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Stability of an embankment on soft clay Vasey, Joseph Steele 1969

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S T A B I L I T Y OF AN EMBANKMENT ON SOFT CLAY by JOSEPH S T E E L E B.S.,  Seattle  A THESIS SUBMITTED  VASEY  University,  IN PARTIAL  THE REQUIREMENTS  FULFILMENT OF  FOR THE DEGREE OF  MASTER OF A P P L I E D  i n the  1961  SCIENCE  Department of  Civil  We a c c e p t  this  Engineering  thesis  as c o n f o r m i n g t o  required standard  The U n i v e r s i t y  of B r i t i s h  April,  1969  Columbia  the  In  presenting  an  advanced  the  for  thesis  degree  Library  I further  this  shall  agree  scholarly  in partial  fulfilment  of the requirements f o r  a t the U n i v e r s i t y  of British  Columbia,  make that  permission  purposes  may  by  h i s representatives.  of  this  written  thes.is  i t freely  be g r a n t e d  gain  of  Civil  Engineering  The University of British V a n c o u v e r 8, Canada  April  25,  1969.  Columbia  copying  b y t h e Head  It i s understood  for financial  f o r reference  f o r extensive  permission.  Department  Date  available  shall  that  n o t be a l l o w e d  and  thesis  Department or  that  Study.  of this  o f my  copying  I agree  or  publication  without  my  Abstract The  soils  the design with  r e s p o n s i b l e f o r the adequacy of  of embankments r e g u l a r l y  finds  himself  t h e p r o b l e m o f c o n s t r u c t i n g an embankment  dation This  engineer  consisting  thesis  successful the pore  of s o f t , p o t e n t i a l l y  presents solution  t h e method u s e d to this  upon a f o u n -  unstable  to arrive  confronted  soils. at a  p r o b l e m and a d i s c u s s i o n o f  pressures developed  i n the f o u n d a t i o n  as t h e em-  bankment was c o n s t r u c t e d . The of  determination  of the shear  s t r e n g t h parameters  t h e f o u n d a t i o n m a t e r i a l s f o r use i n s t a b i l i t y  and  the type  of s t a b i l i t y  The  use of e f f e c t i v e  shear  analysis  used  analyses  are discussed.  s t r e n g t h parameters i n the  stability  analyses  developed  i n t h e f o u n d a t i o n as t h e embankment was c o n s t r u c t e d  be  r e q u i r e d that the excess  measured and 10 p i e z o m e t e r s  tion  t o p r o v i d e the necessary  pore  were i n s t a l l e d pore  pressure  i n the founda-  data.  A c o m p a r i s o n between t h e measured e x c e s s and  the excess  distribution embankment  pore  pressures  indicated  m e a s u r e d and t h e o r e t i c a l p o r e at  t h e t o e o f t h e embankment Stability  gave h i g h e r  analyses  pore  that a t h e o r e t i c a l  s h o u l d have d e v e l o p e d  load i s included.  pressures  stress  under t h e  D i f f e r e n c e s between t h e p r e s s u r e s a r e noted  particularly  slope.  u s i n g the t h e o r e t i c a l  safety factors  pressures  than  those  obtained  pore from  pressures analyses.  when c o m p a r e d w i t h u s i n g t h e m e a s u r e d p o r e The o n l y p r a c t i c a l method o f d e t e r m i n i n g pressures be by  pressures.  excess  c a u s e d by an a p p l i e d l o a d was c o n c l u d e d  instrumentation.  pore to  iii. Table  of  Contents. Page  Chapter 1  9  I  1  Introduction  1  2.  Georaorphology of  3.  Site Exploration  4  4.  Soil  5  5.  Embankment M a t e r i a l s  17  6.  Shear S t r e n g t h o f S u r f a c e M a t e r i a l s O v e r l y i n g the F i n e - g r a i n e d S o i l s  18  7..  Stability  18  8,  Safety Factor  9,  Design Stage S t a b i l i t y  10,  the F i s h e r  Tests  Analysis  Method  Criteria Analyses  T y p e of  and I n s t a l l a t i o n  for  Piezometers  the  24  12„  Stability  Vertical  Analyses Using Estimated were not  22  Method  S e l e c t i o n of H o r i z o n t a l and Piezometer Locations Pore P r e s s u r e s  3  21  11,  Chapter  River Valley  Performed  Excess  26 28  II  1..  Embankment C o n s t r u c t i o n  30  2.  Pore P r e s s u r e s  31  3.  S t a b i l i t y A n a l y s e s f o r t h e 20 F o o t F i l l Using the Measured Excess Pore -Pressures  33  4.  S t a b i l i t y Analyses for Using Projected Excess  34  5.  C o m p a r i s o n of M e a s u r e d and T h e o r e t i c a l Excess Pore P r e s s u r e s  M e a s u r e d by P i e z o m e t e r s  t h e 25 F o o t F i l l Pore P r e s s u r e s  36  iv. 6.  S a f e t y F a c t o r s f o r t h e 20 F o o t F i l l  38  7.  D i s c u s s i o n of S a f e t y F a c t o r s f o r 20 F o o t F i l l  39  8. 9. 10.  Chapter  D i s c u s s i o n on t h e L o c a t i o n s for the Piezometers  the  Selected 41  Excess Pore P r e s s u r e s Developed Assuming No P r e s s u r e D i s s i p a t i o n  42  C o m p a r i s o n of P r e s s u r e Heads A s s u m i n g No D i s s i p a t i o n and T h e o r e t i c a l P r e s s u r e Heads  44  III  1.  Summary and C o n c l u s i o n  47  2.  Recommendations  48  Chapter  1.  I  Introduction The  c o n s t r u c t i o n of L i b b y Dam  on t h e K o o t e n a y R i v e r i n  w e s t e r n M o n t a n a i s a p o r t i o n o f t h e U n i t e d S t a t e s commitment w i t h Canada under the C o l u m b i a R i v e r T r e a t y and The will  U n i t e d S t a t e s i n 1964.  r e s e r v o i r behind  be 90 m i l e s l o n g , t h e u p p e r 42 m i l e s b e i n g  province will  The  s i g n e d by  of B r i t i s h C o l u m b i a .  The  filling  f l o o d 43 m i l e s o f t h e e x i s t i n g G r e a t  t r a n s c o n t i n e n t a l m a i n l i n e and r e l o c a t i o n of a p p r o x i m a t e l y  Canada the  i n the  of t h i s r e s e r v o i r Northern  therefore, requires  60 m i l e s of r a i l w a y .  Railway the The  western  p o r t i o n o f t h e r e l o c a t e d r a i l w a y as shown on t h e map, will  dam  l i e i n t h e F i s h e r R i v e r v a l l e y and w i l l  be  on  figure  an  embankment s e c t i o n r a n g i n g t r o m 15 t o 65 f e e t i n h e i g h t . The by  F i s h e r R i v e r v a l l e y was  lakes.  The  grained s o i l  present  d e p o s i t s f o r m e d by t h e s e d i m e n t a t i o n  s t r e n g t h and  w i t h t h i s type  occupied  v a l l e y b o t t o m c o n s i s t s of s o f t ,  c l a y p a r t i c l e s i n these shear  i n g l a c i a l times  lakes.  of s i l t  and  Because of the r e l a t i v e l y  low  permeability characteristics  of d e p o s i t t h e d e s i g n and  associated  c o n s t r u c t i o n of  embankments o f t h e m a g n i t u d e p r o p o s e d c o n s t i t u t e d a design  fine-  difficult  problem.  This t h e s i s presents  t h e methods used t o s o l v e  this  d e s i g n p r o b l e m p e r m i t t i n g t h e s a t i s f a c t o r y c o n s t r u c t i o n of t h e embankments on t h e l a k e b e d a r r i v e at a s a t i s f a c t o r y  foundation.  s o l u t i o n were:  The  steps used  to  1,  a  s  t h e s e l e c t i o n o f a n embankment s e c t i o n w h i c h experience  s u g g e s t e d m i g h t be a d e q u a t e f o r  c o n s t r u c t i o n on a l a k e b e d b.  foundation.  f r o m t h e r e s u l t s o f l a b o r a t o r y t e s t s on samples of the f o u n d a t i o n m a t e r i a l s but  conservative  soil  soil  reasonable  s t r e n g t h parameters were  chosen. c.  u s i n g these analyses  s t r e n g t h parameters  stability  were p e r f o r m e d t o check t h e adequacy  of t h e s e l e c t e d embankment s e c t i o n . d.  b a s e d on t h e r e s u l t s o f t h e s e  analyses  restrictions  on t h e r a t e a t w h i c h t h e embankment c o u l d be c o n s t r u c t e d were i n c l u d e d i n t h e c o n t r a c t e.  t h e f o u n d a t i o n was i n s t r u m e n t e d to  measure t h e p o r e p r e s s u r e s  fill  was c o n s t r u c t e d  of these f.  pore  using these stability  did The  and t h e r a t e o f d i s s i p a t i o n  w e r e made a s t h e f i l l  was  t o i n s u r e t h a t a n embankment  during  failure  t h e c o n s t r u c t i o n o f t h e embankd e v e l o p e d were c o n s i d e r e d  of such a magnitude t h a t t h e s t a b i l i t y  the f i l l  further  not occur.  only occasion  jeopardy  d e v e l o p e d as t h e  measured pore p r e s s u r e s  ment when t h e p o r e p r e s s u r e s  in  piezometers  pressures.  analyses  constructed  with  documents.  occurred  t o be  o f t h e embankment was  on S e p t e m b e r 2 3 , 1966 when t h e t o p o f  r e a c h e d an e l e v a t i o n o f 20 f e e t .  The  stability  analyses  presented  pressures 20  developed  have  25 f o o t  2.  Geomorphology of  were  scoured  out  t i l l the that  in  the lake  water The  to  while  settled  in  feet  of  these  As  the  in  more  Kootenay  ice  plugged  and m o r a i n a l  deeper  and  was  hot  resistant  the  drained  uniform. slow  were  retreated  silts  down  spurs  These  were  of  the  the  the  of  The rapid when  The that  local  plug  river  rock  at  began rate  the  mouths  of  into  and  its  the  cut  this  lake.  Fisher  mouth.  to  down down  Once through cutting  followed  encountered  river in  a r e a s , have  has the  the  hundred  glacial  River  river  present  melt-  Several  the  of  causing  clays.  e r o s i o n were  present were  the  did  mouth  lake  and  lake. in  than  the  this  of  retreated  deposits  carried  Kootenay  morainal  cutting  materials.  valley.  up  near  deposited  and c l a y s . Periods  rock  clays  portions  sediments  erode  deposited  ice  River  which  a layer  rapidily  were  lake  scoured  last  gravels  to  in  the  silts  the  entrenched  As  gravels,  silts  the  masses  and p l a c e d  sands,  the  to  and F i s h e r  ice  carried  been  more  by  Into  lake.had  of  twice,  valley.  the  periods  Kootenay  Fisher  ice  bed  the  melted  ice  pore  Valley  the  the  began  Era  surfaces.  with  excess  therefore,  River  bedrock  The  the  sections.  Fisher  mass  of  limited,  least  to  valley  River  and  streams  River  at  Kootenay.  streams  sands  rock  River  form  the  valleys  the  Fisher  been  Pleistocene  the  the  discussion  embankment  occupied,  against Fisher  high  the  valleys  a  the  and  During  of  and  become ice  resulted  in  by  4. a r e l a t i v e l y slow r a t e of d o w n c u t t i n g l e a v i n g an undetermined t h i c k n e s s of l a k e b e d d e p o s i t s s t i l l s c o u r e d v a l l e y bottom.  r e m a i n i n g above t h e i c e  D r i l l h o l e s e s t a b l i s h e d t h a t the  f i n e - g r a i n e d d e p o s i t s have a t h i c k n e s s i n excess of 120 f e e t i n some reaches of the alignment chosen f o r t h e r a i l w a y . 3.  Site Exploration P r e l i m i n a r y e x p l o r a t i o n holes along  the proposed  r a i l w a y alignment showed t h a t the v a l l e y bottom c o n s i s t e d of a s u r f a c e l a y e r of one t o t h r e e f e e t of o r g a n i c u n d e r l a i n by 5 t o 10 f e e t of r e c e n t sandy g r a v e l s .  streambed d e p o s i t s of  The g l a c i a l l a k e s i l t  u n d e r l i e these surface d e p o s i t s .  silt  and c l a y  deposits  A l i m i t e d number of  l a b o r a t o r y t e s t s on s o i l samples from these p r e l i m i n a r y  drill  h o l e s i n d i c a t e d t h a t an embankment s t a b i l i t y problem might ' develope w h i l e c o n s t r u c t i n g the proposed f i l l s . extensive  A more  program of e x p l o r a t i o n , s a m p l i n g , and t e s t i n g  was deemed n e c e s s a r y t o a d e q u a t e l y e v a l u a t e  the fine-grained  soils. An O s t e r b e r g Sampler was a c q u i r e d  t o obtain the best  s o i l samples p o s s i b l e from these a d d i t i o n a l d r i l l T h i s sampler i s l o w e r e d t o and f i r m l y h e l d a g a i n s t at the bottom of t h e d r i l l h o l e .  