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Model study of sloped tailings deposits Stuckert, Brian John-Adam 1982

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MODEL STUDY OF  SLOPED T A I L I N G S  DEPOSITS  by  B R I A N JOHN-ADAM S T U C K E R T B.A.Sc, University of British  A THESIS SUBMITTED OF  THE OF  Columbia,  IN PARTIAL  R E Q U I R E M E N T S FOR MASTER OF A P P L I E D in  THE  FULFILMENT DEGREE  SCIENCE  THE FACULTY OF GRADUATE STUDIES in  the Department of  Civil  We  accept to  THE  this  the required  UNIVERSITY (c)  Engineering  thesis  OF  as  conforming  standard  B R I T I S H COLUMBIA  Brian Stuckert,  1979  1982  AUTHORIZATION 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 the r e q u i r e ments f o r an advanced d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l able f o r r e f e r e n c e and study. I f u r t h e r agree that permission f o r e x t e n s i v e copying o f 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 o f my department or by h i s o r her representatives. I t i s understood t h a t copying o r 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 g a i n s h a l l not be allowed without my written permission.  ABSTRACT  Present  t a i l i n g s d i s p o s a l methods are s u b j e c t to l i m i t a t i o n s  t h a t warrent the development of a l t e r n a t i v e d i s p o s a l A r e c e n t l y proposed method  techniques.  i s the thickened discharge d i s p o s a l  method, which i n v o l v e s s l o p i n g t a i l i n g s towards a downstream embankment, thereby required  reducing  the height of the embankment  to s t o r e a given volume of waste m a t e r i a l .  seismic s t a b i l i t y  of such slopes i s a concern  were performed to i n v e s t i g a t e t h e i r  The  and model s t u d i e s  stability.  The model was composed of a sloped d e p o s i t of f i n e sand 81 cm l o n g , 20 cm wide and a downstream b a r r i e r 14 cm h i g h . ranging  from 4 to 14 percent were subjected  ranging  from .025 g to .10 g.  Slopes  to base a c c e l e r a t i o n s  Test d e p o s i t s subjected to  a c c e l e r a t i o n s above a c r i t i c a l a c c e l e r a t i o n , dependent on the slope angle, were observed  to l i q u e f y and flow.  d e p o s i t s came to r e s t at a f i n a l  These t e s t  slope of approximately  one  percent. Model deformations observed  were recorded  to behave s i m i l a r l y to a v i s c o u s f l u i d .  f l u i d model was found reasonably w e l l . limited  and l i q u e f i e d d e p o s i t s were  to p r e d i c t a c t u a l p a r t i c a l  Although  to s i z e e f f e c t s ,  liquified  A viscous displacements  a p p l i c a t i o n of t e s t r e s u l t s may be  i t seems a p p r o p r i a t e to analyze  c o h e s i o n l e s s m a t e r i a l as a v i s c o u s  -  ii  -  fluid.  2  I t i s suggested that a s t a t i c a l l y s t a b l e sloped  tailings  deposit,  upon l i q u e f a c t i o n t o a s i g n i f i c a n t depth, may become  unstable.  The r e s u l t i n g flow, governed by p o s t - l i q u e f a c t i o n  mechanical p r o p e r t i e s , could overtop a downstream embankment.  -  i i i -  TABLE OF CONTENTS Chapter  Page Table  of Contents  iv  L i s t of Tables  vi  L i s t of F i g u r e s  vii  Acknowledgments  x  1  INTRODUCTION  1  2  METHODS OF DISPOSAL  4  2-1  Introduction  4  2-2  Present  6  2- 3  3  D i s p o s a l Methods  2-2-1  Upstream C o n s t r u c t i o n Method  6  2-2-2  Downstream C o n s t r u c t i o n Method  8  2-2-3  Comparison with Conventional Earth Dam  12  Recently Proposed Method of D i s p o s a l Thickened Discharge D i s p o s a l  15  2-3-1  Advantages of Thickened Discharge  16  2- 3-2  L i m i t a t i o n s of Thickened Discharge  19  PRELIMINARY TESTING  22  3- 1  Test M a t e r i a l  22  3-2  Comparison of T e s t Sand with T y p i c a l Tailings Material  29  3- 2-1  Grain Size D i s t r i b u t i o n  30  3-2-2  Permeability  33  3-2-3  R e l a t i v e Density  35  3-2-4  L i q u e f a c t i o n Resistance  36  iv  and C o m p r e s s i b i l i t y  TABLE OF CONTENTS  (Cont'd)  Chapter 4  Page MATERIAL BEHAVIOUR  41  4-1  Liquefaction  41  4-2  Post Liquefaction  53  4-2-1  Viscosity  57  4-2-2  Yield  62  Shear S t r e n g t h  5  DEPOSITIONAL BEHAVIOUR OF T A I L I N G S COMPARED TO THE RESPONSE OF A L I Q U E F I E D DEPOSIT  66  6  REVIEW OF PREVIOUS MODEL STUDIES  71  7  TESTING PROGRAM  75  7-1  Model T e s t Equipment  78  7-2  Test Procedures  84  8  TEST RESULTS  85  9  FLUID ANALYSIS  100  10  PREDICTED P A R T I C L E DISPLACEMENTS  107  11  FLOW FAILURES  111  1'2  CONCLUSIONS  115  References  118  Appendix  124  v  LIST OF TABLES Table  Page  I  Volume C h a r a c t e r i s t i c s f o r T e s t Sand Versus Thickened Discharge Deposit  35  II  C o r r e c t i o n F a c t o r s f o r I n i t i a l Slope  49  Summary o f T e s t i n g Program  87  III  vi  L I S T OF  FIGURES  Figure 1 2  Page Flow Chart  for Typical Disposal  . Upstream C o n s t r u c t i o n  System  5 7  Method  3  Safe  4  Downstream C o n s t r u c t i o n  Method  10  5  Centerline Construction  Method  1 3  6  Conventional  7  Thickened  Discharge  8  Expansion  of Storage  9  Grain  Size  10  e  log(k)  11  Schematic Layout of Testing Apparatus  12  Liquefaction Resistance  Curve  13  Typical Cyclic  Triaxial  Test  14  Tailings Grain  Size  Distributions  31  15  Tailings Grain  Size  Distributions  3 2  16  V a r i a t i o n of  17  E f f e c t of P l a s t i c i t y Resistance  18  Liquefaction Resistance  19  C y c l i c Strength vs. Void Plasticity Tailings  20  Response of Medium Dense Sand Monotonic Loading  21  Response of Loading  vs.  Dam  Using  Upstream Construction  Earth  14  Dam  17  Method  18  Facility  2 3  Distribution  2 4  Relationship Cyclic  Permeability on  Loose Sand  vi i  9  Triaxial  2 6 27  Record  with  D-|Q  28  34  Liquefaction  37  of T a i l i n g s  3 9  Ratio  f o r Low  Under  Under Monotonic  39 4 2 4 4  L I S T OF  FIGURES  (Cont'd)  Figure 22  Page Response of Garnet T a i l i n g s Monotonic Loading  23  a) R e s p o n s e o f L o o s e S a n d b) R e s p o n s e o f L o o s e S a n d Effective Stress Path  Under  To C y c l i c to Cyclic  45 Loading Loading -  46 47  24  C y c l i c Shear S t r e s s Required to Develop Shear S t r a i n  10%  49  2.5  Liquefaction Resistance S t a t i c Shear  for  50  26  Terminal Residual  27  Bingham  Rheological  28  Bingham  Model  29  A G e n e r a l Pore P r e s s u r e (Water C o n t e n t ) Dependent Bingham P l a s t i c Model  56  30  Variation Content  58  3 1  Dependence o f V i s c o s i t y Concentrat ion  32  Dependence of L a b o r a t o r y Concentration  33  Viscosity  34  Curve Corrected  Pore Pressures  Flow  52  Model  55  Curve  55  of P l a s t i c V i s c o s i t y  w i t h Water  on S o l i d s  60  S l o p e on S o l i d s  Spectrum  (a)  Rheogram f o r Water Divided Galena  (b)  Effect  of S o l i d s  60 61  Suspension of F i n e l y  Concentration  35  Yield  36  Observed Pore Pressures Table Test  37  Model  38  Boundary  o n "C  63  v  Shear Strength Spectrum  64  for a Shaking  73  Test Deposit Dimensions Conditions vi ii  f o r Steady State  63  76 Seepage  76  L I S T OF  FIGURES  (Cont'd)  Figure  Page  39  Flow Net  f o r 6° S l o p e  77  40  S c h e m a t i c o f T a b l e Loop  79  41  T y p i c a l T a b l e R e s p o n s e a t 5 Hz  81  42  Model C o n t a i n e r  82  43  Breakdown o f T e s t i n g  44  Results  o f T e s t #7  45  Results  o f T e s t #12  89  46  Results  o f T e s t #13  90  47  Results  o f T e s t #14  91  48  Results  o f T e s t #16  92  49  Results  o f T e s t #17  93  50  E f f e c t of I n i t i a l Angle  51  A c c e l e r a t i o n Level Versus F i n a l Slope Angle  96  52  Threshold Acceleration Angle  97  53  E f f e c t of S l o p e d Base cn Model Response  54  E f f e c t o f V i s c o s i t y on B o u n d a r y L a y e r T h i c k n e s s  103  55  Comparison of P r e d i c t e d D i s p l a c e m e n t s f o r an 8"  and O b s e r v e d P a r t i c l e Slope  108  56  Comparison of P r e d i c t e d D i s p l a c e m e n t s f o r an 4°  and O b s e r v e d P a r t i c l e Slope  110  57  T a i l i n g s Flow F a i l u r e Case H i s t o r y - G r a i n Size Distribution  113  58  T a i l i n g s Flow F a i l u r e Case H i s t o r y - D e p o s i t Configuration  114  Program  86 -  Slope Angle  ix  on F i n a l S l o p e  versus I n i t i a l  Slope  88  95  99  ACKNOWLEDGEMENTS  I would l i k e t o express my s i n c e r e thanks t o Dr. Peter M. Byrne and Dr. Yogi P. V a i d f o r t h e i r guidance and support throughout t h i s study. I would a l s o l i k e t o thank my w i f e , L i n d a , f o r her p a t i e n c e and moral support, without which t h i s e f f o r t would not have been possible. F i n a l l y , I would l i k e t o thank E r t e c Western f o r a s s i s t a n c e i n t y p i n g the f i n a l manuscript.  - x -  1  CHAPTER 1 INTRODUCTION The d i s p o s a l effective  manner  of mine waste m a t e r i a l is a  attention  i n recent  techniques  are s u b j e c t  2,  such  that  warranted.  subject  years.  that Present  such  c r i t i c a l l y evaluated  and  cost  considerable  used  as d i s c u s s e d  disposal  i n Chapter  of a l t e r n a t i v e techniques  proposed  t o assess  received  commonly  to l i m i t a t i o n s ,  the development Any  has  i n a safe  a l t e r n a t i v e methods  must  is be  t h e i r v i a b i l i t y as an economical,  s a f e s o l u t i o n to the t a i l i n g s d i s p o s a l problem. One method  such  a l t e r n a t i v e i s the thickened  (Robinski,  creating  1975, R o b i n s k i ,  a mildly  sloped  1978).  conically  discharge  This  shaped  method  tailings  disposal involves deposit,  thereby e l i m i n a t i n g the need f o r a high and c o s t l y embankment as required  f o r conventional  ened d i s c h a r g e  t a i l i n g s d i s p o s a l systems.  method, as d i s c u s s e d  i n Chapter 2, has proven to  be an e c o n o m i c a l s o l u t i o n t o t h e t a i l i n g s However,  the s t a b i l i t y  earthquake determine  i s a design  A shaking assess  deposit  consideration  i f the thickened  native appropriate  to  of a sloped  The t h i c k -  discharge  that  d i s p o s a l problem. during  must  method  and a f t e r an  be assessed  i s a viable  alter-  f o r widespread use.  t a b l e model t e s t i n g program was developed t o help  the s e i s m i c  stability  of  sloped  tailings  deposits.  Due t o the wide degree of v a r i a b i l i t y of t a i l i n g s m a t e r i a l duced uniform  to  i n the mining deposition  industry,  and problems a s s o c i a t e d  of f i n e - g r a i n e d m a t e r i a l s  with  prothe  i n the l a b o r a t o r y ,  2  a  uniform  fine-grained  haviour. it  The  loading.  to the point the  sented havior  t o model t a i l i n g s  i s described  study  Not only  i n Chapter  tailings  cluded  where  materials.  i s the response o f a s o i l  deposit  i s the response o f the m a t e r i a l  and p o s t - l i q u e f a c t i o n m a t e r i a l 4.  Possible  fundamentals with deposit  The  3,  be-  up  o f l i q u e f a c t i o n o f i n t e r e s t , e v e n more p e r t i n e n t i s  i n Chapter  tailings  regard  are discussed  behaviour  ramifications to seismic  Fundamentals o f are  pre-  of material  be-  stability  of a  sloped  i n C h a p t e r 5.  d e v e l o p m e n t o f m o d e l t e s t e q u i p m e n t and p r o c e d u r e s i n a review pf previous  model s t u d i e s , d i s c u s s e d  i n Chapter  The t e s t i n g p r o g r a m , i n c l u d i n g e q u i p m e n t and p r o c e d u r e s , i s  discussed cussed  i n Chapter  analysis fluid  along The  cussed  results  are presented  with  The f l u i d  and  dis-  the p a r t i c l e analysis  modification  measured  enormous, i n Chapter  and 11.  particle  of a  i s described  several A  displacements  tailings case  disposal  i n l i m i t e d damage,  involved  a  i n Chapter i n Chapter  f o r comparison. facility  failure  h i s t o r i e s are b r i e f l y  particularly  of  movements w i t h i n  p a r t i c l e displacements are presented  consequences  resulting  l e d t o the empirical  describing  body.  9, and p r e d i c t e d  be  Test  r e s u l t s obtained  fluid  viscous  7.  i n C h a p t e r 8.  The  can  selected  p o s t - l i q u e f a c t i o n response o f the deposit.  liquefaction  10,  material  interest i n this  to c y c l i c  a  was  i s compared t o a v a r i e t y o f t y p i c a l Of  6.  test  sand  relevant  case  dis-  history,  t h e l i q u e f a c t i o n and  3  post-liquefaction in  Chapter  flow of  sloped  tailings  material,  11.  Conclusions  drawn  are presented  i n Chapter  12.  as  discussed  4  CHAPTER 2 METHODS OF DISPOSAL 2-1  Introduction T a i l i n g s are waste m a t e r i a l  mineral  e x t r a c t i o n processes of  chart  for a typical  shown  in  sidered gain.  r e s u l t i n g from the g r i n d i n g  Fig. to  be  The  tailings  1.  The  a  capital  mining  of  operation.  and  disposal  tailings  expenditure  can  resulting in  depend  flow  i s generally  for t a i l i n g s disposal.  properties  A  system i s  no  The  con-  economic  the mining company i s t h e r e f o r e  mize the c a p i t a l o u t l a y marginal  production  disposal  i n t e r e s t of  a mining  and  to  mini-  viability  upon economical  of  tailings  disposal. The  economic  resulted to  be  the  in  a  that  mountainous embankments methods. been  Several  of  Hoare operations  i n the  (Wahler and  terrain were  the in  increase  many open  with  required  and  the  inherent  use these  until  using  mining  (1974) estimated have  suffered  have p e r f o r m e d  valleys,  material  Compounded are  in  retaining  general in  disposal  did  not  the  disposal  failures  occurred.  discussed  i n Chapter  of  Canada's  instability  of  some kind,  analyses  with  traditionally  90%  stability  has  situated  tailings  in  catastrophic  that  waste  dams has  problems  briefly  ore  higher  present  industry  stability  are  1976).  tailings  grade  of  operations  the  of  low  amount  Schlick,  narrow  several  failures  mining  p i t mining  construction  empirical  methods  26%  of  The  recognize  of  large  disposed  fact  feasibility  (Mittal,  large  mining  while  1974).  11.  only As  a  Ore Body  Crushing  Grinding  Concentrating  Tailings (about 99%)  Mineral Concentrate (about X %)  Stored Tailings  Tailings Dam  FLOW CHART FOR TYPICAL DISPOSAL SYSTEM (After Jeyapalan,1980)  FIGURE  1  6  result much The  governmental  more  active  role  at  earthquake of being  Buffalo 1965  enforced  world.  and  Creek,  throughout  the  Aberfan  and  the  i n many and  as  Chilean now  parts  of  control of  as w e l l as f o r the alone  a  tailings.  r e g u l a t i o n s are  govern s t a b i l i t y  Abandonment  take  failures  during  strict  to  of  costs of  and  America  the mine's l i f e  facility.  begun  disposal  social  North  These r e s t r i c t i o n s  have  the  were enormous and  contaminants during ment o f  agencies  i n governing  monetary, e n v i r o n m e n t a l  experienced  the  regulatory  abandon-  p o s e s major  design  problems (D'Appolonia et a l . , 1972 ).  2-2  Present There  D i s p o s a l Methods are  several  tailings  disposal  methods  i n use.  The  most common procedure i n v o l v e s the c o n s t r u c t i o n of an embankment behind which the  the  embankment  tion.  waste m a t e r i a l  construc-  struction  the  methods.  upstream, In  2-2-1  This  upstream  method was  method  used p r i o r  failures.  I t was  considered  storage  facility.  For  incremental  for  tailings  raised  quickly  disposal a relatively using  a low  is  initiated  con-  by  the  dam.  i s depicted  to the  trophic  an  dam  centreline  Method  construction  widely  the  and  toe, or s t a r t e r ,  Upstream C o n s t r u c t i o n The  method  downstream  a l l three  c o n s t r u c t i o n of a p e r v i o u s  the  of  There are t y p i c a l l y three methods of embankment are  by  performance  construc-  They  affected  The  of  tion.  i s greatly  i s stored.  in  Fig.  aforementioned  to be  the  height small  2.  catas-  most economical  increase  required  dyke, which can  be  volume of c o n s t r u c t i o n m a t e r i a l , i s  Dyke r a i s e d by scooping Coarse T a i l i n g s from beach  UPSTREAM CONSTRUCTION  FIGURE  S  8  required.  