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The outer banks of the Fraser River delta : engineering properties and stability considerations Scotton, Steven 1978

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THE OUTER BANKS OF THE FRASER RIVER DELTA; ENGINEERING PROPERTIES AND S T A B I L I T Y CONSIDERATIONS by STEVEN SCOTTON B.A. S c . , U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1971 A THESIS SUBMITTED I N PARTI A L FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF A P P L I E D SCIENCES i n t h e FACULTY- OF GRADUATE STUDIES .-Dept. of C i v i l Engineering We. a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF B R I T I S H COLUMBIA MAY, 1977 © Steven Scotton, 1978 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h Co lumb ia , I a g ree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s tudy . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . It i s u n d e r s t o o d that c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i thout my w r i t t e n p e r m i s s i o n . S t e v e n S c o t t o n Department o f C i v i l E n g i n e e r i n g The U n i v e r s i t y o f B r i t i s h Co lumbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date F e b r u a r y 6 t h , 1 9 7 8 i i ABSTRACT Roberts Bank and Sturgeon Bank are the leading edges of the Fraser River Delta. In the past h a l f century various aspects of the del t a , and the banks, have been studied by geologists, geomorphologists and engineers. Published papers and reports of these studies form the primary data base for th i s t h e s i s . The geology and geomorphology reports comple-mented the engineering data. Logs of 6 8 boreholes were found i n the engineering reports made available for th i s thesis. These boreholes were located such as to give a reasonable coverage of both Roberts Bank and Sturgeon Bank. The reported holes were sampled ext-ensively with Standard Penetration Test s p l i t spoon samplers and a few thin wall Shelby tube samples were taken. The engineering reports presented the results of numerous tests performed on the samples, including shear t e s t s , t r i a x i a l tests and consolidation t e s t s . The upper 80 feet of sediments, which i s the zone of concern for strength and s t a b i l i t y analyses, are primarily granular i n nature. These sediments e x i s t at a medium to loose density with a r e l a t i v e density as low as 40 percent suggested for large areas of the banks. Some of the deeper sediments are moderately compressible i n nature and are presently normally consolidated. The nature of the s u r f i c i a l sediments i s such that, i n the e x i s t i n g seismic environment i n which they are located, there i s the p o s s i b l i t y of earthquake induced l i q u e f a c t i o n . Methods of assessing the p r o b a b i l i t y of l i q u e f a c t i o n are discussed and the results of one such assessment are presented. The subaqueous slopes of Roberts Bank and Sturgeon Bank, which average 1.5 degrees but exceed 23 degrees i n a few spots, are shown to be at le a s t nominally stable with respect to mass wasting. There are some indications that these slopes could be subject to some erosional i n s t a b i l i t y . The physical environment of the banks (wind, wave, temperature) i s not p a r t i c u l a r l y harsh, and presents no problems to engineering development. Certain aspects of the ecology of the banks, however, are of s u f f i c i e n t importance to warrant consideration as part of the design process for any project on the banks. TABLE OF CONTENTS Abstract Table of Contents L i s t of Tables L i s t of Figures Acknowledgements INTRODUCTION AREA OF STUDY SLUMP STRUCTURE ENGINEERING PARAMETERS Subsurface Sediments. Grain Size D i s t r i b u t i o n Relative Density F r i c t i o n Angle Consolidation Parameters Atterburg Limits Compression Index Estimates SETTLEMENT CASE HISTORY PROBABLE EARTHQUAKE ACCELERATIONS LIQUEFACTION POTENTIAL OF THE BANKS Liquefaction Empirical Liquefaction C r i t e r i a A n a l y t i c a l Liquefaction Potential SUBAQUEOUS SLOPE STABILITY Erosional I n s t a b i l i t y Mass Wasting E f f e c t of Surface Waves E f f e c t of Earthquake Motions V ADDITIONAL DESIGN CRITERIA 9 7 Wind 9 8 Wave 99 Ecology 1 0 1 CONCLUSIONS 1 0 2 APPENDIX 1 APPENDIX 2 APPENDIX 3 v i LIST OF TABLES TABLE Page 1. Test Results 29 2. H i s t o r i c a l Earthquakes 50 3. Earthquake P r o b a b i l i t y A n a l y s i s 51 4. Earthquake Duration 62 5. Cumulative Winds - 1953 t o 1971 98 V I 1 LIST OF FIGURES FIGURE Page 1. The F r a s e r D e l t a and the S t r a i t of Georgia showing the l o c a t i o n of Sturgeon Bank and Roberts Bank. 3 2. Photographs taken from a P i s c e s Submersible on March' 22 , 19 75. 5 3. Geologic Map of the Fraser R i v e r D e l t a .9 4. I n t e r p r e t e d Continuous Seismic P r o f i l e across the Slump S t r u c t u r e s 11 5. Grain S i z e D i s t r i b u t i o n curves f o r the 3 surface samples taken on Sturgeon Bank 2 4 6. The Gibbs and H o l t z and the Bazaraa curves of R e l a t i v e Density vs. N - value 26 7. The de M e l l o r e l a t i o n s h i p of jtfr vs. N - value 32 8. P o s s i b l e r e l a t i o n s h i p between the r a t i o of the Compression Index over the Void R a t i o plus one (C /1+e), and the measured water contents -l i q u i d l i m i t and n a t u r a l moisture content 41 9. Terminal of the Westshore Terminals Bulk Loading F a c i l i t y showing the l o c a t i o n of settlement Gauges 7 and 12 and the i n i t i a l l o c a t i o n of the c o a l s t o c k p i l e s 44 10. Settlement of gauges 7 and 12 45 11. Extended settlement Record 48 12. P r e d i c t e d maximum ground surface a c c e l e r a t i o n s 52 13. Comparison of the Ohsaki and K i s h i d a l i q u e f a c t i o n c r i t e r i a 56 14. Cumulative r e s u l t s of Standard P e n e t r a t i o n Tests 59 15. Results of the Seed and I d r i s s S i m p l i f i e d L i q u e f a c t i o n a n a l y s i s 64 16. Two Sections of the subaqueous slope p l o t t e d t o n a t u r a l s c a l e 72 v i i i 17. Location of cross sections S and R 73 18. Freebody diagram of c i r c u l a r s l i p arc 77 19. Relationship between excess Pore Pressure and applied Shear Stress 83 20. Derivation of the f a i l u r e c r i t e r i o n used to place the f a i l u r e l i n e on F i g . 19 84 21. Two possible relationships between the Pore Pressure Parameter and the Number of Cycles 86 22. Slope analysed by Sarma Program 88 2 3. Relationship between C r i t i c a l Acceleration and Pore Pressure Parameter for surfaces 4 and 5 89 24. Long deep section analysed to approximate the possible o r i g i n of the slump structures 91 25. Tracing of Hypsographic P r o f i l e s H, I and J 94 26. Location of Hypsographic P r o f i l e l i n e s H, I and J 95 i x ACKNOWLEDGEMENTS / The names o f a l l t he p e o p l e who have g i v e n me a s s i s t -ance w i t h t h i s t h e s i s wou ld f i l l a n o t h e r vo lume. As I am l i m i t e d i n space I wou ld l i k e t o he reby thank eve r ybody who l e n t a s s i s t a n c e and r e q u e s t t h a t you no t t a k e o f f e n c e i f you r name i s not s p e c i f i c a l l y m e n t i o n e d . I n t he Department o f C i v i l E n g i n e e r i n g I w i s h t o t hank D r . W.D.L. F i n n f o r h i s g u i d a n c e d u r i n g t h e r e s e a r c h and h i s a s s i s t a n c e d u r i n g t he w r i t i n g o f t h i s t h e s i s . D r . P.M. By rne and Dr . R.G. Campane l l a a r e t o be t h a n k e d f o r t h e i r encouragement and a s s i s t a n c e . Thanks a r e a l s o due t o f e l l o w g r ad s t u d e n t N e i l Wedge f o r s h a r e d r e s e a r c h and work . L a s t but no t l e a s t I w i s h t o acknowledge t he a s s i s t a n c e o f t h e s e c r e t a r i e s , p a r t i c u l a r l y D e s i Cheung. Dr . J.W. Mur ray o f t he Department o f Geo logy p r o v i d e d v a l u a b l e a s s i s t a n c e d u r i n g t he r e s e a r c h and c r i t i c a l r e v i e w d u r i n g t he w r i t i n g , f o r w h i c h I t hank h i m . The Vancouve r O f f i c e o f t he G e o l o g i c a l Su rvey o f Canada, and i n p a r t i c u l a r D r . J . L . L u t e r n a u e r , have been o f g r e a t a s s i s t a n c e t o me I n t h i s t h e s i s - a s s i s t i n g w i t h t h e f i e l d e x c u r s i o n t o S t u r g e o n Bank, t o l e r a t i n g my p r e s e n c e around t h e i r o f f i c e s , a l l o w i n g me a c c e s s t o t h e i r g r e a t s t o r e o f l i t e r a t u r e and d a t a - t h a n k you G.S .C. Others to whom I owe thanks are Cook, Pickering and Doyle Ltd., Swan Wooster Engineering Co. Ltd., National Harbours Board, Acres Consulting Services Ltd. and the firm for which I am presently employed, R.M. Hardy and Associates Ltd. F i n a l l y I would l i k e to thank my wife Marika f o r her patience, for supporting me and for her help with the hard-est part of the t h e s i s , the typing. F i n a n c i a l support for t h i s thesis was kindly provided by the National Research Council (Grant 67-1498) and Energy Mines and Resources (Grant 65-1652) for which I am g r a t e f u l . INTRODUCTION Roberts Bank and Sturgeon Bank, comprising some 90 odd square miles of t i d a l f l a t s , have i n recent years taken on great importance as p o t e n t i a l locations f o r large scale development, some of which has already taken place. The advantages of a location adjacent to deep sea shipping channels was recognized with the construction of the West Shore Terminals Bulk Loading F a c i l i t y , and future expansions to many times the si z e of the present i n s t a l l a t i o n s have been proposed. Also proposed i s an extension of the Vancouver International A i r p o r t runway system out onto Sturgeon Bank. This may represent only a small f r a c t i o n of the i n t e r e s t i n Roberts Bank and Sturgeon Bank as p o t e n t i a l s i t e s f o r develop-ment. With the present and p o t e n t i a l i n t e r e s t i n the area, i t appeared that a general i n v e s t i g a t i o n of the s o i l s and engineering environment of Roberts Bank and Sturgeon Bank might be of value. In t h i s thesis an attempt has been made to compile a l l e x i s t i n g data available f o r Roberts Bank and Sturgeon Bank, e s p e c i a l l y subsurface data. This data was used to determine c h a r a c t e r i s t i c s o i l parameters for use i n various types of s t a b i l i t y analyses. The data gathered and most of the analyses performed conform to standard pr a c t i c e i n the engineering community. Where possible and p r a c t i c a l supple-mentary information, such as l i s t i n g s of computer programs used i n analyses, have been included i n the appendices. 2. This t h e s i s i s concerned w i t h general c o n d i t i o n s at Roberts Bank and Sturgeon Bank and the kinds of engineering problems t h a t may be faced during f u r t h e r developments. AREA OF STUDY Roberts Bank and Sturgeon Bank are l o c a t e d a t a p p r o x i -mately 49° 00' t o 49° 15' North L a t i t u d e and 123° 05' to 12 3° 15' West Longitude. This i s the southwest corner of mainland B r i t i s h Columbia, Canada. These banks form the western (seaward) e x t r e m i t y of the d e l t a of the F r a s e r R i v e r , and are the youngest p a r t of the d e l t a . F i g . 1 shows the l o c a t i o n of Roberts Bank and Sturgeon Bank w i t h r e spect t o surrounding prominent f e a t u r e s . The D e l t a of the F r a s e r R i v e r , which has an area of about 130 square m i l e s , extends from i t s apex a t New Westminster some 19 m i l e s to the S t r a i t of Georgia. The outer banks (Roberts Bank and Sturgeon Bank) which form the l e a d i n g edge of the d e l t a have a 23 mile perimeter w i t h the S t r a i t of Georgia. Sturgeon Bank l i e s between the main channel of the Fraser R i v e r and the North Arm of the: F r a s e r R i v e r . Roberts Bank extends south from the main channel to P o i n t Roberts and i s b i s e c t e d by Canoe Passage. Sturgeon Bank and Roberts Bank w i l l be c o l l e c t i v e l y r e f e r r e d t o as "the banks." The top surf a c e s of the banks are t i d a l f l a t s which are covered by water at high t i d e and exposed a t low t i d e . These f l a t s slope very g e n t l y from the c u l t i v a t e d land to the l e a d i n g edge of the D e l t a , and are the sub a e r i a l p o r t i o n of the banks. From the l e a d i n g edge, the d e l t a d i p s beneath 3. ^ (Bowerf f BurrardTV T — r - ^ r " \. < JEnlet-P o i n t > ~ — — GreyV. VANCOUVER T^FRASER jCr)) RIVER Sturgeon //>ScL V^/ Bank V GULF • v - ISLANDS P o i n t T _ \, \. Roberts % i ^ A c t i v e " - J r--Pass > UNITED STATES j s N OF AMERICA SCALE 1 inch = 8 miles Sturgeon Bank and Roberts Bank, Fi g . 1 The Fraser Delta and the S t r a i t of Georgia showing the loc a t i o n of Sturgeon Bank and Roberts Bank. 4. the surface of Georgia S t r a i t i n what Mathews and Shepard (1962) have termed the fore-set beds. The banks have an average width of 4 miles from the edge of the c u l t i v a t e d land to the fore-slope of the d e l t a . The subaqueous slopes average one and one-half degrees but exceed 23 degrees i n a few spots, as plotted from Marine Charts, and contour maps in the "Outer Port Development" report (Swan Wooster, 1967). The fore-set beds extend to a water depth of about 300 f e e t (Luternauer and Murray, 1974). The S t r a i t of Georgia i s a t i d a l body of water with cons t r i c t e d passages to the P a c i f i c Ocean. I t i s protected from most influences of the open ocean such as large ocean waves. The t i d a l e f f e c t s , however, are s i g n i f i c a n t and intense t i d a l currents which sweep past the delta f r o n t are generated i n t h i s semi-contained body of v/ater, responding to the t i d a l changes of the open P a c i f i c Ocean. A surface expression of these currents i s the manner i n which the out— flowing waters of the Fraser River are swept northward by the flood t i d e . Evidence of the current action at depth i s shown i n the underwater photos taken by the Pisces submer-s i b l e on March 22, 1975 (Luternauer, 1976) at 75 meters depth and on the side-scan sonar recordings taken i n July, 1976 (unpublished to date). Three of the photos, reproduced i n F i g . 2 through the courtesy of J.L. Luternauer, show sand r i p p l e s consistent with sediment transport, which suggests the existence of currents strong enough to transport the sand. These are the only photos taken of the fore-slope, and they were a l l taken i n the same area, so they can not be 5. F i g . 2 Photographs taken from a P i s c e s Submersible on March 22, 1975. These photos were taken a t 75 meters depth on the f o r e - s l o p e of Roberts Bank opposite the super port and show evidence of e r o s i o n . Photos courtesy of Dr. J . L. Luternauer. 