holes. the s o i l  A- 3 i n c h diameter 3 f o o t  l o n g s t e e l sample tube i s then h y d r a u l i c a l l y f o r c e d down i n t o the s o i l . maintaining  The s o i l sample i s h e l d i n t h e tube by  a p a r t i a l vacuum on the upper end of the tube:.-  5.  as the sample i s withdrawn from the  soil.  In removing the s o i l samples from the tubes p r e p a r i n g specimens f o r t e s t i n g a l a y e r e d or s t r u c t u r e was  noted.  l a m i n a t i o n s was  and  laminated  In some i n s t a n c e s the break between  fairly  easy to see, i n others i t was  not.  T h i n l e n s e s of f i n e sand were a l s o noted i n some of the samples. was  The  h o r i z o n t a l c o n t i n u i t y of these sand lenses  not e s t a b l i s h e d i n the e x p l o r a t i o n program and, t h e r e f o r e ,  the q u e s t i o n of whether or not these sand lenses would p r o v i d e drainage paths f o r the d i s s i p a t i o n of the pore pressures caused by the embankment l o a d c o u l d not be answered. 4.  S o i l Tests a.  General The  soil  t e s t i n g program c o n s i s t e d of g r a d a t i o n ,  A t t e r b e r g L i m i t , dry d e n s i t y , n a t u r a l water content,  shear  and c o n s o l i d a t i o n t e s t s .  hole  The  l o g of a t y p i c a l d r i l l  w i t h the r e s u l t s of the A t t e r b e r g L i m i t , n a t u r a l water content  and dry d e n s i t y t e s t s are shown i n f i g u r e 2.  The  A t t e r b e r g L i m i t t e s t r e s u l t s i f p l o t t e d on a P l a s t i c i t y Chart would f a l l  along or j u s t above the A - l i n e .  The  would be c l a s s i f i e d as non to medium p l a s t i c s i l t s and The undrained,  Q,  clays.  shear t e s t s program c o n s i s t e d of u n c o n s o l i d a t e d and c o n s o l i d a t e d - u n d r a i n e d , R, t r i a x i a l  The Q t e s t specimens were t e s t e d at the water content cut  soils  from the samples.  The  tests. as  R t e s t specimens were s a t u r a t e d  by a p p l y i n g a back p r e s s u r e .  Along with the Q and R t e s t  6, v a l u e s a n o t h e r s e t o f s h e a r s t r e n g t h p a r a m e t e r s , R', was o b t a i n e d by u s i n g during  t h e pore p r e s s u r e s d e v e l o p e d and measured  the R t e s t s .  A l l t h e s h e a r t e s t s w e r e r u n on 1„4 i n c h  diameter by 3 i n c h long c o n t r o l l e d equipment.  samples  and were p e r f o r m e d  The t i m e t o f a i l u r e f o r t h e Q t e s t s  r a n g e d f r o m 7 t o 17 m i n u t e s w i t h while  an average  A soil  an a v e r a g e v a l u e o f 8 8  specimen  p l o t of d e v i a t o r  s t r e s s r e a c h e s a maximum v a l u e .  If  s t r e s s v e r s u s a x i a l s t r a i n has a d e f i n i t e  peak t h e v a l u e of t h e peak d e v i a t o r shear strength  minutes.  t e s t e d i n s h e a r may be s a i d t o have  f a i l e d when t h e d e v i a t o r  the  o f 14.5 m i n u t e s  t h e t i m e t o f a i l u r e f o r t h e R t e s t s v a r i e d f r o m 56  t o 133 m i n u t e s w i t h  the  i n strain  of t h e specimen  s t r e s s i s used i n d e f i n i n g .  I f the deviator  stress-  a x i a l s t r a i n c u r v e does n o t have a d e f i n i t e peak b u t t h e deviator  stress increases  at a d e c r e a s i n g r a t e w i t h  increasing  a x i a l s t r a i n the deviator  s t r e s s f o r an a r b i t r a r i l y  chosen  percentage of a x i a l at f a i l u r e . for  The d e v i a t o r  stress versus a x i a l  t h e R and Q t e s t s r e p o r t e d  have d e f i n i t e peaks axial at  s t r a i n i s s e l e c t e d as t h e d e v i a t o r  i n t h i s paper  and t h e d e v i a t o r  s t r a i n was a r b i t r a r i l y  chosen  strain  stress  curves  d i d not u s u a l l y  s t r e s s a t 15 p e r c e n t as t h e d e v i a t o r  stress  failure. b.  Q Tests  : ;b ( 1 )  Theory . In the Q t e s t the water content of the t e s t  specimen  i s n o t a l l o w e d t o change d u r i n g  application  of the c o n f i n i n g  or t h e l o a d i n g  the  pressure,  ,  of the specimen t o f a i l u r e  by  the  a p p l i c a t i o n of the d e v i a t o r  The  t o t a l applied  the  pore water at a l l s t a g e s of a Q t e s t i f  C  3  will  (a)  the specimen i s  (b)  the c o m p r e s s i b i l i t y  stress  be c a r r i e d  by  saturated. of t h e pore  w a t e r and t h e s o i l p a r t i c l e s i s n e g l i g i b l e when c o m p a r e d w i t h compressibility (c)  of the s o i l  the structure.  t h e r e i s a unique r e l a t i o n s h i p tween e f f e c t i v e s t r e s s  and  be-  void  ratio. These g e n e r a l assumptions r e g a r d i n g test  t h e o r y have b e e n v e r i f i e d by  t e s t s w h i c h h a v e shown t h a t confining  Q  laboratory  a change i n the  p r e s s u r e does produce  an e q u a l  c h a n g e i n t h e p o r e w a t e r p r e s s u r e i f no change i n water c o n t e n t i s a l l o w e d . the  strength  sample  c h a r a c t e r i s t i c s of a  a r e dependent  stresses  and  the a p p l i c a t i o n of a  effective stresses,  Q test  soil  o n l y on t h e e f f e c t i v e  p r e s s u r e i n the Q t e s t does not the  Since  confining  change  the r e s u l t s of a  are independent of the  confining  8  pressure. When p l o t t e d u s i n g the Mohr's c i r c l e c o n v e n t i o n of shear s t r e s s v e r s u s  total  normal s t r e s s the r e s u l t s of Q t e s t s  on  s a t u r a t e d samples of the same s o i l at the same v o i d r a t i o s h o u l d g i v e c i r c l e s of the same r a d i u s l o c a t e d a l o n g the normal s t r e s s axis.  The  s t r e n g t h envelope  f o r the Q  t e s t r e s u l t s would then be a l i n e drawn through the tops of the c i r c l e s . Laboratory Results F i g u r e 3 i s a p l o t of shear s t r e n g t h v e r s u s normal s t r e s s o b t a i n e d from the Q t e s t s performed on specimens from the d r i l l h o l e shown on f i g u r e 2.  The  loca-  t i o n i n the d r i l l h o l e and the Q s t r e n g t h of a p a r t i c u l a r sample are marked by  the  same l e t t e r on the r e s p e c t i v e f i g u r e s . T h i s system of i d e n t i f y i n g the t e s t r e s u l t s of specimens w i l l be used throughout  the  paper. The v a l u e s of shear s t r e n g t h o b t a i n e d from the Q t e s t s f o r any p a r t i c u l a r sample, as shown on f i g u r e 3, d i d not l i e a l o n g a h o r i z o n t a l l i n e as t h e o r y d i c t a t e s should.  they  For example, shown on f i g u r e 3  9 connected by a dashed l i n e a r e 4 t e s t r e s u l t s f o r Q t e s t s of specimens c u t from sample 0.  These 4 t e s t s were r u n on s p e c i -  mens t a k e n as c l o s e t o g e t h e r as p o s s i b l e i n sample 0.  The 4 t e s t r e s u l t s s h o u l d , i f  they followed the general Q t e s t theory, l i e on a s t r a i g h t l i n e .  A l s o shown connected  by a dashed l i n e a r e t h e t e s t r e s u l t s of specimens t a k e n from sample L .  The t e s t  r e s u l t s f o r sample 0 a r e t h o s e which d e v i a t e f a r t h e s t from t h e o r y w h i l e those f o r L best approach a h o r i z o n t a l  straight  line. A r e v i e w of t h e l a b o r a t o r y the f o l l o w i n g p o s s i b l e  data  indicates  reasons f o r these  v a r i a t i o n s from t h e o r y : (a)  t h e samples were not 100 p e r c e n t s a t u r a t e d when s h e a r e d .  Since the  samples were o b t a i n e d below t h e n a t u r a l water t a b l e a t t h e s i t e i t was i n c o r r e c t l y thought t h a t the samples would be s a t u r a t e d and no s p e c i a l e f f o r t was made t o s a t u r a t e them b e f o r e t e s t i n g . saturation varied and  The degree of  from 90 t o 100  averaged 97.3 p e r c e n t .  10. (b)  t h e v o i d r a t i o of specimens c u t as c l o s e t o g e t h e r as p o s s i b l e i n t h e same sample v a r i e d as much as .29 a l t h o u g h t h e average was g e n e r a l l y about .10.  (c)  i n t h e same specimen zones of s o i l s with different plasticity, indices were  Considering  evident. t h e wide s c a t t e r of r e s u l t s  the f i g u r e of .6 tons per square f o o t , as shown oh f i g u r e 3, was s e l e c t e d f o r use i n s t a b i l i t y a n a l y s e s as a c o n s e r v a t i v e but r e a s o n a b l e v a l u e f o r t h e f u l l t h i c k n e s s of the f i n e - g r a i n e d f o u n d a t i o n  materials.  R Tests (1)  Theory In t h e R t e s t complete c o n s o l i d a t i o n of the t e s t specimen i s p e r m i t t e d c o n f i n i n g p r e s s u r e , CJ" . 3  under t h e  Then w i t h t h e  water c o n t e n t h e l d c o n s t a n t a d e v i a t o r s t r e s s , <o, - ^ 3 , i s a p p l i e d and i n c r e a s e d u n t i l t h e specimen f a i l s .  The t h e o r e t i c a l  shear s t r e n g t h envelope drawn from R t e s t , r e s u l t s s h o u l d c o n s i s t of 2 p a r t s .  The  s l o p e of t h a t p o r t i o n of t h e envelope f o r  11 normal s t r e s s e s between zero and the preconsolidation  pressure i s dependent  upon the p r e c o n s o l i d a t i o n  pressure.  The  p o r t i o n of the envelope f o r normal s t r e s s e s greater  than the p r e c o n s o l i d a t i o n  i s not dependent on the  pressure  preconsolidation  pressure but depends upon the e f f e c t i v e s t r e s s changes between s o i l p a r t i c l e s caused by the c o n f i n i n g p r e s s u r e . example, i f a s a t u r a t e d preconsolidated  For  specimen has been  by a l o a d of 3 tons per  square foot the a p p l i c a t i o n of a c o n f i n i n g p r e s s u r e of 2 tons per square f o o t would produce no change i n the e f f e c t i v e s t r e s s between s o i l p a r t i c l e s .  The shear  strength  of the specimen would then be dependent on the p r e c o n s o l i d a t i o n  load and not on the  confining pressure.  On the other hand i f  the c o n f i n i n g pressure used had been 4 tons per  square f o o t then the s t r e n g t h  of the  specimen would depend on the change i n e f f e c t i v e s t r e s s between s o i l p a r t i c l e s induced by the c o n f i n i n g Laboratory  pressure.  Results  The wide range i n Mohr's c i r c l e s  obtained  from the R t e s t r e s u l t s as shown on f i g u r e 4,  12 was s u c h t h a t no one s t r e n g t h  envelope  c o u l d be d r a w n u s i n g a l l t h e t e s t By  grouping  the t e s t  results  results.  of specimens  w i t h a b o u t t h e same d e n s i t y , v o i d r a t i o a n d plasticity were drawn.  index  better strength  Dividing the foundation  zones t o w h i c h t h e shear s t r e n g t h obtained results  envelopes  from the grouping  into  parameters  of the t e s t  a p p l i e d proved i m p r a c t i c a l .  The  number o f z o n e s r e q u i r e d i n t h e f o u n d a t i o n because of t h e v a r i a t i o n of s o i l  character-  i s t i c s w i t h o n l y minor changes i n d e p t h w o u l d make t h e p e r f o r m i n g analyses To  of s t a b i l i t y  d i f f i c u l t and time  consuming.  e l i m i n a t e t h e n e c e s s i t y of d i v i d i n g  the f o u n d a t i o n shear strengths  i n t o zones o f d i f f e r e n t forstability  analyses  p u r p o s e s , one s h e a r s t r e n g t h d e f i n e d by an angle and  o f i n t e r n a l f r i c t i o n , 0 , o f 14 d e g r e e s  a cohesion,  foot,  c , o f .4 t o n s p e r s q u a r e  a s shown on f i g u r e  chosen as b e i n g  4, was  arbitrarily  a conservative value f o r  the R shear s t r e n g t h of t h e f u l l  thickness  of t h e f i n e g r a i n e d  Variation  foundation.  