Longard tube applications manual

l C - 3 ' 1 5 6 - O 2

M A Y 1982

LCNGARD TUBE APPLICATIONS

MANUAL

PREPARED FOR

ALDEK A-S

TABLE OF CONTENTS SECTION PAGE PREFACE L I S T OF FIGURES L I S T OF TABLES

1.0 LONGARD TUBE APPLICATIONS ^ 1.1 SEA WALLS, BULKHEADS AND

REVETMENTS ^ 1.2 A R T I F I C I A L CREATION OF PROTECTIVE BEACHES 5 1.2.1 G r o i n s g 1.2.2 O f f s h o r e B r e a k w a t e r s 9 1-2.3 P e r c h e d B e a c h e s 2^2 . 1.2.4 Composite Schemes 14 1.3 BLUFF STABILIZATION ^4 1.4 MISCELLANEOUS USES 1.4.1 R i v e r T r a i n i n g / F l o o d C o n t r o l S t r u c t u r e s i 6 1.4.2 J e t t i e s -^q 1.4.3 Dredge C o n t a i n m e n t 20 1.4.4 A r t i f i c i a l I s l a n d s 20

2.0 GENERAL DESIGN GUIDELINES 22 2.1 PHYSICAL PROPERTIES 22 2.1.1 Tube M a t e r i a l s and S i z e s 22 2.1.2 F i l l i n g M a t e r i a l s 22 2.1.3 G e o m e t r i c P r o p e r t i e s 25 2.1.4 P r o t e c t i v e C o a t i n g 25 2.2 EARTH PRESSURES 25 2.3 WAVE FORCES 33 2.3.1 Wave F o r c e s on a F u l l y Submerged Tube 33 2.3.2 B r e a k i n g Wave F o r c e s on a Non-submerged Tube 38 3.0 REFERENCES 42

PREFACE

I n May 1981, T e t r a T e c h I n c . s u b m i t t e d a r e p o r t t o Aldek A-S e n t i t l e d " O v e r v i e w o f L o n g a r d Tube A p p l i c a t i o n and D e s i g n . " As a r e s u l t o f recommendations made i n t h a t r e p o r t , A l d e k AS r e q u e s t e d T e t r a T e c h t o p e r f o r m s i t e i n s p e c -t i o n s o f v a r i o u s L o n g a r d -tube i n s -t a l l a -t i o n s i n Europe, which would b r o a d e n T e t r a T e c h ' s e x p e r i e n c e b a s e o f p r o j e c t s u s i n g the L o n g a r d t u b e s y s t e m . s i t e v i s i t s t o p r o j e c t s i n I t a l y , Belgium, and Germany were made i n O c t o b e r 1981.

From i n f o r m a t i o n c o l l e c t e d p r e v i o u s l y , and t h e i m p r e s -s i o n from t h e -s i t e v i -s i t -s i n E u r o p e , T e t r a T e c h p r e p a r e d t h i s r e p o r t , " A p p l i c a t i o n Manual f o r L o n g a r d Tube S t r u c t u r e s " , f o r A l d e k AS. The i n t e n t o f t h i s r e p o r t i s t o p r o -v i d e p o s s i b l e a p p l i c a t i o n s o f t h e L o n g a r d tube s y s t e m i n c o a s t a l and. h y d r a u l i c a p p l i c a t i o n s . I t i s n o t i n t e n d e d t o be a s u b s t i t u t e f o r sound e n g i n e e r i n g d e s i g n p r a c t i c e s w h i c h i s b a s e d on e x p e r i e n c e and t h o r o u g h u n d e r s t a n d i n g o f t h e hv-drodynamic and p h y s i c a l p r o c e s s e s , b u t i s s u i t a b l e f o r most p r e l i m i n a r y p l a n n i n g and d e s i g n p u r p o s e s .

T e t r a T e c h i s e s p e c i a l l y a p p r e c i a t i v e o f t h e t i m e and i n f o r m a t i o n o f f e r e d by p e r s o n s who have been i n v o l v e d w i t h the L o n g a r d p r o j e c t s . I n I t a l y , o u r h o s t was E n g i n e e r G u i s e p p e S a r t i t o whom we a r e g r a t e f u l . We would a l s o l i k e t o t h a n k E n g i n e e r s F e r d i n a n d o G a m b a r d e l l a and S e r g i o M o n t o r i , t h e o f f i c i a l s r e s p o n s i b l e f o r t h e p r o j e c t s i n I t a l y ; Mr. L . B u r k i o f Dragages D e c l o e d t and F i l s , and t h e B e l g i a n o f f i c i a l s Mr. V e r s l y p e and Mr. Blommer f o r showing us t h e p r o j e c t s a t K l e m s k e r k e and N i e u w p o o r t ; and t h e German o f f i c i a l s Mr. F e l d e n and Mr. Ukena f o r t h e i r v a l u a b l e i n p u t i n t o t h e p r o j e c t a t Norderney. The p e o p l e from A l d e k A-S made t h i s p r o j e c t p o s s i b l e , and we e x t e n d o u r g r a t i t u d e t o Mr. P e t e r Thomsen, Mr. W i l l y Konge, and Mr. John L a r s e n .

L I S T OF FIGURES

FIGURE ^^^^

• PAGE 1 SEAWALL AND BULKHEAD SECTION 3

2 SEAWALL FOR EMERGENCY SHORE

PROTECTION ^ 3 REVETMENT SECTION 5

4 GROIN PLAN Q 5 WAVE TRANSMISSION OVER

SUBMERGED BREAKWATERS 10 6 OFFSHORE BREAKWATER PLAN H 7 PERCHED BEACH CONCEPT I 3 8 HEADLANDS CONCEPT 15 9 BLUFF S T A B I L I Z A T I O N I 7 10 RIVER TRAINING GROINS 1 I 9

11 A R T I F I C I A L ISLANDS 21 12 SATURATED WEIGHT VS RELATIVE

DENSITY OF F I L L MATERIAL 24 13 GEOMETRIC PROPERTIES OF F I L L E D

LONGARD TUBES 26 14 ACTIVE EARTH PRESSURE WITH

HORIZONTAL B A C K F I L L 29 15 A C T I V E EARTH PRESSURE WITH A

SLOPING BACKFILL 31 16 APPROXIMATE SOLUTION TO ACTIVE EARTH

PRESSURE WITH A SLOPING BACKFILL 32 17 WAVE FORCES ON A FULLY SUBMERGED TUBE 35

18 MAXIMUM FORCE C O E F F I C I E N T S FOR WAVES

ON A FULLY SUBMERGED TUBE 35 19 LINEAR APPROXIMATIONS FOR NEAR BOTTOM

WATER PARTICLE KINEMATICS UNDER

NON-BREAKING WAVES 37 20 DIMENSIONLESS MINIKIN WAVE PRESSURE

AND FORCE (AFTER SPM, 1977) 39 21 EXAMPLE PROBLEM FOR BREAKING WAVE

L I S T OF TABLES.