The  tailings,  which  point  dyke  is generally  separate  of d i s c h a r g e .  constructed  hydraulically  The  progression  using  from the  the  coarse  f i n e s near  the  of the dam's c e n t r e l i n e i s  i n the upstream d i r e c t i o n . The found  stability  to  be  progresses fine and  of dams c o n s t r u c t e d  inadequate  upstream,  waste  i n many  subsequent  material.  e x h i b i t very  low  These  by  t h i s method has  instances. dykes must  f i n e s are  shear s t r e n g t h .  As be  often  For  the  to be  The tion  fine  owing  induced can  by  i s also highly  i t s loose,  underconsolidated  t h i s reason,  rates  buildup.  able of  supporting  slimes  resulting  the  a l . , 1978),  handling  t a i l i n g s dam 2-2-2  subjected  liquefied  i s employed  i s depicted  the outer  mass and  can be c o n s t r u c t e d basic  to r e l a t i v e l y  in sufficient  Upon l i q u e f a c t i o n ,  A safe upstream dam  material  are  state.  liquefac-  It  i f the  saturated  s u s c e p t i b l e to  earthquake, b l a s t i n g or c o n s t r u c t i o n v i b r a t i o n s .  pressure  et  for s t a t i c  be  strain  (Nyren  there i s  L i q u e f a c t i o n can  a l s o occur  shear  over  satisfied.  material  to  embankment  constructed  a l i m i t i n g height to which the s t r u c t u r e can be b u i l t stability  been  earth  dam  (Mittal,  cumulative shell  engineering 1974).  A  pore  i s incap-  f a i l u r e would i f proper  rapid  result.  monitoring and  proper  safe upstream  i n F i g . 3.  Downstream C o n s t r u c t i o n Method The  downstream method, F i g . 4,  a more s t a b l e s t r u c t u r e than the balanced  by  the  increased  i s considered  upstream method.  expenditure  required  to  to r e s u l t  in  T h i s gain i s ach'ieve  this  SAFE DAM USING UPSTREAM METHOD (After Casagrande and Maclver,1971)  FIGURE  3  Cyclone  Starter dam  DOWNSTREAM METHOD  F I G U R E <4  11  end.  The downstream  construction  method  requires  a much  This  material  i s generally  material.  cycloning  the t a i l i n g s ,  fractions  o f the m a t e r i a l ,  used  f o r construction.  controlled  t o ensure  construction the  separating  the coarse  The cyclone the p r o p e r  material.  combined  cycloning  with  does not y i e l d  by  and f i n e r  o r sands  being  operation  must be c a r e f u l l y  gradation  i s obtained f o r  The sand y i e l d  a larger  obtained  the c o a r s e r  fraction,  downstream method, as a low y i e l d  crest If  thus  l a r g e r volume of  volume  is a critical  factor i n  r e s u l t s i n a slow of m a t e r i a l  sufficient  rising  or be s t o r e d .  volumes o f sand, borrow  m a t e r i a l must be used. The the  fines  are u s u a l l y  spigotted  dam, while the sands are s p i g o t t e d  resulting The  i n the c e n t r e l i n e  possibility  through ated the  moving  face,  downstream.  o f l i q u e f a c t i o n o f the sands can be e l i m i n a t e d  compaction.  i n the design deposit's  face of  o f f the downstream  progressively  Drainage  facilities  susceptibility  must be determined Brenda mines  can a l s o be  incorpor-  to l i m i t the degree of s a t u r a t i o n , and hence, to liquefaction.  methods can be used t o guard a g a i n s t  at  o f f the upstream  or both  l i q u e f a c t i o n and the needs  f o r i n d i v i d u a l operations.  (Mittal,  Either  1974) i n d i c a t e s that  In s i t u  testing  compaction  i s not  necessary i f proper drainage i s ensured. Besides disadvantage changes place  the increased exists.  as the c r e s t  over many years,  cost  of t h i s  The downstream elevation  method, face  i s raised.  another  major  o f the s t r u c t u r e Construction  and no e r o s i o n p r o t e c t i o n  takes  can be a p p l i e d  12  until  the  stream  final  face  crest  i s therefore  p e r i o d s of time, and Another literature is  i s the  crest  2-2-3  of  the  method  c e n t r e l i n e method. downstream  structure  rises  similar  to  dams.  those  There  design  used  are,  c o n s t r u c t i o n method and preclude  the  e a r t h dam,  Earth  depicted  as  in  ture.  that  the 5,  technique.  Dam  for  a  tailings  water  dam  retention  d i f f e r e n c e s due  considered  a  are earth  to  stored  the that  conventional  i n F i g . 6.  Under s t a t i c l o a d i n g c o n d i t i o n s the slimes have a low strength  long  i t is raised.  nature of the m a t e r i a l being  s t r u c t u r e from b e i n g  for  described  vertically  inherent  down-  T h i s method, F i g .  conventional  however,  erosion  construction  procedures  for  The  develop.  commonly  modified  and  reached.  to surface  Comparison with Conventional Analytical  been  e r o s i o n channels can  the  a  has  subjected  construction  essentially  The  elevation  contributes  This material  to the s t a t i c s t a b i l i t y  of the  shear struc-  i s h i g h l y s u s c e p t i b l e to l i q u e f a c t i o n  and,  f o r design purposes, i t i s u s u a l l y considered  the e n t i r e d e p o s i t  is  and  in  a  liquefied  Under these siderably  state  (Klohn,  c o n d i t i o n s the  greater  than  that  of water and  design  load.  quickly  result  in a r a p i d  could could  be  considered  result  in  decreased s t r e n g t h s  The  undrained  increased  Finn  Byrne,  s p e c i f i c weight of the  hydrostatic and  1979,  fines shear  (Klohn  pore  there  are  fluid  i s an  likely  to  1976). i s con-  increased liquefy  stress a p p l i c a t i o n that and  Maartman, 1972).  pressures  w i t h i n the embankment.  and  This  corresponding  Cyclone  Underdrains CENTRELINE CONSTRUCTION  FIGURE  5  CONVENTIONAL EARTH DAM  FIGURE  e  15 The the  dam,  coarser the  tailings  material,  separate  through  a  surface  tailings  pore pressures provides  i n the  a detailed  exception  drains the  are  T h i s has the  of  i n a beach made up  of  The  underconsolidated  The  itself  of p o s s i b l y not  the  due  design  excess  Mittal  (1974)  criteria  for a  i s u s u a l l y homogeneous, with and  toe d r a i n s .  installed  and  therefore  as  flow  to the  blanket  i s not  lowering  analysis of  slimes.  a n a l y s i s and  surface  crest  i s much more complex  dam  from  the e f f e c t of  dam.  seepage  generally  phreatic  dam.  within  dam  t a i l i n g s structure. the  spigotted  hydraulically resulting  m a t e r i a l near the  phreatic  when  effective  as  Vertical  control  in a  over  conventional  structure.  Another major d i s t i n c t i o n t i o n of a t a i l i n g s dam time.  The  lies  i n the  well  construction  from  controlled  the  process,  tailings. rate  of  i s performed  Recently The  the  This  feed,  The c o n s t r u c t i o n mine's l i f e .  2-3  and  grade  and  change  discharge  Robinski,  1978).  o p e r a t i o n a l at 13 mines as o f 1978, at s e v e r a l o t h e r s .  suits  by  the  considerably  the  obtained milli  ng technique. ue. o v e r the  Discharge  been p r o p o s e d  and  This and  is  separation  method has  a l t e r n a t i v e to the c o n s t r u c t i o n of high,  considered  material  i s defined  of ore  can  of  A l s o , c o n s t r u c t i o n i s not  Proposed Method o f Disposal-Thickened  1975,  construc-  at a r a t e t h a t  construction  material  material  thickened  (Robinski,  that  takes p l a c e over a much longer p e r i o d  requirements o f the mining o p e r a t i o n . as  fact  as  an  c o s t l y , embankments  method was  becoming  implementation was  being  1  Essentially, ening, that  of  the t o t a l  will  result  approximtely is a  also  6%.  A  that  involves  tailings  in a  possible  site  shown  t h e method  to a pre-determined  conical  typical  i n F i g . 8.  using The  deposit  deposit  t o implement  has been  the dewatering,  with  conventional can  be  thick-  water outer  i s depicted  the thickened  system  an  or  content slope  i n Fig.  discharge  6  7.  method  disposal  techniques,  adapted  to  almost  of It at as any  terrain.  2-3-1  Advantages The  use  capital much  smaller of  waste  eliminates  The  A  situated reaches  runoff.  fine  This  pond  ever  Because  reach  tire  deposit,  wind  erosion  the surface  life.  to store of  a  large  A  given  tailings  i n the  design,  structures.  t h e need  for a  at the toe of the  found  low by  problems  The  and  wetted.  associated  runoff  systems.  over  This  small  pond i s  a l l  drainage  continuously  natural  a very  area.  design,  special  i s constantly  only  decant  tailings  t o receive  that  t h e pond  i s deposited  and e n v i r o n m e n t a l  considerable  the mine's  i s designed  constructing  the t a i l i n g  in  problems  eliminates  pond  i n the topographical i t without  and  o f such  I t has been  tailings  over  elimination  costs  small  results  i s required  The  inherent  relatively  and  facility  as proposed,  i s required.  of  initially  and m a i n t e n a n c e  tailings  amount  the  Discharge  discharge  material.  facility,  system. deposit  both  impoundment  construction  and  thickened  savings,  volume dams  of  of Thickened  the en-  eliminates  with  dusting.  Discharge Line  Conical deposit of total tailings  Tailings pond  Reclaim pond  THICKENED DISCHARGE METHOD (Robinski,1978)  FIGURE  7  18  Existing Pond -90 foot dam  Thickened Discharge System -additional 20 year capacity -6% tailings slopes -Fixed discharge points  Conventional Expansion —additional 20 year capacity -requires 225 foot dam  EXPANSION OF STORAGE FACILITY (Robinski,1978)  FIGURE  S  19  Although costs  thickened  f o r energy  conventional It  the  has  used  major  of  chemical material  f o r pumping  found t h a t  both the t a i l i n g s and  ties  i s more d i f f i c u l t i s reduced  from t h a t o f  the r e t u r n l i n e  advantage  the  deposit  of  this  that  a  system  i s the  Robinski  also  states  that  inherent  abandonment.  fertilizers  a uniformly  required  for  f o r r e c y c l e d water.  facilitate  n e u t r a l i z e r s and to provide  s m a l l e r p i p e l i n e s are  can be  treated  s u r f a c e slope a l s o p r o v i d e s good s u r f a c e the  proper-  Appropriate  added to the waste  surface  layer.  The  drainage.  stability,  both  under earthquake c o n d i t i o n s , i s s u p e r i o r to t h a t of systems.  to pump,  system because of the reduced volume to be pumped.  a l s o been  A  material  T h i s statement i s q u e s t i o n a b l e  and  static  and  conventional  i s d i s c u s s e d i n the  next s e c t i o n . 2-3-2  L i m i t a t i o n s of Thickened The  deposit  considered  to  however, of  the  be  under  earthquake  slope  is  cosity)." in  formed  by  the  statically  reasoning  by  thickened  safe.  behind  conditions.  "determined  Discharge  One  Robinski  i t s angle  which p r o v i d e s  to oppose movement during  must  be  method  of  (1978) s t a t e s internal  a large  i n a two  reserve  fold of  the (vis-  increase friction  earthquakes.  Although an i n c r e a s e i n the angle of i n t e r n a l f r i c t i o n result  safe  that  friction  angle  is  skeptical,  a s s e s s i n g the d e p o s i t s as  C o n s o l i d a t i o n w i l l then r e s u l t  viscosity,  discharge  from c o n s o l i d a t i o n , the i n c r e a s e may  will  not be s u f f i c i e n t  to  20  resist  flow  account  upon r e l i q u e f a c t ion. f a c t t h a t an  above reasoning  earthquake w i l l  likely  f l u i d mass of much g r e a t e r depth than present  during  The  f o r the  The  shear s t r e s s e s at the  depth, and angle of  i f the  tible  are  state  liquefaction,  (1978) s t a t e s that the and  reduces  the  liquefaction the  occur to  during  assume  depth. sal  would be  gradient the  likely,  were l a r g e  shear s t r e n g t h A  detailed  and  of the  be  mentioned  that  geometry  t h a t could r e s u l t  ensures  stability  the  static  resistance  considering  I t would be  liquefy  the h i l l ,  liquefied  the  5.  the  to  a  prudent  considerable  shear s t r e s s result  reveri f the  of  However  the  the  at  depth  from an earthquake.  for  this  The  failure  it  should  as determined  i s not of  flow  point,  deposit  material  considerable  than  material. conditions  geometry of  behavior for a  of  to  l i q u e f a c t i o n would  l a r g e deformations could  discussion  i n Chapter  stable  Robinski  1981),  that  suscep-  enough t o cause shear s t r e s s e s g r e a t e r  presented  depositional  Chern,  in a  3-2-4.  Although  event.  could  p r o f i l e of  is  the  seismic  deposit low  1979),  increased  highly  the d e p o s i t ' s  i t is likely  a significant  to the  in Section  liquefaction.  Finn,  fluid  material  to be  low p r o f i l e of the h i l l  and  the  considered  increase  in a  result.  cohesionless  as d i s c u s s e d  not  deposition.  i n c r e a s e with  flow w i l l  a fine, are  the m a t e r i a l  that  Due  and  likely  (Vaid  nature o f  angle,  dangers of  shear s t r e s s e s w i l l  fluid  result  shear s t r e s s e s exceed the  generally  saturated to  increased  internal f r i c t i o n  Tailings loose,  base of the  does  by  necessarily  liquefied  a  material  shear s t r e s s e s at  the  21  base o f the l i q u e f i e d  m a t e r i a l would  those  present  deposition.  shear  strength In  during  of the liquefied  summary,  existing  ject  to limitations.  very  expensive,  is  maximized.  questioned have  The  able  seismic  damage  does  Chapter stable  exist.  sloped  under  or less,  of the method  8,  discharge  be o f  discharge  of  program  loading  and t h e r e f o r e  may  question-  significant discussed  of  final with  be  i n  statically  conditions.  concern  deposits  been  thickened also  indicate that  has  failures,  the response  cyclic  deposit  flow  the possibi1ity testing  the  of construction i s  and r e s u l t i n g  may  than  d i s p o s a l a r e sub-  the upstream  The  than  result.  stability  damage.  model  i n Chaper  of thickened  of  t o assess  material  would  method  effective, and  The  designed  presented  one p e r c e n t  stability  cost  are greater  of tailings  failures,  stability,  7 was  results,  stability  very  flow  downstream  i n catastrophic  although  mass,  the resultant  a s embankment  resulted  method,  are  however  be much g r e a t e r  I f they  methods  The  likely  slope the  Test angles seismic  warranted.  22  CHAPTER 3 PRELIMINARY TESTING  Preliminary material,  and  provide  ings  material.  3-1  Test The  Ottawa  t e s t i n g was  performed  a basis  material silica  used  sand.  in this  This  a specific  Several  gravity, G  standard  tests  Lambe  performed  resultant  and  the  i n F i g . 9.  60/D10 =  Fig.  The  head  void  10.  For  test,  to  data  tail-  is a  fine-grained  subrounded,  quartz  2.67.  performed  according  A  sieve  grain  has  standard size  of  to  pro-  analysis  distribution  a coefficient  produce  ranging  range tests  in  by  were  ratios. dry  tests  were  was  curve  uniformity,  the  vs.  e  from  log(k)  The  The  method  for  the  was  .78  from  ratio  compared  to  were  void  compares  formula,  K =  of was the  100  at  is  Cu  a  =  va-  shown  used  .0105  each  permeability  maximum v o i d and  to  at  determination  plot  material  .75  performed  Hazen's e m p i r i c a l  run  performed  permeability  were  reliability.  predicted  standard  typical  a uniform  h y d r a u l i c a l l y deposited  a  ensure  void  to  ratios  Successive  mum  were  was  sand  =  s  permeability  the  cm/s.  Tests  of  (1951).  soil  ratios  void  corresponding  that  test  8  of  model  with  model  - -  1  Variable riety  study  type  c e d u r e s o u t l i n e d by  D  f o r comparison  the  Material  sand w i t h  shown  to define  in  in the  obtained, to  .0145  ratio well  to with  D-|g2.  minimum obtained  and  maxi-  using  relatively  the quick  23  GRAIN SIZE DISTRIBUTION  FIGURE  S  .002  C o e f f i c i e n t of Hydraulic  .005,  Conductivity  K(cm/s)  .01  .02  V o i d Ratio Q  Q  vs. L o g ( K )  FIGURE  10  .8  and  simple  (1970). A  methods  Agreeable  minimum  density,  void  Dr,  Dr =  is  ratio,  e i m  triaxial  tests  established  plot.  on  in detail in F i g .  