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

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STABILITY OF AN EMBANKMENT ON SOFT CLAY by JOSEPH STEELE VASEY B .S . , S e a t t l e U n i v e r s i t y , 1961 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the Department of C i v i l Eng inee r i ng We accept t h i s t h e s i s as conforming to the r e q u i r e d s t anda rd The U n i v e r s i t y of B r i t i s h Columbia A p r i l , 1969 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d S t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d b y t h e Head o f my D e p a r t m e n t o r b y h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s . i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t o f C i v i l Engineering The U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, C a n a d a D a t e A p r i l 25, 1969. A b s t r a c t The s o i l s engineer r e s p o n s i b l e f o r the adequacy of the design of embankments r e g u l a r l y f i n d s himself confronted w i t h the problem of c o n s t r u c t i n g an embankment upon a foun-d a t i o n c o n s i s t i n g of s o f t , p o t e n t i a l l y u n stable s o i l s . T h i s t h e s i s presents the method used t o a r r i v e at a s u c c e s s f u l s o l u t i o n t o t h i s problem and a d i s c u s s i o n of the pore p r e s s u r e s developed i n the foundation as the em-bankment was c o n s t r u c t e d . The d e t e r m i n a t i o n of the shear s t r e n g t h parameters of the fo 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 analyses and the type of s t a b i l i t y a n a l y s i s used are d i s c u s s e d . The use of e f f e c t i v e shear s t r e n g t h parameters i n the s t a b i l i t y analyses r e q u i r e d that the excess pore pressures developed i n the f o u n d a t i o n as the embankment was c o n s t r u c t e d be measured and 10 piezometers were i n s t a l l e d i n the founda-t i o n t o p r o v i d e the necessary pore p r e s s u r e data. A comparison between the measured excess pore pressures and the excess pore p r e s s u r e s that a 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 have developed under the embankment l o a d i s i n c l u d e d . D i f f e r e n c e s between the measured and t h e o r e t i c a l pore p r e s s u r e s are noted p a r t i c u l a r l y at the toe of the embankment s l o p e . S t a b i l i t y analyses u s i n g the t h e o r e t i c a l pore p r e s s u r e s gave higher s a f e t y f a c t o r s than those obtained from analyses. when compared w i t h u s i n g the measured pore p r e s s u r e s . The o n l y p r a c t i c a l method of d e t e r m i n i n g excess pore p r e s s u r e s caused by an a p p l i e d l o a d was c o n c l u d e d t o be by i n s t r u m e n t a t i o n . i i i . Tab l e of Contents . Page Chapter I 1 19 I n t r o d u c t i o n 1 2. Georaorphology of the F i s h e r R i v e r V a l l e y 3 3. S i t e E x p l o r a t i o n 4 4 . S o i l T e s t s 5 5. Embankment M a t e r i a l s 17 6. Shear S t r eng th of Sur face 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.. S t a b i l i t y A n a l y s i s Method 18 8, Sa fe t y F a c t o r C r i t e r i a 21 9, Des ign Stage S t a b i l i t y Ana l yses 22 1 0 , Type of and I n s t a l l a t i o n Method f o r the P iezometers 24 1 1 , S e l e c t i o n of H o r i z o n t a l and V e r t i c a l P iezometer L o c a t i o n s 26 12„ S t a b i l i t y Ana l y ses Us ing Es t ima ted Excess Pore P ressu res were not Performed 28 Chapter II 1. . Embankment C o n s t r u c t i o n 30 2. Pore P r essu res Measured by P iezometers 31 3. S t a b i l i t y Ana l y ses f o r the 20 Foot F i l l Us ing the Measured Excess Pore -Pressures 33 4. S t a b i l i t y Ana l y se s f o r the 25 Foot F i l l Us ing P r o j e c t e d Excess Pore P r essu res 34 5. Compar ison of Measured and T h e o r e t i c a l Excess Pore P r e s su res 36 i v . 6. S a f e t y F a c t o r s f o r t h e 20 Foot 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 the 20 Foot F i l l 39 8. D i s c u s s i o n on t h e L o c a t i o n s S e l e c t e d f o r the P i e z o m e t e r s 41 9. 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 10. Comparison of P r e s s u r e Heads Assuming 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 C h a p t e r I I I 1. Summary and C o n c l u s i o n 47 2. Recommendations 48 Chapter I 1. I n t r o d u c t i o n The c o n s t r u c t i o n of L i b b y Dam on the Kootenay R i v e r i n w e s t e r n Montana i s a p o r t i o n of the U n i t e d S t a t e s commitment w i t h Canada under th e Columbia R i v e r T r e a t y s i g n e d by Canada and The U n i t e d S t a t e s i n 1964. The r e s e r v o i r b e h i n d t h e dam w i l l be 90 m i l e s l o n g , t h e upper 42 m i l e s b e i n g i n the p r o v i n c e of B r i t i s h C o l u m b i a . The f i l l i n g of t h i s r e s e r v o i r w i l l f l o o d 43 m i l e s of t h e e x i s t i n g G r e a t N o r t h e r n R a i l w a y 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 t h e r e f o r e , r e q u i r e s t h e r e l o c a t i o n of a p p r o x i m a t e l y 60 m i l e s of r a i l w a y . The w e s t e r n p o r t i o n of 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, f i g u r e 1, w i l l l i e i n t h e F i s h e r River v a l l e y and w i l l be on an embankment s e c t i o n r a n g i n g t r om 15 t o 65 f e e t i n h e i g h t . The F i s h e r R i v e r v a l l e y was i n g l a c i a l t i m e s o c c u p i e d by l a k e s . The p r e s e n t v a l l e y bottom c o n s i s t s of s o f t , f i n e -g r a i n e d s o i l d e p o s i t s formed by the s e d i m e n t a t i o n of s i l t and c l a y p a r t i c l e s i n t h e s e l a k e s . Because of the r e l a t i v e l y low shear s t r e n g t h and p e r m e a b i l i t y c h a r a c t e r i s t i c s a s s o c i a t e d w i t h t h i s t y p e of d e p o s i t the d e s i g n and c o n s t r u c t i o n of embankments of the magnitude proposed c o n s t i t u t e d a d i f f i c u l t d e s i g n problem. T h i s t h e s i s p r e s e n t s t h e methods used t o s o l v e t h i s d e s i g n problem p e r m i t t i n g the 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 the l a k e b e d f o u n d a t i o n . The s t e p s used t o a r r i v e at a s a t i s f a c t o r y s o l u t i o n were: a s t h e s e l e c t i o n of an embankment s e c t i o n w h i c h e x p e r i e n c e s u g g e s t e d might be adequate f o r c o n s t r u c t i o n on a l a k e b e d f o u n d a t i o n . b. from the r e s u l t s of l a b o r a t o r y t e s t s on s o i l samples of the f o u n d a t i o n m a t e r i a l s r e a s o n a b l e but c o n s e r v a t i v e s o i l s t r e n g t h parameters were chosen. c. u s i n g these s t r e n g t h parameters s t a b i l i t y a n a l y s e s were performed 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. based on t h e r e s u l t s of the s e a n a l y s e s r e s t r i c t i o n s on t h e r a t e at 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 the c o n t r a c t documents. 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 w i t h p i e z o m e t e r s t o measure the pore p r e s s u r e s d e v e l o p e d as t h e f i l l was c o n s t r u c t e d and the r a t e of d i s s i p a t i o n of t h e s e pore p r e s s u r e s . f . u s i n g t h e s e measured pore p r e s s u r e s f u r t h e r s t a b i l i t y a n a l y s e s were made as t h e f i l l was c o n s t r u c t e d t o i n s u r e t h a t an embankment f a i l u r e d i d not o c c u r . The o n l y o c c a s i o n d u r i n g the c o n s t r u c t i o n of the embank-ment when t h e pore p r e s s u r e s d e v e l o p e d were c o n s i d e r e d t o be of such a magnitude t h a t the s t a b i l i t y of the embankment was i n j e o p a r d y o c c u r r e d on September 23, 1966 when the top of the f i l l r e a c h e d an e l e v a t i o n of 20 f e e t . The s t a b i l i t y a n a l y s e s p r e s e n t e d and t h e d i s c u s s i o n o f t h e e x c e s s p o r e p r e s s u r e s d e v e l o p e d have b e e n l i m i t e d , t h e r e f o r e , t o t h e 20 and 25 f o o t h i g h embankment s e c t i o n s . 2 . G e o m o r p h o l o g y o f t h e F i s h e r R i v e r V a l l e y D u r i n g t h e P l e i s t o c e n e E r a t h e K o o t e n a y and F i s h e r R i v e r v a l l e y s we re o c c u p i e d , a t l e a s t t w i c e , by i c e masses w h i c h s c o u r e d out t h e v a l l e y s t o b e d r o c k and p l a c e d a l a y e r o f t i l l a g a i n s t t h e r o c k s u r f a c e s . As t h e l a s t i c e r e t r e a t e d t h e F i s h e r R i v e r v a l l e y mass m e l t e d more r a p i d i l y t h a n d i d t h a t i n t h e K o o t e n a y . T h e K o o t e n a y i c e p l u g g e d t h e mouth o f t h e F i s h e r R i v e r w i t h i c e and m o r a i n a l d e p o s i t s c a u s i n g a l a k e t o f o r m i n t h e F i s h e r v a l l e y . I n t o t h i s l a k e m e l t -w a t e r s t r e a m s c a r r i e d s a n d s , g r a v e l s , s i l t s a n d c l a y s . T h e s a n d s and g r a v e l s we re d e p o s i t e d n e a r t h e mouths o f t h e s t r e a m s w h i l e t h e s i l t s and c l a y s were c a r r i e d i n t o and s e t t l e d i n t h e d e e p e r p o r t i o n s o f t h e l a k e . S e v e r a l h u n d r e d f e e t o f t h e s e s e d i m e n t s we re d e p o s i t e d i n t h e g l a c i a l l a k e . As t h e i c e r e t r e a t e d up the K o o t e n a y R i v e r t h e F i s h e r R i v e r b e g a n t o e r o d e the m o r a i n a l p l u g a t i t s m o u t h . Once t h e l a k e . h a d b e e n d r a i n e d t h e r i v e r b e g a n t o c u t down t h r o u g h t h e l a k e b e d s i l t s and c l a y s . The r a t e o f t h i s down c u t t i n g was ho t u n i f o r m . P e r i o d s o f r a p i d e r o s i o n were f o l l o w e d by p e r i o d s o f s l o w down c u t t i n g when t h e r i v e r e n c o u n t e r e d more r e s i s t a n t m a t e r i a l s . The p r e s e n t r i v e r has become e n t r e n c h e d i n r o c k s p u r s t h a t were p r e s e n t i n t he i c e s c o u r e d v a l l e y . T h e s e l o c a l r o c k a r e a s , have r e s u l t e d i n 4. a r e l a t i v e l y slow r a t e of downcutting l e a v i n g an undetermined thickness of lakebed deposits s t i l l remaining above the i c e scoured v a l l e y bottom. D r i l l holes e s t a b l i s h e d that the f i n e - g r a i n e d d e p o s i t s have a thickness i n excess of 120 feet i n some reaches of the alignment chosen f o r the r a i l w a y . 3 . S i t e E x p l o r a t i o n 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 that the v a l l e y bottom c o n s i s t e d of a surface l a y e r of one to three feet of organic s i l t u n d e r l a i n by 5 t o 10 f e e t of recent streambed deposits of sandy g r a v e l s . The g l a c i a l lake s i l t and c l a y deposits u n d e r l i e these surface d e p o s i t s . 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 d r i l l holes i n d i c a t e d that an embankment s t a b i l i t y problem might ' develope wh i l e c o n s t r u c t i n g the proposed f i l l s . A more extensive program of e x p l o r a t i o n , sampling, and t e s t i n g was deemed necessary to adequately evaluate the f i n e - g r a i n e d s o i l s . An Osterberg Sampler was acquired to 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 h o l e s . This sampler i s lowered to and f i r m l y held against the s o i l at the bottom of the d r i l l h o l e . A- 3 i n c h diameter 3 foot long s t e e l sample tube i s then h y d r a u l i c a l l y forced down i n t o the s o i l . The s o i l sample i s held i n the tube by maintaining 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 s o i l . In removing the s o i l samples from the tubes and preparing specimens for testing a layered or laminated structure was noted. In some instances the break between laminations was f a i r l y easy to see, i n others i t was not. Thin lenses of fine sand were also noted i n some of the samples. The horizontal continuity of these sand lenses was not established i n the exploration program and, therefore, the question of whether or not these sand lenses would provide drainage paths for the d i s s i p a t i o n of the pore pressures caused by the embankment load could not be answered. 