of s o i l c h a r a c t e r i s t i c s w i t h i n s a m p l e s a n d s p e c i m e n s i s t h e most r e a s o n a b l e  explanation  for  the d i s c r e p a n c y between the  laboratory  r e s u l t s and what would n o r m a l l y be from t h e o r e t i c a l  expected  considerations.  R T e s t s w i t h Pore P r e s s u r e Measurements (1)  Theory The  effective stress p r i n c i p l e i n s o i l  mechanics, f i r s t proposed by s t a t e s that  : CJ^=•  + M-  Terzaghi,  where <ST i s the T  t o t a l a p p l i e d s t r e s s , x - i s the i n the pore f l u i d , s t r e s s i n the s o i l  i s the e f f e c t i v e skelton.  I f , as shown on f i g u r e 5 and for  pressure  as was  done  a l l the R t e s t s , the pore p r e s s u r e  i n d u c e d i n a specimen by a p a r t i c u l a r a p p l i e d s t r e s s i s measured the e f f e c t i v e s t r e s s i s a l s o known.  S i n c e the r e l a t i o n -  s h i p between a p p l i e d s t r e s s and i s also recorded during  axial strain  a t e s t , Mohr's  c i r c l e s of e f f e c t i v e s t r e s s can be for  any  plotted  v a l u e of a x i a l s t r a i n d e s i r e d .  For  a p a r t i c u l a r v a l u e of a x i a l s t r a i n the e f f e c t i v e s t r e s s c i r c l e s from a number of t e s t s can be p l o t t e d on the same f i g u r e the tangent t o these c i r c l e s used t o an envelope of developed shear for  that s t r a i n .  and  define  strength  T h i s envelope i s shown  14  on f i g u r e 5 as e n v e l o p e  1.  I f t h e d i r e c t i o n of the u l t i m a t e plane w i t h r e s p e c t t o the major  failure  principal  p l a n e i s assumed t h e same f o r a l l s p e c i m e n s t e s t e d and d r a w n on t h e e f f e c t i v e circles for a particular  axial  l i n e c o n n e c t i n g t h e p o i n t s of  stress  strain,  the  intersection  o f t h e c i r c l e s and f a i l u r e p l a n e s c a n  be  used t o d e f i n e another envelope of d e v e l o p e d shear s t r e n g t h . this  Envelope  2 on f i g u r e  5 is  e n v e l o p e w i t h Q d e f i n i n g t h e assumed  d i r e c t i o n of t h e u l t i m a t e f a i l u r e p l a n e . S t r e n g t h envelopes d e r i v e d from R w i t h pore p r e s s u r e measurements a r e and w i l l R'  tests generally  be r e f e r r e d t o i n t h i s t h e s i s  envelopes.  The  method d e s c r i b e d above  and shown on f i g u r e 5 e n v e l o p e . 2 was f o r o b t a i n i n g R' Envelope on f i g u r e  2 was  as  shear s t r e n g t h  chosen  parameters.  p r e f e r r e d s i n c e , as shown  5, f o r a p a r t i c u l a r n o r m a l  envelope 2 would d e f i n e a lower s t r e s s t h a n e n v e l o p e 1 and w o u l d  stress  shear therefore  be a more c o n s e r v a t i v e e s t i m a t e o f s h e a r strength. Laboratory Results The  v a l u e s of the pore p r e s s u r e s measured  15. in  the shearing of the test  specimens i n  the R t e s t s v a r i e d  c o n s i d e r a b l y both during  an i n d i v i d u a l t e s t  and from t e s t  to test.  I n a l l t e s t s when t h e a p p l i c a t i o n deviator  stress  first  of t h e  commenced t h e p o r e  p r e s s u r e s i n d u c e d were p o s i t i v e . the shear t e s t s silts  In a l l  of specimens of  non-plastic  the pore pressures developed  were  n e g a t i v e f o r a x i a l s t r a i n s above 9 p e r c e n t . The  pore p r e s s u r e s developed  silts of  i n testing the  and c l a y s w i t h p l a s t i c i t y  4 t o 10 w e r e i n c o n s i s t e n t .  these t e s t s  indices I n some o f  the value of the induced  pressure reached  a maximum p o s i t i v e  for axial strains  pore value  of about 5 p e r c e n t and  then decreased  but always  remained  In other t e s t s  on t h e s e s i l t s  positive.  and c l a y s t h e  development of t h e pore p r e s s u r e s f o l l o w e d a pattern plastic  s i m i l a r t o those f o r t h e non-  silts.  plasticity  Shear t e s t s  indices  on specimens w i t h  o f 11 t o 18 i n d u c e d  p o s i t i v e pore p r e s s u r e s a t a l l stages of the t e s t s . reached and  The maximum p o r e p r e s s u r e was  at a x i a l s t r a i n s of 3 t o 7 percent  then remained  only s l i g h t l y  constant or decreased  throughout  the rest  of the  16 test.  The p l o t  of induced pore  pressure  versus a x i a l s t r a i n f o r a t e s t specimen f r o m s a m p l e S i s shown on f i g u r e  6.  Mohr's c i r c l e s w e r e d r a w n u s i n g t h e effective  s t r e s s e s measured at s e l e c t e d  percentages  of a x i a l  specimen t e s t e d . a t an a n g l e , @  s t r a i n f o r each  A f a i l u r e plane , o f 60 d e g r e e s  inclined  w i t h the  m a j o r p r i n c i p a l p l a n e was assumed a n d d r a w n on a l l t h e M o h r ' s  circles.  P l o t s of t h e v a l u e s of t h e s h e a r X  , v e r s u s e f f e c t i v e normal  stress,  stress,  ^  ,  N  on t h e assumed f a i l u r e p l a n e f o r i n c r e a s i n g a x i a l s t r a i n showed g e n e r a l l y t h a t f o r s t r a i n s of 2 or 3 percent  increased f o r  an a p p r o x i m a t e l y c o n s t a n t o r d e c r e a s i n g F o r a x i a l s t r a i n s b e t w e e n 3 and 15 p e r c e n t  i any  i n c r e a s e i n \o"  increase i n  caused  N  F o r a x i a l s t r a i n s above  15 p e r c e n t i n c r e a s i n g caused  ^  or a decrease of  in X  versus  s a m p l e S. versus  i n some t e s t s  u  a proportional increase i n f  other tests increasing  plot  a proportional  ^T^,  . ^o  N  Qr  N  caused  in  no c h a n g e  F i g u r e 6 shows t h e f o r a specimen from  F i g u r e 7 shows t h e p l o t s o f  iC  f o r 7, 1 0 , 1 3 , and 17 p e r c e n t  axial  strain  Figure  tor  8 is  all  a plot  maximum p r i n c i p a l , tor  all /  w  versus  the a  R  or  less  tested.  strengths  developed  were  failure  chosen  shear  the  percent  specimens  strain  specimens  efiective  values stress  of  tested.  axial,  of  the  ratio, strain  A maximum v a l u e  reached  10 p e r c e n t  of  tests.  1  s  the  tor  axial  strains  for  80 p e r c e n t  For  this  at as  of  reason  of  of the  the  shear  10 p e r c e n t  axial  representing  the  strength  tor  use  in  stability  analyses. As  shown  strength  on f i g u r e  parameters  10  percent  could  of  internal  degrees  and  of  of  a 0'  was 5.  -Embankment Several  were  for  materials  in  with  than  less  but  contractor  the  the  of of  for  axial  from  0 ,  of  28  zero  to  a 0'  1  use  The  with in  shear  strains  ranged  zero.  28 d e g r e e s  borrow  vicinity sources  sources  10 p e r c e n t  These  c',  a c'  assigned  in  these  sieve.  have  efiective  an  angle  degrees of  lower  a c'  of  of  stability  37 limit  zero analyses.  Materials  areas  acquired  for  friction,  and c o h e s i o n ,  7 the  areas  were had  were  of  of  the  f i l l  primarily  by w e i g h t shown  the  on  option  materials. granular  passing  the of  proposed  the  contract obtaining  No.  embankment The soils 200  documents material  of  18  any type from any o t h e r source he w i s h e d .  Because of weather  c o n d i t i o n s and the r e l a t i v e l y h i g h m o i s t u r e c o n t e n t s of t h e t i n e - g r a i n e d s o i l s at the s i t e i t was thought t h a t the c o n t r a c t o r would use o n l y g r a n u l a r m a t e r i a l s i n t h e embankment.  Shear s t r e n g t h parameters ot a 0 of 30 degrees and a  c o h e s i o n ot z e r o were a s s i g n e d as a r e a s o n a b l e  estimate f o r  the s t r e n g t h ot the t i l l m a t e r i a l s . Shear S t r e n g t h ot S u r f a c e M a t e r i a l s u v e r l y i n g t h e Fine-grained  Soils  a.11 the s u r f a c e l a y e r ot o r g a n i c s i l t s o v e r l y i n g the streambed d e p o s i t s of sanely g r a v e l s were removed b e f o r e any embankment m a t e r i a l s were p l a c e d ,  ho shear t e s t s of the  streambed sandy g r a v e l s were performed,  A. shear  strength  of a j6 of 35 degrees and c o h e s i o n of z e r o was a r b i t r a r i l y assigned to t h i s m a t e r i a l . 7.  Stability  Analysis_Method  In a l l t h e s t a b i l i t y a n a l y s e s r e p o r t e d i n t h i s paper a s u r f a c e r e p r e s e n t e d by a c i r c u l a r the f a i l u r e s u r f a c e .  a r c was assumed t o be  The type of c i r c u l a r  arc s t a b i l i t y  a n a l y s i s used i s g e n e r a l l y termed "The Method of I n f i n i t e s imal  Slices". In t h i s method of s t a b i l i t y a n a l y s e s t h e i n - p l a c e  u n i t weight of the s o i l above a p o i n t on the axe i s d i v i d e d by the u n i t weight of water t o o b t a i n a c o n s t a n t . For any p o i n t on the a r c the depth ot s o i l above t h e p o i n t i s m u l t i p l i e d by t h i s c o n s t a n t t o e q u i v a l e n t column of w a t e r .  yive  the depth of an  I f t h e r e a r e zones of s o i l s  19 with  varying  must  be  densities  computed f o r  zone m u l t i p l i e d by of  the  constants  thickness point  is  represents  on t h e  arc.  and  the  the  the  thickness  constant.  respective  the  point  on the  of  a c o l u m n of  weight  of  soil  weight  above  slice  of  the  of  each  summation zone  arc.  H,  constant  of  The  their  an i n f i n i t e s i m a l  assumed t h e n  a different  by  height,  to  point  applicable  above  the  equivalent  is  its  the  zone  multiplied  weight  dx  each  plotted  If  above  This  water the  of  point  horizontal  slice,  width  tV, i s  V=Htf dx w  where  t  is  w  the  infinitesimal arc  is  arc  and  and the  dL  slice  and B  the  unit  is  weight  width the  normal  the  dx t h e  angle  horizontal  unit  of  then  force,  n,  unit  are  is  therefore  t  projection The  of  the  s u m m a t i o n of  respective  net  arc the  areas  meter.  The  forces  between  the  unit  obtaining is  to  forces which be  are  B)  to  of  the  force,  t,  w  each  B)  (cos  on the  actual  obtained  length,  the dL,  the  normal  horizontal  represented  for  B)  B)  summation of  readily  arc  ( s i n  on t h e  adjusted  incremental  B  (cos  them  than are  cos  the  plot  rather  must  tangent  tangential  = H #  w  forces  length  |  the  n = H T (cos  and t a n g e n t i a l  the  the  w  but  m e t h o d of  for  infinitesimal  between the  If  Y d* (sin B ) j £  t - H  A convenient  water.  arc by by  length. their plani-  difference on w h i c h  the  20. forces  actually  which of  t  a c t and the h o r i z o n t a l  the forces a n d n must  cos  B.  the  t  and  The  moment to  o f 4Jr  or  —'—_ .  cos B n=n =H J ^ .  A  n  graphical  solution  for a particular  A  of s a f e t y ,  R about  resisting  cause  by t h e r a t i o  i s the values  t, = t = H $w s i n B a n d a d j u s t e d  factor  radius  That  d x , on  ax  A complete A  assumed t o a c t .  be a d j u s t e d  The a d j u s t e d  of  were  projection,  f o r an a r c a l o n g  slice  a r e shown  with  on f i g u r e  F . S . , f o r an assumed f a i l u r e  i t s center rotation,  A  is  the r a t i o  of the  M , to the total r  9.  arc  total  moment  tending  r o t a t i o n M-^.  M = R I N (tan r  4>)  + RcL  M= R£ T t  a  For 3  zones  of s o i l  arc  _ ZN(tan ^ ) t c L Z T  p  9 t h e summation  of n  A  f o r the  a r e N-j_, N £ , a n d N3 a n d t h e s u m m a t i o n  forces,  T while  this  d  t h e a r c on f i g u r e  tangential +  n  those  t  A  ,  tending  resisting  £ N (tan  t o cause  rotation  4>) = N, tan  0 ,+H  rotation  a r e shown tan  z  ^ +  N  of the  shown a s  as - T . 