initial strain This  found  m a x  The  =  .86.  relative  by:  by Chern  11.  The  chart  1 Hz.  for  In  (B = 1.00)  (1981).  equipment The  system  resistance  conditions  and  with  the  s t r a i n s were measured A  typical  r a t i o s used was  record  represen-  a l l t e s t s , care was and  is  taken  t e s t s were performed  very l a r g e s t r a i n s r e s u l t e d a f t e r  Liquefied  associated  i s reasonable  and  range of v o i d  Note t h a t  liquefaction. potential  the  liquefaction  recorder.  model t e s t c o n d i t i o n s .  at  A  using  R e l a t i v e d e n s i t i e s f o r each t e s t are shown  to ensure sample s a t u r a t i o n undrained  Yemington  yielding e  obtained.  were performed  a strip  shown i n F i g . 13. of  was  Load, p o r e p r e s s u r e  simultaneously  tative  .56,  (1970) and  for i s o t r o p i c consolidation  i s shown i n F i g . 12. on- the  =  n  f o r t h i s sand i s t h e r e f o r e  schematically  curve was  Burmister  r e s u l t s were o b t a i n e d ,  procedures d e s c r i b e d shown  by  (.86-e)/.3.  Cyclic and  proposed  low  samples  exhibited  a contractive  flow  relative densities  unlimited structure. used  (Dr  =  30%). A  s e r i e s of  vestigate Both  drained  ples. the  the  After  drained  tions,  standard  shear  triaxial  strength  c h a r a c t e r i s t i c s of  and  undrained  the  a p p l i c a t i o n of  test  tests  r e s u l t s , to  the r e s u l t s y i e l d 0'  t e s t s were performed to i n -  were performed Bishop's energy  correct  = 30.5°.  to  the on  material. loose  sam-  corrections  constant volume  to  condi-  V Function Generator  Electropneumatic Transducer  •Back Pressure j — ^Regulator j — p  •Double-acting Air Piston  Load Cell Eyed Connecting Ring  -® LVDT To  Recorders  Porewater Pressure Transducer To Recorder Cell Pressure Transducer  CYCLIC TRIAXIAL TEST APPARATUS (After Chern,1981 j  FIGURE  11  .4  .3  b"  .2  1  34.8% 31.5%  ^  28.5%  26.5%  6  •  0  1  2  5  10  20  50  100  Cycles to Liquefaction  LIQUEFACTION RESISTANCE CURVE  FIGURE  12  ^1  29  In  both  cyclic  were c o n s o l i d a t e d Ideally,  and  to an  static  ence has reliable  have  been performed  to those found i n the  shown t h a t  lower  r e s u l t s (Vaid,  c o n f i n i n g pressure  testings,  a l l samples  i s o t r o p i c e f f e c t i v e s t r e s s of .5 kg/cm2.  t e s t i n g should  corresponding  triaxial  used are  The  felt  lower  stresses,  model t e s t , however e x p e r i -  confining  1981).  at  pressures  may  r e s u l t s of the  to be reasonably  not  yield  t e s t s at  the  representative  of the m a t e r i a l response under model t e s t c o n d i t i o n s . The  coefficient  triaxial  test  initial  showed c o n s i d e r a b l e estimated  using  fairly and  Byrne  s c a t t e r , but  a  from  very  typical  ( 1980), using  data.  The  from  values  cyclic  obtained  were reasonably c l o s e to  Yoshimi  similar  values  (1975),  sand  value,  v  estimated  C  v  at  who  very  studied low  = 3 ft^/s,  from Lambe  and  t e s t sand p e r m e a b i l i t y ,  those the  confining  also  agreed  Whitman  (1969)  and  is felt  to  for test conditions.  Comparison of Test Sand with T y p i c a l T a i l i n g s M a t e r i a l The  material  used  g r a i n s i z e to simulate The  main c o n s t r a i n t on  was  that  i t be  sand was to  consolidation  average C  with  be a p p r o p r i a t e 3-2  of  The  well  c o n s o l i d a t i o n was  results  compressibility pressures.  of  do  over  a  satisfy material  in  the  testing  of  chosen by i t s  material  beyond  resembling  from a t e s t i n g p o i n t  of  h y d r a u l i c a l l y through water, and  a reasonable  number  t e s t i n g program was  t a i l i n g s m a t e r i a l as c l o s e l y as p o s s i b l e .  practical  deposited  so  i n the  tests.  length A  requirements.  i s generally  of  uniform It  a more w e l l  time,  and  f i n e sand  be  graded  view. was  material  The  chosen  reproducible  was  i s recognized  tailings  chosen  that with  to  tailings a  high  30  degree  of  material  ore in  size  i n the  The able,  silt  particles  l a b o r a t o r y was  c h a r a c t e r i s t i c s of  depending  being  on  mined.  the  tailings  to the  schemes,  the  deposition  materials  process,  there  the  The  separation  model d e p o s i t  regarding the  material  3-2-1  operation.  a  and  vari-  type  inherent  c h a r a c t e r i s t i c s can The  thickened uniform  deposition The  (Robinski,  properties  as  1978).  information  i s f o r the t o t a l t a i l i n g s produced Corresponding  be  discharge  deposit  following  of  of  the  by  test  included f o r comparison.  Grain Size Distributon Typical  and  during  a l s o uniform.  various t a i l i n g s  milling  sand are  was  rock  g r a v i t a t i o n a l separation  however, r e s u l t s i n a r e l a t i v e l y  is l i t t l e  such  are h i g h l y  host  h i g h l y v a r i a b l e w i t h i n a given d e p o s i t . method,  of  deemed i m p r a c t i c a l .  milling  Due  many d i s p o s a l  but  15.  grain  size  d i s t r i b u t i o n s are  Most mining o p e r a t i o n s  tailing.  For c o a l t a i l i n g s ,  to g r a v e l  s i z e s are  result  coarse  produced  by  shown  in a  sand  p a r t i c l e s i n the coarse  sand  crushing  i s often  faction  considered  i s dependent  on  that  the  bounds are shown i n F i g . 15(d) some sent.  tailings, I f one  could r e s u l t fines  are  many  grain  use  F i g . 15(d)  distribution.  size as  saturated  clay  process.  a strict  state highly  to l i q u e Typical  In the case of  particles  in the assessment o f the d e p o s i t .  in a loose,  while  susceptibility  size  clay  to  operation,  ( I s h i h a r a , 1980).  cohesionless  were to  the  silt  14  fine  s i z e t o f i n e sand r e s u l t from the f l o t a t i o n It  i n Figures  The  are  guide,  preerror  cohesionless  susceptible  to  100  Percent Finer By Weight  Percent Finer  100  By Weight  8 0  80-J 60  *  60 H 40  '  J 40  20  Mittal  .  1—•  5  1  Particle S i z e " ^ m m )  Test sand  T0 5  .02  1  01  1.0  -T—  a) Copper Tailings  Guerra  Vs  1  1-  Particle Size c)  100  Percent Finer By  " Jeyapalan  \  20  Girucky  100  "  Test sand  J  1.0  • — Murthy  02  (mm).05  .01  Iron Tailings  Percent Finer  Weight 80  -I  By  Weight  Jeyapalan  80  Sandic  6 0 -J 60  4 OH  20H  1.0  A  Sandic  40  Test sand  Nyren&Mittal  i  Tj  r  Particle Size (mm).05 •>) Oil Sand Tailings 1  20 H  —i— .02  .01  1.0  Test sand  —i • r Particle Size ( m ) - 0 5 d) Lead Tailings m  TAILINGS GRAIN SIZE DISTRIBUTIONS  FIGURE  14  .02  .01  100 100  Percent Finer By Weight  Percent Finer 8 0  By Weight  40  -I  20  4  •» Uranium Tailings  P a r  ^ l e Size (mm)  .0!  1.0  2  1  O Molybdenum'Tailings"  100  05  Particle Size (mm)  100  Percent Finer By Weight  5  Percent Finer By Weight  80  80  Boundaries for H  most liquefiable soil  60H  40  Boundaries for potentially liquefiable soil  Test Sand  20-1  10  -5  .2  > Coal Tailings  b  -»  Particle Size (mm)  r—  1  r  ' Particle Size (mm) d) Liquefaction Susceptible Soils (Ishihara) 2  TAILINGS GRAIN SIZE DISTRIBUTIONS  FIGURE  15  0 1  33  liquefaction. to  be l e s s  The  I f the  susceptible to  sand  used  f o r most  siderably  uniform  more  Note  Hazen's  they  fall  empirical  test  sand  tailings,  higher  than  This  than  most  has  a D50  that  considered.  typical  formula,  tend  i s  fairly  I t i s  con-  tailings.  .0001  t o be  Typical ft /s.  indicative  of  loading  would  value  has  a  laying  pore  1976).  to the l i n e  100  D]q2,  plotted  and  part  a  C  As  of C  v  relatively  i n which  by  soils. to  some  a p e r m e a b i l i t y much  t o be  would  for a  C  t h e most  test  condi-  under  are of  the t e s t  easily at  of  sand  implies  liquefied  i s  that  during  i t s boundaries,  p e r i o d o f time.  to  was  v  i n the order  This  important  leading  than  sand  i s allowed longer  higher C  material.  be more  com-  3-1,  value  v  low  in Section  for tailings high  response  a relatively  considerably  mentioned  drainage  liquefied  pressure  determined  i s comparable  with  value  v  draining  tailings  found  i n F i g . 16.  f o r granular  has  f t ^ / s f o r the test  rapidly  remain been  in  values  cohesionless  cyclic  3  The  2  =  p e r m e a b i l i t y , coupled  material.  tions.  close  i s shown  tailings.  most  estimated  tailings  b u t f o r t h e most  results  tailings  K  shown  most t o t a l  high  several  reasonably  pressibility,  al.,  study  of the t a i l i n g s  i s also  copper  and  they  liquefaction.  permeability of  that  most  plastic,  P e r m e a b i l i t y and C o m p r e s s i b i l i t y The  The  are moderately  i n t h e model  representative  3-2-2  fines  The  parameter  liquefaction  Cv  i n de-  (Seed  et  © Lead (Williams et al,1978)  't  1 0  '  1 6  10-5  1  1 0  1  -4  1  K (cm/s)  VARIATION OF PERMEABILITY WITH D  FIGURE  *\  16  1 0  0  .  3  1— 1  0  2  35  3-2-3  Relative A  Density  relative  density  of  approximately  30%  was  obtained  for  the model t e s t s .  A r e l a t i v e d e n s i t y of 25-45% i s r e p r e s e n t a t i v e  of  deposits  most  tailings  (Finn  r a t h e r than r e l a t i v e density., may  &  Byrne,  serve  the denseness or looseness  because  wide range  sand  in a  values  the  typical  for a  (Robinski, 1.sand  are  and  havior  of  a typical  thickened  a material,  liquefaction  the  in solids  thickened  therefore  over  to  1980).  Typical  test  discussed  be  reasonably  This  Void R a t i o , e Percent  by Weight  test  parameter  post-liquefaction  in Section  4.2.  The  representative  of  TABLE 1  Gs  method  sand i n Table  behaviour.  Specific Gravity,  coarse  discharge  deposit.  the  as  Parameter  deposit  f r a c t i o n , Cs, between the  discharge  control  from c l a y  (Ishihara,  compared to t h a t of the  considerable  should  by  ratio,  of a t a i l i n g s  sizes,  deposit  formed  Note the s i m i l a r i t y  exhibits  sand  tailings  deposit  1978)  in grain  Void  as a more u s e f u l parame-  t e r to d e s c r i b e of  1976).  T e s t Sand Deposit  Thickened Discharge Deposit  2.67  2.9  .77  .95  77  75  S o l i d s F r a c t i o n , Cs  . 56  .54  Water Content, w  .29  .32  betest  post-  36  3-2-4  Liquefaction The  Resistance  interest  i n the l i q u e f a c t i o n r e s i s t a n c e  materials  has been  embankment  construction.  of  the t a i l i n g s  gradation Of  l a r g e l y confined This  material  The  response of f i n e grained of the t o t a l  coarse grained  discard.  i s generally  an embankment Klohn,  this  fine  tailings  i s assumed t o be more  than  the response  the f i n e m a t e r i a l  state  o f the  s t o r e d be-  to l i q u e f a c t i o n (Byrne,  1980, Wahler  little  data e x i s t s .  and S c h l i c k ,  I t s loose,  1976,  saturated,  i s the b a s i s of t h i s  published  data  con-  i s a v a i l a b l e to  notion. and M o r r e l l  coal-mine  (1979) performed  discard.  These  the p l a s t i c i t y  in  plastic  total  Some of the t a i l i n g s  resistance  on  cyclic  tailings  c h a r a c t e r i s t i c s to most t y p i c a l  their  no p u b l i s h e d  and M o r r e l l , 1979).  very  mining o p e r a t i o n s . and  o f the coarse  susceptible  underconsolidated  however,  Taylor  size  sand o f s i m i l a r  p r i o r to s e p a r a t i o n  assumed that  i s very  1972, T a y l o r  clusion,  on  a natural  i s the c y c l i c  tailings  1979, I s h i h a r a ,  cohesionless,  confirm  the coarse f r a c t i o n  study  Unfortunately,  representative  Guerra,  used i n  p a r t i c u l a r i n t e r e s t i n the present  f i n e components.  1980,  t o the m a t e r i a l  (Byrne, 1980).  and  hind  tailings  i s generally  and behaves much l i k e  response o f t a i l i n g s  It  of  t o l i q u e f a c t i o n was  index  ( F i g . 17).  triaxial  tests  had s i m i l a r tailings  exhibited  grain-  from  other  plasticity,  found t o be dependent  The pore pressure  specimens was much more gradual  than  buildup  in non-plastic  EFFECT OF PLASTICITY ON LIQUEFACTION RESISTANCE (TaYlor&ft1orrel,1979)  FIGURE  17  38  samples.  T e s t s were c a r r i e d out  reasonably pared  in  undisturbed the  laboratory  liquefaction  liquefied  "C/0" ' =  .15,  were  found  to  be  samples.  in less  which  remolded specimens  Those n o n - p l a s t i c  than undisturbed  specimens o  ones.  both on  than  20  i s s i m i l a r to  specimens  pre-  more s u s c e p t i b l e  Most of the  cycles the  and  at  non-plastic  a stress  resistance  to  of  ratio,  the  test  sand. Taylor, on  the  Kennedy  and  susceptibility  liquefaction. typical  The  tailings  generally  MacMillan  of  coarse  material discussed  (1979) p e r f o r m e d  grained  of  considerably  coarser  in Section  3-2-1.  material  pore pressure  findings  appear  discard  The  found to be more r e s i s t a n t to l i q u e f a c t i o n , t h i s  equalization  agree  conclusive,  believed  to  have  with  the  study  t e s t e d was  a t t r i b u t e d , by the authors, to i t s high  these  colliery  a  throughout  the  the  concepts  disastrous  resulted  shear s t r e n g t h  from  of  sample.  than was being rapid  Although  liquefaction  tip failure  the  and  to  and  at A b e r f a n  l i q u e f a c t i o n of  is  similar  coarse d i s c a r d . Ishihara tests  on  ably  finer  tailings  resistance sand,  (1980) p e r f o r m e d  Fig.  than curves 18.  materials. typical were The  The  total  similar  e f f e c t of  r e s i s t a n c e i s shown i n F i g . 19. and  compares  plot,  one  obtained  can  fairly see  well  to  series slimes  of  cyclic  triaxial  t e s t e d were  consider-  tailings. to  that  void The  The  obtained  ratio  on  liquefaction for  the  test  the l i q u e f a c t i o n  t e s t sand i s shown p l o t t e d ,  a v a r i e t y of  that d e p o s i t s  i n the thickened  a  From  this  at v o i d r a t i o s s i m i l a r to  that  discharge  tailings.  method o f d i s p o s a l  (e =  .95)  Cyclic Stress Ratio  Cyclic Stress Ratio rD  cr m o o  c  AC  m Tl  o  H  O"  o cr  6  D O  m  D. Q.  O z  <  CO CO  o  3  o  ro  CD  CO  o  yc  m O  CL <  3  CO  ber  TA  CD  •U  •z. c  Tl  tn  —1  >  •z.  o  CO  Cyclic Stress Ratio causing 5% D.A. Strain in 20 Cycles  L> in.  I  N>  1  u  1  ; t.  o  Sri o CO H >  rn  CO O H —I  O X< H -< H < > o o LT)  CO  > o  <  o  X O • < £ p O — o o O 171  —I  33  D c  cr  o cr  O  o_ a.  O  CL  a. CL < •< TT re  re  40  would  be  at  least  as  susceptible  to  liquefaction  as  the  test  sand.  Neither increase Nor  of  above  i n resistance  d i d they  exists  the  account  I t  reduce  the  to  due  i s believed  degree  this  rapid  factor  resistance  f o r the  possible  to s t a t i c  shear.  of underconsolidation  to r e l a t i v e l y  that  liquefaction  accounted  l i q u e f a c t i o n due  f o r any  i n the deposit  tion.  studies  of  a  rates  could  of  that  deposi-  substantially  non-plastic  tailings  deposit.  It testing the of  i s felt  that  standpoint,  cyclic tailings  the  and  response, material.  at  test  sand  i s practical  the  same  time  as w e l l  as  from  reasonably  the p o s t - l i q u e f a c t i o n  a  model  represents behavior,  41  CHAPTER 4 MATERIAL BEHAVIOUR 4-1  Liquefaction Extensive  to understand  research  progressed  leading  to  varying  The is  arise  i f the  definition  i s the  state  into  This  reaching  dilative  reduced  pore  shear  forward of  s t a t e as  state-of-thethe  (Seed,  mechanisms  1979).  literature  How-  and  ambi-  adhered  to  by Youd  in  this  (1973).  thesis  "Liquefac-  a consequence o f to  initial  solid  increased  pore  liquefaction  as  (1967).  behaviour, and  and  reasonably  increased  This  exhibits  limited  potential  behaviour  under  monotonic  a  dense  further straining  deformation. flow  years  a g r a n u l a r m a t e r i a l from a  liquefaction,  pressures  and  15  used i n i n c o n s i s t e n t .  liquefaction  is equivalent  and S e e d  the  terminology  t h a t put  a liquefied  d e f i n e d by L e e  hibits  of  in  last  The  i n t h a t time,  exists  transformation  pressures."  