FOUNDATION
ASPECTS
OF COASTAL
STRUCTURES
Proceedings volume
3
International Symposium on Soil
Mechanics Research
and Foundation Design for the
Oosterschelde Storm Surge Barrier.
Delft,The Netherlands,
Symposium Committee
H. Engel, chairman R i j k s w a t e r s t a a t * J. F. Agema W. Bol<lioven J. M. Sciietters J. C. Slagter P. A. van de Velde A. F. van Weele R i j k s w a t e r s t a a t F o u n d a t i o n ' S t i c h t i n g W a t e r b o u w k u n d i g L a b o r a t o r i u m ' * * / Delft Soil M e c h a n i c s L a b o r a t o r y D o s b o u w v.o.f.*** R i j k s w a t e r s t a a t Delft University of T e c h n o l o g yRoyal I n s t i t u t i o n of Engineers in The N e t h e r l a n d s N e t h e r l a n d s S o c i e t y for Soil M e c h a n i c s a n d F o u n d a t i o n Engineering
Scientific Committee
W. J. Heijnen, chairman J. D. Nieuwenhuis, secretary K. D'Angremond J. W. Boehmer J. M. van Geest T. W. Lambe A. Verruilt Delft Soil M e c h a n i c s L a b o r a t o r y Delft Soil M e c h a n i c s L a b o r a t o r y D o s b o u w v.o.f. R i j k s w a t e r s t a a t R i j k s w a t e r s t a a t M a s s a c h u s e t t s I n s t i t u t e of T e c h n o l o g y Delft University of T e c h n o l o g yOrganizing Committee
J. K. Nieuwenhuis, chairman J. D. Nieuwenhuis, secretary E. H. de Leeuw L R. de Vlugt R i j k s w a t e r s t a a t Delft Soil M e c h a n i c s L a b o r a t o r y Delft Soil M e c h a n i c s L a b o r a t o r y Delft H y d r a u l i c s Laboratory * R i j k s w a t e r s t a a t is the D u t c h Public W o r k s D e p a r t m e n t * * The F o u n d a t i o n c o m p r i s e s the Delft H y d r a u l i c sL a b o r a t o r y and the Delft Soil M e c h a n i c s L a b o r a t o r y * * * D o s b o u w v.o.f. is the c o n s o r t i u m of b u i l d i n g
c o n t r a c t o r s t h a t is b u i l d i n g the O o s t e r s c h e l d e S t o r m Surge Barrier.
C O N T E N T S V O L U M E 1
Review of the Project and History of the Design
\. 1 Overall p i c t u r e of t h e p r o j e c t by H. Engel I. 2 Review of the v a r i o u s d e s i g n s by F. S p a a r g a r e n I. 3 S p e c i a l g e o t e c h n i c a l s t u d i e s a n d their u n e x p e c t e d e f f e c t s by J . W. B o e h m e r
Stress-strain Behaviour of Oosterschelde S a n d s
II. 1 S t r e s s - s t r a i n behaviour f r o m s t r e s s path t e s t s by W. A. Marr, K. H0eg
II. 2 S t r e s s - s t r a i n behaviour for f i n i t e e l e m e n t m e t h o d s by A. W. W . M. B l e g s t r a a t e n , C. J . Kenter
II. 3 Pore pressure g e n e r a t i o n
by F. P. S m i t s , K. H. A n d e r s e n , G. G u d e h u s
Predictions by Theoretical Methods
III. 1 P r o b a b i l i s t i c a p p r o a c h t o d e t e r m i n e l o a d s a n d s a f e t y f a c t o r s by D. K o o m a n , T h . Mulder, J . K. V r i j i i n g , L de Quelerl] III. 2 C o m p u t a t i o n by f i n i t e e l e m e n t s
by C. J . Kenter, P. A. Vermeer
III. 3 S i m p l e n u m e r i c a l m e t h o d s t o d e t e r m i n e d i s p l a c e m e n t s a n d s t a b i l i t y of piers (spring c o n s t a n t and B r i n c h Hansen)
by J . B. S e l l m e i j e r
III. 4 Excess pore pressures a n d d i s p l a c e m e n t s d u e t o w a v e i n d u c e d l o a d i n g of a c a i s s o n f o u n d a t i o n as p r e d i c t e d by p l a s t i c i t y a n a l y s i s
C O N S T E N T S V O L U M E 2
Predictions by Model T e s t s
IV. 1 C a i s s o n t e s t s at N e e l t j e J a n s , The N e t h e r l a n d s by T. W. L a m b e , J . W. Boehmer, W. F. R o s e n b r a n d IV. 2 Model t e s t s on piers, s c a l e 1 : 10
by L. de Q u e l e r i j , J . J . Broeze IV. 3 C e n t r i f u g e t e s t s
by P. W. Rowe
Site investigation and Densification Studies
V. 1 Site i n v e s t i g a t i o n of s o i l s by J . V e r m e i d e n , P. L u b k i n g , E. F. J . de M u l d e r V. 2 L a b o r a t o r y i n v e s t i g a t i o n s r e g a r d i n g t h e a r t i f i c i a l d e n s i f i c a t i o n of s a n d a n d gravel m a t e r i a l s in the O o s t e r s c h e l d e by P. G. J . Davis V. 3 S t a t i s t i c a l s t u d y of in-situ m e a s u r e m e n t s of s o i l p r o p e r t i e s by W. E. J a w o r s k i V. 4 D e n s i f i c a t i o n In f i e l d p r a c t i c e - M e t h o d s a n d r e q u i r e m e n t s by A. A. Pladet Soil-structure Interaction VI. 1 G r o u n d w a t e r f l o w a n d d y n a m i c g r a d i e n t s by F. B. J . B a r e n d s , R. T h a b e t
VI. 2 I n t e r a c t i o n f o r c e s b e t w e e n piers a n d sill s t r u c t u r e by J . D. N i e u w e n h u i s , J . M. v a n Geest, P. M o l e n k a m p
V I . 3 Full s c a l e t e s t s on e l e m e n t s representing on t h e pier-sill I n t e r f a c e by E. P. H u d i g , D. W. de H a a n , C. J . van R o s s e n , F. S t a m
VI. 4 Sill d e s i g n
C O N T E N T S V O L U M E 3 O p e n i n g C e r e m o n y 7 — A d d r e s s of W e l c o m e by H. Engel, Director of t h e D e l t a d i e n s t of R i j k s w a t e r s t a a t 9 — O p e n i n g A d d r e s s by J . W. T o p s , Director-General of R i j k s w a t e r s t a a t 9 D i s c u s s i o n s 11
— S e s s i o n I, Review of the project a n d h i s t o r y of t h e d e s i g n 11 — S e s s i o n II, Stress-strain behaviour of O o s t e r s c h e l d e s a n d s 19
— S e s s i o n III, P r e d i c t i o n s by t h e o r e t i c a l m e t h o d s 35
— S e s s i o n IV, P r e d i c t i o n s by model t e s t s 55 — S e s s i o n V, Site i n v e s t i g a t i o n a n d d e n s i f i c a t i o n s t u d i e s 77
— S e s s i o n V I , S o i l - s t r u c t u r e i n t e r a c t i o n 87
Inserted lecture 88
The d e s i g n of t h e barrier in r e l a t i o n t o the d e f o r m a t i o n s , by J . M. van Geest 88
C l o s i n g C e r e m o n y 93 — T e c h n i c a l C l o s i n g by W. J . H e i j n e n , C h a i r m a n of t h e S c i e n t i f i c C o m m i t t e e 93
— F o r m a l C l o s i n g by A. F. van W e e l e , President of t h e N e t h e r l a n d s S o c i e t y for
Soil M e c h a n i c s a n d F o u n d a t i o n Engineering 96
Corrigenda Proceedings Vol. 1 & V o l . 2 99
ADDRESS OF WELCOME by H. Engel
Director of tfie Deitadienst of Rili<swaterstaat L a d i e s and Gentlemen,
On b e h a l f o f t h e Symposium Committee I b i d y o u welcome t o D e l f t , welcome t o o u r symposium. F o u n d a t i o n A s p e c t s o f C o a s t a l S t r u c t u r e s .
I w o u l d l i k e t o e x t e n d a s p e c i a l word o f welcome t o t h e d i r e c t o r - g e n e r a l o f o u r Department o f P u b l i c Works, Water c o n t r o l and T r a f f i c , g e n e r a l l y c a l l e d R i j k s -w a t e r s t a a t . He -w i l l h o l d t h e o p e n i n g a d d r e s s .
Between a l l o u r d i s t i n g u i s h e d g u e s t s I w o u l d l i k e , t o m e n t i o n t h e l a d i e s who had t h e courage t o come w i t h t h e i r husbands t o a c o u n t r y where t h e O r g a n i z i n g Com-m i t t e e t e l l s y o u t h a t t h e t e Com-m p e r a t u r e seldoCom-m r i s e s above 15 d e g r e e s , and t h a t r a i n c o a t s a r e a d v i s a b l e . We a r e v e r y g l a d you a r e w i t h u s , we hope t o see y o u and we hope y o u w i l l l i k e D e l f t , t h e p l a c e we chose n o t o n l y because i t i s t h e c r a d l e o f D u t c h e n g i n e e r s , b u t a l s o because i t i s a l o v e l y o l d t o w n .
The Symposium has t h r e e m a j o r o b j e c t i v e s , t h e f i r s t i s a v e r y e g o i s t i c one, t o g i v e a l l t h e p e o p l e w o r k i n g on t h e s t o r m s u r g e b a r r i e r a c l e a r v i e w o f what t h e g e o t e c h n i c a l p e o p l e f o u n d and what t h e i r c o n c l u s i o n s a r e . The second i s t h a t we i n v i t e d y o u as e x p e r t s t o h e a r t h e s e speeches and h o p e f u l l y y o u w i l l c r i t i c i z e them, because f r o m c r i t i c i s m s p r i n g s t r u t h . The t h i r d and t h e l a s t i s t h e n o b l e r e a s o n i n t h e programme, t o i n f o r m o u r c o l l e a g u e s f r o m a l l o v e r t h e w o r l d o f o u r f i n d i n g s .