1 SPECIFICATIONS FOR LONGARD

SYSTEM 23

2 IN-PLACE WEIGHT OF LONGARD

LONGARD TUBE APPLICATIONS

1 . 1 SEA WALLS, BULKHEADS AND REVETMENTS

S e a w a l l s , b u l k h e a d s , and r e v e t m e n t s a r e s t r u c t u r e s p l a c e d p a r a l l e l t o t h e s h o r e l i n e , t o s e p a r a t e a l a n d a r e a from a w a t e r a r e a . The p r i m a r y p u r p o s e o f a b u l k h e a d i s t o r e t a i n o r p r e v e n t s l i d i n g of t h e l a n d , w i t h an a d d i t i o n a l purpose o f p r o v i d i n g p r o t e c t i o n t o t h e u p l a n d a g a i n s t damage by wave a c t i o n . The p r i m a r y p u r p o s e o f a s e a w a l l o r r e v e t -ment i s t o p r o t e c t t h e l a n d and u p l a n d p r o p e r t y from damage by waves. T h e r e a r e no p r e c i s e d i s t i n c t i o n s between t h e t h r e e t y p e s o f s t r u c t u r e s , and o f t e n t h e names a r e used i n -t e r c h a n g e a b l y . T h e s e s -t r u c -t u r e s a r e g e n e r a l l y u s e d where i -t i s n e c e s s a r y t o m a i n t a i n t h e p o s i t i o n o f a s h o r e l i n e , where t h e r e i s a s c a n t s u p p l y o f l i t t o r a l m a t e r i a l , and l i t t l e o r no p r o t e c t i v e b e a c h , o r where i t i s d e s i r e d t o m a i n t a i n a depth o f w a t e r a l o n g t h e shoreline» The p l a n n i n g o f s e a w a l l s , b u l k h e a d s , and r e v e t m e n t s c o n s t r u c t e d u s i n g t h e L o n g a r d t u b e s y s t e m i s an e l e m e n t a r y p r o c e s s , s i n c e t h e i r p r i m a r y f u n c t i o n i s s i m p l y t h e main-t e n a n c e o f f i x e d b o u n d a r i e s . F a c main-t o r s i n d e s i g n i n g main-t h e s e s t r u c t u r e s a r e : u s e and shape o f s t r u c t u r e , l o c a t i o n w i t h r e s p e c t t o s h o r e l i n e , l e n g t h , h e i g h t , and s t a b i l i t y . E a r t h and w a t e r p r e s s u r e s , and t h e b e a r i n g c a p a c i t y o f t h e f o u n -d a t i o n -d e t e r m i n e t u b e s t a b i l i t y . Of p a r t i c u l a r c o n s i d e r a t i o n i n t h e d e s i g n o f t h e s e s t r u c t u r e s a r e t h e i r p l a c e m e n t r e l a t i v e t o p o s s i b l e w a t e r l e v e l s and i m p o r t a n t l a n d a r e a s , and t h e s p e c i f i c d e t a i l s o f c o n n e c t i o n s o r t r a n s i t i o n s e c t i o n s w h i c h must be d e s i g n e d t o p r e v e n t unwanted e r o s i o n , s e t t l e m e n t o r u n d e r m i n i n g o f t h e s t r u c t u r e . Adequate d r a i n a g e o f t h e b a c k f i l l m a t e r i a l , e s -p e c i a l l y f o r s e a w a l l s s u b j e c t e d t o wave o v e r t o -p -p i n g , must be m a i n t a i n e d t o p r e v e n t p i p i n g o f f i n e s t h r o u g h t h e s o i l m a t r i x , o r t h e l i q u e f a c t i o n o f b a c k f i l l m a t e r i a l r e s u l t i n g 1

i n e x c e s s l a t e r a l p r e s s u r e s on t h e r e t a i n i n g t u b e s . Employ-i n g g r a v e l b l a n k e t s , d r a Employ-i n s and s y n t h e t Employ-i c f Employ-i l t e r m a t e r Employ-i a l s a r e p o s s i b l e methods f o r c o n t r o l l i n g p o r e p r e s s u r e and groundwater. End o r t r a n s i t i o n s e c t i o n s o f t h e s e s t r u c t u r e s s h o u l d be t i e d b a c k i n t o t h e s h o r e l i n e t o p r e v e n t f l a n k i n g by wave a c t i o n r e s u l t i n g i n t h e l o s s o f b a c k f i l l around t h e ends o f t h e s t r u c t u r e . T y p i c a l p l a n s and c r o s s s e c t i o n s o f s e a w a l l s , b u l k -h e a d s , and r e v e t m e n t s a r e s-hown i n F i g u r e s 1 t -h r o u g -h 3. 2

\ — 25 cm (;6 ANCHOR T U B E ( S E A W A L L NO S C A L E B A C K F I L L — — B U L K H E A D NO S C A L E F I G U R E 1: S E A W A L L AND B U L K H E A D S E C T I O N 3

S E C T I O N NO S C A L E

F I L T E R C L O T H S E C T I O N DEADMEN S E L E C T F I L L G R A V E L D R A I N A G E B L A N K E T E A R T H R E I N F O R C E M E N T D O U B L E l O O a n ^ T U B E F I L T E R V HWL V : MLW S E C T I O N F I G U R E S : R E V E T M E N T S E C T I O N

1.2 A K T I F I C I A L CREATION OF PROTECTIVE BEACHES

S t r u c t u r e s w h i c h c a u s e l i t t o r a l m a t e r i a l t o be a r t i f i -c i a l l y r e t a i n e d upon the s h o r e l i n e -can . e f f e -c t i v e l y r e d u -c e e r o s i o n p r o b l e m s by p r o d u c i n g t h e p r o t e c t i o n q u a l i t i e s a t t r i b u t a b l e t o n a t u r a l b e a c h e s . A r t i f i c i a l b e a c h e s a r e formed from t h e r e t a i n e d m a t e r i a l , c a u s i n g wave e n e r g y t o be d i s s i p a t e d b e f o r e r e a c h i n g e r o d i b l e dunes or b l u f f s . T e c h n i q u e s f o r r e t a i n i n g l i t t o r a l m a t e r i a l g e n e r a l l y i n -v o l -v e g r o i n s , o f f s h o r e b r e a k w a t e r s , or a r t i f i c i a l beach n o u r i s h m e n t ( p e r i o d i c a l l y p l a c i n g s a n d on t h e s h o r e l i n e by d r e d g i n g o r o t h e r m e a n s ) . P e r i o d i c beach n o u r i s h m e n t i n c o n j u n c t i o n w i t h g r o i n s or b r e a k w a t e r c o n s t r u c t i o n i s g e n e r a l l y t h e most e f f e c t i v e m e a s u r e f o r r e t a i n i n g a p r o t e c -t i v e b e a c h . I n any c a s e , -t h e c r e a -t i o n of a r -t i f i c i a l b e a c h e s r e q u i r e s an a d e q u a t e s u p p l y o f l i t t o r a l rröterial. 1.2.1 G r o i n s

G r o i n s a r e among t h e o l d e s t known methods o f s h o r e p r o -t e c -t i o n . Where -t h e r e i s an a b u n d a n -t s u p p l y o f l i -t -t o r a l d r i f t , t h e r o l e o f t h e g r o i n i s t o b u i l d o r w i d e n a beach t h r o u g h t h e t r a p p i n g o f t h e s e d i m e n t moving a l o n g t h e s h o r e . F u r t h e r m o r e , p r o p e r l y d e s i g n e d g r o i n s w i l l r e d u c e t h e l o n g -s h o r e t r a n -s p o r t o f -s e d i m e n t by r e o r i e n t i n g t h e compartmented s h o r e l i n e , so t h a t i t w i l l be i n c l o s e r e q u i l i b r i u m t o t h e predominant wave d i r e c t i o n . P o s s i b l e d i s a d v a n t a g e s o f g r o i n s t r u c t u r e s a r e i n c r e a s e d o f f s h o r e s e d i m e n t l o s s e s r e s u l t i n g from the f o r m a t i o n o f c o n c e n t r a t e d r i p c u r r e n t s , the f o r m a t i o n of s c o u r h o l e s around t h e ' g r o i n s w h i c h maybe h a z a r -dous t o b a t h e r s on r e c r e a t i o n a l b e a c h e s , and t h e r e d u c t i o n i n t h e s u p p l y o f l i t t o r a l d r i f t a v a i l a b l e t o t h e d o w n d r i f t c o a s t . The l a t t e r d i s a d v a n t a g e c a n be p a r t i c u l a r l y s e r i o u s where e x p e r i e n c e h a s shown t h a t a t t e m p t s t o m i t i g a t e an e r o -s i o n problem w i t h a g r o i n f i e l d h a -s o f t e n r e -s u l t e d i n an a g g r a v a t e d e r o s i o n p r o b l e m d o w n d r i f t .