3  tan  For  <^  3  a n d IT-. +T>(-T). The  excess  the  applied  the  normal  pore  load forces  pressures  i n the foundation  o f t h e embankment only  since  to  act perpendicular  at  a point  N'  = N - U and the factor  the pore  to the a r c .  i s U and the e f f e c t i v e  p o r.5.  If  0  T  the excess  is  ) -t c L -  i n a reduction of  pressures  normal  of safety  _ N' ( t a n -  result  —  caused by  force,  a r e assumed pore N',  pressure then  21. A arcs for  program which  for the  of  method of  electronic  results the  this  reported  computer.  and T  for  the  arc.  of  N  on  the  arc  the  arc  on t h e  by  the  summation  by  of  The analyses  Factor  for  the  from  represents materials  the  from the  of  the  the would  pressures during  factor  the  the  the  wanted the  of The of  N,  the  factor  excess  pore  portion  pore  for  summation  pressures  summation the  0),  characteristics  for  that  of  N(tan  safety  pore  the  use  solution  of  pressure  of  of  acting  the  N'  was  pressures  plotted  curve  computer  data.  Q tests.  have  caused  by  factor  Q test  strength  since the  strength  analyses The  minimum s h e a r ever  permitted'for  shear  stability  the  by  from  the  Criteria  A minimum s a f e t y  results  obtained  occur  under  depended upon the  analyses.  to  area  acted.  summation  minimum s a f e t y  the  pore  the  the  as  plotting  projection  pressures  N obtained  Safety  by  for  written  analyses  different  as w e l l  of  been  summation  with  summation  has  circular  stability  data  was  for  obtained  the  soil  factor  determined  subtracting  represented  8.  N the  were  of  passes  horizontal  on w h i c h  found  of  safety  of  was  zone  the  output  consists  factor  analysis  All  paper  computer  arc  safety  stability  this  arc  the  instead  1  heads  If  in  each  through which  the  computer.  The  a particular  cL,  gives  1.25  using  the  The  used  in  allowed strengths  strength  construction period.  was  shear  shear that  stability  parameters  no d i s s i p a t i o n  f i l l  construction  of  the  foundation of are use  the  excess  assumed of  a  22.. s a f e t y f a c t o r as l o w a s 1.25 i s p e r m i s s i b l e excess pore pressure, dissipate with  The  the construction  i n shear  of t h e f o u n d a t i o n  strength  period.  R shear s t r e n g t h parameters represent  strength  some  a l t h o u g h how much i s unknown, w i l l  an accompanying i n c r e a s e  occurring during  since  materials  the shear  a t some p o i n t  when some b u t n o t a l l o f t h e e x c e s s p o r e p r e s s u r e s by  the f i l l  c o n s t r u c t i o n have d i s s i p a t e d .  caused  A minimum f a c t o r  of s a f e t y of 1.50 was c a l l e d f o r i n t h e s t a b i l i t y using  the shear s t r e n g t h from the R The  analyses  R' s h e a r s t r e n g t h  tests.  p a r a m e t e r s c a n be u s e d i n s t a b i l i t y  the excess pore pressures  embankment l o a d a r e known.  was made t o e s t i m a t e  In the design  measured and s t a b i l i t y  s t a g e no a t t e m p t During the  the excess pore pressures analyses  measured pore p r e s s u r e s .  performed using  were these  The embankment s t a b i l i t y  f a c t o r a s i n d i c a t e d by t h e s e a n a l y s e s t h a n 1.25 a t a l l t i m e s d u r i n g time the excess  c a u s e d by  the excess pore pressures.  embankment c o n s t r u c t i o n  Any  analyses  t o o b t a i n s a f e t y f a c t o r s at a l l s t a g e s of the  construction provided the  h a d t o be  the construction  pore pressures  the measured pore p r e s s u r e  period.  i n d i c a t e d that  Design Stage S t a b i l i t y first  stability  the safety until  d i s s i p a t i o n i n d i c a t e d that the  f a c t o r o f s a f e t y was g r e a t e r  The  safety  greater  f a c t o r was l e s s t h a n 1.25 c o n s t r u c t i o n was t o s t o p  9.,  i n time  t h a n 1.25. Analyses  analyses  performed used  shear  23 strengths  f r o m t h e Q a n d R t e s t s a n d w e r e r u n on t h e maximum  embankment obtained  s e c t i o n o f 65 f e e t i n h e i g h t .  i n these  criteria.  analyses  The s a f e t y f a c t o r s  were w e l l below t h e e s t a b l i s h e d  The c o n s t r u c t i o n , s e a s o n a t t h e s i t e i s l i m i t e d  by w e a t h e r c o n d i t i o n s t o t h e p e r i o d b e t w e e n A p r i l November  and  and t h e c o n t r a c t o r c o u l d n o t c o m p l e t e t h e embank-  ment i n one c o n s t r u c t i o n s e a s o n b e c a u s e o f t h e q u a n t i t y o f materials involved. t o what h e i g h t first  The n e x t d e s i g n  the f i l l  s t e p s were t o determine  c o u l d be s a f e l y c o n s t r u c t e d  c o n s t r u c t i o n s e a s o n and w h e t h e r o r n o t t h e e x c e s s  pore p r e s s u r e s  caused by t h e f i l l  dissipate sufficiently  c o n s t r u c t i o n would  over the w i n t e r  layoff period to  allow the contractor t o f i n i s h the f i l l tion  i n the next  construc-  season. The G r e a t N o r t h e r n  had  i n the  requested  Railway  that a l l f i l l  h o r i z o n t a l t o one v e r t i c a l . only question concerning flatter a stable  slopes  i n t h e r e l o c a t i o n agreement  s l o p e s be no s t e e p e r This  the f i l l  request  The  o r t o e berms m i g h t be r e q u i r e d t o p r o v i d e  embankment.  50 f e e t w e r e a n a l y s e d  arcs analysed  ranging  of d e s i g n  strengths  F i g u r e 10 shows t h e g r o u p o f  f o r t h e 40 f o o t h i g h f i l l  obtained  f r o m 10 t o  f o r s t a b i l i t y using the shear  f r o m t h e Q, R, and R» t e s t s .  stage  was g r a n t e d .  s l o p e s was w h e t h e r o r n o t  Embankment s e c t i o n s w i t h h e i g h t s  factors  than 2  and t h e s a f e t y  f o r the v a r i o u s shear s t r e n g t h s .  At t h i s  no a t t e m p t was made t o p r e d i c t what t h e  24, v a l u e s of t h e excess pore p r e s s u r e s might  be a n d c o m p l e t e  d i s s i p a t i o n o f t h e s e p o r e p r e s s u r e s was assumed f o r a l l t h e analyses using the R  f  s t r e n g t h parameters.  The a n a l y s e s  u s i n g Q s h e a r s t r e n g t h s i n d i c a t e d t h e maximum h e i g h t o f embankment t h a t c o u l d be c o n s t r u c t e d w i t h s a f e t y meeting  the design c r i t e r i a  would  factors  be b e t w e e n 30 a n d 35 f e e t .  C o n s o l i d a t i o n a n a l y s e s , assuming  2-way d r a i n a g e w i t h  a maximum d r a i n a g e p a t h o f 45 f e e t , i n d i c a t e d t h a t t h e t i m e r e q u i r e d f o r 100 p e r c e n t p r i m a r y c o n s o l i d a t i o n w o u l d minimum o f 275 d a y s .  be a  V i s u a l examination of t h e s o i l  samples,  as p r e v i o u s l y d i s c u s s e d , f o u n d t h i n l a m i n a t i o n o f s a n d which i f continuous provide drainage paths that decrease the c o n s o l i d a t i o n time. t h e e x c e s s pore p r e s s u r e heads b e ? dissipate?" s t i l l  would  The q u e s t i o n , "What w i l l M  a n d , "How f a s t w i l l  d i d not have r e l i a b l e answers.  t h a n s p e n d more d e s i g n t i m e m a k i n g t h e o r e t i c a l  theyv  Rather  studies  w i t h q u e s t i o n a b l e r e s u l t s t h e d e c i s i o n was made t o i n s t a l l p i e z o m e t e r s i n t h e f o u n d a t i o n and measure t h e e x c e s s  pore  p r e s s u r e s a t a l l . stages of c o n s t r u c t i o n . 10.  Type o f and I n s t a l l a t i o n Method f o r t h e P i e z o m e t e r s The  contract s p e c i f i c a t i o n s c a l l e d f o r gas-operated  piezometers i n s t a l l e d at  indrill  the toe of the f i l l .  holes with a terminal  board  The c o n t r a c t o r s e l e c t e d t h e  H a l l Hydrostatic Pressure C e l l  as t h e type of piezometer  best s u i t e d f o r the i n s t a l l a t i o n c a l l e d f o r i n the c o n t r a c t . The  Hall Cell  i s a n i t r o g e n a c t i v a t e d , c l o s e d type  piezometer  25. approximately  1.5 i n c h e s i n d i a m e t e r  made e n t i r e l y o f s t a i n l e s s s t e e l . external leads to the c e l l .  by 3 i n c h e s  long  T h e r e a r e two n y l o n  One a c t s a s t h e i n f l o w a n d  t h e o t h e r as t h e o u t f l o w l i n e f o r t h e n i t r o g e n g a s . base of t h e c e l l  i s a porous stone  a calibrated stainless steel The water  cell  itself  and b e h i n d  The p r e s s u r e o f t h e  c l o s e s t h e v a l v e by f o r c i n g t h e  diaphragm a g a i n s t a base p l a t e c l o s i n g tween t h e i n and out f l o w t u b e s . of  t h i s stone i s  diaphragm.  a c t s as a v a l v e .  surrounding the c e l l  At the  the f l o w path be-  Increasing the pressure  t h e n i t r o g e n g a s on t h e i n f l o w s i d e o f t h e c e l l  forces  t h e d i a p h r a g m away f r o m t h e b a s e p l a t e a l l o w i n g g a s t o pass i n t o the outflow tube. not f a s t e n e d t o t h e c e l l and  used as a bubble  tube of  The e n d o f t h e o u t f l o w  i s submerged i n a tube  indicator.  of water were f o r m i n g from  one p e r s e c o n d  tube  of water  When g a s b u b b l e s t h e o u t f l o w tube  i n the at the r a t e  t h e g a s p r e s s u r e a s r e a d on t h e r e g u l a t o r  gage on t h e i n f l o w l i n e i s s a i d t o e q u a l t h e p r e s s u r e o f the water 1  surrounding  The p i e z o m e t e r s  on f i g u r e 1 1 .  Holes  the c e l l . were i n s t a l l e d  at the locations  6 inches i n diameter  to  t h e r e q u i r e d depths w i t h Osterberg s o i l  in  the l a s t  10 f e e t o f h o l e .  t e s t s performed The in  samples  taken  The r e s u l t s o f c l a s s i f i c a t i o n  type w i t h o n l y s m a l l changes  and t h e sand l e n s e s n o t e d  were found  drilled  on t h e s e s a m p l e s a r e a l s o shown on f i g u r e 11  same v a r i a t i o n s i n s o i l depth  were  shown  i n these  samples.  i n t h e e x p l o r a t i o n sample  26. A of a  sand bed  each  piezometer  burlap  placed  on t o p  of  placed  the  was  cell  coarse  sand  bed.  the  made b y  the  pressure  The  hole  was  then  nylon  in  and  out  to  the  toe  of  set  up.  extending been  observation functional 11.  check  and  Selection  of  head  cell  9 inch  whether water  buried  leads  f i l l  where  were  attached  whole the  known  Horizontal  of  not  the  the  in  drill  a  grout  trench  terminal to  given  the a  board  gages  and  final  ground water  and V e r t i c a l  bag of  chemical  the  system  and  check  or in  a  inside  layer  functional  of  bottom  the  flow  the  the  placed  with  the  against  and  at  was  backfilled  The. l e a d s  tubes  A  observing  read  and t h e  cell  Another  cell.  would  hole.  had  The  sand  above  deposited  hole.  with  the  then  d e e p was  drill  bag f i l l e d  s a n d was  cell  9 inches  table.  Piezometer  Locations The h o r i z o n t a l and" t h e figure  depths 1 1 , were  foundation these be  of  points  developed  stress  to  points  excess  pore  throughout  predict as  the the  by  the  cells  the  of  known p o r e  installed,  was  , were  electronic  in  in  The  12 w a s  which  solved  these  for  computer.  the  were  to  theoretical  used  constructed.  on  From  equipotentials  on f i g u r e  shown  pressure.  foundation.  