6. used to determine trends i n e r o s i o n or sediment t r a n s p o r t . Roberts Bank and Sturgeon Bank are not e n t i r e l y comparable. The f o r e - s l o p e of Sturgeon Bank, as expressed by subsurface depth contours, i s remarkably smooth and r e g u l a r , even i n the v i c i n i t y of where the Middle Arm of the F r a s e r discharges during f r e s h e t s . The f o r e - s l o p e of Roberts Bank, although g e n e r a l l y smooth, i s crossed by a number o f prominent g u l l y f e a t u r e s . One of the l a r g e s t of these g u l l i e s , l o c a t e d approximately 2.3 m i l e s south of the present l o c a t i o n of the main channel, may represent a previous l o c a t i o n of the main channel. The other i r r e g u l a r i t i e s are l o c a t e d such t h a t they may be r e l a t e d to Canoe Passage, which i s a d i s t r i b u t a r y d u r i n g f r e s h e t s . The s t r i k e of the Sturgeon Bank f o r e - s l o p e i s p r e -dominantly North-South. The s t r i k e of the Roberts Bank f o r e -slope v a r i e s from N.N.W. - S.S.E. i n the North t o W.N.W. -E.S.E. near Tsawwassen F e r r y Terminal to N.W. - S.E. near P o i n t Roberts. The depth contours on the Roberts Bank f o r e -slope are g e n e r a l l y smooth curves, other than a t the l o c a t i o n of g u l l i e s , showing no abrupt changes i n the gen e r a l s t r i k e d i r e c t i o n . The d i f f e r e n c e s i n s t r i k e d i r e c t i o n between Roberts Bank and Sturgeon Bank should cause d i f f e r e n t responses t o surface and i n t e r n a l waves and t i d a l c u r r e n t s . The F r a s e r R i v e r has a drainage b a s i n area of about 90,000 square m i l e s and a discharge ranging from as low as 28,000 c . f . s . to as great as 350,000 c . f . s . (Hoos and Packman, 1974) . The drainage b a s i n was completely covered by i c e 7 . during the l a s t major g l a c i a t i o n , and the present delta began to form when the l a s t major g l a c i a t i o n receded some 8 , 0 0 0 to 1 0 , 0 0 0 years ago. The products of g l a c i a l erosion have contributed, and continue to contribute to the large sediment load of the Fraser River. Mathews and Shepard ( 1 9 6 2 ) showed that the delta i s r a p i d l y advancing ( 28 f t . / y r . at 3 0 0 f t . depth) o f f the main channel of the r i v e r from the deposition g of 7 x 10 cubic feet of sediments per year. Because of processes such as i s o s t a t i c rebound and eustatic adjustment (Matthews, Fyles and Nasmith, 1 9 7 0 ) , i t i s not known whether the Delta grew r e g u l a r l y and smoothly to i t s present si z e , or i f i t had a complex pattern of growth (Luternauer, 1 9 7 4 ) . There i s some evidence to suggest that portions of Roberts Bank are much older than the r e s t of the banks (Dr. J.W. Murray, personal comment). The suggest-ion i s that some of the southern Roberts Bank sediments are r e l i c g l a c i a l or p r e g l a c i a l deposits. A d e t a i l e d study of a v a i l a b l e borehole logs indicates that these possible differences i n age and source of sediments do not appear to be r e f l e c t e d by corresponding changes i n the engineering parameters. Whether the d e l t a developed r e g u l a r l y or i r r e g u l a r l y , there i s general agreement among most geologic i n v e s t i g a t o r s of the Fraser Delta that the s u r f i c i a l deposits of the banks are composed of recent sediments. Most of the sediments c a r r i e d by the Fraser River are deposited o f f the mouth of the South Arm (which i s the main channel), but t h i s deposi-t i o n i s not the only process e f f e c t i n g changes on the d e l t a 8 -front. The fore-set slopes are also subject to wave act i o n and t i d a l currents. F i g . 3, which i s reproduced from Figure 3.1 i n "The Fraser River Estuary, Status of Environmental Knowledge to 1974", shows a complex pattern of advancing, r e t r e a t i n g and stable areas of the d e l t a f r o n t . This f i g u r e also shows, very roughly, the area! d i s t r i b u t i o n of the s u r f i c i a l deposits. Members of the Geological Survey of Canada, under the d i r e c t i o n of John L. Luternauer, have made a number of expeditions onto the banks c o l l e c t i n g surface samples. An analysis of the r e s u l t s of t h i s sampling program has shown that there i s a seasonal s h i f t i n the gradation of the s u r f i c i a l deposits (Luternauer, 1976). In general the s u r f i c i a l deposits vary from r e l a t i v e l y clean uniform sand near the leading edge of the banks to s i l t y -clayey-sandy deposits toward the dykes which mark the edge of the c u l t i v a t e d land. There are s i g n i f i c a n t areas of marsh adjacent to the dykes along the eastern edge of much of the banks. Mathews and Shepard (1962) presented the r e s u l t s of a sampling program conducted on the subaqueous slopes of the d e l t a which showed that the sediments d i r e c t l y o f f the mouth of the main channel are predominantly sand, and the sediments become markedly f i n e r as the water depth increases and as one moves to the north. SLUMP STRUCTURE In 1962, Mathews and Shepard described the existence of hummocky topography o f f the mouth of the main channel. Since that time, these slump structures (as they came to be known) have been the topic of one thesis (Mayers, 1968), G ene ralized G E O L O G I C M A P OF T H E F R A S E R R IVER D E L T A and adjacent areas LEGEND RECENT 7 FRASER DELTA DEPOSITS 7a - twamp and bog deposits - peat or peat below veneer of till. 7b - tilt and clay deposit*, minor sand - tidal Hat, flood plain, upper fore slop*. 7c - sand deposits - mainly lidai flats. 7d - salt marsh. 6 CHANNEL AND FLOODPLAIN DEPOSITS OF LOWLAND STREAMS * s i lt, c lay , sand and organic Stringers or p o d s . 5 BEACH DEPOSITS • sand and gravel. PLEISTOCENE 4 EARLY POST-GLACIAL RAISED LITTORAL AND CHANNEL DEPOSITS - sand, gravel and a few shell beds. 3 GL AC IO - MARINE DEPOSITS - silts and clays deposited in offshore environment. 2 GLACIAL DEPOSITS - sandy to silry till deposited as ground moraine or subsequent till -like deposits derived from floating glacier ice . 1 IN TE RG LACI AL AND OLDER DEPOSITS -sand and lesser amounts of silt, clay and peat in sea cliffs . dyked land. ytffijgt^ dredge spoil dumping area. -•— d — p r i n c i p a l dredging areas. //// areas of crescent shaped swales possibly caused by former - land-slide movements.{?) areas of incipient slumping. general areas of delta - front advance or retreat . — I nter national Boundary. Geologic boundary (shore -high tide line may also be a geologic boundary) cable area Fig. 3 Geologic Map of the Fraser River Delta. Reproduced from "The Fraser River Estuary, Status of Environmental Knowledge to 1974" by permission of Environment Canada and J .L . Luternauer. m e n t i o n e d i n a n o t h e r ( T i f f i n , 1969) and d i s c u s s e d i n n u m e r o u s p a p e r s . I n J a n u a r y 1966 a number o f c o n t i n u o u s s e i s m i c p r o -f i l i n g s e c t i o n s w e r e t a k e n a c r o s s t h e s l u m p s t r u c t u r e s , a n d t h e a u t h o r s o f t h e t h e s e s a n d p a p e r s w h i c h p o s t d a t e t h e c o n t i n u o u s s e i s m i c p r o f i l e s h a v e b a s e d t h e i r i n t e r p r e t a t i o n s o f t h e s t r u c t u r e s on t h e s e r e c o r d s . D r . J.W. M u r r a y o f t h e D e p a r t m e n t o f G e o l o g y a nd t h e I n s t i t u t e o f O c e a n o g r a p h y a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a h a s made t h e i n t e r p r e t e d r e s u l t s o f t h e c o n t i n u o u s s e i s m i c p r o f i l e s a v a i l a b l e f o r p r e s e n t a t i o n i n t h i s t h e s i s . F i g . 4 shows t h e p r o f i l e r u n n i n g a p p r o x i m a t e l y E a s t - W e s t t h r o u g h t h e c e n t e r o f t h e s l u m p s t r u c t u r e s , a n d a l o c a t i o n p l a n a n d t h r e e a d d i t i o n a l p r o f i l e s h a v e b e e n i n c l u d e d i n A p p e n d i x I . F i v e d i s t i n c t r e f l e c t i n g h o r i z o n s h a v e b e e n shown o n t h e p r o f i l e s a n d a r e i d e n t i f i e d by t h e b l o c k l e t t e r s A t h r o u g h E. H o r i z o n A i s a b e d r o c k r e f l e c t o r , h o r i z o n s B a n d C a r e r e l a t i v e l y f l a t - l y i n g s e d i m e n t r e f l e c t o r s , h o r i z o n D i s t h e s e d i m e n t - w a t e r i n t e r f a c e a n d h o r i z o n E r e p r e s e n t s t h e t o p o f t h e d e f o r m e d s l u m p s t r u c t u r e s w h e r e b u r i e d by more r e c e n t s e d i m e n t s . M. d e n o t e s a m u l t i p l e r e f l e c t i o n o f t h e s e d i m e n t -w a t e r i n t e r f a c e a n d as s u c h i s n o t a r e f l e c t i n g h o r i z o n . T h e r e i s b a s i c a g r e e m e n t as t o t h e p h y s i c a l c h a r a c t e r -i s t i c s o f t h e s l u m p s t r u c t u r e s amongst i n v e s t i g a t o r s who made u s e o f t h e c o n t i n u o u s s e i s m i c p r o f i l e s . To p a r a p h r a s e T i f f i n (1969) , t h e s l u m p s t r u c t u r e s a p p e a r t o be p a r t o f a s i n g l e m a s s i v e s l i d e l a y e r m o v i n g o v e r a deep g l i d e p l a n e a t l e a s t 250 t o 300 f e e t d e e p i n p l a c e s . When t h e s l i d e mass came t o r e s t , t h e s o i l s b u c k l e d t o f o r m w a v e l i k e u n d u l a t i o n s SEC . INTERPRETED CONTINUOUS SEISMIC PROFILE THROUGH THE SLUMP STRUCTURES somewhat resembling a w a f f l e i n t h a t the undula t i o n s form a wave p a t t e r n both i n the down-slope d i r e c t i o n and i n the cro s s slope d i r e c t i o n . The u n d u l a t i o n s , viewed from e i t h e r d i r e c t i o n , have a r e l i e f o f 50 to 100 f e e t and a wavelength of about 2,000 t o 2,500 f e e t . D i s c o n t i n u i t i e s of r e f l e c t o r s w i t h i n the s l i d e mass have been concluded to be c o n s i s t e n t w i t h rupture phenomena a s s o c i a t e d w i t h one s i n g l e mass move-ment. L a t e r sedimentation has been f i l l i n g i n the troughs and encroaching on the s l i d e m a t e r i a l from the top down as evidenced by h o r i z o n E. T i f f i n (1969) made some estimates of the age of forma-t i o n of the slump s t r u c t u r e s using the sedimentation r a t e s worked out by Mathews and Shepard (1962). He c a l c u l a t e s a minimum age of 6 0 years and a probable age of about 160 years. He r e v i s e s t h i s estimate to 200 years i n a 1971 paper co-authored w i t h Murray, Mayers and G a r r i s o n . However, unless the age can be r e l a t e d t o a s p e c i f i c event such as an e a r t h -quake, then the age i s o f academic i n t e r e s t o n l y . There i s no known event which might have t r i g g e r e d a s l i d e which c o i n c i d e s w i t h the estimated age of t h i s s l i d e . No other f e a t u r e s s i m i l a r to the above d e s c r i b e d slump s t r u c t u r e s have been reported o f f the Fr a s e r D e l t a . This does not r u l e out the e x i s t e n c e of other s , s i n c e the subaqueous i n v e s t i g a t i o n s c a r r i e d out t o date have not been d e t a i l e d enough t o give t o t a l knowledge of the subaqueous landforms. This i s the only known l a r g e s c a l e s l i d e on the subaqueous p a r t of the F r a s e r D e l t a and i t i s l o c a t e d o f f the mouth of the main channel; t h e r e f o r e there i s some i n d i c a t i o n that the rapid deposition which occurs o f f the mouth of the main channel created a deposit of sediments which had more p o t e n t i a l for s l i d i n g than adjacent delta deposits. The conclusion of the geologists and gecphysicists that the slump structures represent, one s p e c i f i c event rather than a series of events i s evidence that something unusual triggered the s l i d e . The estimated age (160 to 200 years) of the s l i d e and the lack of evidence of subsequent s l i d e s suggest that the event which triggered the s l i d e i s reasonably rare. Mayers (1968) c i t e d s i x possible t r i g g e r i n g agents which could have started the s l i d e Among these, earthquakes, f a u l t i n g , i n t e r n a l waves, surface waves, r i v e r floods and the introduction pf peptizing agents to the f l o c c u l a t e d sediments, are p o s s i b i l i t i e s . Of these p o s s i b i l i t i e s , i t i s u n l i k e l y that i n t e r n a l or i • surface waves could be the necessary rare event. The S t r a i t of Georgia i s a semi-confined body of water of f i n i t e size and i t i s almost c e r t a i n that the maximum possible waves are generated a number of times per century and probably more often than that. One possible exception would be a freak earthquake generated wave. Mayers himself r u l e s out f a u l t i n g as a t r i g g e r mechanism, The introduction of peptizing agents, which Mayers r e l a t e s to r i v e r floods, does not appear to.be a rare event. A r i v e r flood or an earthquake d e f i n i t e l y f u l f i l l s the c r i t e r i o n of a rare event, the bigger the f l o o d or earthquake the rarer the event,. The Fraser River has had unusually large floods twice d u r i n g recorded h i s t o r y (1894 and 1903), but there were no reported s l i d e s a s s o c i a t e d with e i t h e r event. This i s not s u r p r i s i n g s i n c e at t h a t time there would be no way of know-i n g i f a subaqueous s l i d e had occurred or not, however, the continuous s e i s m i c p r o f i l e s do not i n d i c a t e any s l i d e d e p o s i t s c o n s i s t e n t w i t h these dates (unless the minimum age of 60 years estimated f o r the slump s t r u c t u r e s can be shown to be more reasonable than the 200 year e s t i m a t e ) . Both f l o o d s r e f e r r e d t o overflowed the customary channels of the Fraser R i v e r . I t would seem l o g i c a l t h a t once a r i v e r has over-flowed i t s channels and flooded the lowlands i t would take a very l a r g e i n c r e a s e i n flow t o produce a s m a l l i n c r e a s e i n sedimentation at the mouth of a channel. Of the s i x p o s s i b l e t r i g g e r s o r i g i n a l l y mentioned, only earthquake and r i v e r f l o o d are probable. The s e i s m i c a c t i v i t y of the area surrounding the F r a s e r D e l t a i s w e l l known and documented (Milne, 1963). There are many e a r t h -quakes i n the area every year which, although below the l e v e l of human d e t e c t i o n , have a measurable energy a t the banks. Every few years there i s an earthquake which i s n o t i c e a b l e to the people of the lower mainland. As i f t o exemplify t h i s p o i n t there have been two t h i s year (1976) which were w i t h i n the range of human d e t e c t i o n . The p o t e n t i a l c e r t a i n l y e x i s t s f o r an earthquake, w i t h s u f f i c i e n t energy r e l e a s e to t r i g g e r a s l i d e , to have occurred i n the past and t o occur i n the f u t u r e . Earthquake would appear to be the most probable t r i g g e r mechanism f o r the s l i d e , but r i v e r f l o o d can not be r u l e d out. The combination of earthquake duri n g severe f l o o d i n g i s a l s o a p o s s i b i l i t y . I f intense seismic s t u d i e s were c a r r i e d out on the d e l t a w i t h equipment which c o u l d produce good r e s o l u -t i o n through some 1,200 f e e t of sediments i t i s q u i t e p o s s i b l e t h a t more r e l i c slump s t r u c t u r e s would be found b u r i e d i n the d e l t a . I f such s t r u c t u r e s were found and reasonable estimates of t h e i r age were made then i t might be p o s s i b l e t o g a i n some a p p r e c i a t i o n f o r the frequency of the t r i g g e r i n g events. Subaqueous s l i d e s are of concern to the engineer p r i m a r i l y i f they w i l l a f f e c t a p r o j e c t or i n s t a l l a t i o n . For the F r a s e r D e l t a , i f the s u p p o s i t i o n s t h a t the s l i d e s are r a r e events and are only probable at the