4. S o i l Tests a. General The s o i l testing program consisted of gradation, Atterberg Limit, dry density, natural water content, shear and consolidation t e s t s . The log of a t y p i c a l d r i l l hole with the results of the Atterberg Limit, natural water content and dry density tests are shown i n figure 2. The Atterberg Limit test results i f plotted on a P l a s t i c i t y Chart would f a l l along or just above the A - l i n e . The s o i l s 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 clays. The shear tests program consisted of unconsolidated-undrained, Q, and consolidated-undrained, R, t r i a x i a l tests. The Q test specimens were tested at the water content as cut from the samples. The R test specimens were saturated by applying a back pressure. Along with the Q and R test 6, v a l u e s a nother s e t of shear 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 t h e pore p r e s s u r e s d e v e l o p e d and measured d u r i n g t h e R t e s t s . A l l the shear t e s t s were run on 1„4 i n c h d i a m e t e r by 3 i n c h l o n g samples and were performed i n s t r a i n c o n t r o l l e d equipment. 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 ranged from 7 t o 17 minutes w i t h an average of 14.5 minutes w h i l e the time t o f a i l u r e f o r the R t e s t s v a r i e d from 56 t o 133 minutes w i t h an average v a l u e of 8 8 m i n u t e s . A s o i l specimen t e s t e d i n shear 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 s t r e s s reaches a maximum v a l u e . I f th e p l o t of d e v i a t o r 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 the v a l u e of the peak d e v i a t o r s t r e s s i s used i n d e f i n i n g t h e s h e a r s t r e n g t h of t h e specimen . I f the d e v i a t o r s t r e s s -a x i a l s t r a i n c u r v e does not have a d e f i n i t e peak but the d e v i a t o r s t r e s s i n c r e a s e s at a d e c r e a s i n g r a t e w i t h i n c r e a s i n g a x i a l s t r a i n t he d e v i a t o r s t r e s s f o r an a r b i t r a r i l y chosen p e r c e n t a g e of a x i a l s t r a i n i s s e l e c t e d as the d e v i a t o r s t r e s s a t f a i l u r e . - The d e v i a t o r s t r e s s v e r s u s a x i a l s t r a i n c u r v e s f o r the R and Q t e s t s r e p o r t e d i n t h i s paper d i d not u s u a l l y have d e f i n i t e peaks and the d e v i a t o r s t r e s s at 15 p e r c e n t a x i a l s t r a i n was a r b i t r a r i l y chosen as the d e v i a t o r s t r e s s at f a i l u r e . b. Q T e s t s : ;b ( 1 ) Theory . I n t h e Q t e s t the water c o n t e n t of the t e s t specimen i s not a l l o w e d t o change d u r i n g the a p p l i c a t i o n of the c o n f i n i n g p r e s s u r e , , or the l o a d i n g 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 s t r e s s The t o t a l a p p l i e d C 3 w i l l be c a r r i e d by the pore water at a l l s t a g e s of a Q t e s t i f ( a ) t h e specimen i s s a t u r a t e d . ( b ) t h e c o m p r e s s i b i l i t y of t h e pore w a t e r and the 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 compared w i t h the c o m p r e s s i b i l i t y of the s o i l s t r u c t u r e . ( c ) t h e r e i s a unique r e l a t i o n s h i p be-tween e f f e c t i v e s t r e s s and v o i d r a t i o . These g e n e r a l assumptions r e g a r d i n g Q t e s t t h e o r y have been v e r i f i e d by l a b o r a t o r y t e s t s w h i c h have shown t h a t a change i n the c o n f i n i n g p r e s s u r e does produce an e q u a l change i n the pore water 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 . S i n c e the s t r e n g t h c h a r a c t e r i s t i c s of a s o i l sample are dependent o n l y on the e f f e c t i v e s t r e s s e s and 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 i n the Q t e s t does not change the e f f e c t i v e s t r e s s e s , the r e s u l t s of a Q t e s t are independent of the c o n f i n i n g 8 pressure. When p l o t t e d using the Mohr's c i r c l e convention of shear s t r e s s versus t o t a l 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 should give c i r c l e s of the same radius l o c a t e d along the normal s t r e s s a x i s . 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 R e s u l t s Figure 3 i s a p l o t of shear s t r e n g t h versus normal s t r e s s obtained from the Q t e s t s performed on specimens from the d r i l l hole shown on f i g u r e 2. The l o c a -t i o n i n the d r i l l hole 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 . This 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 values of shear s t r e n g t h obtained 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 along a h o r i z o n t a l l i n e as theory d i c t a t e s they should. For example, shown on f i g u r e 3 9 connected by a dashed l i n e are 4 t e s t r e s u l t s f o r Q t e s t s of specimens cut from sample 0. These 4 t e s t s were run on s p e c i -mens taken as clo s e together 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 should, 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 are the t e s t r e s u l t s of specimens taken from sample L . The t e s t r e s u l t s f o r sample 0 are those which deviate f a r t h e s t from theory w h i l e those f o r L best approach a h o r i z o n t a l s t r a i g h t l i n e . A review of the l a b o r a t o r y data i n d i c a t e s the f o l l o w i n g p o s s i b l e reasons f o r these v a r i a t i o n s from theory: (a) the samples were not 100 percent saturated when sheared. Since the samples were obtained below the n a t u r a l water t a b l e at the s i t e i t was i n c o r r e c t l y thought that the samples would be saturated and no s p e c i a l e f f o r t was made to saturate them before t e s t i n g . The degree of s a t u r a t i o n v a r i e d from 90 t o 100 and averaged 97.3 percent. 10. (b) the v o i d r a t i o of specimens cut as clos e together as p o s s i b l e i n the same sample v a r i e d as much as .29 although the average was g e n e r a l l y about .10. (c) i n the same specimen zones of s o i l s w i t h d i f f e r e n t p l a s t i c i t y , i n d i c e s were evident. Considering the 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 analyses as a conservative but reasonable value f o r the f u l l t h ickness of the f i n e - g r a i n e d foundation m a t e r i a l s . R Tests (1) Theory In the 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 permitted under the c o n f i n i n g pressure, CJ"3 . Then w i t h the water content held constant a dev i a t o r s t r e s s , <o, - ^ 3 , i s a p p l i e d and increased u n t i l the specimen f a i l s . The t h e o r e t i c a l shear stren g t h envelope drawn from R t e s t , r e s u l t s should c o n s i s t of 2 p a r t s . The slope of that p o r t i o n of the envelope f o r 11 normal stresses between zero and the preconsolidation pressure i s dependent upon the preconsolidation pressure. The portion of the envelope for normal stresses greater than the preconsolidation pressure i s not dependent on the preconsolidation pressure but depends upon the e f f e c t i v e stress changes between s o i l p a r t i c l e s caused by the confining pressure. For example, i f a saturated specimen has been preconsolidated by a load of 3 tons per square foot the application of a confining pressure of 2 tons per square foot would produce no change i n the e f f e c t i v e stress 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 preconsolidation load and not on the confining pressure. On the other hand i f the confining pressure used had been 4 tons per square foot then the strength of the specimen would depend on the change i n e f f e c t i v e stress between s o i l p a r t i c l e s induced by the confining pressure. Laboratory Results The wide range i n Mohr's c i r c l e s obtained from the R test results as shown on figure 4, 12 was such t h a t no one s t r e n g t h envelope c o u l d be drawn u s i n g a l l the t e s t r e s u l t s . By g r o u p i n g the t e s t r e s u l t s of specimens w i t h about the same d e n s i t y , v o i d r a t i o and p l a s t i c i t y i n d e x b e t t e r s t r e n g t h e nvelopes were drawn. D i v i d i n g t h e f o u n d a t i o n i n t o zones t o w h i c h the shear s t r e n g t h parameters o b t a i n e d from the g r o u p i n g of the t e s t r e s u l t s a p p l i e d p r o v e d i m p r a c t i c a l . The number of zones 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 the v a r i a t i o n of s o i l c h a r a c t e r -i s t i c s w i t h o n l y minor changes i n depth would make the p e r f o r m i n g of s t a b i l i t y a n a l y s e s d i f f i c u l t and time consuming. To 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 i n t o zones of d i f f e r e n t shear s t r e n g t h s f o r s t a b i l i t y a n a l y s e s p u r p o s e s , one shear s t r e n g t h d e f i n e d by an angle of i n t e r n a l f r i c t i o n , 0, of 14 degrees and a c o h e s i o n , c, of .4 t o n s per square f o o t , as shown on f i g u r e 4, was a r b i t r a r i l y chosen as b e i n g a c o n s e r v a t i v e v a l u e f o r th e R shear s t r e n g t h of 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 . V a r i a t i o n 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 samples and specimens i s t h e most r e a s o n a b l e e x p l a n a t i o n f o r the discrepancy between the l a b o r a t o r y r e s u l t s and what would normally be expected from t h e o r e t i c a l c o n s i d e r a t i o n s . R Tests w i t h Pore Pressure Measurements (1) Theory The e f f e c t i v e s t r e s s p r i n c i p l e i n s o i l mechanics, f i r s t proposed by Terzaghi, s t a t e s that : CJ^ =• + M- where <STT i s the t o t a l a p p l i e d s t r e s s , x- i s the pressure i n the pore f l u i d , i s the e f f e c t i v e s t r e s s i n the s o i l s k e l t o n . I f , as shown on f i g u r e 5 and as was done f o r a l l the R t e s t s , the pore pressure induced 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. Since 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 a x i a l s t r a i n i s a l s o recorded during 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 p l o t t e d f o r any value 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 value 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 and the tangent to these c i r c l e s used to define an envelope of developed shear stren g t h f o r that s t r a i n . This envelope i s shown 14 on f i g u r e 5 as envelope 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 f a i l u r e p l a n e w i t h r e s p e c t t o the major p r i n c i p a l p l a n e i s assumed the same f o r a l l specimens t e s t e d and drawn on the e f f e c t i v e s t r e s s c i r c l e s f o r a p a r t i c u l a r a x i a l s t r a i n , t h e l i n e c o n n e c t i n g t h e p o i n t s of i n t e r s e c t i o n of the c i r c l e s and f a i l u r e p l a n e s can be used t o d e f i n e a n other envelope of d e v e l o p e d shear s t r e n g t h . Envelope 2 on f i g u r e 5 i s t h i s envelope w i t h Q d e f i n i n g the assumed d i r e c t i o n of the 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 e n v e l o p e s d e r i v e d from R t e s t s w i t h pore p r e s s u r e measurements are g e n e r a l l y and w i l l be r e f e r r e d t o i n t h i s t h e s i s as R' e n v e l o p e s . The method d e s c r i b e d above and shown on f i g u r e 5 envelope. 