The o r g a n i s a t i o n o f t h i s symposium was s t a r t e d a b o u t a y e a r ago under t h e r e s p o n s i b i l i t y o f t h e N e t h e r l a n d s S o c i e t y f o r S o i l Mechanics and F o u n d a t i o n E n g i n -e -e r i n g as a j o i n t v -e n t u r -e b-etw-e-en t h -e D -e l f t S o i l M-echanics L a b o r a t o r y and t h -e R i j k s w a t e r s t a a t .
I t was backed up and s u p p o r t e d b y t h e D e l f t U n i v e r s i t y o f T e c h n o l o g y , t h e R o y a l I n s t i t u t i o n o f E n g i n e e r s i n t h e N e t h e r l a n d s , and t h e c o n t r a c t o r s i n v o l v e d i n the b a r r i e r d e s i g n . There a r e about 2 0 0 p a r t i c i p a n t s , a b o u t a t h i r d o f them come f r o m a b r o a d . I t i s my s i n c e r e w i s h t h a t a l l o f y o u s h o u l d e n j o y t h i s symposium b o t h t e c h n i c a l l y and s o c i a l l y . Thank y o u . May I i n v i t e t h e d i r e c t o r - g e n e r a l o f t h e R i j k s w a t e r s t a a t t o h o l d h i s o p e n i n g address„ OPENING ADDRESS by J. W. Tops
Director-Generai of ttie Riil(swaterstaat Mr„ Chairman, l a d i e s and g e n t l e m e n .
F o u n d a t i o n s p l a y an i m p o r t a n t , i f n o t a c r u c i a l r o l e i n t h e c o n s t r u c t i o n o f o u r c o a s t a l d e f e n c e s . As y o u a l r e a d y know, o r w i l l see i n t h e f i l m t h a t w i l l be shown a f t e r my i n t r o d u c t i o n , a v e r y i m p o r t a n t p a r t o f t h e N e t h e r l a n d s l i e s below s e a - l e v e l and has t o be p r o t e c t e d a g a i n s t t h e N o r t h Sea.
F a i l u r e i n t h e c o n s t r u c t i o n o f o u r c o a s t a l d e f e n c e s can cause f l o o d i n g o f 50% o f o u r c o u n t r y . The D e l t a P r o j e c t r e d u c e s t h i s r i s k by h e i g h t e n i n g and/or s t r e n g t h -e n i n g t h -e d y k -e s , b y c l o s i n g a numb-er o f -e s t u a r i -e s and b y b u i l d i n g a s t o r m surg-e b a r r i e r i n t h e E a s t e r n S c h e l d t .
N e a r l y 2 5 y e a r s ago, when t h e D e l t a P r o j e c t was s t a r t e d , t h e c l o s i n g o f a b i g e s t u a r y l i k e t h e E a s t e r n S c h e l d t was c o n s i d e r e d v e r y d i f f i c u l t , and we d e c i d e d t h a t we w o u l d d e v e l o p new methods and g a i n e x p e r i e n c e w h i l e r e a l i z i n g t h e c l o s -i n g o f s m a l l e r sea-arms. T h -i s -i s t h e r e a s o n why t h e E a s t e r n S c h e l d t , w h -i c h has a t i d a l volume a b o u t t w i c e as b i g as t h e o t h e r e s t u a r i e s i n t h e D e l t a P r o j e c t ,
was t o be t h e l a s t sea-arm t o be p r o t e c t e d . I n t h e l a s t t w e n t y y e a r s t h e con¬ s t r u c t i o n o f o u r c i v i l - e n g i n e e r i n g works was, however, more and more i n f l u e n c e d by e n v i r o n m e n t a l c o n s i d e r a t i o n s . These e n v i r o n m e n t a l c o n s i d e r a t i o n s l e d t o t h e c h o i c e o f a s t o r m surge b a r r i e r f o r t h e E a s t e r n S c h e l d t i n s t e a d o f a permanent-l y c permanent-l o s e d dam. Three c o n d i t i o n s a r e a t t a c h e d t o t h i s d e c i s i o n , t a k e n by t h e government m 1974: 1. t h e e x t r a c o s t s a r e l i m i t e d t o a f i x e d , b u t v e r y c o n s i d e r a b l y amount; 2. t h e p r o j e c t has t o be r e a d y i n 1985; 3. t h e p r o j e c t has t o be t e c h n i c a l l y f e a s i b l e .
The f i r s t c o n d i t i o n i n d i c a t e s c l e a r l y how much t h e government i s p r e p a r e d t o pay f o r t h e p r e s e r v a t i o n o f such an i m p o r t a n t e n v i r o n m e n t as t h e E a s t e r n S c h e l d t . A l t h o u g h e n v i r o n m e n t a l a s p e c t s a r e v e r y d i f f i c u l t t o f i t i n a c o s t - b e n e f i t
ana-l y s i s , v e r y much i m p o r t a n c e was a t t a c h e d t o t h e e n v i r o n m e n t a ana-l v a ana-l u e o f t h i s a r e a . We can be s u r e t h a t e n v i r o n m e n t a l and s o c i a l c o n s i d e r a t i o n s w i l l , i n t h e f u t u r e d e t e r m i n e t o a l a r g e e x t e n t o u r i n f r a - s t r u c t u r a l c o n s t r u c t i o n s . T h i s i s , o f c o u r s e , o n l y p o s s i b l e when adequate t e c h n i c a l s o l u t i o n s can be founds
The second c o n d i t i o n s - t h e t i m e f a c t o r - has been i n t r o d u c e d n o t t o w i t h h o l d d e l t a - s a f e t y f r o m t h e p o p u l a t i o n a r o u n d t h e E a s t e r n S c h e l d t any l o n g e r t h a n ne-c e s s a r y .
The l a s t c o n d i t i o n no d o u b t t h e most i m p o r t a n t one f o r you r e g a r d s t h e d i f -f i c u l t y o -f t h e a s s i g n e d t a s k .
I t can be s a i d t h a t t h e p r o j e c t i s o f a u n i q u e c h a r a c t e r i n many a s p e c t s . Pract i c a l l y a l l elemenPracts o f Pract h e p a r Pract i a l l y opened c o n s Pract r u c Pract i o n a r e Pract e c h n i c a l l y w e l l -known i n p r i n c i p l e and have been used b e f o r e . However, t h e extreme s c a l e o f t h e s e e l e m e n t s and t h e c o m b i n a t i o n o f them i n a r o u g h a r e a such as t h e mouth o f t h e E a s t e r n S c h e l d t r e p r e s e n t s a c o m p l e t e l y new s i t u a t i o n . The p r o b l e m o f t h e f o u n d a t i o n , i n w h i c h t h e D e l f t S o i l Mechanics L a b o r a t o r y i s d e e p l y i n v o l v e d , ^ i s an a s p e c t o f e x t r e m e i m p o r t a n c e . D u r i n g one and a h a l f y e a r s o f s t u d y , t o ex p l o r e whether t h e f i x e d c o n d i t i o n s c o u l d be met, i t was p r o v e d s e v e r a l t i m e s t h a t we a r e c l o s e l y a p p r o a c h i n g t h e l i m i t s o f our t e c h n i c a l know-how.
Mr. Chairman, I am o f t h e o p i n i o n t h a t a symposium l i k e t h i s can c o n t r i b u t e t o make everyone u n d e r s t a n d c l e a r l y t h e way i n w h i c h we have d e a l t w i t h t h e p r o -b l e m o f t h e f o u n d a t i o n o f t h e s t o r m s u r g e -b a r r i e r i n t h e E a s t e r n S c h e l d t .
We are p r o u d o f t h e f a c t t h a t we have been a b l e t o make t h i s s t o r m s u r g e b a r r i e r i n t h e E a s t e r n S c h e l d t . I l e a v e i t up t o you t o d e c i d e whether t o agree w i t h t h e s t a t e m e n t o f o u r f o r m e r m i n i s t e r W e s t e r t e r p , t h a t t h e s t o r m s u r g e b a r r i e r m t h e E a s t e r n S c h e l d t i s t o be t h e g r e a t e s t c i v i l - e n g i n e e r i n g work o f t h e c e n t u r y . I hope t h a t t h e e x p e r i e n c e g a i n e d i n t h e r e s e a r c h f o r t h e b e s t p o s s i b l e f o u n d -a t i o n o f t h e s t o r m s u r g e b -a r r i e r , w i l l p r o v i d e o t h e r e n g i n e e r s w i t h s o l u t i o n s f o r p r o b l e m s t h a t t h e y w i l l meet i n t h e f u t u r e .
Mr. Chairman, i t i s my p r i v i l e g e a f t e r t h i s i n t r o d u c t i o n , t o w i s h you a success-f u l symposium, and y o u , l a d i e s and g e n t l e m e n , a number o success-f i n s t r u c t i v e days. Thank y o u .