pattern  centerline  a distribution  pressure the  section  were  give  f i l l  £^  from  to  shown  stresses,  obtained  the  selected  the  develope  vertical were  which  distribution  attempt would  at  offsets  in  an  equipotentials Only  and The  all  the solutions  stress  27. distribution found  for The  weight  the  programmed  assumed t o to  print  fraction, in  of  vertical  where of  at  vertical  equals feet  the  unit  ^"  the  the  for  most A  an  of  the  line  angle  of  projected  of  60 d e g r e e s  imation  of  the  .10  for  of  the  f i l l  to  all be  Based ment  necessary on t h e heights  or  stress the  were  at  of  f i l l  various  being  value QT =H)fl 2  and H i s  of  f i l l  the  stress  for  the  height  45 a n d  .90  stress  at  which  distribution l o a d was  the  103  50 f o o t  foundation  of  from  the  the  along  85 f e e t  f i l l .  the with  equipotential  toe  horizontal  contour  from  the  of is  Outside  this for  and d e p t h s  of  the a  were  60 d e g r e e  the the  f i l l  good  stress  No p i e z o m e t e r s  distributions  offsets  a  heights.  downward  located  at  embankment  the  the  heights.  as  f i l l ,  from the  depths  stress  then  feet.  in  from  was  pattern  point  the  foundation  theoretical  and 65 f e e t  bracketing range  the  applied  placed  f i l l  any  centerline  were  to  stresses  actual  of  in  Two p i e z o m e t e r s  intention  50 f e e t  computer  a grid  at  obtained  of  the  in  f  f i l l  the  through  a f o u n d a t i o n by  The  The  weight  below  to  vertical  foot  of  10  embankment  one.  10  centerline  the  scale  stress,  stress  the  be  to  I,  90 p e r c e n t  for  at  centerline  depth  of  applied  foundation.  the  f i l l  The the  the  is  t  the  stress  embankment  points the  sections  increments.  vertical  was  decimal  f i l l  5 foot  of  contact  for  various  at  approx-  distribution thought line. embank-  locations  for  28. the  r e m a i n i n g 8 p i e z o m e t e r s were s e l e c t e d t o g i v e t h e b e s t  p o s s i b l e c o v e r a g e t o t h e zone of a n t i c i p a t e d e x c e s s  pore  pressures. 12.  S t a b i l i t y Analyses Using Estimated Excess P r e s s u r e s Were Not  Pore  Performed  I f t h e increment of pore p r e s s u r e at a p o i n t i n the f o u n d a t i o n i s t o be e q u a l t o t h e i n c r e m e n t o f t h e  vertical  s t r e s s t h e n t h e f o l l o w i n g a s s u m p t i o n s must be t r u e . the  foundation soils  h a v e t o be s a t u r a t e d .  Because  of t h e  m e t h o d o f d e p o s i t i o n and t h e l o c a t i o n o f t h e g r o u n d t a b l e , a p p r o x i m a t e l y 4 f e e t below fill  First,  water  the ground s u r f a c e at the  s i t e , t h e assumption t h a t the s o i l s were c o m p l e t e l y  s a t u r a t e d was c o n s i d e r e d t o be j u s t i f i e d e v e n t h o u g h t h e shear t e s t specimens tion  of l e s s  i n d i c a t e d an i n p l a c e d e g r e e  t h a n 100 p e r c e n t .  of s a t u r a -  The l o s s o f w a t e r  lowering  the  d e g r e e o f s a t u r a t i o n was t h o u g h t t o h a v e o c c u r r e d d u r i n g  the  p r e p a r a t i o n of the specimens Second,  t h e f o u n d a t i o n s o i l s must be assumed t o be  homogeneous, i s o t r o p i c , elastic  for testing.  materials.  i n f i n i t e i n e x t e n t and t o a c t as  T h i s a s s u m p t i o n i s known t o be  e r r o n e o u s , b u t no a c c e p t a b l e m e t h o d o f e v a l u a t i n g o r a d j u s t ing as  f o r t h e e r r o r s w e r e known and t h e a s s u m p t i o n was a c c e p t e d true. The t h i r d  is the  a s s u m p t i o n w h i c h must be a c c e p t e d as t r u e  t h a t no d i s s i p a t i o n o f e x c e s s p o r e p r e s s u r e s o c c u r i n c o n s t r u c t i o n time p e r i o d .  For t h i s  a s s u m p t i o n t o be  29. true  the  to  the  of  time  pore  embankment  foundation. is  required  pressure  heights  of  load  must  This  is  for  be  impossible  construction.  d i s s i p a t i o n which  f i l l  applied  constructed  and  occurs the  instantaneously  since The  some  amount  depends  time  period of  upon  taken  excess the  in  construc-  the  contract-  tion. The or's  uncertainties  rate  of  material  involved placement  pressure  d i s s i p a t i o n were  analyses  using  performed.  estimates  the for  in and  predicting the  principle these  pore  rate  of  reasons  excess no  pressures  pore  stabilit were  30^  Chapter I I l  Embankment C o n s t r u c t i o n  a  The c o n t r a c t o r f i n i s h e d on J u l y 1 9 , 1966„  No f i l l  s e c t i o n immediately  over  the piezometer  installation  m a t e r i a l was p l a c e d i n t h e  the piezometers  u n t i l S e p t e m b e r 2,  1966 b u t a m i n o r amount o f c o n s t r u c t i o n o c c u r r e d d u r i n g  thee  l a s t week o f A u g u s t i n t h e v i c i n i t y o f t h e i n s t a l l a t i o n causing  an i n c r e a s e i n t h e measured p o r e p r e s s u r e s .  readings  The  i n t h e p e r i o d b e t w e e n J u l y 19 a n d S e p t e m b e r 2  showed t h a t t h e c e l l s w e r e f u n c t i o n i n g a c c u r a t e l y by i n d i c a t i n g t h e known g r o u n d w a t e r s u r f a c e . B e t w e e n S e p t e m b e r , 2 a n d 12 e l e v e n f e e t o f f i l l p l a c e d over to  the piezometers.  20. no f i l l  fill  m a t e r i a l was p l a c e d .  was p l a c e d  piezometers  over  1 through  5 f e e t of f i l l  September.13  An a d d i t i o n a l 9 f e e t of  t h e r i g h t s i d e of t h e f i l l  (over  6 ) b e t w e e n S e p t e m b e r 21 and 23 w i t h  b e i n g p l a c e d over  embankment a t t h i s height  I n t h e p e r i o d from  was  time.  t h e r e m a i n d e r of t h e  The f i l l  was b r o u g h t t o a  o f 20 f e e t b e t w e e n O c t o b e r 11 a n d 13.>  uniform  Weather  f o r c e d t h e c o n t r a c t o r t o s t o p h i s embankment c o n s t r u c t i o n . operations  a f t e r O c t o b e r 13 f o r t h e 1966 s e a s o n .  He  recommenced h i s o p e r a t i o n on May 5, 1967 a n d b r o u g h t t h e fill  t o g r a d e on O c t o b e r 9, 1 9 6 7 .  Except f o r the p e r i o d  b e t w e e n J u l y 3 a n d A u g u s t 2 when t h e f i l l  h e i g h t was i n c r e a s e d  f r o m 30 t o 48 f e e t t h e c o n t r a c t o r p l a c e d f i l l  material  i n t e r m i t t e n t l y t h r o u g h o u t t h e 1967 c o n s t r u c t i o n s e a s o n .  31. Figure  11  shows  the  principal  dates  of  embankment  material  placement. 2.  Pore  Pressures  Figures pressures water the  in  13 a n d  of  head  piezometer water  above  water  measurements These  taken  was  the  difference pressure  office f i l l  be  the  load.  reported  heighth  each at  excess of  location pore  these  were  was of  pressures  installed  in  as  to  how  ground or  pore  this  static  caused  by  the  below  started  ground water  pressures  the  4 feet  pressure  constructed  the  excess  were  plotted  sketched  30 f o o t the the  pore  On a  piezometers  then  assumptions  be  arid  the  head the  was  em-  field  measured  and  the  pressure  head  day.  the  underlying  ground  built.  above  construction  pressure  pore  been  scale  f i l l  computed.  immediately  to  had  the  was  The  pore "pressure  the  measured  pore  assumed t o  approximately  f i l l  data  the  the  was  time.  and  pore  total  pressures  versus  that  represented  each  field  piezometer  the  the  for  From the  After  measured  embankment  indicated  the  Piezometers the  when p l o t t e d  excess  As  of  inch  by  any  between the which  the  piezometer  horizontal  ground s u r f a c e .  bankment  each  measurements  table  assumed to  square  before  locations  by  plots  represented  the  pore  14 a r e  pounds per  elevation  head  Measured  section the  values  and  the  in.  zone  in  the  pore  of  to  scale  the  equipotentials  Since  ground s u r f a c e excess  drawn  at  no  piezometers  foundation arbitrary  pressures  were  32.  distributed  in  this  zone were  1.  made.  These of  assumptions  the  surface  layer  gravelly  was  10 f e e t  and c o n t i n u o u s  were:  materials  across  the  section. 2.  the  permeability  of  was  much  than  greater  fine-grained no  excess  3.  the  excess  could a  be  feet  above pore  of example,  arc  and  the  excess  the  tials  was  zero,  7,  15,  and  if  at  this  pore  28 f e e t  in  the  and. d i s s i p a t i o n  of  head  excess at  the  of  22 a r e head  period.  versus Also  from  pressure  below  plots  the  of  shown  for  would the  the  on t h e s e  bottom  layer. of  a  particular  ground the  arc  ground  measured  time  at  excess  surface  equipoten-  head would  on t h e  the  the  arc  zero  below  points  surface.  line  surface  intersect  foundation  any  to  determined pore  to  ground  intersection  20 f e e t  respectively  15 and feet  linearly  equipotentials  the  along  be  layer.  upwards in  therefore,  could  surface  horizontal  gravelly  line  a n d 21 f e e t  17.5 feet  Figures  the  pressure  the  pressures  point  horizontal  14,  pressures  the  line  below  and  pressure  extended  decrease  For  pore  layer  underlying  pressures  this  horizontal  20 4.  in  gravelly  the  materials  pore  developed  this  10,  be 12.5,  surface.  excess 1966  pore construction  figures  are  two  33, projected pages  values  34 a n d  25 f o o t during 3.  42.  f i l l the  using  obtained  from  analyses  for  the  f i l l .  Figure  the  Figures  scale  In and  on  pore the  of  before arcs  any  used  the  overlaying along  pressure  any  obtained  by  from  computer  the  The  pore  figure  projection for  the The  printout excess give  factor  of  are  particular  planimeter.  forces.  the  the  stability were  the  pore  those  stability  pressures  10  and  analyses  50  had  feet  constructed.  of  pressure  the  for  the  20  foot  equipotentials  safety  pore be  the  same  pressure  determined.  was  then  plotted  arc  and  the  area  under  the  of  area  of  then  the  to  same  arc  pressure  for  the  the  summation  summation  the  could  and  was  to  were drawn  arc  the  arc  drawn  with  along  data  pore  not  figures  distribution  projection  to  for  between  the  excess  two  area  Using  embankments were  in  these  imetered  Fill  used i n  excess  heights  practice  the  the  dissipation  equipotentials  no  shown  summation of  for  f i l l .  horizontal  the  20 F o o t  Solutions  24 a s  by  horizontal  pressure  f i l l  24 s h o w s  are  on  Pressures  23 a n d  distribution The  the  20 f o o t  scale.  all  increments  23 s h o w s  the  tests.  f  discussed  a s s u m i n g no  parameters  condition  for  Figure  for  pore R  are  pressures  f i l l  for  Pore  strength the  which  period.  Analyses  the  obtained  5 foot  20 f o o t  Excess  shear  pressure projected  construction  analyses  in  the  Stability  The  pore  These  and  Measured  been  of  under  total  normal  reduced  represented the arc  by by  effective was  the  ES.-N*  the  curve  forces  the the  plan-  normal (tan T  28°).  34, The  factors  arcs  for  the  pore  pressures.  of  figure  arc is  of  7 the  safety  20 f o o t  23. 2.30  and  is  factor  pressures  had  normal  pressures  using  4.  Excess The that of  the  of  the  and i f  feet  would in  the  The caused was  by  he  to  measured foot for  25, the  for  f i l l the  shown  safety.for  and  on f i g u r e  25  total  effective  pore  pressure  on f i g u r e  25 F o o t  7  respectively,  the  excess  arc  computer  shown  give  excess  Fill  24.  Using  Projected  stability  analyses  indicated  of  21,  the  on S e p t e m b e r  20 f e e t  22,  top  jeopardize  23., 1 9 6 6 .  