2 was chosen f o r o b t a i n i n g R' shear s t r e n g t h p a r a m e t e r s . Envelope 2 was p r e f e r r e d s i n c e , as shown on f i g u r e 5, f o r a p a r t i c u l a r normal s t r e s s e nvelope 2 would d e f i n e a l o w e r shear s t r e s s than envelope 1 and would t h e r e f o r e be a more c o n s e r v a t i v e e s t i m a t e of shear s t r e n g t h . L a b o r a t o r y R e s u l t s The v a l u e s of the pore p r e s s u r e s measured 15. i n t he s h e a r i n g of the t e s t 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 b o t h d u r i n g an i n d i v i d u a l t e s t and from t e s t t o t e s t . I n a l l t e s t s when the a p p l i c a t i o n of t h e d e v i a t o r s t r e s s f i r s t commenced the pore 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 . I n a l l the shear t e s t s of specimens of n o n - p l a s t i c s i l t s the pore p r e s s u r e s d e v e l o p e d 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 d e v e l o p e d i n t e s t i n g t h e s i l t s and c l a y s w i t h p l a s t i c i t y i n d i c e s of 4 t o 10 were i n c o n s i s t e n t . I n some of th e s e t e s t s the v a l u e of the i n d u c e d pore p r e s s u r e reached a maximum p o s i t i v e v a l u e f o r a x i a l s t r a i n s of about 5 p e r c e n t and t h e n d e c r e a s e d but always remained p o s i t i v e . I n o t h e r t e s t s on the s e s i l t s and c l a y s the development of the pore p r e s s u r e s f o l l o w e d a p a t t e r n s i m i l a r t o those f o r the non-p l a s t i c s i l t s . Shear t e s t s on specimens w i t h p l a s t i c i t y i n d i c e s of 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 at a l l s t a g e s of t h e t e s t s . The maximum pore p r e s s u r e was re a c h e d at a x i a l s t r a i n s of 3 t o 7 p e r c e n t and then remained c o n s t a n t or d e c r e a s e d o n l y s l i g h t l y throughout the r e s t of the 16 t e s t . The p l o t of i n d u c e d pore p r e s s u r e v e r s u s a x i a l s t r a i n f o r a t e s t specimen from sample S i s shown on f i g u r e 6. Mohr's c i r c l e s were drawn u s i n g the e f f e c t i v e s t r e s s e s measured at s e l e c t e d p e r c e n t a g e s of a x i a l s t r a i n f o r each specimen t e s t e d . A f a i l u r e p l a n e i n c l i n e d at an a n g l e , @ , of 60 degrees w i t h the major p r i n c i p a l p l a n e was assumed and drawn on a l l the Mohr's c i r c l e s . P l o t s of t h e v a l u e s of the shear s t r e s s , X , v e r s u s e f f e c t i v e normal s t r e s s , ^ N , on the 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 p e r c e n t i n c r e a s e d 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 or d e c r e a s i n g For a x i a l s t r a i n s between 3 and 15 p e r c e n t i any i n c r e a s e i n \o"N caused a p r o p o r t i o n a l i n c r e a s e i n For 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 ^ u i n some t e s t s caused a p r o p o r t i o n a l i n c r e a s e i n f i n o t h e r t e s t s i n c r e a s i n g Qr N caused no change or a d e c r e a s e i n X . F i g u r e 6 shows the p l o t of v e r s u s ^oN f o r a specimen from sample S. F i g u r e 7 shows t h e p l o t s of iC v e r s u s T^^ , f o r 7, 10, 13, and 17 p e r c e n t a x i a l s t r a i n t o r a l l t h e s p e c i m e n s t e s t e d . F i g u r e 8 i s a p l o t of t h e v a l u e s o f t h e maximum p r i n c i p a l e f i e c t i v e s t r e s s r a t i o , , v e r s u s p e r c e n t of a x i a l , s t r a i n t o r a l l t h e R 1 t e s t s . A maximum v a l u e o f / w a s r e a c h e d t o r a x i a l s t r a i n s o f 10 p e r c e n t o r l e s s f o r 80 p e r c e n t o f t h e s p e c i m e n s t e s t e d . F o r t h i s r e a s o n t h e s h e a r s t r e n g t h s d e v e l o p e d a t 10 p e r c e n t a x i a l s t r a i n were c h o s e n as r e p r e s e n t i n g t h e f a i l u r e s h e a r s t r e n g t h t o r u s e i n s t a b i l i t y a n a l y s e s . A s shown on f i g u r e 7 t h e e f i e c t i v e s h e a r s t r e n g t h p a r a m e t e r s f o r a x i a l s t r a i n s o f 10 p e r c e n t c o u l d have r a n g e d f r o m an a n g l e o f i n t e r n a l f r i c t i o n , 0 1 , o f 28 d e g r e e s and c o h e s i o n , c ' , o f z e r o t o a 0' of 37 d e g r e e s and a c ' o f z e r o . T h e l o w e r l i m i t o f a 0 ' of 28 d e g r e e s w i t h a c ' o f z e r o was a s s i g n e d f o r u se i n s t a b i l i t y a n a l y s e s . 5. -Embankment M a t e r i a l s S e v e r a l a r e a s i n t h e v i c i n i t y of t h e p r o p o s e d embankment we re a c q u i r e d f o r b o r r o w s o u r c e s of f i l l m a t e r i a l s . The m a t e r i a l s i n t h e s e s o u r c e s were p r i m a r i l y g r a n u l a r s o i l s w i t h l e s s t h a n 10 p e r c e n t by w e i g h t p a s s i n g t h e N o . 200 s i e v e . T h e s e a r e a s we re shown on t h e c o n t r a c t d o c u m e n t s bu t t h e c o n t r a c t o r had t h e o p t i o n o f o b t a i n i n g m a t e r i a l o f 1 8 any type from any other source he wished. 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 high moisture contents of the 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 that the con t r a c t o r would use only granular m a t e r i a l s i n the embank-ment. Shear strength parameters ot a 0 of 30 degrees and a cohesion ot zero were assigned as a reasonable estimate f o r the strength ot the t i l l m a t e r i a l s . Shear Strength ot Surface M a t e r i a l s u v e r l y i n g the Fine-grained S o i l s a.11 the surface l a y e r ot organic s i l t s o v e r l y i n g the streambed depo s i t s of sanely gravels were removed before any embankment m a t e r i a l s were placed, ho shear t e s t s of the streambed sandy gravels were performed, A. shear s t r e n g t h of a j6 of 35 degrees and cohesion of zero 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. S t a b i l i t y Analysis_Method In a l l the s t a b i l i t y analyses reported i n t h i s paper a surface represented by a c i r c u l a r arc was assumed to be the f a i l u r e s u r f a c e . 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 S l i c e s " . In t h i s method of s t a b i l i t y analyses the i n - p l a c e u n i t weight of the s o i l above a point on the axe i s d i v i d e d by the u n i t weight of water to obta i n a constant. For any point on the arc the depth ot s o i l above the point i s m u l t i p l i e d by t h i s constant to yive the depth of an equivalent column of water. I f there are zones of s o i l s 19 w i t h v a r y i n g d e n s i t i e s above t h e p o i n t a d i f f e r e n t c o n s t a n t must be c o m p u t e d f o r e a c h zone and t h e t h i c k n e s s of e a c h zone m u l t i p l i e d by i t s a p p l i c a b l e c o n s t a n t . T h e summat i on of t h e c o n s t a n t s m u l t i p l i e d by t h e i r r e s p e c t i v e z o n e t h i c k n e s s i s p l o t t e d above t h e p o i n t on t h e a r c . T h i s p o i n t r e p r e s e n t s t h e h e i g h t , H, o f a c o l u m n of w a t e r o f w e i g h t e q u i v a l e n t t o t h e w e i g h t of s o i l above t h e p o i n t on t h e a r c . I f an i n f i n i t e s i m a l s l i c e of h o r i z o n t a l w i d t h dx i s assumed t h e n t h e w e i g h t o f t h e s l i c e , tV, i s V=Htf wdx where tw i s t h e u n i t w e i g h t o f t h e w a t e r . I f f o r t h e i n f i n i t e s i m a l s l i c e w i d t h dx t h e i n f i n i t e s i m a l l e n g t h o f a r c i s dL and B i s t h e a n g l e b e t w e e n t h e t a n g e n t t o t h e a r c and t h e h o r i z o n t a l t h e n t h e u n i t t a n g e n t i a l f o r c e , t , and t h e u n i t n o r m a l f o r c e , n , a r e | t - H Y w d* (sin B) j£ b u t i s t h e c o s B t h e r e f o r e t = H # w ( s i n B ) ( c o s B) n = H T w ( c o s B ) ( c o s B ) A c o n v e n i e n t m e t h o d of o b t a i n i n g t h e s u m m a t i o n o f t h e n o r m a l and t a n g e n t i a l f o r c e s i s t o p l o t them on t h e h o r i z o n t a l p r o j e c t i o n o f t h e a r c r a t h e r t h a n on t h e a c t u a l a r c l e n g t h . The s u m m a t i o n of t h e f o r c e s a r e e a c h r e p r e s e n t e d by t h e i r r e s p e c t i v e ne t a r e a s w h i c h a r e r e a d i l y o b t a i n e d by p l a n i -m e t e r . The f o r c e s must be a d j u s t e d f o r t h e d i f f e r e n c e b e t w e e n t h e u n i t i n c r e m e n t a l a r c l e n g t h , d L , on w h i c h t h e 20. f o r c e s a c t u a l l y a c t and t h e h o r i z o n t a l p r o j e c t i o n , d x , on w h i c h t h e f o r c e s we re assumed t o a c t . T h a t i s t h e v a l u e s o f t and n must be a d j u s t e d by t h e r a t i o o f 4Jr o r — '—_ . ax cos B T h e a d j u s t e d t, = t A = H $w s i n B a n d a d j u s t e d n = n A = H J ^ . c o s B. A c o m p l e t e g r a p h i c a l s o l u t i o n f o r an a r c a l o n g w i t h t h e t A and n A f o r a p a r t i c u l a r s l i c e a r e shown on f i g u r e 9 . The f a c t o r o f s a f e t y , F . S . , f o r an assumed f a i l u r e a r c o f r a d i u s R a b o u t i t s c e n t e r i s t h e r a t i o o f t h e t o t a l moment r e s i s t i n g r o t a t i o n , M r , t o t h e t o t a l moment t e n d i n g t o c a u s e r o t a t i o n M- .^ M r = R I N (tan 4>) + R c L M t= R £ T a n d p _ Z N ( t a n ^ ) t c L Z T F o r t h e a r c on f i g u r e 9 t h e summat i on o f n A f o r t h e 3 z o n e s o f s o i l a r e N-j_, N £ , and N3 and t h e s u m m a t i o n o f t h e t a n g e n t i a l f o r c e s , t A , t e n d i n g t o c a u s e r o t a t i o n shown as + T w h i l e t h o s e r e s i s t i n g r o t a t i o n a r e shown as - T . F o r t h i s a r c £ N (tan 4>) = N, tan 0 , + Hz tan ^ + N 3 t an < 3^ and IT-. +T>(-T). T h e e x c e s s p o r e p r e s s u r e s i n t h e f o u n d a t i o n c a u s e d by t h e a p p l i e d l o a d o f t h e embankment r e s u l t i n a r e d u c t i o n o f t h e n o r m a l f o r c e s o n l y s i n c e t h e p o r e p r e s s u r e s a r e a s sumed t o a c t p e r p e n d i c u l a r t o t h e a r c . I f t h e e x c e s s p o r e p r e s s u r e a t a p o i n t i s U and t h e e f f e c t i v e n o r m a l f o r c e , N ' , t h e n N ' = N - U a n d t h e f a c t o r o f s a f e t y i s p o _ N' ( t a n 0 ) -t cL r . 5 . - — T -21. A p r o g r a m w h i c h g i v e s t h e s a f e t y f a c t o r f o r c i r c u l a r a r c s f o r t h i s m e t h o d o f s t a b i l i t y a n a l y s i s has b e e n w r i t t e n f o r t h e e l e c t r o n i c c o m p u t e r . 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 s u l t s r e p o r t e d i n t h i s p a p e r were o b t a i n e d by t h e u s e o f t h e c o m p u t e r . The c o m p u t e r o u t p u t d a t a f o r t h e s o l u t i o n o f a p a r t i c u l a r a r c c o n s i s t s o f t he summat i on o f N , N ( t a n 0), c L , and T f o r e a c h zone o f s o i l w i t h d i f f e r e n t c h a r a c t e r i s t i c s t h r o u g h w h i c h t h e a r c p a s s e s as w e l l as t h e s a f e t y f a c t o r f o r t h e a r c . I f t h e s a f e t y f a c t o r was w a n t e d f o r t h e s u m m a t i o n o f N 1 i n s t e a d o f N t h e s u m m a t i o n o f t h e p o r e p r e s s u r e s a c t i n g on t h e a r c was d e t e r m i n e d by p l o t t i n g t h e e x c e s s p o r e p r e s s u r e h e a d s on t h e h o r i z o n t a l p r o j e c t i o n o f t h a t p o r t i o n o f t h e a r c on w h i c h t h e p r e s s u r e s a c t e d . T h e s u m m a t i o n of N ' was f o u n d by s u b t r a c t i n g t h e s u m m a t i o n o f t h e p o r e p r e s s u r e s r e p r e s e n t e d by t h e a r e a u n d e r t h e p l o t t e d c u r v e f r o m t h e s u m m a t i o n o f N o b t a i n e d f r o m t h e c o m p u t e r d a t a . 8 . S a f e t y F a c t o r C r i t e r i a T h e minimum s a f e t y f a c t o r p e r m i t t e d ' f o r t h e s t a b i l i t y a n a l y s e s d e p e n d e d upon t h e s h e a r s t r e n g t h p a r a m e t e r s u s e d i n t h e a n a l y s e s . A min imum s a f e t y f a c t o r o f 1 .25 was a l l o w e d f o r t h e r e s u l t s o f s t a b i l i t y a n a l y s e s u s i n g s h e a r s t r e n g t h s o b t a i n e d f r o m t h e Q t e s t s . T h e Q t e s t s h e a r s t r e n g t h r e p r e s e n t s t h e minimum s h e a r s t r e n g t h t h a t t h e f o u n d a t i o n m a t e r i a l s w o u l d e v e r h a v e s i n c e no d i s s i p a t i o n o f t h e e x c e s s p o r e p r e s s u r e s c a u s e d by t h e f i l l c o n s t r u c t i o n a r e assumed t o o c c u r d u r i n g t h e c o n s t r u c t i o n p e r i o d . T h e use o f a 22.. s a f e t y f a c t o r as low as 1.25 i s p e r m i s s i b l e s i n c e some exces s pore p r e s s u r e , a l t h o u g h how much i s unknown, w i l l d i s s i p a t e w i t h an accompanying i n c r e a s e i n shear s t r e n g t h o c c u r r i n g d u r i n g the c o n s t r u c t i o n p e r i o d . The R shear s t r e n g t h parameters r e p r e s e n t the shear s t r e n g t h of the f o u n d a t i o n m a t e r i a l s at some p o i n t i n time when some but not a l l of the excess pore p r e s s u r e s caused 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 . 