The l e n g t h , s p a c i n g , e l e v a t i o n , and number o f g r o i n s a r e v e r y i m p o r t a n t and s h o u l d be d e v e l o p e d t h r o u g h s i t e s p e c i f i c d e s i g n e f f o r t s by a q u a l i f i e d c o a s t a l e n g i n e e r . However, f o r p l a n n i n g p u r p o s e s , t h e g e n e r a l g u i d e l i n e s p r e s e n t e d below can be f o l l o w e d . The t y p i c a l g r o i n e x t e n d s from t h e b r e a k e r zone t o t h e t o p o f t h e beach berm, and l a n d w a r d t o a p o i n t where t h e g r o i n w i l l n o t be endangered by f l a n k i n g d u r i n g i t s d e s i g n l i f e . The minimum c r e s t e l e v a t i o n i s s e t e q u a l t o t h e h e i g h t o f t h e d e s i r e d beach berm. The h e i g h t o f the shoreward s e c t i o n o f g r o i n above t h i s l e v e l i s t h e n a c a r e -f u l t r a d e - o -f -f b e t w e e n d e s i r e d l e v e l s o -f b e a c h b u i l d u p and sand b y - p a s s i n g q u a n t i t i e s n e c e s s a r y t o n o u r i s h d o w n d r i f t b e a c h e s . G r o i n s p a c i n g i s d e t e r m i n e d by t h e p r e d i c t e d shape o f c o m p a r t m e n t a l i z e d s h o r e l i n e s , and as a g e n e r a l g u i d e l i n e ' i s u s u a l l y two t o t h r e e t i m e s t h e l e n g t h o f t h e i n d i v i d u a l g r o i n s •

The shape o f f u t u r e s h o r e l i n e s a r e g e n e r a l l y assumed t o a l i g n i t s o r i e n t a t i o n t o p a r a l l e l t h e i n c i d e n t wave c r e s t s under p r e d o m i n a n t c o n d i t i o n s , t a k i n g i n t o a c c o u n t wave r e -f l e c t i o n , r e -f r a c t i o n , and d i -f -f r a c t i o n . B e a c h e s w i t h wave c l i m a t e s h a v i n g a d i s t i n c t s e a s o n a l characteriötics i n wave d i r e c t i o n s h o u l d c o n s i d e r p r e v a i l i n g wave c o n d i t i o n s by s e a s o n i n a d d i t i o n t o a n n u a l p r e d o m i n a n t wave c o n d i t i o n s . G e n e r a l l y , g r o i n s s h o u l d be p l a n n e d a s a f i e l d o f m u l t i p l e s t r u c t u r e s o f u n i f o r m l e n g t h r a t h e r t h a n a s an i n d i v i d u a l s t r u c t u r e . G r o i n f i e l d s s h o u l d be c o n s t r u c t e d i n s t a g e s , s t a r t i n g a t t h e extreme d o w n d r i f t end o f t h e a r e a t o be p r o t e c t e d . I n t h i s way, t h e e f f e c t o f a s i n g l e g r o i n can be s t u d i e d c a r e f u l l y b e f o r e c o m p l e t i n g t h e l a y o u t o f t h e g r o i n f i e l d .

Example g r o i n p l a n s and c r o s s - s e c t i o n s a r e shown i n F i g u r e 4.

P L A N

N O T E : CONTOURS SHOWN IN m

F I G U R E 4: GROIN PLAN

1 - 2 . 2 O f f s h o r e B r G a k w a t e r s

O f f s h o r e b r e a k w a t e r s can be used t o m i t i g a t e t h e f o r c e and v a r y t h e d i r e c t i o n o f waves s t r i k i n g t h e s h o r e , and t h e r e f o r e can be u s e d t o r e d u c e shore e r o s i o n . They a r e l o c a t e d away from t h e s h o r e , and a r e n o r m a l l y p a r t i a l l y s u b -merged d u r i n g a l l t i d a l l e v e l s . B r e a k w a t e r s t e n d t o r e d u c e l i t t o r a l t r a n s p o r t i n t h e l e e o f t h e s t r u c t u r e , and under c e r t a i n c o n d i t i o n s w i l l i n d u c e t h e f o r m a t i o n of a tombolo O f f s h o r e b r e a k w a t e r s y s t e m s p r o v i d e e r o s i o n p r o t e c t i o n w i t h o u t i m p a i r i n g t h e u s e f u l n e s s o f the beach and can p r o -v i d e s h e l t e r e d w a t e r f o r b a t h i n g . Because s e d i m e n t t r a n s p o r t i s d i r e c t l y r e l a t e d t o t h e incoming, wave a c t i o n , t h e degree o f wave a t t e n u a t i o n by an o f f s h o r e b r e a k w a t e r w i l l d e t e r m i n e t h e e x t e n t t o w h i c h l i t t o r a l d r i f t w i l l be impounded i n t h e l e e of a b r e a k w a t e r .

H y d r a u l i c model s t u d i e s p e r f o r m e d a t t h e D a n i s h H y d r a u -l i c I n s t i t u t e h a v e examined t h e e f f e c t i v e n e s s o f Longard tube b r e a k w a t e r s i n r e d u c i n g wave h e i g h t , and r e s u l t s o f t h e s e t e s t s may be used i n c a l c u l a t i n g i n c i d e n t wave c h a r a c t e r i s t i c s . F i g u r e 5 p r e s e n t s wave h e i g h t t r a n s m i s s i o n c o e f -f i c i e n t s as a -f u n c t i o n o -f t h e r e l a t i v e submergence o -f a Longard tube b r e a k w a t e r . D e t e r m i n a t i o n o f t h e o p t i m a l a l i g n m e n t , h e i g h t , l e n g t h , s p a c i n g and d i s t a n c e o f f s h o r e f o r b r e a k w a t e r s s h o u l d o n l y be e s t a b l i s h e d w i t h f u l l c o n s i d e r a t i o n o f s i t e s p e c i f i c c o n d i t i o n s . I f s h o r e l i n e s t a b i l i z a t i o n i s t h e p r i m a r y o b j e c -t i v e , i -t i s u s u a l l y d e s i r a b l e -t o employ a s e r i e s o f segmen-t e d o f f s h o r e b r e a k w a segmen-t e r s w h i c h w i l l r e g u l a segmen-t e segmen-t h e r a segmen-t e o f l o n g s h o r e s a n d movement w i t h o u t c o m p l e t e l y impounding l i t t o r a l m a t e r i a l s . F i g u r e 6 p r e s e n t s t y p i c a l p l a n s and c r o s s -s e c t i o n -s f o r a d e t a c h e d b r e a k w a t e r -s y -s t e m . 9

% H, J 00 H i 90 80 70 60 50 40 30 20 10 O _{_ L _} 0.5 O X /

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O R I G I N A L B O T T O M S E C T I O N A - A C L O S U R E F I T T I N G O R I G I N A L B O T T O M F I L T E R C L O T H 2 5 CM0 A N C H O R T U B E B R E A K W A T E R E N D S A N C H O R E D B Y N A T U R A L S C O U R S E C T I O N B - B F I G U R E S : O F F S H O R E B R E A K W A T E R PLAN 11

1 . 2 . 3 P e r c h e d B e a c h e s

The p e r c h e d beach c o n c e p t i n v o l v e s r e t a i n i n g a wide p r o -t e c -t i v e beach o r s h a l l o w o f f s h o r e a r e a by means o f -t e r r a c i n g w i t h t h e c o n s t r u c t i o n o f beach r e t a i n i n g s i l l s . V7ave energy i s d i s s i p a t e d w h i l e p r o p a g a t i n g o v e r t h i s s h a l l o w r e g i o n by b r e a k i n g and t h r o u g h bottom f r i c t i o n . Waves h e n c e have a reduced e r o s i v e e f f e c t upon i m p i n g i n g on t h e s h o r e l i n e . I n g e n e r a l , p e r c h e d b e a c h shore p r o t e c t i o n schemes a r e most a p p l i c a b l e a l o n g s h o r e l i n e s w i t h a r e l a t i v e l y f l a t , g e n t l y s l o p i n g n e a r s h o r e p r o f i l e . As w i t h o t h e r p r o t e c t i v e beach c o n c e p t s , an abundant s u p p l y of l i t t o r a l m a t e r i a l i n t h e a c t i v e wave zone i s n e c e s s a r y f o r beach s i l l s t o f u n c t i o n p r o p e r l y .

I n t h e p l a n n i n g o f a p e r c h e d b e a c h s y s t e m , t h e w i d e s t p r a c t i c a l b e a c h w i d t h s h o u l d be o b t a i n e d f o r maximum e f f e c -t i v e n e s s i n v/ave energy' a -t -t e n u a -t i o n . S e v e r a l -t e r r a c e s may be the most e f f e c t i v e i n o r d e r t o o b t a i n s h a l l o w w a t e r f o r a l l t i d a l s t a g e s . F i g u r e 7 d e m o n s t r a t e s t h e p e r c h e d b e a c h con-c e p t .