reached  The  contractor  and  23 i n c r e a s e d  this of  was  rate  the  f i l l  of  the  On  on t h e  in  the the  material  to  stability  3  this  right  f i l l  height  placement  elevation  be  measured  in the  excess top  equal as  to  the  pore  of  the  the f i l l  pressures  that  f i l l  20 t o  from  26  increase height  in  was  the  would 25  feet  be  feet  excess  increased  side  day  days.  raising to  20  23 a n d  of  the  no  analyses  factors  Also  of  o b t a i n e d when t h e  reduced  continued  increase  assumed  pressures  2  arc.  1.89  the  condition  found between  section.  raised  next  of  occurred  September  have  the  c o n s t r u c t i o n would  embankment  9  in  23 f o r  Pressures  elevation  of  manual  o c c a s s i o n when t h e  f i l l  period  the  Analyses  embankment  a f i l l  25 i s  been  the  Pore  only  further  date  for  Stability  the  same  safety  normal  equipotentials  for  from f i g u r e s  the  on f i g u r e  are  generally  for  of  tabulated  difference 2.28  difference analyses  f i l l  Figure The  manual the  of  pore  from  35. 15 t o  20 f e e t .  25 f o o t with  f i l l  the  excess changed pore  22  15 t o  Using  for  27  arcs  for  and  the  the  no  stresses  safety  safety  of the  operation  the  f i l l  greater for  increment  of  as  the  f i l l  on f i g u r e s  in  shown these  height  of  excess  pressures  1966.  field  15 are  of  The  time  only no  of  figure  reduced  was  the  informed until  the  September  measured  excess  pore  and  the  factor  23  additional the  1966  dis-  stopped  during  23,  that  the  time  September  4 were  minimum,  contractor  a small  the  respectively.  indicated  after  by  26  normal  3 and  1.31  below  factors  condition.  2,  stopped  pressures  the  and  office  1.25.  1,  analyses  safety  effective  arcs  s h o u l d be  At  the  were  the  3 was  placed  of  arcs  give for  of  stability  pressure  arc  than  the  equipotentials  to  pore  s e a s o n were those  pore  1.21  a period  material  as  the  are  1.26,  for the  excess  Of  great  1.42,  and  resumed work  construction  measured  values  in  on t h e s e  factors  factor  when he f i l l  the  pressures  projected  tabulation  described  be  1.25  was  for  pore  and  for  used  pressure  safety  computed t o  of  f i l l  excess  normal  sipation  pressures  occurred  These  arcs  total  construction  as  the  pore  of  that  equipotentials  excess  allowable  pore  excess  20 f e e t  25 f o o t  the  The  his  at  feet.  the  f i l l  The  the  increase  shows  25 f o o t  stresses.  of  f i l l  excess  26.  method p r e v i o u s l y  then  sum o f  20  and the  Figure  the  the the  on f i g u r e  of. the  projected  pressure  pressure  shown  the  of  from  through  for  was  top  pore  The  and  quantity  1967 pressures  safety  36. factors 5.  as  the  f i l l  was  C o m p a r i s o n of  being  built  Measured  were  always  and T h e o r e t i c a l  above  1,25,  Excess  Pore  Pressures As pore  previously  pressures  stresses be  used  and  were in  the ment  obtained  future  in  l o a d was  pressure  the  U,  at  by  $  and  inplace the  value  of  foundation  caused  distribution  Two  this by  on f i g u r e  pressure  on f i g u r e  of  of  f i l l  per  cubic the  foot  f i l l of  by  the  of  to  measured the all  embankpore  is  water  27 indicated  reasonably  assumed f o r stresses  were  found  to;  design in  the  from  the  Excess  from the  theoretical  f i l l  shown  as  the  close  U computed.  are  the  excess  material  be  of  guide  using  foundation  vertical  20 f o o t  20 f o o t  the  on p a g e  to  excess  Assuming that  weight  f i l l  12 a n d v a l u e s  the  the  unit  the  equipotentials for  in  a  of  made  caused  water  defined  value the  pore  the  the  135 pounds  Using  pore  tests  weight  purposes.  equation  is  density  unit  is  w  was  stresses  point  As  a comparison  12.  using  distribution  purposes.  pressures  the  any  where  Field  problems  vertical  analyses  a theoretical  , -from f i g u r e  carried  head,  stability  design  pore  stresses,  increase  for  design  excess  no  from  attempted  theoretical  vertical  stated  stress  dashed  lines  24. significant  theoretical  excess  differences  pore  pressure  between  the  measured  equipotentials  for  and  the  37  20  foot  f i l l  are  evident  excess  pore  in  foundation  the  variation tion  of  pressures  could  w o u l d , be of  the  laminations above  in  the  and between  clays.  This the  by  theoretical  The  vertical  stress  pressures  with  the  measured  pressures  indicated  should  the  have  sand  lenses  observed  soils  were  continuous  along  which  the  f i l l  and  the  depend but  the  could value  of  reason of  the  layer  measured  This  false  load this  assump-  made  the  to  the  The  horizontal  act  layers  for  variation  foundation.  be  as  of  stiffeners  silts  the  f o u n d a t i o n would  at  any  point  the  below  under  the  toe  theoretical  in  the  they  samples would  pore  excess  of  that  This  and tend  t o  indicated  caused  by  rather  upon  the  pressure  gradient  f i l l  the  the  compared  horizontal  foundation  drainage  under  pressures  stresses  excess  distribution  appears  the  paths.  high  the  If  provide  pressures  pore  of  stress  developed.  dissipated. the  relatively  upon  drainage  the  and  not  these  actually  f i l l .  for  theoretical  of  is  been  excess be  to  the  analysis.  second v a r i a t i o n  pore  the  part  flexible  strengthening  those  of  f o u n d a t i o n would more  First,  embankment  nature  gravelly  the  reduce the  Another  surface  than  in  applied  anisotropic  24.  center  attributed  analysis.  the  higher  the  instantaneously  theoretical  effect  are  below  be  on f i g u r e  the  the to  paths  center be  under  the the  applied  developed  of case  toe  load  along  38, 6.  Safety The  defined  Factors  for  restrictions the  contract  contractor  was  allowed  any  above of  the  was  placed  other  from  pressures  that  occurred  these  as  28.  the  the  first  such  required  to  assure  noted  one  21 t o  from  23.  20 f o o t  that  the  of  f i l l  20 f e e t  material  the  placement  the  stability  first  20 f e e t  September  2 to  Assuming that  f i l l  without  the  interruption  values  for  sum o f  values  of  the  excess  12 a n d  the  increase  the  on S e p t e m b e r 21  and  uninterrupted  The  stability  had  a factor  analyses of  safety  23.  excess  of  pore  Equipotentials  construction for  of  12  reasonable  September  for  were  of  previously  the  construction  rate  2 periods,  between  embankment  arc 1.50  are  shown  7 using  these  as  shown  on  25.  The shown  the  measured  equipotentials figure  be  pressures  on f i g u r e  with  14 d a y s  might  pressures  build  September  of  pore  of  in  had b u i l t  a period  to  As  Fill  specifications  regulated  embankment.  contractor in  he w i s h e d  20 f e e t  the  f i l l  rate  20 F o o t  regarding  in  at  the  factors  on f i g u r e  distributions  of  of  safety  23 w e r e excess 1.  the  for  the  pore  the  the  of  the  20 f o o t  following  f i l l  four  pressures:  excess  pore  pressures  23 a n d shown  estimated  on f i g u r e 3.  arcs  computed f o r  September 2.  the  pore  measured  on f i g u r e  pressures  on  24.  shown  28.  condition  of  no  excess  pore  pressures.  39. 4.  t h e d i s t r i b u t i o n of e x c e s s  pore  pressures  b a s e d on t h e t h e o r e t i c a l s t r e s s a n a l y s i s . The  t a b u l a t i o n of f a c t o r s of s a f e t y f o r t h e s e  t i o n s i s g i v e n on f i g u r e 7.  29.  r e v i e w i n g t h e s a f e t y f a c t o r t a b u l a t i o n and  l o c a t i o n s i n the foundation  f a c t o r s of s a f e t y were o b t a i n e d Deep a r c s s u c h as the excess  3 and  8 had  pore pressure  First  lower  f o r the shallower  arcs.  distributions.  Several  p a s s i s d e f i n e d o n l y i n terras o f an a n g l e  for  8 had  t h e c o n d i t i o n o f no e x c e s s  expected  but  shown n o t  t o be  the  the  of  internal  should  t h e most c r i t i c a l .  a r c s had  the lower  was  at  felt  This  was  safety factors  zone i n t h e f o u n d a t i o n w h e r e a c r i t i c a l  i n the area  therefore,  be h i g h e r  some c o n c e r n  i n f o r m a t i o n a b o u t t h e d e v e l o p m e n t of e x c e s s was  arcs  case.  Second, the s h a l l o w e r and  which the  p o r e p r e s s u r e was,  s i n c e the pore pressures  t h e d e e p e r a r c s m i g h t be  foundation  the h i g h e s t s a f e t y f a c t o r s  d e p t h u n d e r t h e c e n t e r of t h e f i l l that  inves-  f a c t o r s of s a f e t y  s t r e n g t h of t h e s o i l s t h r o u g h  T h a t a r c s 3 and  fill  adequate s a f e t y f a c t o r s f o r  i n c r e a s e w i t h d e p t h of a r c p e n e t r a t i o n i n t o t h e  friction.  the  the  t i g a t o r s h a v e shown t h a t s t a b i l i t y  the shear  Fill  o f t h e a r c s f o r t h e 20 f o o t  s e v e r a l p o i n t s of i n t e r e s t w e r e n o t e d .  if  distribu-  D i s c u s s i o n of S a f e t y F a c t o r s f o r t h e 20 F o o t In  all  four  pore  need f o r pressures  30 f e e t , b e l o w t h e g r o u n d s u r f a c e b e l o w  o u t s i d e t h e t o e of t h e f i l l .  With a l l the  piezometers  and  40. located  below  the  excess  had  to  arc  be  pore  towards  on a s s u m p t i o n s lowest  safety  6 using  the  excess  pore  feet.  20  developed with This  by  the  design  should  not  have  A  factor  construction  and September tentials  shown  tion  of  been  shortened  f i l l  the  instead  of  22,  and  23.  for  a  only The  for  total  time  required that  construction  period.  have  been measured  in  7 day  those  The  construction  were  is  of  the  for  specifications to  (September  1 to  drawing  a  9 feet  period  full  excess  function  the  20 f o o t  pore f i l l  therefore, to  safety be  of  less  arc than  of  same the  3  of  feet f i l l 21,  regardless amount  length  been  of  which  in  and  of the would  constructed  greater  6 assuming 1.15  have  pressures  had been  have developed for  could  pressures  have  12  September  the  feet.  construc-  rate  pore  the  20  equipo-  20 f e e t  placed  s h o u l d be  excess  the  uninterrupted  the  in  minimum  construction  this  for  assumed  the  construction  The  p e r i o d would  data.  construction  below  contract  14 d a y s  the  f i l l  construction while  estimated  factor  the  Actually  height  period would,  which  period.  if  was  assumed i n  upper  occurs  on f a c t u a l  were  used  for  area  which  increase  embankment  dissipation  a  the  critical  pressures  of  if  had been  than  f i l l  o b t a i n e d was  28 f o r  7 days  this  the  1.15,  and  f i l l .  of  factor,  safety  was  figure  to  day  given  the  on  in  rather  unrestricted  23)  20 f o o t  per  of  period  21 t o  center  uninterrupted  criteria  allowed  the  distribution  the  to  of  and  Third,  have  of  zone  pressure  based  would  set  this  the a  than  14 7  day  day  possibly  41. m i g h t be l e s s t h a n o n e . 8,  Discussion  on t h e L o c a t i o n s  Selected  f o rthe  Piezometers In the design in  the foundation  s t a g e t h e l o c a t i o n s of t h e p i e z o m e t e r s  were s e l e c t e d u s i n g  d i s t r i b u t i o n as a g u i d e .  the t h e o r e t i c a l s t r e s s  As d i s c u s s e d  above, t h e measured  and  t h e o r e t i c a l excess pore pressures  and  t h e p i e z o m e t e r l o c a t i o n s s e l e c t e d were not p a r t i c u l a r l y  w e l l suited f o r developing  the excess pore pressure  b u t i o n u n d e r t h e 20 f o o t f i n .  