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 the s t a b i l i t y a n a l y s e s u s i n g the shear s t r e n g t h from the R t e s t s . The R' shear s t r e n g t h parameters can be used i n s t a b i l i t y a n a l y s e s 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 c o n s t r u c t i o n p r o v i d e d the excess pore p r e s s u r e s caused by the embankment l o a d are known. I n the d e s i g n s t a g e no attempt was made t o e s t i m a t e the exc e s s pore p r e s s u r e s . D u r i n g the embankment c o n s t r u c t i o n the excess pore p r e s s u r e s were measured and s t a b i l i t y a n a l y s e s performed u s i n g t h e s e measured pore p r e s s u r e s . The embankment s t a b i l i t y s a f e t y f a c t o r as i n d i c a t e d by t h e s e a n a l y s e s had t o be g r e a t e r t h a n 1.25 at a l l times d u r i n g the c o n s t r u c t i o n p e r i o d . Any time t h e excess pore p r e s s u r e s i n d i c a t e d t h a t the s a f e t y f a c t o r was l e s s than 1.25 c o n s t r u c t i o n was t o s t o p u n t i l t h e measured pore p r e s s u r e d i s s i p a t i o n i n d i c a t e d t h a t the f a c t o r of s a f e t y was g r e a t e r than 1.25. 9., D e s i g n Stage S t a b i l i t y A n a l y s e s The f i r s t s t a b i l i t y a n a l y s e s performed used shear 23 s t r e n g t h s from t h e Q and R t e s t s and were r u n on t h e maximum embankment s e c t i o n of 65 f e e t i n h e i g h t . The s a f e t y f a c t o r s o b t a i n e d i n t h e s e a n a l y s e s were w e l l below the e s t a b l i s h e d c r i t e r i a . The c o n s t r u c t i o n , season at the s i t e i s l i m i t e d by weather c o n d i t i o n s t o the p e r i o d between A p r i l and November and t h e c o n t r a c t o r c o u l d not complete t h e embank-ment i n one c o n s t r u c t i o n season because of the q u a n t i t y of m a t e r i a l s i n v o l v e d . The next d e s i g n s t e p s were t o determine t o what h e i g h t the f i l l c o u l d be s a f e l y c o n s t r u c t e d i n the f i r s t c o n s t r u c t i o n season and whether or not t h e excess pore p r e s s u r e s caused by the f i l l c o n s t r u c t i o n would d i s s i p a t e s u f f i c i e n t l y over the w i n t e r l a y o f f p e r i o d t o a l l o w t h e c o n t r a c t o r t o f i n i s h the f i l l i n the next c o n s t r u c -t i o n s eason. The G r e a t N o r t h e r n R a i l w a y i n the r e l o c a t i o n agreement had r e q u e s t e d t h a t a l l f i l l s l o p e s be no s t e e p e r t h a n 2 h o r i z o n t a l t o one v e r t i c a l . T h i s r e q u e s t was g r a n t e d . The o n l y q u e s t i o n c o n c e r n i n g the f i l l s l o p e s was whether or not f l a t t e r s l o p e s or t o e berms might be r e q u i r e d t o p r o v i d e a s t a b l e embankment. Embankment s e c t i o n s w i t h h e i g h t s r a n g i n g from 10 t o 50 f e e t were a n a l y s e d f o r s t a b i l i t y u s i n g t h e shear s t r e n g t h s from the Q, R, and R» t e s t s . F i g u r e 10 shows t h e group of a r c s a n a l y s e d f o r t h e 40 f o o t h i g h f i l l and the s a f e t y f a c t o r s o b t a i n e d 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 s t a g e of d e s i g n no attempt was made t o p r e d i c t what the 24, v a l u e s of t h e excess pore p r e s s u r e s might be and complete d i s s i p a t i o n of these p o r e p r e s s u r e s was assumed f o r a l l the a n a l y s e s u s i n g the R f s t r e n g t h p a r a m e t e r s . The a n a l y s e s u s i n g Q shear 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 of 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 f a c t o r s m e e t i n g the d e s i g n c r i t e r i a would be between 30 and 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 of 45 f e e t , i n d i c a t e d t h a t t h e time 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 would be a minimum of 275 days. V i s u a l e x a m i n a t i o n 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 , found t h i n l a m i n a t i o n of sand w h i c h i f c o n t i n u o u s p r o v i d e d r a i n a g e p a t h s t h a t would d e c r e a s e the c o n s o l i d a t i o n t i m e . The q u e s t i o n , "What w i l l t h e excess pore p r e s s u r e heads b e ? M and, "How f a s t w i l l t h e y v d i s s i p a t e ? " s t i l l d i d not have r e l i a b l e answers. Rather t h a n spend more d e s i g n time making t h e o r e t i c a l s t u d i e s w i t h q u e s t i o n a b l e r e s u l t s the 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 the f o u n d a t i o n and measure the excess pore p r e s s u r e s a t a l l . s t a g e s of c o n s t r u c t i o n . 10. Type of and I n s t a l l a t i o n Method f o r the P i e z o m e t e r s The c o n t r a c t s p e c i f i c a t i o n s c a l l e d f o r g a s - o p e r a t e d p i e z o m e t e r s i n s t a l l e d i n d r i l l h o l e s w i t h a t e r m i n a l board at t he t o e of the f i l l . The c o n t r a c t o r s e l e c t e d the H a l l H y d r o s t a t i c P r e s s u r e C e l l as the t y p e of p i e z o m e t e r 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 H a l l C e l l 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 t ype p i e z o m e t e r 25. a p p r o x i m a t e l y 1.5 i n c h e s i n d i a m e t e r by 3 i n c h e s l o n g made e n t i r e l y of s t a i n l e s s s t e e l . There a re two n y l o n e x t e r n a l l e a d s t o the c e l l . One a c t s as t h e i n f l o w and th e o t h e r as t h e o u t f l o w l i n e f o r the n i t r o g e n gas. At the base of t h e c e l l i s a porous stone and be h i n d t h i s s t o n e i s a c a l i b r a t e d s t a i n l e s s s t e e l diaphragm. The c e l l i t s e l f a c t s as a v a l v e . The p r e s s u r e of the water s u r r o u n d i n g the c e l l c l o s e s t h e v a l v e by f o r c i n g the diaphragm a g a i n s t a base p l a t e c l o s i n g the f l o w p a t h be-tween the i n and out f l o w t u b e s . I n c r e a s i n g the p r e s s u r e of t he n i t r o g e n gas on the i n f l o w s i d e of the c e l l f o r c e s t h e diaphragm away from the base p l a t e a l l o w i n g gas t o pass i n t o the o u t f l o w t u b e . The end of the o u t f l o w tube not f a s t e n e d t o the c e l l i s submerged i n a tube of water and used as a bubble i n d i c a t o r . When gas bubbles i n the tube of water were f o r m i n g from the o u t f l o w tube at the r a t e of one per second the gas p r e s s u r e as 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 the p r e s s u r e of t h e water s u r r o u n d i n g the c e l l . 1 The p i e z o m e t e r s were i n s t a l l e d at the l o c a t i o n s shown on f i g u r e 11. Holes 6 i n c h e s i n d i a m e t e r were d r i l l e d t o t h e r e q u i r e d depths w i t h O s t e r b e r g s o i l samples t a k e n i n the l a s t 10 f e e t of h o l e . The r e s u l t s of c l a s s i f i c a t i o n t e s t s performed on these samples a r e a l s o shown on f i g u r e 11 The same v a r i a t i o n s i n s o i l t y p e w i t h o n l y s m a l l changes i n depth and the sand l e n s e s n o t e d i n the e x p l o r a t i o n sample were found i n t h e s e samples. 2 6 . A s a n d b e d 9 i n c h e s d e e p was d e p o s i t e d a t t h e b o t t o m o f e a c h p i e z o m e t e r d r i l l h o l e . The c e l l was p l a c e d i n s i d e a b u r l a p bag f i l l e d w i t h c o a r s e s a n d and t h e c e l l and bag p l a c e d on t o p o f t h e s a n d b e d . A n o t h e r 9 i n c h l a y e r o f s a n d was p l a c e d above t he c e l l . A f u n c t i o n a l c h e c k o f t h e c e l l was t h e n made by o b s e r v i n g w h e t h e r o r n o t t h e c e l l w o u l d r e a d t h e p r e s s u r e h e a d o f w a t e r i n t h e d r i l l h o l e . The h o l e was t h e n b a c k f i l l e d w i t h a c h e m i c a l g r o u t and t h e n y l o n i n and ou t f l o w l e a d s b u r i e d i n a t r e n c h e x t e n d i n g t o t h e t o e o f t h e f i l l where t h e t e r m i n a l b o a r d had b e e n s e t u p . The. l e a d s were a t t a c h e d t o t h e gages and o b s e r v a t i o n t u b e s and t h e who l e s y s t e m g i v e n a f i n a l f u n c t i o n a l c h e c k a g a i n s t t h e known g r o u n d w a t e r t a b l e . 1 1 . S e l e c t i o n o f H o r i z o n t a l and V e r t i c a l P i e z o m e t e r  L o c a t i o n s T h e h o r i z o n t a l o f f s e t s f r o m t h e s e c t i o n c e n t e r l i n e and" t h e d e p t h s a t w h i c h t h e c e l l s were i n s t a l l e d , shown on f i g u r e 1 1 , we re s e l e c t e d t o g i v e a d i s t r i b u t i o n i n t h e f o u n d a t i o n o f t h e p o i n t s o f known p o r e p r e s s u r e . F rom t h e s e p o i n t s e x c e s s p o r e p r e s s u r e e q u i p o t e n t i a l s we re t o be d e v e l o p e d t h r o u g h o u t t h e f o u n d a t i o n . T h e 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 shown on f i g u r e 12 was u s e d i n an a t t e m p t t o p r e d i c t t h e p a t t e r n i n w h i c h t h e s e e q u i p o t e n t i a l s w o u l d d e v e l o p e as t h e f i l l was c o n s t r u c t e d . O n l y t h e v e r t i c a l s t r e s s e s , £ ^ , we re s o l v e d f o r and a l l s o l u t i o n s were o b t a i n e d by t h e e l e c t r o n i c c o m p u t e r . T h e s t r e s s 27. d i s t r i b u t i o n f o r f i l l s e c t i o n s o f 10 t h r o u g h 50 f e e t we re f o u n d f o r 5 f o o t i n c r e m e n t s . T h e v e r t i c a l s t r e s s a p p l i e d t o a f o u n d a t i o n by t h e w e i g h t o f t h e embankment a t t h e embankment t o f o u n d a t i o n c o n t a c t was a s sumed t o be o n e . T h e c o m p u t e r was t h e n p rogrammed t o p r i n t t o s c a l e i n a g r i d p a t t e r n as a d e c i m a l f r a c t i o n , I, t h e v e r t i c a l s t r e s s e s a t v a r i o u s p o i n t s i n t h e f o u n d a t i o n . T h e a c t u a l t h e o r e t i c a l v a l u e o f t h e v e r t i c a l s t r e s s , ^ " f a t any p o i n t b e i n g QT 2=H)fl w h e r e t i s t h e u n i t w e i g h t o f t h e f i l l , and H i s t h e h e i g h t o f t h e f i l l a t c e n t e r l i n e i n f e e t . The d e p t h b e l o w t h e c e n t e r l i n e o f t h e f i l l a t w h i c h t h e v e r t i c a l s t r e s s o b t a i n e d f r o m t h e s t r e s s d i s t r i b u t i o n e q u a l s 90 p e r c e n t o f t h e a p p l i e d embankment l o a d was 103 f e e t f o r t h e 10 f o o t f i l l and 65 f e e t f o r t h e 50 f o o t f i l l . Two p i e z o m e t e r s we re p l a c e d i n t h e f o u n d a t i o n a l o n g t h e c e n t e r l i n e o f t h e f i l l a t d e p t h s o f 45 and 85 f e e t w i t h t h e i n t e n t i o n o f b r a c k e t i n g t h e . 9 0 s t r e s s e q u i p o t e n t i a l f o r most o f t h e r a n g e o f f i l l h e i g h t s . A l i n e p r o j e c t e d downward f r o m t h e t o e o f t h e f i l l a t an a n g l e o f 60 d e g r e e s f r o m t h e h o r i z o n t a l i s a good a p p r o x -i m a t i o n o f t h e . 1 0 s t r e s s c o n t o u r f r o m t h e s t r e s s d i s t r i b u t i o n f o r a l l o f t h e f i l l h e i g h t s . No p i e z o m e t e r s were t h o u g h t t o be n e c e s s a r y o r l o c a t e d O u t s i d e t h i s 60 d e g r e e l i n e . B a s e d on t h e s t r e s s d i s t r i b u t i o n s f o r t h e v a r i o u s embank -ment h e i g h t s t h e o f f s e t s and d e p t h s o f t h e l o c a t i o n s f o r 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 the b e s t p o s s i b l e coverage t o the zone of a n t i c i p a t e d excess pore p r e s s u r e s . 12. S t a b i l i t y A n a l y s e s U s i n g E s t i m a t e d Excess Pore  P r e s s u r e s Were Not 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 the increment of the v e r t i c a l s t r e s s t h e n the f o l l o w i n g assumptions must be t r u e . F i r s t , the f o u n d a t i o n s o i l s have t o be s a t u r a t e d . Because of the method of d e p o s i t i o n and the l o c a t i o n of the ground water t a b l e , a p p r o x i m a t e l y 4 f e e t below the ground s u r f a c e at the f i l l s i t e , the 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 even though the shear t e s t specimens i n d i c a t e d an i n p l a c e degree of s a t u r a -t i o n of l e s s than 100 p e r c e n t . The l o s s of water l o w e r i n g the degree of s a t u r a t i o n was thought t o have 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 f o r t e s t i n g . Second, the 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 , i n f i n i t e i n e x t e n t and t o a c t as e l a s t i c m a t e r i a l s . T h i s assumption i s known t o be e r r o n e o u s , but no a c c e p t a b l e method of e v a l u a t i n g or a d j u s t -i n g f o r the e r r o r s were known and the assumption was a c c e p t e d as t r u e . The t h i r d assumption w h i c h must be a c c e p t e d as t r u e i s t h a t no d i s s i p a t i o n of excess pore p r e s s u r e s occur i n the c o n s t r u c t i o n time p e r i o d . For t h i s assumption t o be 29. t r u e t h e embankment l o a d must be a p p l i e d i n s t a n t a n e o u s l y t o t h e f o u n d a t i o n . T h i s i s i m p o s s i b l e s i n c e some p e r i o d o f t i m e i s r e q u i r e d f o r c o n s t r u c t i o n . T h e amount o f e x c e s s p o r e p r e s s u r e d i s s i p a t i o n w h i c h o c c u r s d e p e n d s u p o n t h e h e i g h t s o f f i l l c o n s t r u c t e d and t h e t i m e t a k e n i n c o n s t r u c -t i o n . T h e u n c e r t a i n t i e s i n v o l v e d i n p r e d i c t i n g t h e c o n t r a c t -o r ' s r a t e o f m a t e r i a l p l a c e m e n t and t h e r a t e o f e x c e s s p o r e p r e s s u r e d i s s i p a t i o n we re t h e p r i n c i p l e r e a s o n s no s t a b i l i t a n a l y s e s u s i n g e s t i m a t e s f o r t h e s e p o r e p r e s s u r e s we re p e r f o r m e d . 