Session I
Review of the Project and History of the Design
chairman:
I have t h e p l e a s u r e t o open t h e f i r s t s e s s i o n o f t h i s symposium. S e c t i o n I con-c e r n s a r e v i e w o f t h e p r o j e con-c t and t h e h i s t o r y o f t h e d e s i g n . I t f o con-c u s e s on t h e theme o f t h e c o n f e r e n c e s , S o i l Mechanics Research and F o u n d a t i o n D e s i g n f o r t h e E a s t e r n S c h e l d t Storm Surge B a r r i e r . F o c u s i n g i m p l i e s d i s t a n c e and w i l l i n g n e s s t o s e l e c t . A l l t h r e e s p e a k e r s o f t h i s m o r n i n g have p l a y e d and a r e s t i l l p l a y i n g an i m p o r t a n t r o l e i n managing and p e r f o r m i n g t h e s t u d y o f t h e c l o s u r e o f t h e E a s t e r n S c h e l d t . They a r e a l l R i j k s w a t e r s t a a t c o l l a b o r a t o r s and y o u w i l l r e a l i s e t h i s m o r n i n g t h a t t h e i r approach t o t h e t o p i c s t o be d i s c u s s e d shares common c h a r a c t e r i s t i c s , namely awareness o f t h e many p r o b l e m s i n r e s p e c t o f d e s i g n i n g c o a s t a l works i n t h e N e t h e r l a n d s , more emphasis on b o u n d a r y c o n d i t i o n s t h a n on t h e d e s i g n d e t a i l s , and f i n a l l y d e v e l o p e d o r adapted c o n s t r u c t i o n t e c h n i q u e s based on new s c i e n t i f i c and t e c h n i c a l knowledge. These common c h a r a c t e r i s t i c s i n my o p i n i o n bear w i t n e s s t o a f i n e R i j k s w a t e r s t a a t t r a d i t i o n i n d e s i g n i n g and b u i l d i n g c o a s t a l e n g i n e e r i n g p r o d u c t s o f h i g h s t a n d a r d . L a d i e s and g e n t l e m e n , I hope t h a t t h i s i n t r o d u c t o r y s e s s i o n o f t h e g e o t e c h n i c a l symposium p r o v i d e s a c l e a r framework f o r t h e c o n t r i b u t i o n s o f t h e o t h e r s e s s i o n s . I w o u l d l i k e now t o i n t r o d u c e Mr. E n g e l t o g i v e an o v e r a l l p i c t u r e o f t h e p r o -j e c t . Mr. E n g e l i s head o f t h e D e l t a d i e n s t , t h a t i s a s p e c i a l d e p a r t m e n t o f R i j k s w a t e r s t a a t w h i c h i s i n c h a r g e o f t h e e x e c u t i o n o f t h e D e l t a P r o j e c t . I t i s e v i d e n t t h a t Mr. E n g e l i s i n t h e b e s t p o s i t i o n t o g i v e t h a t o v e r a l l p i c t u r e . May I ask Mr. E n g e l t o t a k e t h e f l o o r f o r h i s c o n t r i b u t i o n .
OVERALL PICTURE OF THE PROJECT by H. Engel
Vol. 1, Paper 1.1 Chairman :
Thank you Mr. E n g e l , y o u r e a l l y succeeded i n y o u r paper and now a g a i n on t h e f l o o r , t o i l l u s t r a t e t h e i m p l i c a t i o n s o f t h e p r o j e c t , i n v i e w o f t h e e n v i r o n - ^ m e n t a l a s p e c t s . As you p o i n t e d o u t , t h i s c o n f r o n t a t i o n l e d t o a t o t a l l y d i f f e r
e n t d e s i g n , much more c o m p l i c a t e d t h a n t h e o r i g i n a l , and i n my o p i n i o n never b e f o r e i n t h e N e t h e r l a n d s has so b i g a p e r c e n t a g e been a p p l i e d f o r r e s e a r c h f o r b i g c i v i l e n g i n e e r i n g p r o j e c t s .
Thank y o u v e r y much. Mr. E n g e l .
May I now i n v i t e Mr. Spaargaren f o r h i s c o n t r i b u t i o n c o n c e r n i n g a r e v i e w o f t h e v a r i o u s d e s i g n s .
REVIEW OF THE VARIOUS DESIGNS by F. Spaargaren
Vol. 1, Paper 1.2 Chairman:
Thank y o u . Mr. Spaargaren. You i l l u s t r a t e d v e r y w e l l t h e many b o u n d a r y c o n d i - ^ t i o n s t o be r e s p e c t e d d u r i n g t h e d e s i g n w o r k . Of t h e s e c o n d i t i o n s t h e s o i l me c h a n i c a l c o n d i t i o n s had g r e a t i n f l u e n c e on t h e d e s i g n . T h i s c o n f e r e n c e d e a l s o n l y w i t h f o u n d a t i o n a s p e c t s . I t i s i m p o r t a n t t h a t y o u succeeded so w e l l t o r e -l a t e t h e s o i -l m e c h a n i c a -l c o n d i t i o n s t o a -l -l o t h e r c r i t e r i a t o be c o n s i d e r e d .
T h i s a v o i d s f o r a l l t h o s e who a r e n o t i n v o l v e d i n t h i s p r o j e c t t h e r i s k o f o v e r -e s t i m a t i n g t h -e r o l -e o f t h -e g -e o t -e c h n i c a l -e n g i n -e -e r , w h i c h o f c o u r s -e r -e m a i n s o f u t m o s t i m p o r t a n c e . Thank y o u v e r y much, Mr. Spaargaren.
May I i n v i t e t h e l a s t speaker o f t h i s s e s s i o n , Mr. Boehmer. Mr. Boehmer i s s e n i o r e n g i n e e r i n s c i e n c e and e n g i n e e r i n g a n a l y s i s o f t h e D e l t a D e p a r t m e n t o f R i j k s w a t e r s t a a t . Mr. Boehmer has been i n v o l v e d i n a l l s o i l mechanics and f o u n d -a t i o n p r o b l e m s f r o m t h e v e r y b e g i n n i n g o f t h e d e s i g n s t u d y o f t h e c l o s u r e o f t h e E a s t e r n S c h e l d t . W i t h t h e c o n t r i b u t i o n o f Mr. Boehmer we a r e i n e v i t a b l y a p p r o a c h -i n g t h e theme o f t h e c o n f e r e n c e .
SPECIAL GEOTECHNICAL STUDIES AND THEIR UNEXPECTED EFFECTS by J. W. Boehmer
Uo/. 1, Paper 1.3
Chairman:
Thank y o u v e r y much, Mr. Boehmer. I s a i d b e f o r e Mr. Boehmer s t a r t e d t h a t we were a p p r o a c h i n g t h e theme o f t h e c o n f e r e n c e , b u t y o u have seen y o u r s e l f t h a t we a r e a l r e a d y i n t h e m i d d l e o f t h e theme. Thank y o u v e r y much, Mr. Boehmer, f o r y o u r c o n t r i b u t i o n and f o r y o u r e n t h u s i a s t i c p e r f o r m a n c e .
L a d i e s and g e n t l e m e n , we have 15 m i n u t e s f o r d i s c u s s i o n .
I t h i n k t h a t e s p e c i a l l y t h e c o n t r i b u t i o n o f Mr. Boehmer, on page 16 o f h i s p a p e r y o u have seen a number o f c o n c l u s i o n s , can g i v e t h e p o s s i b i l i t y f o r a number o f q u e s t i o n s .
Who w i l l p u t t h e f i r s t q u e s t i o n ? G. de Josselin de Jong
I t has been p o i n t e d o u t by Mr, E n g e l t h a t t h e O o s t e r s c h e l d e p r o j e c t i s an unusu-a l p r o j e c t , r e q u i r i n g t h e c o l l unusu-a b o r unusu-a t i o n o f m u l t i - d i s c i p l i n unusu-a r y teunusu-ams. I n d e e d t h e s i t u a t i o n i s u n u s u a l w i t h r e s p e c t t o t h e s o i l mechanics a s p e c t s , because t h e sand has an e x c e p t i o n a l l o w d e n s i t y and shows an u n s t a b l e b e h a v i o u r .
P e r s o n a l l y , I was n o t i n v o l v e d i n t h e s t u d i e s , b u t I was aware o f them, s i n c e much a c t i v i t y was g o i n g on a l l around me. I was much i m p r e s s e d b y t h e c o u r a g e o f t h e young p e o p l e t o d e v e l o p computer programmes f o r t h e sand b e h a v i o u r and t h e i r p e r s e v e r a n c e t o t a c k l e a l l k i n d o f d i f f i c u l t a s p e c t s . I t was o f b e n e f i t t o s o i l mechanics t h a t g r e a t e f f o r t was made t o implement more f i m d a m e n t a l me-c h a n i me-c a l p r i n me-c i p l e s , t h a n me-commonly used i n s o i l meme-chanime-cs.
However, t h e b e h a v i o u r o f l o o s e sand i s s t i l l n o t c o m p l e t e l y u n d e r s t o o d , b a s i c -a l l y . Wh-at we need i s more i n s i g h t i n t o t h e mech-anics o f d e f o r m -a t i o n . Then, p o s s i b l y , c o n s t i t u t i v e r e l a t i o n s c o u l d be d e v e l o p e d i n a s i m i l a r manner, as Rowe d i d f o r h i s s t r e s s - s t r a i n r e l a t i o n s .
My q u e s t i o n t o Mr. E n g e l i s how much c o n f i d e n c e R i j k s w a t e r s t a a t has i n s o i l me- , c h a n i c s i n i t s p r e s e n t s t a g e i n t a k i n g t h e i m p o r t a n t d e c i s i o n s w i t h r e s p e c t t o the g r e a t works t h e y a r e r e s p o n s i b l e f o r ? Has s o i l mechanics enough r e l i a b i l i t y a t t h i s moment?