^ « ^ ™ ^ « L Z Z Z I MM •' : • i

S E C T I O N NO S C A L E

1.2.4 Composite Schemes

A c o m b i n a t i o n o f v a r i o u s schemes f o r r e t a i n i n g a p r o t e c -t i v e beach i s o f -t e n -t h e p r e f e r r e d me-thod f o r p r o -t e c -t i n g a s h o r e l i n e w h i l e p r o v i d i n g t h e maximum b e n e f i t s . As an e x -ample, g r o i n s a r e u s e f u l i n s t a b i l i z i n g s h o r e l i n e s but can be d e t r i m e n t a l t o t h e r e c r e a t i o n a l v a l u e of a b e a c h due t o n e a r s h o r e s c o u r holeö h a z a r d o u s t o b a t h e r s , t h e f o c u s i n g o f wave energy and t h e i r u n s i g h t l y a p p e a r a n c e . A l s o , d u r i n g

e x c e p t i o n a l l y h i g h s t o r m wave c o n d i t i o n s , r i p c u r r e n t s formed along t h e g r o i n s t r a n s p o r t l i t t o r a l d r i f t f a r t h e r o f f -s h o r e than what would n o r m a l l y o c c u r w i t h o u t t h e g r o i n -s , t h u s removing t h i s m a t e r i a l from t h e a c t i v e l i t t o r a l zone. To l e s s e n t h e s e a d v e r s e e f f e c t s , a c o m p o s i t e scheme of g r o i n s and o f f s h o r e b r e a k w a t e r s can be u s e d . S a f e b a t h i n g a r e a s a r e c r e a t e d i n t h e l e e o f t h e b r e a k w a t e r s , w h i l e s h o r e r e a l i g n m e n t and b e a c h b u i l d u p c a n s t i l l be o b t a i n e d w i t h t h e use of g r o i n s . The r e d u c t i o n o f i n c i d e n t wave e n e r g y by t h e b r e a k w a t e r s w i l l a l s o d e c r e a s e t h e i n t e n s i t y of r i p c u r r e n t s and t h e l o s s o f m a t e r i a l o f f s h o r e .

A c o m p o s i t e scheme c o m b i n i n g r e v e t m e n t s w i t h m a s s i v e b e a c h f i l l s c a n a l s o be employed t o c r e a t e a r t i f i c i a l h e a d -l a n d s and a s e r i e s o f p o c k e t b e a c h e s . F i g u r e 8 p r e s e n t s composite schemes w i t h t h e L o n g a r d tube s y s t e m .

1.3 BLUFF S T A B I L I Z A T I O N

E r o s i o n o f c o a s t a l b l u f f s i s c a u s e d by g r o u n d w a t e r o r s o i l d i s c o n t i n u i t i e s , s u r f a c e r u n o f f and t o e e r o s i o n by wave a c t i o n . I n a l l c a s e s o f b l u f f s t a b i l i z a t i o n , p r o t e c t i o n o f t h e toe from wave e r o s i o n i s o f p r i m a r y c o n c e r n . Upper b l u f f s t a b i l i z a t i o n c a n n o t be e f f e c t i v e u n t i l wave e r o s i o n i s t e r m i n a t e d . Methods o f m i t i g a t i n g toe e r o s i o n a r e i d e n t i c a l t o t h o s e p r e s e n t e d a s t h o s e f o r h a r d e n i n g t h e s h o r e -l i n e or r e t a i n i n g p r o t e c t i v e b e a c h e s . T h a t i s , s e a w a -l -l s , b u l k h e a d s , r e v e t m e n t s , g r o i n s , o f f s h o r e b r e a k w a t e r s , p e r c h e d

b e a c h e s and c o m b i n a t i o n s of t h o s e a r e a l l p o s s i b l e m e t h o d s

f o r p r o v i d i n g t o e p r o t e c t i o n t o e r o d i n g b l u f f s .

S t a b i l i z a t i o n of the upper b l u f f can be a c c o m p l i s h e d b y i n s t a l l i n g L o n g a r d tube r e t a i n i n g w a l l s a l o n g w i t h approp r i a t e g r a d i n g , v e g e t a t i v e approp l a n t i n g s , dune f e n c e s and d r a i n -age p r o v i s i o n . C o n t r o l l i n g g r o u n d w a t e r s e e p s and g u l l y i n g e f f e c t s of s u r f a c e w a t e r r u n o f f i s the m a j o r o b j e c t i v e i n s t a b i l i z i n g t h e upper b l u f f . F i g u r e 9 p r e s e n t s t h e d e s i g n f e a t u r e s of a s t a b i l i z e d c o a s t a l b l u f f . 1.4 MISCELLANEOUS USES The u n i q u e c h a r a c t e r i s t i c s o f t h e L o n g a r d s y s t e m p r e -s e n t -s v a r i o u -s a p p l i c a t i o n -s which a r e o f t e n not f e a -s i b l e by o t h e r c o n s t r u c t i o n methods. The f l e x i b i l i t y o f t h e s y s t e m a l o n g w i t h t h e a b i l i t y t o f i n a tube i n n o r m a l l y i n a c c e s -s i b l e a r e a -s t r e m e n d o u -s l y r e d u c e -s -s i t e p r e p a r a t i o n and a c c e -s -s r e q u i r e m e n t s a l o n g w i t h a s s o c i a t e d m o b i l i z a t i o n and d e m o b i l i z a t i o n c o s t s . Equipment needs a r e m i n i m a l , n o r m a l l y c o n -s i -s t i n g o n l y o f t h e p a t e n t e d f i l l i n g machine, w a t e r pump, and f r o n t - e n d l o a d e r . Examples o f m i s c e l l a n e o u s a p p l i c a ¬ t i o n s a r e p r e s e n t e d below. ^•^•^ R^ZgJ T r a i n i n q / F l o o d C o n t r o l S t r u c t u r e . ^

Bank s t a b i l i z a t i o n and e r o s i o n c o n t r o l i s somewhat s i m -i l a r xn c o n c e p t t o t h a t a p p l -i c a b l e on t h e open c o a s t ; t h e major d i f f e r e n c e s b e i n g t h e a b s e n c e o f l a r g e waves and n o r -m a l l y a u n i - d i r e c t i o n a l flow p a t t e r n . G r o i n s a r e t y p i c a l s t r u c t u r e s c o n s t r u c t e d w i t h L o n g a r d t u b e s and u s e d t o reduce bank e r o s i o n and t o s t a b i l i z e m e a n d e r i n g r i v e r s .

G r o i n s , s p u r s , o r s p u r d i k e s , f u n c t i o n by c o n t r a c t i n g r i v e r f l o w . T h e s e s t r u c t u r e s a r e u s e d t o e s t a b l i s h normal c h a n n e l w i d t h ; d i r e c t the a x i s o f f l o w ; promote s c o u r and sediment d e p o s i t i o n where r e q u i r e d ; and t o b u i l d up new banks. i n t h e u s e o f r i v e r g r o i n s , e x p e r i e n c e i s c h i e f l y