30^ Chapter I I l a Embankment C o n s t r u c t i o n The c o n t r a c t o r f i n i s h e d the p i e z o m e t e r i n s t a l l a t i o n on J u l y 19, 1966„ No f i l l m a t e r i a l was p l a c e d i n the s e c t i o n i m m e d i a t e l y over the p i e z o m e t e r s u n t i l September 2, 1966 but a minor amount of 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 of August i n t h e v i c i n i t y of t h e i n s t a l l a t i o n c a u s i n g an i n c r e a s e i n t h e measured pore p r e s s u r e s . The r e a d i n g s i n t h e p e r i o d between J u l y 19 and September 2 showed t h a t t h e c e l l s were 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 the known ground water s u r f a c e . Between September,2 and 12 e l e v e n f e e t of f i l l was p l a c e d over t h e p i e z o m e t e r s . I n t h e p e r i o d from September.13 t o 20. no f i l l m a t e r i a l was p l a c e d . An a d d i t i o n a l 9 f e e t of f i l l was p l a c e d over t h e r i g h t s i d e of the f i l l ( o v e r p i e z o m e t e r s 1 th r o u g h 6) between September 21 and 23 w i t h 5 f e e t of f i l l b e i n g p l a c e d over the remainder of the embankment at t h i s t i m e . The f i l l was brought t o a u n i f o r m h e i g h t of 20 f e e t between October 11 and 13.> 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 . o p e r a t i o n s a f t e r October 13 f o r the 1966 sea s o n . He recommenced h i s o p e r a t i o n on May 5, 1967 and brought the f i l l t o grade on October 9, 1967. Except f o r the p e r i o d between J u l y 3 and August 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 from 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 m a t e r i a l i n t e r m i t t e n t l y throughout the 1967 c o n s t r u c t i o n season. 3 1 . F i g u r e 11 shows t h e p r i n c i p a l d a t e s o f embankment m a t e r i a l p l a c e m e n t . 2 . P o r e P r e s s u r e s M e a s u r e d by t h e P i e z o m e t e r s F i g u r e s 13 and 14 a r e p l o t s o f t h e m e a s u r e d p o r e p r e s s u r e s i n pounds p e r s q u a r e i n c h v e r s u s t i m e . T h e g r o u n d w a t e r e l e v a t i o n above e a c h p i e z o m e t e r was a s sumed t o be t h e h e a d o f w a t e r r e p r e s e n t e d by t h e p o r e " p r e s s u r e m e a s u r e m e n t s t a k e n b e f o r e any embankment had b e e n b u i l t . T h e s e head m e a s u r e m e n t s when p l o t t e d t o s c a l e above t h e p i e z o m e t e r l o c a t i o n s i n d i c a t e d t h a t t h e g r o u n d o r s t a t i c w a t e r t a b l e was h o r i z o n t a l and a p p r o x i m a t e l y 4 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 . A f t e r t h e f i l l c o n s t r u c t i o n s t a r t e d t h e d i f f e r e n c e b e t w e e n t h e m e a s u r e d p o r e p r e s s u r e arid t h e p o r e p r e s s u r e w h i c h r e p r e s e n t e d t h i s g r o u n d w a t e r h e a d was a s s u m e d t o be t h e e x c e s s p o r e p r e s s u r e c a u s e d by t h e em -bankment l o a d . As t h e f i l l was c o n s t r u c t e d t h e f i e l d o f f i c e r e p o r t e d t h e t o t a l p o r e p r e s s u r e s m e a s u r e d and t h e f i l l h e i g h t h f o r e a c h d a y . F rom t h e f i e l d d a t a t h e e x c e s s p o r e p r e s s u r e h e a d a t e a c h p i e z o m e t e r was c o m p u t e d . On a s e c t i o n drawn t o s c a l e a t t h e l o c a t i o n o f t h e p i e z o m e t e r s t h e v a l u e s o f t h e e x c e s s p o r e p r e s s u r e s were p l o t t e d and t h e e q u i p o t e n t i a l s o f t h e s e p r e s s u r e s t h e n s k e t c h e d i n . S i n c e no p i e z o m e t e r s were i n s t a l l e d i n t h e 30 f o o t zone i n t h e f o u n d a t i o n i m m e d i a t e l y u n d e r l y i n g t h e g r o u n d s u r f a c e a r b i t r a r y a s s u m p t i o n s as t o how t h e e x c e s s p o r e p r e s s u r e s were 3 2 . d i s t r i b u t e d i n t h i s z o n e were made . T h e s e a s s u m p t i o n s w e r e : 1. t h e s u r f a c e l a y e r o f g r a v e l l y m a t e r i a l s was 10 f e e t and c o n t i n u o u s a c r o s s t h e s e c t i o n . 2 . t h e p e r m e a b i l i t y o f t h i s g r a v e l l y l a y e r was much g r e a t e r t h a n t h e u n d e r l y i n g f i n e - g r a i n e d m a t e r i a l s and t h e r e f o r e , no e x c e s s p o r e p r e s s u r e s c o u l d be d e v e l o p e d i n t h i s s u r f a c e l a y e r . 3. t h e e x c e s s p o r e p r e s s u r e e q u i p o t e n t i a l s c o u l d be e x t e n d e d upwa rds t o i n t e r s e c t a h o r i z o n t a l l i n e i n t h e f o u n d a t i o n 20 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 . 4 . above t h i s h o r i z o n t a l l i n e t h e e x c e s s p o r e p r e s s u r e s a l o n g any a r c w o u l d d e c r e a s e l i n e a r l y t o z e r o a t t h e b o t t o m o f t h e g r a v e l l y s u r f a c e l a y e r . F o r e x a m p l e , i f a t t h e p o i n t o f i n t e r s e c t i o n o f a p a r t i c u l a r a r c and t h e h o r i z o n t a l l i n e 20 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 t h e e x c e s s p o r e p r e s s u r e h e a d d e t e r m i n e d f r o m t h e e q u i p o t e n -t i a l s was 28 f e e t t h e e x c e s s p o r e p r e s s u r e h e a d w o u l d be z e r o , 7 , 1 4 , and 21 f e e t a t t h e p o i n t s on t h e a r c 1 0 , 1 2 . 5 , 1 5 , and 1 7 . 5 f e e t r e s p e c t i v e l y b e l o w t h e g r o u n d s u r f a c e . F i g u r e s 15 and 22 a r e p l o t s o f m e a s u r e d e x c e s s p o r e p r e s s u r e s i n f e e t o f head v e r s u s t i m e f o r t h e 1966 c o n s t r u c t i o n and. d i s s i p a t i o n p e r i o d . A l s o shown on t h e s e f i g u r e s a r e two 3 3 , p r o j e c t e d v a l u e s o f p o r e p r e s s u r e w h i c h a r e d i s c u s s e d on p a g e s 34 and 4 2 . T h e s e p r o j e c t e d p r e s s u r e s a r e f o r t h e 25 f o o t f i l l and t h e 20 f o o t f i l l a s s u m i n g no d i s s i p a t i o n d u r i n g t h e c o n s t r u c t i o n p e r i o d . 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 U s i n g t h e M e a s u r e d E x c e s s P o r e P r e s s u r e s T h e s h e a r s t r e n g t h p a r a m e t e r s u s e d i n t h e s t a b i l i t y a n a l y s e s u s i n g t h e p o r e p r e s s u r e e q u i p o t e n t i a l s we re t h o s e o b t a i n e d f r o m t h e R f t e s t s . S o l u t i o n s f o r t he s t a b i l i t y a n a l y s e s f o r t h e c o n d i t i o n o f no e x c e s s p o r e p r e s s u r e s had b e e n o b t a i n e d f o r a l l f i l l h e i g h t s be tween 10 and 50 f e e t i n 5 f o o t i n c r e m e n t s b e f o r e any embankments we re c o n s t r u c t e d . F i g u r e 23 shows t h e a r c s u s e d i n t h e a n a l y s e s o f t h e 20 f o o t f i l l . F i g u r e 24 shows t h e e x c e s s p o r e p r e s s u r e e q u i p o t e n t i a l s f o r t h e 20 f o o t f i l l . F i g u r e s 23 and 24 as shown a r e no t d rawn t o t h e same s c a l e . In p r a c t i c e t h e s e two f i g u r e s were d rawn t o t h e same s c a l e and by o v e r l a y i n g t h e f i g u r e w i t h t he p o r e p r e s s u r e d i s t r i b u t i o n a l o n g any p a r t i c u l a r a r c c o u l d be d e t e r m i n e d . T h e p o r e p r e s s u r e d i s t r i b u t i o n a l o n g t h e a r c was t h e n p l o t t e d on t h e h o r i z o n t a l p r o j e c t i o n f o r t h e a r c and t h e a r e a u n d e r t h e h o r i z o n t a l p r o j e c t i o n f o r t he a r c and the a r e a u n d e r t h e c u r v e o b t a i n e d by p l a n i m e t e r . The summat i on o f t o t a l n o r m a l f o r c e s f r o m the c o m p u t e r p r i n t o u t d a t a was t h e n r e d u c e d by t h e s u m m a t i o n o f t h e e x c e s s p o r e p r e s s u r e r e p r e s e n t e d by t h e p l a n -i m e t e r e d a r e a t o g i v e t h e s u m m a t i o n o f t h e e f f e c t i v e n o r m a l f o r c e s . The f a c t o r o f s a f e t y f o r t h e a r c was E S . - N * ( t a n 2 8 ° ) . T 3 4 , T h e f a c t o r s o f s a f e t y t a b u l a t e d on f i g u r e 23 f o r t h e a r c s f o r t h e 20 f o o t f i l l a r e f o r t h e c o n d i t i o n o f no e x c e s s p o r e p r e s s u r e s . F i g u r e 25 i s t h e m a n u a l a n a l y s e s f o r a r c 7 o f f i g u r e 2 3 . T h e d i f f e r e n c e i n t h e f a c t o r s o f s a f e t y . f o r a r c 7 o f 2 . 3 0 and 2 . 2 8 f r o m f i g u r e s 23 and 2 5 , r e s p e c t i v e l y , i s t h e d i f f e r e n c e g e n e r a l l y f o u n d be tween t h e c o m p u t e r and m a n u a l a n a l y s e s f o r t h e same a r c . A l s o shown on f i g u r e 25 i s t h e f a c t o r o f s a f e t y o f 1 .89 o b t a i n e d when t h e t o t a l n o r m a l p r e s s u r e s had b e e n r e d u c e d t o g i v e t h e e f f e c t i v e n o r m a l p r e s s u r e s u s i n g t h e m e a s u r e d e x c e s s p o r e p r e s s u r e e q u i p o t e n t i a l s f o r t h e 20 f o o t f i l l shown on f i g u r e 2 4 . 4 . S t a b i l i t y A n a l y s e s f o r t h e 25 F o o t F i l l U s i n g P r o j e c t e d  E x c e s s P o r e P r e s s u r e s T h e o n l y o c c a s s i o n when t h e s t a b i l i t y a n a l y s e s i n d i c a t e d t h a t f u r t h e r f i l l c o n s t r u c t i o n w o u l d j e o p a r d i z e t h e s t a b i l i t y o f t h e embankment o c c u r r e d on Sep t embe r 23., 1 9 6 6 . On t h i s d a t e a f i l l e l e v a t i o n o f 20 f e e t was r e a c h e d on t h e r i g h t s i d e o f t h e embankment s e c t i o n . T h e c o n t r a c t o r i n t h e 3 day p e r i o d o f S e p t e m b e r 2 1 , 2 2 , and 23 i n c r e a s e d t h e f i l l h e i g h t 9 f e e t and i f he c o n t i n u e d t h i s r a t e o f m a t e r i a l p l a c e m e n t w o u l d h a v e r a i s e d t h e t o p o f t h e f i l l t o e l e v a t i o n 26 f e e t i n t h e n e x t 2 d a y s . T h e i n c r e a s e i n e x c e s s p o r e p r e s s u r e s t h a t w o u l d be c a u s e d by r a i s i n g t h e t o p o f t h e f i l l f r o m 20 t o 25 f e e t was assumed t o be e q u a l t o t h e i n c r e a s e i n t h e e x c e s s p o r e p r e s s u r e s m e a s u r e d as 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 3 5 . 15 t o 20 f e e t . The p r o j e c t e d e x c e s s p o r e p r e s s u r e s f o r t h e 25 f o o t f i l l was t h e sum of t h e e x c e s s p o r e p r e s s u r e s m e a s u r e d w i t h t h e t o p o f t h e f i l l a t 20 f e e t and t h e i n c r e m e n t of e x c e s s p o r e p r e s s u r e i n c r e a s e t h a t o c c u r r e d as t h e f i l l h e i g h t c h a n g e d f r o m 15 t o 20 f e e t . T h e s e p r o j e c t e d v a l u e s o f e x c e s s p o r e p r e s s u r e f o r t h e 25 f o o t f i l l a r e shown on f i g u r e s 15 t h r o u g h 22 and t h e e q u i p o t e n t i a l s f o r t h e s e p r e s s u r e s a r e shown on f i g u r e 2 6 . F i g u r e 27 shows t h e a r c s u s e d i n t h e s t a b i l i t y a n a l y s e s o f . t h e 25 f o o t f i l l and t h e t a b u l a t i o n o f t h e s a f e t y f a c t o r s f o r t h e a r c s f o r t h e no e x c e s s p o r e p r e s s u r e c o n d i t i o n . U s i n g the e x c e s s p o r e p r e s s u r e e q u i p o t e n t i a l s o f f i g u r e 26 t h e t o t a l n o r m a l s t r e s s e s on t h e s e a r c s we re r e d u c e d by t h e me thod p r e v i o u s l y d e s c r i b e d t o g i v e t h e e f f e c t i v e n o r m a l s t r e s s e s . T h e s a f e t y f a c t o r s f o r a r c s 1, 2 , 3 and 4 were t h e n c o m p u t e d t o be 1 . 