E. Engel:
W e l l , Mr. Chairman, t h i s i s a d i f f i c u l t q u e s t i o n . I n t h e f i r s t p l a c e P r o f . De J o s s e l i n de Jong s t a t e s t h e p r o b l e m o f t h e s o i l m e c h a n i c s , and t h a t i s i n d e e d i n t h i s case t h e most s e r i o u s p r o b l e m . W e l l p e r h a p s h y d r o l o g i s t s o r e n v i r o n -m e n t a l i s t s w o u l d p u t t h e -most s e r i o u s p r o b l e -m s so-mewhere e l s e . You s t a t e t h a t t h e s o i l c o n s i s t s o f a n o t t o o good sand, w e l l , t o a n o t h e r a u d i e n c e I w o u l d say i t c o n s i s t s o f sand a t t h a t i s much b e t t e r t h a n most o f t h e s o i l s t h a t we have i n t h e N e t h e r l a n d s . W e l l , t h e n about t h e c o n f i d e n c e , i t i s o f c o u r s e a method f o l l o w e d i n t h e p a s t t h a t y o u show a l o t o f c o n f i d e n c e a t t h e s t a r t and a f t e r -wards have t o r e g r e t i t b i t t e r l y , because y o u f i n d t h i n g s t h a t y o u w o u l d have
f o u n d e a r l i e r i f y o u d i d n o t p u t t h a t c o n f i d e n c e so h i g h . So o u r a i m was n o t t o p r e j u d g e t h e r e s u l t s . What e n g i n e e r s used t o d o , i s t o t r y t o f i n d t h e l i m i t s
o f o u r s a f e t y . I mean t h a t i f we ask a s o i l mechanics e x p e r t t o g i v e us t h e w o r s t i d e a he can g i v e a b o u t t h e c o n s t r u c t i o n , t h e n we w i l l a c c e p t t h a t as a b o u n d a r y u n t i l t h e t i m e when we know b e t t e r . And w i t h i n t h i s l i m i t i n g way we as e n g i n e e r s a r e s u r e t h a t we can make a s a f e s t o r m s u r g e b a r r i e r and o n l y on t h i s a s s u m p t i o n c o u l d we s t a r t t h e f u r t h e r d e s i g n a f t e r t h e one and a h a l f y e a r s t h e government gave us t o come t o t h i s c o n c l u s i o n . Of c o u r s e t h e r e w x l l always be new t h i n g s f o u n d when y o u do r e s e a r c h , and o f c o u r s e we always need new models t o g i v e a b e t t e r i d e a o f what r e a l l y happens. B u t I t h i n k I speak f o r t h e w h o l e team o f d e s i g n e r s t h a t o u r f i n d i n g s u n t i l now g i v e us t h e e n g i n -e -e r i n g p r o g n o s i s t h a t w-e can mak-e a s o l i d and s t a b l -e s t o r m s u r g -e b a r r i -e r . C.J. Sammons:
The a u t h o r m e n t i o n e d t h a t p r o t e c t i o n f r o m e r o s i o n on t h e i n l a n d s i d e o f t h e b a r r i e r was t o be p r o v i d e d by 5-10 t o n s heavy b l o c k s . Have t h e d e s i g n e r s e x p e r i e n c e w i t h u s i n g t h i s s i z e o f b l o c k s f o r p r o t e c t i o n a g a i n s t e r o s i o n b y h i g h f l o w s ? I f n o t , what c r i t e r i a o r f o r m u l a have t h e y used i n t h e d e s i g n , and how much c o n f i d e n c e have t h e y i n i t s use f o r f l o w s o f t h e s i z e e n v i s a g e d ? F. Spaargaren:
W e l l , I m e n t i o n e d t h e s e heavy b l o c k s as a t o p l a y e r o f t h e s i l l . Your q u e s t i o n i s Do we have e x p e r i e n c e i n p r a c t i c e w i t h t h o s e t y p e s o f l a y e r s and t h e d i -mensions o f s t o n e s , and I have t o say: No, u n t i l now we have e x p e r i e n c e w i t h much s m a l l e r s t o n e s , up t o say a b o u t one t o n i n t h e a c t u a l gaps we have a l r e a d y
c l o s e d i n t h e D e l t a p l a n , so what i t means i s t h a t we e x t r a p o l a t e d b y means o f model t e s t s t h e s t a b i l i t y o f t h i s t o p l a y e r , and we have t h e back up o f t h e f o r -mer model t e s t s t o t h e a c t u a l gaps, and we have c o n f i d e n c e t h a t based on t h e s e new model t e s t s t h e s e t y p e s o f b l o c k s can w i t h s t a n d t h e heavy c u r r e n t .
J. Blaauwendraad:
I t ' s a p i t y , Mr. Chairman, t h a t Mr. Boehmer c o u l d n o t do e v e r y t h i n g he wanted f o r I t h i n k t h e a s p e c t o f t h e r e l a t i o n between t h e g e o t e c h n i c a l e n g i n e e r and t h e d e s i g n e r w o u l d have been a n i c e t o p i c t o p r e s e n t t o t h i s a u d i e n c e . I t must be a r e a l p r o b l e m t o do t h i s i n a p r o p e r way and i t may be c o n n e c t e d w i t h h i s s l i d e i n w h i c h he showed a r e l a t i o n between t h e t o t a l c o s t o f t h e t o t a l p r o j e c t and t h e c o s t s w h i c h a r e n e c e s s a r y f o r t h e s t u d i e s , and I t h i n k i t was q u i t e c h a l l e n g i n g what he s a i d , t h a t when y o u r e d u c e t h e c o s t s f o r s t u d i e s and r e -s e a r c h y o u may i n c r e a -s e y o u r t o t a l c o -s t -s . I can u n d e r -s t a n d y o u do t h i -s , y o u use l e s s money i n - t h e e a r l y phase o f y o u r t o t a l s t u d y , b u t c o u l d he p l e a s e ex-p l a i n i f i t i s ex-p o s s i b l e t o have so much s t u d y i n a ex-phase o f t h e t o t a l ex-p r o j e c t i n w h i c h y o u r d e s i g n i s more o r l e s s f i x e d a l r e a d y . J. W, Boehmer: I t h i n k t h e r e i s a b a s i c d i f f e r e n c e between t h i s p r o j e c t and o t h e r p r o j e c t s . I c a l l t h i s a p r o j e c t o f f l e x i b l e b i d d i n g i n w h i c h t h e b i d d i n g on some p a r t s o f t h e d e s i g n i s s t i l l open a f t e r f i x i n g t h e b i d s and s t a r t i n g c o n s t r u c t i o n on o t h e r p a r t s o f t h e d e s i g n . My f e e l i n g i s t h a t a f t e r t h e c o n t r a c t o r has l e a r n e d f r o m t h e d e s i g n s t u d i e s what t h e p o t e n t i a l p r o b l e m s o r "spooks" d u r i n g c o n s t r u c t i o n can be he t h e n has t h e r i g h t t o come up w i t h t h e s e spooks when he makes h i s b i d . I f
t h e s e spooks have n o t been s o l v e d y e t , he may say: " W e l l , h e r e i s a b i d I have t o make, t h e r e a r e a b o u t s i x spooks i n t h e r e and I add 10% f o r each spook." Now, i f t h e r e s e a r c h e r s a r e p r e s e n t and i f t h e y can i m p r o v e t h e i r knowledge on t h e b a s i s o f c o n d i t i o n c o n t r o l measurements, t h e y can h e l p e l i m i n a t e t h e s e
spooks, so t h e c o s t o f t h e b i d d i n g goes down a g a i n . I f t h e y a r e n o t p r e s e n t , con-s t r u c t i o n c o con-s t con-s may r i con-s e above t h e i n i t i a l e con-s t i m a t e con-s acon-s a r e con-s u l t o f t h e con-s e con-spookcon-s. I t h i n k t h i s i s t h e essence. I t h i n k t h i s w i l l be t h e most i m p o r t a n t f a c t o r w h i c h c o n t r o l s t h e u n c e r t a i n t y i n t h e b i d d i n g c o s t s o f t h i s p r o j e c t and w h i c h r e q u i r e s e x t r a c o s t s f o r s t u d y . The second f a c t o r i s t h a t t h e d e s i g n e r has t o keep m c l o s e c o n t a c t w i t h h i s r e s e a r c h e r s , as l o n g as n o t a l l p a r t s o f t h e d e s i g n have
been f i x e d .
For example, i f he makes t h e p i e r s h e a v i e r o r i f he r e p l a c e s more s o i l , o r i f he makes h i s s i l l h e a v i e r , t h e n n o t o n l y c o n s t r u c t i o n p r o b l e m s c o u l d become b i g g e r b u t a l s o t h e w h o l e d e s i g n c o u l d become more e x p e n s i v e as w e l l . These a r e two components w h i c h b e s i c a l l y i n f l u e n c e c o s t s b e f o r e 1 9 8 5 . Then t h e r e i s a
t h i r d component, w h i c h i s t h e m a i n t e n a n c e c o s t s . A l t h o u g h t h e y o n l y e n t e r a f t e r 1 9 8 5 ,
t h e y a r e i n e f f e c t p a r t o f t h e t o t a l p r o j e c t c o s t s . A l t h o u g h we aim f o r a d e s i g n w i t h a minimum o f m a i n t e n a n c e c o s t s I can i m a g i n e t h a t t h e e x t r a know-how w h i c h w i l l r e s u l t f r o m c o n d i t i o n c o n t r o l o f t h e b a r r i e r and f r o m f u r t h e r r e s e a r c h m i g h t d e c r e a s e m a i n t e n a n c e c o s t s i n case u n f o r e s e e n p r o b l e m s a r i s e . The q u e s t i o n r a m s i n s how you can make a c o s t b e n e f i t a n a l y s e s i n w h i c h you i n -c l u d e t h e s e t h r e e f a -c t o r s and w h i -c h r e s u l t s a r e a s o n a b l e g u i d e l i n e f o r f u r t h e r s t u d y e f f o r t . I t h i n k t h e r e a r e p o s s i b i l i t i e s t o do t h i s w i t h a p r o b a b i l i s t i c a p p r o a c h , b u t i t w i l l t a k e some t i m e b e f o r e we work t h a t o u t .