s e e r o -r e l i e d upon i n d e t e -r m i n i n g a p p -r o p -r i a t e s i z i n g and a l i g n m e n t o f the g r o i n s . I n g e n e r a l , l a r g e i s o l a t e d g r o i n s t r u c t u r e s s h o u l d be a v o i d e d where a group of s m a l l e r g r o i n s , i n a g r o i n f i e l d , c a n be u s e d t o o b t a i n t h e d e s i r a b l e r e s u l t s more g r a d u a l l y . A b r u p t m o d i f i c a t i o n s t o t h e n a t u r a l r i v e r f l o w regime may o f t e n r e s u l t i n u n d e s i r a b l e e f f e c t s a l o n g a n o t h e r r e a c h o f t h e r i v e r , e s p e c i a l l y i f a s t r u c t u r e i i n s t a l l e d c a u s i n g a s h a r p change i n flow d i r e c t i o n . ' F i g u r 10 p r e s e n t s an example o f L o n g a r d tubes used t o c o n t r o l s i o n along t h e Po R i v e r , I t a l y . 1.4.2 J e t t i e s A j e t t y i s a s t r u c t u r e e x t e n d i n g i n t o t h e w a t e r t o c o n -f i n e r i v e r o r t i d a l -f l o w i n a c h a n n e l , and t o m i t i g a t e s h o a l i n g o f t h e c h a n n e l by l i t t o r a l d r i f t . When l o c a t e d a l o n g n a v i g a b l e e n t r a n c e c h a n n e l s , they a l s o s e r v e t o e l i m i -n a t e c r o s s c u r r e -n t s a-nd t o p r o v i d e wave p r o t e c t i o -n . The d e s i g n o f j e t t i e s r e q u i r e s a c a r e f u l u n d e r s t a n d i n g o f both t h e l i t t o r a l r e g i m e and h y d r a u l i c c h a r a c t e r i s t i c s o f t h e i n l e t o r c h a n n e l . The e f f e c t o f a j e t t y on l o n g s h o r e sediment t r a n s p o r t , t i d a l p r i s m , s a l i n i t y i n t r u s i o n and i n l e t f l o w c h a r a c t e r i s t i c s must be a s s e s s e d t o a v o i d u n d e s i r a b l e i m p a c t s , and t o a c h i e v e d e s i r a b l e r e s u l t s . B e c a u s e o f t h e complex n a t u r e o f t h i s d e s i g n problem, t h e u s e o f g e n e r a l g u i d e l i n e s f o r optimum i n l e t c r o s s - s e c t i o n a l a r e a s and j e t t y s i z i n g and a l i g n m e n t a r e n o t recommended. However, once o p t i m a l j e t t y l o c a t i o n s and a l i g n m e n t s a r e d e t e r m i n e d , t h e use of Longard t u b e s i n t h e a c t u a l c o n s t r u c t i o n o f t h e j e t t y i s a s i m p l e m a t t e r . F o r s m a l l i n l e t s i n a r e a s o f l i m i t e d t i d a l range, s i n g l e 100cm o r 180cm d i a m e t e r t u b e s c a n s e r v e a s j e t t i e s f o r i n l e t s t a b i l i z a t i o n .

SAND S H O A L P L A N H I G H R I V E R S T A G E N A T U R A L S A N D B U I L D U P I S O C M ^ Z J T U B E R I P R A P T O E r — P R O T E C T I O N • F I L T E R W / A N C H O R T U B E S S E C T I O N A - A F I G U R E 1 0 : R I V E R T R A I N I N G G R O I N S 1 9

1 . 4 . 3 D r e d g e _ j : o n l a i n n i e n t DiV. es e r -es . e s e Dredging o f h a r b o r s , c h a n n e l s and o t h e r n a v i g a b l e wat ways o f t e n i n v o l v e s s p o i l s w i t h a h i g h p e r c e n t a g e of f i n H y d r a u l i c d r e d g i n g o f t h i s m a t e r i a l w i t h d i s p o s a l onshor c r e a t e s a need f o r r e t a i n m e n t d i k e s or berms t o p r e v e n t t h i s l u r r y from r u n n i n g back t o t h e s e a , w h i l e p r o v i d i n g a wid s e t t l i n g b a s i n . The b e n e f i t s i n u s i n g dredge c o n t a i n m e n t d i k e s a r e t w o f o l d : f i r s t , a g r e a t e r ' a m o u n t of dredge s p o i l i s r e t a i n e d and s e c o n d , t h e r e i s r e d u c e d t u r b i d i t y of t h e r e t u r n i n g d r e d g e e f f l u e n t w h i c h i s l e s s d i s t u r b i n g t o t h e environment. The use o f L o n g a r d t u b e s f o r c o n t a i n m e n t d i k e s i s an economic a l t e r n a t i v e t o c o n v e n t i o n a l e a r t h d i k e c o n s t r u c -t i o n . A 180cm -tube can p r o v i d e a d i k e a p p r o x i m a -t e l y 1.8m h i g h r e q u i r i n g l e s s f i l l , w i t h s e l e c t m a t e r i a l , and a s h o r t e r c o n s t r u c t i o n t i m e t h a n t h e c o n v e n t i o n a l e a r t h d i k e . 1-4.4 A r t i f i c i a l I s l a n d s A r t i f i c i a l i s l a n d s c o n s t r u c t e d w i t h t h e Longard t u b e s y s t e m p r e s e n t s an a d d i t i o n a l use f o r both u n d e r w a t e r c o n -s t r u c t i o n t e c h n i q u e -s and -s h o r e p r o t e c t i o n -scheme-s. U-se-s f o r t h e s e i s l a n d s i n c l u d e w o r k i n g p l a t f o r m s f o r o f f s h o r e e n e r g y e x p l o r a t i o n and development, o f f s h o r e t e r m i n a l s and r e c -r e a t i o n a l p u -r p o s e s . A d v a n t a g e s f o -r u s i n g t h e Longa-rd tube s y s t e m f o r a r t i f i c i a l i s l a n d c o n s t r u c t i o n i n c l u d e the r e -d u c t i o n of r e q u i r e -d f i l l m a t e r i a l s , spee-d o f c o n s t r u c t i o n and low r e l a t i v e c o s t s . I s l a n d r e m o v a l i s a l s o e a s i l y a c c o m p l i s h e d a s i s o f t e n r e q u i r e d f o r t e m p o r a r y energy e x p l o r a t i o n s t r u c t u r e s . F i g u r e 11 p r e s e n t s a c o n c e p t u a l i s l a n d c o n s t r u c t i o n scheme u s i n g t h e L o n g a r d t u b e s .

2 • O GE,\-ERAL DESIGN GUIDEED^ES

2.1 PHYSICAL PROPERTIES

2.1.1 Tube M a t e r i a l s and S i z e s

The L o n g a r d tube a c t u a l l y c o n s i s t s o f two t u b e s : an i n

-n e r t u b e o f impermeable p o l y e t h y l e -n e s h e e t a-nd a-n o u t e r tube o f woven p o l y e t h y l e n e f a b r i c . The f u n c t i o n o f t h e i n n e r tube i s t o a i d i n t h e f i l l i n g p r o c e s s . S t r u c t u r a l s t r e n g t h i s p r o v i d e d by t h e o u t e r tube, w h i c h i s woven o f a h i g h den-s i t y p o l y e t h y l e n e f a b r i c , i den-s U V - den-s t a b i l i z e d and h a den-s g r e a t r e s i s t a n c e t o r o t , o i l and c h e m i c a l s l i k e l y t o o c c u r i n c o a s t a l z o n e s . T e c h n i c a l s p e c i f i c a t i o n s f o r t h e tube m a t e r i a l a r e p r e s e n t e d i n T a b l e s 1 t h r o u g h 4. L o n g a r d t u b e s a r e a v a i l a b l e i n s t a n d a r d d i a m e t e r s o f 25, 100 and 180cm / ^nd i n l e n g t h s up ^ ° ^20 m. , The 25 cm tube i s t y p i c a l l y u s e d a s an a n c h o r f o r t h e f i l t e r c l o t h ; where t h e f i l t e r s h e e t and a n c h o r tube a r e sewn t o g e t h e r w i t h s p e c i f i e d f i l t e r w i d t h s . S i n g l e 100 o r 180cm t u b e s c o m p r i s e t h e p r i -mary s t r u c t u r a l e l e m e n t s o f t h e L o n g a r d t u b e s y s t e m . Double

t u b e s a r e a l s o a v a i l a b l e . T h e s e t u b e s a r e woven t o g e t h e r i n t o one u n i t and a r e f i l l e d s i m u l t a n e o u s l y . The u s e o f d o u b l e 100 cm t u b e i s recommended where e x t r a l a t t e r a l s t a b i l i t y i s r e q u i r e d .