Upon  i n the  are w e l l understood  terminology  consistent with  tion  to  considerably  liquefaction  g u i t i e s may  been p e r f o r m e d  t h e phenomenon o f l i q u e f a c t i o n .  a r t has  ever,  has  strain  loading  strength  hardening  upon  in  resistance of  liquefaction.  i s shown  ex-  results  and  type  sand  i n F i g . 20  material Typical (Castro,  1969. Typically, nature, fied  will  a  sufficiently  exhibit  and  material,  u n l i m i t e d flow deformation.  condition, dilative  insufficient  loose  tendencies  deformation  contractive I n the  lique-  to reduce pore pressures  continues  until  the  applied  by  are shear  Axial Strain (%)  RESPONSE OF MEDIUM DENSE SAND (After Castro)  FIGURE  SO  43  stresses  are reduced  to a l e v e l  strength  of the l i q u e f i e d  material  haviour  under  1969).  The response o f garnet  is The  shown  monotonic  i n F i g . 22  drained  study  conditions  (Chern,  c o i n c i d e with  was  each  a critical  T y p i c a l deformation  triaxial tions not  Note  with  there  large  regarded  angularity  dilative  work  jected.  (1969).  and  anisotropic  A  stress  found t o  ,  inde-  , f  consolidation  material flow  are shown i n F i g . 23  deformations  occurred  in  in cyclic  study, and any i n d i c a -  behaviour  at l a r g e  at low r e l a t i v e  (Castro,  occurred  s t r a i n s were  d e n s i t i e s i s con-  1969, De A l b a  et a l . , 1976).  are many v a r i a b l e s a f f e c t i n g the p o t e n t i a l deposit,  t o be the r e l a t i v e  t h e most i m p o r t a n t a r e density,  or void  o f the p a r t i c l e s , , the c o m p r e s s i b i l i t y and  characteristics, nature  t o un-  stress r a t i o , ^*1 /^3  i n the present  l i q u e f a c t i o n of a given  generally  material  the e f f e c t i v e  Large. (> 20%) deformations  other  1980).  and s t r e s s path c h a r a c t e r i s t i c s f o r  U n l i m i t e d ' flow  Although  the  ratio  that  t e s t s performed  evident.  loading  and Tobin,  by C a s t r o  investigates  consolidated  of s i g n i f i c a n t  sistent  for  stress  isotropically  samples.  (Highter  studied  effective  ratio.  loose  cyclic  1981).  (Castro,  under monotonic  c y c l e , and l i q u e f a c t i o n was  of  (Chern,  T y p i c a l be-  i n F i g . 21  cohesionless  also  1981)  pendent  loose,  the low shear  s i m i l a r t o t h a t of sand.  loading  within  with 1973).  i s shown  tailings  response of saturated cyclic  recent  loading  (Youd,  f o r comparison  response i s very The  compatible  the i n i t i a l  and d u r a t i o n  stress  state  o f the s t r e s s e s  ratio,  drainage  o f the m a t e r i a l t o which  and  i t i s sub-  RESPONSE OF LOOSE SAND (After Castro)  FIGURE  S1  RESPONSE OF G A R N E T TAILINGS  (AFTER HIGHTER A N D T O B I N , 1980)  FIGURE  22  RESPONSE OF LOOSE SAND TO C Y C L I C LOADING (AFTER C H E R N . 1 9 8 1 )  FIGURE  S3A  08  1.0  (q'+03')/2  ^Ts2a  treSS  P  3  t  h  °  f 0  7  . 1.4  1.2  (kg/cm ) 2  0  1  1  0  r  -°  a d i l i g  T  G  S  t  °" °tropically Consolidated Is  RESPONSE OF LOOSE SAND TO CYCLIC LOADING (After Chern,1981)  FIGURE S3 B  48  Of  particular  interest  s t a t e of the m a t e r i a l . tion  resistance  has  The  been  were  found  depending  on  both  the  relative  shear s t r e s s e s and the degree o f shear  more and  magnitude  of  Chern,  less the  1981).  resistant  static  Loose to  shear  stress  (1981) found that high s t a t i c shear s t r e s s l e v e l s  in  less  lies to  i n the  the  fact  critical  static  stress  study on present 24.  resistant  material,  that  the  effective  levels.  and  initial stress  sand.  ratio  used  R e s u l t s from t h e i r  liquefaction shown  test,  slope as  were  study  resistance  i n F i g . 25.  increasing model  resistance  i n the model  line  The  and  reason  lies  closer initial  a similar  g r a d a t i o n than  study  are shown i n F i g .  from  F i g . 24  f o r slopes  are t a b u l a t e d i n Table I I . adjusted  predicted  is consistent  the  the e f f e c t of s t a t i c shear on  obtained  curves  discussed  resulted  at h i g h e r  of d i f f e r e n t  Correction factors r e f l e c t i n g  liquefaction  of stress  ratio.  the  V a i d and F i n n (1979) performed  a uniform Ottawa sand test  p o s t u l a t e d that state  samples  liquefaction  Chern a  stress  liquefac-  t o be dependent on the  (Vaid & F i n n , 1979,  t o be  study i s the i n i t i a l  e f f e c t of s t a t i c shear on  found  d e n s i t y , l e v e l of i n i t i a l stress reversal  in t h i s  for  static  shear  increase in resistance  with  i n Chapter  results 8,  obtained  however  these  The are with  i n the results  must be considered q u a l i t a t i v e as the r e l a t i v e d e n s i t i e s used by Vaid  and  F i n n (50%) were c o n s i d e r a b l y higher than those used i n  the model t e s t . of  more  The r e s u l t s of V a i d and F i n n were used f o r lack  appropriate available  u s e d , i n an a n a l y s i s i n Appendix  data. 1.  The  corrected  curves  are  Dr=50% a '=2Kg/cm  Slope Angle  2  vo  F F (10 cycles) (30 c y c l e s )  N=10 2  Dr=50% a =2Kg/cm N=30 1  vo  1.1  1.1  4°  .14  1.4  1.4  60  .21  1.-7  2.0  .28  2.0  . 8°  1 1 s  .07  ^  2  t /a  2°  v o  CORRECTION FACTORS FOR INITIAL SLOPE  •  CYCLIC SHEAR STRESS REQUIRED TO DEVELOP 10% SHEAR STRAIN a) 10 Cycles  (Loose Ottawa Sand)  b) 30 Cycles  (Loose Ottawa Sand)  FIGURE  24  T A B L E 22  j  2. 3  .4  u n O  <N D  0  •H 4J  «f >-(  W V) w u  •H u u  Adjusted f o r simple shear conditions 0  5  10 Cycles  20  to liquefaction  i  LIQUEFACTION RESISTANCE C U R V E S CORRECTED FOR STATIC SHEAR  FBGURE  SS  51  Initial dual  pore  The  relative  shown  a  to  and  vary  in Fig.  present  exhibit  the  26  cyclic  linearly (Chern,  with  flow  other  enchanced state  r a t i o s of  unity.  over  ratio  than  that  material  used  Tailings  material  is  the  yield  shear  was  generally  more  well-graded  resistance  i s decreased,  effect  the  significantly. ducted factor. sidered  Because that  Yoshimi  material. while  Yoshimi  of  fines  In  the and  in  feels that  the  fine  it will  have  material a  the  f a c t i o n r e s i s t a n c e of a d e p o s i t  of  pressure  sand.  the  pre-  conflicting  that  is  also  suppress  drainage  i s cohesionless effect is  on  the indi-  discrepency  testing  where d r a i n a g e  the  the l i q u e f a c t i o n  It  triaxial  detrimental  in  fine  with  in will  investigations  i s to  suppression  post-  material  indicate  environment.  laboratory, the  studies  field  the  pore  to  affect  quantified  (1977) r e p o r t s  laboratory  the  The  a uniform,  t h e s e f i n e s on Field  depositional  undrained  residual  shown  i s shown  on  of  level,  strength  study  of  that  for  the  in this  resistance  opposite.  been  be  stress  unity  and  a f f e c t of  the  the  l e s s than  present  resi-  confining  can  data  that  results  of  Chern's  state  fines.  regarding  and  shear  not  of  i s independent  to  sence of c o h e s i o n l e s s  function  static  1981).  value  effective  stress ratio, with  viscosity  The  the  initial  c h a r a c t e r i s t i c s has  study,  liquefied  cate  terminal  that t h e o r e t i c a l l y predicted.  r e s i d u a l pore pressure  liquefaction the  than  in a  maximum r e s i d u a l p o r e p r e s s u r e  compare f a v o r a b l y of  results  less  density  theoretically as  shear  pressure  pressure. the  static  is a likely  drainage was is  connot  i t is the  allowed.  a  con-  lique-  52  o  .8 Predicted value .6  -P  ($=30°)  .4  <  0.1 _J 1.0  1.2  0.3  0.2 Ts/a3c'  l 1.6  1.4  TERMINAL RESIDUAL PORE WATER PRESSURE (After Chern,1881)  FIGURE  26  53  The  presence of p l a s t i c  sistance,  and  plasticity sistance  This  nature  index.  to  pressure  the  If  by  material.  Note  strengths,  while  cantly  stronger.  The  i s assumed  i s not  materials  fine discards" 4-2  to  posits, have  they  at  move  the  high  tested void  plastic  same.  re-  The  as  grain  pore  slimes.  a v a r i e t y of  ratios,  or  low  slimes  have s i m i l a r  slimes  are  behaviour  For  evidence suggesting faster  the  i s high  significantly.  plasticity  highly  be  the  signifiof  these  a liquefied  mass,  that the  flows  than  non-plastic the  plastic  ( T a y l o r and M o r r e l l , 1979).  the  loose,  are  liquefied,  to  dered  several  will  be  erally ings.  behave  of  as  fluid  as  to  behavior.  are  fluid. the  most t a i l i n g s  discussed  To  the  the It  Many  facilitate  tailings  of  deposits  were  is therefore  the  of  11. ob-  consi-  behavior  discussion, i t  a r h e o l o g i c a l model  behaviour  de-  i n Chapter  p o s t - 1 i q u e f a c t ion  framework  describing  of  liquefaction.  occurred,  a viscious  the  state  which  to discuss  made w i t h i n accepted  of  failures  appropriate  terms  saturated  susceptible  a l l c a s e s where  served  in  to  upon  Post L i q u e f a c t i o n Due  In  index  p o s t - 1 i q u e f a c t ion  tangible  should  i s dependent  (1980), who  low  the  liquefaction re-  f o r the h i g h l y p l a s t i c  that  d e n s i t i e s , sand and  materials  affect  plasticity  Ishihara  cyclic  "there  the  the  i s more gradual  is illustrated  relative  of  l i q u e f a c t i o n increases  increase  tailings  f i n e s a f f e c t s the  liquefied  gentail-  54  Liquefied There  are  a  Newtonian  law  model  studies. cribes  out et  model  The are  that  most  et  and  a l . , 1977).  The  slurry,  and  can  plastic  used  the Bingham of  model  homogenous  i s fairly  therefore  sand be  and  these,  the  previous  accurately  des-  tailings  flow  constant  (Enos,  through-  homogenous  i s considered described  to  model  i n many  i t c a n be c o n s i d e r e d test  Of  non-  used  and n a t u r a l m u d f l o w s  concentration  liquefied  fashion.  models  a l . , 1977).  has been  characteristics  of the f l u i d ,  common  Bingham  1980, Wasp e t a l . , 1977)  t h e body  non-Newtonian  available to describe  the  (Wasp  i s the simplest  I f the s o l i d s  genous  i n a  models  tailings  fluid  flow  (Jeyapalan,  of  behaviour.  I t i s believed the  1977).  behave  number  liquefied  power  Bingham  large  fluid  describe the  tailings  by  (Wasp  a s a homothe  Bingham  model.  The typical can  Bingham flow  and  whereby tiate of  i s shown  for  two p a r a m e t e r  and  a  model  y  ~C  the t h r e s h o l d  and \ p  which  71 >~C  for  represents  can  of, water  shear be  < "Cy  shear  i s the p l a s t i c  is fully  the threshold  effect  The  i n F i g . 27  as: 7  model  schematically  i n F i g . 28.  + 7p£  y  movement  The  i s shown  £ = 0  rigidity,  above  the  curve  be e x p r e s s e d  ^ = t  model  analagous  stress required  viscosity,  or  to  ini-  coefficient  t o the Newtonian  viscosity  stress.  extended  content,  as  to  three  shown  parameters  i n F i g . 29.  to This  include could  Bingham  fluid  Strain rate, £  BINGHAM RHEOLOGICAL MODEL  FIGURE  27  BINGHAM MODEL FLOW CURVE  FIGURE  28  A GENERAL PORE PRESSURE (WATER CONTENT) DEPENDENT BINGHAM PLASTIC MODEL  FIGURE 2 9  ( A f t e r J e y a p a l a n , 1980)  57  be used to account f o r c o n s o l i d a t i o n e f f e c t s . tative  A l s o , the q u a n t i -  impact of the maximum pore p r e s s u r e r a t i o being l e s s  unity  during  material,  cyclic  loading,  is difficult  for anisotropically  to a s c e r t a i n  and  than  consolidated  i s beyond the scope  the p r e s e n t work, other than to say that f o r pore p r e s s u r e s than  the  higher  initial  shear  confining  s t r e n g t h and  p r e s s u r e the m a t e r i a l  viscosity  than  less  would  i f the pore  of  have  pressure  e q u a l l e d the c o n f i n i n g p r e s s u r e . 4-2-1  Viscosity The  to  the  The  viscosity rate  of  viscosity  interaction govern  shear depends  and  behaviour, 30  shape, and used  the  of  concentration. disposal,  and w = .32  expect  an  (1978)  for a variety  Using  a water  of  principal  to  of m a t e r i a l s , water  mechanical  factors size,  that  distri-  The  solids  .66  fluid  interaction. indicating  content,  content, w =  stress.  d e s c r i b e the  of mechanical  the  or  at the  the  solids time  i n the d e p o s i t (from R o b i n s k i (1978),  i n c r e a s e i n the  to c o n s o l i d a t i o n .  extent  concentration.  the degree  upon  and The  stress  a g i v e n shear  are the p a r t i c l e  Robinski  viscosity  by  nature  the s o l i d s  by  determines  shows data  dependence  due  on  produced  between the p a r t i c l e s .  concentration,  could  strain  the v i s c o s i t y of a s l u r r y  bution  Fig.  i s d e f i n e d as the r a t i o of the shear  viscosity  of roughly  10  of one  times  T h i s n e g l e c t s excess pore p r e s s u r e due to  overburden. Chong (1971) performed that ticle  the r e l a t i v e size,  shape  a study on s i l i c o n  viscosity, 1 and  r  beads,  and showed  = 1 / 1 , i s independent  distribution.  0  The  results  are  of parshown i n  58  107  106  a o CL  cr  ©Curry CP i i d a  105  flow  (1938)-Tailings  A Sharp & N o b l e s (1953)-Debris  -P  @ C a s t i l l o & Williams  o o  G l y c e r i a n suspension  Ul  •H >  $  u  -H +J Ul (0  (1966)-Debris  104  Aber£on  Q Blight ^  (1979) of c o i l  (1967)-Tailings (1980)-Tailings  Jeyapalan  (1980)-Tailings!  103  102 100  10 Water c o n t e n t  (%)  VARIATION OF PLASTIC VISCOSITY WITH WATER CONTENT  FiGURE 30  flow  ( A f t e r Jeyapalan)  slurry  59  Fig. the  31.  viscosity  totic the  solids  for  sults  for  This  In  particle  Fig.  32,  comparison.  presented  solids  no  absolute v i s c o s i t y  i s determined by  interaction,  and  $4, , the  c o n c e n t r a t i o n , which i s dependent on  material.  provided  of  Note that the  in  Note  Figures  concentration,  control  is  results  31  via  dependent on  from R o b i n s k i  the  similarity  and  32,  the  on  asymp-  nature  of  (1978)  are  i n shape of  re-  indicating  viscosity,  the  the  ^o,  the  depositional  the  control  slope  angle.  charactertistics  discussed e a r l i e r . Although  cohesive  clay  particles  i n c r e a s e v i s c o s i t y , T a y l o r and the  effective  the  e f f e c t of p l a s t i c i t y may  results  stress  indicate  crease i n  Morrell  condition  that  are  that  not  be  generally  to  (1979) c a u t i o n that i t i s controls  the  significant.  non-plastic  thought  fines  may  viscosity  and  Chong's (1971) result  in a  de-  viscosity.  Extensive calculations  research  of  allowed the  for  liquefied  The  viscosity  and  that  the  corresponding  slides,  and  subsequent  d e t e r m i n a t i o n of a range of  tailings of  flow  (Jeyapalan, test to  1980),  sand, as a typical  as  back-  viscosities  shown i n F i g .  determined  from F i g .  thickened discharge  33. 30,  deposit A.  (w  =  which 33.  29%  and  respectively)  is  i s s l i g h t l y lower than the The  value used  chosen to vided  32%  be  1 x  reasonable  provided model t e s t  the  best  i n the  10 " 5  cps  predictions correlation  deformations.  the of  5x10  lower bound suggested  analysis for  approximately  described  liquefied fluid  between  cps, in  Fig.  i n Chapter 6  test  sand, and  behaviour. predicted  This and  was pro-  value  observed  DEPENDENCE OF LABORATORY SLOPE ON SOLIDS CONCENTRATION DEPENDENCE OF VISCOSITY ON SOLIDS CONCENTRATION  FIGURE 31  ( A f t e r Chong, 1971)  (After Robinski)  FIGURE  32  61  iQrm  Probable Range for Liquefied Tailings  —-I  Dow-corning g r e a s e  —  106 Pi -  AberCan t a i l i n g s  V i s c o s i t y used i n a n a l y s i s N a t u r a l mudflow T a i l i n g s sand ^ 1 Tailings deposit)  A  s  10  Wet  Viscosity (cps)  lcps=2x!0~ l b - s e c / f t lcps=.001 P a s c a l - s e c 5  cement mortar  2  Machine o i l  10'  Water @ 20°C  VISCOSITY SPECTRUM  FIGURE  (After Jeypalan)  33  p  e  r  F  i  g  <  3 0  62  4-2-2  Y i e l d Shear S t r e n g t h The  quired  yield  shear  to i n i t i a t e  approaches erably,  after  y  increased (Govier  deposition  the  particle Aziz, can  yield  solids  theoretical  1972).  A s a  be e x p e c t e d  f l o w £"y Bingham  1977).  