I ' d l i k e t o i n v i t e you t o h e l p us d o i n g t h a t , because I know i n c o n c r e t e r e s e a r c h , you a r e d i s c u s s i n g t h e same s o r t o f q u e s t i o n s .
ff. Engel:
I f e a r , Mr. Blaauwendraad, t h a t you t r i e d t o g e t Mr. Boehmer o u t o f h i s f i e l d by t h i s q u e s t i o n and I must a d m i t t h a t I agree and d i s a g r e e w i t h Mr. Boehmer. I agree on t h e p o i n t t h a t c o n t i n u e d r e s e a r c h i s n e c e s s a r y t o complement t h e e x e c u t i o n o f t h i s work. I do n o t agree w i t h f i g u r e 21 shown i n t h e p a p e r o f Mr. Boehmer, and I t h i n k we s h a l l a t a l l t i m e s have t o w e i g h o u t t h e r e s e a r c h and t h e r e s u l t s we e x p e c t o f them. And as t o D u t c h c o n t r a c t o r s t h e y may see spooks when i t comes t o b i d d i n g , b u t I am s u r e t h a t most o f them a r e n o t see-i n g spooks a t a l l see-i n r e a l see-i t y . Thank you. R.S. WTignt: Mr. Chairman, I ' d l i k e t o ask a q u e s t i o n o f t h e l a s t s p e a k e r r e g a r d i n g t h e d e p t h o f t h e s c o u r h o l e on t h e down s t r e a m s i d e o f t h e b a r r i e r . He showed t h e 25 m e t r e s e s t i m a t e d d e p t h o f s c o u r and my q u e s t i o n i s , i s t h e r e some l i m i t t o t h e d e p t h o f t h e s c o u r , w h i c h w o u l d be a s e l f l i m i t i n g f e a t u r e r a t h e r t h a n an u n l i m i t e d d e p t h o f s c o u r h o l e . J.W. Boehmer: I f you c o n s i d e r t h e energy l o s s o v e r t h e b a r r i e r i t t u r n s o u t t h a t t h e s i l l i s so h i g h t h a t we have a b o u t t h e maximum e n e r g y l o s s you can have f r o m t h e w a t e r p a s s i n g t h r o u g h t h i s b a r r i e r . As a r e s u l t t h e r e i s a l o t o f t u r b u l e n c e i n t h e r e , and t h e t u r b u l e n c e seems n o t t o damp o u t v e r y f a s t . Even b e h i n d a r i v e r bed p r o t e c t i o n o f 6 0 0 m e t r e s t h e t u r b u l e n c e i s q u i t e heavy, and does n o t depend so much on t h e d e p t h o f t h e w a t e r o v e r w h i c h t h e f l o w i s g o i n g . O n l y deep s c o u r h o l e s w i t h s t e e p s l o p e s w h i c h have been s t a b i l i z e d t o p r e v e n t s l o p e f a i l u r e s , w i l l e v e n t u a l l y r e a c h e q u i l i b r i u m , p r o v i d e d some sand t r a n s p o r t a t i o n r e m a i n s p r e s e n t o v e r t h e b a r r i e r .
Suppose now t h a t t h e s t e e p s l o p e s do f a i l w h i c h r e s u l t s t h a t t h e r i v e r b e d p r o -t e c -t i o n moves down and -t h a -t -t h e d e p -t h o f -t h e w a -t e r i n c r e a s e s , -t h e r e s -t i l l m i g h -t be 25 m e t r e s e x t r a s c o u r h o l e under t h e f u t u r e d e p t h o f t h e edge o f t h e b o t t o m p r o t e c t i o n ( o f c o u r s e i t c o u l d n o t go on u n t i l 5 0 0 m e t r e s ) . T h i s was a r e a s o n t o d e c i d e n o t t o a l l o w any l o s s o f s t a b i l i t y on t h e edge o f t h e b o t t o m p r o t e c t -i o n . A l r e a d y -i n 1 9 7 4 i t was d e c i d e d t h e r e f o r e t o d e n s i f y t h e edge o f t h e b o t t o m p r o t e c t i o n and, i f s l o p e s g e t s t e e p , a l s o t o p r o t e c t t h e s e s l o p e s by a d d i n g g r a v e l o r o t h e r m a t e r i a l s . I n d o i n g t h i s we a r e more f l e x i b l e t o do more r e -s e a r c h on t h e -s c o u r h o l e -s . Chairman: L a d i e s and g e n t l e m e n ,
I am now o b l i g e d t o c l o s e t h e s e s s i o n . I can i m a g i n e t h a t you s t i l l have o t h e r 15
a u e s t i o n s . You oan p u t them i n w r i t i n g on t h e d i s c u s s i o n s h e e t and o f c o u r s e Mr! Boehmer, Mr. Spaargaren and Mr. B n g e l w i l l be a t t e n d i n g ^ ^ ^ ^ ^ J ^ -and you t h e n have t i m e -and t h e p o s s i b i l i t y t o p u t y o u r own q u e s t i o n t o them I woulï l i k e t o t h a n k once a g a i n t h e t h r e e a u t h o r s and t h e speakers ° f t h x s mor-n i mor-n g f o r t h e i r c o mor-n t r i b u t i o mor-n s . I t h i mor-n k we have mor-now t h e frame work o f t h e theme o f t h e c o n f e r e n c e , and I would l i k e t o t h a n k you t o o f o r y o u r p r e s e n c e h e r e . Thank y o u v e r y much, I w i l l now c l o s e t h e s e s s i o n .
Session II
Stress-Strain Behaviour of Oosterschelde Sands
J . T. Christian, Stone and Webster Engineering Corporation, Boston, M a s s a c h u s s e t t s , U.S.A.
chairman:
Good a f t e r n o o n , l a d i e s and g e n t l e m e n .
My name i s John C h r i s t i a n . I am a c o n s u l t i n g e n g i n e e r w i t h Stone and Webster E n g i n e e r i n g C o r p o r a t i o n .
I have been f o r t u n a t e t o be a c o n s u l t a n t t o t h e R i j k s w a t e r s t a a t D e l t a d i e n s t s i n c e 1 9 7 4 on t h i s p r o j e c t . We have t o d a y , t h i s a f t e r n o o n t h r e e p a p e r s t h a t w i l l be p r e s e n t e d .
The f i r s t paper t h a t w i l l be p r e s e n t e d has two a u t h o r s . The f i r s t a u t h o r i s W.A. M a r r , who i s a Research A s s o c i a t e a t t h e M a s s a c h u s e t t s I n s t i t u t e o f T e c h n o l o g y i n Cambridge M a s s a c h u s e t t s i n t h e U n i t e d S t a t e s , and he has been a c o n s u l t a n t t o t h e R i j k s w a t e r s t a a t D e l t a d i e n s t s i n c e 1 9 7 4 .
The second a u t h o r o f t h e p a p e r , who i s n o t h e r e t o d a y , i s Dr. Kare Hoeg, who i s t h e d i r e c t o r o f t h e Norwegian G e o t e c h n i c a l I n s t i t u t e i n O s l o .
The paper w i l l be p r e s e n t e d by Dr. M a r r .
STRESS-STRAIN BEHAVIOUR FROM STRESS PATH TESTS by W. A. Marr
Vol. 1. Paper 11.1 Chairman:
Thank y o u v e r y much.
Does anyone have any q u e s t i o n s ? M. Eamza:
I have two p o i n t s .
The f i r s t one i s : D i d t h e use o f K 7^1 a l t e r t h e v a l u e o f (j)' o f t h e sand? I n s i m i l a r t e s t s I f o u n d t h a t K ^ - t e s t s have a l t e r e d t h e r e s i d u a l shear s t r e n g t h , w h i c h i s an i m p o r t a n t factor°for l i q u e f a c t i o n p o t e n t i a l . A n o t h e r p o i n t i s : D i d y o u use c y c l i c t e s t s t o s i m u l a t e a s t o r m ( e . g . a t r a m o f waves)? W.A, Marr: Your f i r s t q u e s t i o n r e l a t e s t o t h e i m p o r t a n c e o f t h e i n i t i a l s t a t e o f s t r e s s on s t r e n g t h . When we d e s c r i b e t h e s t r e n g t h o f s o i l w i t h a f r i c t i o n a n g l e , t h e v a l u e o f K has l i t t l e i m p o r t a n c e . What I was a t t e m p t i n g t o show i s t h a t one way t o t a l k about s t r e n g t h o f s o i l i s t o r u n a t e s t and see how much s t r e s s i s r e q u i r e d t o cause i t t o f a i l . T h a t i s what I was d e s c r i b i n g r a t h e r t h a n t r a n s l a t i n g t h e s t r e n g t h t o a f r i c t i o n a n g l e . I was a s k i n g what t h e s t r e n g t h i s i f we s t a r t w i t h t h i s s t a t e o f s t r e s s and we t a k e i t t o f a i l u r e ? What s t r e n g t h do we g e t ?
And y o u r second q u e s t i o n d e a l i n g w i t h i r r e g u l a r waves o r b u i l d i n g up a s e t o f wave t r a i n s i n a s t r e s s p a t h t e s t , we have done some o f them. I t i s q u i t e com-p l i c a t e d when one g e t s i n t h e l a b o r a t o r y and has t o a d j u s t com-p r e s s u r e s and l o a d s a c c o r d i n g t o some random number g e n e r a t o r . We have done a l i m i t e d amount o f i t and we t h i n k i t s e f f e c t i s f a i r l y i m p o r t a n t . B u t t h a t i s n o t a v e r y good answer f o r us as e n g i n e e r s , because we c a n n o t say how i m p o r t a n t . I w o u l d guess d i f f e r -e n t p a t t -e r n s o f wav-es c o u l d -e f f -e c t p r -e d i c t -e d d i s p l a c -e m -e n t s by 50% t o 1 0 0 % .