2.1.2 F i l l i n g M a t e r i a l s

The L o n g a r d t u b e s y s t e m c a n be f i l l e d w i t h any c o -h e s i o n l e s s s o i l c a p a b l e o f b e i n g t r a n s p o r t e d -h y d r a u l i c a l l y and graded t o h a v e a maximum g r a i n s i z e d i a m e t e r o f l e s s t h a n a p p r o x i m a t e l y 2-5 cm. N a t u r a l l y o c c u r r i n g b e a c h sand a t t h e p r o j e c t s i t e i s t h e u s u a l c h o i c e o f f i l l m a t e r i a l , however, s e l e c t f i l l m a t e r i a l s h o u l d be c o n s i d e r e d i f a l o c a l b o r r o w a r e a i s not a v a i l a b l e , o r i f t h e f i n e s o r c o a r s e g r a v e l c o n t e n t exceeds a p p r o x i m a t e l y 15 p e r c e n t . T y p i c a l f i l l m a t e r i a l c o n s i s t s o f b e a c h s a n d h a v i n g a g r a i n s i z e r a n g i n g from 0.1 t o 5.0 m i l i m e t e r s i n d i a m e t e r . 22

A c h i e v i n g a r e l a t i v e l y h i g h u n i t w e i g h t f o r a f i l l e d tube i s e s s e n t i a l f o r s t a b i l i t y under s e v e r e h y d r a u l i c con-d i t i o n s where b u o y a n c y e f f e c t s can r e con-d u c e tube s t a b i l i t y . F i g u r e 12 c a n be u s e d t o approximate t h e u n i t w e i g h t o f a f i l l e d tube w i t h t h e knowledge o f a v a i l a b l e f i l l m a t e r i a l . F o r a f u l l y f i l l e d t u b e , t h e r e l a t i v e d e n s i t y w i l l be f i r m t o dense, w i t h a r a n g e i n r e l a t i v e d e n s i t y o f up t o 90 p e r -c e n t . T a b l e 2 p r e s e n t s t y p i -c a l v a l u e s o f w e i g h t p e r u n i t l e n g t h o f f i l l e d L o n g a r d t u b e s . V E R Y - W E L L G R A D E D S I L T Y SANDY G R A V E L WELL G R A D E D SUBANGULAR SAND

UNIFORM SUBANGULAR SAND

MICACEOUS SAND AND S I L T

O 2 0 AO 6 0 8 0 1 O 0 R E L A T I V E D E N S I T Y , X

F I G U R E 1 2 : S A T U R A T E D WEIGHT V S . R E L A T I V E D E N S I T Y O F F I L L M A T E R I A L

TABLE 2

IN-PLACE WEIGHT OF LONGARD TUBES

TUBE DIAMETER (cm) SECTIONAL AREA (m2) w i t h 98% F u l l n e s s

WEIGHT OF TUBE (tonne/n,) TUBE DIAMETER (cm) SECTIONAL AREA (m2) w i t h 98% F u l l n e s s Low D e n s i t y (1.95 tonne/m^) T y p i c a l D e n s i t y (2.08 tonne/m-') High D e n s i t y (2.34 tonne/m^) 25 0.0491 0.10 0.10 0.11 100 0.770 1.5 i.e " l . 8 180 2.49 4.9 5.2 5.8

2 . 1 . 3 G e o m e t r i c P r o p e r t i _ R R

Nominal d i m e n s i o n s f o r Longard t u b e s a r e g i v e n as t h e dxa„eter o f a n e q u i v a l e n t c y l i n d e r h a v i n g t h e same d i a m e t e r as t h e „oven t u b e . i„ p r a c t i c e , t h e c r o s s - s e c t i o n a l shape o f a f i l l e d L o n g a r d t u b e i s a p p r o x i m a t e d by a c i r c l e w i t h a f l a t top, t h e p r o p e r t i e s f o r w h i c h a r e shown i n F i g u r e 13 F r e l d e x p e r i e n c e h a s d e m o n s t r a t e d t h a t i t i s p o s s i b l e t o f i l l Longard t u b e s t o 98 t o 9 9 p e r c e n t o f t h e i r t h e o r e t i c a l maximum c a p a c i t y ; w h i l e 9 5 p e r c e n t f i l l s a r e e a s i l y ob t a i n a b l e w i t h w e l l - g r a d e d sand. F i g u r e 13 c a n be u s e d t o o b t a i n d i m e n s i o n s o f f i l l e d L o n g a r d t u b e s . 2.1.4 P r o t e c t i v e C o a t i n g While u n d e r many c o n d i t i o n s no f u r t h e r p r o t e c t i o n i s r e q u i r e d , i n c e r t a i n s i t u a t i o n s i t may be n e c e s s a r y t o c o n -s i d e r t h e l i v e l i h o o d Of v a n d a l i -s m , o r t h e p o -s -s i b i l i t y o f damage m a p a r t i c u l a r l y h a r s h e n v i r o n m e n t . F o r t h e s e s i t u a t i o n s , an epoxy c o a t i n g ' i s a v a i l a b l e , which :,.y be s p r e a d on a f t e r t h e tube i s i n s t a l l e d and p r o -v i d e s a d u r a b l e y e t f l e > , i b l e p r o t e c t i o n . T h i s c o a t i n g „ay be s p r i n k l e d w i t h t h e s u r r o u n d i n g m a t e r i a l t o v i s u a l l y b l e n d i n w i t h t h e s u r r o u n d i n g s . I t i s c o m p l e t e l y w a t e r p r o o f and may be a p p l i e d t o wet s u r f a c e s . 2.2 EARTH PRESSURES c a l c u l a t i o n s o f e a r t h p r e s s u r e f o r t h e d e s i g n o f L o n g a r d tubes a s r e t a i n i n g w a l l s o r b u l k h e a d s c a n u s e t h e a p p r o x i m a -t i o n s f o r a c -t i v e e a r -t h p r e s s u r e f o r c o h e s i o n l e s s s o i l s . T h i s t h e o r y a s s u . e s t h a t t h e t u b e w i l l d i s p l a c e away from t h e s o i l mass s u f f i c i e n t l y f o r a c t i v e e a r t h p r e s s u r e s t o develop, and i s t h o r o u g h l y p r e s e n t e d i n most s o i l e n g i n e e r -i n g t e x t b o o k s ( -i . e . . Sowers and Sower?, 1 9 7 0 ) .

N O M I N A L T U B E D I A M E T E R T U B E F U L L N E S S 98% OF T H E O R E T I C A L MAXIMUM C A P A C I T Y 1 0 0 c m a H S E C T I O N A L A R E A 44.6cm 94.7cm 0.770m2 95% OF T H E O R E T I C A L MAXIMUM C A P A C I T Y a H S E C T I O N A L A R E A 59.Jcm 90.3cm 0.746m^ 1 8 0 c m 80.3cm 170.5cm 2.49m2 106.4cm 162.6cm 2.42m2 F I G U R E 1 3 : GEOMETRIC P R O P E R T I E S O F F I L L E D L O N G A R D T U B E S

I n g e n e r a l , t u b e s used s i n g l y w i t h l e v e l b a c k f i l l s a r e m a s s i v e enough t o r e s i s t s l i d i n g f o r a l l normal c o n d i t i o n s , and s t a b i l i t y c a l c u l a t i o n s w i l l not be n e c e s s a r y . F o r c o n -d i t i o n s i n v o l v i n g s t a c k e -d tube c o n s t r u c t i o n , s t e e p l y s l o p i n g b a c k f i l l s , or poor d r a i n a g e p r o v i s i o n s and the p o s s i b i l i t y o f the b a c k f i l l becoming f u l l y s a t u r a t e d , e a r t h p r e s s u r e c a l c u l a t i o n s s h o u l d be p e r f o r m e d and t h e s t a b i l i t y of the tube a s s e s s e d .

1

The a c t i v e p r e s s u r e , a t a d i s t a n c e , h below the ground s u r f a c e i s : P A = ( 4 5 -

y\

where H = h e i g h t from t h e bottom o f t h e tube t o t h e top o f t h e b a c k f i l l . F o r h i g h w a t e r - t a b l e s o r f u l l y s a t u r a t e d b a c k f i l l s , t h e e f f e c t i v e s t r e s s i n t h e s o i l m a t r i x i s u s e d f o r c a l c u l a t i n g t h e a c t i v e e a r t h p r e s s u r e and t h e h y d r o s t a t i c w a t e r p r e s s u r e i s added t o o b t a i n t h e n e t h o r i z o n t a l f o r c e . A d e f i n i t i o n s k e t c h f o r c a l c u l a t i n g a c t i v e e a r t h p r e s s u r e s i n v o l v i n g s l o p i n g b a c k f i l l s - i s p r e s e n t e d i n F i g u r e 15. The a p p r o x i m a t i o n s a r e :

V

w h e r e , a - t h e a n g l e b e t w e e n t h e b a c k f i l l s u r f a c e and t h e h o r i z o n t a l . The d i r e c t i o n o f t h i s f o r c e i s p a r a l l e l t o t h e b a c k f i l l s l o p e w i t h a l i n e o f a c t i o n p a s s i n g t h r o u g h a p o i n t 1/3H above t h e b o t t o m o f t h e t u b e . F i g u r e s 14, 15, and 16 p r e -s e n t e x a m p l e p r o b l e m -s and a d e -s i g n a i d f o r c o m p u t i n g e a r t h p r e s s u r e s .