mouths of major channels are v a l i d , then they are only of minimal concern to the engineer. The major channels of the F r a s e r are maintained as navigable channels, therefore, the o n l y s t r u c t u r e s l i k e l y to be d i r e c t l y a f f e c t e d by a s l i d e would be j e t t i e s and n a v i g a t i o n a i d s (such as l i g h t s ) . The o n l y other major category of engineering i n s t a l l a t i o n s which could be d i r e c t l y a f f e c t e d i s subaqueous s e r v i c e s such as p i p e l i n e s (gas, o i l ) and cables (telephone, e l e c t r i c ) . The occurrence of a massive subaqueous s l i d e could t r i g g e r a d e s t r u c t i v e water wave, such as happened a t K i t i m a t , B.C. e a r l y i n 1976, which c o u l d a f f e c t engineering s t r u c t u r e s not o n l y on the banks but elsewhere along the shore i n the v i c i n i t y . I t i s not p o s s i b l e t o p r e d i c t , or design f o r , the e f f e c t s of such waves, however they have been mentioned as a p o s s i b l e i n -d i r e c t e f f e c t of a subaqueous s l i d e . ENGINEERING PARAMETERS The sources f o r a l l the borehole data and most of the laboratory t e s t data for the banks, which form the basis of a l l the following observations and conclusions, are: Cook, 1967, 1968; Cook, Pickering and Doyle Ltd., 1974; Swan Wooster Engineering Co. Ltd., 1967. These reports w i l l be referred to c o l l e c t i v e l y as "the engineering reports." A search of t h i s information has yielded the borehole logs and locations of 68 boreholes d r i l l e d on the banks and the re s u l t s of various tests performed on samples recovered, from these boreholes. The boreholes have a spacing which i s generally i n excess of 1.5 miles, with a c l o s e r spacing o f f Sea Island i n the v i c i n i t y of the proposed a i r p o r t runway extension; i n the v i c i n i t y of the Westshore Terminals bulk loading f a c i l i t y ; and along the Tsawwassen Ferry Terminal causeway. The majority of the boreholes were d r i l l e d to less than 80 feet below the sediment surface, but s i x of the holes were d r i l l e d between 260 and 460 feet below the surface. Subsurface Sediments The borehole log attempts to depict g r a p h i c a l l y the s o i l column penetrated by the borehole, using common symbols for sand, s i l t , clay and organic s o i l . This graphical representation allows one to form a v i s u a l impression of the subsurface s o i l s . This form of presentation requires the draftsperson to divide the s o i l p r o f i l e into d i s t i n c t l a y e r s . This i s a straightforward procedure where d i s t i n c t layers of 17. s o i l e x i s t and the d r i l l e r has made a reasonably c o n s c i e n t i o u s lo g of the hole to complement the samples. I n areas such as the banks where the l a y e r s do. not appear to be d i s t i n c t , but grade one i n t o the other, the procedure of g r a p h i c a l p r e s e n t a -t i o n becomes somewhat a r b i t r a r y . The d r a f t s p e r s o n must d i v i d e the s o i l i n t o l a y e r s based on the v i s u a l c l a s s i f i c a t i o n of the samples, g r a i n s i z e determinations performed on samples and the d r i l l e r ' s l o g . In t u r n , i n t h i s type of s o i l , the d r i l l e r s l o g i s a l s o s u b j e c t i v e ; based on the c u t t i n g s i n the r e t u r n wash water, the r a t e of advance and " f e e l " o f the d r i l l and i n f l u e n c e d by the recovered samples. The boreholes were sampled e x t e n s i v e l y w i t h a 2-inch Standard P e n e t r a t i o n Test sampler, and a few 3-inch F i x e d P i s t o n Shelby Tube samples were taken i n s e l e c t boreholes. The borehole logs presented N-values (number of blows of a 140 l b . hammer dropped 30 inches to produce 12 inches of penetration) f o r the 2-inch Standard P e n e t r a t i o n Test samples, moisture contents where a p p r o p r i a t e , and/or r e l a t i v e q u a n t i t i e s of sand and s i l t (represented i n bar graph form) f o r most of the samples. A number of the 3-inch Shelby Tube samples were t e s t e d i n shear t e s t s , t r i a x i a l t e s t s and c o n s o l i d a t i o n t e s t s . The r e s u l t s of these t e s t s were a l s o presented i n the engineering r e p o r t s . A reasonable estimate of the l a t e r a l c o n t i n u i t y of the banks sediments would be of value i n h e l p i n g determine optimum borehole spacing f o r proposed p r o j e c t s on the banks. The somewhat a r b i t r a r y nature of the borehole l o g p r e s e n t a -t i o n makes i t d i f f i c u l t to form an impression of c o n t i n u i t y based on v i s u a l i n s p e c t i o n . When the l o c a t i o n of the Westshore Terminals bulk l o a d i n g f a c i l i t y was f i n a l i z e d , nine boreholes were d r i l l e d w i t h a much c l o s e r spacing than was used d u r i n g the p r e l i m i n a r y study. Although the Test Hole L o c a t i o n P l a n i s presented without a s c a l e , the hole spacing appears t o range from 700 f e e t to 1,500 f e e t . An i n s p e c t i o n of the borehole logs does not r e v e a l any d i s t i n c t l y i d e n t i f i a b l e l a y e r of sediments which could be used to t r a c e c o n t i n u i t y . There i s a l a y e r of sediments w i t h more than 40 percent s i l t and moisture contents of about 33 percent which s t a r t s a t -^ 57 f e e t i n borehole 1. Borehole 1 bottomed at -80 f e e t , s t i l l i n the l a y e r of s o i l j u s t d e scribed. Surrounding borehole 1 are boreholes 3, 8, 7 and 2 from nearest to f a r t h e s t . Bore-hole 3 has s i m i l a r s o i l from -68 f e e t to beyond -80. f e e t ; boreholes 8 and 7 have no s i m i l a r i d e n t i f i a b l e l a y e r and borehole 2 has a s i m i l a r l a y e r from -61 f e e t to more than -82 f e e t . Borehole 8 i s approximately between boreholes 1 and 2, t h e r e f o r e there does not appear to be reasonable c o n t i n u i t y even at 700 f o o t spacing. The l a c k of l a t e r a l c o n t i n u i t y of the. banks' s e d i -ments, even at 700 f e e t spacing, i s not unreasonable i n l i g h t of the d e p o s i t i o n a l environment. The s m a l l d i s t r i b u t a r y channels which are a c t i v e p r i m a r i l y d u r i n g periods of high r u n o f f (which corresponds to maximum sediment t r a n s p o r t ) f r e q u e n t l y a l t e r t h e i r routes across the banks. The bed load of these channels can be expected t o be s i g n i f i c a n t l y c o arser than the suspended sediments. Some of the suspended sediments w i l l drop out of suspension on the banks adjacent to the channel i f the flow spreads out over the banks and slows to les s than the c r i t i c a l v e l o c i t y necessary to maintain suspension. When the channel s h i f t s p o s i t i o n some of the sediments previously deposited are eroded, and some replacement by sediments with a d i f f e r e n t grain size d i s t r i b u -t i o n takes place. Previous to the s t a b i l i z a t i o n of the main channels by the construction of j e t t i e s the main channels also changed positions with time. Of less importance to the question of l a t e r a l contin-u i t y , but worthy of mention, i s the transport of deposited sediments by wave action and current action. Under normal circumstances neither of these processes would be expected to produce d i s c o n t i n u i t i e s i n the sediments but rather gradual gradational changes. D i s c o n t i n u i t i e s could conceiv-ably be produced i f these processes were somehow focused on a s p e c i f i c section of the de l t a f r o n t , but there i s no evidence to suggest that t h i s has occurred. A few of the borehole logs mention t h i n clay and clayey s i l t layers and a very few of the borehole logs describe a major "layer" of s o i l as being clayey s i l t . These descriptions are based on v i s u a l c l a s s i f i c a t i o n s and grain s i z e analyses of recovered samples. The r e s u l t s of the shear tests and t r i a x i a l tests which have been reported i n the engineering reports indicate c l a s s i c a l cohensionless behaviour for a l l samples tested. The log of one of the s i x deep boreholes makes no mention of the presence of cla y i n the e n t i r e 410 feet of hole. The remaining f i v e boreholes a l l describe layers of clayey s i l t , or s i l t with some c l a y 20. at various depths; but nowhere does one get the impression that the c l a y forms a dominant f r a c t i o n of the sediments. The only t e s t s which have been performed on samples from below -80 feet are a few moisture contents, A t t e r b u r g L i m i t s , torvane and/or penetrometer t e s t s , and #200 sieve screening to d e t e r -mine approximate s a n d - s i l t q u a n t i t i e s . Prom these t e s t s i t i s not p o s s i b l e to determine whether there i s s u f f i c i e n t c l a y content i n the deep sediments to give these sediments any cohesive s o i l c h a r a c t e r i s t i c s . . The boreholes have shown that the surface 80 fe e t of sediments, and probably much deeper, are p r i m a r i l y g r a n u l a r s o i l s and no cohesion should be assumed or used when performing s t r e n g t h or s t a b i l i t y analyses of the banks' sediments. The t o t a l depth of recent sediments on the banks i s not known at most l o c a t i o n s . One borehole, l o c a t e d approximately 0.35 miles N.W. of the Westshore t e r m i n a l s causeway, penetrated i n t o g l a c i a l t i l l at -245 f e e t . There are a l s o a few boreholes on the shore end of the Tsawwassen Ferry Terminal causeway which penetrated through the recent sediments. The deepest contact w i t h s o i l s which d i d not appear to be recent sediments, f o r the causeway h o l e s , i s reported as -51 feet f o r a hole a p p r o x i -mately 0.6 miles from the shore. This borehole was the most seaward of the causeway holes i n which i t was reported the bottom of recent sediments was encountered. The t o t a l depth of sediments, although of great academic I n t e r e s t to many people, i s of only moderate i n t e r e s t to the s o i l s engineer. I f the sediments are shallow enough ( l e s s than 60-80 f e e t ) , then the op t i o n of founding the 21. p r o j e c t on end b e a r i n g p i l e s o r c a i s s o n s e x i s t s . The b o r e -h o l e l o g s i n d i c a t e t h a t t h i s c o n d i t i o n i s met o n l y i n t h e s o u t h w e s t c o r n e r o f R o b e r t s Bank n e a r P o i n t R o b e r t s . The s t r e n g t h o f t h e s o i l , b e c a u s e t h e s o i l i s c o h e s i o n l e s s , i s d i r e c t l y p r o p o r t i o n a l t o t h e e f f e c t i v e s t r e s s a c t i n g on t h e p o i n t i n q u e s t i o n . U n d e r n o r m a l c o n d i t i o n s ( h y d r o s t a t i c p o r e p r e s s u r e ) t h e e f f e c t i v e s t r e s s i s p r o p o r t i o n a l t o t h e d e p t h and deep s e a t e d f a i l u r e i s g e n e r a l l y r u l e d o u t . An i n c r e a s e i n t h e e f f e c t i v e s t r e s s w i l l c a u s e c o n s o l i d a t i o n o f s u s c e p t i b l e s o i l s a t any d e p t h ; h o w e v e r , f o r any p a r t i c u l a r l o a d i n g a n d s o i l c o n d i t i o n s t h e r e i s some d e p t h a t w h i c h t h e c o n s o l i d a t i o n due t o t h e l o a d i n g becomes n e g l i g i b l e and k n o w l e d g e o f t h e c o m p l e t e s e d i m e n t p r o f i l e becomes u n n e c e s s a r y . S o i l i s u n l i k e any o t h e r e n g i n e e r i n g m a t e r i a l , a n d a l a r g e number o f p a r a m e t e r s a r e n e c e s s a r y t o d e f i n e t h e v a r i o u s a s p e c t s o f s o i l b e h a v i o u r . The p a r a m e t e r s a r e m e a s u r e s o f s p e c i f i c p r o p e r t i e s o f t h e s o i l s u c h as p h y s i c a l p r o p e r t i e s a n d s t r e s s - s t r a i n c h a r a c t e r i s t i c s . T h e r e a r e a l s o n u m e r o u s i n d i c e s , s u c h a s t h e A t t e r b u r g L i m i t s f o r s o i l s w i t h some p l a s t i c i t y , w h i c h m e a s u r e some p r o p e r t y o f t h e s o i l r e l a t e d t o some d e f i n e d a s p e c t o f t h e s o i l s ' b e h a v i o u r . The i n d i c e s g i v e a n I n d i c a t i o n o f t h e p r o b a b l e b e h a v i o u r t r e n d s o f t h e s o i l . T h i s t h e s i s i s d e a l i n g w i t h an e x t e n s i v e a r e a f r o m w h i c h r e l a t i v e l y f e w s a m p l e s o f t h e s o i l h a v e b e e n t e s t e d , a n d i n c a s e s s u c h a s t h i s t h e i n d i c e s a r e u s e d t o o b t a i n e s t i m a t e s o f t h e p a r a m e t e r s o r t o p r e d i c t p r o b a b l e e n g i n e e r i n g p e r f o r m a n c e u s i n g c o r r e l a t i o n s b e t w e e n i n d i c e s and p a s t f i e l d b e h a v i o u r . The s a m p l e s r e c o v e r e d f r o m , and t h e ' N - v a l u e s r e c o r d e d f o r the standard p e n e t r a t i o n t e s t s taken at f i v e f e e t i n t e r v a l s i n v i r t u a l l y every borehole, from the surface t o 80 f e e t depth, represent the l a r g e s t p o s s i b l e source of in f o r m a t i o n about the sediments. The samples, although d i s t u r b e d , were used f o r moisture content determinations, g r a i n s i z e a n a l y s i s , and A t t e r b u r g l i m i t determinations where a p p r o p r i a t e . The engineering community recognizes the crudeness and v a r i a b i l i t y of the standard p e n e t r a t i o n t e s t , however w i t h the N-values r e p r e s e n t i n g such a l a r g e pro-p o r t i o n of the a v a i l a b l e i n f o r m a t i o n every e f f o r t was made to u t i l i z e the N-values. The two main parameters f o r a coh e s i o n l e s s s o i l which can be estimated from the N-values are the R e l a t i v e D e n s i t y , D^, and the e f f e c t i v e angle of i n t e r n a l f r i c t i o n 0 . G r a i n S i z e D i s t r i b u t i o n The samples recovered from the standard p e n e t r a t i o n t e s t are of very l i t t l e use f o r most t e s t purposes due t o the very d i s t u r b e d nature of the samples, however one exception t o t h i s i s the g r a i n s i z e a n a l y s i s t e s t . I f the assumption t h a t the sample recovered i s r e p r e s e n t a t i v e of the s o i l sampled i s v a l i d , then the amount of dis t u r b a n c e does not i n f l u e n c e the t e s t r e s u l t s . The m a j o r i t y of the samples recovered from the standard p e n e t r a t i o n t e s t s were given a "one si e v e a n a l y s i s " to determine the percentage of s o i l passing the #200 s i e v e , which has been s e t as the a r b i t r a r y d i v i s i o n between sand and s i l t . A number of the standard p e n e t r a t i o n t e s t samples and many of the f i x e d p i s t o n shelby tube samples were given complete mechanical g r a i n s i z e analyses. For many of these samples the s o i l p a s s ing the #200 siev e was used to perform hydrometer t e s t s , which allowed complete g r a i n s i z e d i s t r i b u t i o n curves t o be p l o t t e d . Three surface samples were taken on Sturgeon Bank i n J u l y , 1975, and mechanical g r a i n s i z e a n a l y s i s t e s t s were performed on the three samples. Hydrometer t e s t s were not performed on the samples as no sample had more than 5% passing the #200 s i e v e . The g r a i n s i z e d i s t r i b u t i o n curves of the three surface samples are presented i n F i g . 