,  the  study  may  <t>, C r ,  f i l l s ,  These and  H  intercepting  surficial or  continue  upslope. M,  area  materials,  destroying  cohesion  removal.  slope  failures  intercepts the  likely  f i l l  road  flow,  reduce  a  to  which  intensity,  or  groundwater  prism  to  near  subsurface  Cut  indices  practices  roads  slopes  tree  pre-  Area  steepening  with  relate  develop  cut  changes  with  materials  stability  the  Study  generated  (3)  according  Near  (1)  engineering  to  the  to:  stability  relative area  associated  surficial  order  and  on  as  in  those  failures based  with  relative  identify  Material  landslides  Problems  at  progressively  of  study  assumptions  Engineering  initiate  (2)  system  engineering  4.1.1  the  CLASSIFICATION  Surficial  slopes mantled  promote  slopes  With  survey  conditions  classification  of  on  near  slope  resulting  given  4 L A N D S L I D E HAZARD  are  subsurface  effective  documented  flow normal  allowing stress  in  areas  seepage and  where  the  pressures  induce  road to  failure.  80  L a n d s l i d e s D19, D20 and S1 are examples of t h i s type of (see  Appendix  F  f o r l a n d s l i d e data and l o c a t i o n s ) . Two  three s l i d e s were r e l a t i v e l y minor, i n v o l v i n g l e s s than and  of  little  failure  consequence  of the 72  to the road. L a n d s l i d e D19,  other hand, blocked approximately  m, 3  on the  25 meters of road with 225  m  3  of s a t u r a t e d sandy morainal d e b r i s (see F i g u r e 4.1). Evidence of  F i g u r e 4.1 Cut-slope f a i l u r e s caused by seepage on the cut face of a l o g g i n g road in the Cariboo Creek area ( L a n d s l i d e D19 - see Appendix F ) .  piping  along root c o n d u i t s can be seen as holes on the cut face  a s s o c i a t e d with free water surface. to  within  0.7  Vegetation at t h i s p a r t i c u l a r  hygric  groundwater  moisture table.  conditions Failures  of  meters site  inferring this  of  the  ground  i n d i c a t e s subhygric a  near-surface  type occur on wet  sites  81  where s o i l elevated  is sufficiently piezometric  observed  in shallow  Minor more  common  with  eventually Minor  cut  slope  failures  drainage  ditches fill  This,  and  that  study  the  to  slope  slopes  of  water  was  not  The  much  usual  road  vertical  material  internal  found  the  1976  drainage  t o be  road and  will  friction.  m a t e r i a l chokes  over  never  is a  known t o c a u s e w a t e r  where s l o u g h i n g  an  predomiate.  to near  surficial  i t s angle  were  faces  area.  (Burroughs et a l .  however,  distances D4  in  s o i l s may  upslope  from  where 0.5  from more t h a n  involved  to  1.0  ravelling  the c o l l u v i a l  of  t r e e r o o t s to anchor  are  a  rock  inside  bed  onto  O'Loughlin  a p r o b l e m near  the  water  soil  ravel retrogressively  cut  as  observed  near  m e t e r s of c o l l u v i u m c o n t i n u e s  largely  v e n e e r s between  subsurface  in places  50 m e t e r s u p s l o p e .  of  rapid  the  diverts  slopes  but  of  area.  landslide ravel  from c u t  have been  regions  Shallow c o l l u v i a l long  near  readjust according  in other  study  of m a t e r i a l  allowance  problems  1973).  in a closed s o i l ,  p r a c t i c e i s to bulldoze cut the  unprotected  the development  where i n t e r f l o w p r o c e s s e s  phenomenon  construction angles  surface  soils  ravelling  deep t o a l l o w  a  rock  The  volumes of  f u n c t i o n of  material  the c o n t i n u i t y  b u t t r e s s e s and  m a t e r i a l to bedrock.  interflow in i n i t i a t i n g  to  the  The  these  ability role  of  failures  is  uncertain. Where friction  slope of  progressively, bed),  or u n t i l  angles  side  cast  either  approach the material,  to  the  fill  base o f  some o b s t r u c t i o n s u c h a s  stump b u t t r e s s e s t h e  fill.  S l i d e s of  loose angles slopes  the  slope  a rock  this  of  type  internal  may  (often a  outcrop  or  fail creek tree  were i n a l l c a s e s  82  restricted area,  to  s i m i l a r to trends  Northwest 1969).  (O'Loughlin  Failures  obstruction water of  slopes  of  running  organic  into  a  along haul  or  by  an  blanket  surface  fill  both  at  but,  upon  surface material  gully  now  crossings  of  1975  the  and  erosion  to  the  due  to  or d e t e r i o r a t i o n  slopes. a  large debris and  avalanche  subsurface  water  n e a r Wragge C r e e k . A initiation  involving  4.2).  Recurrent  p a t h and  within  9800 m  annual maintenance at  slide  flow  transformed  approximately  Figure  -  spoon-  occured  i n c o r p o r a t i o n of w a t e r ,  the  Swanston  flow;  slope;  study  Pacific  water  zone of  (see  the  s a t u r a t i o n due  fill  road  require  along  near  fill  surface  the  34°  regions  Herring  example of  old skidder  surface  material  by:  down t h e  an  t r i g g e r e d by  this road  induced  is  V-shaped  morainal  U t z i g and  buttressing  D1  shear  fill  in other  1973,  are  debris  interception  the  observed  uncontrolled  flow  shaped  i n e x c e s s of  subsurface  Landslide debris  inclined  3  of  failures three  contribute  main  sediment  t o Wragge C r e e k . Where water slopes, and  the  improper  the  D3  embankment  on  placement  slopes  described  in  initiated  solely  were  never  material  near  of  run  will  can  ravelling also  due  to  observed  eat  study  away a t  uniform  area.  Figure cohesion  fill  surface  landsliding.  example of  4.3).  slope  down road  cause  where  which  the  in  turn  Water d i v e r t e d  onto  landslides  (see root  the  l e d to e r o s i o n  initiate  l o s s of  to  i s an  (Figure  3.4.2  on  uncontrolled  sufficiently  a c u l v e r t has  section  the  to  Shannon C r e e k Road  promoted a c c e l e r a t e d natural  allowed  resulting erosion  undercut  Landslide  is  such  3.5).  as  Landslides  following  mantled with  D14  logging surficial  83  F i g u r e 4.2. V-shaped p r o f i l e of the path of a d e b r i s avalanched e b r i s flow caused by the s a t u r a t i o n of road f i l l m a t e r i a l near Wragge Creek Road.  4.1.2  Hazard Classes Stability  landslides, developed for  in the study a r e a . Values  engineering  study  adjacent  to  can be used f o r d i r e c t comparison with slopes to be  natural  variables  i n d i c e s , when c a l c u l a t e d for slopes  slopes are  were  area.  adjacent  given  in  inferred  Results  to  Table in  of E[FS] 14  and  landslides  4.1.  The  P  calculated initiated  values  of  by  model  the same f a s h i o n as slopes i n the  indicate  that  11  of  14  sites  had  84  Figure 4.3. F i l l slope e r o s i o n and r a v e l l i n g r e s u l t i n g improper water c o n t r o l at the c u l v e r t e x i t .  probabilities and  of  failure  greater than  4% p r i o r to engineering  that at the 3 more s t a b l e s i t e s , obvious  such as use of organic d e b r i s i n road f i l l s , diversion,  or  improper  from  engineering e r r o r s , flooding  by  water  switchback layout were r e s p o n s i b l e f o r  l a n d s l i d i n g . I f the small cut slope f a i l u r e o c c u r r i n g on the P = 4% slope l i s t e d consequence  i n Table 4.1 i s  a l l occur  f a i l u r e greater than The  stability  ignored,  landslides  of  major  on slopes with n a t u r a l p r o b a b i l i t i e s of  10%.  indices  for  natural  slopes  are  used  for  85  8  NO DI  32°  BEFORE M.R.* 2-3  TCS  USC  fgMb  ENGINEERING H  4>°  GW-GM 29-36 2 0  AFTER ENGINEERING  Cr  Cs  M  E[FS]  P  0-450  0  . 1  1 . 10 17%  Cr  M  B  H  0  .2  34°  5.0  29-36 .85  o>°  99% 100%  E[FS)  P  D2  30°  3  rCv  GM  38-43 1 0  0-450  0  .1  1.66  0%  0  . 1  40°  3.0  35-40 .87  D3  44°  4  rCa  GW  38-43 2 0  0-450  0  .2  .91  87%  0  .2  44°  2.0  35-40 .72  100%  D5  26°  3  rMb  GW  29-43 2. 0  0-450  0  . 1  1.59  0%  0  . 1  35°  .5  27-40 .92  73%  Dllb  36°  2  gF b  GP  29-38 2.0  0-450  0  . 1  .99  52%  0  . 1  38°  .5  27-36 .76  100%  D12  39°  3  sF b  SP  29-38 2 0  0-450  0  . 1  .90  83%  0  . 1  42°  2.0  27-36 .65  100%  . D14  35°  3  GW  38-43 1 0  0-450  0  . 1  1.40  0%  0 -450  1.0  35°  1.0  38-43 .88  82%  D15  36°  3  ,SC  29-38 2 0  0-450  0  . 1  .99  52%  0  .2  65°  1.0  29-38 .28  100%  D17  34°  3-4  rCv G sF b sMb  SW  34-38 2 0  0-450  0  .2  1.09  13%  D18  38°  3  gMt  SW  34-38 2. 0  0-450  0  . 1  1.00  48%  0 -450  .2  45°  4.0  34-38 .71  100%  D19  28°  5  sMb  SP-SW 32-38 2. 0  0-450  0  .5  1.12  11%  0  .5  62°  1.5  32-38 .28  100%  D20  30°  3  £sMb  SW-SM 29-38 2. 0  0-450  0  . 1  1.23  4%  0  . 1  52°  2.0  29-38 .49  100%  29-38 2 0  0-450  0  . 1  .99  52%  0  . 1  75°  .5  29-38 . 17  100%  GW-GP 29-38 2. 0  0-450  0  .2  .87  89%  0  .2  40°  .5  27-36 .67  100%  G  G  SI  36°  2-3  gF C  Al  40°  3-4  gF t  GP  G  G  *Moisture Regime  Table  4.1 V a l u e s o f E [ F S ] and P c a l c u l a t e d f o r n a t u r a l a d j a c e n t t o 14 l a n d s l i d e s .  comparison failure of  between  involved,  areas  because,  the values  used  depending  in calculating  a p a r t i c u l a r l a n d s l i d e may be q u i t e  in  natural  D2 o c c u r r e d  slope  on a n a t u r a l  However, t a k i n g by  stability  disturbance,  construction,  by b u l l d o z i n g  actual  landslide  conditions  'The fill  at  slope  w i t h E [ F S ] = 1.66  of  and  of s u r f i c i a l  of the slope  destruction  stability  angle  stabilizing  used  landslide P  =  0%.  