al.,  Note  would continue  strength  as  can  result,  yield  without  to  Jeyapalan  F i g . 35, based on C a s t r o ' s  tests lative  sediments. at very  low  densities  cohesion  of  terest  .14  approximately bound suggested  seen  finite  in Fig.  of 34  consolidation after However,  a  s t r u c t u r e reforms  little  finite  yield  (Wasp  strength,  et  flow  the  range  Bell  parameshown i n  (1971) p e r f o r m e d  of s o f t triaxial  c o n f i n i n g p r e s s u r e s , over a wide range of r e -  t o .22  and  psi.  obtained  (Cs =  psf,  and  .55)  which  by Jeyapalan.  values  T h i s corresponds  by Jeyapalan  work 10  is a difficult  (1969) data and the behaviour  the r e s u l t s of F i g . 34  in this  a constant  be  (1980) estimates  Ponce and  (5-95%)  of data presented polating  consid-  indefinitely.  assess.  marine  a material  Upon c e s s a t i o n o f f l o w , a  The y i e l d s t r e s s d u r i n g l i q u e f a c t i o n ter  re-  exists.  i s constant.  that  As  decreases  t o i n c r e a s e ^"y.  fluid's  stress  c o n c e n t r a t i o n as a r e s u l t  interaction,  q u a n t i t a t i v e data of t h i s nature During  shear  l i q u e f a c t i o n "^y r e m a i n s  i n c r e a s e s with  and  i s the  movement of a Bingham f l u i d .  liquefaction,  and  value.  strength, Ty,  f o r the to the  apparent lower  i s shown i n F i g . 34.  to s o l i d s results  is slightly  end  Extra-  c o n c e n t r a t i o n s of i n -  in a y i e l d lower  than  s t r e n g t h of the  lower  The m a t e r i a l used t o produce F i g .  63  a) Rheogram for Water Suspension of Finely Divided Galena (D5Q=50 microns) (After Govier&Aziz,1972)  Volume Fraction of Solids,Cs  EFFECT OF SOLIDS CONCENTRATION ON  FIGURE  34  8000 psf Hard clay 4000 psf Very stiff clay 2000 psf Stiff clay 1000 psf Medium clay 500 psf Soft clay 250 psf Very soft clay 150 psf  Probable Range for Liquefied Tailings  20 psf  *~ j-  10 psf U  Range from Ponce&Bell,1971  Extrapolation of Figure 34  Y I E L D SHEAR STRENGTH SPECTRUM  FIGURE  35  65  34  was  similar  extrapolation provide  of  Bingham  liquefied,  discussion pared  to  statically chapter.  of the  grain  involved  reliable  The  i n  results  size only  the  two  at high  rheological  loose,  to  depositional  deposit,  as  tailings,  points,  however  and  may  not  concentrations.  reasonably  material. behaviour  post-liquefaction  stable  known  solids  model  saturated  typical  describes  the flow  I t i s useful of  behaviour  i s discussed  tailings, of  i n the as  com-  the  resulting  i n the  following  66  >  CHAPTER 5 DEPPSITIONAL BEHAVIOUR OF TAILINGS COMPARED TO THE In  order  d e p o s i t , one of  the  RESPONSE OF A LIQUEFIED DEPOSIT  to  assess  must f i r s t  fluid.  It  angle,  posit  i s determined  well  as  Robinski  by  stability  analyze  l e n g t h of by  the  of  discussed  adequately  only  It  i s a two  threshold These  yield  are  using  parameter shear  properties  depend shear  in Section  described  and  discussed  s t r e s s must  be  the  flow the  the d e p o s i t i o n a l p a t t e r n inherent As  and  the  driving has  flow  tailings  the  behaviour.  base of the  flow  The  the  discharge  de-  the  the  fluid  flow  flow and  of  being  than  and  y  tailings  can  described  by  on  which An  they  applied  to occur.  The  viscosity. they  velocity  and  flow down the  slope,  comes to r e s t . gravity.  i s a c r i t i c a l aspect  The  o f the  The fluid  deposi-  boundary l a y e r i s the r e g i o n next to fluid  a  v i scos i ty, *? p.  4-2-2.  f o r flow  i t eventually  i n which the  be  r h e o l o g i c a l model.  a plastic  4-2-1  are d e p o s i t e d ,  initial  whereas  properties, neglecting  characteristics  in Sections greater  fluid  i n the d i s p o s a l method.  s t r e s s , "C"y,  a boundary l a y e r , which  tional  sloped  that  deposition,  the Bingham f l u i d  i s unsteady, as  f o r c e s are  author  a thickened  during  flow i s then d e s c r i b e d by the p l a s t i c When the  liquefied,  present  fluid  4-2,  model,  the  a  r h e o l o g i c a l p r o p e r t i e s of the  pattern  (1978) d i s c u s s e s  by  slope, of  the  of  the d e p o s i t i o n a l c h a r a c t e r i s t i c s  i s believed  slope  as  and  the  has  had  i t s velocity  the  dimin-  i s h e d because of shearing r e s i s t a n c e created at the boundary  due  67  to a n o - s l i p c o n d i t i o n . order  of one foot  mined using As  The boundary l a y e r t h i c k n e s s  for a typical  liquefied  the m a t e r i a l  flows from the p o i n t o f discharge,  t i o n of mass, the f l u i d boundary  confinement.  l a y e r must t h e r e f o r e  l a y e r e f f e c t becomes  are c h a r a c t e r i z e d  For conserva-  become t h i n n e r , and  f o r laminar flow  1955, Roberson and Crowe, 1975).  flows  i t then  i n c r e a s i n g l y dominant, i n  accordance with boundary l a y e r theory ing,  as d e t e r -  formulae presented by S c h l i c t i n g , 1955.  spreads out due to l a c k o f l a t e r a l  the  tailings,  i s i n the  Most t a i l i n g s  by laminar flow  (Schlictand d e b r i s  (Enos, 1977, Jeyapalan,  1980 ). The  shear  stress within  the boundary  maximum at the base of the f l u i d maximum fluid, This ing",  shear  decreases  varies  from  from a  at the s u r f a c e .  to the t h i c k n e s s the p o i n t  i s one of the mechanisms l e a d i n g  The  o f the  of deposition.  to cessation, or "freez-  o f the flow. v i s c o s i t y manifests  boundary  layer.  decay  translates stress  to a reduction  i n the development  o f the  considerably.  of the v i s c o s i t y .  The amount o f Momentum decay  i n v e l o c i t y , w i t h which  stress  i n the downstream d i r e c t i o n due to the v i s c o u s  nature  result  also varies.  Both  Therefore  the shear  the shear  the m a t e r i a l .  spreading  t h e flow  i s a function  at t h e base  decreases  itself  The boundary l a y e r d i s s i p a t e s the f l u i d momen-  and hence r e t a r d s  momentum  of  i s proportional  and t h e r e f o r e  The  tum  stress  t o zero  layer  the e f f e c t of v i s c o s i t y and the f l u i d  i n decreased  shear  stresses  downstream.  When  68  the  shear  motion  s t r e s s at  ceases.  the  Also,  would  result  in  would  cease  sooner.  stress,  flow  If it  a  the of  initial  one  must  Robinski  pressures  of  not  flow  and  exhibit  material  slope,  as  result  come  depth,  the  now  to  the  final  is  the  flow  a  yield  deposited,  driving  The in  pipe  higher  rest  velocity  and  at  of  shear  exit  base  a  veshear  variety  slope  depth  states  to  per  have  will  over  upon  study  a  that  has  for  of  determining  the  year.  very  material  the  that  present  reserve  angle  of  the  excess  would  during  may  been p e r f o r m e d that  4  the  flow  occur  after  f e e t of  mate-  fluid  pore  ceases  pressures.  material  consoli-  content.  material  feels  2 to  the  in  that  When  high  solids  result  changes  typically  liquefaction  (1978)  that  dissipate, with  in a higher  viscosity  Robinski  mechanisms  account  re 1 i q u e f a c t ion  in  during  viscosity  increased.  w i l l  uniformly  assumed  resulting  result  and  stress,  slope.  strength  change.  given  while  established  quantitative  dissipation  did  volume,  a  fluid  flow,  the  i t is  Upon  ties  given  deposited  pore  yield  or  also  A  shear  indefinitely.  would  deposition.  creased  depth,  increased,  "freezing",  dating,  continue  fluid  be  Having  These  the  would  d e p e n d s on  motion,  If  threshold  stress  gravity  with  is  yield  to  extent  rial  higher  the  pressure  for  stresses.  the  pore  further  i f  slopes,  any  equals  flow  due  locity,  would  greater  would  forces  a  base  exhibit  deposition.  increase,  to determine the  enchanced  friction  an  however the  extent  fluid  available to  i n The no of  properoppose  69  movement  during  improved, have  stability  dered  the  more  ditions  the  will  the The  base  down  like  slope  depth  of  cannot  layer.  fluid  the base  detrimental  itself  of  has  the  effect  8,  be  acts  fluid  on  the  stress  less  fluid  than  of  The  results  that  and  under  viscous  wave,  resulting  the  and  fluid o f the layer i n the  function  of  downstream  conditions, study,  fluid  final  of  liquefied  boundary  any  overtopping  in a  of  i s a  o f the model  the  the  to result  that  these  con-  stresses  the flow  the  flow  I t i s suspected  overtopped  of  is likely  the distance  stress  dramatically  control over  Flow  fluid  at the time  fraction  of  of a  the  the shear  strength  outside  fluid.  than  shear  increased  a  considerable  are indicative  and hence  i s only  i t i s consi-  to a  the boundary  shear  layer  as a s t a n d i n g  likely  discussed  resulting  from  t h e downstream  slope  of  approxi-  shear  stresses  sloped  deposit  percent.  depositional be  liquefy  shear  have  yield  and  indicate  consistently one  to  event,  different  will  The  inviscid  in failure.  liquefaction  The  of  seismic  given  e x h i b i t s much  would  Chapter  mately  the  boundary  an  a  a r e much  liquefaction.  resulting  barrier  is likely  fluid  direction  embankment  in  significant  of the f l u i d ,  the  The  fluid  behaves  a  of freezing,  depth  and hence  entire  having  resist  exceed  material.  a  fluid  of  likely  depth,  to  the time  of  freezing. at  conditions  the  the r h e o l o g i c a l p r o p e r t i e s  able  at  of  deposit  Although  present  Although  of the deposit.  that  fluid  stress  drastically,  the event  depth.  earthquake.  the shear  changed  In  an  considered  flow  structure  to govern  and boundary  the flow  of  a  70  liquefied enhanced  to  any  fluid  significant properties  d e p o s i t i o n would be ses this  that  would  reason  discharge event.  exist  the  method  resulting  able to at  stability  depth.  the of  It from  r e s i s t the base of  doubtful  the  during  liquefied formed by a  that  consolidation  much l a r g e r  a deposit  i s questionable  is  after  shear  stres-  layer. the  significant  any  For  thickened seismic  71  CHAPTER 6 REVIEW OF PREVIOUS MODEL STUDIES Model  studies  have  been  performed  by  many authors  on  the  c y c l i c response of s o i l d e p o s i t s and e a r t h embankments (Yoshimi, 1977;  Prakash,  1977).  The  m a j o r i t y of  these were designed  to  study the s t r u c t u r a l response of embankments and r e t a i n i n g w a l l s for  purposes of design (Prakash, 1977).  ing  performed  high  has  Much of the model t e s t -  been done with e i t h e r dry sand,  accelerations  or with  imposed  boundary  render the r e s u l t s i n a p p l i c a b l e to t h i s Other a soil  studies  the  pore  deposit subjected to c y c l i c  Ishihara, 1966,  observed  1967,  Tanimoto,  De  These  extremely  conditions that  study. pressure  loading  A l b a e t a l . , 1976,  1967).  at  response  within  (Finn et a l . , 1970,  Kawakami,  s t u d i e s p r o v i d e both  1966,  Goto,  qualitative  and q u a n t i t a t i v e d e s c r i p t i o n s of the response l e a d i n g the  lique-  faction.  model  study  Similitude  are  similitude partial  outlined  requirements by  requirements  similitude  gests  that  model  which  i n turn  e n a b l i n g one  Ishihara. cannot,  should studies  can  be  f o r a shaking table  used  He  and  concluded  need  be  sufficient.  be  used  to  to p r e d i c t  to n e g l e c t s i m i l i t u d e  not,  be  Yoshimi  verify field  that  strict  satisfied (1977)  analytical behaviour,  as sug-  tools, thereby  requirements.  R e s u l t s of s t u d i e s using pore p r e s s u r e monitoring at v a r i ous  depths  over  the  al.,  1976,  indicate  depth  of  Yoshimi,  that  the  liquefaction  deposit  1967).  No  (Finn  et  occurs simultaneously a l . , 1970,  such monitoring was  De used  A l b a et i n the  72  present  study  cable.  This  The ters  and i t i s assumed that assumption  was  previous studies  i n the present  confirmed  a l . , showed t h a t  existed not  study.  greater There  over  than  also  response discussed  Accelerations,  at which  20 Hz,  this  a  greatly  program.  in previous  The  triaxial Fig.  the a c c e l e r a t i o n  d i s t r i b u t i o n was  o f the sample.  For  frequencies  more  pronounced.  at which  acceleration  implications  o f t h i s are  behaviour  natural  Threshold  The 1.  Most p r e v i o u s  pressure  response  found  simple  pressure  increase  designed  t o observe pore  been s t u d i e d ,  cyclic  were  than the  a c c e l e r a t i o n s were not being  shear  of  sought  l i q u e f i a b l e shaking  t o be very tests  s i m i l a r to that  (Finn,  of the e f f e c t i v e c o n f i n i n g p r e s s u r e ,  not  studies  i f s l i g h t l y higher,  The pore pressure t y p i c a l l y  Anisotropic  became  frequency  enchanced.  i n Appendix  has been and  36.  soil  studies.  pore  specimens  and  there  performed a t s i m i l a r a c c e l e r a t i o n s , present  frequency  f o r a- sample o f roughly the same depth  the depth  further  observation.  Finn  existed  was  by v i s u a l  to previous studies.  a frequency  uniform  r e s u l t s are a p p l i -  were a l s o used t o s e l e c t t e s t parame-  depths were s e l e c t e d with due regard et  these  triaxial  leading  pressure  exhibiting a static  simple  then e x h i b i t e d  within  a r a p i d pore  These s t u d i e s  a horizontal  response w i t h i n  bias.  shear  1967),  rose t o approximately 60%  sloping  tests  conducted  on  were  deposit.  deposits  but i s assumed t o be s i m i l a r to t h a t or  in cyclic  1970, Yoshimi,  to l i q u e f a c t i o n .  the response  table  has  found i n specimens  Zircon Sand p=150cm H 0 2  a=440 cm/sec2  -i 40  Transducer  Depth  PC1  40 cm  P62  140 cm  PC3  240 cm  1 r 60 80 Time ,t,(sec)  OBSERVED PORE PRESSURES FOR A SHAKING TABLE TEST  FIGURE  36  (After Yoshimi,1967)  74  No  tests  have  been  faction  behaviour  present  model study.  with  regard  s i d e r e d here. liquefied produced  studies solids  that  to describe would  be  the p o s t - l i q u e -  a p p l i c a b l e to the  Most of the work on s l u r r y  Jeyapalan  flow  has been  and are t h e r e f o r e  not con-  (1980) performed an inundation  study o f  pipe  flow  t a i l i n g s using o i l as the v i s c o u s m a t e r i a l . that  i n Chapter  to determine concentration,  equipment here.  i n a sense  to assessing  results  discussed  performed  support 5.  accelerations  study  Robinski  but provided features  "freezing"  no  information  that  behaviour  would  be  at v a r i o u s on the t e s t of  t o observe  of a l i q u e f i e d  i  flow  laboratory  of t a i l i n g s  has been performed  and subsequent  of  (1978) performed  the r e s i d u a l angle  or d e p o s i t i o n a l  No model  the concept  T h i s work  interest threshold deposit.  75  CHAPTER 7 TESTING PROGRAM The  testing  program  comprised  18 model t e s t s  signed  t o determine the response o f sloped,  urated  deposits  Horizontal zontal tion  to horizontal  a c c e l e r a t i o n s simulate  shear  as o b t a i n e d  disposal.  Fine  draulically uniform  d e p o s i t was  deposit.  a l l tests,  This  a sloped  discharge  and e q u a l 37.  tailings,  duced  by a c o n s t a n t  t o 30% +_ 5%.  Steady head  pore pressures  horiassump-  was  deposited  to obtain  hy-  a loose, the same  Model d i m e n s i o n s a r e  s t a t e seepage  upstream  tailings  method o f  The r e l a t i v e d e n s i t y was e s s e n t i a l l y  i n Figure  shown  propagating  t o simulate  the thickened  simulating  sat-  analyses.  a p l e x i g l a s s container  given  initial  using  sand,  into  used  de-  cyclic accelerations.  waves produced d u r i n g an earthquake.  sloped  deposit  cohesionless,  vertically  i s common i n earthquake r e l a t e d The  for  subjected  and was  c o n d i t i o n s were i n -  boundary  condition.  The  were governed by the boundary c o n d i t i o n s  i n F i g u r e 38, and a flow net showing e q u i p o t e n t i a l values  i s shown i n F i g . 