5. These curves are very t y p i c a l of the curves presented i n the engin-e e r i n g r e p o r t s f o r samples w i t h low s i l t contents. The three samples have u n i f o r m i t y c o e f f i c i e n t s of 1.7, 2.1 and 1.2 which c l a s s i f i e s these samples as uniform. From the g r a i n . s i z e d i s t r i b u t i o n curves presented i n the engi n e e r i n g r e p o r t s , i t appears t h a t the u n i f o r m i t y c o e f f i c i e n t of the banks' sediments incre a s e s as the s i l t content i n c r e a s e s , u n t i l the s i l t content dominates. For example, a sample w i t h 14 percent passing #200 has a u n i f o r m i t y c o e f f i c i e n t of 4.9; a sample w i t h 28 percent passing #200 has a un-i f o r m i t y c o e f f i c i e n t of 23.7; and a sample w i t h 70 percent passing #200 has a u n i f o r m i t y c o e f f i c i e n t of 10.0. These are s p e c i f i c values from s p e c i f i c samples which appear t o represent the general trend and these values are not meant to be used as a d e f i n i t e r e l a t i o n s h i p . The u n i f o r m i t y of the banks' sediments i s a f u n c t i o n of the d e p o s i t i o n a l environment. For any given v e l o c i t y of moving water there i s a f i n i t e range of p a r t i c l e s i z e s 24. GRAIN SIZE DISTRIBUTION FRASER DELTA STUDY Project Job. No. Sturgeon Bank Boring No. Location of Project _ Description of Soil Fine-Med. Sand / N O P T H N F S A M P ! E —SurfflCP Tested By. ~ s- Scotton D af e of Testing August 8 , 1 9 7 5 Sample No. 1-Q> 2 - A , 3- Q 100 c c © o o Q. Gravel Sand Fines Coarse to medium Fine Silt Clay 3/4 In. U.S. s j d o < K z z : tandard siei s " 6 < : z : /e sizes • Visual soil description Grain diameter, mm Grey Fine-Med. Sand, some s i l t Soil classification: SP System Unif ied So i l C l a s s i f i c a t i o n F i g . 5 Grain Size D i s t r i b u t i o n curves for the 3 surface samples taken on Sturgeon Bank. 25. w h i c h c a n be t r a n s p o r t e d i n s u s p e n s i o n a nd b e d l o a d . As t h e s e d i m e n t l a d e n r i v e r w a t e r r e a c h e s t h e edge o f t h e d e l t a i t s p r e a d s o u t a n d s l o w s down. As t h e v e l o c i t y d e c r e a s e s , t h e s i z e o f p a r t i c l e w h i c h c a n be k e p t i n m o t i o n a l s o d e c r e a s e s , a n d t h e r e i s a g r a d a t i o n a l . d e p o s i t i o n o f t h e s e d i m e n t s . F u r t h e r r e w o r k i n g o f t h e s e d i m e n t s by waves a n d c u r r e n t s t e n d s t o i n c r e a s e t h e u n i f o r m i t y o f t h e s e d i m e n t s . A c o m p i l a t i o n o f t h e r e s u l t s o f a l l t h e one s i e v e a n a l y s e s i n d i c a t e s t h a t t h e s u r f a c e 80 f e e t o f s e d i m e n t s i n t h e a r e a s a d j a c e n t t o t h e m a i n c h a n n e l o f t h e F r a s e r - ( n o r t h a nd s o u t h s i d e ) a nd s o u t h a n d c e n t r a l S t u r g e o n Bank h a v e a h i g h e r s i l t c o n t e n t t h a n t h e o v e r a l l a v e r a g e . T h e r e i s no r e c o g n i z a b l e t r e n d , h o w e v e r , f o r t h e g r a i n s i z e d i s t r i b u t i o n w i t h r e s p e c t t o d e p t h f o r t h e s u r f a c e 80 f e e t o f s e d i m e n t s . The s i x deep b o r e h o l e s i n d i c a t e t h a t t h e r e i s a g e n e r a l t r e n d t o f i n e r g r a i n s i z e s o v e r g r e a t d e p t h s . R e l a t i v e D e n s i t y B a z a r a a (1967) a n d G i b b s and H o l t z (1969) h a v e s u g -g e s t e d m e t h o d s f o r e s t i m a t i n g t h e R e l a t i v e D e n s i t y , D^, f r o m s t a n d a r d p e n e t r a t i o n t e s t b l o w c o u n t s ( N - v a l u e s ) . B o t h m e t h o d s i n v o l v e t h e i n t e r p o l a t i o n o f t h e r e l a t i v e d e n s i t y f r o m a f a m i l y o f c u r v e s o f r e l a t i v e d e n s i t y p l o t t e d o n a . g r a p h w i t h v e r t i c a l e f f e c t i v e s t r e s s as t h e o r d i n a t e a n d N - B l o w s p e r f o o t as t h e a b s c i s s a . The two f a m i l i e s o f c u r v e s a r e shown i n F i g . 6, w i t h t h e G i b b s & H o l t z c u r v e s 26. i ,—i 1— , 1 1 1 1 0 O I 2 3 4 5 6 VERTICAL PRESSURE - Kips/sq.ft. F i g . 6 The Gibbs and Holtz (___) and the Bazaraa ( ) Relative Density vs. N-value r e l a t i o n s h i p s . shown as s o l i d l i n e s and the Bazaraa curves shown as dashed l i n e s . In his excellent State-of-the Art paper on the Standard Penetration Test, de Mello (1971) compared data from many sources with the Gibbs and Holtz vs N-value i n -terpr e t a t i o n of the U.S.B.R. te s t s . He found cases with reasonable agreement, cases where the estimated values were too high and cases where the estimated values were too low. Although the estimated values based on the N-values may not be the absolutely correct values, the standard penetration t e s t can indicate v a r i a t i o n a l trends within a given deposit. When the deposit being tested i s composed of sediments with reasonably s i m i l a r mineralogy, grain s i z e d i s t r i b u t i o n , and degree of angularity throughout, the estimated, or apparent, values w i l l most probably not be the correct actual values, but they w i l l bear the correct r e l a t i o n s h i p to each other. In other words, i f test A has an apparent r e l a t i v e density less than the apparent r e l a t i v e density of te s t B then the actual r e l a t i v e density at A i s less than at B. The r e l a t i v e density of the banks sediments was estimated f o r every recorded standard penetration t e s t using both r e l a t i o n s h i p s shown i n F i g . 6. The Bazaraa method f o r estimating the r e l a t i v e density gave values which were generally 15 to 20 percentage points lower than the values indicated by the Gibbs and Holtz method. The Bazaraa method indicated an apparent D of less than 40 percent (D = 40 28 . percent i s the lower bound f o r both methods, so values below 40 percent can not be e s t a b l i s h e d ) f o r the mean c o n d i t i o n s encount-ered, w h i l e the Gibbs and H o l t z method i n d i c a t e d a mean va l u e of 50 percent t o 55 percent f o r D r. The mean values are tempered to some extent by value judgements made du r i n g a n a l y s i s . The value judgements i n v o l v e d the c a s t i n g out of r e s u l t s which appeared t o have been i n f l u e n c e d by a "high" s i l t content. The r a t i o n a l e f o r t h i s was t h a t during the a n a l y s i s of the borehole logs i t became apparent t h a t there was a c o n s i s t e n t and s i g n i -f i c a n t decrease i n the blow counts w i t h an i n c r e a s e i n s i l t c ontent. I n many cases these s i l t y l a y e r s were bracketed by sands w i t h s i m i l a r apparent r e l a t i v e d e n s i t i e s and i t seemed unreasonable f o r the i n t e r v e n i n g s i l t y l a y e r t o have such a reduced apparent r e l a t i v e d e n s i t y as i n d i c a t e d by the reduced blow counts. I t i s obvious t h a t when the c o n d i t i o n of s i m i l a r g r a i n s i z e d i s t r i b u t i o n s i s v i o l a t e d the apparent r e l a t i v e d e n s i t i e s are no longer comparable. Nowhere i n the engineering r e p o r t s could an e v a l u a t i o n cf the r e l a t i v e d e n s i t y of the banks' sediments be found w i t h which to compare the values d e r i v e d from the N-values. I n ordei" to determine which method of e s t i m a t i n g D r gave the most reason-able r e s u l t s f o r the banks' sediments, three surface samples were taken on Sturgeon Bank near the l o c a t i o n of three of the boreholes f o r which r e l a t i v e d e n s i t y was estimated. These are the same three samples which were mentioned i n the previous s e c t i o n on g r a i n s i z e d i s t r i b u t i o n . Nominal 3.4 i n c h I.D. Shelby tubes, 2 9 inches long, were c a r e f u l l y pushed i n t o the un-d i s t u r b e d sediments. The depth of p e n e t r a t i o n was marked on the o u t s i d e of the tube and then the tube was dug out w i t h a shovel (as opposed to being p u l l e d out) and the bottom covered before l i f t i n g the tube from the s o i l t o prevent the l o s s of any s o i l . The s o i l i n the tube, which d e n s i f i e d during sampling and h a n d l i n g , was assumed to have occupied the i n s i t u volume represented by the mark on the o u t s i d e of the tube. In the l a b , the samples were each t e s t e d f o r maximum and minimum d e n s i t y (non-standard t e s t s ) , s p e c i f i c g r a v i t y and g r a i n s i z e d i s t r i b u t i o n (standard procedures), and the r e s u l t s of these t e s t s are shown i n Table 1. Table 1 TEST RESULTS Sample 1 2 3 R e l a t i v e Density 43.7% 33.0% 37.0% Void R a t i o .93 .84 .80 S p e c i f i c G r a v i t y 2.70 2.70 2.71 . 15 mm . 2 7 mm . 27 mm .088 mm . 13 mm .23 mm These r e l a t i v e d e n s i t i e s c o m p a r e q u i t e w e l l w i t h the r e l a t i v e d e n s i t i e s i n d i c a t e d f o r t h i s area by the Bazaraa method which i n d i c a t e s t h a t the Bazaraa apparent r e l a t i v e d e n s i t i e s may be more r e a s o n a b l e f o r t h e s e d e p o s i t s t h a n t h e G i b b s and H o l t z apparent r e l a t i v e d e n s i t i e s . E i t h e r r e l a t i o n s h i p would serve to i n d i c a t e the v a r i a t i o n a l t r e n d s , but the Bazaraa apparent r e l a t i v e d e n s i t i e s would appear t o be more appropriate f o r use i n making r o u g h a p p r o x i m a t i o n s o f the s o i l c h a r a c t e r i s t i c s . A study of the borehole logs leads to a few g e n e r a l observations about the apparent r e l a t i v e d e n s i t y . There were enough boreholes where the apparent r e l a t i v e d e n s i t y remained reasonably constant w i t h depth ( f o r the surf a c e 80 feet) t o suggest t h a t t h i s i s the norm r a t h e r than the exception f o r the banks sediments. A constant r e l a t i v e d e n s i t y w i t h depth f o r g r a n u l a r s o i l s i s to be expected i f the d e p o s i t i o n a l environment has remained b a s i c a l l y the same throughout the d e p o s i t i o n of the sediment column. Granular s o i l s undergo very l i t t l e d e n s i f i c a t i o n due to the a d d i t i o n of l o a d . V i b r a t i o n i s necessary t o induce i n t e r g r a n u l a r movement, a l l o w i n g the formation of denser packing arrangements. Under normal c o n d i t i o n s there i s not s u f f i c i e n t v i b r a t i o n to a l l o w the i n t e r g r a n u l a r movements. The north edge of Roberts Bank adjacent t o the main channel and the l e a d i n g (western) edge of Sturgeon Bank have apparent r e l a t i v e d e n s i t i e s lower than the mean; w h i l e c e n t r a l Sturgeon Bank west of Sea I s l a n d has apparent r e l a t i v e d e n s i t i e s higher than the mean. F r i c t i o n Angle In the p r e v i o u s l y mentioned S t a t e - o f - t h e A r t paper on the Standard P e n e t r a t i o n Test, de M e l l o (1971)proposed a r e l a t i o n s h i p between the overburden s t r e s s o " , the N-value and the angle of i n t e r n a l f r i c t i o n , 0. He a l s o presented the r e s u l t s of h i s r e l a t i o n s h i p i n g r a p h i c a l form, and i n 1975 Schmertmann presented an adaptation of the de M e l l o g r a p h i c a l p r e s e n t a t i o n . The form of the Schmertmann p r e s e n t a t i o n i s a f a m i l y of curves of 0' ( e f f e c t i v e angle of i n t e r n a l f r i c t i o n ) p l o t t e d on a graph w i t h N-value as the o r d i n a t e and over-burden s t r e s s as the a b s c i s s a . A v e r s i o n of the Schmertmann adaptation of the de Mellow r e l a t i o n s h i p i s shown i n F i g . 7. Using t h i s figure., the e f f e c t i v e angle of i n t e r n a l f r i c t i o n was estimated f o r every recorded standard p e n e t r a t i o n t e s t . The same comments which were made about the apparent r e l a t i v e d e n s i t i e s a l s o apply to the i n t e r p r e t e d apparent, f r i c t i o n angles. The apparent f r i c t i o n angles may.not.be. the a b s o l u t e l y c o r r e c t f r i c t i o n angles but the comparative r e l a t i o n s h i p between d i f f e r e n t t e s t s i s e s t a b l i s h e d . The r e s u l t s of t e s t s on s o i l s w i t h "high" s i l t contents were ignored because they d i d not conform to the c o n d i t i o n of s i m i l a r g r a i n s i z e d i s t r i b u t i o n s f o r comparison of r e s u l t s . The apparent e f f e c t i v e f r i c t i o n angles determined from the N-values ranged from 22 degrees to 48 degrees, w i t h an apparent e f f e c t i v e f r i c t i o n angle of approximately 35 degrees being a s s o c i a t e d w i t h the mean c o n d i t i o n s encountered by the boreholes. One shear t e s t i s reported i n the engineer-in g r e p o r t s (Cook, 1967) f o r which the e f f e c t i v e f r i c t i o n angle was 1.8.5 degrees at 10 percent s t r a i n f o r a sample w i t h 88 percent passing the #200 s i e v e . Such a m a t e r i a l would not g e n e r a l l y be encountered i n the surf a c e 80 f e e t , although t h i s sample came from -50 f e e t . For the other shear and t r i a x i a l t e s t s reported i n the engineering r e p o r t s the range i n s i l t content was from 2 percent t o 44 percent passing the #200 s i e v e and the range i n e f f e c t i v e f r i c t i o n angle was from 34.5 degrees to 40 degrees. The mean of these l a t t e r t e s t s g i v e s an e f f e c t i v e f r i c t i o n angle of 37 degrees as an "average" e f f e c t i v e angle of i n t e r n a l f r i c t i o n . The trend of the i n d i c a t e d e f f e c t i v e f r i c t i o n angles 32 . F i g . 