material  by r o a d tree  prism roots  r e s u l t s i n E [ F S ] = .87 a n d P = 100% f o r t h e  (see Table the  the  d i f f e r e n t from t h o s e  the loosening  the steepening  caused  the type of  c a l c u l a t i o n s . F o r example,  i n t o account  and t h e  on  slopes  time  4.1).  1  The p r e d i c t i o n  of f a i l u r e  can only  of  stability  be made w i t h  site  infinite slope model, though not u s u a l l y a p p l i e d t o s h o r t s l o p e s , does g i v e an a p p r o x i m a t e e s t i m a t e o f s t a b i l i t y .  86  specific  knowledge o f t h e t y p e  imposed  upon  practices slopes with  the  certain  i n the region study  showing  construction ranges  no e v i d e n c e  time  slopes  engineering occurring have  on s l o p e s w i t h  a  However,'  i t  probabilities  of f a i l u r e  assigned  the  to  'high  may have  critical  greater  is  no  guarantee  techniques  will  on  s l o p e s . The f o u r  be f i n a n c i a l l y  s l o p e s h a d a l a r g e r component their greater is  initiation, than  therefore  of  slides  would  not  do n o t o c c u r  to  be  that  on  potentially slopes  with  area  be  as a s i n g l e l a n d s l i d e extensive  slope,  implications.  landslide preventative  or t e c h n i c a l l y  which o c c u r r e d human  forest  the  10%  financial  that  feasible  slides  of  slides  once on an a r e a l l y and  model.  better  10% i n t h e s t u d y  class,  environmental  there  these  than  the  value  where l a n d s l i d e s  than  appear  road  i n v e r s e approach of  reasonable  hazard'  Moreover,  in  percentage  and  to  of input  given  greater  seems  though o c c u r r i n g o n l y  the  many a r e a s ,  steep  prior  estimates  that,  large  in  to  sometimes c a l c u l a t e d f o r  i n d i c e s i n areas  P values  Indeed,  applied  t h e h a z a r d s on s l o p e s  used  permit  possible  that a r e extremely  unstable.  event,  not  practices,  occurred.  slopes  It i s  be  engineering  be  instability  assumptions  for stability  have n o t o c c u r r e d .  values  of n a t u r a l  did  will  to  indices.  the conservative  simplifying  Unfortunately,  study  i n determining  and low E [ F S ]  reflect  and  analysing  area  of  natural s t a b i l i t y  High P values slopes  alteration  t h e n a t u r a l s l o p e . I t i s assumed t h a t  common  of  of e n g i n e e r i n g  error  possible  on more s t a b l e  responsible  for  and l a n d s l i d e s o c c u r r i n g on s l o p e s w i t h E [ F S ]  1.6 were n o t o b s e r v e d . assigned  The 'moderate h a z a r d ' .  t o the s t a b i l i t y  index  interval  class  P < 10%  87  and  E[FS]  <  1.6,  and  slopes with E[FS] Roads failure,  indicated  observed  fitting  this  hazard'  class,  For  as  and  the  to  The  w h i c h can i.e.  be  study  4.1.3  including  d e l i n e a t e d on  the  prevent  ( f ) or a p r o n  the  and  subsurface  the  region.  authors  of  relative  with  the 70%  a r e a . The  water on Some  including  S3,  slope  stochastic,  the  solutions Enberg  (1963) who  terrain slopes  geotechnical  model,  (b) or  veneers  B).  Slopes  Map not  included.  Techniques would S3  to c o n t r o l  have and  S2  both  is a recurring  been  terrain  i n c l u d e s those  t h a t o c c u r r e d on  have  map  material,  w i t h i n the  (see  techniques  road prism  the  S1  hazard  stability  of b l a n k e t s  material  and  low  surficial  hazard  failure  high  classes  S2,  designates  Remedial E n g i n e e r i n g  landslides  study  the  only  cover  slopes  'very  hazard  (a) s u r f a c e e x p r e s s i o n s a r e  engineering  some of t h e  s l o p e s near  S4,  with  subdivision  roots,  active.  'S'  slopes mantled  terrain  analysed  number  the  landslide  letter  incipient  tree  t h e v e r y h i g h , h i g h , m o d e r a t e , and and  all  to road c o n s t r u c t i o n ,  a r e a a r e of  symbols  the  to  I t i s assumed t h a t  given  P r e v e n t a t i v e And A  area.  the  s l o p e s w i t h more t h a n  fan  show s i g n s of  i s already  (v) of u n c o n s o l i d a t e d s u r f i c i a l with  which  study  s e p a r a t e l y ) . The  'S'  i s assigned  1.6.  purposes,  t h e numbers d e s i g n a t e  unit.  class  s l i d e morphology, exposed  i n the  respectively,  subdivision  slopes  the p r o c e s s  above a r e  D filed  hazard'  horizons, etc. prior  criteria  corresponding  (Map  by  near  mapping  discussed  classes  on  buried soil  were not  'low  v a l u e s g r e a t e r than  developed  as  recently  the  presented  demonstrates that  helped hazard surface  problem in by  various  solutions  88  to  drainage  problems  (drainage  parallel  (drainage  at  found  road  that  drainage  have two  to  right  the  parts:  road)  angles  to  ditches  adjacent  to  in c o n t r o l l i n g  However,  this  technique  has  landslides  i n the  study  area  as  where p o n d i n g and  road  fill  concentrated  water,  downslope, can soils  i s o f t e n the  best  associated  with  uncontrolled  f l o o d i n g of  Where s o i l s sidecast, slopes  are  certain  and  i t tends  as  it  slopes  can  saturation.  be  as  where n a t u r a l d r a i n a g e  flat  as  frequently  as p o s s i b l e  concentrated ditches  possible.  should  water be  handled  moisture  possible.  Where  any  conditions excessive  plant  seepage  problems danger  of  made f o r p r o t e c t i n g  fill  one  and can  road be  be  from with  placed  o r where s l o p e s should  the  spaced amount  Third,  in are as of  inside  maintained.  of be  be  the  culvert.  should  beds  protected  should  regularly  on  the  the  the  indicators  exist  where  toward  the  minimize  p r o p e r l y p i t c h e d and  A r e a s where s u r f a c e and hygric  by  In a r e a s  of  toward  exist  to  The  disposed  cambering  culverts  order  water i n  below.  slopes  channels  Second, in  and  and  r i p r a p o r c u l v e r t s . Where p o s s i b l e , c u l v e r t s areas  of  possible.  avoids  drainage,  First,  soils.  number  e r o s i o n , cambering  concentration  lateral  most  a  is  laterally  solution  provisions  the  granitic  slope s t a b i l i t y .  unstable  with  are  to  saturation  to r i l l  slope  to c o n c e n t r a t e  too e r o d i b l e to allow  from c o n c e n t r a t e d  ponding  slope  drainage  e t a l . (1963)  cut  erodible  drained  water  the  cut  drainage  lateral  contributed  f u r t h e r aggravate  are h i g h l y r e s i s t a n t  sidecast  toward  e r o s i o n on  when  (2)  r o a d ) . Haupt  the  successful  areas  and  the  s u r f a c e s cambered  (1) l o n g i t u d n a l  subhygric  avoided cut  to  wherever face  is  89  encountered, phreatic  p e r f o r a t e d p i p e can  surface  slumping  and  carry  continues,  water  gabion  or  constructed  to h e l p b u t t r e s s the  stabilized  by  a variety  be  installed to  log  the  t o h e l p lower inside  crib  of b i o - m e c h a n i c a l  ditch.  structures  slope. Cutslopes  the  can  techniques  If  can  be  also  be  (Schiechtl  1980) . Where p o s s i b l e , should  be  minimized  p r i s m d e s i g n on developed based  on  by  significantly S3 and  4.2  S2  This  from  frost  road  decrease  Steep  terrain  i n the  unstable  analyses.  risk  study  Rocky  forested  Stability  properties  of  the coherent  Lund  been (1974)  disturbance  road  landslide  and  have  mileage  occurrence  on  by will both  Slopes  other is  soil  haul  constitutes  s t u d y a r e a where r o c k s l i d e s  dominate.  lengths  area.  subdivision  wedging and  slope  slopes  Hendrickson  and of  fill  U s e f u l methods f o r r o a d  Minimizing  density the  c u t and  1979).  (1975) and  s l o p e s i n the  H a z a r d s On  slopes  Prellwitz  skidder  and  (Gardner  potentially  stability  limiting  road widths  mechanical  largely in-situ  t h e major p o r t i o n  or r o c k f a l l s  resulting  weathering  processes  controlled rock  of  mass.  by  the  mechanical  90  4.2.1  Engineering Roads  granitic  on  steep  terrain  during  leading  has  periodic  rockfalls (see  Damage avalanche result are  to  slope  'overbreak'  greater  soils,  on  than the large  result.  has  i n t o the  be  visible of  rock  significant from  at  sidecast.  excessive cut  face,  were  only  dynamite leading  water p r e s s u r e s  to  or  frost  and  debris  downslope  of  D9,  rock cuts creek Near  away has  Because  internal  descending  in these cases. km  thrown  angle  adjacent  l e a s t 25  destruction  steep slopes.  Landslides  a l l examples of  can  to  timber  is  scars  Appendix F are descended  rock cuts  the  blasting  discontinuity  from  due  joint  where r o c k  overblasting  frequently  competent  invariably require  fractured  productive  material,  highly  4.4).  initiation  generally  the-  Unfavourable  t r i g g e r e d by  Figure  from  sidecast  study area  extensively  Area  of  t o wedge f a i l u r e s  where  charges  Study  slopes  construction.  in areas  wedging  rocky  i n the  their  orientations noted  P r o b l e m s Near The  long  D10,  can  slope  site  angles  friction  portions D13  and  where s i d e c a s t  bed.  also  resulted  a  the  A5  in  damage  large  from the  of  material  Environmental D4,  of  scar  failure  91  F i g u r e 4.4. Rock f a i l u r e on lower  Shannon Creek Road.  4.2.2 Hazard Classes High impacts slopes  near  the  resulting study  from  engineering  on  on  the  delineated  as  t e r r a i n map are t h e r f o r e designated as being of the  'very high hazard' stability  rocky  area w i l l undoubtedly occur on s i m i l a r  slopes i n the study a r e a . A l l steep rocky slopes Rs  steep  map  c l a s s and  (Map  D).  