39. Slopes tions  of 2°, 4° and 8° were subjected  ranging  from  .03  g t o .10 g.  t o base a c c e l e r a -  Initially,  varying  down-  stream boundary h e i g h t s were used t o produce the d e s i r e d slope, and  i n the l a t t e r  boundary  height  p o r t i o n of the program a constant  was  used,  while  varying  downstream  the upstream  boundary  height.  A number of t e s t s were performed using a sloped base t o  simulate  a sloping valley  floor.  A l l t e s t s were performed at a  BOUNDARY CONDITIONS FOR STEADY STATE SEEPAGE  FIGURE  38  Seepage Analysis Slope=6 °  22.5 cm 21.6  20.8  19.9  19.1  18.2  17.4  FLOW NET FOR 6°SLOPE '* "i  -  -  • .  FIGURE  |  39  16  78  frequency tive  o f 5 Hz, with  densities.  steady  s t a t e seepage and s i m i l a r  A d i s c u s s i o n of the s e l e c t i o n of t e s t  rela-  parame-  t e r s can be found i n Appendix 1. 7-1  Model Test Equipment An  the  MTS  base  Simulator  accelerations.  controlled of  Earthquake  system.  This  the d e s i r e d motion  console  The system type  was  used  to  provide  i s a closed-loop  servo-  o f system i n v o l v e s the g e n e r a t i o n  and m o n i t o r i n g  table.  Any d i f f e r e n c e between  relayed  as a corresponding  o f the r e s p o n s e o f t h e  the i n p u t  voltage  and t h e o u t p u t  to the servo  a d j u s t s the h y d r a u l i c flow a c c o r d i n g l y .  valve,  Monitoring  is  which  at the t a b l e  i s by way o f an LVDT l o c a t e d at the p i s t o n that moves the t a b l e . A schematic o f the loop The  command  by an Exact  i s shown i n F i g . 40.  s i g n a l was chosen to be a s i n e wave,  340 f u n c t i o n generator.  found t o have l e s s d i s t o r t i o n other  f u n c t i o n generators  acceleration The Pressure spike. test able, lics  tested.  This  equipment  feature  reduced a spike  (Ramsay,  feature 1981).  i n the  displacement.  of the h y d r a u l i c system.  d i d not e l i m i n a t e  undesirable  was  at the peak o f the s i n e wave than  i s an inherent  accumulators This  T h i s f u n c t i o n generator  response o f the t a b l e at i t s maximum  spike  provided  the occurrence  has been Although  obtained a spike  of the  in similar  was  unavoid-  i t could be reduced s u b s t a n t i a l l y by o p e r a t i n g the hydraua t low pressure  a f f e c t the frequency  (150-250  psi).  This  response o f the system.  adjustment  d i d not  Function Generator  Oil Supply  150-250 p:  Servo  V1-V2  Controller Servo Valve V,  Hydraulic Piston  Displacement Feedback  SCHEMATIC OF T A B L E LOOP  FIGURE 4Q  LV DT  80  Several was  found  that  imparting ducible  frequencies  were  a frequency  virtually  used  in preliminary  5 Hz  l e d to  of  undrained  conditions,  tests.  reasonable and  It  results,  provided  repro-  response over the range of a c c e l e r a t i o n s used.  Typical  t a b l e response i s shown i n F i g ; 41. The mately  table i t s e l f 1 000  provide  the  direction two  flat  to  i s made of  necessary  and  In  at  t h i s way  aluminum with  proper  distributed  a c c e l e r a t i o n s were  by  bracing  alignment loads The  by  and  maintained  the  bearings  t a b l e response  a K i s t l e r Model 305  recorded  is  on  to  horizontal  v - s l o t t e d needle bearings  temperature changes.  i t s surface  i t weighs a p p r o x i -  I t moves i n one  by two  unevenly  bending or  cast  rigidity.  i s supported  obtaining  monitored The  It  bearings.  without due  lbs.  i s 4 f e e t by 9 f e e t and  was  accelerometer.  a Visigraph  cathode  ray  recorder. The  model c o n t a i n e r  glass. to  provide  end at  The  and the  the  container  constructed  using  1/2  The  box  was  designed  condition  at  the  upstream  i s shown i n F i g . 42.  a constant  head  boundary  a v a r i a b l e downstream boundary height toe  dam  of  the  provides  upstream  constant  drainage  line  deposit.  a relatively head  boundary  deposit  a . b a f f l e and  by  erosion  It  i s assumed  rigid  boundary  inch  plexi-  to simulate in this  boundary i n the  c o n d i t i o n was  a  due  height.  The  water was  a pervious  that  field.  The  maintained  separated  plastic wall.  to s p l a s h i n g d u r i n g  shaking.  The  dam  study  f i x e d at the h e i g h t r e q u i r e d f o r a given slope  downstream  ated  was  from  by  a and  the  This eliminbase of  the  TYPICAL RESPONSE AT 5 Hz CO  FIGURE  41  Variable Height Of Bottom Weir Hopper 20.4 cm (top) 20.35 cm (bottom)  20.1 cm (top)  Outlet  20.35 cm (bottom) 81.0 cm  Scraper Guide  Pervious Plastic 20.3 cm (top)  Inlet  Outlet  20.4 cm (bottom) SIDE VIEW  a —rr~ Overflow Inlet Height to Bottom of lnlet=16 3 cm Height to Overflow=16.6 cm PLAN VIEW  MODEL CONTAINER  FIGURE  4S  tp  83  box  was  sanded  was  designed  to p r o v i d e  so  that  frictional  i t could  be  resistance.  tilted  to  The  container  simulate  a  sloped  base boundary c o n d i t i o n . A hopper was the  width  surface  of  and  the  box.  The  Smooth  hopper  upon opening had  outlet  to d e p o s i t  1/8"  space was  o u t l e t could  and  an even s l o p e .  The  ing  scraper  adjustable  The  to  different  Particle sand  were recorded  closed  determined  that  scour  was  at i t s base and edges dur-  braced The  for stiffness  sheets  side  i n l a y e r s on  layers,  subsequent affect  on  and  r u n n e r s were smooth  plexiglass wall.  were p l a c e d  noticeable  used  cut to j u s t over h a l f  was to  attached  effects  s i l i c a . b e a d s placed Particle  a grid  scraping,  layers  that  were  minimal  pattern. were had  movements  t o the p l e x i g l a s s .  t r a n s v e r s e l i n e s on the s u r f a c e of the d e p o s i t .  and  The  scraping.  the  on p l a s t i c  filling  approximated, a s c r a p e r was  movements were monitored with against  during  during  even flow over i t s width.  slopes.  reduce d i s t r u r b a n c e d u r i n g  was  a smooth p l e x i g l a s s  s c r a p e r was  to prevent  scraping.  be  over  1 cm t h i c k .  the width of the box  the  sand evenly  the volume of each pass r e s u l t e d i n a  When the d e s i r e d slope was  in  runners,  a reasonably  sand l a y e r approximately  to p r o v i d e  the t e s t  l u b r i c a n t s were used to minimize d i s t u r b a n c e  deposition. and  designed  by  The  The  been  observing g l a s s beads  placement  observed  It  to  previously  have  of no  placed.  84  7-2  Test  Procedures  The then  m o d e l c o n t a i n e r was  blocked  surface. grease  to  i n place to prevent  The  downstream  seal  i t s edges.  facilitate  placement  placements. prior  first  box  outlets  was  draining  placed dried  water  was  The With age  to  to  a  The closed, watch.  as p r e d i c t e d  hydraulics and Table  configuration  the  placed,  beds  and  to  the  was  table  silicone  the o u t s i d e to  to record  was  It  using  p l a c e d on  their  carefully  deposited  prior  was  No  dis-  calibrated  to  then opened inlet  piping  then  would  for  was  opened,  as  run  the  observed  and  through  maintained beads  were  The  oven  void  ratio  the scraper  dried  to drain  and  weighed.  o f f excess steady at  the  was  water.  stage  seep-  downstream  calculations.  s w i t c h e d on, be  Silica  approximated, which  was  pattern.  placement  s l o p e was sand,  grid  inlets  lifts  water  necessry.  in preliminary  were  test  as  with  1 cm  in  height of  pre-determined  accelerations, and  relative  de-aired water  The  o v e r f l o w and  established.  boundary,  then  excess  downstream o u t l e t  was  with  intermittently  the  upstream  was  equipment  water.  When t h e  remove  the  was  weighed  determination. used  of  according sand  grid  the s i l i c a  filled  Sand  6"  was  test.  test.  then  closed.  approximately by  of  A  t o each  movement  boundary  A l l electronic  to the  The  cleaned prior  for  particle  the  20  inlet  cycles  and  outlets  using  displacements, f i n a l  o v e r t o p p i n g volume were  recorded.  a  stop slope  85  CHAPTER 8 TEST RESULTS The of  testing  various  base  of  program was  test  model  accelerations.  final  t o t a l of  provides  18  liquefaction  The  also studied.  lish reproducibility A  d e t e r m i n a t i o n of a c r i t i c a l  induce  configuration.  effect  of  shaking  table  of  throughout  of  displacements.  individual  44  resulted  in  tests  was  figures  are  as  displacement  the  Note  parabolic The  than  1%.  tests  given  base on  test  test to  re-  estab-  the  were performed.  tests  i n terms  sample, base Table  slope  of  and  Figure  degree  of  acquisition  III  provides  a summary  49  depict  the  particle  displacements  for  which  a s i g n i f i c a n t portion  assumed to have l i q u e f i e d . i n i t i a l and  that  boundary e f f e c t s a  the  through  deposit  sample.  a sloping  a  of  test details.  Figures  the  of  throughout  results.  liquefaction  that  of  accelera-  S e v e r a l t e s t s were d u p l i c a t e d  a breakdown  particle  to  a range  Of  the  purpose was  to  response  s l o p e to which a l i q u e f i e d -deposit would come to r e s t .  s u l t s was  43  slopes  the  the  to  primary  study  determine  required  model  to  i n i t i a l surface  The  secondary i n t e r e s t was tion  designed  are  shape,  final  of in  final  the  as  lines  center  minimized, might  be  appears  to  be  of  over  the  the  length  the  these  as  well  of  the  sample, where the  end  i n i t i a l l y v e r t i c a l l i n e s assume expected  s l o p e s obtained are  There  Shown i n each of  surface configuration,  vertical  of  very  a trend,  from  a viscous  fluid.  shallow, a l l being as  shown i n F i g u r e  less 50,  •6-Obtained Particle Displacements  8-Horizontal Base-  1  9 Tests Exhibited Complete Liquefaction -(used in particle displacement prediction comparisons and final slope determinations)  2-Did Not Obtain Particle Displacements  1-Sloped Base-Obtained Particle Displacements  8-Horizontal Base  Tests Exhibited ?"•(used artial Liquefaction in shakedown and for  ustablishing threshold accelgrati ons)  .1-Sloped Base  BREAKDOWN OF TESTING P R O G R A M  FIGURE  43  TEST  INITIAL SLOPE  AMAX  RELATIVE DENSITY  CYCLES  FREQUENCY  LIQUEFACTION PARTIAL TOTAL  FINAL SLOPE  1  4.2°  • 05g  28%  28  5Hz  X  —  2  4°  .05g  29%  20  5Hz  X  —  FIXED  3  8°  .05g  31%  18  5Hz  X  —  UPSTREAM  4  8°  .05g  27%  21  5Hz  X  —  BOUNDARY  5  10°  .05g  35%  22  5Hz  X  —  HEIGHT  6  8°  .05g  25%  33  20Hz  X  7  4.8°  .05g  26%  20  5Hz  8  8°  .05g  38%  22  5Hz  X  —  9  8°  .025g  33%  20  5Hz  —  —  10  4°  .05g  29%  21  5Hz  11  8°  .05g  29%  20  5Hz  12  8°  . lOg  30%  20  5Hz  X  .7%  DOWNSTREAM  13  8°  .08g  37%  20  5Hz  X  .6%  BOUNDARY  14  8°  .06g  31%  21  5Hz  X  3.0%  15  4°  .04g  31%  21  5Hz  16  4°  •045g  37%  21  5Hz  X  ' .5%  17  2°  .04g  28  20  5Hz  X  .3%  18  2°  .03g  35  20  5Hz  = 16.2 cm X  X  Sloped Base Sloped Base  X  —  X  X  .5%  FIXED  HEIGHT = 14.0 cm  — co  SUMMARY OF TESTING PROGRAM TABLE III  RESULTS OF TEST 7  FIGURE  44  S C A L E : 1 inch  RESULTS OF TEST 12  FIGURE  45  CO  SO  S C A L E : 1inch= 10 cm  RESULTS OF TEST 13  FIGURE  46  o  Final Slope 1  1  Displacement of Vertical Line  / '  /  1 /  ,  icJ S C A L E : 1 inch=10cm  RESULTS OF TEST 14  FIGURE  47  /  S C A L E : 1 inch=10cm t  1  RESULTS OF TEST 16  FIGURE  48  \  S C A L E : 1 inch=10 cm  RESULTS OF TEST 17  FIGURE  49 SD  94  whereby  i n c r e a s i n g the  increased  final  i n i t i a l surface  slope of the  the r e s u l t of lower induced initial sed  static  in Section  result as  shear  discussed  ing  final  Another and  slope  a resulting the  strain.  cant  final  of  up  to  could  be  i n shear  could  movement ceased  to h i g h e r  initial  strain, for  I t should  be  would  the  increas-  surface  affect  of  of  the  that higher  account  prior  would be  strength  implies  axial  obtained.  due  be  samples, as d i s c u s -  result  increasing  slope  10%  T h i s could  an  t h r e s h o l d shear s t r e s s ,  the e f f e c t of d i l a t i o n  dilation  slope  tests,  net  Although c y c l i c t r i a x i a l  dilation  degree  higher  The  factor  increase  were imposed, and  and  for  surface  in  l o w e r maximum p o r e p r e s s u r e s  4-2.  angle  material.  i n the steeper  viscosity  contributing  Increasing  ing  The  in Section  results  maximum pore p r e s s u r e s  induced  4-1.  i n a higher  liquefied  slope  slopes. dilation,  material.  shear  strains  i n c r e a s e s with  increas-  t e s t s i n d i c a t e no  signifi-  i t is felt some of noted  that  the  that  to e l i m i n a t i n g the  a  small  increase  in  i n a l l model base a c c e l e r a -  tions. Several subjected  samples at a given  to  relationship  a range of base a c c e l e r a t i o n s to d e t e r m i n e between the  angle.  It  existed,  above which  final  slope  acceleration level  was  angle. on  base  determined the  51  slope  the  a  critical  liquefied  f o r 2°, 4°  Increasing  a c c e l e r a t i o n and  that  Figure  final  was'obtained  results.  i n i t i a l s u r f a c e slope angle were  deposit  shows  angle. and  8°  the  the  the  final  slope  acceleration  level  assumed  effect  of  a  constant  increasing  The  c r i t i c a l acceleration  and  Figure  52 d e p i c t s  i n i t i a l s u r f a c e slope angle  the  results in  1-0 i  All Tests at C =56.5%t1% s  amax£(amax)crit  EFFECT OF INITIAL SLOPE ON FINAL SLOPE  FIGURE  50  2H  0  2  4  Final Slope Angle (Degrees)  A C C E L E R A T I O N L E V E L VERSUS FINAL SLOPE A N G L E  FIGURE  51  6  97  8-i  6H  Threshold Acceleration (%g)  4-  2H  0  2  4  6  Initial Slope Angle (Degrees)  THRESHOLD A C C E L E R A T I O N VERSUS INITIAL SLOPE A N G L E  FIGURE  52  8  98  an  increased  with  the  tance  effect  as  effect  floor)  was  zontal  base  had  accelerations from  Test  sloping final  4  what  had  slope  might  reason,  angle  a  that be  chapter.  for a  test  the  fluid  observed.  on  base  are  a  the  slopes  sloped  resis-  and  effect  on  given  Test the  highly  model  was  (4°)  and  similar  I t was  (sloped  used  were  im-  tests, base  determined  base),  that  a and  slope.  visual  and  behaving  viscous to  53  obtained  Both  both  deposits  was  base  used.  surface  observations,  model  Figure  was  11  hori-  threshold acceleration  initial  a  valley  the  deformations  0.45g, r e s p e c t i v e l y ) . base)  of  conditions.  i n which  surface  This  consistent  sloping  applicability  h o r i z o n t a l base  from  is  liquefaction  (simulating a  the  10,  liquefied  expected  viscous  displacements ing  little  general,  indicated  and  (horizontal  base  In  (.05g  base  f o r comparison  i n i t i a l  This  4-1.  for sloped  for Test  a  level.  stress  determine  results  i n which  identical  shear  sloping  to  shown  16,  static  a  results  Also  test  of  test  acceleration  in Section  studied  the  posed. for  of  discussed  The  shows  critical  measured, similar  fluid.  predict  i s discussed  the  i n the  For  to this  particle follow-  99  LEGEND Horizontal Base — —  Sloped Base  EFFECT OF SLOPED BASE ON MODEL RESPONSE  FIGURE  53  100  CHAPTER 9 FLUID ANALYSIS An acts For  a n a l y s i s was  as  a viscous  liquefied  tion  i n the  stress shear  at  surface the  slope,  base  due  Upon  assumed t o as  the  at  which  28.  as  Over  plastic The then  s t r e s s equals  of  ceases  the  marked  the  exceeded  the  1969;  stress,  the  the  material such  deformation  of  is time  shear s t r e s s ,  depicted  i t i s assumed  assumed  Casagrande,  until  threshold  shear  threshold  been the  fluid  reduc-  static  (Castro,  motion, as  motion  governs  that the  in  Figure  a  unique  material. throughout.  appeared t o behave as a v i s c o u s  rather  material  to a standing  flowing wave.  the  Introduction  i t exhibited  but  of  viscosity  vertical  the  displacements were  horizontal displacedue  to  the  theory.  imposes a n o - s l i p base boundary  (1945) p r o v i d e s a  than  motion  analysis treated  Surface  experimentally  i n water wave  of  Lambe  motion  A preliminary  and  base were g r o s s l y o v e r - p r e d i c t e d ,  n e g l e c t of v i s c o s i t y  condition.  fluid,  downstream,  wave i n water.  to those obtained  the  shear  sand  observations.  