7 The de M e l l o E f f e c t i v e Angle of I n t e r n a l F r i c t i o n i (0 ) v s . N-Value r e l a t i o n s h i p , as reported by Schmertman (1975). i s very s i m i l a r to the trend of the apparent r e l a t i v e d e n s i t i e s . Lower than average values are indicated f o r the north edge of Roberts Bank and the west edge of Sturgeon Bank and above average values are indicated f o r c e n t r a l Sturgeon Bank west of Sea Island. In the cases where the apparent r e l a t i v e density remains reasonably constant with depth, the indicated e f f e c t i v e f r i c t i o n angle also remains reasonably constant with depth. The agreement of the e f f e c t i v e f r i c t i o n angle trends with the r e l a t i v e density trends i s t o t a l l y reasonable, including the trend of constant f r i c t i o n angle with depth. The " c r i t i c a l void r a t i o " concept (Taylor, 1949) explains th i s aspect of the s o i l behaviour. For a s p e c i f i c cohesion-less s o i l at a constant void radio (constant r e l a t i v e density) there i s a " c r i t i c a l e f f e c t i v e s t r e s s " i n excess of which the shear strength of the s o i l w i l l be d i r e c t l y proportional to the e f f e c t i v e s t r e s s . The constant of p r o p o r t i o n a l i t y i s the tangent of the e f f e c t i v e f r i c t i o n angle. For a loose s o i l such as the banks' sediments, the " c r i t i c a l e f f e c t i v e s t r e s s " i s very low. This " c r i t i c a l e f f e c t i v e s t r e s s " i s exceeded i n the surface few feet of sediments, therefore the e f f e c t i v e f r i c t i o n angle should be constant with depth a f t e r the i n i t i a l few feet, where the s o i l and r e l a t i v e density are s i m i l a r with depth. Consolidation Parameters The few fi x e d piston Shelby Tube samples taken of the banks' sediments were assumed to be reasonably undisturbed, 34. and t h e s e s a m p l e s w e re u s e d t o p e r f o r m t e s t s whose r e s u l t s a r e s e n s i t i v e t o s a m p l e d i s t u r b a n c e . One o f t h e s e t e s t s w i t h g r e a t i m p o r t a n c e i s t h e c o n s o l i d a t i o n t e s t , a s s e t t l e m e n t w i l l be one o f t h e g o v e r n i n g f a c t o r s f o r any p r o j e c t on t h e b a n k s . The r e s u l t s o f s i x c o n s o l i d a t i o n t e s t s ' w e r e f o u n d i n t h e e n g i n e e r i n g r e p o r t s , and t h e s a m p l e s t e s t e d w e r e f r o m d e p t h s r a n g i n g f r o m -50 f e e t t o -300 f e e t . The e n g i n e e r i n g r e p o r t s p r e s e n t t h e r e s u l t s o f t h e c o n s o l i d a t i o n t e s t s i n t h e f o r m o f p l o t s o f v o i d r a t i o v s l o g e f f e c t i v e s t r e s s . The c o m p r e s s i o n i n d e x i s t h e c h a n g e i n v o i d r a t i o f o r a c h a n g e o f e f f e c t i v e s t r e s s o f one o r d e r o f m a g n i t u d e , T h e r e i s no u n i q u e c o m p r e s s i o n i n d e x f o r most s o i l s ( e x c e p t , p o s s i b l y , some r e m o u l d e d s o i l s ) b e c a u s e t h e s h a p e o f t h e v o i d r a t i o v s l o g e f f e c t i v e s t r e s s c u r v e i s n o t u s u a l l y a s t r a i g h t l i n e . T h e r e a r e , h o w e v e r , u s u a l l y two d i s t i n c t p a r t s o f t h e c u r v e w h i c h c a n be a p p r o x i m a t e d by s t r a i g h t l i n e s — t h e r e b o u n d , c u r v e a n d t h e v i r g i n c u r v e . The r e b o u n d c u r v e r e p r e s e n t s t h e s o i l r e s p o n s e t o e f f e c t i v e s t r e s s e s w h i c h a r e l e s s t h a n t h e maximum e f f e c t i v e s t r e s s e s t o w h i c h t h e s o i l h a s p r e v i o u s l y b e e n s u b j e c t e d . The v i r g i n c u r v e r e p r e s e n t s t h e s o i l r e s p o n s e t o e f f e c t i v e s t r e s s e s w h i c h a r e g r e a t e r t h a n p r e v i o u s s t r e s s l e v e l s . S i n c e t h e s h a p e o f t h e v o i d r a t i o v s l o g e f f e c t i v e s t r e s s c u r v e s do n o t i n d i c a t e any p r e c o n s o l i d a t i o n ( c o n s o l i d a -t i o n u n d e r s t r e s s e s i n e x c e s s o f e x i s t i n g I n s i t u s t r e s s e s ) , a n d t h e r e i s no g e o l o g i c e v i d e n c e t o s u g g e s t any p r e c o n s o l i -d a t i o n , t h e c o m p r e s s i o n i n d e x o f t h e v i r g i n c u r v e i s o f t h e most v a l u e t o t h e s o i l s e n g i n e e r . The c o m p r e s s i o n i n d i c e s o f t h e s a m p l e s t e s t e d r a n g e d f r o m 0.22 t o 0.36 and t h e r e was no apparent trend w i t h respect to depth. The compression index can be used t o estimate settlements due to d i f f e r e n t load c o n d i t i o n s . The accepted method of e s t i m a t i n g settlements i s by the formula ' C_ • S = H l o g 1 0 p o •+ p 1 + e0 Po (Terzaghi and Peck, 1948) where S = settlement i n f e e t , H = t h i c k n e s s of the l a y e r i n f e e t , C c = compression index, e Q = i n i t i a l i n s i t u v o i d r a t i o , Po = e x i s t i n g i n s i t u e f f e c t i v e v e r t i c a l s t r e s s i n p . s . f . , and P = change i n v e r t i c a l s t r e s s i n p . s . f . Any other s e t of compatible u n i t s can be used w i t h t h i s formula. The c o n s o l i d a t i o n t e s t s provide values f o r C c and the r e l a t i o n s h i p Gw = Se ... (4-2) where G = s p e c i f i c g r a v i t y of s o l i d s , w = n a t u r a l moisture content, S = degree of s a t u r a t i o n , and e = v o i d r a t i o of the sample (Lambe and Whitman, 1969), provides a value f o r the v o i d r a t i o i f the s p e c i f i c g r a v i t y of the s o l i d s i s known, the moisture content has been determined and 100 percent s a t u r a t i o n can be assumed. C o n s o l i d a t i o n i s a time dependant process; t h e r e f o r e , along w i t h an estimate of the t o t a l settlement expected, the engineer must a l s o know the nature of the settlement w i t h respect t o time. The c o e f f i c i e n t of c o n s o l i d a t i o n , C v, must be determined to a l l o w estimates of the settlement w i t h respect t o time t o be made. C v i s not a constant f o r a given s o i l , but i s a f u n c t i o n of the e f f e c t i v e s t r e s s and the s t r e s s h i s t o r y of the s o i l . From one dimensional c o n s o l i d a t i o n theory (Terzaghi and Peck, 1948) comes the equation 36. t = T y H 2 ... (4-3) where t = time to n p e r c e n t c o n s o l i d a t i o n , T v = time f a c t o r f o r n p e r c e n t c o n s o l i d a t i o n , H = l e n g t h of drainage path, and C = c o e f f i c i e n t of c o n s o l i d a t i o n . Graphs or t a b l e s of v a l u e s f o r T f o r a range of degrees o f c o n s o l i d a t i o n f o r v a r i o u s boundary c o n d i t i o n s can be found i n most b a s i c s o i l mechanics t e x t books. Although v a l u e s of C v can be d e r i v e d from the s t a n d a r d c o n s o l i d a t i o n t e s t , no v a l u e s o f C v f o r the banks' sediments have been r e p o r t e d i n the e n g i n e e r i n g r e p o r t s . One d i m e n s i o n a l c o n s o l i d a t i o n t h e o r y assumes no l a t e r a l d rainage of porewater d u r i n g the c o n s o l i d a t i o n p r o c e s s . Standard p r a c t i c e f o r e s t i m a t i n g s e t t l e m e n t times i s to s e t H e q u a l t o o n e - h a l f the t o t a l t h i c k n e s s of the l a y e r i n q u e s t i o n f o r a double drainage s i t u a t i o n . T h i s p r a c t i c e assumes no i n t e r m e d i a t e d r a i n a g e l a y e r s . Both assumptions j u s t mentioned l e a d t o c o n s e r v a t i v e e s t i m a t e s of c o n s o l i d a t i o n times. For any p r o j e c t of f i n i t e s i z e t h e r e w i l l be some degree o f l a t e r a l drainage which w i l l speed up the c o n s o l i d a -t i o n p r o c e s s . The nature of the banks' sediments make i t v e r y p r o b a b l y t h a t t h e r e are numerous t h i n l a y e r s of more permeable sediments d i s t r i b u t e d through the c o n s o l i d a t i n g l a y e r which sho r t e n the drainage path H. E x p e r i e n c e has shown t h a t due t o these d e p a r t u r e s from one d i m e n s i o n a l c o n s o l i d a t i o n t h e o r y , even when C v v a l u e s are measured from c o n s o l i d a t i o n t e s t s the s e t t l e m e n t time c a l c u l a t i o n s o n l y p r o v i d e an upper bound. The g e n e r a l p r a c t i c e i s to i n s t a l l s e t t l e m e n t gauges when l o a d i n g i s begun and monitor them, p l o t t i n g the settlements as the readings are taken. This i s best i l l u s t r a t e d by example and a case h i s t o r y from, the Westshore Terminals bulk loading f a c i l i t y w i l l he d i s c u s s e d l a t e r . The s e t t l e m e n t t i m e s shown i n the case h i s t o r y are representative of settlement times for other projects at various locations on the d e l t a (personal knowledge) and i t i s reasonable to assume s i m i l a r behaviour at other locations on the banks. Atterburg Limits The Atterburg Limits are determined by procedures which completely remould the s o i l and hence the disturbed nature of the samples recovered from the Standard Penetration Test has no e f f e c t upon the r e s u l t s of the Atterburg Limit determinations. Most of the samples recovered from the banks were too coarse f o r Atterburg limit, determinations, but the l i m i t s were determined f o r many of the s i l t and clayey s i l t samples. The P l a s t i c Limit ranged from 18 percent to 30 percent; the Liquid Limit ranged from 32 percent to 50 percent; the i n s i t u Moisture Content ranged from 23 percent to 42 percent; the P l a s t i c i t y Index ranged from 4 percent to 26 percent and the L i q u i d i t y Index ranged from -0.3 to 1.8 for the samples tested. The sample with the L i q u i d i t y Index of -0.3 i s a single unusual sample and the next lowest value i s 0.3. Samples tested from the t o p 80 f e e t of sediments gave widely divergent r e s u l t s and no general trends of t he i n d i c e s are apparent. Samples tested from below -90 feet have a range of L i q u i d i t y Index from 1.0 to 0.4 and there 38. appears to be a g e n e r a l t r e n d o f d e c r e a s i n g L i q u i d i t y Index w i t h i n c r e a s i n g depth. As t h e r e are r e s u l t s from o n l y seven samples from -90 f e e t , and one of these does not f i t the s t a t e d p a t t e r n , t h i s i n d i c a t e d t r e n d should not be r e l i e d upon without a d d i t i o n a l s u p p o r t i n g d a t a . A L i q u i d i t y Index of 1.0 i n d i c a t e s a n a t u r a l m o i s t u r e c o n t e n t e q u a l to the L i q u i d L i m i t . I f the n a t u r a l m o i s t u r e c o n t e n t i s g r e a t e r than the L i q u i d L i m i t then the L i q u i d i t y Index i s g r e a t e r than 1.0 and v i c e v e r s a . A s o i l w i t h a n a t u r a l m oisture content equal t o or g r e a t e r than the L i q u i d L i m i t i s g e n e r a l l y c o n s i d e r e d to be normally c o n s o l i d a t e d . A s o i l a t depth with a n a t u r a l m o i s t u r e c o n t e n t l e s s than the L i q u i d L i m i t does not n e c e s s a r i l y i n d i c a t e o v e r c o n s o l i d a t i o n , s i n c e the sediments w i l l undergo some c o n s o l i d a t i o n due t o the s t r e s s o f the s o i l s d e p o s i t e d above them. T h i s con-s o l i d a t i o n w i l l reduce the n a t u r a l m o i s t u r e c o n t e n t but the sample may s t i l l be n ormally c o n s o l i d a t e d f o r the i n s i t u s t r e s s c o n d i t i o n s . I t i s the o p i n i o n of t h i s w r i t e r t h a t the t r e n d t o d e c r e a s i n g L i q u i d i t y Index w i t h depth below -90 f e e t r e f l e c t s t h i s c o n s o l i d a t i o n to the i n s i t u s t r e s s c o n d i t i o n s , and does not r e p r e s e n t any o v e r c o n s o l i d a t i o n . The A t t e r b u r g L i m i t r e s u l t s were i n c l u d e d f o r the sake of complete r e p o r t i n g of a v a i l a b l e i n f o r m a t i o n . The s o i l s b e i n g t e s t e d are predominantly s i l t w i t h l i t t l e c l a y content, and the r e s u l t s would p r o b a b l y have v e r y poor r e p r o d u c i b i l i t y . The A t t e r b u r g L i m i t s were proposed f o r c l a y s o i l s , which e x p e r i e n c e has shown g i v e r e a s o n a b l y r e p r o d u c i b l e r e s u l t s . I t i s the r e p r o d u c a b i l i t y o f the r e s u l t s which gave 39. the A t t e r b u r g L i m i t s some c r e d i b i l i t y as a guide to p r o p e r t i e s of the s o i l . S o i l s which are predominantly s i l t do not have t h i s r e p r o d u c a b i l i t y emd the A t t e r b u r g L i m i t s determined f o r these s o i l s should be used only to i n d i c a t e trends w i t h respect t o area or depth. Compression Index Estiraa.tes Despite the c a u t i o n about the use of At t e r b u r g L i m i t s determined f o r predominantly s i l t y s o i l s , an e f f o r t was made t o evaluate the usefulness of the L i m i t s f o r e s t i m a t i n g other s o i l s parameters. Terzaghi (1948) presented a r e l a t i o n s h i p f o r e s t i m a t i n g the compression index, Cc» from the l i q u i d l i m i t , L , f o r c l a y s of medium to low s e n s i t i v i t y . The proposed w r e l a t i o n s h i p i s C =0.009 (L -10%). ...(4-4) 1 c w At t e r b u r g L i m i t s were determined, and presented i n the engineering r e p o r t s , f o r the s i x samples upon which the p r e v i o u s l y d i s cussed c o n s o l i d a t i o n t e s t s were performed. R e l a t i o n s h i p (4-4) was a p p l i e d to the reported l i q u i d l i m i t s f o r purposes of comparing the c a l c u l a t e d compression i n d i c e s to the measured compression i n d i c e s . The measured compress-i o n i n d i c e s ranged from 0.22 t o 0.36 and the c a l c u l a t e d compression i n d i c e s ranged from 0.18 t o 0.32. Some of the c a l c u l a t e d values were g r e a t e r than the measured values and some of the c a l c u l a t e d values were l e s s than the measured v a l u e s . The l a r g e s t discrepancy was on the order of 34 percent l e s s than the measured val u e , but there was no apparent p a t t e r n t o the v a r i a t i o n . The poor degree of r e p r o d u c i b i l i t y of l i q u i d l i m i t s f o r s i l t s o i l s may be l a r g e l y r e s p o n s i b l e f o r the l a r g e 40. d i s c r e p a n c i e s and the random v a r i a b i l i t y of the c a l c u l a t e d vs. the measured values of the compression i n d i c e s . The n a t u r a l moisture content, which i s a measured p h y s i c a l property of the s o i l not p a r t i c u l a r l y dependent upon t e s t procedures, should have a high degree of r e p r o d u c i b i l i t y . For a normally c o n s o l i d a t e d a l l u v i a l s o i l the n a t u r a l moisture content should bear some r e l a t i o n s h i p to the l i q u i d l i m i t even at great depths. This leads t o s p e c u l a t i o n t h a t the n a t u r a l moisture content of the predominantly s i l t y banks' sediments may provide a means of making f i r s t order s e t t l e -ment estimates. I n order to evaluate t h i s p o s s i b i l i t y the measured C ,/1+e values were p l o t t e d v s . the corresponding l i q u i d l i m i t s and n a t u r a l moisture contents on semi-log paper, as shown i n F i g . 8 . The s o l i d l i n e on F i g . 8 represents the r e l a t i o n s h i p obtained by s u b s t i t u t i n g the n a t u r a l moisture content, w, f o r the l i q u i d l i m i t , L , i n equation (4-4); combining the r e s u l t i n g r e l a t i o n s h i p w i t h equation (4-2); s e t t i n g G=2.70 and S=100 percent and s o l v i n g f o r C /1+e. The r e l a t i o n s h i p d e r i v e d by t h i s process i s C c/l+e = 0.239 l o g 1 Q w -0.253. ... (4-5) The measured values of C c/l+e p l o t t e d v s. the l i q u i d l i m i t s have completely random d i s t r i b u t i o n , w i t h some p o i n t s above and some p o i n t s below the s o l i d l i n e . The p o i n t s which represent the p l o t t i n g of the measured C c/l+e values vs. the n a t u r a l moisture content l i e c o n s i s t e n t l y above the s o l i d l i n e . This suggests t h a t a r e l a t i o n s h i p s i m i l a r t o (4-5), such as the r e l a t i o n s h i p represented by the heavy dashed l i n e i n F i g . 8, may i n f a c t provide a reasonable means F i g . 