delineated  Composite  as  units  R3  on  class.  slope  on the t e r r a i n  a c c o r d i n g to t h i s d e s i g n a t i o n , must i n c l u d e at l e a s t order to be assigned to the R3 hazard  the  30%  Rs  map, in  92  Rock  slopes  inclined  at  less  35°  criteria  for this  hazard  bedrock  coupled  with  material  b e i n g m e c h a n i c a l l y w e a t h e r e d make t h e s e  stable,  depending  discontinuities required  in  on  the  rock  construction  Because b l a s t e d m a t e r i a l s w i l l  sidecast  s l o p e s and w i l l  map  4.2.3 P r e v e n t a t i v e And R e m e d i a l E n g i n e e r i n g  blasting in  terrain.  overbreak,  and  'Presplitting' blasting fractured slopes  a l . (1976)  emphasizes  t e c h n i q u e s when c o n s t r u c t i n g r o a d s  steep  will  prevent  objective the  the cut slope usually  rock  below.  The  to  is  to  throwing  is  over  the  rest  of  both  where  bedrock  i n p l a c e on  class  these  and a r e  (Map D ) .  Techniques t h e need through  f o r proper  hard  minimize  bedrock  cut  slope  m a t e r i a l downslope.  objectives  trucked to safer  of  usually  areas  , f o l l o w e d by c o n t r o l l e d  accomplish be  inclination  i n t h e 'low h a z a r d '  a s R1 on t h e s l o p e s t a b i l i t y  et  fairly  not t h r e a t e n the downslope a r e a s ,  s l o p e s a r e d e s i g n a t e d as being  Burroughs  slopes  in flatter  usually  of  of repose of  Blasting  and p l a c e d  surface.  delineated  and  mass. except  s u b g r a d e m a t e r i a l c a n be i m p o r t e d  strength  below t h e a n g l e  orientation  the  do n o t f i t t h e  The h i g h m e c h a n i c a l  slope angles  within  road  class.  than  areas  production  thus without  allowing damaging  93  4.3 H a z a r d s On C o l l u v i a l The those  colluvial  slopes  falling  a p r o n and f a n  which  from c l i f f s  mechanical  serve  properties  Engineering A  Creek  engineering At  of  the  height  W1,  colluvial (Carson  drainage  W2,  of c o l l u v i a l  a n d W3,  minor  material,  due  incipient instability.  Area  the  only  ravelling  cliffs  the  i t i s possible  continual  following annual colluvial volumes  that  colluvial than  that,  ravelling  with  from  only  the d e t e r i o r a t i o n of b u t t r e s s i n g attention. aprons  In  other  frequently  of m a t e r i a l  from  B u r r o u g h s e t a l . 1976).  long  regions, involve  trees roads  the  distances  or  root high  from  low  prior to  associated fill  will  slopes require  constructed  ravelling  upslope  stable  from  one y e a r  slopes  has  tree  time, problems  cut  blocks  i s largely  derived  the area.  and  aprons d e r i v e d those  of  material  angularity,  B e c a u s e t h e r o a d was c o n s t r u c t e d  survey,  with  the f a c t  i n the  study  of r u b b l e  However, t h e r o a d  a r e n a t u r a l l y more s t a b l e  cliffs. the  and  apron  example  a p r o n s near  t o t h e p o s i t i v e e f f e c t s of p a r t i c l e  cohesion,  rockfall  1977).  from t h e r o a d c u t o n t o t h e r o a d bed s u g g e s t s t h a t some  debris  l a r g e l y by t h e  r o a d on a 40° c o l l u v i a l provides  include  of rock  i s governed  P r o b l e m s Near The S t u d y  behaviour  sites  subdivisions  zones of a c c u m u l a t i o n  recently constructed  Wragge  terrain  above. Morphology  f r e q u e n c y , and r o c k f a l l  4.3.1  A p r o n s And F a n s  of  on large  ( B a i l y 1971 and  \  94  4.3.2  Hazard  Class  Landslide study  area  p r o b l e m s on  are  likely  colluvial  to occur  slopes  elsewhere.  Where  allowed  forest  development  and  s l o p e s can  subject  rockfall  fans,  to  identified  hazard' stability  4.3.3  and  other  B,  the  fans  more  should  symbol  the  with  be R2  of  albeit  aprons  given on  have base  stable,  and  a  'high  the  slope  by  Slopes  formed  active,  not  avoided available.  for preventing  gabion  structures.  will  also  wherever  help  The  cut  most slope  'End-hauling' alleviate  the  Fans by  fluvial  between  be  problem.  Debris  to both  are  Techniques  measure  m a t e r i a l to safe areas  H a z a r d s On  should  alternatives  buttressing  downslope r a v e l l i n g  still  on Map  the  rockfalls  In g e n e r a l , c o l l u v i a l  by  successful control  is  anywhere  t o be  in  experience  where a p r o n s l i e a t  Remedial E n g i n e e r i n g  aprons  unless  common and  similar  fans  map.  possible  excavated  Cf  delineated  Colluvial  4.4  and  P r e v e n t a t i v e And  ravel  infrequent  expected  hazards.  as Ca  rating  be  and  i n v i e w of p a s t  similar  high c l i f f s ,  aprons  5°  d e b r i s f l o w d e p o s i t i o n have and and  colluvial  fans  and  morphologies are  inclined  3 5 ° . Where d e p o s i t i o n a l p r o c e s s e s  some p a r t i c u l a r  engineering  problems  exist.  are  95  4.4.1  E n g i n e e r i n g P r o b l e m s In O t h e r Roads c o n s t r u c t e d on a c t i v e  near  the  study  area  were  used  to predict  with  them. Debris  colluvial  have  they  are  boulders descend  f l o w s w h i c h can in  excess  these  to  (Nasmith  and  Eisbacher  The  flatter  be  incised,  f l o w s may  colluvial cliffs.  of  during this  likely  to  be  are  more R2  hazard  d e b r i s flow channels cause  severe  meter  with  little  and M e r c e r  to those by  than  of  slurry gravity  are threatened Slurries  by  with  have been known t o  forewarning 1979,  be  classification.  damage.  i n diameter  can  associated  formed  stable  fans study.  f e a t u r e s elsewhere  they  the  p o r t i o n s of t h e  f l o w may  debris  and  M i l e s and  great  Kellerhals  1982).  e n g i n e e r i n g except  engineering  terrain  generally  of one  channels  destructiveness 1981  encountered  because  slopes  which c r o s s a c t i v e  periodic  active  material properties similar  f a n s . However,  dominated c o l l u v i a l Roads  recently  t h e t y p e s of h a z a r d s  fans  deposition,  or  not  However, e x p e r i e n c e w i t h t h e s e  Regions  a t the  lower  isolated  f a n s pose channel  little  to which a d e b r i s  c o n f i n e d . However, a r e a s where c h a n n e l s affect  p r o p e r t i e s of  a much l a r g e r the s u b s t r a t u m  fans, p a r t i c u l a r l y  a r e a . On are  hazard  a r e not  the upper  similar  well fans,  to those  on d e b r i s f a n s a t t h e base of  of  high  96  4.4.2  Hazard  Class  Because range,  angles  i t i s useful  subdivision is  slope  felt  into  on  debris  fans  t o somewhat a r b i t r a r i l y two  that slopes  hazard  inclined  i n excess  inclined hazard' D)  upper d e b r i s  hazard' noted  the  F2  symbol.  and  are d e l i n e a t e d with  rating that  However,  found  class  slope  debris the  to the  FI S1  causes  t h e F1  Remedial E n g i n e e r i n g  where r o a d s or  cross  rock  fill road  with concrete  w a l l s on  1978  and  Gagoshidze  by  obstructing  channel  debris  class  the  class  b r i d g e s , and  debris pressure  channels, t o be  It  is  they  are  bottom.  t o be  given  Techniques successfully  and  stone  (Heinrich  increase  withstood,  and  employed  paths.  sills  and  1969). T h e s e m e a s u r e s r e d u c e debris  as  (Map  'moderate  valley  large corrugated  embankments  map  symbol.  torrent  checkdams  bed,  'high  rating.  p r o t e c t i v e m e a s u r e s have been  masonry  c u l v e r t s used  hazard  Steeply  the  f a n s have a  hazard 'low'  to  stability  the d e b r i s flow  d e b r i s m a t e r i a l above t h e  enabling  the  is similar  to run.  assigned  in  r a t h e r than  slope angle. It  fans are c o n f i n e d  likely  other  other areas  retaining  lower  t o one  P r e v e n t a t i v e And  include  Lower  terrain  (upper  adjacent  Certain in  a r e d e l i n e a t e d on  t h e FI  'moderate'  4.4.3  are  and  frequently  a  areas  the  fill  d e b r i s flows are  fan  broad  a s s o c i a t e d w i t h c u t and  class  with  20°  a  are  Hazards a s s o c i a t e d with  where p e r i o d i c  20°  over  fans)  slope  areas  i n v o l v e hazards  of  to  to  divide  c l a s s e s at the  much more l i k e l y ravelling.  vary  to  They retain  steel  sheet  log crib-type  1978,  Hattinger  water  velocity  bridge  strength  protect  channel  97  slopes large  from  erosion  near  road  enough t o c a r r y p e r i o d i c  little  damage t o r o a d  influxes  cross-section  1978). Upper d e b r i s f a n s in  areas  4.5  other  H a z a r d s On Steep  features  concentrated in  within  and  should  be  treated like  small  only  be  to  be  with  gully  design to  the  (Hattinger  colluvial  fans  critical  described  in  occurring naturally  roads  in  where s l o p e s a r e  u n i t s a t the  linear  slopes are  classes  landslides  mapped as  r e p r e s e n t e d as  with  paths.  hazard  associated  i n the areas  be  Gullies  the  Many  i s to  channel  the  locally  g r o u n d w a t e r d i s c h a r g e a r e a s . T e r r a c e s and  too  debris  according  debris  t e r r a c e f r o n t s and  sections.  flowing  the c u l v e r t the  d e b r i s flow  linear  area  of  T e r r a c e s And  found  previous study  than  of  embankments. A r u l e - o f - t h u m b  t h e a p p r o x i m a t e c r o s s - s e c t i o n of approximate  c r o s s i n g s . Culverts should  the  i n the  region  are  steepened  and  gullies  are  usually  1:20,000 s c a l e and  symbols w i t h i n  the  other  can  hazard  units.  