a  T h i s has  test  m a t e r i a l appeared t o l i q u e f y simultaneously  ments near  of  slope  i n nature  this  fluid  problem as a standing close  the  a v i s c o u s Newtonian  period  viscosity  surface  similar  the  the  test  experienced  to cause flow.  d r i v i n g shear point  that  to  exceeding  liquefied  i t i s assumed t h a t  failures  behave  assuming  c o n s i s t e n t with  deposits  stress required  1971).  the  fluid,  test  mechanism i n flow  It  performed  line  a qualitative description due  to  a standing  wave  in a  101  viscous to  fluid.  Motions o f the boundary l a y e r are very  those obtained  solution  i n the model t e s t .  No r i g o r o u s ,  could be found f o r a standing  similar  closed  wave i n a h i g h l y  form  viscous  fluid. Liu  and Davis  (1977) study  a standing  account f o r the v i s c o s i t y o f the water.  wave  i n water and  T h e i r model e s s e n t i a l l y  involves  two boundary  l a y e r s capable of t r a n s f e r r i n g shear,  bounding  an i n v i s c i d  interior  boundary  l a y e r s are r e q u i r e d  fluid.  The l o w e r  to satisfy  and upper  the c o n s t r a i n t s of no-  s l i p a t the base and zero shear at the f r e e s u r f a c e . It layer  i s assumed t h a t  could  thickness close for in the  this  t h e o r e t i c a l model of the boundary  be r e p r e s e n t a t i v e  of the l i q u e f i e d  of the t e s t  deposit.  the boundary boundary  layer.  layer,  Vertical  i n the i n t e r i o r  fluid,  The " s t r e t c h e d " normal c o o r d i n a t e  fluid,  predictions accuracy  the t r a n s f o r m a t i o n  were  made using  show  viscous  that  cribe f i e l d  i s required to obtain fluid.  Having no  became u n n e c e s s a r y . A l l  "unstretched"  test  not t o propose  behavior.  t o be  coordinates  and the  neglecting  The primary o b j e c t i v e of t h i s a n a l y s i s was  the model  fluid,  system  are assumed  o f the p r e d i c t i o n s e m p i r i c a l l y s u b s t a n t i a t e  transformation.  calls  displacements a t the edge of  c o r r e c t displacements r e l a t i v e t o the i n t e r i o r  to  The theory  the use o f a transformed, o r " s t r e t c h e d " , c o o r d i n a t e  interior  The  o f the lower boundary l a y e r was determined t o be very  to the t h i c k n e s s  small.  the  t e s t model.  material that  could  this  be d e s c r i b e d  model be used  as a  t o des-  102  The slip  theory,  as proposed by L i u and  c o n d i t i o n of  the  base through  Davis,  the  enforces  the  no-  i n s e r t i o n of a boundary  l a y e r of t h i c k n e s s ; £= where  (2V/w)  V=  1/2  / j " = kinematic  viscosity  f  =  19 50  w  =  k Co = angular  k  =  2*r/wave length = wave number  Co  =  [g tan h ( k d ) / k ] / 2  g/cm  3  frequency  1  = wave speed Using and  the V=  l e n g t h of  ( *l = 2x10^  .1 m2/s  thickness  of  the model c o n t a i n e r  20  cm,  which  depth of the model d e p o s i t . Fig. for  the wave length  obtains  is slightly  a boundary  greater  layer  t h a n the  mean  i s shown i n  54 as a f u n c t i o n of v i s c o s i t y over the range o f  viscosities  liquefied  t a i l i n g s determined i n S e c t i o n 3-2-1.  solving  layer,  the  using  a  boundary unstretched  sionless velocities  «"  The  1/2  boundary t h i c k n e s s  In dary  c p s ) , one  as  problem of  coordinates,  the  one  bottom boun-  obtains  as:  u  =  ^-^-^U s i n hiB  -  "  l  ^-J—  value  l  sin(t-_f)  s i n ( t ) - e"  f  cos t i t - / - ) + 1/2  +  "  f  /  -met-/)-  c o s ( t ) - 1/2  sin(t)7  dimen-  Dow-corning grease Aberfan tailings-—i ANALYSIS -1 Natural mudflow ~~|  f  Probable range for  ^  liquefied tailings r  Kinematic Viscosity, ,(m2/t)  EFFECT OF VISCOSITY ON BOUNDARY LAYER THICKNESS  FIGURE 5 4  1 04  where  (A(t)  accounts  for  the  A,  with  amplitude,  B  =  k d 2  f = Integrating particle  /\  *  =  C  *  -  *y  -  c  velocities  A  e  s  f  i  n  h  [-  1  ^  + f-^"  *  b  (-  at  ,  *  b  +  [  — b  cos(bt)  "  b  C  O  S  b  2  where  a  =  -2k  b  =  kCr,  2  V*  b  t  )  one  obtains  as:  , a +  .  £Z  s  i  n  (  b  t  >  ) ]  sin(bt-/)  2  (  _  +  2  - —  • 1  2  2  (  sin(bt-/)  ,, ,  ) - 1  time,  ,>  cos(bt-j-) + 2  M b  sin(bt)  1  — 2  Q  2  + — b  b  to  1  (  —  wave  kC t  +  ^— s i n (bt-_f) + a  +  the  i/<- s »•<>>« ^ •*•><>*;;  -J c o s ( b t - / )  b  t =  dimensionally  .  at  —  respect  2  (^Tp)  cos(bt-/)  1  with  expressed  e  °*° f f f ^  time,  of  v*B  +  sin(kx)  oo  slow  decay  2  displacements,  n x  the  kz  viscous  b  cos(bt)  +  a . .. - sin(bt) b 2  ., )]  105  For test,  prediction  The f i r s t  c y c l i c loading. related  deposit. testing at the  displacements  i t i s necessary t o p r o v i d e c o r r e c t i o n s  displacements.  is  of p a r t i c l e  original  settlement surface.  f o r settlement due to  at the node  T h i s could be determined position  to the t h e o r e t i c a l  I t was assumed t h a t the settlement at any p o i n t  t o the settlement  any other  which  f a c t o r accounts  i n t h e model  simply by o b s e r v i n g the p o s t -  of the s u r f a c e p o i n t .  p o i n t was assumed depth  at that  was assumed  i n the centre o f the  The s u r f a c e settlement  t o be d i r e c t l y  point.  linear  proportional to  On a v e r t i c a l  from  l i n e , the  z e r o t o t h e base  to the  S u r f a c e s e t t l e m e n t s at the node were found t o be 1-2%,  agress  well with  t h e 1-3% e s t i m a t e d by Y o s h i m i  et a l .  (1975). Another c o r r e c t i o n was imposed t o account assumption  of a s i n u s o i d a l  surface.  determined  at the s u r f a c e  and decreased  Due  to the shallow  sinusoidal  surface  slopes was  f o r the necessary  the c o r r e c t i o n linearly  with  i n v o l v e d i n the study,  reasonable  f a c t o r was depth.  the assumed  and the c o r r e c t i o n  factors  r e l a t i v e l y small. The lines.  initial  control  the c o o r d i n a t e s used  particle  positions.  the maximum p a r t i c l e to  assume  positions  vertical  displacements.  iteratively.  i n c r e m e n t a l l y over  were  in vertical  i n the above a n a l y s i s are the mean  The i n i t i a l  a mean p a r t i c l e  displacements for  particle  correspond t o  I t was t h e r e f o r e necessary  position  and solve f o r the p a r t i c l e  Particle  one-quarter  lines  displacements  of a c y c l e  were  solved  of wave motion.  106  The the  Bingham  before that of  analysis  1/4  does not  fluid. of  The  a cycle  d r i v i n g shear  the  i n Chapter  at  the  intended but  is  observed was  10  the  v i s c o s i t y used  representative  for  material  been c o m p l e t e d . equalled  were  the  those  vertical  corresponding  in  analysis  to  be  at  was This  stress  in  the  pre-  to  the  time  the  i n the  point  upstream  model  selected  test.  as  analysis  being is  not  r e s u l t s i n terms of v i s c o s i t y , the  observed  c h a r a c t e r i s t i c response of  found  shear  used  of  slightly  threshold  displacement  investigate  motion  at t h i s  final  the  aspect  I t was  displacement  quantitative  to  frictional  ceased  liquefied tailings.  to provide designed  f o r the  p a r t i c l e displacements  corrected  equalled  The  had  The  dictions  antinode  actual  stresses  material.  which  account  the  i n agreement w i t h  phenomenon.  l i q u e f i e d model  the  selected  The  deposit  viscous  fluid  model. The predict  successful model  extrapolation deposits  would  test can  application behaviour  does  made 'to  field  be  likely  be  of  the  not  necessarily  behaviour.  o f much g r e a t e r  geometry t h a n p r e s e n t i n the  a n a l y t i c a l model  model t e s t .  imply  Liquefied  d e p t h and  to that  field  more c o m p l e x  1 07  CHAPTER PREDICTED  The  fluid  predict  Predictions was  made  value  only  8°  cosity. able  This  47.  movement ing  one  tive  to  pore  test  was  c a n be  effects  particle  a r e n o t made  sidered  i n the analysis.  i n Figure  a s was  for a  first  employed,  a  qualitatively  finite  displacements 55.  Actual  imply  that  of the  fluid  viscous  fluid  Treat-  appears  approximation.  Although  o f one t e s t  discussed  to  with  rela-  regard  to  concentration.  displacements  A  to  prob-  out i n  quantities.  viscosities  of vis-  of  pointed  I t i s t h e nature  not absolute  slopes  t h e range  a r e n o t meant  as  of the  of kinematic  near  t h e downstream  due t o d i s t o r t e d d e f o r m a t i o n s  o f the boundary.  Predicted  i s within  material  deposit  predictions are  surface  value  tailings,  and s o l i d s  topping  shown  .1 m^/s,  tests.  nature  base,  to  bases.  single  predictions  results  another  Predicted dary  a  used  the entire  for initial  i s the interest,  viscosity  pressure  =  c a n be  t o t h e complex  c a n be q u a n t i f i e d .  reasonable  only  V  using  9  i n t h e model  i n which  horizontal  for liquefied  the liquefied  give  with  Accurate  that  Due  displacements  value,  viscosity  obtained  involving a sloping  obtained  viscosities  Figure the  problem  were  i n Chapter  fortests  liquefy.  particle  and  presented  only  f o rdeposits  The 4°  to  DISPLACEMENTS  displacements  a r e made  observed  boundary  PARTICLE  analysis  particle  10  boundary  f o r an  height  i n i t i a l  displacements  created was  slope  obtained  boun-  by  over-  not con-  of  8° a r e  i n Test  #13,  1 0 8  LEGEND — -  Actual Displacements Predicted Displacements  COMPARISON OF PREDICTED AND OBSERVED SLOPE MOVEMENTS FOR 8° SLOPE  t  FIGURE  55  1 09  where  a  m  a  =  x  comparison. motion  ,08g  >(a  m a x  Excellent  appears  t o be  )  crit,  are  agreement  also  was  shown p l o t t e d f o r  obtained.  predicted well  using  The  the  particle  viscous  fluid  standing wave model. Predicted  displacements  shown  i n Figure  where  a  m  a  =  x  comparison.  56.  Actual  . 0 5g  >(a  r n a x  f o r an  initial  displacements  )  crit,  are  slope  obtained  of  4°  are  i n Test  #7,  a l s o shown p l o t t e d f o r  P r e d i c t i o n s compare very w e l l with  actual p a r t i c l e  motions. The  fact  that  the  the  particle  motions  the  liquefied  material  employed  a boundary  fluids.  Whether the  as  i s the  viscous lends as  fluid  discharge  summary,  stand  displaced  credibility  a viscous  flow  i s i n the  case of a l i q u e f i e d  to  fluid.  sloped  the  treatment  The  a n a l y s i s used  analyses of  predicted  of  the  discussed  t e s t r e s u l t s imply  lines  of  viscous wave,  d e p o s i t , or i n  as  displacements,  obtained  t h a t a flow f a i l u r e  i n the  boundary  i n Chapter using  wave model, a c c u r a t e l y d e s c r i b e the  vertical  of  a standing  model t e s t  effect  T h i s p o i n t was  the  realm  the  flow as occurs d u r i n g d e p o s i t i o n i n the  method,  must be c o n s i d e r e d . In  model a c c u r a t e l y p r e d i c t s  l a y e r , e s s e n t i a l i n the  the case of u n r e s t r a i n e d thickened  fluid  a  layer 5. viscous  shape of a c t u a l  model t e s t s .  i n the f i e l d could  from l i q u e f a c t i o n of a sloped n o n - p l a s t i c t a i l i n g s  The result  deposit.  Distance of Section from Upstream Boundary (in cm)  10 cm  0  5  20 cm  0  30 cm  0  5  5  0  Displacement (cm) Maximum Acceleration = .05g  LEGEND • —  Actual Displacements .  Predicted Displacements  COMPARISON OF PREDICTED AND OBSERVED SLOPE MOVEMENTS FOR 4° SLOPE  FIGURE  56  111  CHAPTER 11 FLOW FAILURES In  the event  Quantities extensive have  facility,  large  o f m a t e r i a l can flow downstream, r e s u l t i n g  i n an  inundation  considerable  inent  of these  Buffalo  Creek  and  zone.  Several  are the Aberfan failure  catastrophic  and S c h l i c k ,  1976),  1980), the and the E l  These f a i l u r e s a l l  and flow o f mine t a i l i n g s .  failures  failures  The most prom-  (Jeyapalan,  (Dobry and A l v a r e z , 1967).  of these  i t suffices  disaster  (Wahler  the l i q u e f a c t i o n  discussion  of a t a i l i n g s  a t t e n t i o n i n the l i t e r a t u r e .  Cobre dam f a i l u r e inolved  of f a i l u r e  i s not considered  A detailed  necessary  here,  t o r e p o r t t h a t hundreds o f l i v e s were l o s t and  hundreds o f m i l l i o n s of d o l l a r s damage r e s u l t e d . Jeyapalan predict these,  (1980) used  the flow  a viscous  model t o a c c u r a t e l y  c h a r a c t e r i s t i c s and extent o f flow" i n v o l v e d i n  and other,  f a i l u r e s . . The c o n s i d e r a t i o n o f a boundary  l a y e r was fundamental i n determining determined  fluid  that a given f l u i d  the extent o f flow.  I t was  could come t o r e s t on a v a r i e t y o f  s l o p e s , the flow d i s t a n c e being l o n g e r f o r steeper s l o p e s . Of  particular  occurring Castro  a t mild  interest slopes.  (1969) p r o v i d e  t o the p r e s e n t  consisted degrees,  Casagrande  limited  f a i l u r e d i s c u s s e d by W i l l i a m s history  in this  (1971),  Youd  failures (1973) and  failures.  A  (1978) i s the most a p p l i c a b l e case  study.  to slopes  are flow  d e s c r i p t i o n s o f such  of d e p o s i t i n g coarse similar  study  The t a i l i n g s tailings  used  d i s p o s a l scheme  at s l o p e s o f 3 t o 4  i n the p r e s e n t  study.  The  1 12  material test  has  sand,  coarser Figure  similar  a s shown  and l e s s 58.  Note  i n Figure  sults  f o r sloped  to  base  deposits  final  slope  deposit  excess  pore  pressures  measures  faction  The due  The t a i l i n g s  were  i n Chapter  exhibited  angle  t o an unknown  source,  failure,  and  The  material,  although  statically  model  test  therefore behaviour  produced deposit appear  for this  mass  upthrusting exhibited  to  be  during  very  stable  case  model  also  test rediffer-  instability  a  similar  stable  experienced  lique-  by s a n d  occurred at 3 to 4  behaviour,  representative  history.  due  statically  boils  and  downslope. degrees,  the toe of the slope.  reasonably  particular  deposit  c o n s t r u c t i o n , and  then  movement  at  i s slightly  noticeable  as evidenced  of  of the  threshold acceleration).  stable deposit  extent  and  sand 8,  no  to obtain  the  flowed  sand  had e x h i b i t e d p r e v i o u s  employed  apparently  or  generated  to that  c o n f i g u r a t i o n i s shown i n  to the test  (as discussed  tailings  deposit.  57.  The d e p o s i t  The  remedial  characteristics  the similarity 58  i n either  size  i n Figure  uniform.  shown  ence  grain  The  and  would  of  field  1 13  100  Percent Finer By Weight  0.05 Particle Diameter  Sand  TAILINGS FLOW F A I L U R E CASE HISTORY GRAIN SIZE DISTRIBUTION  FIGURE  57  Silt  FIGURE  58  11 5  CHAPTER 12 CONCLUSIONS A shaking gate  t a b l e model study  the s t a b i l i t y  during  and a f t e r  stability  o f sloped,  literature  cohesionless,  cyclic-loading.  o f sloped  ened d i s c h a r g e  has been performed t o i n v e s t i -  tailings  Of p a r t i c u l a r  deposits  d i s p o s a l method.  saturated  created  deposits  interest using  i s the  the t h i c k -  In a d d i t i o n t o model t e s t i n g , a  review o f c o n v e n t i o n a l  d i s p o s a l techniques,  typical  t a i l i n g s m a t e r i a l p r o p e r t i e s and the behaviour of v i s c o u s was performed.  Based on the r e s u l t s obtained  fluids  i n t h i s study, the  f o l l o w i n g c o n c l u s i o n s are made: 1.  Conventional  tailings  disposal  techniques  are s u b j e c t  to  l i m i t a t i o n s such that the development o f a l t e r n a t i v e methods of d i s p o s a l i s warranted.  The upstream c o n s t r u c t i o n method  does not, i n g e n e r a l , meet s t a b i l i t y requirements, downstream  construction  c o s t s f o r design, 2.  The thickened  method  results  discharge  t o that  of t y p i c a l  stability.  cohesionless  The p o s t - l i q u e f a c t i o n response reasonably  high  method o f d i s p o s a l has proven t o be  The model t e s t sand used has a l i q u e f a c t i o n r e s i s t a n c e similar  4.  i n extremely  c o n s t r u c t i o n and abandonment.  