8 P o s s i b l e r e l a t i o n s h i p between the r a t i o o f the Compression Index over the V o i d R a t i o p l u s one ( C c / l + e ) , and the measured water contents -l i q u i d l i m i t and n a t u r a l moisture content. of making f i r s t , order estimates of p o t e n t i a l settlements for the banks' sediments. The r e l a t i o n s h i p represented by the heavy dashed l i n e can be expressed as C c/l+e = 0.239 l o g 1 ( ) W -0.235. ... (4-6) This r e l a t i o n s h i p i s proposed as a possible means of making f i r s t order approximations of settlement potentials for a s p e c i f i c deposit of sediments based on the t e s t r e s u l t s a v a i l a b l e and t h i s r e l a t i o n s h i p should not be used unless the user i s f u l l y aware of i t s severe l i m i t a t i o n s . I f i t were deemed desirable to v e r i f y or r e f i n e t h i s r e l a t i o n s h i p , i t i s reasonable to assume that the s o i l s of the delta proper, at depth, are very s i m i l a r to the s o i l s of the banks, and that the r e s u l t s of tests on these s o i l s should s a t i s f y the same r e l a t i o n s h i p i f such a r e l a t i o n s h i p e x i s t s . The sur-f i c i a l d e l t a deposits have more clays and organics than the banks sedimenrs and would not be expected to conform to the same r e l a t i o n s h i p . With a l l the development which has taken place on the d e l t a there should be a wealth of information a v a i l a b l e which could be plotted to assess the usefulness of the r e l a t i o n s h i p . SETTLEMENT CASE HISTORY The Westshore Terminals Bulk Loading F a c i l i t y i s located on Roberts Bank about midway between Canoe Passage and the Tsawwassen Ferry Terminal. I t i s shown i n F i g . 3 and as can be seen i t consists of a large man-made area connected to the mainland by a long causeway. The s i t e provides open storage for very large windrows of coal, has conveyor systems 43. f o r moving and handling the c o a l , and has bulk l o a d i n g f a c i l i t i e s f o r l o a d i n g deep sea s h i p p i n g . The dredging t o create the f i l l f o r the bulk l o a d i n g f a c i l i t y was begun on J u l y 1, 1968 and continued to the end of May - e a r l y June of 1969. The s i t e grade was r a i s e d from an average of -10 f t . t o an average of +22.5 f t . g i v i n g an average t o t a l depth of 32.5 f e e t of f i l l . There were 12 settlement gauges placed around the t e r m i n a l area d u r i n g the commencement of dredging. Swan Wooster Engineering Co. L t d . , who d i d the o v e r a l l engineering f o r t h i s p r o j e c t , have made a v a i l a b l e the settlement records of the settlement gauges and of some of the i n s t a l l a t i o n s which were constructed on the f i l l a f t e r the completion of dredging. During the course of the dredging the settlement gauges were o f t e n bent and even broken. Whenever t h i s happened the survey crew attempted t o r e - e s t a b l i s h the gauge at i t s proper e l e v a t i o n . The r e s u l t i n g records r e f l e c t the extreme d i f f i c u l t y of accomplishing t h i s t a s k , e s p e c i a l l y i f a number of days passed between the breaking of a gauge and the d i s c o v e r y of the broken gauge. F i g . 9 shows the l o c a t i o n of gauges 7 and 12, the settlement records of which have been chosen as r e p r e s e n t a t i v e of a l l the settlement r e c o r d s . The p r e d i c t e d settlement due t o the s i t e f i l l i s 3.5 t o 4.0 f e e t . For the purposes of p l o t t i n g and comparison, the settlement records f o r gauges 7 and 12 were "normalized" by d i v i d i n g the settlements by 3.5. F i g . 10 shows p l o t s of the percent of p r e d i c t e d settlements as recorded along w i t h the p r e d i c t e d settlement curve. 4 4 . F i g . 9 Terminal of the Westshore Terminals Bulk Loading F a c i l i t y showing the location of settlement Gauges 7 and 12 and the i n i t i a l l o c a t i o n of the coal s t o c k p i l e s . TIME - DAYS F i g . 10 Settlement at gauges 7 and 12. The s o l i d l i n e s show the actual data and the predicted settlement. The dashed l i n e s represent the r a t i o n a l i z e d settlement curves. Cn The p r e d i c t e d settlement curve i s based on one dimensional c o n s o l i d a t i o n theory and instantaneous l o a d i n g . Working' on the assumption t h a t d u r i n g continuous l o a d i n g there should be continuous settlement, and t h a t the major d i s c o n t i n u i t i e s i n the curves are due t o gauge damage, the curves were " r a t i o n a l i z e d " by connecting together a l l reasonably continuous segments i n such a manner as to produce a s i n g l e continuous smooth curve. The r a t i o n a l i z e d curve i s represented by the dashed l i n e s and any symbols which appear on the dashed curves are f o r i d e n t i f i c a t i o n only and do not represent p l o t t e d p o i n t s . The r a t i o n a l i z e d curves do not all o w f o r changes i n slope due to changes i n r a t e s of l o a d i n g d u r i n g the dredging o p e r a t i o n and thus may be o v e r s i m p l i f i e d . Conversations w i t h Swan Wooster personnel have i n d i c a t e d t h a t the i n i t i a l f i l l placement was t a k i n g p l a c e much nearer t o gauge 12 than gauge 7 and the f i l l i n g advanced on gauge 7 g r a d u a l l y , which would account f o r the d i f f e r e n c e s i n slope between gauges 7 and. 12 over the f i r s t 200 days. The f i r s t reading f o r gauge 7 i s J u l y 26, 1968 and f o r gauge 12 i s August 1, 1968. I t has been assumed t h a t these dates represent day zero f o r these gauges. There i s l i t t l e to be learned from f u r t h e r d i s c u s s i o n of the i n d i v i d u a l gauge records s i n c e the gauge damage has rendered the i n t e r p r e t a t i o n s u b j e c t t o pers o n a l judgements. A f t e r the completion of dredging, c o n s t r u c t i o n of the f a c i l i t i e s was begun and the r a i l s f o r the l a r g e moving stacker which t r a v e l s between the c o a l s t o c k p i l e s were soon l a i d . Settlement records were kept f o r each j o i n t of each r a i l from the time of i n s t a l l a t i o n up to September 1973, a t reasonable time i n t e r v a l s . To get an extended time - s e t t l e -ment curve the settlement record f o r the r a i l j o i n t nearest gauge 7 was added onto the r a t i o n a l i z e d settlement curve f o r gauge 7. The r e s u l t i n g settlement curve i s shown i n F i g . 11. along w i t h the time placement of the events which would be expected t o i n f l u e n c e the settlements. I f one can accept the r a t i o n a l i z e d curve f o r gauge 7 as being somewhat reasonable, then the extended settlement curve presented i n F i g . 11 i s very reasonable and i n t e r e s t -i n g . The settlement due t o the s i t e f i l l alone was v i r t u a l l y complete when the s t o c k p i l i n g of c o a l was s t a r t e d , which i n i t i a t e d f u r t h e r s ettlements. The settlement due t o the s i t e f i l l appears t o have, been w i t h i n the range p r e d i c t e d by Cook (1968). The s t o c k p i l i n g of the c o a l was s t a r t e d 675 days a f t e r day zero f o r gauge 7 and the extended s e t t l e -ment curve shows an immediate response t o the a d d i t i o n a l loads. Although the settlement due t o t h i s l o a d i n g was probably not complete a t the time of the next major l o a d i n g , the settlement curve suggests t h a t the a d d i t i o n a l settlement at t h i s p o i n t would have been about 2 f t . The p r e d i c t e d settlement was 3 to 4 f t . under the center of a c o a l p i l e and 1.5 f t . between the c o a l p i l e s . The s t a c k e r r a i l from which t h i s p a r t of the settlement r e c o r d i s taken i s l o c a t e d between the p i l e s and hence i t appears t h a t the a c t u a l settlement between the p i l e s i s s l i g h t l y i n excess of the p r e d i c t e d settlement. In February of 1972 the t e r m i n a l area l a y o u t was expanded to accommodate two a d d i t i o n a l s t o c k p i l e s Approximate time o f Expansion of t e r m i n a l S t o c k p i l i n g o f c o a l t o i n c l u d e 2 a d d i t i o n a l Dredging on 2 i n i t i a l p i l e s c o a l p i l e s f: pjx •1 1 :!" ft 1 : M- • : '1' i!:|: rl! : j: IIT TI :t: : X TTOTT ' :.BI i r-;.t T l- - -j : : : hi: .Iii: • -" I-I-" ir r W\ +1 if I t 1' 1 : | T j;; - if i - X -' ! J-l • :i.. -(• --Li : :::ji . 1. T 1 ' i T I 1; P I • \ :: :j 1- - . };.•: "::F: 1. i: Ll Ti •rt : ilT- \u Ur - 1 "If -r 1 j ; 1 l f - i :.!: T gto • - j Iff i; I- -ii it j. •I'M J;Hi TJTJ.'" •iii .1 X W'| :| i - i 1 T|ft .... -. I 1 T f' :| ; i Ii j-r fit ; j ± b - : :| 1 r r f ft •i :i : : : : : [ : - • • - If -M - ";| ;|; T j H-il: ! U:: l l | I.- lit •1: -•}• - :::"]+ ll ::::|- I I. 1 t| j- if" •i •I- ii i J. }.L 1 1: xxtt x+^ : _ ™ i -1 - - i . r ii I F if m" •+ J t i r i-Tix : J:. i: t" 4f "if I f : x: 1; f " :::••! r : . | xt •.: xr: \ -;| f |f ': -T |i TJ-i fM n a ; t JLLL-ic ma •!•! 1 i i 2 4 - • 11 -i-" • ;r ' & |.y.f s< :|±: if . . |. - rf "~-'X if i.t !-r - H - -J X " ± . x.xi - - ""1 i 1 j ll - !•'• f; ii".-: g au g< S ]?' If i i i - 1 s m (X 111:]. u i h xl: l"l ; -i : it ; : r l - j: - -i j-t- i-: : " i if 1 ii M: 1- -H-;i. •i- jl|; -F t T -I- • -i Ii s-o ?e!tcer m p i h 1 »'-!f 1 tf : - ;i L:i L!J rf •H.rr X Wt -I-t 1-•'!• f i 1 J:: II •I tPF dl mf aoc-III f :a' ••.I- -:|:': m ; f'j : x j4 :-"l T I X i-l-il 1 "1 If :":[, .1 :i T:: i i HI l"!i i : j Tt X : 1 4 . f! o fjj g p igs ;7.:r i i f : ' \'\ ll- -;| i ; i-i-rr • : .j:' j:: : i . II: •lr E:ff -' '-f :| 1 -\ '• 1 .: :. J-- -i- f jx' ;t ':} i : - t 111 •ii 'I'l'F!-T -i I- - - I; j. ' -1 •i i ; - i t : : -i. !.i jl -$; -Ti -; Tf : : : :[:;!! T f:; -H- -Ti-i I f : | •I-i. . #: - - |: r - - - : x: Tff •i ; 1 JJ i ! y •-! T :" • -! $ ] if - i : .] j •F -F nT : ;i • -M-TP ft 1 T •F| 1 •$: :x:f-t .44 - I-: l l ' m :jl" "!T Th j:::: -H- -rT: ' 1 r -1-"-T - . i - i . . . i--1 FI t b l fi I ll-i jj:jx |:: ' "it -•i - 1 :i ij "hr \ mv . . . .l.j-: : . .!:;•. j' • | .) . . . f .::(: ::!l -fel ;i- : ± -i- -i i-i : | 1 : : :l: : |il -DJ i ±i. X i : fi 3 2oo 4 0 O Boo (000 \ZOO 1460 1600 leoo TIME - DAYS F i g . 11 Extended S e t t l e m e n t r e c o r d r e l a t e d t o s i g n i f i c a n t events, formed by combining, the r a t i o n a l i z e d s e t t l e m e n t curve f o r gauge 7 w i t h the s e t t l e m e n t r e c o r d of the j o i n t on the St a c k e r R a i l c l o s e s t t o the l o c a t i o n of gauge 7. •49. of c o a l . This development i s c l e a r l y r e f l e c t e d by the a c c e l e r a t e d settlement o c c u r r i n g a f t e r t h a t time. The extended settlement record c o r r e l a t e s very w e l l w i t h the l o a d i n g h i s t o r y of the t e r m i n a l area. Because the loadi n g was not instantaneous, but v/as spread over a. long p e r i o d of time, i t i s not p o s s i b l e t o make accurate estimates of the time t o 90 percent c o n s o l i d a t i o n . The settlement r e c o r d does i n d i c a t e t h a t the settlement due t o the f i l l was about 90 percent complete by 450 days a f t e r the i n s t a l l a t i o n of settlement gauge 7. I n s t a l l a t i o n , maintenance and monitoring of settlement gauges i s the only r e l i a b l e method of determining the settlement h i s t o r y . Any p r o j e c t on the banks which i n v o l v e s any type of pr e l o a d should be very c a r e f u l l y monitored and the d e c i s i o n t o remove the prel o a d should be based p r i m a r i l y on the settlement vs. time curves d e r i v e d from the settlement gauge readings. PROBABLE EARTHQUAKE ACCELERATIONS The N a t i o n a l B u i l d i n g Code of Canada d i v i d e s Canada i n t o seismic zones based on the a c c e l e r a t i o n amplitude which has a 1 i n 100 p r o b a b i l i t y of being exceeded i n any given year. There are f o u r zones d e f i n e d , ranging from zone 0, f o r a c c e l e r a t i o n amplitudes l e s s than 1 percent of g r a v i t y , to zone 3 f o r a c c e l e r a t i o n amplitudes g r e a t e r than 6 percent of g r a v i t y . Roberts Bank and Sturgeon Bank are l o c a t e d i n a zone 3 r e g i o n and p o s s i b l e seismic a c t i v i t y must be one of the design parameters f o r a p r o j e c t on the banks. Dr. W. Mil n e of the V i c t o r i a Geophysical Observatory prepared, on request, an estimate of expected a c c e l e r a t i o n s w i t h c e r t a i n r e t u r n periods f o r a s i t e near Roberts Bank. The earthquake catalogue f o r t h i s r e g i o n l i s t s 2443 e a r t h -quakes f o r the p e r i o d 1899 t o 1970 i n c l u s i v e . C a l c u l a t i o n s i n d i c a t e t h a t 42 of these earthquakes could have been f e l t a t Roberts Bank. Table 2 l i s t s the date, e p i c e n t r a l d i s t a n c e , magnitvide and expected maximum a c c e l e r a t i o n a t the banks f o r each of the 42 earthquakes. An extreme value s t a t i s t i c a l a n a l y s i s was a p p l i e d to the 42 events l i s t e d i n Table 2, and Table 2 H i s t o r i c a l Earthquakes Date Day/Month/Year Distance Magnitude m i l e s R i c h t e r Max. Expected A c c e l e r a t i o n . Percent G 4/ 9/1899 10/ 9/1899 9/10/1900 17/ 3/1904 11/ 1/1909 29/ 9/1911 18/ 8/1915 3/10/1915 22/ 2/1916 1/ 7/1917 23/12/1917 6/12/1918 10/10/1919 24/ 1/1920 12/ 2/1923 7/ 9/1926 1/11/1926 4/12/1926 8/ 5/1927 26/ 5/1929 18/ 4/1931 13/11/1939 29/11/1943 15/ 2/1946 23/ 6/1946 17/ 7/1946 13/ 4/1949 22/ 8/1949 30/ 3/1954 5/ 8/1954 20/11/1954 1063 1010 1063 111 20 25 85 649 29 227 227 158 72 22 20 38 243 39 38 380 44 110 44 119 99 270 128 543 8 13 12 8.2 8.6 8.2 6.0 5.6 4.3 5.5 7.75 4.3 6.4 6.5 7.0 5.5 5.0 4.3 5.5 6.6 4.3 5.5 7.0 4.3 5.75 5.0 5.75 7.30 6.50 7.0 8.0 3.0 3.0 3.0 0 0 0 0 4 0 0 0 0 0 0 1 0 2 1 1 0 0 1 0 0 0 0 0 4 0 1 0 0 0 0 51. Max. Expected Date Distance Magnitude A c c e l e r a t i o n Day/Month/Year mi l e s R i c h t e r Percent G 26/ 4/1955 13 3.0 0 26/ 1/1956 57 5.0 0 21/12/1956 328 6.75 0 10/ 7/1958 869 7.9 0 4/ 9/1959 18 3.4 0 14/ 7/196 4 24 4.6 1 29/ 4/1965 118 6.5 1 1/11/1966 21 3.5 0 25/ 5/1967 27 4.1 0 20/ 6/1967 8 3.6 1 14/ 2/1969 8 4.2 2 the a n a l y s i s y i e l d e d the maximum probable ground surf a c e a c c e l e r a t i o n s f o r c e r t a i n r e t u r n periods along w i t h the 99 and 95 percent confidence l i m i t s f o r the same r e t u r n p e r i o d s . The r e t u r n p e r i o d i s the i n v e r s e of the s t a t i s t i c a l probab-i l i t y t h a t the given maximum probable ground surface a c c e l e r a t i o n w i l l be exceeded i n any given year. The r e s u l t s of the a n a l y s i s f o r the s i t e near Roberts Bank are given i n Table 3. Table 3 Earthquake P r o b a b i l i t y A n a l y s i s r n P e r i o d A c c e l e r a t i o n 95% Conf. L i m i t s 99% Conf . L i m i t s Years Percent G Percent G Perc ent G 3. 0.30 0 .28 0.34 0.27 0.35 10. 1.03 0 .90 1.18 0.85 1.25 30. 3.36 2 .80 4.02 2.60 4.34 50. 5.86 4 .79 7.18 4.40 7.81 100. 12.54 9 .93 15.83 9.01 17.46 200. 26.90 20 .66 35.04 18.48 .39.17 300. 42.08 31 .71 55.83 28.15 62.88 1000. 158.98 113 .34 223.01 98.29 257.14 F i g . 12 shows the i n f o r m a t i o n contained i n Table 3 p l o t t e d on Log-Log paper. An i n s p e c t i o n of the a c c e l e r a t i o n s and the confidence l i m i t s r e v e a l s t h a t the confidence l i m i t s F i g . 