4.5.1  gully  E n g i n e e r i n g P r o b l e m s Near The Engineering  problems  slopes are  identical  mantled cause  with  surficial  landslides  itself,  but  These following  also  which the  slopes  associated to those material.  may  stream are  Study  effect channels  affected  d e f o r e s t a t i o n . Since  Area  with  terrace fronts  described for Various not  by  loss  slopes  f a c t o r s combine  only  at the  steep  and  the  road  base of t h e of  root  l o g g i n g o c c u r r e d about  to  prism  slope. cohesion 15  years  98  ago,  numerous  slides  Shannon Creek, one  have  developed  on  t e r r a c e f r o n t s near  of which i s shown in F i g u r e  4.5. These s l i d e s  Figure 4.5. L a n d s l i d e on a t e r r a c e slope near Shannon Creek i n i t i a t e d by l o s s of root cohesion ( L a n d s l i d e D3 - see Appendix F).  are not  r e l a t e d to skidder  diversion. after was  The  logging  roads  nor  to  flooding  from  water  occurrence of these l a n d s l i d e s 10 years or more  suggests that the slow d e t e r i o r a t i o n of t r e e  responsible.  evapotranspiration  It  is  may  have  also  possible  allowed  that  piezometric  roots  decreased pressures  to  99  rise.  Where s i d e c a s t m a t e r i a l s choke s t e e p g u l l i e s  1  crossing,  periodic  following  a heavy  large-scale nature  4.5.2  were n o t f o u n d  Hazard  fronts  landslides  the  slope  to these  are frequently a s s o c i a t e d with  high hazard' is  class  i s assigned  made between g u l l i e s  stability  techniques linear  attention  debris  by  material  map  safe  should  be  during  storm  a  (Map  D),  gullies  to  these  and t e r r a c e  as  problems  of both  conservatively events  and  Techniques  f o r S4 a n d S3 s l o p e s c a n be Where  be g i v e n  placing  areas,  f o r drainage  given  features.  should  correctly to  Provisions  cause  each a r e s i m i l a r .  Engineering  special  runoff  area.  P r e v e n t a t i v e And R e m e d i a l E n g i n e e r i n g  applied  surface  1981). However, p r o b l e m s o f t h i s  the study  distinction  associated with  4.5.3  concentrated  road  Class  No  on  (Ziemer  near  t e r r a c e s , t h e 'very  features.  of  a  r a i n f a l l may m o b i l i z e t h e d e b r i s a n d  d e b r i s flow  Because and  influxes  at  roads  cross  t o the proper  culverts,  subsurface  designed  due t o s u b s u r f a c e  containment of  trucking  buttressing  road and  to allow  gullies,  excavated cut  slopes.  surface  water  f o r runoff  .surges  flow c o n c e n t r a t i o n .  Roads l o c a t e d on t e r r a c e b e n c h e s s h o u l d  not  divert  water  'The effect o f d e f o r e s t a t i o n on p i e z o m e t r i c pressures is uncertain, as r e s e a r c h e r s have p r e s e n t e d c o n f l i c t i n g t h e o r i e s t h a t r e q u i r e f u r t h e r t e s t i n g ( d e V r i e s a n d Chow 1978, C h a m b e r l a i n 1972, O ' L o u g h l i n 1973 and L i n s l e y 1975).  100  over  the  should be  break  be a v o i d e d ,  harvested  slope  4.6  in  slope  and  particularly  on t h e s e  seepage a r e a s  near  s l o p e s as r o o t c o h e s i o n  Summary Of The H a z a r d summary,  primarily  to  subdivided  behaviour  of  Classification  hazard  according  further  should  not  may be c r i t i c a l t o  natural  terrain  according  similar  slopes  in  hypothetical  s l o p e , and c a n be u s e d  planners  criteria  the  other  the hazard  of each c l a s s .  making  purposes,  and c o m p l i c a t e  as  the issue,  more s p e c i f i c the  high,  hazard  engineer  information.  and  areas.  hazard  then  engineering 4.6  s y s t e m on a  reference to t h a t many  rating  complex  reason,  are divided  Figure  classification  particularly  d e c i s i o n s a r e b e i n g made. F o r t h i s moderate,  observed  I t i s noted  more  area  subdivisions,  as a quick  p r e f e r t o use a 3 t o 4 c l a s s  decision confuse  of  to  the  defining  use  System  c l a s s e s i n the study  illustrates  both  Trees  stability.  In  low,  streams.  on t e r r a c e f a c e s  the  land-use  system  systems  for  tend t o  when m u l t i p l e - u s e  the  four  ratings:  v e r y h i g h were a s c r i b e d t o t h e n i n e  classes discussed in and t h e p l a n n e r  this  chapter.  c a n more e a s i l y  Thus,  u t i l i z e the  101  MANTLE OF  RELATIVE HAZARD  high  j  F1  S1  CRITERIA  mod  j  1  o "35 o  j ! !  «  j j  o  !  V  |  CM A  1 # | o 1 v  o  0. 1 ®  O  CD  CM  4.7  hazard  extensive the  of  rugged,  between  1  u.  O  c  <a^  o  w O  k_ u  0  CD  CO  _  0  ca  U-  CD >  Ui  o  S I  o  1 1 1  /!••  1  !  UJ  Ca  Mb  Of  Hazard  Classes  R3  and  s l o p e s a r e by  any  the  four lower road  class  glaciated drainage  i n the  far  Rs  study  topography basins.  the  Rm  of  In  the  to  construction.  southeast  of t h e mouth  encroach  on  of  sides  Wee of  One  Sandy the  rib  Creek  areally  alpine  pose  areas  ribs  are  formidable  occurs  where  the  i t includes  p l a c e s , rock  such  valley.  of  most  a r e a as  s l o p e s of t h e v a l l e y s and  barriers  both  R2  hazard  recently  a l l  e x p o s e d on  1 O | c 1 " 1 * o 1 a.  R1  R3  high very low high  A h y p o t h e t i c a l s l o p e i l l u s t r a t i n g t h e use l a n d s l i d e hazard c l a s s i f i c a t i o n system.  Distribution High  • •  •  1i  u  m  CFf  TCS  R2  S1  !  1 1UJ  A  !  % !  4.6.  >(S  v.  J  84  a c  I  CO  S3  | low I mod high very high | low 1 | i I 1 I 1  J 1 1 HAZARD  I S2  COLLUVIUM  tt  F2  HAZARD CLASS  AND  r  J  MATERIAL  SUBDIVISION  Figure  ROCK  DEBRIS FAN  UNCONSOLIDATED  pron  TERRAIN  R3  to  the  slopes  Farther upvalley,  R3  1 02  slopes again  occur  the  in  valley  Chapter  adjacent  the  t o one a n o t h e r  vicinity  of the l a r g e cascade  sides  of  described i n  2.  In t h e l o w e r frequently  at  p o r t i o n s of the v a l l e y s ,  t h e base o f t h e h i g h  distinguish which case  between c o l l u v i a l the composite  where s t e e p  discontinuous  R2 s l o p e s o c c u r  south-facing c l i f f s  Nemo a n d Wee Sandy C r e e k B a s i n s . I t i s  arise  on o p o s i t e  sometimes  most  of both  difficult  b l a n k e t s and c o l l u v i a l  aprons, i n  symbol R2-S3 i s u s e d . ' D i f f i c u l t i e s  rocky  terrain  colluvial  aprons,  units such  of Wee Sandy L a k e . I n t h e s e a r e a s  include  to  also  numerous  but  as s l o p e s t o the southeast  the composite  symbol R3-R2  is  employed. In  the  s t r e a m s have Farther  u p p e r Wee Sandy C r e e k B a s i n , S4 s l o p e s o c c u r incised  into  downvalley,  morainal  failures  blankets  are  occurring  slopes adjacent  t o R3 a n d S3 u n i t s ,  gully  f e e d i n g d e b r i s flow channels.  networks  or  debris  fans.  on s t e e p  and on t h e u p p e r  where  uniform  slopes  of  In p l a c e s , t e r r a c e  f r o n t s a r e e x t e n s i v e enough a l o n g  lower  mappable  as  Some o f t h e most e x t e n s i v e a n d  obviously  u n s t a b l e S4 s l o p e s  S4  B a s i n . The lower the  lower  including High slopes exist  hazard  are  found  show  evidence  of r e c e n t  the l a r g e debris avalanche hazard  S3 s l o p e s i n c l u d e a  flatter  concave p r o f i l e  lower  to  Nemo  shown  landslide  be  Creek 5 km o f  activity,  i n F i g u r e 2.5.  major  portion  of  forest  Nemo a n d Wee Sandy C r e e k B a s i n s . They f r e q u e n t l y  as the t r a n s i t i o n and  in  Creek  north-facing slopes along approximately  valley  of both  upslope  units.  Wee Sandy  unit  between R3  S2 o r S1 h a z a r d  typical  of g l a c i a t e d  or  R2  hazard  classes  u n i t s downslope, a l o n g the valleys  (see Figure 4.6).  1 03  Moderate confined study  to  to  area,  the  except  north-facing Basins, alpine  areas  f o r the long of  both  rock  to  moderate  lower  major  basins  as  slopes  are  Nemo  and  F2  been  extensive  of the on t h e  Wee Sandy  o f t h e main S l o c a n have  largely  floors  S2 and S1 s l o p e s  glacially  hazard  along  S1  uniform  materials  a s s o c i a t e d with  distributed  Valley  Creek  V a l l e y . In  deposited  R1 r o c k  a n d F1 d e b r i s  benches.  fan units are  t h e base o f t h e s o u t h - f a c i n g c l i f f s discussed  i n Chapter  F1  slopes  on  S2 a n d S1 s l o p e s  scoured  of  2, a n d a l s o i n t h e  are  b o t t o m s and a r e commonly a d j a c e n t  confined  to the  t o S2 a n d S1 s l o p e s i n  areas. Gullies  commonly  incised  occur  with  into  surficial  R3 and S3 s l o p e s  Nemo a n d Wee Sandy C r e e k B a s i n s . along  and  benches, a r e a l l y  upper S h a r p e C r e e k D r a i n a g e .  these  S2  bottoms o r c i r q u e b a s i n  where g l a c i a l  flat  High  the  valley  sides  closely  widely  hazard  and t h e e a s t - f a c i n g s l o p e s  relatively occur  low  t h e major or t r i b u t a r y  Nemo C r e e k .  materials on t h e s o u t h  Fluvial  creek  or  bedrock  s i d e s of both  terraces a r e only  channels  of  Wee  Sandy  found and  1 04  CHAPTER 5 ROAD CORRIDOR ASSESSMENTS  5.1  General The  in  utility  Chapter  logging  4 c a n be d e m o n s t r a t e d  road alignments  primary yet  objective  economically Several  by  B.C.  road  will  to  of shown  meet  road  classes  at  main  on  sound  alignments.  the  slope  located  impact,  i f any, these  The f i v e  flagged  o f 1981. These map,  requirements  o f s l o p e s c a n be d e t e r m i n e d  t r a v e r s e d by e a c h .  