4 2 , 1 . 2 6 , 1 .21 and 1.31 r e s p e c t i v e l y . T h e s a f e t y f a c t o r f o r a r c 3 was b e l o w t h e minimum, a l l o w a b l e of 1 .25 and t h e f i e l d o f f i c e was i n f o r m e d t h a t c o n s t r u c t i o n o f t h e f i l l s h o u l d be s t o p p e d u n t i l t h e d i s -s i p a t i o n o f t h e e x c e s s p o r e p r e s s u r e s i n d i c a t e d t h e f a c t o r o f s a f e t y was g r e a t e r t h a n 1 . 2 5 . T h e c o n t r a c t o r s t o p p e d h i s o p e r a t i o n f o r a p e r i o d o f t ime a f t e r S ep t embe r 23 a n d when he r e s u m e d wo rk p l a c e d o n l y a s m a l l a d d i t i o n a l q u a n t i t y Of f i l l m a t e r i a l i n 1 9 6 6 . A t no t i m e d u r i n g t h e 1967 c o n s t r u c t i o n s e a s o n were t h e m e a s u r e d e x c e s s p o r e p r e s s u r e s as g r e a t as t h o s e o f S e p t e m b e r 2 3 , 1966 and t h e s a f e t y 3 6 . f a c t o r s as t h e f i l l was b e i n g b u i l t we re a l w a y s above 1 , 2 5 , 5. C o m p a r i s o n o f M e a s u r e d and T h e o r e t i c a l E x c e s s P o r e P r e s s u r e s A s p r e v i o u s l y s t a t e d no s t a b i l i t y a n a l y s e s u s i n g e x c e s s p o r e p r e s s u r e s o b t a i n e d f r o m a t h e o r e t i c a l d i s t r i b u t i o n o f s t r e s s e s were a t t e m p t e d f o r d e s i g n p u r p o s e s . A s a g u i d e t o be u s e d i n f u t u r e d e s i g n p r o b l e m s a c o m p a r i s o n o f t h e m e a s u r e d and t h e o r e t i c a l e x c e s s p o r e p r e s s u r e s was made u s i n g t h e v e r t i c a l s t r e s s e s , , -from f i g u r e 1 2 . A s s u m i n g t h a t a l l t h e i n c r e a s e i n t h e v e r t i c a l s t r e s s e s c a u s e d by t h e embank -ment l o a d was c a r r i e d by t h e p o r e w a t e r t h e e x c e s s p o r e p r e s s u r e h e a d , U, a t any p o i n t i n t h e f o u n d a t i o n i s where $ w i s t h e u n i t w e i g h t o f w a t e r and i s d e f i n e d on page 27 F i e l d d e n s i t y t e s t s o f t h e f i l l m a t e r i a l i n d i c a t e d t h e i n p l a c e u n i t w e i g h t o f t h e f i l l t o be r e a s o n a b l y c l o s e to ; t h e v a l u e o f 135 pounds p e r c u b i c f o o t a s sumed f o r d e s i g n p u r p o s e s . U s i n g t h i s v a l u e t h e v e r t i c a l s t r e s s e s i n t h e f o u n d a t i o n c a u s e d by t h e 20 f o o t f i l l were f o u n d f r o m t h e e q u a t i o n on f i g u r e 12 and v a l u e s o f U c o m p u t e d . E x c e s s p o r e p r e s s u r e e q u i p o t e n t i a l s f r o m t h e 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 f o r t h e 20 f o o t f i l l a r e shown as d a s h e d l i n e s on f i g u r e 2 4 . Two s i g n i f i c a n t d i f f e r e n c e s be tween t h e m e a s u r e d and t h e o r e t i c a l e x c e s s p o r e p r e s s u r e e q u i p o t e n t i a l s f o r t h e 37 20 f o o t f i l l a r e e v i d e n t on f i g u r e 2 4 . F i r s t , t h e t h e o r e t i c a l e x c e s s p o r e p r e s s u r e s a r e h i g h e r t h a n t h o s e a c t u a l l y m e a s u r e d i n t h e f o u n d a t i o n b e l o w t h e c e n t e r o f t h e f i l l . T h i s v a r i a t i o n c o u l d be a t t r i b u t e d i n p a r t t o t h e f a l s e a s s u m p -t i o n o f i n s t a n t a n e o u s l y a p p l i e d embankment l o a d made f o r t h e t h e o r e t i c a l a n a l y s i s . A n o t h e r r e a s o n f o r t h i s v a r i a t i o n wou ld , be t h e a n i s o t r o p i c n a t u r e o f t h e f o u n d a t i o n . The e f f e c t o f t h e s u r f a c e g r a v e l l y l a y e r and t h e h o r i z o n t a l l a m i n a t i o n s i n t h e f o u n d a t i o n w o u l d be t o a c t as s t i f f e n e r s above and be tween t h e more f l e x i b l e l a y e r s o f s i l t s and c l a y s . T h i s s t r e n g t h e n i n g o f t h e f o u n d a t i o n w o u l d t e n d t o r e d u c e t h e v e r t i c a l s t r e s s a t any p o i n t b e l o w t h a t i n d i c a t e d by t h e t h e o r e t i c a l a n a l y s i s . T h e s e c o n d v a r i a t i o n i s t h e r e l a t i v e l y h i g h e x c e s s p o r e p r e s s u r e s m e a s u r e d u n d e r t h e t o e o f t h e f i l l c o m p a r e d w i t h t h e p r e s s u r e s t h e 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 s h o u l d have b e e n d e v e l o p e d . I f t h e h o r i z o n t a l s a n d l e n s e s o b s e r v e d i n t h e s a m p l e s o f t h e f o u n d a t i o n s o i l s were c o n t i n u o u s t h e y w o u l d p r o v i d e d r a i n a g e p a t h s a l o n g w h i c h t h e e x c e s s p o r e p r e s s u r e s u n d e r t h e c e n t e r o f t h e f i l l c o u l d be d i s s i p a t e d . T h i s a p p e a r s t o be t he c a s e and t h e v a l u e o f t h e e x c e s s p o r e p r e s s u r e s u n d e r t h e t o e d e p e n d n o t u p o n t h e s t r e s s e s c a u s e d by t h e a p p l i e d l o a d b u t r a t h e r upon t h e p r e s s u r e g r a d i e n t d e v e l o p e d a l o n g t h e s e d r a i n a g e p a t h s . 3 8 , 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 T h e r e s t r i c t i o n s r e g a r d i n g embankment c o n s t r u c t i o n d e f i n e d i n t h e c o n t r a c t s p e c i f i c a t i o n s were s u c h t h a t t h e c o n t r a c t o r was a l l o w e d t o b u i l d t h e f i r s t 20 f e e t o f f i l l a t any r a t e he w i s h e d w i t h t h e r a t e o f m a t e r i a l p l a c e m e n t above 20 f e e t r e g u l a t e d as r e q u i r e d t o a s s u r e t h e s t a b i l i t y o f t h e embankment . As p r e v i o u s l y n o t e d t h e f i r s t 20 f e e t o f f i l l was p l a c e d i n 2 p e r i o d s , one f r o m Sep t embe r 2 t o 12 t h e o t h e r f r o m Sep t embe r 21 t o 2 3 . A s s u m i n g t h a t t h e c o n t r a c t o r had b u i l t t h e 20 f o o t f i l l w i t h o u t i n t e r r u p t i o n i n a p e r i o d o f 14 d a y s r e a s o n a b l e v a l u e s f o r e x c e s s p o r e p r e s s u r e s m i g h t be t h e sum of t h e v a l u e s o f t h e e x c e s s p o r e p r e s s u r e s m e a s u r e d on S e p t e m b e r 12 and t h e i n c r e a s e t h a t o c c u r r e d b e t w e e n Sep t embe r 21 and 2 3 . E q u i p o t e n t i a l s o f t h e s e p r e s s u r e s f o r u n i n t e r r u p t e d c o n s t r u c t i o n a r e shown on f i g u r e 2 8 . T h e s t a b i l i t y a n a l y s e s f o r a r c 7 u s i n g t h e s e e q u i p o t e n t i a l s h a d a f a c t o r o f s a f e t y o f 1 .50 as shown on f i g u r e 2 5 . T h e f a c t o r s o f s a f e t y f o r t h e a r c s o f t h e 20 f o o t f i l l shown on f i g u r e 23 we re c o m p u t e d f o r t h e f o l l o w i n g f o u r d i s t r i b u t i o n s o f e x c e s s p o r e p r e s s u r e s : 1. t h e e x c e s s p o r e p r e s s u r e s m e a s u r e d on S e p t e m b e r 23 and shown on f i g u r e 2 4 . 2 . t h e e s t i m a t e d p o r e p r e s s u r e s shown on f i g u r e 2 8 . 3. t h e c o n d i t i o n o f no e x c e s s p o r e p r e s s u r e s . 39. 4. the d i s t r i b u t i o n of excess pore p r e s s u r e s based 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 f o u r d i s t r i b u -t i o n s i s g i v e n on f i g u r e 29. 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 the 20 Foot F i l l In 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 the l o c a t i o n s i n t h e f o u n d a t i o n of the a r c s f o r the 20 f o o t f i l l s e v e r a l p o i n t s of i n t e r e s t were n o t e d . F i r s t the lower f a c t o r s of s a f e t y were o b t a i n e d f o r the s h a l l o w e r a r c s . Deep a r c s such as 3 and 8 had adequate s a f e t y f a c t o r s f o r a l l t he excess pore p r e s s u r e d i s t r i b u t i o n s . S e v e r a l i n v e s -t i g a t o r s have shown t h a t s t a b i l i t y f a c t o r s of s a f e t y i n c r e a s e w i t h d epth of a r c p e n e t r a t i o n i n t o t h e f o u n d a t i o n i f the shear s t r e n g t h of the s o i l s t h r o u g h w h i c h th e a r c s pass i s d e f i n e d o n l y i n terras of an a n g l e of i n t e r n a l f r i c t i o n . That a r c s 3 and 8 had the h i g h e s t s a f e t y f a c t o r s f o r the c o n d i t i o n of no e x c e s s pore p r e s s u r e was, t h e r e f o r e , e x p e c t e d but s i n c e the pore p r e s s u r e s s h o u l d be h i g h e r at d e p t h under the c e n t e r of the f i l l some c o n c e r n was f e l t t h a t the deeper a r c s might be the most c r i t i c a l . T h i s was shown not t o be the c a s e . Second, the s h a l l o w e r a r c s had the lower s a f e t y f a c t o r s and the zone i n the f o u n d a t i o n where a c r i t i c a l need f o r i n f o r m a t i o n about the development of excess pore p r e s s u r e s was i n the a r e a 30 f e e t , below the ground s u r f a c e below and o u t s i d e the t o e of t h e f i l l . With a l l the p i e z o m e t e r s 4 0 . l o c a t e d b e l o w t h i s zone and t o w a r d s t h e c e n t e r o f t h e f i l l t h e e x c e s s p o r e p r e s s u r e d i s t r i b u t i o n i n t h i s c r i t i c a l a r e a h a d t o be b a s e d on a s s u m p t i o n s r a t h e r t h a n on f a c t u a l d a t a . T h i r d , t h e l o w e s t s a f e t y f a c t o r , 1 . 1 5 , o b t a i n e d was f o r a r c 6 u s i n g t h e e x c e s s p o r e p r e s s u r e s w h i c h were assumed w o u l d have d e v e l o p e d w i t h u n i n t e r r u p t e d f i l l c o n s t r u c t i o n t o 20 f e e t . T h i s f a c t o r o f s a f e t y was b e l o w t h e minimum s e t by t h e d e s i g n c r i t e r i a and t h e c o n t r a c t s p e c i f i c a t i o n s s h o u l d n o t have a l l o w e d u n r e s t r i c t e d c o n s t r u c t i o n t o 20 f e e t . A c o n s t r u c t i o n p e r i o d o f 14 d a y s ( S e p t e m b e r 1 t o 12 and S e p t e m b e r 21 t o 23 ) was assumed i n d r a w i n g t h e e q u i p o -t e n t i a l s shown on f i g u r e 28 f o r t h e u n i n t e r r u p t e d c o n s t r u c -t i o n o f t h e 20 f o o t f i l l . A c t u a l l y t h i s p e r i o d c o u l d have b e e n s h o r t e n e d t o 7 d a y s i f t h e c o n s t r u c t i o n r a t e o f 3 f e e t o f f i l l p e r d a y h a d b e e n u s e d f o r t h e f u l l 20 f e e t o f f i l l i n s t e a d o f o n l y f o r t h e u p p e r 9 f e e t p l a c e d S e p t e m b e r 2 1 , 2 2 , and 2 3 . T h e t o t a l i n c r e a s e i n e x c e s s p o r e p r e s s u r e s f o r a g i v e n embankment h e i g h t s h o u l d be t h e same r e g a r d l e s s o f t h e t i m e r e q u i r e d f o r c o n s t r u c t i o n w h i l e t h e amount o f d i s s i p a t i o n t h a t o c c u r s i s a f u n c t i o n o f t h e l e n g t h o f t h e c o n s t r u c t i o n p e r i o d . T h e e x c e s s p o r e p r e s s u r e s w h i c h w o u l d have b e e n m e a s u r e d i f t h e 20 f o o t f i l l h ad b e e n c o n s t r u c t e d i n a 7 d a y p e r i o d w o u l d , t h e r e f o r e , have b e e n g r e a t e r t h a n t h o s e w h i c h we re e s t i m a t e d t o h a v e d e v e l o p e d i n t h e 14 day p e r i o d . T h e f a c t o r o f s a f e t y f o r a r c 6 a s s u m i n g a 7 day c o n s t r u c t i o n p e r i o d w o u l d be l e s s t h a n 1 .15 and p o s s i b l y 41. might be l e s s than one. 8, D i s c u s s i o n on the L o c a t i o n s S e l e c t e d f o r the P i e z o m e t e r s I n the d e s i g n 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 i n the f o u n d a t i o n were s e l e c t e d u s i n g 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 as a g u i d e . As d i s c u s s e d above, the measured and t h e o r e t i c a l excess pore p r e s s u r e s d i d not agree t o o w e l l and the 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 s u i t e d f o r d e v e l o p i n g the exc e s s pore p r e s s u r e d i s t r i -b u t i o n under the 20 f o o t f i n . Whether t h e s e l e c t e d l o c a t i o n s would have been adequate i f the f u l l embankment s e c t i o n had been c o n s t r u c t e d i n a s h o r t e r t ime p e r i o d w i t h the d e v e l o p -ment of p r e s s u r e s of a magnitude s u f f i c i e n t l y h i g h t o endanger the s t a