7 s = UNIT WEIGHT OF B A C K F I L L M A T E R I A L UNIT WEIGHT OF WATER

FRESHWATER =1.00 tonne/m^ SALTWATE R 7 ^ = ^ -^^B 1onne/m^ R = RESISTANCE TO SLIDING C A S E I. W A T E R T A B L E I S A T T H E B O T T O M O F T H E T U B E Pa =7sH tan^ ( 4 5- 0/ 2 ) = % 7 sH 2 tan^ ( 4 5- 0/ 2 ) C A S E I I . W A T E R T A B L E L O C A T E D A T T O P O F B A C K F I L L 'Pa = <Ts-7w) H tan^ ( 4 5- 0/ 2 ) 'Pa - l^{7s-7w) tan2 ( 4 5- 0/ 2 ) ''total " '"a ''w R E S I S T A N C E T O S L I D I N G CAN BE C A L C U L A T E D A S : R =/iW W H E R E W = W E I G H T O F T H E F I L L E D T U B E AND At = S T A T I C C O E F F I C I E N T O F F R I C T I O N A T T H E SLIP P L A N E . F I G U R E 1 4 : A C T I V E E A R T H P R E S S U R E WITH HORIZONTAL B A C K F I L L

E X A M P L E : D E T E R M I N E T H E S T A B I L I T Y OF A 180cm 0 T U B E WITH A L E V E L B A C K F I L L S U B J E C T E D TO WAVE O V E R T O P P I N G . G I V E N : <p-30°. UNIT W E I G H T OF B A C K F I L L = 1.92 lonne/m^, AND UNIT WEIGHTC L O N G A R D T U B E = 2.08 tonne/m^. S O L U T I O N : FOR A 180cm 0 T U B E F I L L E D TO 98% C A P A C I T Y , S E C T I O N A L A R E A 2.49m2, H - - 1 7 0 , 5 c m WEIGHT OF T U B E = (2.49m2) ( 2.08tonne/m^ = 5.18tonne/mT S L I D I N G R E S I S T A N C E R = /iW = tan 3 0 ° (5.18 tonne/m ) ' 2.99 tonne/m A C T I V E E A R T H P R E S S U R E '"a = ( Ts - 7w ) tan^ (45 - 0/2) = y. ( 1 . 9 2 - 1.025) (l.lObf t a n 2 ( 4 5 - 3 0 / 2 ) = , 0 , 4 3 4 'V. 1.025 ( 1 . 7 0 5 ) 2 - ' 1 . 4 9 0 t o n n e / m PA = P \ + P A T O T A L A ^ ' ^ W = 0.434 + 1.490 = 1.924 t o n n e / m F A C T O R O F S A F E T Y FOR S L I D I N G P - S . - R / Pa. , „ . ^ ^ ^ = 2.99/ 1 . 9 2 4 = 1 . 5 5 . ' . T U B E IS S T A B L E

T O C A L C U L A T E A C T I V E E A R T H P R E S S U R E : Pa= ! 4 7 H 2 CO5/? ( C O S/ 3 - ^ / C O S 2 ^ - C O S 2 0 ) / (C O S ^ + ^ C O S ^ C O S ^ 0) T O T A L D I S P L A C E M E N T F O R C E O N T U B E C O N S I S T S O F E A R T H P R E S S U R E A N D W A T E R P R E S S U R E D U E T O D I F F E R E N T I A L E L E V A T I O N S O F S T A T I C H E A D O N T H E T W O S I D E S O F T H E T U B E . E X A M P L E : D E T E R M I N E T H E S T A B I L I T Y O F A 180cm 0 T U B E B A C K F I L L E D W I T H S A N D H A V I N G A S L O P E O F 3.0 H O R I Z O N T A L O N 1 0 V E R T I C A L C O N S I D E R A W E L L D R A I N E D B A C K F I L L E D W I T H : 0= 3 0 ° A N D U N I T W E I G H T = 1.92 tonne/m"^ F R O M E X A M P L E 1. T H E T U B E ' S S T A T I C R E S I S T A N C E T O S L I D I N G = Z 9 9 tonne/m A C T I V E E A R T H P R E S S U R E :

P ^ - ' A y H ^ cosp {coip- ^ c o j ^ ^ - cos^0) / (cos^ + ^ c o s ^ / J _ cos20)

F R O M F I G U R E 17 F O R m - 3 . 0 A N D 0 = 3 0 ° c o s ^ ( c o s ^ - c o s 2 / 3 - 005^0) / ( c o s ^ + v ^ c o s / J - cos2 0) = 0 . 4 0 H = T U B E H E I G H T * 1 . 7 0 5 m Pa= % ( 1.92) ( 1 . 7 0 5 9 ) ^ 0 . 4 0 ) = .1.12 t o n n e / m H O R I Z O N T A L C O M P O N E N T S O F P ^ Pa^^ = Pa '=°5^ = 1 .li^cos 18.4° = 1.Ub t o n n e / m F A C T O R O F S A F E T Y F O R S L I D I N G F . S . = R / P , = 2.99/ 1 .Ub = Z.tiZ . ' . T U B E I S S T A B L E G U R E 1 5 : A C T I V E E A R T H P R E S S U R E W I T H A S L O P I N G B A C K F I L L

2 . 3 _{WAVE FORCES}

The a p p r o x i m a t i o n o f wave f o r c e s on Longard tube s t r u c -t u r e s i s u s e f u l -t o a s s e s s -t h e s -t a b i l i -t y o f a -tube s u b j e c -t -t o wave a t t a c k . F o u r g e n e r a l wave c o n d i t i o n s o f wave a t t a c k on a s h o r e p a r a l l e l t u b e a r e :

I . Wave f o r c e s on a f u l l y submerged tube,

I I . N o n - b r e a k i n g wave f o r c e s on a non-submerged o r m a r g i n a l l y submerged tube,

I I I . B r e a k i n g wave f o r c e s on a non-submerged o r m a r g i n a l l y submerged tube, and

I V . B r o k e n wave f o r c e s on a non-submerged t u b e . Only a p p r o x i m a t e methods a r e a v a i l a b l e t o e s t i m a t e t h e s e f o r c e s , h e n c e , f o r s t r u c t u r e s r e q u i r i n g p r e c i s e e s t i m a t e s o f wave f o r c e s , h y d r a u l i c model s t u d i e s w i l l be r e q u i r e d . C o n d i t i o n s I o r I I I w i l l n o r m a l l y c o n s t i t u t e t h e d e s i g n c o n d i t i o n , w i t h t h e l a t t e r g e n e r a l l y b e i n g c a p a b l e o f p r o -d u c i n g t h e g r e a t e s t f o r c e . Metho-ds f o r a p p r o x i m a t i n g wave f o r c e s under t h e s e c o n d i t i o n s , w i t h t h e wave's d i r e c t i o n p e r p e n d i c u l a r t o t h e t u b e , a r e g i v e n i n t h e f o l l o w i n g s e c -t i o n s . S e l e c -t i o n o f a f a c -t o r o f s a f e -t y -t o a p p l y -t o -t h e s e f o r c e s s h o u l d w e i g h t h e s e r i o u s n e s s o f f a i l u r e o f t h e tube s t r u c t u r e and s h o u l d be made w i t h a q u a l i f i e d e n g i n e e r . Non-breaking wave f o r c e s on a non-submerged tube and b r o k e n waves f o r c e s ( c a s e s I I and I V ) c a n be p r e d i c t e d u s i n g methods p r e s e n t e d i n p u b l i c a t i o n s s u c h a s t h e Shore P r o t e c t i o n Manual ( 1 9 7 7 ) .