and  stability  and l o c a t i o n  roads  were  f o r summer will  have  by i d e n t i f y i n g t h e  separate  road  options  Options  r o a d o p t i o n s were t e n t a t i v e l y  Nemo C r e e k B a s i n . The l o n g e s t o f begins  at  location For  the  S l o c a n Lake a p p r o x i m a t e l y  Wee Sandy C r e e k .  of  presented  be d i s c u s s e d i n d e t a i l .  Three  of  detail  F o r e s t s d u r i n g t h e summer  grade  o p e r a t i o n s . What  5.2 Nemo C r e e k Road  road  by l o o k i n g i n  r o a d o p t i o n s were t e n t a t i v e l y  the s t a b i l i t y  hazard  system  i n Nemo and Wee Sandy C r e e k B a s i n s . The  feasible  locations,  logging  classification  i s t o d e l i n e a t e t h e most e n v i r o n m e n t a l l y  Ministry  engineered  on  of the hazard  The n a t u r e  t h e lower  three  4 km, t h e r o a d  from  i s option  a s s o c i a t e d with  the slope s t a b i l i t y  t r a v e r s e s low h a z a r d  Sharp Creek B a s i n , c r o s s e s a rock  Hoben C r e e k v i a a ' n o t c h '  f o r access  easily  A  into and  2 km s o u t h o f t h e mouth o f  of the hazards  c a n be i n t e r p r e t e d  the f i r s t  located  this map.  S1 s l o p e s  r i b to the north  d i s c e r n a b l e on t h e map, t h e n  105  unavoidably blasting.  t r a v e r s e s some s h a l l o w At  km  6.7,  the road begins  h a z a r d o u s R3 a n d S3 s l o p e s blasting. grades  These  slopes  needed t o a t t a i n  which are  in  then  t h e Nemo C r e e k B a s i n p r o p e r .  gully  which w i l l  require special  Continuing the  road  with  derived  from  mostly  stable  12.3 i n  occurring  form  to on  near  bench,  A t km 8.9, t h e r o a d c r o s s e s a  treatement stream  i n order  to  prevent  siltation.  crossed  several  a  meters  north.  The  However, which  The r o a d  avoid  hazardous  would  then  S2 in  and F1 diameter  substratum  a total  is  of 5 a c t i v e  require  special  c r o s s e s Nemo C r e e k a t  particularly  threatening Terrace  snow fronts  s i d e o f Nemo C r e e k demand p a r t i c u l a r  a b r i d g e c r o s s i n g where e n g i n e e r i n g  techniques  care can  stability.  traverses  t o t h e west on t h e s o u t h both  near  the broader  these  s i d e o f Nemo C r e e k , t h e  S3 a n d F2 s l o p e s t h a t have been  t e r r a c e f r o n t s near  located  of the road  v i a the  the n o r t h s i d e of the c r e e k .  on t h e s o u t h  require  t o s t e e p R3 s l o p e s  descends,  to the  areas.  engineering.  order  Continuing road  are  may  because  of moderately  boulders  these  paths  path  locating  maintain  in  areas  potentially  b a s i n on t h e n o r t h s i d e o f Nemo C r e e k ,  the high c l i f f s  flow  avalanche  in  the  scattered  precautionary km  up  traverses a series  slopes  debris  and s u b s e q u e n t  intermittent  to traverse  unavoidable  into  avalanching  requiring  some  a bench a d j a c e n t  Nemo C r e e k a t km 9.0. The r o a d  debris  soils  the  creek.  terrace fronts.  The  road  incised to  should  n o t be  A t km 14.0, t h e r o a d  upper Nemo C r e e k B a s i n where t h e main h a u l  enters  road  is  terminated. A  summary  of  total  l e n g t h s of road c o r r i d o r  A traversing  106  t h e , number o f k i l o m e t r e s  PH  CN  ft.  0  0  .3  0  1.8 .2  .9  .9  .2  0  0  0  2.9 4.6 5.5 2.0  0  1  5  1  BI  9.4 .3  3.6  .3  0  .3  0  1.8 .2  0  0  1.1 .2  0  .3  2.3 5.5 .3  1. 1 .2  3  5  1  B2  9.4 .8  3.2 1.1 .3  0  .3  .2  1.8 .2  0  0  1. 1 .4  0  .3  2.2 6.1 .8  1.1 .6  3  5  2  C  9.0 .9  2.5 .4  0  . 1 .6  1.3 1.5  0  0  0  . 1 1.0 .6  4.2 3.8 .9  1.0 .7  2  3  1  .3  . 1 .8  1.3 1.5  0  0  0  6  3  1  D 11.0 2.6  2.6  1.0  .6 .6  S4, R3 - VERY HIGH  Figure  S3, R2, F2 - HIGH  0  0  .8  3.4 3.9 2.9  S2, F l - MODERATE  0  1.1  SI, RI - LOW  5.1. H a z a r d s t r a v e r s e d by v a r i o u s p r o p o s e d r o a d i n Nemo and Wee Sandy C r e e k B a s i n s .  likely  to require either  during  road c o n s t r u c t i o n .  Nemo  Creek  approximately approximately  road  intermittent  option  4.6  km s h o r t e r t h a n  access  Slocan  Lake, the road encounters  cause  engineered. gully,  B  or  corridors  continuous  begins  1.8 km s o u t h o f t h e mouth o f  direct  to  VERY HIGH  1.6  Bi  S2-R3  1.5  PS  R3-R1  2.6  CO  to  to  KILOMETRES OF EACH RELATIVE HAZARD  S2-R1  5.6  m  Sl-Rl  A 14.0  C/1  S3-R3  CN  ROAD OPTION  TOTAL LENGTH  KILOMETRES OF EACH HAZARD CLASS TRAVERSED  cn  Table  channels,  TERRACES CROSSED  and  d e b r i s flow  DEBRIS FLOWS CROSSED  traversed,  the  GULLIES CROSSED  fronts  number o f g u l l i e s ,  in  CONTINUOUS BLASTING  terrace  5.1. I n c l u d e d  INTERMITTENT BLASTING  and  of the t o t a l  i n Table  LOW  a tally  i s given  MODERATE  is  class  HIGH  each hazard  on  Nemo  blasting  Slocan  Creek.  Lake It i s  o p t i o n A and p r o v i d e s a more  t o t h e Nemo C r e e k B a s i n . T r a v e r s i n g s o u t h w e s t from  stability The  road  problems then  a n d t r a v e r s e s S2 s l o p e s  w i t h i n 0.5 km a major g u l l y a p t i f  the  switches likely  road back, to  is  not  properly  again crosses the  require  some  minor  1 07  blasting road  because  begins  of s h a l l o w  to  descend  towards  steepened  S4  this  slopes are steeper  area,  slope  surficial  spoon-shaped emerges from soon  blasting At  during  risk  area  route,  then  joins  via a  of recent  locally  l a n d s l i d i n g . In  35° a n d i n c l u d e g u l l i e s  their onto  soils  Creek  the  with  h e a d s . A t km 2.4, t h e r o a d a low h a z a r d  likely  S1  to require  slope  but  intermittent  road c o n s t r u c t i o n .  with  up w i t h a  road  more  labeled  into  (1)  during  immediately  B2, i n t e r s e c t s  an  upper,  route  o p t i o n A a t km 4.3, a n d (2)  favourable  require blasting  0.2 km on a R3 s l o p e  lower  grade  that  will,  r o a d c o n s t r u c t i o n f o r 0.1  adjacent  t o Nemo C r e e k . The  an a c t i v e  slide  r o a d o p t i o n A a t km 5.0. From t h i s  at  km  4.6,  p o i n t , o p t i o n s B1  B2 f o l l o w t h e same r o u t e a s o p t i o n A. Table  and  B2  linear  5.1 summarizes t h e t o t a l  traversing  hazard  Road  options  environmental scheme, should  acceptable, lower  hazard  B1  and  class  and  B2  and the t o t a l  have  critical  to  option l i k e l y  t o minimize  which  case  in this  c o n s i d e r a t i o n s dominate  and  each  disadvantages.  considerations are  be c h o s e n ,  financial  A,  advantages  the road  financial  each  l e n g t h of road c o r r i d o r s  B1  number o f  features crossed.  environmental  if  at  . shallow  route  unfortunately,  and  faces  B1 w h i c h l i n k s  lower  to  than  km 3.3, r o a d o p t i o n B s p l i t s  labeled a  the high  encounters  Nemo  showing e v i d e n c e  scarp  m a t e r i a l s . A t km 1.9,  environmental  When  and  the  and where  development  landslide  occurrence  w o u l d be o p t i o n A. However, the  picture,  consequences  of  p e r h a p s o p t i o n B1 s h o u l d be c h o s e n  construction costs.  economic  and  i f the  landsliding are because  of i t s  108  5.3 Wee  Sandy C r e e k Road  Two  corridor  i n t o Wee see  Options  options  stability  map  and T a b l e  where r o a d o p t i o n A b e g i n s For  3.0,  the f i r s t S1  and  the  will  dominated  Creek B a s i n proper have  at  Sandy C r e e k , the  creek  avalanche  and  at  steep  require  ridge,  R3  some  time  three  elevation  road  crosses  adjacent  i n order  steepness enters  switch-back  unavoidable  between  km  o f t h e canyon  the  B a s i n . A t km  veneered  with  blasting  for  into  broader  notch  t h e Wee  gullies,  front  Sandy  a l l of  and t h e n  to avoid steeper  9.0 in this  upper Wee  active  grade.  series  impact  i s t e r m i n a t e d . A summary  Wee  crosses  s l o p e s and snow  on Wee  failing and  At  area.  this  F1  paths,  i n order to point,  of h i g h h a z a r d Sandy C r e e k  the  S3 and R3 immediately  S4 s l o p e s a r e  10.2  of  d e b r i s flow  on a d e b r i s f a n s l o p e  and m a i n t a i n p r o p e r  t o have some  low  side.  to the south. A c t i v e l y  unavoidable  Creek.  t o t h e west, t h e r o a d t r a v e r s e s a s e r i e s  an  Lake  traverses  slope  major  D,  i n v o l v e d d e b r i s f l o w s . Once near  on t h e s o u t h  takes a double  likely  road  descends  F2 s l o p e s , c r o s s e s t h r e e r e c e n t l y  slopes  Sandy  continuous  then  intersecting  km 6.6  paths  gain  road  a  at Slocan  Sharp Creek  the road descends a t e r r a c e  Continuing and  the  (option  0.7 km. A t k i l o m e t r e 3.7, t h e r o a d e n t e r s a  bedrock  which  kilometres,  encounters  which  approximately a  three  2 km s o u t h o f Wee  f o r access  two  5.1) b e g i n s  S2 s l o p e s o f t h e lower  road  colluvium  on  located  Sandy C r e e k B a s i n . The l o n g e s t o f t h e  slope  hazard  were t e n t a t i v e l y  virtually  because of t h e extreme At  km  11.0,  the  road  Sandy C r e e k B a s i n where t h e main of  the  total  lengths  of  road  109  corridor  D  critical  linear  Wee option of  traversing  Wee  road  and  surficial  option C begins  traverses directly  material  R3  descend grade  over  blasting  Sandy C r e e k a t  km  slopes  the  likely  i s maintained, and  during  2.0,  to the creek  2.5  avoid  road  result  Farther  emerge o n t o  a  terrace  landsliding  directly  into  descending  Creek at  km  At  km  o p t i o n D t o upper Wee summary of t h e c l a s s and  in Table  it  is  involving unavoidable  C  impacts.  