b i l i t y of the f i l l i s open t o c o n j e c t u r e . R e v i e w i n g the s t a b i l i t y a n a l y s e s f o r the 25 f o o t f i l l w i t h the p r o -j e c t e d excess pore p r e s s u r e s , a r c 3 wh i c h had the l o w e s t f a c t o r of s a f e t y , 1.21, i s i n the same r e l a t i v e p o s i t i o n t o the toe of the 25 f o o t f i l l as a r c 6 i s t o the toe of the 20 f o o t f i l l . Assuming t h a t e x c e s s pore p r e s s u r e s had d e v e l o p e d under t h e f u l l embankment s e c t i o n an a r c l o c a t e d i n the same r e l a t i v e p o s i t i o n t o the f u l l f i l l s e c t i o n as a r c s 3 and 6 a r e t o the 20 and 25 f o o t f i l l 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 would be the c r i t i c a l a r c . T h i s a r c would pass t h r o u g h the f o u n d a t i o n s l i g h t l y above p i e z o m e t e r s 2 and 4 and 20 or 25 f e e t below p i e z o m e t e r s 3 and one. The pore p r e s s u r e s a l o n g the p o r t i o n of the a r c 4 2 . u n d e r t h e f i l l w o u l d be w e l l d e f i n e d b u t no f a c t u a l i n f o r m a -t i o n abou t t h e p r e s s u r e d i s t r i b u t i o n a l o n g t h e a r c o u t s i d e t h e t o e w o u l d be a v a i l a b l e . T h e l o c a t i o n s o f t h e i n s t a l l e d p i e z o m e t e r s i n d i c a t e d by n u m b e r s , t h e a ssumed c r i t i c a l a r c f o r t h e 60 f o o t f i l l and a r c s 3 a n d 6 f o r t h e 20 and 25 f o o t f i l l s , r e s p e c t i v e l y , a r e shown on f i g u r e 3 0 . A l s o on t h i s f i g u r e , i n d i c a t e d by l e t t e r s , a r e p r o p o s e d p i e z o m e t e r l o c a t i o n s w h i c h w o u l d h a v e g i v e n a b e t t e r d i s t r i b u t i o n o f p o i n t s o f known p o r e p r e s s u r e s f o r u s e i n d e v e l o p i n g e x c e s s p o r e p r e s s u r e e q u i p o t e n t i a l s . T h e p r o p o s e d l o c a t i o n s f o r p i e z o m e t e r s A , B, and C w o u l d p r o v i d e i n t h e c r i t i c a l a r e a o u t s i d e and a t a s h a l l o w e r d e p t h b e n e a t h t h e t o e o f t h e f i l l 3 p o i n t s o f known p r e s s u r e whe re none was a v a i l a b l e w i t h t h e l o c a t i o n s a c t u a l l y u s e d . 9 . E x c e s s P o r e P r e s s u r e s D e v e l o p e d A s s u m i n g No  P r e s s u r e D i s s i p a t i o n Two c u r v e s a r e p l o t t e d on e a c h o f t h e f i g u r e s 15 t h r o u g h 2 2 . The c u r v e shown as a s o l i d l i n e i s a p l o t o f t h e e x c e s s p o r e p r e s s u r e h e a d s a c t u a l l y m e a s u r e d d u r i n g t h e c o n s t r u c t i o n o f t h e 20 f o o t f i l l . The o t h e r i n d i c a t e d by a d a s h e d l i n e r e p r e s e n t s t h e e x c e s s p o r e p r e s s u r e heads t h a t w o u l d have d e v e l o p e d i f no d i s s i p a t i o n o f p r e s s u r e s h a d o c c u r r e d d u r i n g t h e c o n s t r u c t i o n p e r i o d i n w h i c h t h e 20 f o o t f i l l was b u i l t . I n d e v e l o p i n g . t h e d a s h e d c u r v e s t h e f a c t t h a t t he p i e z o m e t e r s r e s p o n d e d a l m o s t i n s t a n t a n e o u s l y w i t h an i n c r e a s e i n p r e s s u r e r e a d i n g when f i l l m a t e r i a l . : 43. was p l a c e d and a d e c r e a s e i n m e a s u r e d p r e s s u r e when m a t e r i a l p l a c i n g s t o p p e d a l l o w e d t h e c u r v e o f m e a s u r e d h e a d s t o be d i v i d e d i n t o two p o r t i o n s . T h e p o r t i o n o f t h e c u r v e f o r w h i c h t h e p r e s s u r e h e a d s we re i n c r e a s i n g r e p r e s e n t i n g t h e c o n s t r u c t i o n p e r i o d and t h e o t h e r p o r t i o n when t h e p r e s s u r e heads were d e c r e a s i n g w i t h t i m e r e p r e s e n t e d t h e p e r i o d when no f i l l m a t e r i a l s we re b e i n g p l a c e d o r d i s s i p a t i o n p e r i o d . A p a r t i c u l a r v a l u e o f p r e s s u r e h e a d i f m e a s u r e d i n t h e c o n s t r u c t i o n p e r i o d w i l l be m e a s u r e d a g a i n i n t h e d i s s i p a t i o n p e r i o d . I f t h i s p r e s s u r e h e a d i s a s sumed t o r e p r e s e n t t h e a v e r a g e p r e s s u r e f o r a one d a y p e r i o d •§• a d a y b e f o r e and •§- a d a y a f t e r t h e t i m e o f t h e p r e s s u r e measu rement t h e n a r e a s o n a b l e a s s u m p t i o n f o r t h e amount o f d i s s i p a t i o n t h a t o c c u r r e d i n t h i s one d a y p e r i o d w o u l d be t h e d i f f e r e n c e b e t w e e n t h e p o r e p r e s s u r e h e a d v a l u e s o b t a i n e d f r o m t h e d i s s i p a t i o n p o r t i o n of t h e c u r v e -§- day b e f o r e and a f t e r t h e p a r t i c u l a r p r e s s u r e h e a d c h o s e n . F o r e x a m p l e , as shown on f i g u r e 1 9 , t h e e x c e s s p o r e p r e s s u r e h e a d m e a s u r e d by p i e -z o m e t e r 5 on Sep t embe r 22 was 1 2 . 5 f e e t and i n c r e a s i n g . On S e p t e m b e r 29 t h e h e a d was a g a i n 1 2 . 5 f e e t b u t d i s s i p a t i n g . In t h e one d a y p e r i o d , •§• a d a y b e f o r e and a f t e r S ep t embe r 29 t h e p o r e p r e s s u r e d i s s i p a t e d one f o o t . The amount o f d i s s i p a t i o n w h i c h o c c u r e d i n t h e one day t i m e p e r i o d , •§• a d a y b e f o r e and a f t e r S e p t e m b e r 2 2 , w a s , t h e r e f o r e , a s sumed t o be e q u a l t o one f o o t . I n t h i s manner t h e amount o f d i s s i p a -t i o n w h i c h o c c u r r e d f o r e a c h one day p e r i o d as t h e p o r e 4 4 , p r e s s u r e s were i n c r e a s i n g was f o u n d . T h e s t e p s u s e d , once t h e amount o f d a i l y d i s s i p a t i o n h a d b e e n o b t a i n e d , t o d e r i v e t h e h e a d v a l u e s t o p l o t t h e c u r v e s o f e x c e s s p o r e p r e s s u r e h e a d c o r r e c t e d f o r d i s s i p a -t i o n v e r s u s t i m e a r e shown i n t h e f o l l o w i n g t a b u l a t i o n f o r a 5 d a y p e r i o d when t h e m e a s u r e d h e a d s were z e r o , 1 . 0 , 2 . 3 , 4 . 0 , and 6 . 0 . Day M e a s u r e d e x c e s s p o r e p r e s s u r e h e a d s V a l u e o f e x c e s s p o r e p r e s s u r e d i s s i p a t e d V a l u e o f e x c e s s p o r e p r e s -s u r e h e a d f o r c o n d i t i o n o f no d i s s i p a t i o n 1 . 0 0 0 2 . 1 ,0 , 3 1 , 0 + , 3 = 1,3 3.. 2 , 3 *5 1.3 + ( 2 * 3 - 1 . 0 ) + . 5 = 3,1 4 . 4 , 0 , 8 3.1 + ( 4 . 0 - 2 . 3 ) + . 8 = 5,6 5 . 6 . 0 ' 1,2 5..6 + ( 6 . 0 - 4 . 0 ) + 1.2 = 8 , 8 U s i n g t h i s me thod t h e v a l u e s o f t h e e x c e s s p o r e p r e s s u r e h e a d s f o r t h e c o n d i t i o n o f no d i s s i p a t i o n were d e t e r m i n e d f o r e a c h p i e z o m e t e r f o r t h e c o n s t r u c t i o n p e r i o d o f t h e 20 f o o t f i l l . 10-. C o m p a r i s o n o f 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 One o f t h e a s s u m p t i o n s made i n o b t a i n i n g t h e e x c e s s p o r e p r e s s u r e s f r o m t h e 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 was t h a t t h e f i l l l o a d was a p p l i e d i n s t a n t a n e o u s l y a l l o w i n g no t i m e f o r d i s s i p a t i o n o f p o r e p r e s s u r e s . T h e p r e s s u r e heads o b t a i n e d by t h e 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 f a l l t h e o t h e r a s s u m p t i o n s a b o u t t h e s t r e s s d i s t r i b u t i o n p r e v i o u s l y d i s c u s s e d were t r u e , s h o u l d h a v e b e e n i n r e a s o n a b l y c l o s e 45. agreement w i t h the v a l u e s of the excess pore p r e s s u r e s c o r r e c t e d f o r the d i s s i p a t i o n t h a t o c c u r r e d i n the c o n s t r u c -t i o n p e r i o d . The f o l l o w i n g i s a t a b u l a t i o n of these p r e s s u r e s . P i e z o m e t e r Excess pore p r e s s u r e head Column l x i 0 0 Column 2 from f i g u r e s 15 t h r u 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 (column 22 1) from 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 (column 2) 1 18.5 6.9 268.0 2 16.0 32.0 - 50.0 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 6.05 248.0 As i n t h e p r e v i o u s comparison of measured and t h e o r e t i c a l p r e s s u r e s the g r e a t e s t v a r i a t i o n o c c u r s at p i e z o m e t e r s 1 and 10 under t h e toe of the t i l l . The r e s t of the measured r e a d i n g s a re a g a i n l e s s t h a n the t h e o r e t i c a l a n a l y s i s i n d i c a t e s t h e y s h o u l d be. I n the R' t r i a x i a l t e s t s the r a t i o of the i n d u c e d pore p r e s s u r e t o t h e d e v i a t o r s t r e s s f o r one or 2 p e r c e n t a x i a l s t r a i n s ranged from .4 t o .8 w i t h an average v a l u e of a p p r o x i m a t e l y .6. For s t r a i n s above 2 p e r c e n t the v a l u e of t h i s r a t i o d e c r e a s e d . I n some of the t e s t s the de c r e a s e 46. was o n i y s l i g h t w h i l e i n o t h e r t e s t s the r a t i o d e c r e a s e d t o a n e g a t i v e v a l u e . The v a l u e s of excess pore p r e s s u r e head l i s t e d i n column one of the p r e c e d i n g t a b u l a t i o n may be c o n s i d e r e d comparable t o the v a l u e s of pore p r e s s u r e d e v e l o p e d i n t h e l a b o r a t o r y t e s t s and t h e a p p l i e d l o a d of t h e 20 f o o t f i l l compared t o the l a b o r a t o r y d e v i a t o r s t r e s s . The r a t i o of the heads from column one t o a column of water e q u i v a l e n t i n weight t o the 20 f o o t f i l l w o uld be f o r p i e z o m e t e r 5 e q u a l t o 33.0 or .762. The 43.27 f o l l o w i n g t a b l e g i v e s the v a l u e s of t h i s r a t i o f o r a l l the p i e z o m e t e r s . P i e z o m e t e r Column one 43.27 Pie z o m e t e r 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 pore p r e s s u r e s d e v e l o p e d t o the a p p l i e d l o a d f o r the t r i a x i a l t e s t s a t low s t r a i n s and f o r the f i l l c o n s t r u c t i o n have about the same range and average v a l u e . Whether t h i s reasonably, good agreement between the l a b o r a -t o r y t e s t r e s u l t s and the f i e l d measurements has any meaning c o u l d not be d e t e r m i n e d s i n c e the a c t u a l s t r a i n s d e v e l o p e d i n the f o u n d a t i o n were unknown. 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 of the Q and R t e s t s were so i n c o n s i s t e n t t h a t the d e t e r m i n a t i o n of shear s t r e n g t h parameters f o r use i n s t a b i l i t y a n a l y s e s was e x t r e m e l y d i f f i c u l t . The r e s u l t s of t h e R' t e s t s , a l t h o u g h some v a r i a t i o n s were n o t e d , were c o n s i d e r e d t o be more r e l i a b l e t h a n t h o s e of the Q and R t e s t s . Because of the 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 the t e s t r e s u l t s the shear parameters s e l e c t e d were the lower or more c o n s e r v a t i v e v a l u e s . By u s i n g the R 1 shear s t r e n g t h parameters and the ex c e s s pore p r e s s u r e s measured as the 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 a n a l y s e s 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 than i f the Q or R shear parameters a l o n e had been used. The excess pore p r e s s u r e s d e v e l o p e d and measured 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 t h o s e w h i c h 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 s h o u l d have been d e v e l o p e d . The exce s s pore p r e s s u r e s c o r r e c t e d f o r d i s s i p a t i o n at the f i l l t oe were 2.5 t i m e s as h i g h as those e s t i m a t e d 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 p r e s s u r e s c o r r e c t e d f o r d i s s i p a t i o n under the f i l l were from |- t o 5. of the e s t i m a t e d v a l u e s . C o n s i d e r i n g the range of the v a r i a t i o n s between measured and e s t i m a t e d pore p r e s s u r e s the o n l y r e l i a b l e method of d e t e r m i n i n g pore p r e s s u r e s i s by i n s t r u m e n t a t i o n . 48^ T h e m e a s u r e d p o r e p r e s s u r e s c o r r e c t e d f o r d i s s i p a t i o n when u s e d i n s t a b i l i t y a n a l y s e s gave s a f e t y f a c t o r s l o w e r t h a n t h o s e o b t a i n e d f r o m a n a l y s e s u s i n g t h e p r e s s u r e s e s t i m a t e d f r o m t h e s t r e s s d i s t r i b u t i o n . T h e use o f a 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 t o p r e d i c t t h e e x c e s s p o r e p r e s s u r e s w h i c h w i l l a c t u a l l y d e v e l o p e when a f i l l i s b u i l t c o u l d , t h e r e f o r e , c a u s e e r r o r s on t h e u n s a f e s i d e and j e o p a r d i z e t h e s t a b i l i t y o f an embankment . 