M, Eamza:
I f y o u do a K_ = 1 t e s t as i s o t r o p i c a l l y c o n s o l i d a t i o n t e s t and compare i t w i t h t h e same mean s t r e s s w i t h ^ 1 , i . e . u n i s o t r o p i c a l c o n s o l i d a t i o n t h e n shear
(J)-peak w o u l d be t h e same b u t c j) - r e s i d u a l w o u l d be d i f f e r e n t . I f y o u a r e t a l k i n g about t h e e f f e c t o f c y c l i c l o a d i n g and l i q u e f a c t i o n t h e n t h e r e s i d u a l e f f e c t w i l l be i m p o r t a n t . The 4 ) - r e s i d u a l appears more when you do K q 7^ 1 t e s t t h a n when you do = 1 t e s t .
W.A. Maw:
Thank you^ C e r t a i n l y someone f r o m I m p e r i a l C o l l e g e s h o u l d be an e x p e r t on r e -s i d u a l -s t r e n g t h .
Chairman:
The n e x t p a p e r has two a u t h o r s . The f i r s t i s Ton B l e g s t r a a t e n , who i s w i t h t h e D e l t a d i e n s t o f t e R i j k s w a t e r s t a a t . He has been most a c t i v e i n t h e d e v e l o p m e n t o f n u m e r i c a l t e c h n i q u e s f o r a n a l y s i n g t h e b e h a v i o u r o f t h e v a r i o u s d e s i g n schemes t h a t have been p r o p o s e d . The second a u t h o r i s Cor K e n t e r , who i s w i t h t h e LGM. He has been a g r o u p l e a d e r and has been a c t i v e i n v a r i o u s a s p e c t s o f t h e d e s i g n and a n a l y s e s o f t h e O o s t e r s c h e l d e p r o j e c t f r o m i t s i n c e p t i o n . I be-l i e v e t h e f i r s t speaker on t h e s u b j e c t w i be-l be-l be Ton B be-l e g s t r a a t e n ,
STRESS-STRAIN BEHAVIOUR FOR FINITE ELEMENT METHODS by A. W. W. M. Blegstraaten and C. J. Kenter
Vol. 1, Paper 11.2 M. Eamza:
w i t h r e g a r d t o t h e s t r e s s s t r a i n r e l a t i o n , y o u a r e v i o l a t i n g t h e e n e r g y r e q u i r e ment by u s i n g Hooke's l a w and a t t h e same t i m e w h i l e c a l c u l a t i n g s t r e s s , y o u a s
sume t h e t n o r m a l s t r e s s may g i v e r i s e t o s h e a r s t r a i n a l t h o u g h t h e s o i l i s a s -sumed t o be i s o t r o p i c ? Can you p r o v e u n i q u e n e s s o f s o l u t i o n s ?
A.VI.}f.M. Biegstraaten:
I f I u n d e r s t a n d y o u r q u e s t i o n c o r r e c t l y , y o u want t o know i f by t h e a d d i t i o n o f d i l a t a n c y u n i q u e n e s s o f t h e s o l u t i o n i s v i o l a t e d .
W e l l , l e t us assume you f o r m u l a t e d t h e p r o b l e m i n a n o t h e t way. You a r e f a m i l i a r w i t h t h e e l a s t o - p l a s t i c approach?
I t o o k some t i m e t o f i n d what I was a c t u a l l y d o i n g by a d d i n g a l l t h o s e k i n d s o f i n i t i a l s t r a i n methods and a l l t h o s e k i n d s o f i t e r a t i o n p r o c e d u r e s and I have w r i t t e n a t e s t programme. I compared t h e e l a s t o - p l a s t i c a p p r o a c h w h i c h can a l s o be f o r m u l a t e d f o r e q u a t i o n s l i k e I j u s t d e s c r i b e d , and I c o u l d n o t f i n d a d i f f e r -ence. T h a t i s t h e o n l y answer I can g i v e t o y o u . I do n o t know i f t h e u n i q u e n e s s i s v i o l a t e d o r n o t , I can o n l y say I f o u n d t h e same answers by u s i n g t h e e l a s t o -p l a s t i c a -p -p r o a c h and t h e Consol a -p -p r o a c h .
I want t o say f u r t h e r m o r e , I t h i n k i t i s f a r b e t t e r t o use t h e e l a s t o - p l a s t i c a p p r o a c h , b u t i t i s a m a t t e r o f t i m e and e f f o r t w h i c h was n o t a v a i l a b l e t o app l y t h a t method i n C o n s o l , so we had t o use t h e f o r m u l a t i o n s w h i c h were d e v e l o app -ed i n t h e l a s t 4 y e a r s .
M. Eamza:
I am i n t e r e s t e d because i t i s v e r y good i f i t i s r e a l l y p r o v e d t o be t h e e a s i e s t way o u t , because y o u r f o r m u l a t e d m a t r i x uses a v e r y s i m p l e l a w , Hooke's l a w , and t h e n y o u go d u r i n g t h e i t e r a t i o n , y o u o b t a i n t h e s t r e s s e s , y o u m o d i f y them and c a r r y on i t e r a t i o n . B u t t h e o n l y t h i n g i s a l e a k i n t h e s o l u t i o n . T h a t ' s a l l . Because i t i s a good method. The e l a s t o - p l a s t i c approach sometimes g i v e s many p r o b l e m s d u r i n g i t e r a t i o n s .
A.V.W.M. Biegstraaten:
W e l l , I t h i n k t h e e l a s t o - p l a s t i c p r o c e s s i s m a t h e m a t i c a l l y more c o m p l i c a t e d , b u t I t h i n k i t i s v e r y much l e s s e x p e n s i v e t o use t h a n t h e method I j u s t d e s
-c r i b e d . The method I have j u s t d e s -c r i b e d i s t h a t f i r s t y o u make a -c o m p u t a t i o n by Hooke's l a w and t h e n y o u see, t h e s t r e s s e s a r e t h a t and t h e s t r a i n s a r e so, and I had a c o r r e c t i o n h e r e and a c o r r e c t i o n t h e r e , and y o u a p p l y t h a t c o r r e c t i o n and p u t some 5 i t e r a t i o n s t o t h a t s t e p and f i n d a s o l u t i o n . And t h e s o l u -t i o n i s a c c u r a -t e enough. T h a -t i s a l s o checked b u -t I -t h i n k y o u can do b e -t -t e r w i t h t h e e l a s t o - p l a s t i c a p p r o a c h , b u t as I s a i d b e f o r e , t i m e and e f f o r t were u n a v a i l a b l e t o me, t o t h e p e o p l e who worked w i t h t h e programme t o a p p l y t h a t p r o c e d u r e , b u t I t h i n k t h e method I d e s c r i b e d i s j u s t as good as t h e e l a s t o -p l a s t i c a -p -p r o a c h and y o u can o f c o u r s e d i s c u s s i f t h e e l a s t o - -p l a s t i c a-p-proach
i s u n i q u e . T h a t i s a n o t h e r p o i n t . M. Hamza:
Thank y o u . G. Gudehus:
I want t o add a p o i n t t o t h i s p r o b l e m o f u n i q u e n e s s . I f y o u compare t h e e l a s t o -p l a s t i c and t h i s i n c r e m e n t a l e l a s t i c a -p -p r o a c h , t h e y can -p r a c t i c a l l y c o i n c i d e , b u t t h e y do n o t g e n e r a l l y , I want t o c a l l y o u r a t t e n t i o n t o work on D r . Darve i n G r e n o b l e some y e a r s ago where he f i r s t s t a r t e d w i t h a Hooke t y p e o f ap-p r o a c h , as y o u d i d , and l a t e r on he e x t e n d e d i t a l i t t l e b i t . The d i f f e r e n c e between e l a s t o - p l a s t i c and Hooke-type a p p r o a c h i s o n l y t h a t y o u e i t h e r use o r do n o t use a symmeric m a t r i x . I f I u n d e r s t a n d you, y o u have used a s y m m e t r i c a l i n c r e m e n t a l s t i f f n e s s m a t r i x and t h e e l a s t o - p l a s t i c approach does n o t g i v e a s y m m e t r i c m a t r i x . F o r a r a t h e r w i d e c l a s s o f boundary v a l u e p r o b l e m s y o u w i l l g e t p r a c t i c a l l y t h e same answer.
For c e r t a i n b o u n d a r y p r o b l e m s y o u c a n n o t g e t t h e same answers and j u s t f o r t h e p r o b l e m s o f i n t e r e s t h e r e y o u c a n n o t e x p e c t g e n e r a l l y t h e same answer. The main p o i n t i s e i t h e r y o u have a c o n s t r a i n t b y c o n s t a n t volume, t h e n t h e approaches may f a i l and y o u c a n n o t e x p e c t t h e same r e s u l t w i t h t h e e l a s t i c p l a s t i c and t h e i n c r e m e n t a l l y e l a s t i c a p p r o a c h . The o t h e r p o i n t i s i f y o u come t o any t y p e o f f a i l u r e o f t h e system, t h a t i s sudden l a r g e d i s p l a c e m e n t s o r c o l l a p s e , t h a t means y o u come c l o s e t o t h e l o s s o f u n i q u e n e s s o f d e f o r m a t i o n s , t h e n y o u can n e v e r e x p e c t t h e same r e s u l t s w i t h t h e t w o approaches and y o u c a n n o t even e x p e c t u n i q u e n e s s ,
Chairman:
Thank you, I ' d l i k e t o make a comment on t h a t t o o . I guess t h e c h a i r m a n i s n o t supposed t o do t h a t , b u t I w i l l . I t seems t o me t h a t t h e r e a r e some v e r y p r o -f o u n d d i -f -f e r e n c e s between e l a s t i c and e l a s t o - p l a s t i c approaches and I am n o t s u r e t h a t r e a l l y r e q u i r e s v e r y much commenting on.