evident  5.0,  the  this  Wee  extremely  total  front  the  would  o p t i o n C c r o s s e s two  road  front  and  i n t e r s e c t s an  showing  creek.  terrace front  terrace  will  favourable  causing environmental  Sandy C r e e k  Any  almost  damage. debris  flow  c r o s s i n g Nemo follows  road  Basin.  l e n g t h s of  road o p t i o n C  number of c r i t i c a l  that  and  D  attempt  From T a b l e portions  environmental with  a  of  linear  traversing  features crossed  5.1.  options  environmental  veneers  to  a t e r r a c e bench a t  unstable  t o t h e west, r o a d  4.3.  allowable  highly  in landslides  as  mouth  moderate  encounters  the  before  Road  point  b e d r o c k w h i c h would r e q u i r e  maximum  gullies  given  same  n o r t h towards the  below. I f a r o a d can  of  5.1.  t o produce u n s t a b l e d e b r i s which  to l o c a t e a road a c r o s s  each hazard  at the  unavoidably  attempt  A  in Table  road c o n s t r u c t i o n . Approaching  of a c t i v e  certainly  t h e number  route crosses  competent  evidence  is  t o the  and  R3-S2 s l o p e s , some of w h i c h have s h a l l o w  intermittent  steep  class  i s given  Sandy C r e e k . T h i s more d i r e c t  s t e e p S2  km  hazard  features crossed  Sandy C r e e k D then  each  either  5.1 of  to  minimize  cost  and  and  t h e above  description,  road  requiring  blasting  damage  due  to  option.  Financial  landsliding and  and are  environmental  1 10  considerations  suggest  However,  because  potential  affect  decision  is left  that  a host the  of  choice  to the  land  option  D  is  considerations of  final  planner.  road  a  better  other  than  location,  the  choice. landslide ultimate  111  The  first  describe  and  controlling deemed  CHAPTER 6 SUMMARY AND  CONCLUSIONS  of  this  two  determine the  in  geologic,  vegetative  landslide  processes  possible  landslide  observations  to  landsliding.  The  • which  general  observation  a  the  likely  to  it  more e a s i l y  study  area  type  the a  less  ground  t r a n s f e r r e d from  t h e model  necessary could  be  surface  a p p l i e d to  model  based  number  are  certain that  material,  forest  i t has  of  it  classification the  engineering. than  statistical  factors,  occur  physically the  was  affect  failures  surficial  the  it  to  operator-dependent  b a s e d on  dominant  area,  a hazard  by  of  likely  o n l y be  affected  were e n c o u n t e r e d  first which  physical  evaluated  f u n d a m e n t a l v a r i a b l e s of was  the  be  is  c h o s e n and  some d i f f i c u l t i e s  can  which to b u i l d  models which a r e  subjectively  of  and  considerations.  initial  but  slopes mantled with  Moreover, because  It  assumptions  considered  for uniform  empirical  that  regions  pedologic  model g r e a t l y s i m p l i f i e s  framework on  most  are  s u r f a c e s w i t h i n 2 m e t e r s of  u n i t s . A d v a n t a g e s of  being  hydrologic,  factors  area. other  study  be  of  in  i n the  factors  slopes  Factors  currently active  satisfies  to  of  map,  study  and  m o d e l . The  system  occurrence  to  factors  nature  geotechnical  provides  i n the  was  fundamental  the  infer  shear  partially  terrain  slopes  of  v a r i a b l e s in a d d i t i o n to engineering from  planar  of  geomorphologic,  However,  on  thesis  the p r e d i c t i b i l i t y  stability  important  include  o b j e c t i v e s of  the  other  a n a l y s i s of advantage  r e g i o n t o r e g i o n . However,  i n a c c u r a t e l y q u a n t i f y i n g the i n the  study  area.  to d e l i n e a t e those evaluated  slopes  according  to  i n the the  11 2  geotechnical  model.  Classification  System  basis that  of  genetic  less  t h a n one  evaluated  variable  many  were  i n the  Therefore, estimate  it  properties. fails  generally and  that  colluvial analysis.  the  be  geotechnical were  found  accurately  relative  for  very  values  colluvial  and  accurately,  stronger morainal  than  less  soils  fluvioglacial  be  to  constraints. roughly  landslide  uncertainties for  in  a  extremely  complex  shear  strength  developed  more  materials  in  this  at  a  successful with  though the  fact  values  appear  associated  angular are  strength,  accounted  morainal  the  root  absolute  does  example, even  material,  means t o  <t> v a l u e s  determine it  be  addition,  The  characterizing  However,  be  model. to  estimating  method of  could could  fundamental  partially  found  In  time  slopes.  The  m a t e r i a l s . For  or  of  and  the  were d i f f i c u l t  d e v e l o p the  these  can  the  to  in  the  <f> v a l u e s  logistical  difficulties  determining  determined  to  area  genetic  depth to shear plane  estimates  site.  of  due  Terrain  I t was  that  strength,  over  to  slopes  soil  factors  particular  genetic  the  study  conditions.  values  of  expression.  i n the  shear  the  u n i t s p r i m a r i l y on  groundwater  and  materials  to  slopes  necessary  version  Genetic  surface  m o d e l . Of  likely  i n the  stochastic  leading  was  the  controlling involved  field  slope  using  complex a s s e m b l a g e s of  as  pressure,  done  t o map  the  to the  such  piezometric  thesis  h a l f of  t o p o g r a p h y , and  parameters  measure  (TCS)  was  m a t e r i a l and  according  evaluated,  This  different  absolute  soils  in  could  that c o l l u v i a l fluvioglacial  ranges not  soils  be  are  materials,  u n p r e d i c t i b l e than e i t h e r is  born  out  in  the  11 3  A  particular  delineating factor  difficulty  on t h e map t h e d i s t r i b u t i o n  most  fundamental  slopes are obscured evaluated  with  complexity an  not  to  aerial  over  slope  of  stability.  photographs.  I n many  s l o p e c l a s s e s be g i v e n  which a f a i r l y  angles,  be  the  areas,  accurately  Moreover,  topographic  10°  intervals,  wide r a n g e o f s l o p e e q u i l i b r i u m  c a n be c a l c u l a t e d . T h i s , however,  unique  slope  by t h e t r e e c a n o p y and c a n n o t  demanded t h a t  interval  values  e n c o u n t e r e d was t h a t o f a c c u r a t e l y  isa difficulty  that i s  t o t h i s m e t h o d o l o g y and i s one o f t h e p r i m a r y  reasons  why a r e a l a s s e s s m e n t s o f s t a b i l i t y  cannot  replace  site-specific  evaluations. Semi-quantitative  variables  in  this  thesis affect  t h e m s e l v e s a f f e c t e d by many of t h e f a c t o r s d e s c r i b e d in  other  regions and  regions.  For  i s the case.  clarifies  the  fact  is,  in  landsliding.  Similarly,  demonstrates not only associated  with  piezometric  pressures  contributing  t o them.  according of  deforestation  little  e x p l a n a t i o n as  The p h y s i c a l model, on t h e o t h e r loss  fact,  of  the  the  fact  terrace  controlling  that  fronts,  and  root  factor  i n the study  locally  stability  cohesion directly  area,  landslides but  flows  c o u l d be i n f e r r e d  For  following influencing  also  are that  steepened  in  hand,  t h e s t o c h a s t i c model  areas  t o t h e g e o t e c h n i c a l model were i n f e r r e d  s l o p e morphology and g e n e s i s .  debris  i n many  between  sometimes w i t h  that  deforestation  Factors  relationship  occurrence,  t o why t h i s  authors  example, e m p i r i c a l e v a l u a t i o n s  have drawn a d i r e c t  landslide  by  or a r e  example,  from e v i d e n c e  commonly elevated  slopes  are  not  evaluated  from  knowledge  hazards  of past  due  debris  to flow  1  activity  such  as  large boulders  d e p o s i t e d on  objective  this  levees adjacent  14  to  channels. The  second  landslides similar  initiated  to those  system  based  calculated  by  of t h e on  for  past  be  developed  i n the  to  n a t u r a l f a c t o r s and occur  greater  than  model.  Engineering  include  inadequate  slope  10%  for  slopes  after of of  stability to  probabilities host that  a  slopes  problems  results  with  by  the a c t u a l  and  indicated  stochastic  associated  of  evidence  lead  failure  variety  by  slopes  with  of  to  failure  geotechnical  these  failures  improper  fill  i n c o r p o r a t i o n of o r g a n i c d e b r i s i n failure of  this  than  landslide  similar  10%  types  v a l u e may  hazard  before  10%  problems,  values  mean i n r e a l  a b s e n c e of more a c c u r a t e l y d e t e r m i n e d  that the i t can  i n the  of p r o b l e m s ,  study  i f the  according slopes  with  study  area  be  inferred  area  will  r e g a r d l e s s of what  physical  model  probabilities  classes  near  or  estimates  consequence  fact  fill  calculated  either  expected  little  the  g r e a t e r than  of  also  that conservative  i s of  From  were  instability  to higher  experience.  10%  with  probabilities  the  a r e g r o u p e d t o form  involve  induced  p r o v i s i o n s f o r water d r a i n a g e ,  s l o p e s with g r e a t e r than  likewise the  wide  landslides  when  tend  Fortunately,  of  indices,  e n g i n e e r i n g misjudgement, l a n d s l i d e s on  input values  engineering  Stability  rating  due  probabilities  indices  hazard  f o r comparison  a r e a . The  examine  that  showing no  failure.  a  were u s e d  road c o n s t r u c t i o n , i n d i c a t i n g  model  develop  to  i n environments  to  as d e t e r m i n e d  construction  m a t e r i a l s . High  was  adjacent  study  primarily  a r e a and  experience.  