12 P r e d i c t e d Maximum Ground S u r f a c e A c c e l e r a t i o n s f o r V a r i o u s Return P e r i o d s f o r Roberts Bank, from an a n a l y s i s by Dr. M i l n e . became f a i r l y d i v e r g e n t as the Return P e r i o d approaches and exceeds the p e r i o d of r e c o r d (72) years. This i s t o be expected i n a s t a t i s t i c a l a n a l y s i s when the behavior of a n a t u r a l event i s being e x t r a p o l a t e d beyond the time span of the i n p u t data. As the p e r i o d of record becomes longer, improvement can be made t o both the a c c e l e r a t i o n p r e d i c t i o n s and the 95 and 99 percent confidence l i m i t s ; however, i t w i l l take s u b s t a n t i a l i n c r e a s e s i n the p e r i o d of r e c o r d t o produce a s i g n i f i c a n t change i n the a n a l y s i s . LIQUEFACTION POTENTIAL OF THE BANKS L i q u e f a c t i o n In the l a b o r a t o r y and i n the f i e l d , s a t u r a t e d g r a n u l a r s o i l s from medium sands t o f i n e sandy s i l t s have been observed to l o s e t h e i r shear stren g t h when subjected t o c y c l i c shear s t r e s s e s under c o n d i t i o n s where the drainage i s impeded or prevented. The equation f o r the shear s t r e n g t h of a co h e s i o n l e s s s o i l i s : T = («r- u) tan 0 ... (6-1) where f = shear s t r e n g t h , cr = t o t a l normal (confining), s t r e s s , u = pore water pressure, 0 = angle of i n t e r n a l f r i c t i o n of the s o i l . I f the drainage i s impeded the c y c l i c shear s t r e s s e s cause a r i s e i n pore water pressure, and the pore water pressure may continue t o r i s e w i t h each c y c l e of s t r e s s u n t i l the pore water pressure equals the t o t a l c o n f i n -i n g s t r e s s . From equation (6-1) i t can be seen t h a t a t t h i s p o i n t the s o i l w i l l have zero shear s t r e n g t h , and i t i s t h i s c o n d i t i o n of zero shear s t r e n g t h which i s known as l i q u e f a c t i o n . The c l a s s i c example of l i q u e f a c t i o n i n the f i e l d under c y c l i c l o a d i n g occurred i n N i i g a t a , Japan, during the 1964 earthquake. N i i g a t a i s l o c a t e d on an a l l u v i a l f l o o d p l a i n and d e l t a on the North West coast of Honshu I s l a n d . The c i t y i s founded on g e o l o g i c a l l y recent f l u v i a l d e p o s i t s which i n c l u d e e x t e n s i v e d e p o s i t s of loose sand w i t h standard penet-r a t i o n t e s t blow counts of l e s s than 10 ( K i s h i d a , 1965) . The water t a b l e i s very near the surface throughout t h i s area, r e s u l t i n g i n s a t u r a t e d d e p o s i t s . On June 16, 1964 an earthquake of magnitude M=7.5 occurred, at an e p i c e n t r a l d i s t a n c e of approximately 32 m i l e s from N i i g a t a , and t h i s earthquake had a recorded maximum ground surface a c c e l e r a t i o n of 0.16g and a d u r a t i o n of 40 seconds (Seedand I d r i s s , 1971). There were many r e p o r t s of phenomena o c c u r r i n g during the N i i g a t a earthquake which can be r e l a t e d to l i q u e f a c t i o n of the foundation s o i l s . Some of the reported phenomena were the appearance of geysers spouting water and sand i n t o the a i r and forming sand cones (sudden r e l e a s e of b u i l t up pore water p r e s s u r e ) ; b u r i e d tanks, p i p e -l i n e s and other b u r i e d o b j e c t s f l o a t i n g to the ground s u r f a c e ( s o i l behaving as a dense l i q u i d ) ; and b u i l d i n g s s e t t l i n g and r o t a t i n g i n t o the s o i l although s u f f e r i n g l i t t l e s t r u c t u r a l damage ( l o s s of bearing c a p a c i t y from reduced shear strength) ( K i s h i d a , 1965; Evans, 1964). I t was observed t h a t some areas of N i i g a t a had exten-s i v e l i q u e f a c t i o n and foundation f a i l u r e s w h i l e o ther areas had l i t t l e or no evidence of l i q u e f a c t i o n . Ohsaki (1970), K i s h i d a (1965) and others conducted i n v e s t i g a t i o n s of the i n s i t u s o i l c o n d i t i o n s before and a f t e r the earthquake i n an attempt to e x p l a i n the d i f f e r e n c e i n l i q u e f a c t i o n p o t e n t i a l . On the b a s i s of t h e i r s t u d i e s they proposed a number of e m p i r i c a l l i q u e f a c t i o n c r i t e r i a . Standard p e n e t r a t i o n t e s t blow counts represented the most abundant source of sub-surface i n f o r m a t i o n and the e m p i r i c a l c r i t e r i a proposed were based on the N-value. E m p i r i c a l L i q u e f a c t i o n C r i t e r i a Of the numerous e m p i r i c a l c r i t e r i a proposed a f t e r the N i i g a t a earthquake as i n d i c a t i o n s of whether a s i t e w i l l or w i l l not l i q u e f y d u r i n g earthquake l o a d i n g , the c r i t e r i o n proposed by Ohsaki (1970) i s perhaps the s i m p l e s t . Ohsaki's observations of s i t e s which d i d and d i d not l i q u e f y at N i i g a t a , and the N-values of the s o i l s a t these s i t e s , l e d him t o propose t h a t the r e l a t i o n s h i p N-2z (where N = standard p e n e t r a t i o n t e s t blow count and z = depth i n meters) r e p r e s -ents a c r i t i c a l c o n d i t i o n and t h a t l i q u e f a c t i o n of the s o i l s i s p o s s i b l e "during an earthquake of a c o n s i d e r a b l e i n t e n s i t y " i f the N-values are l e s s than t h i s c r i t i c a l v a l u e . This c r i t e r i o n i s shown i n F i g . 13 as a s o l i d l i n e from 0 t o 15 meters depth and as a dashed l i n e from 15 t o 20 meters depth. Ohsaki proposed h i s c r i t e r i o n f o r d e p o s i t s of 15 t o 20 meters depth; and i t has been shown dashed from 15 to 20 meters t o i n d i c a t e t h a t t h i s i s the extreme l i m i t f o r which i t was proposed. The Ohsaki c r i t e r i o n was used i n e v a l u a t i n g the s i t e of a paper manufacturing p l a n t at Hachinohe as a guide to the necessary d e n s i f i c a t i o n of the foundation s o i l s . F i g . 13 Comparison of the Ohsaki and K i s h i d a l i q u e f a c t i o n c r i t e r i a The s o i l s i n qu e s t i o n were very loose, c l e a n , saturated medium and f i n e sands from the surface t o 5 meters depth. V i b r o f l o t a t i o n was used t o d e n s i f y the s o i l , at the l o c a t i o n of important b u i l d i n g s and i n s t a l l a t i o n s , to meet.the Ohsaki c r i t e r i o n . One and a h a l f years a f t e r c o n s t r u c t i o n was completed, the May 16, 1968 Tokachioki earthquake occurred. The earthquake had a magnitude of M=7-8; had an e p i c e n t e r approximately 112 miles from the s i t e ; and a reported maxi-mum ground sur f a c e a c c e l e r a t i o n of 0.21g w i t h a d u r a t i o n of 45 seconds (Seed and I d r i s s , 1971). There was extensive l i q u e f a c t i o n of the untreated areas but only minor s e t t l e -ments and damage of the t r e a t e d areas, which i n d i c a t e d t h a t the Ohsaki c r i t e r i o n had some m e r i t . Using pre-earthquake and post-earthquake subsurface t e s t data, K i s h i d a (1965) s t u d i e d the s o i l s c o n d i t i o n s under s t r u c t u r e s which had no damage, l i g h t damage and heavy damage durin g the N i i g a t a earthquake. K i s h i d a concluded th a t the boundary between l i g h t and heavy damage was an N-value of 15 from 0-5 meters, an N-value of 25 from 10-15 meters and a l i n e a r i n c r e a s e of N-value from 15 to 25 between depths 5 and 10 meters. The K i s h i d a c r i t e r i o n i s a l s o shown i n F i g . 13 and i t . terminates a t 15 meters depth si n c e K i s h i d a has not proposed a c r i t e r i o n f o r s o i l s below 15 meters. The a v a i l a b l e subsurface data f o r Roberts and Sturgeon Banks c o n s i s t p r i m a r i l y of the r e s u l t s of standard penetration t e s t s made i n 37 boreholes which were chosen t o be broadly r e p r e s e n t a t i v e of the subsurface s o i l c o n d i t i o n s of the e n t i r e banks area. The t e s t r e s u l t s are p l o t t e d i n Pig.l4 w i t h Depth ( i n feet) as the or d i n a t e and N-value as the a b s c i s s a . The column on the extreme l e f t of the N-value a x i s , l a b e l e d P ( f o r push), represented attempted SPT t e s t s f o r which the weight of the d r i l l rods was s u f f i c i e n t to cause 1 f o o t of p e n e t r a t i o n w i t h no blows of the hammer, which i n d i c a t e s very loose s o i l . The numbers l o c a t e d on the graph represent the t o t a l number of SPT t e s t s made a t th a t p a r t i c u l a r depth which had t h a t N-value. The Ohsaki and K i s h i d a c r i t e r i a i l l u s t r a t e d i n F i g . 13 have been superimposed on F i g . 14. I t i s evident t h a t v i r t u a l l y a l l the banks sediments l i e on the heavy damage s i d e of the K i s h i d a c r i t e r i o n . I n s p e c t i o n of the Ohsaki c r i t e r i o n i n d i c a t e s t h a t below 20 f e e t depth almost a l l the s o i l s have N-values l e s s than the c r i t i c a l N-values and above 20 f e e t depth more than h a l f the s o i l s have N-values. l e s s than the c r i t i c a l N-values. From t h i s one can conclude t h a t i f the banks were subjected to 40 to 45 seconds of earthquake l o a d i n g v/ith maximum ground surface a c c e l e r a t i o n s i n the range of 0.16g to 0.21g then extensive l i q u e f a c t i o n i s i n d i c a t e d . A n a l y t i c a l L i q u e f a c t i o n P o t e n t i a l In 1971 Seed and I d r i s s proposed a s i m p l i f i e d a n a l y -t i c a l procedure f o r e v a l u a t i n g the l i q u e f a c t i o n p o t e n t i a l of a sat u r a t e d cohesionless s o i l . The proposed method a p p r o x i -mates the c y c l i c shear s t r e s s e s induced i n the s o i l by e a r t h -quake l o a d i n g and compares those s t r e s s e s to the r e s u l t s of 59. -p Q) EH PM W Q N - V A L U E F i g . 14 Cumulative r e s u l t s o f Standard P e n e t r a t i o n T e s t s from 3 7 bore h o l e s on the banks. 6 0 . laboratory c y c l i c shear tests to obtain an approximate estimate of the l i q u e f a c t i o n p o t e n t i a l of the i n s i t u s o i l . The approximation of the c y c l i c shear stresses induced i n the s o i l involves converting an earthquake acceleration record, which i s characterized by i t s maximum acceleration and magnitude, into an equivalent number of cycles of aver-age c y c l i c shear stress for any point i n the s o i l column. This average shear stress,Zav, i s defined as: T a v ^ 0 . 6 5 Xh a 'r, • ' ... ( 6 - 2 ) g where a = maximum ground surface acceleration, 0.65 = max ^ fac t o r to approximate equivalent average acceleration, y = t o t a l u n i t weight of s o i l , h = depth, g = acceleration of gravity, and r ^ = reduction f a c t o r to account for the deform-able nature of the s o i l column. I t has been shown (Finn, Pickering and Bransby, 1971) that there i s a unique r e l a t i o n s h i p between the i n i t i a l e f f e c t -ive stress r a t i o ( r a t i o o f the c y c l i c shear stress to the i n -i t i a l v e r t i c a l e f f e c t i v e stress) and the number of cycles of stress to i n i t i a l l i q u e f a c t i o n for a given s o i l a t a given r e l a t i v e density, regardless of the magnitude of the stresses. The second part of the Seed and I d r i s s s i m p l i f i e d analysis involves determining the i n i t i a l e f f e c t i v e stress r a t i o which w i l l cause i n i t i a l l i q u e f a c t i o n i n the same number of cycles by comparing the i n s i t u s o i l to laboratory tested s o i l s and applying appropriate correction f a c t o r s . There are two basic corrections which must be made t o the laboratory data, providing the number of cycles of stress to f a i l u r e f o r the laboratory specimen are the same as f o r the i n s i t u analysis, and the s o i l s themselves are s i m i l a r . 61. The most i m p o r t a n t c o r r e c t i o n t o make i s t o a l l o w f o r t h e d i f f e r e n t i n i t i a l s t r e s s c o n d i t i o n s w h i c h may e x i s t b e t w e e n t h e l a b o r a t o r y s p e c i m e n a n d t h e i n s i t u s o i l . I f t h e l a b -o r a t o r y t e s t s w e r e c o n d u c t e d i n a s i m p l e s h e a r a p p a r a t u s t h e n t h e i n i t i a l c o n f i n i n g s t r e s s e s w e r e a n a l o g o u s t o t h e i n i t i a l i n s i t u s t r e s s e s a n d no c o r r e c t i o n i s n e c e s s a r y . I f , h o w e v e r , t h e l a b o r a t o r y t e s t s w e r e c o n d u c t e d i n a t r i a x i a l c o m p r e s s i o n a p p a r a t u s t h e n t h e i n i t i a l c o n f i n i n g s t r e s s e s o f t h e l a b o r a t o r y s p e c i m e n w e re s i g n i f i c a n t l y d i f f e r e n t t h a n t h o s e o f t h e i n s i t u s o i l . I n t h e t r i a x i a l c e l l t h e i n i t i a l c o n f i n i n g s t r e s s i s t h e same f o r any o r i e n t a t i o n w h e r e a s f o r t h e i n s i t u s o i l t h e i n i t i a l h o r i z o n t a l c o n f i n i n g s t r e s s i s u s u a l l y o n l y a f r a c t i o n ( a b o u t 0.3) o f t h e i n i t i a l v e r t i c a l c o n f i n i n g s t r e s s . S e e d a nd I d r i s s i n d i c a t e t h a t t h e a p p r o -p r i a t e c o r r e c t i o n f a c t o r v a r i e s w i t h t h e r e l a t i v e d e n s i t y a n d t h e y h a v e s u g g e s t e d c o r r e c t i o n f a c t o r s o f 0.55 t o 0.68 f o r r e l a t i v e d e n s i t i e s o f 30 t o 80 p e r c e n t , r e s p e c t i v e l y . The o t h e r m a j o r c o r r e c t i o n w h i c h may be n e c e s s a r y i s ; a c o r r e c t i o n f o r any d i f f e r e n c e b e t w e e n t h e i n s i t u r e l a t i v e d e n s i t y a n d t h e r e l a t i v e d e n s i t y a t w h i c h t h e l a b o r a t o r y t e s t s w e r e p e r f o r m e d . S e e d a nd I d r i s s s u g g e s t t h a t t h e a p p r o p r i a t e c o r r e c t i o n f a c t o r i s t h e r a t i o o f t h e i n s i t u r e l a t i v e d e n s i t y o v e r t h e r e l a t i v e d e n s i t y o f t h e l a b o r a t o r y s p e c i m e n . By f o l l o w i n g t h e o u t l i n e d p r o c e d u r e a r e l a t i o n s h i p b e t w e e n t h e maximum g r o u n d s u r f a c e a c c e l e r a t i o n a n d r e l a t i v e d e n s i t y c a n be o b t a i n e d f o r i n i t i a l l i q u e f a c t i o n i n t h e number o f c y c l e s f o r w h i c h t h e a n a l y s i s i s p e r f o r m e d . S e e d and I d r i s s i n c l u d e d p l o t s o f r e p r e s e n t a t i v e v a l u e s o f t h e c o r r e c t i o n f a c t o r s and c y c l i c t r i a x i a l t e s t data to f a c i l i t a t e the use of t h e i r method. The only f a c t o r necessary t o perform t h i s a n a l y s i s f o r the banks sediments which has not yet been di s c u s s e d i s the number of s i g n i f i c a n t s t r e s s c y c l e s to use. An i n s p e c t i o n of the earthquake data i n Table 2 i n d i c a t e s t h a t earthquakes i n excess of magnitude M=8.0 have occurred close enough to have been f e l t a t the banks, and t h a t the h i g h e s t recorded a c c e l e r a t i o n , .04g, was reached twice dur i n g the 72 year p e r i o d from earthquakes of magnitude M=5-6 and M=7.3- Table 4 shows the number of s i g n i f i c a n t s t r e s s c y c l e s a s s o c i a t e d w i t h d i f f e r e n t magnitudes of earthquake presented by Seed and I d r i s s (1971). Comparing the magnitudes of the earthquakes Table 4 Earthquake Duration Number of Earthquake Magnitude S i g n i f i c a n t S t r e s s Cycles R i c h t e r Nc 7.0 10 7.5 20 8.0 30 which have p r e v i o u s l y occurred c l o s e enough t o have been f e l t a t the banks w i t h the corresponding number of s i g n i f i c a n t s t r e s s c y c l e s i n d i c a t e s t h a t from 10 to 30 c y c l e s of s i g n i f i -cant s t r e s s could be expected i n the event of an earthquake which c o u l d a f f e c t the banks. The Seed and I d r i s s s i m p l i f i e d procedure was used t o evaluate the l i q u e f a c t i o n p o t e n t i a l of the banks sediments. The g r a i n s i z e d i s t r i b u t i o n curves presented i n F i g . 