ment o f p r e s s u r e s  i n a shorter  stability  of t h e f i l l  the  stability  analyses  time p e r i o d with  the develophigh  i s open t o c o n j e c t u r e .  f o r t h e 25 f o o t f i l l  j e c t e d excess pore pressures,  locations  embankment s e c t i o n h a d  of a magnitude s u f f i c i e n t l y  the  distri-  Whether t h e s e l e c t e d  w o u l d have been adequate i f t h e f u l l been c o n s t r u c t e d  d i d not agree t o o w e l l  t o endanger Reviewing  with  the pro-  a r c 3 w h i c h had t h e l o w e s t  f a c t o r o f s a f e t y , 1 . 2 1 , i s i n t h e same r e l a t i v e p o s i t i o n t o the  t o e o f t h e 25 f o o t  20 f o o t f i l l .  fill  Assuming that excess pore pressures  d e v e l o p e d under t h e f u l l in  as a r c 6 i s t o t h e t o e of t h e  embankment s e c t i o n an a r c l o c a t e d  t h e same r e l a t i v e p o s i t i o n t o t h e f u l l  arcs  had  3 a n d 6 a r e t o t h e 20 a n d 25 f o o t  fill  fill  s e c t i o n as  s e c t i o n s and  h a v i n g a 120 f o o t r a d i u s w o u l d be t h e c r i t i c a l  arc.  arc would pass through the foundation  above  slightly  This  p i e z o m e t e r s 2 a n d 4 and 20 o r 25 f e e t b e l o w p i e z o m e t e r s 3 and one.  The p o r e p r e s s u r e s  along  t h e p o r t i o n of the a r c  42. under tion the  the about  toe  and  arcs  are  shown  be  the  3 and  letters,  of  the  the  The  proposed locations  developing  depth  beneath  where  none  9.  the  The  the  excess  the  construction  by  pore  a dashed  that  would  occurred  toe  Pore  Two c u r v e s 22.  for  of  line have  during  for  this  the  the  arc  informaoutside  figure,  points  of  the  f i l l  with  Pressures  the  and  indicated  by  would  known p o r e  piezometers A,  f i l l  respectively,  which  pressure  outside  indicated  60 f o o t  f i l l s ,  locations  pore  area  available  Pressure  factual  piezometers  25 f o o t  on  of  excess  critical  was  Excess  through  Also  distribution  the  no  along  arc  proposed piezometer  use  in  installed  20 a n d  30.  for  provide  but  distribution  assumed c r i t i c a l 6 for  a better in  defined  available.  on f i g u r e are  be w e l l  pressure  locations  numbers,  given  would  the  would  The by  f i l l  have  pressures  equipotentials. B,  at  3 points  and C a  shallower  of  locations  would  known  pressure  actually  used.  D e v e l o p e d A s s u m i n g No  Dissipation are  plotted  curve  shown  pressure of  the  a  if  the  f i l l  was  built.  In  fact  that  the  piezometers  with  an i n c r e a s e  solid  the  The  excess  pore  developing.the  in  reading  15  a plot  other  of  of  during indicated  pressure  heads  pressures  which  dashed  responded almost  pressure  is  measured  f i l l .  period  figures  line  no d i s s i p a t i o n  construction  foot  of  actually  20 f o o t  developed  in  as  heads  represents  the  on e a c h  the  curves  had  20 the  instantaneously  when f i l l  material.:  43. was  placed  and  a decrease  placing  stopped  divided  into  the  two  pressure  period  and  allowed  decreasing with materials  were  period.  If  pressure  •§- a d a y  after  a  reasonable  occurred between  value  for  the  pore  pressure  the  19,  29  one  pore  be  and  equal  tion  the  day  h e a d was  to  which  which after one  again  •§• a d a y  12.5  feet  before  the  one  occurred  for  In  22, was, this  each  one  day  and as  the  time  the  shown  on  by  pie-  as  On  dissipating. September  •§• a  assumed of  the  29  of  period,  amount  period  the  after  amount  therefore,  manner  that  increasing.  but  The  day  and  then  from  and a f t e r  occured  the  difference  measured and  the  dissipation  before  example,  feet  in  dissipation the  head  f i l l  represent  For  foot.  foot.  the  before  one  September  in  obtained  dissipated in  of  were  measured  -§- d a y  12.5  construction  heads  measurement  be  values  pressure  22 w a s  if  again  amount  curve  the  which  period.  assumed t o  chosen.  pore  period,  head  be  for  p e r i o d when no  pressure  the  to  curve  p e r i o d •§• a d a y  head  the  the  pressure  p e r i o d would  head  excess  pressure  dissipation before  day  5 on S e p t e m b e r  September  the  for  one  figure  the  material  heads  representing the  is  day the  of  dissipation  head  of  of  measured  be m e a s u r e d  this  portion  or  p r e s s u r e when  portion  pressure  one  assumption  pressure  the  a  time  particular  In  of  in  dissipation  zometer  placed  pressure  the  of  increasing  period will  average  The  represented  being  this  curve  p o r t i o n when  time  A particular construction  were  other  measured  the  portions.  heads  the  in  day  to  dissipapore  44, pressures The  steps  had been curves tion a  were  found.  used,  the  amount  excess  versus  2.3,  was  obtained,  of  5 day  increasing once  to  derive  pore  time  are  pressure shown  p e r i o d when t h e  4.0,  and  the  in  head  head the  measured  1.  daily  values  dissipation to  corrected  following heads  plot  for  the  dissipa-  tabulation  were  zero,  for  1.0,  6.0.  Measured excess V a l u e of excess pore pressure pore pressure dissipated heads 0 0  Day  of  Value of excess pore p r e s s u r e head f o r c o n d i t i o n of no d i s s i p a t i o n 0  2.  1,0  ,3  1,0+  ,3  3..  2,3  *5  1.3 +  (2*3-1.0)+ .5  =  3,1  4.  4,0  ,8  3.1  +  (4.0-2.3)+  =  5,6  5.  6.0  1,2  5..6  + ( 6 . 0 - 4 . 0 ) + 1.2 = 8 , 8  Using  this  heads  for  for  each  foot  '  method the the  values  condition  piezometer  for  the  excess  pore  no d i s s i p a t i o n were  the  construction  1,3  .8  pressure determined  period  of  the  20  f i l l .  10-.  C o m p a r i s o n of  Pressure  and T h e o r e t i c a l One  of  the  pressures  that  the  f i l l  time  for  dissipation  obtained  by  from load  the  were  was of  about  true,  made  applied pore  the  A s s u m i n g No  Dissipation  Heads  theoretical  theoretical  assumptions  discussed  the  Heads  Pressure  assumptions  pore  other  of  of  =  in  obtaining  stress  excess  distribution  instantaneously  pressures.  the  The  allowing  pressure  no  heads  stress  distribution  if  stress  distribution  previously  s h o u l d have  been  in  reasonably  all  was  the  close  45. agreement w i t h t h e v a l u e s of t h e e x c e s s corrected  f o r the d i s s i p a t i o n that  tion period. Piezometer  The f o l l o w i n g  pore  pressures  occurred i n the c o n s t r u c -  i s a tabulation  of these  pressures.  Excess pore p r e s s u r e head f r o m f i g u r e s 15 t h r u 22 f r o m t h e o r e t i c a l Column l i 0 0 f o r c o n d i t i o n o f no s t r e s s d i s t r i b u - Column 2 d i s s i p a t i o n ( c o l u m n 1) t i o n (column 2) x  1  18.5  6.9  2  16.0  32.0  3  32.0  41.1  77.9  4  22.5  40.2  56.0  5  33.0  42.9  77.0  6  23.2  39.3  59.1  7  21.1  41.1  51.4  8  28.1  42.4  66.3  9  16.7  34.6  48,4  10  ' 15.0  268.0 -  6.05  50.0  248.0  As i n t h e p r e v i o u s c o m p a r i s o n of measured and t h e o r e t i c a l pressures and  the greatest v a r i a t i o n occurs  10 u n d e r t h e t o e o f t h e t i l l .  readings indicates  are again less  The r e s t  1  of t h e measured  than the t h e o r e t i c a l  analysis  they should be.  I n t h e R' t r i a x i a l pressure  at piezometers  t o the deviator  tests  the r a t i o of the induced  stress  f o r one o r 2 p e r c e n t  pore  axial  s t r a i n s r a n g e d f r o m .4 t o .8 w i t h an a v e r a g e v a l u e o f approximately  .6.  For strains  of t h i s r a t i o d e c r e a s e d .  above 2 p e r c e n t  I n some o f t h e t e s t s  the value the decrease  46. was  oniy s l i g h t while  to a negative head l i s t e d be  value.  stress.  i n c o l u m n one  of t h e  preceding  comparable t o the v a l u e s laboratory  fill  r a t i o of  table gives  tabulation  of p o r e the  laboratory  20  5 e q u a l t o 33.0 or 43.27  the v a l u e s  of t h i s  load  deviator to  a  foot  fill  .762.  The  ratio for a l l  Piezometer  Column one 43.27  1  .427  6  .536  2  .370  7  .488  3  .740  8  .649  4  .520  9  .386  5  ,762  10  .347  .  The  r a t i o of p o r e p r e s s u r e s  for  the  triaxial  c o n s t r u c t i o n have about the Whether t h i s  reasonably,  t o r y t e s t r e s u l t s and could the  not  be  developed t o the  t e s t s a t low  s t r a i n s and  same r a n g e and  f o r the  w e r e unknown.  load  fill  average  f i e l d m e a s u r e m e n t s has  determined s i n c e the  foundation  applied  good a g r e e m e n t b e t w e e n t h e  the  may  pressure  applied  i n weight to the  the p i e z o m e t e r s . Piezometer Column one 43.27  in  pressure  t h e h e a d s f r o m c o l u m n one  f o r piezometer  following  t e s t s and  compared t o the  column of w a t e r e q u i v a l e n t w o u l d be  decreased  of e x c e s s p o r e  foot The  ratio  values  developed i n the 20  t e s t s the  The  considered  of t h e  i n other  any  value. laborameaning  a c t u a l s t r a i n s developed  47.  Chapter I I I 1.  Summary and C o n c l u s i o n s The r e s u l t s o f t h e Q a n d R t e s t s w e r e s o i n c o n s i s t e n t  that the determination in stability  of shear  a n a l y s e s was e x t r e m e l y  o f t h e R' t e s t s , a l t h o u g h considered tests.  s t r e n g t h parameters f o r use difficult.  The  results  some v a r i a t i o n s w e r e n o t e d ,  t o be more r e l i a b l e  than those  were  o f t h e Q and R  Because of t h e i n c o n s i s t e n c i e s f o u n d i n a l l t h e  t e s t r e s u l t s the shear  parameters s e l e c t e d were t h e lower  o r more c o n s e r v a t i v e v a l u e s . p a r a m e t e r s and t h e e x c e s s  By u s i n g t h e R  1  shear  strength  pore p r e s s u r e s measured as t h e f i l l  was c o n s t r u c t e d i n s t a b i l i t y  analyses  b e t t e r c o n t r o l of the  embankment s t a b i l i t y was p o s s i b l e t h a n i f t h e Q o r R  shear  p a r a m e t e r s a l o n e had been used. The e x c e s s  pore pressures  developed  and m e a s u r e d i n  the f o u n d a t i o n d i d not agree t o o f a v o r a b l y w i t h those the t h e o r e t i c a l s t r e s s d i s t r i b u t i o n i n d i c a t e d should been d e v e l o p e d .  The e x c e s s  d i s s i p a t i o n at the f i l l  pore pressures  t o e w e r e 2.5 t i m e s  as h i g h as those  from the s t r e s s d i s t r i b u t i o n w h i l e the pore  pressures  c o r r e c t e d f o r d i s s i p a t i o n under t h e f i l l values.  have  corrected f o r  estimated  f r o m |- t o 5. o f t h e e s t i m a t e d  which  were  C o n s i d e r i n g the  r a n g e o f t h e v a r i a t i o n s b e t w e e n m e a s u r e d and e s t i m a t e d pore pressures  t h e o n l y r e l i a b l e method o f d e t e r m i n i n g  pore pressures  i s by i n s t r u m e n t a t i o n .  48^ The measured pore when u s e d i n than  those  estimated  from  pressures could,  the  the  from  analyses  of  dation  to  analyses least  measure one  are  pressures  The  use  the  when a unsafe  of  a  excess f i l l  side  pore  is  built  and  embankment.  excess  piezometer  installed pore  the  maximum f i l l  embankment  and  at  tion. this  In  thesis  a depth  that the  the is of  selected  a  case  written 20 w o u l d for  the  characteristics  been  responsible  pore  pressures  and Bishop  and  at  of  the  stress pore  toe  the  is  been  a f i l l  distributions  ,  from can  dissipate.  the in  as  in  a distance toe  of  the  founda-  feet  location  than  fact  that  f o u n d a t i o n may the  the  measured  generally the  pore  at  the  30  of  d i s c u s s e d by  c a u s e d by  stability  which  The  of  of  foun-  on  distance  particular  variations  at  depth  piezometer.  