slopes  activities,  thesis  engineering a c t i v i t i e s  study  engineering  to  of  input  t e r m s . In values  the and  11 5  statistical the  study  analyses  area,  the  relative  recourse  available.  not  b e c a u s e of  apply  according terrain  to  past  units.  The  of p r o b a b i l i t y  In a r e a s limiting  which and  classed  as  slopes  as  'very  well  include c o l l u v i a l  slopes  mantled with  failure  greater  hazards  include  10%.  lower  10%  expected  slopes  factors  bedrock dominated The  have no  map  over  doubt  tool, and  the  the  rocky  to  i n c l u d e those by  slopes.  with  probabilities safety less  safety greater  be  morphology  'High  hazard'  fans,  and  probabilities  'moderate'  of  landslide  and  slopes mantled  with  of  failure  than  than  1.6.  surficial than  slopes  1.6  less 'Low  hazard'  materials and  having  gently sloping  terrain.  large  are  does  natural  assumed  indicated  f a n s and  areas  in characterizing natural where a v a i l a b l e d a t a  l e d t o some b r o a d  level,  i s then  m a t e r i a l s having  Slopes  f a c t o r s of  of  only  assigned  in similar  u p p e r p a r t s of d e b r i s  uncertainties involved  conditions  level  as  i n c l u d e s l o p e s mantled with  expected  hazards are  hazard'  steep  debris  m a t e r i a l s having  and  as  fans,  surficial  local  high  surficial  than  the  of  unit.  show s i g n s of a c t i v e f a i l u r e vegetation,  is  g e o t e c h n i c a l model  experience  behaviour  for slopes  system  assumptions,  engineering the  rating  where t h e  engineering  homogeneous t h r o u g h o u t Units  hazard  distributions  g e n e r a l i z a t i o n s , which,  i n e r r o r . 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Management o f s t e e p l a n d e r o s i o n : an J o u r , of Hydrology (NZ), i n p r e s s .  overview.  APPENDIX A  SOIL TEST DATA  125  SAND NO WS1 WS2 WS3 WS4 WS5 WS6 WS7 WS20 WS21 WS23 WS25 WS26 WS27 N10 Nil N12 N13 N14  P.I.  — — — — — — — — — — — — — — — — — — — — — — — — — 15.3  STONES  COBBLES  GRAVEL  COARSE  MEDIUM  FINE  SILT  CLAY  0  10  0  5  20  14.1  25.1  24.9  4.8  1.1  SP-SM  50  4.4 .  7.2  13.7  18.3  1.4  GM  0 5  0  0  7.7  33.5  14.1  34.4  8.5  SM  20  45  7.4  10.0  7.4  4.7  0.4  GW  3 1  40  20  5.6  7.5  11.2  9.6  3.0  GM  10  20  12.7  16.0  24.2  16.0  0.1  SM  0  0  8  4.9  19.9  30.2  34.9  2.0  SM  0  5  25  13.9  21.2  23.7  9.7  1.5  SP-SM  1  10  5  10.0  12.6  28.2  30.0  3.1  SM  5  5  5  6.4  10.7  42.1  23.4  2.4  SM  5  20  30  12.6  12.0  12.6  7.2  0.6  GP-GM  USC  2  25  25  7.3  10.6  12.9  15.9  1.2  GM  0  0  0  2.2  8.9  40.0  44.2  4.6  SM  0  0  20  10.8  20.2  22.0  24.0  2.9  SM  30  15  20  5.5  11.6  7.1  1.0  1.1  GP  10  10  15  9.9  20.9  15.7  15.9  2.6  SM  10  15  20  8.8  15.8  11.6  16.0  2.8  GM  5  5  20  10.3  25.4  15.4  15.4  3.4  SM  0  0  0  0.6  1.2  32.4  53.9  11.9  ML  0  10  40  12.3  20.7  14.8  1.9  0.3  GP  5  10  30  10.1  14.0  13.6  15.4  1.9  GM  5  15  20  4.8  16.6  20.8  15.9  1.8  GM  5  15  20  15.6  29.9  12.3  1.4  0.7  SP  5  20  15  15.0  22.8  10.2  10.5  1.4  SW-SM  5  10  20  17.1  25.9  15.1  6.3  0.5  SW-SM  0  2  7  3.4  11.4  32.0  36.3  7.8  SM  2.7  0  1  5  4.4  13.2  21.4  42.8  12.2  ML  Nl+lOO  ~  1  5  35  10.3  15.8  13.2  18.1  1.7  SM  Nl+100-2  5.6  1  5  35  8.0  19.1  12.7  15.7  3.4  SM  N2+40  2.8  5 ;••  5  15  9.3  22.8  16.3  19.3  7.2  SM  N3+25  — — — — — — — —  5  25  35  8.0  11.2  8.0  6.6  1.1  GW-GM  — — —  25.5  15.0  26.2  14.9  16.9  1.3  SM  30  10.8  15.9  13.9  16.6  1.5  SM SM  1  — — —  N15 N17 N18 N19-1 N19-2 N20 N21 N22 NO+80  N4+07 Rl R2 R3 R4 R5 R6 1 2 3  3.7  5.4  11.0  1  10  7.6  7.4  15.5  22.4  34.4  13.2  5.9  4.3  23.4  45.8  17.4  3.1  SM  5  5  15.2 •  23.5  18.1  21.1  11.1  SM  1  5  20  17.0  20.6  12.7  19.9  3.8  SM  5  5  30  13.5  22.1  17.1  6.9  0.4  SW-SM  5  5  15  17.2  27.4  16.4  11.6  2.4  SM  — —  — —  43  14.5  19.7  12.0  9.5  1.5  SW-SM  19.2  13.5  26.1  11.9  20.1  9.1  SM  APPENDIX B  STOCHASTIC GEOTECHNICAL MODEL  127  The  stochastic  represents  the  geotechnical  summary  Swanston e t a l ( 1 9 7 3 ) , and  the  determines of  hillside  an e x p e c t e d  failure,  P.  of  factor  Input  the of  model  from  equation The  which  the  by  this  study  ideas presented  Brown and  'infinite  Sheu  by  (1975)  slope' variety.  E [ F S ] , and  are those Chapter  probabilistic  in  Simons e t a l ( 1 9 7 8 ) . I t  safety,  variables  e a c h o f w h i c h were d i s c u s s e d i n  of  (1974),  as d e v e l o p e d is  used  refinement  O'Loughlin  Simons e t a l ( 1 9 7 6 ) ,  assumes  and  model  shown  3.  probability  in Figure  The  model'  is  It  3.1,  deterministic developed  is  3.6. expected  E[FS]  factor  of s a f e t y  = L1(E[C]  i s expressed  as  + E[Cr]) + L2(E[tan*]) (1)  The  v a r i a n c e of t h e  factor  of  safety  i s formulated  as  V A R [ F S ] = L 1 ( V A R [ C ] + E [ C ] •+ 2E[C] E [ C r ] + V A R [ C r ] + E [ C r ] ) + L2 (VAR[tan«s] + E[tanc*]) + 2L1 L2 E [ t a n * ] ( E [ C l + E [ C r ] ) - E[FS] (2)  In e q u a t i o n s expected brackets values,  (1) and  values  ( 2 ) , the  and  variances  respectively. the expected  t h e v a r i a n c e as  of  ] and  the  VAR[  variable  Assuming-uniform d i s t r i b u t i o n s  v a l u e of a random v a l u e X  E[X]  and  symbols E[  =  (Xmax + Xmin)/2  ]  are  the  inside  the  for  i s expressed  input as  (3)  1 28  VAR[X] =  where Xmax and input  value  Xmin a r e  (Xmax - Xmin)/12  t h e upper and  respectively.  The  lower  c o n s t a n t s L1  (4)  l i m i t s of and  L2  the  random  are  =  Li  rHsin2£(qo/rH) +  [(ysat/y)M]  +  (rwet/r)(1-M) (5)  and  (qo/yH) + L2  (ysat/y-l)M +  [ywet/y(1-M)]  = [(qo/yH) +  ( sat/y)M + r  (ysat/y(1-M))]tan* (6)  Values  of E [ F S ]  be  to  used  and  VAR[FS] computed  estimate  probability  of  probability  from  of  equations  failure.  1 and  By  definition,  failure is  p[FS<1] = P  where  P  is  cumulative Ward  probability the  found  probability  equation  t h a t FS  that  a  of  of  an  t h e v a l u e of t h e  (7)  failure  is less  than  reasonable  i s the normal or G a u s s i a n  computation  determining the  the  probability  (1976)  2 can  and or  p[FS^1] i s the equal  to  1.0.  d i s t r i b u t i o n of  failure  d i s t r i b u t i o n which  allows  approximate  value  non-dimensional  of  variate  P  by  first  U by  using  1 29  U =  The  value  of  (1-E[FS])/(VAR[FS])  U i s then  used  0 5  (8)  t o compute t h e c u m u l a t i v e  failure  ' k' by t h e e x p r e s s i o n  k = 0.4|U|  i f |U|<0.13  (9)  or  k = -0.01314 + 0.49494|U| - 0.15804|U| if  2  + 0.01661 I U |  3  |U|>0.13  (10)  Equations  9 a n d 10 a r e a p p r o x i m a t i o n s  p e r c e n t . From U and k, t h e p r o b a b i l i t y  with errors of f a i l u r e  P = 0.5 + k  if  U>0  P = 0 . 5 - k  if  U<0  P = 0.5  if  U=0  (11)  (12)  (13)  of l e s s  than 1  P i s f o u n d as  APPENDIX C  UNIFIED SOIL CLASSIFICATION  Field Identification Procedures (Excluding particles larger than 3 in. and basing fractions c estimated weights)  s8  ml mi lis*.  Symbols! Well graded gravels, gravel* sand mixtures, little or no fines  Predominantly one size or a range of sizes with some intermediate sizes missing Nonplastic fines (for identification procedures see ML below)  |1  'MS ij  3 tl  -a c-  ft  Il I! i i i 11 'Sis  I So  Wide range in grain size and substantial amounts of all intermediate particle sizes  :  1=1=1  Plastic fines (for identification procedures, see CL below)  Clayey gravels, poorly graded gravcl-sand-clay mixtures  Wide range In grain sizes and substantia] amounts of all intermediate particle sizes  Well graded sands, gravelly sands, little or no fines  Predominantly one size or a range of sizes with some intermediate sizes missing Nonplastic fines (for identification procedures, see ML below) Plastic fines (for identification procedures, see CL below)  Clayey sands, poorly sand-clay mixtures  Greater than 4  j~2  •few)  1  Give typical name; indicate approximate percentages of sand and gravel: maximum size; angularity, surface condition, and hardness of the coarse grains; local or geologic name and other pertinent descriptive information; and symbols in parentheses For undisturbed soils add information o n stratification, degree of compactness, cementation, moisture conditions and drainage characteristics Example: Silly sand, gravelly; about 2 0 % hard, angular gravel particles i - i n . maximum size: rounded and subangular sand grains coarse to fine, about 15 % nonplastic fines with low dry strength; well compacted and moist in place: alluvial sand; (SM,  graded  Between 1 and 3  Not meeting all gradation requirements for G I F Atterbcrg limits below " A " line, or PI less than 4 g (9(^10 ^ g  o "5  u u <8  Atterbcrg limits above " A " line, with PI greater than 7  Above " A " line with PI between 4 and 7 are borderline cases requiring use of dual symbols  Greater than 6  <Oao>'  Between I and 3  N o t meeting all gradation requirements for SW  iSJi Q  Atterbcrg limits below "A" line with PI greater than 7  Above " A " line with PI between 4 and 7 are borderline cases requiring use o f dual symbols  Identification Procedures on Fraction Smaller than N o . 