For one t h i n g i t i s f a i r l y c l e a r t h a t y o u c a n o n l y g e t f a i l u r e i n p u r e l y e l a s t i c approaches i f y o u do some i n t e r e s t i n g t h i n g s t o t h e a n a l y s i s when y o u s t a r t
g e t t i n g n e a r f a i l u r e and y o u r s t r e s s e s s t a r t l o o k i n g l i k e what o u g h t t o be f a i l -u r e s t r e s s e s . B -u t I t h i n k I ' d l i k e t o d i s a g r e e a b o -u t t h e l i m i t a t i o n s on t h e Hooke's law. You can most c e r t a i n l y g e t shear s t r e s s e s w i t h a p u r e l y Hookeian m a t e r i a l .
A l l y o u have t o do i s r o t a t e t h e p r i n c i p a l axes enough so t h a t y o u have g o t o f f d i a g o n a l t e r m s i n t h e s t i f f n e s s m a t r i x . And y o u most c e r t a i n l y w i l l g e t shear s t r e s s e s . T h a t i s n o t an argument n e c e s s a r i l y f o r u s i n g e l a s t i c m a t e r i a l s , b u t I do n o t t h i n k y o u r comment on t h e r e s t r i c t i o n s i s c o m p l e t e l y a c c u r a t e . S e c o n d l y , on t h e q u e s t i o n o f symmetry o f t h e s t i f f n e s s m a t r i x , y o u can g e t s y m m e t r i c a l s t i f f n e s s m a t r i x e s w i t h e l a s t o - p l a s t i c m a t e r i a l s p r o v i d e d t h e y happened t o a b i d e by t h e v a r i o u s n o r m a l i t y p r i n c i p l e s . T h a t i s a p e c u l i a r p r o b l e m when y o u a r e d e a l i n g w i t h s o i l s and i f y o u do n o t have n o r m a l i t y y o u can a l s o g e t non-symme-t r i c a l s non-symme-t i f f n e s s m a non-symme-t r i x e s . I non-symme-t always seemed non-symme-t o me non-symme-t h a non-symme-t one o f non-symme-t h e non-symme-t h i n g s non-symme-t h a non-symme-t ' s h a p p e n i n g when y o u a r e g e t t i n g n o n - s y m m e t r i c a l s t i f f n e s s m a t r i x e s i s t h a t y o u a r e l i k e l y t o s t a r t t o g e t non-unique s o l u t i o n s . Anyway, y o u had s o m e t h i n g f u r t h e r t o say t h o u g h , I t h i n k .
M. Hamza:
No, I mean w i t h t h e i s o t r o p i c a l Hooke's law you w i l l n e v e r g e t shear s t r a i n s , I mean he was s p e a k i n g a b o u t i s o t r o p i c a l m a t e r i a l . You commented assuming an-i s o t r o p y o f c o u r s e . I f you have a n an-i s o t r o p an-i c m a t e r an-i a l and you g an-i v e an-i t a l l - r o u n d p r e s s u r e you always g e t shear s t r a i n s . The o t h e r p o i n t P r o f , Gudehus was t a l k -i n g about -i s t h a t some p r o b l e m s w -i l l n e v e r c o -i n c -i d e . I t h -i n k -i n any p a r t -i c u l a r case o f r o c k i n g f o u n d a t i o n you w i l l n e v e r c o i n c i d e , because t h e p r i n c i p l e s t r e s s i n c r e m e n t and t o t a l p r i n c i p l e s t r e s s r o t a t i o n o c c u r r i n g under t h e edge under t h e m i d d l e w i l l n e v e r c o i n c i d e .
Chairman:
W e l l , i t seems t o me t h a t one o f t h e b i g d i f f e r e n c e s , and one t h a t we w i l l be coming back t o l a t e r ( a t l e a s t I hope Dr. Marr w i l l have s o m e t h i n g f u r t h e r t o say about t h i s ) i s t h i s . I f you l o o k a t t h e way f i n i t e e l e m e n t p r o b l e m s g e t t h e m s e l v e s f o r m u l a t e d , you s t a r t o f f w i t h some law t h a t somebody g e n e r a t e d o r some model o r w h a t e v e r you want t o c a l l i t , w h i c h i s t h e p r o d u c t o f e x p e r i m e n t -a l work o r somebody's i m -a g i n -a t i o n , b u t i n -any c-ase you h-ave t h i s r e l -a t i o n be-tween s t r e s s and s t r a i n o r i n c r e m e n t a l s t r e s s and i n c r e m e n t a l s t r a i n and t i m e and so f o r t h . And some f i n i t e e l e m e n t p e r s o n who u s u a l l y s i t s i n a s m a l l room i n t h e back o f t h e o f f i c e s i t s down and w i t h a l a r g e p i e c e o f p a p e r r e d u c e s t h i s t h i n g t o an i n c r e m e n t a l r e l a t i o n w h i c h , as f a r as t h e f i n i t e e l e m e n t p r o -gramme sees i t , i s a l m o s t i n e v i t a b l y a r e l a t i o n s h i p between some i n c r e m e n t a l s t r e s s and some i n c r e m e n t a l s t r a i n , and i t l o o k s an a w f u l l o t l i k e an e l a s t i c s t r e s s - s t r a i n r e l a t i o n . Then t h i s i s used f o r s o l u t i o n s and you do v a r i o u s k i n d s o f i t e r a t i o n s t o make sure t h a t e v e r y t h i n g i s back on w h a t e v e r y i e l d c r i t e r i a t h a t you have o r t h a t you have s a t i s f i e d w h a t e v e r v i s c o u s r e l a t i o n s you have.
But a l m o s t a l l t h e s e s o l u t i o n s p r o c e e d by w o r k i n g i n c r e m e n t a l l y as t h o u g h you were w o r k i n g e l a s t i c a l l y . I t seems t o me t h a t one o f t h e g r e a t p r o b l e m s t h a t we have i n t h i s a r e a - and i t r e a l l y i s n o t an a n a l y t i c a l p r o b l e m , i t i s a p r o b l e m w i t h our knowledge o f t h e s o i l s - i s t h a t as you t r y t o h a n d l e a c y c l i c l o a d i n g p r o b l e m l i k e t h i s you b e g i n t o g e t i n t o o t h e r s e r i o u s p r o b l e m s such as what w i l l happen when you s t a r t u n l o a d i n g t h e s e models. You can, as Dr„ Gudehus and s e v e r a l o t h e r p e o p l e p o i n t e d o u t , g e t v e r y good agreement between h y p e r b o l i c r e l a t i o n s and e l a s t o - p l a s t i c r e l a t i o n s p r o v i d e d t h e t h i n g you a r e t e s t i n g , t h e model you a r e r u n n i n g , t h e f i n i t e e l e m e n t p r o b l e m you a r e c a l c u l a t i n g , l o o k s
l i k e t h e t h i n g you r a n i n t h e l a b o r a t o r y . And you can l o a d i t and g e t i t t o agree and t h e r e i s a huge p i l e o f l i t e r a t u r e a r o u n d , some o f i t u n p u b l i s h e d , i n w h i c h p e o p l e have d e v e l o p e d v a r i o u s k i n d s o f model w h i c h worked b e a u t i f u l l y so l o n g as t h e y have k e p t t h e same geometry f o r t h e i r a n a l y s e s as t h e y had f o r t h e t e s t f r o m w h i c h t h e y g o t t h e p r o p e r t i e s .
Then t h e y t a k e t h e s e numbers and t h e y p l u g them i n t o s o m e t h i n g l i k e , say a p l a n e s t r a i n s i t u a t i o n , and a l l o f a sudden s o m e t h i n g does n o t l o o k q u i t e r i g h t . T h a t and t h e p r o b l e m o f r e v e r s i n g a l o a d seem t o me t h e r e a l d i f f i c u l t i e s , more so t h a n t h e q u e s t i o n o f p r e c i s e l y w h i c h o f t h e numerous k i n d s o f n o n l i n e a r s t r e s s -s t r a i n r e l a t i o n -s you choo-se t o u-se.
Are t h e r e any o t h e r q u e s t i o n s ? P,A. Vermeer:
I ' d l i k e t o ask a q u e s t i o n , because i n t h e p r o c e e d i n g s i t i s w r i t t e n t h a t p r o -gramme Consol-Genesis i s based on a n o t h e r t y p e o f model. Has t h i s a n y t h i n g t o do w i t h t h e f a c t t h a t you wanted t o have a s y m m e t r i c a l m a t r i x , yes o r no? F u r t h e r m o r e , I want t o remark t h a t I f i n d i t a l i t t l e b i t p e c u l i a r t h a t you d e m o n s t r a t e h e r e t h a t you have a good model and now you go t o t h e f u t u r e and you change t o a q u i t e d i f f e r e n t model.
Chairman:
T h a t i s a good q u e s t i o n . A.W.W.M, Biegstraaten:
I e x p e c t e d t h e q u e s t i o n . The f i r s t p o i n t was t h e s y m m e t r i c a l m a t r i x o f C o n s o l Genesis The model Mr. Vermeer i s t a l k i n g about i s t h e Camclay model o f some changed v e r s i o n o f i t . I t i s n o t e x a c t l y t h e Camclay m o d e l , because we made an a d j u s t m e n t w h i c h makes t h e r e l a t i o n b e t t e r , Maybe I can e x p l a i n i t m a few m i n u t e s . You know i n t h e Camclay-model t h e i d e a l e l l i p s e i s g o i n g t h r o u g h t h e o r i g i n o f t h e s t r e s s p a t h d i a g r a m . When you remove t h a t c o n s t r a i n t you have an e x t r a degree o f freedom how t h e e l l i p s e w i l l move. We a r e u s i n g i t by a l s o spe-c i f y i n g t h e shear s t r a i n as a f u n spe-c t i o n o f t h e s t r e s s p a t h . Next t o what i s ^ u s u a l l y t h e v o l u m e t r i c s t r a i n . So we made an improvement o f t h e model. T h a t i s i n t e r m e d i a t e . W e l l , I do n o t t h i n k t h e s o l u t i o n chosen f o r Consol-Genesis has a n y t h i n g t o do w i t h t h e s y m m e t r i c a l o r n o n - s y m m e t r i c a l m a t r i x , because t h e r e a r e s o l u t i o n s known by w h i c h t h e programma can have a s y m m e t r i c a l m a t r i c and s t i l l s i m u l a t e s a n o n - s y m m e t r i c a l m a t r i x by means o f an i n i t i a l s t r e s s o r an i n i t i a l s t r a i n p r o c e d u r e . So I do n o t t h i n k t h a t we have chosen t h i s model because we can o n l y h a n d l e a s y m m e t r i c a l m a t r i x .