an economic a l t e r n a t i v e of q u e s t i o n a b l e 3.  while the  representative  of the model  of cohesionless  under model t e s t c o n d i t i o n s .  tailings  curve  material.  test  sand i s  tailings  material  1 16  5.  When to  subjected  cause complete  significant The  final  cent.  liquefaction  reduction slope  All  Density  6.  t o h o r i z o n t a l base  test  fraction  similar  thickened  discharge  deposit.  to that  liquefaction  a c c e l e r a t i o n was  angle,  one per-  formed  at a R e l a t i v e  which  t r a n s l a t e s to  obtained  in a typical  a c c e l e r a t i o n was observed f o r each i n i t i a l  above which complete cal  t o be approximately  30 p e r cent,  a solids  deposit a obtained.  were  slope  sufficient  was  deposits  o f approximately  A critical  of the model t e s t  i n the d e p o s i t  was observed  model  accelerations  found  was obtained.  to increase  and ranged from approximately  with  slope,  The c r i t i -  initial  slope  .035g, a t 2 degrees, t o  .060g, a t 8 degrees. 7.  The model  test  the  until  field  results  cannot  be r e l i a b l y  extrapolated t o  f u r t h e r s t u d i e s are made to q u a n t i t a t i v e l y  assess model geometry e f f e c t s . 8.  Model  test  a viscous fects. model  deformations fluid  model t h a t  test  results,  A sloped  deposit  necessarily  layer ef-  with  that  a review o f p e r t i n e n t  liquefied  tailings  can be  fluid.  liquefied  stable  f o r boundary  using  of the v i s c o u s model t o p r e d i c t  combined  i t i s suggested  viewed as a v i s c o u s  prior  accounts  Based on the success  literature,  9.  can be e m p i r i c a l l y p r e d i c t e d  just  to 1iauefaction.  to a considerable  because  depth  i t is statically  is  not  stable  Post-liquefaction stability i s  1 17  dependent  on  the  depth  of  liquefaction  p r o p e r t i e s o f the l i q u e f i e d m a t e r i a l .  as  well  as  the  1 18  REFERENCES  1.  Almes, R. 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S c h l i c h t i n g , H. , ( 1955), "Boundary H i l l Book Co. Inc., New York, N.Y.  49.  Seed, H. B. and I d r i s s , I. M., (1970), " S o i l M o d u l i i and Damping F a c t o r o r Dynamic Response A n a l y s e s " , U n i v e r s i t y o f C a l i f o r n i a , Report No. EERC 70-10.  50.  Seed, H. B., M a r t i n , P. P. and Lysmer, J . , (1976), "Porewater P r e s s u r e Changes D u r i n g S o i l L i q u e f a c t i o n " , ASCE G e o t e c h n i c a l Eng. D i v . , V o l . 102, GT4, pp. 323-346.  51.  Seed, H. B., (1979), " S o i l L i q u e f a c t i o n and C y c l i c M o b i l i t y E v a l u a t i o n f o r L e v e l Ground During Earthquakes", ASCE Geot e c h n i c a l Eng. D i v . , V o l . 105, GT2, pp. 201-255.  52.  S i d d h a r i t h a n , R., (1981), "R. , (1981), " S t a b i l i t y of Buried P i p e l i n e s Subjected t o Wave Loading", Masters T h e s i s , UBC, Vancourver.  53.  Sorenson, R. M., Wiley & Sons, New  Layer Theory",  Van-  McGraw-  (1978), " B a s i c C o a s t a l E n g i n e e r i n g " , John York, N.Y.  1 22  54.  Tanimoto, R., (1967), " L i q u e f a c t i o n o f Sand Layer Subjected t o Shock and V i b r a t o r y Loads", T h i r d A s i a n Regional Conference on S o i l Mechanics and Foundation E n g i n e e r i n g , V o l . 1, pp. 362-365.  55.  T a y l o r , R. K., Kennedy, G. W. and MacMillan, G. L., (1978), " S u s c e p t i b i l i t y of Coarse-grained Coal-mine D i s c a r d to L i q u e f a c t i o n " , 3rd I n t e r n a t i o n a l Congress of th I n t . Ass'n of E n g i n e e r i n g G e o l o g i s t s , Madrid, pp. 91-100.  56.  T a y l o r , R. K., MacMillan, G. I. and M o r r e l l , G. R., (1978), " L i q u e f a c t i o n Response o f • C o a l - m i n e T a i l i n g s to E a r t h quakes", 3rd I n t e r n a t i o n a l Congress o f the I n t . Ass'n of E n g i n e e r i n g G e o l o g i s t s , Madrid, pp. 79-90.  57.  T a y l o r , R. K. and M o r r e l l , G. R. , (1979), "Fine Grained C o l l i e r y D i s c a r d and I t s S u s c e p t i b i l i t y to L i q u e f a c t i o n and Flow Under C y c l i c S t r e s s " , E n g i n e e r i n g Geology, No. 14, pp. 219-229.  58."  V a i d , Y. P. and F i n n , W. D. L. , ( 1979), " S t a t i c Shear and L i q u e f a c t i o n P o t e n t i a l , ASCE G e o t e c h n i c a l Engineering D i v i s i o n , V o l . 105, GT10, pp. 1233-1246.  59.  V a i d , Y. P.,  60.  W a h l e r , W. A. and S c h i c k , D. P., (1976), "Mine R e f u s e Impoundments i n the United S t a t e s " , Proc. ICOCD, Mexico, V o l . 1, pp. 279-319.  61.  Wasp, E. J . , Kenny, J . P. and G h a n d i , R. L., ( 1 977 ), " S o l i d - L i q u i d Flow S l u r r y P i p e l i n e T r a n s p o r t a t i o n " , Trans Tech P u b l i c a t i o n s , C l a u s t h a l , Germany.  62.  Watermeyer, P., W i l l i a m s o n , R., ( 1 9 7 8 ) , "Ergo Dam-Cyclone S e p a r a t i o n A p p l i e d to a Fine G r i n d T a i l i n g s D i s p o s a l Today, V o l . 2, pp. 369-396.  63.  W i l l i a m s , M. P. A., (1978), " T a i l i n g s Dam H i s t o r y " , T a i l i n g s D i s p o s a l Today, V o l . 2,  64.  Yemington, E. G., (1970), "Suggested Method of T e s t f o r Minimum D e n s i t y of Nonchoesive S o i l s and Aggregates", ASTM STP 479, p. 125.  65.  Yen, B. C , (1967), " V i s c o s i t y o f S a t u r a t e d Sand Near L i q u e f a t i o n " , I n t e r n a t i o n a l Symposium on Wave Propogation and Dynamic P r o p e r t i e s of E a r t h M a t e r i a l s , New Mexico, pp. 877-888.  66.  Yoshimi, Y., (1967), "An Experimental Study of L i q u e f a c t i o n of S a t u r a t e d Sands", S o i l and Foundation, V o l . 7, No. 2, pp. 20-32.  (1981), Personal  Communication.  Tailings Product",  F a i l u r e Case pp. 428-433.  1 23  67.  Yoshimi, Y., Fumio, K. and K o h j i , T. , ( 1975), "One Dimens i o n a l Volume Change C h a r a c t e r i s t i c s of Sands at Very Low C o n f i n i n g P r e s s u r e s " , S o i l and Foundation, V o l . 15, No. 3, pp. 51-60.  68.  Yoshimi, Y., (1977), " L i q u e f a c t i o n and C y c l i c Deformation of S o i l s Under U n d r a i n e d C o n d i t i o n s " , P r o c . 9th I n t e r n a t i o n a l Conference on S o i l Mechanics and Foundation E n g i n e e r i n g , V o l . 2, Tokyo, pp. 613-623.  69.  Youd, T. L., (1973), " L i q u e f a c t i o n , Flow and A s s o c i t e d Ground F a i l u r e " , G e o l o g i c a l Survey C i r c u l a r 688, Washington, D. C.  1 24  APPENDIX 1 Parameter S e l e c t i o n The  t e s t parameters  dary  height,  parameters  considered  acceleration  use  was  and  made  of  model s t u d i e s ,  available  i n the present  study.  As  previously,  mentioned  strictly  be  met,  and  dynamic s i m i l a r i t y be  For  complete  ever, to  Ishihara  h  for  being  height.  acceleration model  similitude, must  have  geometric  test  therefore  behaviour of  the  A =  displacements  these  requirements, and  requires  guideline  1967). dimensions  Fig. Al(a).  accelerations  similitude.  are  It  m/ p  is  required therefore A  Where  being  length  for  a model to  for  t h i s study.  does  not  strictly  represent  the  complete  similitude  are  and field The  protype  p r i o r to l i q u e f a c t i o n as model for  sat-  similitude, satisfied  and How-  must be  n  s i m i l i t u d e , Jl  was  not  that both geometric  similarity,  n  tests  need  a useful  both d e p o s i t  =  previous  preliminary  (Ishihara,  1.0,  required  selecting  requirements  J? m/^fp  geometric  deposit  boun-  incomplete s i m i l i t u d e .  Incomplete  r a t i o of  downstream  In  used as  very l a r g e  scale r a t i o ; incomplete  be  satisfied  to s a t i s f y only  denotes the isfied  similitude  shows that  s a t i s f y complete  practical  similitude  Similitude  geometric  slope,  frequency.  however they can  displacements  the  analytical tools  in parameter s e l e c t i o n .  surface  are  surface  extremely  h igh. Dynamic s i m i l i t u d e must this  analysis.  satisfy elastic  and  inertial  forces  in  .01  El Centro  A =15 cm p  T » . 1—4.0 sec p  a -.2g p  1 1/1000  1/750 Am/A  b) Prototype parameter*  1/500  p  c) Model parameters.  SIMILITUDE DATA  FIGURE A1  126  A i  A  =  Ae  ^m/Yp  A  am/ap  £*m/£p  G  m/ p  S i m i l i t u d e requires that  Ai  =  =  *m/flp Satisfying G  =  m  =  T  A Tp  =  Ishihara Fig.  This A =  A /Ap  =  m  =  .1%,  A /A m  data 1/25  1/750..  parameters  and  the  predicted  incomplete  This  s i m i l i t u d e has For  surface  cyclic  triaxial used  a /ap  =  m  been 1,  one  d e f l e c t i o n corresponds  tests.  i n the  s t r a i n s of  piping  configuration at  the  of  The  above  "SEEPAGE", developed  at UBC  niques,  was  a  used  gradient  to of  obtain i  =  flow .11,  .1%  implied  the  model  using net, well  analysis  model t e s t appear by  rea-  incomplete  record.  test  downstream boundary was  program  hydraulic  i n a s i m i l i t u d e study,  i s reasonable f o r a t y p i c a l earthquake  geometric of  to use  which i s the approximate l e v e l of s t r a i n p r i o r to  the  bility  implies  i n t h i s study.  that  the  data  impies  implies  similitude  Yp  assuming;  period)  i n the  For  <fm/^p  m  p  liquefaction  sonable,  =  m  prototype  for  satisfied  m  p  Y  (T =  provides  obtains  therefore  e  y /d-  p  and  V A *  Al(b).  £"  m  Gp  «m/aP  m  G /G  X,  incomplete geometric s i m i l i t u d e , and  £~A/H,  to  VA  =  G  the  proba-  assessed.  finite  element  providing  below the  The tech-  a maximum  value  of  1.0  1 27  required  for piping.  No  piping occurred  during  any  of  the  tests. Early and  tests  were performed with  v a r i a b l e downstream  angle. tion did  I t was  and  found  occur..  (Siddharthan, pore  depths  t h a t there  slope, a c r i t i c a l  not  dissipation  This  increase  of  due  Mv  this  a n a l y s i s i s necessary test,  change  initial  i n slope was  portion  of  upstream ticle  the  In  order  curve,  to perform  to  g e n e r a t i o n curve  allows while  effective stress. the d r a i n e d  tailings  for  chang-  Note that  c o n d i t i o n of  deposit could  be  serious error. are  shown i n F i g . A2.  The  abrupt  a c o n s i s t e n t f e a t u r e i n t e s t s where only a mass l i q u e f i e d .  were  totally  recorded.  i t i s assumed liquefied,  and  Relatively  that  soil  l a r g e par-  small  particle  i n the n o n l i q u e f i e d m a t e r i a l . the  analysis,  for static  amax  incremental  and  pore p r e s s u r e s ,  =  -  u 5  the  shear,  numbers of c y c l e s to l i q u e f a c t i o n responding  slope  liquefaction  the  shearing  to analyze  results  occurred  adjusted  calculates  cyclic  excess  change had  displacements  displacements  to  without  soil  from the  desired  i n v e s t i g a t e d using "STAB.W"  whereas a t y p i c a l  test  the  depth  e x i s t e d , f o r a given a c c e l e r a -  f o r the reduced  t r e a t e d as undrained Typical  obtain  program  incremental  to account  upstream s o i l  depth at which complete  ing  the.model  to  T h i s phenomenon was  1981).  pressure  a constant  9-  used  under a T  n  shown i n F i g . A3(a)  data implied using a value of  was  liquefaction resistance  •& =  e  to determine /0"1  1  =  i s o t r o p i c pore was .7.  .18,  the cor-  pressure  used, and t r i a x i a l  test  A back a n a l y s i s of  test  TYPICAL PARTIAL LIQUEFACTION RESULTS,  FIGURE A 2 00  DC a> 3  0.  •2  .4  .6  .8  1.0 Depth (cm)  Cycle Ratio N/NL.  b) Analytical Pore Pressure Generation  a)Theoretical and Experimental Pore Pressure Generation Curves  PORE PRESSURE GENERATION.  FIGURE A3 M VO  1 30  results  provided  determined expected the  i n Section  using  pore  a compressibility slightly 5-2-2 ( C  v  = .4 f t ^ / s ) .  the i s o t r o p i c pore p r e s s u r e  pressure  generation  lower t h a n This  generation  i s more r a p i d  than  that  c o u l d be curve, as  i f anisotropy  were accounted f o r . It  should  be n o t e d  qualitatively maximum shown a  pore  pressure  of s o i l  dramatically.  This  curve  f o r varying  i m p l i e s that  corresponds  such  consolidated  pressure  critical  depths are  there  i s indeed  of the d e p o s i t to the abrupt  changes  change i n  This  of a c r i t i c a l merely  can be e x p l a i n e d  generation  samples,  generation  i t would  Typical,  by the  as c o m p r e s s i b i l i t y , used may not be  pressure  i n the model.  existence  curve  while  anisotropic  has the a f f e c t curve,  height  applies  to  iso-  conditions  of " s t r e t c h i n g " the  b u t would n o t e l i m i n a t e t h e at which  liquefaction  i n c r e a s e mv r e q u i r e d t o p r o v i d e  would  a given  height.  use o f c o n s i s t e n t input parameters  successfully  predicted  various  slopes,  curves.  The c r i t i c a l  with  obtained  testing.  i n model t e s t s .  The pore  tropically  occur,  during  the response  depth  parameters,  correct.  exist  This  made  o f the a n a l y s i s c o n f i r m  the r e s u l t s o f the model t e s t  analysis,  The  ratios  at which  the slope obtained Although  the r e s u l t s  the o b s e r v a t i o n s  i n F i g . A3(b).  depth  pore  that  analytical  which  ( & = .7, m  the a p p r o p r i a t e have d i f f e r e n t  v  = .4 p s f ^ )  critical  height f o r  -  liquefaction  potential  h e i g h t s determined e x p e r i m e n t a l l y ,  results,  were  used  to establish  coupled  a downstream  131  boundary  height  f o r which  the e n t i r e  soil  mass would  liquefy  under the e x c i t a t i o n s used i n the l a t t e r p o r t i o n o f the t e s t i n g program.  The s e l e c t e d h e i g h t proved t o be s a t i s f a c t o r y f o r t h i s  purpose. Another depth ing  a n a l y s i s was p e r f o r m e d  of the d e p o s i t .  the frequencies  analysis pirical  requires relation  where G  This  corresponding  elastic  of the f i r s t  the choice  analysis involved  o f the estimat-  5 modes o f v i b r a t i o n .  The  the s e l e c t i o n of a shear modulus and the emproposed  by Seed  = 1000(K2)max(  m a x  to assess  m') ^ 1  and I d r i s s P  2  s f  «  (1970) was used,  Appropriate  values,  t o t e s t c o n d i t i o n s and v a r i o u s depths were used t o 5  obtain by  G  m a x  .  The v a l u e  the equation  that  the t a b l e  of G  mentally The  d i d not impart  near  the n a t u r a l  i n the procedure was es-  frequency  (.03 g - .10 g) are f e l t  of f i e l d  obtained  experi-  accelerations  that  t o be  might  reasonably  be expected.  s i n u s o i d a l frequency o f 5 Hz was chosen f o r aforementioned considerations  earthquake motion.  and i s f e l t  De A l b a  t o be r e p r e s e n t a t i v e of  et a l . (1976) c o n s i d e r  of 4 Hz t o be a r e p r e s e n t a t i v e  is  I t was e s t a b l i s h e d  accelerations  Confidence  i s supported  by Finn et a l . (1969) t o w i t h i n 10%.  a c c e l e r a t i o n s used  practical  All  psf  (1977).  by p r e d i c t i n g the n a t u r a l  representative The  = 1 x 1 0  proposed by R i c h a r t  frequency o f the d e p o s i t . tablished  m a x  a frequency  frequency.  t e s t s were run f o r the a r b i t r a r y number o f 20 c y c l e s , which considered  seismic  t o be a r e a l i s t i c  event.  Seed  number of uniform  e t a l . (1976) s u g g e s t  that  cycles f o r a 20  uniform  1 32  c y c l e s are a p p r o p r i a t e f o r an earthquake of R i c h t e r magnitude of 7-1/2. In the given  determination site  distance should  the  from  site  of the a p p r o p r i a t e design earthquake f o r a geology, a r e a l a t t e n u a t i o n  causitive fault  be estimated  determined.  durations  the model t e s t  tative  of  sidered and  were  to  extent  The  discussed  particular  seismic  be  reasonably  representaive  to  depth of  produce  h e r e i n are not  event,  liquefaction  rather of of  possible the  resand  represen-  they  in order to observe the p o s t - l i q u e f a c t i o n behaviour rial .  rupture  accelerations, frequencies  any  chosen  and  f o r a r e a l i s t i c e v a l u a t i o n of the s o i l  ponse t o be of  and  characteristics,  are  con-  conditions  model  deposit  of the mate-  

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