40 Sieve Size Dry Strength (crushing characteristics)  Toughness (consistency near plastic limit) Inorganic silts and very fine sands, rock (lour, silty or clayey fine sands with slight plasticity  None to slight  is 8  « —3  Dilatancy (reaction to shaking)  M  None to very slow  Organic silts and organic : ctays of low plasticity  -|J  Inorganic silts, micaceous or diatomaceous fine sandy or silty soils, elastic silts  E o  s  Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays  III Highly Organic Soils  High to very high  Inorganic clays or high plasticity, fat clays None to very slow  Organic clays of medium to high plasticity .  Readily identified by colour, odour, sponjjy feel and frequently by fibrous texture  Give typical name; indicate degree and character of plasticity, amount and maximum size of coarse grains: colour in wet condition, odour if any, local or geologic name, and other pertinent descriptive information, and symbol in parentheses For undisturbed soils add information on structure, stratification, consistency in undisturbed and remoulded states, moisture and drainage conditions Example: Clayey sill, brown: slightly plastic: small percentage of fine sand; numerous vertical root holes: firm and dry in place: loess: (ML)  0  10 20 30 40 50 60 70 80 90 100 Liquid limit Plasticity chart for laboratory classification of fine grained soils  From Wagner, 1957. * Boundary classifications. Soils possessing characteristics of two groups are designated by combinations of group symbols. For example GW-GC, well graded gravel-sand r xture with clay binder. A l l sieve sizes on this chart are U . S . standard. Field Identification Procedure for Fine Grained Soils or Fractions These procedui e to be performed on the minus N o . 40 sieve size particles, approximately J,f in. For field classification purposes, screening is not intended, simply remove by hand the coarse particles thai interfere with the tests. Dilatancy (Reaction to shakin Dry Strength (Crushing characteristics): Toughness (Consistency near plastic limit): After removing particles larger than N o . 40 sieve sire, prepare a pat of After removing particles larger than N o . 40 sieve size, mould a pat of soil After removing particles larger than the N o . 40 sieve size, a specimen o f moist soil with a volume of about one-half cubic inch. A d d enough to the consistency of putty, adding water if necessary. Allow the pat to soil about one-hajf inch cube in size, is moulded to the consistency o f water if necessary to make the soil soft but not sticky. dry completely by oven, sun or air drying, and then test its strength by putty. If too dry, water must be added and if sticky, the specimen Place the pat in the open palm of one hand and shake horizontally, striking breaking and crumbling between the fingers. This strength is a measure should be spread out in a thin layer and allowed to lose some moisture vigorously against the other hand several times. A positive reaction of the character and quantity of the colloidal fraction contained in the by evaporation. Then the specimen is rolled out by hand on a smooth consists of the appearance of water on the surface of the pat which soil. The dry strength increases with increasing plasticity. surface or between the palms into a thread about one-eight inch in changes to a iivery consistency and becomes glossy. When the sample High dry strength is characteristic for clays of the C H group. A typical diameter. T h e thread is then folded and re-rolled repeatedly. During is squeezed between the fingers, the water and gloss disappear from the inorganic silt possesses only very slight dry strength. Silty fine sands this manipulation the moisture content is gradually reduced and the surface, the pat stiffens and finally it cracks or crumbles. The rapidity and silts have about the same slight dry strength, but can be distinguished specimen stiffens, finally loses its plasticity, and crumbles when the of appearance of water during shaking and of its disappearance during by the feel when powdering the dried specimen. Fine sand feels gritty plastic limit is reached. squeezing assist in identifying the character of the fines in a soil. whereas a typical silt has the smooth feel of flour. After the thread crumbles, the pieces should be lumped together and a Very fine clean sands give the quickest and most distinct reaction whereas slight kneading action continued until the lump crumbles. a plastic clay has no reaction. Inorganic silts, such as a typical rock The tougher the thread near the plastic limit and the stiffer the lump when flour, show a moderately quick reaction. it finally crumbles, the more potent is the colloidal clay fraction in the soil. Weakness of the thread at the plastic limit and quick loss of coherence of the lump below the plastic limit indicate either inorganic clay of low plasticity, or materials such as Vaolin-iype clays and organic clays whjch occur below the A-line. Highly organic clays have a very weak and spongy feel at the plastic limit. D  4  APPENDIX D  R E L A T I V E DENSITY DETERMINATION  TECHNIQUE  , CONSISTENCY Very  soft  (Tsf)  u  0.25  BLOWS „ PER FOOT  RULE-OF-THUMB Core (Height = twice the diameter) sags under own weight  0 - 1  Soft  0.25 - 0..50  Can be pinched i n two between thumb and f o r e f i n g e r  2 - 4  Firm  0.50 - 1..00  Can be i m p r i n t e d fingers  5 - 8  Stiff  1.00 - 2..00  Can be i m p r i n t e d w i t h c o n s i d e r a b l e p r e s s u r e from f i n g e r s  2.00 - 4..00  B a r e l y can be i m p r i n t e d by p r e s s u r e from f i n g e r s  16 - 30  Cannot be imprinted by fingers  Over 30  Very  stiff  Hard  q  q  4.00+  i s unconfined  easily  with  9 - 15  compressive s t r e n g t h i n t o n s / s q . f t .  Blows as measured w i t h 2 - i n . OD, 1 3/8-in. ID sampler d r i v e n 1 f t by 140-lb hammer f a l l i n g 30 i n . See T e n t a t i v e Method f o r P e n e t r a t i o n Test and S p l i t - B a r r e l Sampling o f S o i l s , ASTM D e s i g n a t i o n : D1586-58T.  APPENDIX E  TERRAIN C L A S S I F I C A T I O N  SYSTEM  Texture SIZE mm 256 64 ROUNDNESS ROUNDED BOULDERY COBBLY PEBBLY b k E ROUND OR ANGULAR  SANDY s  .0039  SILTY  GRAVELLY  ROUNDED  ANGULAR  .062  FINES f  BLOCKY a  RUBBLY r  Genetic M a t e r i a l Anthropogenic — A Morainal Colluvial C Organic Eolian E Bedrock Fluvial F Saprolite Ice I Volcanic Lacustrine L Marine  M 0 R S V W  Qualifying Descriptor B Glacial F Active S Inactive  G A I  Bog — Fen — Swamp  Apron Blanket Fan Hummocky Level  Avalanched Bevelled Cryoturbated Deflated Channeled Failing Kettled  Surface E x p r e s s i o n a Subdued b Ridged f Steep h Terraced 1 Veneer Modifying A B C D E F H  m r s t v  Process Karst modified Nivated Piping Soliflucted Gullied Washed  K N P S V W  Modifying  Process  Texture b^- F  Genetic M a t e r i a l "Surface E x p r e s s i o n Qualifying Descriptor  CLAYEY c  APPENDIX F  LANDSLIDE DATA AND  LOCATIONS  LANDSLIDES ASSOCIATED WITH ROADS ON SLOPES MANTLED WITH SURFICIAL MATERIAL SLIDE DIMENSIONS W D VOL. 2  NO. DI  TYPE DA-DF  1  L  *l  6  s  ' TCS  390  10  5  9800  34°  33°  fgMb  USC  BEDROCK  GW-GM  GRAN  2-3  M  D2  DA  6  20  3  360  40°  30°  rCv  GM  SS  3  D3  R  50  20  2  2000  44°  44°  rCb  GW  PHY  4  D5  SF  2  15  .5  15  35°  26°  rMb  GW  PHY  3  .5  —  38°  36°  gF b  GP  ARG  2  25  2  3750  42°  39°  sF b  SP  GRAN  3  D14 DA-DF 1500  6  1  2700  32°  35°  rCb  GW  GRAN  3  D15  SC  9  100  1  900  65°  36°  sF b  SC  D17  DA  15  7  1  105  —  34°  sMb  SW  60  15  4  3600  45°  38°  sMb  SW  225  62°  28°  sMb  72  52°  30°  fsMb  75°  36°  gF b  DUb  R  — —  D12  R  75  D18 DA-DF  G  G  G  D19  SC  6  25  1.5  D20  SC  6  6  2  SI  R  Al  DA  40  30  .5  600  40°  40°  gF b  A6  SC  20  10  10  200  50°  50°  rMb  —ravel  G  G  road washouts and stream  siltation  — — — — —  damage to road bed from o r g a n i c d e b r i s d e t e r  1.0  d e b r i s flow blocked major highway  fill  slope d e b r i s i n g u l l y  fill  s l o p e f a i u l u r e c a u s i n g stream  siltation  fill  slope damage and stream  siltation  fill  slope damage and stream  siltation  3-4  — —  PHY  3  . 1  road washout stream  SP-SW  MONZ  5  .5  road blockage  from f i l l  slope f a i l u r e s  SW-SM  ARG  3  road blockage  from f i l l  slope f a i l u r e s  GP GW-GP  — —  .2  IMPACT  — PHY  3  2-3 3-4  — — —  water d i v e r s i o n l e a d i n g t o road  blockage  damage t o road bed  road  blockage  damage t o road  siltation  LANDSLIDES ASSOCIATED WITH ROADS IN STEEP ROCKY TERRAIN SLIDE DIMENSIONS W D VOL.  USC  BEDROCK  MR  2  NO.  TYPE  D4  RF  D9  DA  1  L  10  1.5  D10  RF-DA 30  10  2  D13  RF-DA  A5  DA  —- rock 40  3  M  IMPACT  44° rCv/R  GW  SYE  2  R o c k f a l l on road causing blockage  1400  47°  47° rCv=R  GW  PHY  3  Damage t o creek by b l a s t e d  600  65°  41° rCv=R  GW  DIOR  2  Road blockage, damage to creek  66°  43° R/rCv  rubb  GRAN  3  Road blockage, damage to creek  80°  39° rCv=R  rubb  GRAN  2  Damage t o creek, road bed threatened  failure  8  s  TCS  84°  rockfall 90  *1  S  960  rock  LANDSLIDES ASSOCIATEDi WITH ROADS ON COLLUVIAL APRONS  WI  R  W2  R  W3  R  1  R-Ravel  2  i n meters  3  6^-slope  —d i s c r e t e —d i s c r e t e —d i s c r e t e  ravel  —  54°  40°  rCa  GW  GRAN  2  Road  blockage  ravel  —  58°  42°  rCa  GW  GRAN  2  Road  blockage  ravel  —  46°  41°  rCa  GW  GRAN  2  Road  blockage  DA-Debris avalanche  inclination  RF-Rock f a i l u r e  S F - F i l l slope f a i l u r e  a t zone of s l i d e i n i t i a t i o n  TCS-Terrain C l a s s i f i c a t i o n  8 - i n c l i n a t i o n of e n t i r e g  USC-Unified S o i l C l a s s i f i c a t i o n  w i t h r e s p e c t to the shear plane (see Chapter 3)  SC-Cut s l o p e f a i l u r e  DF-Debris  flow  hillslope  MR-Moisture Regime  M - R e l a t i v e h e i g h t o f water t a b l e  139  

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