2-3.1 Wave F o r c e s on a F u l l y Submerged Tube

P r e d i c t i o n o f wave f o r c e s on a f u l l y submerged tube can use models and data, d e v e l o p e d f o r wave f o r c e s on submarine p i p e l i n e s . F o r n o n - b r e a k i n g waves and a w a t e r depth much g r e a t e r t h a n t h e t u b e d i a m e t e r , a method p r o p o s e d by Grace

p a r t i c l e k i n e m a t i c s and t h e p h y s i c a l p r o p e r t i e s o f t h e w a t e r and o f t h e t u b e . R e f e r r i n g t o F i g u r e 17, t h e f o l l o w -i n g e q u a t -i o n s c a n be used t o e s t -i m a t e peak f o r c e s : * / T , D 2 \ . ^ V A V "MAX , 1 F MAX P MAX where. ^MAX , < 1

' ^ i ^

"Lx . >

Peak h o r i z o n t a l and v e r t i c a l f o r c e s c a n be assumed t o o c c u r s i m u l t a n e o u s l y f o r d e s i g n p u r p o s e s . E s t i m a t i o n of w a t e r p a r t i c a l k i n e m a t i c s , i . e . , U^^ax and U^ax' c a n be made w i t h t h e a p p r o p r i a t e wave t h e o r y . F i g u r e 19 a l l o w s an approxima-t i o n o f n e a r boapproxima-tapproxima-tom k i n e m a approxima-t i c s w i approxima-t h l i n e a r wave approxima-t h e o r y by:

E X A M P L E : E S T I M A T E T H E W A V E F O R C E O N A F U L L Y S U B M E R G E D 100cm (p T U B E W H E R E d - m H = 1 ,8 m AND T = 8 s e c . IP_ 4 , 6 m 100cm 0 T U B E D « 3.3' Lo = % { g / 7 r ) T 2 = 14(J»Fü/7r) ( B ^ ) - 100 m d / L j j - 4 . 6 / 1 0 0 = 0 , 0 4 6 F R O M F I G U R E 19 1/sinh ( 2 7 r d / L) - 1.69 U ( ? r H / T \ M / ï i n h / 9 - ! r H / ! \ \ ~ I-n ' a V / 1 CQ ( , 1 I Q m./< I ~ I , I ^ III/ J l 2 7 r / T ) U ^ „ - | 2 7 r / 8 ) (1 J 9 > 0 , 9 3 t n / s ' ' / ' - U = ' m « / ' j n « x D- M 9 ^ / ( 0. 9 3 ) ( 1 ) = 1,52 F R O M F I G U R E 18 _{= 3-78} max K' =4.20 _max

f'mHv = C ' 14P ( D l ) U^ _{max max ' ' max}

(3.78)%(71»slugs/ni^) ( 1 X I ) U^^ 190 kg f / m i

Pm« = K ' %P ( D l l U^ _{max max max}

( 4 . 2 0 ) % (71 s l u g s / m 3 (1 x I ) U2 max

" 2 1 1 kg f / m i

T O T A L R E S U L T A N T MAXIMUM F O R C E 1 90^ + 2 1 1 '

= 284 kg f / m

.1.0 h

2-0 3.0 4.0 5.0 6.0 7.0 8.0 10.0

. i// - / Ü D

F I G U R E 18: MAXIMUM F O R C E C O E F F I C I E N T S FOR W A V E S ON A F U L L Y S U B M E R G E D T U B E

where, H = wave h e i g h t T = wave p e r i o d d = w a t e r depth, and L = wave l e n g t h . An example c a l c u l a t i o n f o r u s i n g t h i s method i s g i v e n i n F i g u r e 17.

^'^'^ B r e a k i n g Wave F o r c e s on a Non-submerged j;ube

L o n g a r d t u b e s p l a c e d p a r a l l e l t o s h o r e i n t h e a c t i v e s u r f zone w i l l n o r m a l l y be s u b j e c t e d t o b r e a k i n g waves d u r -ing d e s i g n c o n d i t i o n s . These f o r c e s a r e o f s h o r t d u r a t i o n and a r e g e n e r a l l y n o t a p p l i c a b l e f o r a s s e s s i n g t h e s t a t i c e q u i l i b r i u m o f a s i n g l e tube s y s t e m . However, i t s impor-t a n c e f o r n o n - impor-t y p i c a l impor-tube p l a c e m e n impor-t s , i . e . , p y r a m i d a l shaped b r e a k w a t e r s , must be r e c o g n i z e d and c o n s i d e r e d i n d e s i g n . The M i n i k i n method f o r e s t i m a t i n g b r e a k i n g wave f o r c e s c a n be u s e d t o a p p r o x i m a t e t h e magnitude of t h e i m p a c t l o a d i n g due t o b r e a k i n g w a v e s .

I n t h i s method," t h e maximum p r e s s u r e i s assumed t o a c t a t t h e s t i l l w a t e r l e v e l and i s g i v e n by

Ptn = V C^ ^ ^ s ) - h e r e ,

w = u n i t w e i g h t o f t h e w a t e r = b r e a k i n g wave h e i g h t

D = d e p t h one wave l e n g t h i n f r o n t o f t h e tube ' dg = d e p t h a t t h e t o e o f t h e t u b e

L D = wave l e n g t h i n w a t e r o f depth D

The p r e s s u r e d i s t r i b u t i o n i s assumed t o d e c r e a s e p a r a b o l i c -a l l y from -a t t h e s t i l l w -a t e r l i n e t o z e r o -a t -a d i s t -a n c e o f Hb/2 above and below t h e s t i l l w a t e r l i n e , a s shown i n F i g u r e 20. The h o r i z o n t a l f o r c e due t o t h i s p r e s s u r e d i s ¬ t r i b u t i o n i s e q u a l t o :

I f t h e t o p e l e v a t i o n o f t h e t u b e i s l o c a t e d b e l o w an e l e v a -t i o n o f Hb/2 a b o v e -t h e s -t i l l w a -t e r l i n e , i . e . , -t h e -t u b e i s o v e r t o p p e d by t h e b r e a k i n g wave, a p r e s s u r e d i s t r i b u t i o n t r u n c a t e d a t t h e t o p e l e v a t i o n o f t h e t u b e c a n be assumed. F i g u r e 20 i s an a i d f o r c a l c u l a t i n g t h e peak d y n a m i c p r e s -s u r e and f o r c e -s , a n d F i g u r e 21 p r e -s e n t -s an e x a m p l e p r o b l e m .

E X A M P L E : _{E S T I M A T E T H E B R E A K I N G WAVE F O R C E ON A 100cm 0 T U B E} USED IN A P Y R A M I D A L B R E A K W A T E R C O N S T R U C T I O N SHOWN IN T H E D I A G R A M BELOW T - 4sec, Hj^-Q 9 m d » 0 , 9 / 4 2 = 0,05625 m/s2 FROM F I G U R E 20 P m / w H t , - 1 3 Pm ' 13 (1 , 0 2 5 ) ( 0 , 9 ) = 12 ,0 t / m ^ T O T A L B R E A K I N G W A V E F O R C E ON B R E A K W A T E R F H - ( 1 2 ) ( 0 , 9 ) / 3 = 3 , 6 t / m F O R C E ON TOP T U B E IS E Q U A L TO T H E A R E A UNDER T H E P R E S S U R E DIAGRAM B E T W E E N SWL A N D y, H SWL TOP = 1/3 ( p ^ ) ( H , / 2 ) = 1/3 ( 1 2 ) : ( 0 , 9 ) / 2 ) 1 ,8 t / m \

3.0 REFERENCES D a n i s h H y d r a u l i c I n s t i t u t e ( 1 9 7 0 ) : Model T e s t i n g o f S a n d - F i l l e d Tubes a s B r e a k w a t e r s - S k a l l i n g e n d e " Denmark. ' G r a c e , R . G . ( 1 9 7 8 ) : Marine O u t f a l l S y s t e m s , P l a n n i n g . D e s i g n , and C o n s t r u c t i o n , P r e n t i c e - H a l l . i n c . P ^ I V -wood C l i f f s , New J e r s e y .

Sowers, G.B. and G.F. Sowers ( 1 9 7 0 ) : I n t r o d u c t o r y 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 , 3 r d E d . , The MacmilHTTT' Company, New York, New Y o r k .

Shore P r o t e c t i o n Manual ( 1 9 7 7 ) : U.S. Army Corps of E n -g i n e e r s , C o a s t a l E n -g i n e e r i n -g R e s e a r c h C e n t e r , F o r t B e l v o i r , V i r g i n i a .