those  use  embankment  distribution  be  for  a better  recognized and,  Bjerrum  pressures  this  the  shallow  horizontal  have  embankment  outside  particular  outer  of  for  a  an  installed  height  relatively of  in  pressures  s h o u l d be  half  as  an  lower  Recommendations When p i e z o m e t e r s  at  on t h e  dissipation  factors  the  predict  develope  errors  stability  using  to  for  safety  distribution.  actually  cause  corrected gave  distribution  will  therefore,  analyses  stress  stress  which  jeopardize 2.  stability  obtained  theoretical  pressures  have excess  Kenny~  pressures  expected  based  movement  of  on  water  49,  These authors t o e of a f i l l  may  suggest o r may  upon t h e c h a r a c t e r i s t i c s was  t h a t the pore p r e s s u r e s at  not  i n c r e a s e w i t h time  depending  of t h e f o u n d a t i o n s o i l s .  As  f o u n d a t i o n i n c r e a s e d b u t when p l a c e m e n t  t h e p o r e p r e s s u r e s b e g a n t o d i s s i p a t e and The  increase with  noted  u s e d was  i n a l l p r o b a b i l i t y t o o c l o s e t o t h e t o e of  fill  at the t o e .  no  stopped  t i m e was  t o d e t e c t whether or not  by B i s h o p piezometer  If  permit  occur  and  the  proposed  a.more-suitable  necessary  instruments  then  stress,  s h o u l d a l s o be  installed  a b e t t e r d e t e r m i n a t i o n of the b e h a v i o r  f o u n d a t i o n as t h e embankment i s c o n s t r u c t e d . . particular f i l l  foundation discussed i n this  most s o f t f o u n d a t i o n s  For  and  in  l o a d i s a l l the i n s t r u m e n t a t i o n  that a s t a b i l i t y  f a i r u r e does not  occur.  laboratory  the r e l a t i o n s h i p s between the a p p l i e d  s t r e s s e s , s t r a i n s and  induced  pore pressures  p a r t i a l l y w a s t e d s i n c e t h e q u e s t i o n "Do duplicate f i e l d  the  thesis  the expense e n t a i l e d i n p e r f o r m i n g  t e s t s to determine  the  pore pressures developed  the f o u n d a t i o n under the f i l l  Nevertheless  ot  t o r g r a n u l a r embankments p i e z o m -  e t e r s t o measure the excess  required to assure  the  effect.  are thought  settlement  location  the type of i n c r e a s e d i s c u s s e d  l o c a t i o n w o u l d have been i n  piezometers  s t r a i n and  outer piezometer  and K e n n y d i d o r d i d n o t  p o s i t i o n f o r measuring t h i s  for  fill  b e i n g p l a c e d the p o r e p r e s s u r e s measured i n t h i s  particular  to  the  i s at  least  laboratory tests  c o n d i t i o n s ? " remains unanswered.  Two  50 questions, pore  pressures  stress have  verified  and  in  the  possibly  instruments  the  those  that  c o m p a r i s o n of  could  caused  distribution?"  l o a d were the  "What  order the  have  had been  determined  and  the  variations  "Would  between  from  field  the  c a u s e d by  the  of  2 percent  as  1 or  field  been  and  laboratory  answered  if  stress  measured  theoretical  strain  strains  the  measurements embankment  indicated pore and  by  pressures?", strain  used.  1.  Kenney, T . C . , " P o r e P r e s s u r e s and B e a r i n g C a p a c i t y of L a y e r e d C l a y s " , J o u r n a l of the S o i l M e c h a n i c s and F o u n d a t i o n s D i v i s i o n , A S C E , V o l . 9 0 , N o . SM4, J u l y 1964, pp. 27-55.  2.  B i s h o p , A . W . a n d B j e r r um, L . , "The Relevance of the T r i a x i a l T e s t t o the S o l u t i o n of S t a b i l i t y Problems", P r o c e e d i n g s , A S C E R e s e a r c h C o n f e r e n c e on S h e a r Strength of C o h e s i v e S o i l s , B o u l d e r , C o l o . , 1 9 6 0 , p p . 437-501.  Bibliography B i s h o p , A . W. a n d B j e r r u m , L . , " T h e R e l e v a n c e o f t h e T r i a x i a l T e s t t o the S o l u t i o n of S t a b i l i t y Problems", P r o c e e d i n g s , A S C E R e s e a r c h C o n f . on S h e a r S t r e n g t h of Cohesive S o i l s , Boulder, C o l o . , 1960, pp. 437-501.  .  . B i s h o p , A.W. and H e n k e l , D . J . , "The Measurement of Soil P r o p e r t i e s i n the T r i a x i a l T e s t " , 1964, Edward A r n o l d . Kenny, T . C . ^ " P o r e P r e s s u r e s and B e a r i n g C a p a c i t y of L a y e r e d C l a y s " , J o u r n a l of t h e S o i l M e c h a n i c s and F o u n d a t i o n s D i v i s i o n , A S C E , V o l . 9 0 , N o . SM4, J u l y 1 9 6 4 , pp. 27-55. " L a b o r a t o r y S o i l s T e s t i n g " , EM-1110-2-1906, 1965, Manuals - C o r p s of E n g i n e e r s . "Stability of 1960, Manuals  E a r t h and R o c k f i l l Dams", EM-1110-2-1902, - Corps of E n g i n e e r s .  Scott, R.F., "Principles Addison-iAfesley.  of  Soil  Mechanics",  T e r z a g h i , K. a n d P e c k . , R . B , , "Soil P r a c t i c e " , . J o h n lA/iley a n d S o n s .  Mechanics  1963, in  Engineering . '  BRITISH  GREAT NORTHERN LINE CHANGE  COLUMBIA  p  >i... . t i .  GRADING CONTRACTS Figure 1  LOG  r~ OL Id  OF HOLE  ML,.'  0. *"/ G r a v e l  WATER  LIMITS LL . PI  :  ML-CL  23  4  B  CL  2.8  9  D  ML-CL, CL  23,27  E  ML-CL, C L  F  CL  H  ML-CL,CL ML-CL,CL  '23.26,  5,10  j 2.4,28  4,11  CL  25,28  S,©  I  G5-DD-79Z  CONTENT  D R Y UNIT WEIGHT  AO  */  80  F T  90  3  IOO  no  5,9 4,10.  l&  IO  /  M  CL  N  ML-CL  O  ML  •26,39,42 8,15,16  1"" IN.P  P  s T  7  -  N.PZ3  CL  22,37  S,IS  CL  124,30  8,io  V X  CL  \zz  Y  GL  CL  '  26,31  13 10,13  M L - 5ILT, ML, *". -  N=E3  Gravally  CLAY,  N = NUMBER  M L - C L - SILTY C L A Y ,  BLOWS SCALE  STANDARD  G V L - SILTY  PENETRATION  GRAVEL  TEST  f=10V  Figure  2  1 •  ^4 /  z  \ \  if)  in LU  ^6  cr  \  h  (/)  or <  -2  I  jcE  B  .6  ^-O  5TRENGTH  ENVELOPE  L  x—-  ____  \  * Y  xT  ~x  L  I  2 .  • Tl  era c  Y  V  m  S U M M A R Y  3 .. O F  •.  N O R M A L Q  T E S T  4-  5  S T R E S S  T O N S /  R E S U L T S  F  T  2  T)  M»  era  c  H  3  NORMAL •,  -  . SUMMARY  5  A-  STRESS OF  R  TONS/c-rZ TEST  RESULTS  6  7  .  8  9  ENVELOPE 1 ENVELOPE  5,4  G  3  E  = TOTAL  S T R E 5 5 E S  i <S' «= E F F E C T I V E S T R E S S E S X< = P O R E P R E S S U R E 3  N O R M A L  S T R E S S  J 5 P E R C E N T  10 A X I A L  1. 15  t 2 0  ' S T R A I N  Figure 6  * , ' --•6  in m tcn  CQ OLA  «»  7 ^  4  AXIAL  £  STRAIN'  a  EFFECTIVE NORMAL  13^7 A X I A L  Z  12  io  A-  S  '  8  STRAIN  IO  EFFECTIVE NORMAL STRE55  5TRE55  - - 6t IA  in I-  4  <  UJ  2  4  6  8  EFFECTIVE NORMAL STRESS  OP  c rb  17"% A X I A L  STRAIN  12  10 :  -'• .'• EFFECTIVE NORMAL STRESS  12  MAXIMUM  PRINCIPAL  EFFECTIVE  STRESS  UJ  1/1  —T-  N  + H  —TT  +.  m o  I  "1  + or + • + 7) 0  + H  _+ + xl  H  + X  £  O  +•  RATIO  4Q' FILL - ARC 5 *]. S C A L E  I" = 4 0 f  „ '  1  Ys»TliS-oo  z o n e i (FIL.O ZOHE 2 ZONE 2 2 0 HE 3  A  B  c  V  30.oo  o  2.16  35.00  o  Z.OB  72.50  SS.oo.  a  1.16  6 0.00  ZB-oo  0  0.16  •'  '  /3d.00  -T»='l.4£5CONVERSION F A C T O R A I INCH' »(20'y20'yg.Z.4%T >)„ l  FRICTION'  ' ••.  ?tj$ ' •  ' DRIVING,. .  ., -  {.9.34(6 - \.16S) as" - is 5  r.75. (T^Has')" • i . a x f , -  o.lfl  (TAN 3 5 * ) »  I72,0>5\  6.1 it 11.0 0  1  1 1 . 0 0 1 - (25" )=»7S-. 0 1 5 " K  FACTOR F  '  5  \  OF SAFETY  zTf  I U . 0 1 5 -: r »° ,  t  Figure  f T D  .GRADE  <OC T.  9, 1967.'  '•4 2LL  25  \C»,  CS  PI  LL PI u.*  LL PI 215 104.1 19 ZOA 31 IZ 52.0 S3.%J  £9.2 2C.440.1  3  LL PI  LL PI S« 7*  15  2-> B  31  *p  i 241 23.5  ss.s  2*3 £1.1  «l •)5.I  >*5 LL P I  '•»•»  28  ZZ.t  2LI IM  4»  LL PI  NP  eo.* 33 12 29.T ST 17 2*6  to  ix.s  LL  m  &  Ml  11  LL 21 *LR  1  P I ur'1 to SO.I 24.4 24.4  *p  1  s  z«  PIEZOMETER 4  c II ro  fp  O S 7 liV I  <.  21.4 *-•» S9.4 19.0 III.O rz.4  •  .  PI  PIEZOMETER" LOCATIONS $ . D A T E 5 " 0 F FILL' CONSTRUCTION S C A L E  l"»**0'  NUMBER.  LOCATION  2  ^ =  [a ( 0 ( 4  2  F R O M  + <*')  6  " P R 1 N C I P L . E S I N  T  H  B R I D G E P U B L I C  E  O F  4  B R  U O  T A  M D  (  S O I L  D E S I G N A  lr  E S  N ,  S  - <*' )J  +x  M E C H A N I C S  O F T  <A+  "  D E C .  ,  R E T A I N I N G B Y  L . A .  I N V O L V E D W A L L S  £  P A L M E R ,  ( V O L .  \ %  N O .  io)  F i g u r e 12  TOTAL' PORE PRESSURES MEASURED BY P I E Z O M E T E R S IN R 5 . I .  3 NOV. 1,1966 /  y'^^ /  h  UJ LJ  LL  7.  10  .  PORE P R E S S U R E FOR  70  s o  CORRECTED  DISSIPATION  /  P  PORE PRESSURE Y PROJECTED. FOR 2 S' FILL  <L  LU I  "GO  5  ACTUAL PORE  ZO  30  MEASURED PRE5SURE.  ,  PIEZOMETER *IO PORE  /  PRESSURE  CORRECTED DISSIPATION!  NOV. 1,1966  FOR ;  — —  PROJECTED PORE PRESSURE FOR 2 5 ' FILL  ACTUAL MEASURED PORE PRESSURE  . . Y Y  J-OCT.-I, I9G6  •'. |-5EPT. |}|9C6 10  ZO  30  TIME DAYS PIEZOMETER * 1  40  50  GO  F i g u r e 15  20 PORE FOR  PRESSURE  CORRECTED  DISSIPATION  15  UJ  o  GO  80  70  "PROJECTED PORE PRESSURE FOR 25' FILL  UJ  -X  ACTUAL MEASURED PORE PRESSURE  30 TIME DAYS PIEZOMETER *9 PORE FOR  PRESSURE  40  CORRECTED  DISSIPATION /  70  GO  80  /  +  m  '  u.  PROJECTED  FOR  PORE  PRESSURE  25* FILL  ACTUAL PORE  MEASURED PRESSURE  Q  UJ  5  I •  L  S E P . I, 10  1966 . 20 TIME  •  30  40  50  60  DAYS  PIEZOMETER *2  F i g u r e 16  35  f—PORE j  FOR  PRESSURE DISSIPATION  CORRECTED :  | + — PROJECTED PORE PRESSURE, I FOR 25' FILL  PIEZOMETER *3 F i g u r e 17  PORE PRESSURE CORRECTED FOR DISSIPATION  /.  / /  '  / /  iPROJECTED PORE PRESSURE / FOR  25' FILL  /  GO 70 ACTUAL MEASURED PORE PRESSURE  30  40  50  60  GO  TIME - DAYS . PIEZOMETER * 4  F i g u r e 18  35  (——PORE PRESSURE CORRECTED I FOR DISSIPATION  10  20  ' TIME  30  AO  DAYS  PIEZOMETER  ^5  50  GO  PORE PRESSURE CORRECTED FOR DISSIPATION-  PROJECTED PORE PRESSURE FOR 25* FILL  f  60  so  MEASURED / V-ACTUAL PORE PRESSURE  A  10  70  /  20  30 TIME  DAYS  40  50  60  P I E Z O M E T E R *Q>  F i g u r e 20  25r PORE PRESSURE CORRECTED FOR DISSIPATION  /  7  PROJECTED PORE PRESSURE FOR 25* FILL  r  . / / •  /.  80 ACTUAL MEASURED PORE PRESSURE  20  30 TIME DAYS  PIEZOMETER *~7  F i g u r e 21  30/  /  /'.  I  I I  I -PORE PRESSURE CORRECTED FOR DISSIPATION  TIME  D A Y S  PIEZOMETER  *8  [ Figure 22  & or  S A F E T Y FACTOR  1  2.14  r\KV  +  5 +ARC U  0=  r =7  I35*/FT  CENTERS-^  2. 3 *r 5 6 7  8 +  1  3  3 0 °  '  2 . 5 ^ F T  3  0=35  tt= G O * / F T *  PIEZOMETERS  P-4  20' FILL  SCALE  l"=20'  8  2.01 2.57 2.13 2.35 • 1 . 8 4 .; 2.36 2.52  .-THIS FILL HAD NOT BEEN PLACED ON ( DATE PORE PRESSURES WERE MEASURED  .  2 0 ' FILL  PORE PRESSURE EQUIPOTENTIALS SCALE 1"= 4o'  PORE PRESSURES FROM EQUIPOTENTIALS . FROM FIG. 24 SHOWN BY "x" <£ FROM FIG. 28 BY . THE NUMBER BESIDE AN 'V OR A I S VALUE OF EXCESS PORE PRESSURE AT THAT PART\CULAR POINT ON . THE ARC.  =  .0Stan30°-T- . 3 t a n 3 5 ° + N t A n 2 & % . 0 b t a 3 5 3  e  n  4 . 8 7 - 1.89  F.5.= 2.28 NO AX F.S.= 1.89 WITH MEASURED JU (FIG. 24) F.5.= 1.50 WITH PROJECTED AX (FIG. 2 8 ) Figure  P R O J E C T E D P R E S S U R E  E X C E S S  —+5 +7  25'  SCALE  P O R E  EQUI P O T E N T I A L S  FILL  |"=4-C>  25' S C A L E  FILL r ' = Z O '  EXCESS (SUM  OF  PORE  INCREASE  AND  PRESSURE  EXCESS IN  PORE  EXCESS,  EQUIPOTENTIALS  PRESSURES PORE  OF  PRESSURES"  Z 3 , \°><i>(o) S C A L E  • |"=  40'  FOR  SERlZJ9<b6> B E T W E E N  EO'  FILL  AND SEP.  THE Z\  FACTORS OF SAFETY FOR ARC  FOR MEASURED .FOR PROJECTED NO EXCESS PORE PORE PRESSURES PORE PRE5SURE5 PRESSURES  1.  c  H  a  PORE PRESSURES FROM STRESS DISTRIBUTION  1.28  2.14  1.31  1.21  2.01  1.33  2.16  1.79  2.57  I.G5  ' 1.34  2.13  1.50  5  1.95  I-.G2  2.35  1.57  <3  1.40  1.15  1.84  1.38  7.  1.90  1.53  2.30  , ' 1-57  8  2.1 9  I.8S  I.GI  3 •  SO FOOT FILL  ^  .  '  . I.GI  ;  • •• I.8Z • "  :  G C FILL SCALE  I"-40'  

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