The second p o i n t i s comparison o f t h e C o n s o l model and t h i s e l l i p s e , t h i s camclay model. The Consol-Genesis programma must become a s o r t o f o f f i c i a l v e r s i o n used by everyone o f t h e R i j k s w a t e r s t a a t . I t h i n k t h a t i s v e r y i m p o r t -a n t , bec-ause t h e progr-amme I ' v e j u s t t -a l k e d -about i s , you c-an n e -a r l y s-ay -a p r i v a t e programme, because I am t h e o n l y one who knows what i s i n i t . I do n o t t h i n k t h a t i t i s a good t h i n g t o p u b l i c i s e , t o g i v e i t t o p e r s o n s w o r k i n g m o t h e r d e p a r t m e n t s and so o n , so t h e r e had t o come an o f f i c i a l v e r s i o n . A t t h e t i m e t h a t was chosen f o r t h e Camclay model i t was n o t y e t c l e a r how t h e C o n s o l model w o u l d behave when i t was made e l a s t o - p l a s t i c . Mr. Vermeer has made h i s own programme w h i c h i s e l a s t o - p l a s t i c and w h i c h r e s e m b l e s t h e C o n s o l model, b u t he has some, l e t us say p e r s o n a l e x p e r i e n c e , he i s n o t , i n v o l v e d i n t h e Consol-Genesys p r o j e c t and we c o u l d ask f o r a d v i c e o f c o u r s e , b u t I t h i n k i t i s b e t t e r when you want t o b u i l d a more o r l e s s o f f i c i a l programme t h a t you have y o u r e x p e r i e n c e n e a r . So one o f t h e main r e a s o n s was we were n o t q u i t e
s u r e how t h e C o n s o l model w o u l d behave when i t was e l a s t o - p l a s t i c . T h a t i s why we chose t h e Camclay model o r t h e analogous t y p e t h a t we d e v e l o p e d .
Chairman:
Ton, I'm g o i n g t o i n t e r r u p t r i g h t now.
We w i l l c o n t i n u e t h i s d i s c u s s i o n a f t e r t h e l a s t t a l k . Thank you v e r y much. a r e We have one more paper t o be p r e s e n t e d , t h i s paper has t h r e e a u t h o r s They F r a n s S m i t s f r o m t h e D e l f t S o i l Mechanics L a b o r a t o r y , t h e LGM, who w i l l be p r e
-s e n t i n g t h e p a p e r . 4-1. h =
The o t h e r two a u t h o r s a r e f o r t u n a t e l y a l s o w i t h us t o d a y . The second a u t h o r i s Knut A n d e r s e n , f r o m t h e Norwegian G e o t e c h n i c a l I n s t i t u t e and t h e t h i r d i s P r o f . Gerd Gudehus, f r o m t h e U n i v e r s i t y o f K a r l s r u h e ; you have a l r e a d y h e a r d h i m e a r l i e r i n some o f t h e d i s c u s s i o n s a t t h e end o f F r a n s Smits'- p r e s e n t a t i o n .
PORE PRESSURE GENERATION by F. P. Smits
Vol. 1, Paper 11.3
Chairman:
Thank you v e r y much.
Are t h e r e any q u e s t i o n s f o r Mr. S m i t s ?
J. Marti:
I w o u l d l i k e t o ask a q u e s t i o n c o n c e r n i n g t h e shear s t r e s s t h a t y o u a p p l y f o r the p o r e p r e s s u r e c o m p u t a t i o n i n t h e models. Are y o u r e f e r r i n g t o a maximum v a l u e o f t h e shear s t r e s s o r a r e you u s i n g a h o r i z o n t a l shear s t r e s s and i n any case how do y o u r e l a t e t h a t t o t h e l i q u e f a c t i o n t e s t i n g w h i c h n o r m a l l y has one-d i m e n s i o n a l shear?
F.P. Smits:
A p p a r e n t l y y o u a r e r e f e r r i n g t o t h e p r o b l e m o f r o t a t i o n o f p r i n c i p a l axes o f s t r e s s e s . I t s e f f e c t on p o r e p r e s s u r e g e n e r a t i o n i s n o t w e l l u n d e r s t o o d a t p r e s e n t . I have s e l e c t e d t h e c y c l i c shear s t r e s s a m p l i t u d e i n t h e model as h a l f t h e t o t a l change o f shear s t r e s s on t h e p l a n e where t h e shear s t r e s s v a r i a t i o n r e a c h e s a maximum. C l o s e t o t h e c e n t r e o f a s y m m e t r i c a l l y l o a d e d s t r u c t -ure such a v a l u e o f approaches t h e h o r i z o n t a l shear s t r e s s a m p l i t u d e , where-as t o w a r d s t h e edges f o r an e l e m e n t u n d e r p u r e r o c k i n g a c t i o n i t t e n d s t o ap-p r o a c h h a l f t h e maximum v a r i a t i o n o f ap-p r i n c i ap-p a l s t r e s s e s .
I w o u l d l i k e t o ask Knut Andersen t o d e s c r i b e t h e shear s t r e s s s e l e c t i o n p r o -cedure i n t h e i r Hammen 17 c a i s s o n s t u d y .
K,H. Andersen:
The shear s t r e s s l e v e l w h i c h was used f o r t h e p o r e p r e s s u r e c o m p u t a t i o n s was the s i n g l e a m p l i t u d e o f t h e maxim.iam shear s t r e s s r a t i o T^/a'. The p o r e p r e s s -u r e s i n t h e v a r i o -u s s o i l e l e m e n t s b e n e a t h t h e c a i s s o n were e v a l -u a t e d f r o m measured p o r e - p r e s s u r e s i n l a b o r a t o r y t e s t s w i t h t h e same T^/a' as computed f o r t h e i n d i v i d u a l s o i l e l e m e n t s b e n e a t h t h e c a i s s o n . Two d i f f e r e n t c a l c u l a t i o n s were p e r f o r m e d . I n t h e f i r s t c a l c u l a t i o n i t was assumed t h a t a l l e l e m e n t s behav-ed l i k e s i m p l e shear samples. I n e v a l u a t i n g T^/a' f o r t h e s i m p l e shear t e s t s , a ¥^ o f 0,3 was assumed. I n t h e second c a l c u l a t i o n , s i m p l e shear t e s t r e s u l t s were used i n zones b e n e a t h t h e c a i s s o n where s i m p l e shear mode o f d e f o r m a t i o n s i s most r e l e v a n t , and t r i a x i a l t e s t r e s u l t s i n zones a t and b e n e a t h t h e edges. J. Marti:
I am s o r r y , I s t i l l have a s h o r t q u e s t i o n . I f y o u a r e c o n s i d e r i n g a shear s t r e s s , t h e maximum v a l u e o f t h e shear s t r e s s i s g e n e r a l l y used f o r t h e computer p r o -gramme. You g i v e h e r e a case f o r example i n w h i c h y o u have a c o n s t a n t maxim.um shear s t r e s s w h i c h i s r o t a t i n g i n t h e p l a i n and so d e p e n d i n g on how y o u l o o k a t i t . You have more c y c l e s a c t u a l l y .
Every 360 degrees o f r o t a t i o n o f t h e s h e a r s t r e s s y o u have a d o u b l e r e v e r s a l o f d e r i v a t i o n o f t h e shear s t r e s s . B u t i f t h e computer programme i s o n l y con-s i d e r i n g what t h e v a l u e o f t h e maximum con-shear con-s t r e con-s con-s i con-s t h a t w i l l n o t be n o t e d by t h e programme and w i l l n o t p r o d u c e p o r e p r e s s u r e g e n e r a t i o n . So i s t h a t t h e v a l u e o f t h e maximum shear s t r e s s t h a t y o u a r e u s i n g ?
K.H, Andersen:
A p r i n c i p a l s t r e s s r o t a t i o n may cause some p o r e p r e s s u r e g e n e r a t i o n even i f t h e change i n maximum x/a' r e l a t i v e t o t h e i n i t i a l s t r e s s c o n d i t i o n i s z e r o ( i . e . T(./a' = 0 ) . F o r Tc/CJ' = 0, o u r c a l c u l a t i o n p r o c e d u r e w i l l p r e d i c t z e r o p o r e p r e s s u r e g e n e r a t i o n . T h i s i s one l i m i t a t i o n o f o u r c a l c u l a t i o n p r o c e d u r e . A.M. Sohofield:
Can I j u s t ask what t h e r e l a t i o n s h i p i s between say f i g u r e 11 o f p a p e r 1.2, where we see p i e r s w i t h s i l l s , box beam, and s l u i c e g a t e s w h i c h a r e e s s e n t i a l l y
3 - d i m e n s i o n a l . They have a 50 m e t r e - d i m e n s i o n w h i c h may c o r r e s p o n d t o t h e 46 met r e d i m e n s i o n o f met h e example p r o b l e m i n I I 3 . B u met i f we l o o k i n met h e o met h e r d i -r e c t i o n t h e -r e i s a v e -r y much s h o -r t e -r d i m e n s i o n . Does t h e example p -r o b l e m w h i c h i s under d i s c u s s i o n and a p l a i n p r o b l e m , i s t h a t c o n s i d e r e d t o have a m a j o r r e -l a t i o n s h i p w i t h t h e p i e r s w i t h s i -l -l , box beams and s -l u i c e g a t e s now t o be con-s i d e r e d ?