2 . R e c o m m e n d a t i o n s When p i e z o m e t e r s a r e i n s t a l l e d i n an embankment f o u n -d a t i o n t o m e a s u r e e x c e s s p o r e p r e s s u r e s f o r u se i n s t a b i l i t y a n a l y s e s one p i e z o m e t e r s h o u l d be i n s t a l l e d a t a d i s t a n c e a t l e a s t h a l f t h e maximum f i l l h e i g h t o u t s i d e t h e t o e o f t h e embankment and a t a r e l a t i v e l y s h a l l o w d e p t h i n t h e f o u n d a -t i o n . I n t h e c a s e o f t h e p a r t i c u l a r embankment on w h i c h t h i s t h e s i s i s w r i t t e n a h o r i z o n t a l d i s t a n c e o f 30 f e e t a t a d e p t h o f 20 w o u l d have b e e n a b e t t e r l o c a t i o n t h a n t h a t s e l e c t e d f o r t h e o u t e r p i e z o m e t e r . The f a c t t h a t t h e c h a r a c t e r i s t i c s o f t h i s p a r t i c u l a r f o u n d a t i o n may have b e e n r e s p o n s i b l e f o r t h e d i s t r i b u t i o n o f t h e m e a s u r e d e x c e s s p o r e p r e s s u r e s i s r e c o g n i z e d a n d , as d i s c u s s e d by Kenny~ and B i s h o p and B j e r r u m , v a r i a t i o n s o f t h e p o r e p r e s s u r e s a t t h e t o e o f a f i l l f r o m t h o s e g e n e r a l l y e x p e c t e d b a s e d on s t r e s s d i s t r i b u t i o n s c a n be c a u s e d by t h e movement o f w a t e r as p o r e p r e s s u r e s d i s s i p a t e . 49, These a u t h o r s suggest t h a t the pore p r e s s u r e s at the t o e of a f i l l may or may not i n c r e a s e w i t h time depending upon the c h a r a c t e r i s t i c s of the f o u n d a t i o n s o i l s . As f i l l was b e i n g p l a c e d the pore p r e s s u r e s measured i n t h i s p a r t i c u l a r f o u n d a t i o n i n c r e a s e d but when placement stopped t h e pore p r e s s u r e s began t o d i s s i p a t e and no i n c r e a s e w i t h time was noted a t the t o e . The o u t e r p i e z o m e t e r l o c a t i o n used 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 the toe of the f i l l t o d e t e c t whether or not the type o f i n c r e a s e d i s c u s s e d by B i s h o p and Kenny d i d or d i d not occur and t h e proposed p i e z o m e t e r l o c a t i o n would have been i n a . m o r e - s u i t a b l e p o s i t i o n f o r measuring t h i s e f f e c t . I f p i e z o m e t e r s a r e thought n e c e s s a r y t h e n s t r e s s , s t r a i n and s e t t l e m e n t i n s t r u m e n t s s h o u l d a l s o be i n s t a l l e d t o p e r m i t 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 ot the f o u n d a t i o n as the embankment i s constructed.. For the p a r t i c u l a r f i l l f o u n d a t i o n d i s c u s s e d i n t h i s t h e s i s and f o r most s o f t f o u n d a t i o n s t o r g r a n u l a r embankments piezom-e t e r s t o measure the e x c e s s pore p r e s s u r e s d e v e l o p e d i n the f o u n d a t i o n under the f i l l 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 r e q u i r e d t o a s s u r e t h a t a s t a b i l i t y f a i r u r e does not o c c u r . N e v e r t h e l e s s t h e expense e n t a i l e d i n p e r f o r m i n g l a b o r a t o r y t e s t s t o d e t e r m i n e 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 i n d u c e d pore p r e s s u r e s i s at l e a s t p a r t i a l l y wasted s i n c e the q u e s t i o n "Do l a b o r a t o r y t e s t s d u p l i c a t e f i e l d c o n d i t i o n s ? " remains unanswered. Two 50 q u e s t i o n s , "What c a u s e d t h e v a r i a t i o n s be tween t h e m e a s u r e d p o r e p r e s s u r e s and t h o s e d e t e r m i n e d f r o m 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 ? " and " W o u l d f i e l d s t r a i n m e a s u r e m e n t s have v e r i f i e d t h a t t h e s t r a i n s c a u s e d by t h e embankment l o a d we re i n t h e o r d e r o f 1 o r 2 p e r c e n t as i n d i c a t e d by t h e c o m p a r i s o n o f t h e f i e l d and l a b o r a t o r y p o r e p r e s s u r e s ? " , c o u l d p o s s i b l y have b e e n a n s w e r e d i f s t r e s s a n d s t r a i n i n s t r u m e n t s had b e e n u s e d . 1. K e n n e y , 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 o f L a y e r e d C l a y s " , J o u r n a l o f 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 , p p . 2 7 - 5 5 . 2 . B i s h o p , A .W . and B j e r r um, 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 t h e S o l u t i o n o f S t a b i l i t y P r o b l e m s " , 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 S t r e n g t h o f 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 . 4 3 7 - 5 0 1 . B i b l i o g r a p h y B i s h o p , A . W. and 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 t h e S o l u t i o n o f S t a b i l i t y P r o b l e m s " , . 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 o f 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 . 4 3 7 - 5 0 1 . . B i s h o p , A . W . and H e n k e l , D . J . , " T h e Measu rement o f S o i l P r o p e r t i e s i n t h e T r i a x i a l T e s t " , 1 9 6 4 , Edward A r n o l d . K e n n y , 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 o f L a y e r e d C l a y s " , J o u r n a l o f 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 , p p . 2 7 - 5 5 . " L a b o r a t o r y S o i l s T e s t i n g " , E M - 1 1 1 0 - 2 - 1 9 0 6 , 1 9 6 5 , M a n u a l s - C o r p s o f E n g i n e e r s . " S t a b i l i t y o f E a r t h and R o c k f i l l D a m s " , E M - 1 1 1 0 - 2 - 1 9 0 2 , 1 9 6 0 , M a n u a l s - C o r p s o f E n g i n e e r s . S c o t t , R . F . , " P r i n c i p l e s o f S o i l M e c h a n i c s " , 1 9 6 3 , A d d i s o n - i A f e s l e y . T e r z a g h i , K. and Peck., R . B , , " S o i l M e c h a n i c s i n E n g i n e e r i n g P r a c t i c e " , . J o h n lA/iley and S o n s . . ' BRITISH COLUMBIA GREAT NORTHERN LINE CHANGE p >i... . t i . GRADING CONTRACTS F i g u r e 1 Id 0. r~ OL -M L , . ' *"/ G r a v e l M L - C L L O G O F H O L E G 5 - D D - 7 9 Z W A T E R C O N T E N T B CL D E F H I M N O P s T V X Y M L - C L , C L ML-CL, C L C L M L - C L , C L M L - C L , C L C L CL M L - C L M L CL C L C L C L G L ML, - *" . Graval ly L I M I T S : L L . P I 23 4 2.8 9 23,27 5,9 4,10. l& IO '23.26, 5,10 j 2.4,28 4,11 25,28 S , © •26,39,42 1"" 8,15,16 7 IN.P -N.PZ3 22,37 S,IS 124,30 8,io \zz ' 13 26,31 10,13 AO D R Y UNIT WEIGHT * / F T 3 8 0 9 0 IOO no / M L - 5ILT, C L A Y , M L - C L - SILTY C L A Y , GVL- SILTY G R A V E L N=E3 N= NUMBER BLOWS S T A N D A R D PENETRATION TEST S C A L E f = 1 0 V F i g u r e 2 1 • z if) in LU cr h (/) or < I m ^4 --2 B .6 -^O 5 T R E N G T H ENVELOPE / ^ 6 jcE * Y x T L x—- __  ~x \ \ \ V Y \ L • Tl era c I 2 3 4- 5 . . . •. N O R M A L S T R E S S T O N S / F T S U M M A R Y O F Q T E S T R E S U L T S 2 3 A- 5 6 7 . 8 9 NORMAL S T R E S S TONS/c -rZ T) M » • , - . S U M M A R Y OF R T E S T RESULTS era c H E N V E L O P E 1 E N V E L O P E E 5 , 4 G 3 = T O T A L S T R E 5 5 E S i <S'3«= EFFECT IVE S T R E S S E S X< = PORE P R E S S U R E N O R M A L S T R E S S J 1. t 5 1 0 1 5 2 0 P E R C E N T A X I A L ' S T R A I N Figure 6 in m t-cn 7 ^ A X I A L S T R A I N ' 4 £ a io EFFECTIVE NORMAL 5 T R E 5 5 12 OP c rb 2 4 6 8 10 12 EFFECTIVE NORMAL STRESS : * , ' --•6 CQ OLA «» 13^7 A X I A L S T R A I N Z A- S ' 8 IO 12 EFFECTIVE NORMAL STRE55 - - 6t IA in I- 4 < UJ 17"% A X I A L S T R A I N -'• .'• EFFECTIVE NORMAL STRESS M A X I M U M P R I N C I P A L E F F E C T I V E S T R E S S R A T I O UJ —T-1/1 — T T N + H + . m o I "1 + or + • + 7) 0 + H _+ + x l H + X £ O + • 4Q' FILL - ARC 5 *]. S C A L E I" = 4 0 f „ ' Ys»T- 1 c V z o n e i (FIL.O l i S - o o ' •' 30.oo o 2.16 ZOHE 2 A / 3 d . 0 0 3 5 . 0 0 o Z.OB ZONE 2 B 72.50 SS.oo. a 1.16 20 HE 3 6 0.00 ZB-oo 0 0.16 CONVERSION FACTOR A I INCH' »(20'y20'yg.Z.4%Tl>)„ ?tj$ FRICTION' ' • • . ' • r.75-. (T^Has')" • i.axf, o.lfl (TAN 3 5 * ) » 6.1 it 1 1 . 0 0 1 11 .001- (25"K)=»7S-. 0 1 5 " FACTOR OF SAFETY F ' 5 \ zTf IU.015 -: ,r t»° -T»='l.4£5-' DRIVING,. . ., -{.9.34(6 - \.16S) as"5- is I 7 2 , 0 > 5 \ Figure f T D .GRADE <OC T. 9, 1967.' \C», L L PI 25 £9.2 C S 2C.4-40.1 LL PI 19 3 215 104.1 ZOA 31 IZ 52.0 S3.%J 7* LL PI * p i 241 « l 23.5 •)5.I 31 LL PI '•»•»S« 2-> 15 B ZZ.t 2LI IM NP 2*3 ss.s £1.1 LL PI *p to 1 z « s >*5 c . II ro '•4 2-4 » LL PI u.* 33 ST 12 17 eo.* 29.T 2*6 m Ml LL PI <. 28 ix. s 21.4 S9.4 19.0 rz.4 *-•» III.O L L PI f p 11 & 1 liV IOS-7 LL PI ur'1 to SO.I 21 24.4 *LR 24.4 • PIEZOMETER LOCATION 4 NUMBER. PIEZOMETER" LOCATIONS $ .DATE5"0F FILL' CONSTRUCTION S C A L E l"»**0' 2 ^ 2= [a (0 (4 6 + <*') 4 lr ( <A+ + x - <*' )J F R O M " P R 1 N C I P L . E S O F S O I L M E C H A N I C S , I N V O L V E D I N T H E D E S I G N O F R E T A I N I N G W A L L S £ B R I D G E A B U T M E N T S " B Y L . A . P A L M E R , P U B L I C R O A D S , D E C . ( V O L . \ % N O . io) Figure 12 TOTAL' PORE PRESSURES MEASURED BY PIEZOMETERS IN R 5 . I . 3 h UJ LJ LL 10 7. P <L LU I 5 / NOV. 1,1966 " G O . 7 0 s o y ' ^ ^ PORE P R E S S U R E C O R R E C T E D F O R D I S S I P A T I O N / / Y PROJECTED. PORE PRESSURE FOR 2 S' FILL A C T U A L M E A S U R E D P O R E P R E 5 S U R E . ZO 30 , PIEZOMETER *IO P O R E P R E S S U R E C O R R E C T E D F O R D I SS I PAT ION ! ; — — / NOV. 1,1966 PROJECTED PORE PRESSURE FOR 25' FILL ACTUAL MEASURED PORE PRESSURE . . Y Y •'. |-5EPT. |}|9C6 J-OCT.-I, I9G6 10 ZO 3 0 TIME DAYS PIEZOMETER * 1 40 50 G O Figure 15 20 1 5 P O R E P R E S S U R E C O R R E C T E D F O R D I S S I P A T I O N UJ o U J -X GO 70 80 "PROJECTED PORE PRESSURE FOR 25' FILL ACTUAL MEASURED PORE PRESSURE 30 40 TIME DAYS PIEZOMETER *9 m u. Q UJ 5 I • P O R E P R E S S U R E C O R R E C T E D F O R D I S S I P A T I O N / L S E P . I, 1966 GO 70 80 / + P R O J E C T E D P O R E P R E S S U R E ' FOR 25* FILL A C T U A L M E A S U R E D P O R E P R E S S U R E 10 . 20 • 3 0 T I M E D A Y S PIEZOMETER *2 40 50 60 Figure 16 35 f — P O R E P R E S S U R E C O R R E C T E D j F O R D I S S I P A T I O N : | + — PROJECTED PORE PRESSURE, I FOR 25' FILL PIEZOMETER *3 Figure 17 PORE PRESSURE CORRECTED FOR DISSIPATION /. / / ' / iPROJECTED PORE PRESSURE / / FOR 25' FILL / GO 70 ACTUAL MEASURED PORE PRESSURE 30 40 TIME - DAYS . 50 60 GO PIEZOMETER * 4 Figure 18 3 5 (——PORE PRESSURE CORRECTED I FOR DISSIPATION 10 20 ' 30 AO 50 GO TIME DAYS PIEZOMETER ^5 PORE PRESSURE CORRECTED FOR DISSIPATION-A / V / fPROJECTED PORE PRESSURE FOR 25* FILL 6 0 70 -ACTUAL MEASURED PORE PRESSURE so 10 2 0 30 T I M E D A Y S P I E Z O M E T E R *Q> 40 5 0 60 Figure 20 25r PORE PRESSURE CORRECTED FOR DISSIPATION / 7 . / / • / . rPROJECTED PORE PRESSURE FOR 25* FILL ACTUAL MEASURED PORE PRESSURE 20 30 TIME DAYS PIEZOMETER *~7 80 Figure 21 30-/ / /'. I I I I -PORE PRESSURE CORRECTED FOR DISSIPATION T I M E D A Y S P I E Z O M E T E R * 8 [ Figure 22 U I 3 5 * / F T 3 0= 3 0 ° 5 +-A R C C E N T E R S - ^ + 1 + 8 & or S A F E T Y r \ K V F A C T O R 1 2.14 2 . 2 . 0 1 3 2 . 5 7 *r 2 . 1 3 5 2 . 3 5 6 • 1 . 8 4 .; 7 2 . 3 6 ' 8 2 . 5 2 r = 7 2 . 5 ^ F T 3 0 = 3 5 tt= G O * / F T * P I E Z O M E T E R S P - 4 20' FILL S C A L E l " = 2 0 ' .-THIS FILL HAD NOT BEEN PLACED ON ( DATE PORE PRESSURES WERE MEASURED . 2 0 ' F I L L 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 IS VALUE OF EXCESS PORE PRESSURE AT THAT -PART\CULAR POINT ON . THE ARC. = .0Stan30°-T- . 3 t a n 3 5 ° + N 3tAn2& % . 0 b t a n 3 5 e 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 E X C E S S P O R E P R E S S U R E EQUI P O T E N T I A L S — + 5 +7 2 5 ' F I LL S C A L E |"=4-C> 2 5 ' F I L L S C A L E r ' = Z O ' E X C E S S P O R E P R E S S U R E E Q U I P O T E N T I A L S F O R E O ' F I L L ( S U M O F E X C E S S P O R E P R E S S U R E S O F S E R l Z J 9 < b 6 > A N D T H E I N C R E A S E IN E X C E S S , P O R E P R E S S U R E S " B E T W E E N S E P . Z\ A N D Z 3 , \°><i>(o) S C A L E • | "= 4 0 ' FACTORS OF SAFETY FOR SO FOOT FILL ARC FOR MEASURED PORE PRESSURES .FOR PROJECTED PORE PRE5SURE5 NO EXCESS PORE PRESSURES PORE PRESSURES FROM STRESS DISTRIBUTION 1 . I.GI 1.28 2.14 1.31 ' : 1.21 2.01 1.33 3 2.16 1.79 2.57 . I.GI • ^ . 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.8Z • " c H a GC FILL SCALE I"-40' 

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