4 i n d i c a t e t h a t a mean g r a i n s i z e , D r n, of 0.2 mm. would be J u r e p r e s e n t a t i v e of the banks sediments. From the data presented by Seed and I d r i s s , the corresponding values of i n i t i a l s t r e s s r a t i o of 0.24 and 0.21, f o r 10 and 30 c y c l e s to i n i t i a l l i q u e f a c t i o n r e s p e c t i v e l y , where chosen. The water t a b l e was assumed to be at the surface and the a n a l y s i s was performed f o r a depth of 20 f e e t , which i s approximately the c r i t i c a l depth when the water t a b l e i s near the s u r f a c e . Values f o r the c o r r e c t i o n f a c t o r s were taken from the p l o t s presented by Seed and I d r i s s . F i g . 15 shows the c a l c u l a t e d i n i t i a l l i q u e f a c t i o n l i n e s f o r 10 c y c l e s and 30 c y c l e s of s t r e s s , based on the above c o n d i t i o n s , p l o t t e d on a graph of maximum ground surf a c e a c c e l e r a t i o n v s . r e l a t i v e d e n s i t y . A l s o shown are the N-values corresponding t o 40, 60 and 80 percent r e l a t i v e d e n s i t y as determined by the Gibbs and H o l t z and the Baazara c o r r e l a t i o n curves. The borehole data has i n d i c a t e d t h a t there are extensive areas of the banks sediments which have a r e l a t i v e d e n s i t y on the order of 40 percent. The Seed and I d r i s s s i m p l i f i e d procedure i n d i c a t e s t h a t 10 c y c l e s of s t r e s s w i t h a maximum ground surface a c c e l e r a t i o n of 0.075g o r 30 c y c l e s of s t r e s s w i t h a maximum ground surface a c c e l e r a t i o n of 0.065g would be s u f f i c i e n t to cause i n i t i a l l i q u e f a c t i o n of these s o i l s a t 20 f e e t depth. I t i s common p r a c t i c e to use the earthquake a c c e l e r a -t i o n which has a 1 i n 100 annual p r o b a b i l i t y of being exceeded as the design a c c e l e r a t i o n f o r e ngineering works. The extreme value s t a t i s t i c a l a n a l y s i s prepared by Dr. Mil n e I O H EH a w u a s JO 20 3 0 SPT Gibbs & ""46 SO 60 TO So" RELATIVE DENSITY - pe r c e n t H o l t Z g to —i 18 loo .SPT-Bazaraa ~so_ 21 3 8 F i g . 15 R e s u l t s of the Seed and I d r i s s S i m p l i f i e d l i q u e f a c t i o n a n a l y s i s . Assumptions - Depth = 2 0 f t . , D^Q = 0.2 mm, water t a b l e a t s u r f a c e . ov gave a value of 0.125g as the maximum ground surf a c e a c c e l e r a t i o n f o r rock or f i r m s o i l w i t h a 1 i n 100 annual p r o b a b i l i t y of being exceeded. The response of the sediment column to the bedrock motions can modify those motions i n such a manner t h a t the ground surface a c c e l e r a t i o n s can e i t h e r be a m p l i f i e d or diminished (Seed,1969). I t i s necessary t o be aware t h a t a m p l i f i c a t i o n i s p o s s i b l e s i n c e t h i s represents the most dangerous s i t u a t i o n s ; however, s i n c e t h i s a n a l y s i s i s based on g e n e r a l i z e d s o i l c o n d i t i o n s and g e n e r a l i z e d t e s t r e s u l t s from numerous sources and s o i l s , the r e s u l t s of the Seed and I d r i s s s i m p l i f i e d procedure w i l l be d i s cussed i n terms of the a c c e l e r a t i o n s p r e d i c t e d by Dr. Mil n e . F i g . 15 i n d i c a t e s t h a t a r e l a t i v e d e n s i t y of g r e a t e r than 61 percent would be necessary t o withstand 10 c y c l e s and gr e a t e r than 67 percent to withstand 30 c y c l e s of s t r e s s w i t h a maximum ground surface a c c e l e r a t i o n of 0.125g without l i q u e f y i n g . The Seed and I d r i s s s i m p l i f i e d procedure i n d i c a t e s t h a t e x t e n s i v e areas of the banks could l i q u e f y i f subjected to 10 c y c l e s of s t r e s s w i t h a maximum ground surface a c c e l e r a t i o n of 0.125g. Based on the Baazara i n t e r p r e t a t i o n of the N-values, some areas of Sturgeon Bank have s u f f i c i e n t r e l a t i v e d e n s i t y t o withstand 10 and p o s s i b l y even 30 c y c l e s of the s t r e s s d e s c r i b e d . However, when the p o s s i b i l i t y of a m p l i f i c a t i o n i s considered then even those areas have some p r o b a b i l i t y of l i q u e f y i n g . I f a development i s contemplated f o r the banks then a l i q u e f a c t i o n p o t e n t i a l a n a l y s i s should be undertaken f o r the 66. s p e c i f i c s i t e chosen. The f i r s t s tep i s to undertake a d e t a i l e d s u b s u r f a c e i n v e s t i g a t i o n and sampling program which would p r o v i d e a r e a s o n a b l e estimate of the e x i s t i n g i n s i t u r e l a t i v e d e n s i t y and would y i e l d samples s u i t a b l e f o r t e s t i n g i n t r i a x i a l c e l l s , or o t h e r apparatus s u i t a b l e f o r c o n t r o l l e d c y c l i c l o a d i n g t e s t s . The o b j e c t o f the t e s t i n g program i s to produce a f a m i l y of curves which r e l a t e the shear s t r e s s r a t i o ( r a t i o of shear s t r e s s t o c o n f i n i n g s t r e s s ) , the c y c l e s of s t r e s s t o l i q u e f a c t i o n and the r e l a t i v e d e n s i t y . The t e s t i n g program c o u l d c o n s i s t of r u n n i n g t e s t s t o l i q u e f a c t i o n f o r v a r i o u s r e l a t i v e d e n s i t i e s a t a chosen shear s t r e s s r a t i o , and r e p e a t i n g the s e r i e s a t enough shear s t r e s s r a t i o s to produce the f a m i l y of curves d e s i r e d . A p r e f e r a b l e form of p r e s e n t a t i o n would be as a p l o t w i t h c y c l i c shear s t r e s s r a t i o as the o r d i n a t e and r e l a t i v e d e n s i t y as the a b s c i s s a and showing the curves f o r d i f f e r e n t chosen c y c l e s of s t r e s s to i n i t i a l l i q u e f a c t i o n . The b a s i c l a b o r a t o r y d a t a must then be m o d i f i e d to account f o r the d i f f e r e n c e i n the i n i t i a l mean c o n f i n i n g s t r e s s between the t e s t apparatus and the i n s i t u s o i l . I f the t e s t s were performed i n a simple shear d e v i c e then t h i s step i s not n e c e s s a r y . F i n n , P i c k e r i n g and Bransby (1971) p r e s e n t e d a p r e c i s e r e l a t i o n s h i p between the s t r e s s r a t i o s of the c y c l i c t r i a x i a l t e s t and the c y c l i c simple shear t e s t (which i s analagous t o i n s i t u s o i l under e a r t h -quake l o a d i n g ) ; however, as c e r t a i n approximations and assumptions e n t e r i n t o the other p o r t i o n s of the l i q u e f a c t i o n p o t e n t i a l a n a l y s i s , the c o r r e c t i o n f a c t o r s , C^, p r e s e n t e d by Seed and I d r i s s would be adequate f o r d a t a c o n v e r s i o n . Once the b a s i c data has been p l o t t e d i n the d e s i r e d form, an a n a l y s i s s i m i l a r to the b a s i c steps of the Seed and I d r i s s s i m p l i f i e d procedure can be c a r r i e d out, or a more r i g o r o u s a n a l y s i s p o s s i b l y using computer programs can be run. For the s i m p l i f i e d approach the e q u i v a l e n t average shear s t r e s s , " 2 " a v i s c a l c u l a t e d (as per equation (6-2) ) from the maximum design a c c e l e r a t i o n . I n c l u s i o n of the f a c t o r r ^ i s not recommended because a value f o r r , i s r a t h e r u n c e r t a i n s i n c e the a c t u a l response of the s o i l column to earthquake a c c e l e r a t i o n s i s u n c e r t a i n . I t i s c o n s e r v a t i v e t o exclude r^,. For any depth of i n t e r e s t , and knowing the p o s i t i o n of the water t a b l e , the e q u i v a l e n t average shear s t r e s s r a t i o , ^V^, can be c a l c u l a t e d ^ o and the p l o t s of s t r e s s r a t i o vs. r e l a t i v e d e n s i t y can be entered d i r e c t l y f o r an estimate of the l i q u e f a c t i o n p o t e n t i a l . One form of more rig o r o u s a n a l y s i s pointed out by Seed (1969), i s to model the s o i l column i n a computer s i m u l a t i o n , feed i n v a r i o u s earthquake records a t the base of the s o i l , and observe the s o i l response a t v a r i o u s depths of i n t e r e s t . The shear s t r e s s vs. time record at any p o i n t can then be converted i n t o c y c l e s of e q u i v a l e n t average shear s t r e s s , and again the shear s t r e s s r a t i o can be c a l c u l a t e d and the data p l o t s entered d i r e c t l y . The above d e t a i l e d t e s t i n g program and subsequent a n a l y s i s would be expensive to perform, however the apparent l i q u e f a c t i o n p o t e n t i a l of the banks' sediments i s h i g h enough t h a t , f o r a p r o j e c t which represents a s u b s t a n t i a l c a p i t a l investment and has a long p r o j e c t e d l i f e - s p a n , t h i s form of a n a l y s i s should be considered. 68. SUBAQUEOUS SLOPE STABILITY The two b a s i c forms of i n s t a b i l i t y which can a f f e c t subaqueous slopes are e r o s i o n a l i n s t a b i l i t y and mass wasting or slumping. These processes can a c t independently of one another or can be i n t e r r e l a t e d . A mass wasting can erode ( t u r b i d i t y c u r r e n t s ) or i t can c r e a t e c o n d i t i o n s which are more s u s c e p t i b l e t o e r o s i o n than the c o n d i t i o n s which e x i s t e d p r i o r to the mass wasting. E r o s i o n can a l t e r an i n i t i a l l y s t a b l e slope to the p o i n t where mass wasting i s suddenly triggered» E r o s i o n a l I n s t a b i l i t y F i g . 3 shows a number of areas of the f o r e s l o p e which recent surveys have i n d i c a t e d are r e t r e a t i n g . There i s one area near the center of Sturgeon Bank, one area near the center of Roberts Bank and one area j u s t north of Westshore Terminals bulk l o a d i n g f a c i l i t y . These areas of r e t r e a t represent areas where e r o s i o n i s i n excess of d e p o s i t i o n ; c r e a t i n g a net l o s s of sediments at these p o i n t s . Luternauer and Murray (1973) 6 estimate a volume l o s s of 294 x 10 cubic f e e t of sediments f o r the r e t r e a t i n g s e c t i o n s of Roberts Bank between October 1968 to A p r i l 1972. This estimate i s based on hyposgraphic p r o f i l e s taken a t the times s t a t e d , 3 1/2 years a p a r t . R e l i a b l e sounding records do not cover a long enough time span to i n d i c a t e whether or not areas of r e t r e a t have been a s s o c i a t e d w i t h the d e l t a f o r a long p e r i o d of time. I f e r o s i o n had been a c t i v e at s p e c i f i c l o c a t i o n s along the f o r e -slope of the d e l t a f o r a longer p e r i o d of time then the l e a d i n g edge of the d e l t a would have developed a c o n f i g u r a t i o n which 69. would r e f l e c t t h i s c o n d i t i o n . The l e a d i n g edge, as expressed by the subaqueous depth, contour, would be i n d e n t e d a t l o c a t i o n s o f consistent, e r o s i o n . The subaqueous contours o f the F r a s e r R i v e r D e l t a are remarkably smooth and r e g u l a r , o t h e r than o f f the mouth of major d i s t r i b u t a r i e s , w i t h no i n d e n -t a t i o n s c o n s i s t e n t w i t h long term e r o s i o n . There are two p l a u s i b l e e x p l a n a t i o n s o f the above o b s e r v a t i o n s which are worth mentioning. One e x p l a n a t i o n i s t h a t the e r o s i o n i s a long term p r o c e s s , the l o c a t i o n o f which i s c o n s t a n t l y s h i f t i n g i n such a manner t h a t the net e f f e c t over l o n g p e r i o d s of time i s to maintain, the r e g u l a r , smooth advance of the d e l t a . The o t h e r e x p l a n a t i o n i s t h a t the e r o s i o n c o u l d be a v e r y r e c e n t event which has not y e t been r e f l e c t e d by n o t i c a b l e changes i n the depth c o n t o u r s . I f i t i s a r e c e n t event i t c o u l d be r e l a t e d t o some n a t u r a l geomorphic phenomenon but i s more probably r e l a t e d to the i n f l u e n c e of man. In v e r y r e c e n t g e o l o g i c time man has s t a b i l i z e d the main channels of the r i v e r and b u i l t a number of causeways out onto the banks. Such a c t i v i t y may have upset the balance of some p r e v i o u s l y s t a b l e geomorphic p r o c e s s ( e s ) , t r i g g e r i n g the p r e s e n t e r o s i o n * I t i s of v i t a l i n t e r e s t t o o b t a i n a d e t a i l e d under-s t a n d i n g of the e r o s i o n and the c o n t r o l l i n g parameters which determine where the e r o s i o n w i l l occur and a t what r a t e . There i s i n s u f f i c i e n t data a v a i l a b l e a t t h i s time t o a l l o w any c o n c l u s i o n s beyond the c o n c l u s i o n t h a t e r o s i o n i s p r e s e n t l y t a k i n g p l a c e . A p r o j e c t can be p r o t e c t e d from e r o s i o n by p l a c i n g an e r o s i o n r e s i s t a n t m a t e r i a l over the 7 0 . erodable m a t e r i a l s . When the o n l y i n f o r m a t i o n a v a i l a b l e i s t h a t e r o s i o n i s t a k i n g p l a c e then the e r o s i o n r e s i s t a n t m a t e r i a l must be p l a c e d by i n t u i t i o n and a l a r g e f a c t o r o f s a f e t y may s t i l l be inadequate. With a knowledge o f the parameters c o n t -r o l l i n g the e r o s i o n , the f a c t o r of s a f e t y can be reduced and a l t e r n a t e p o s s i b i l i t i e s such as a c t u a l l y c o n t r o l l i n g the l o c a t i o n o f e r o s i o n can be c o n s i d e r e d . Mass Wasting Mass wasting i s the downslope movement of a mass o f m a t e r i a l as opposed t o e r o s i o n which i s a g r a i n by g r a i n type of p r o c e s s . The volume o f m a t e r i a l i n v o l v e d i n mass wasting ranges from a few c u b i c yards of m a t e r i a l t o i n excess o f a b i l l i o n c u b i c yards of m a t e r i a l . The movement o f the m a t e r i a l can be a sudden a c c e l e r a t i n g downslope rus h , or i t can be a slow g r a d u a l and even i n t e r m i t t e n t downslope c r e e p i n g o f the m a t e r i a l . In some i n s t a n c e s a s i n g l e event can be i d e n t i f i e d as t r i g g e r i n g the mass wasting and i n o t h e r cases a number of phenomena can be shown t o have grad u a l y c r e a t e d an u n s t a b l e c o n d i t i o n l e a d i n g t o a mass wasting. In many cases the cause of the mass wasting can o n l y be guessed a t . There are a number of phenomena which have been shown t o c o n t r i b u t e t o i n s t a b i l i t y and even to t r i g g e r subaqueous mass wasting. In the absence of any f o r c e s o t h e r than g r a v i t y then the s t a b i l i t y o f the subaqueous s l o p e s f o r a g r a n u l a r m a t e r i a l would be c o n t r o l l e d by the angle of repose of t h a t m a t e r i a l . The e f f e c t o f o t h e r f o r c e s , such as wave p r e s s u r e s , c u r r e n t a c t i o n and earthquake l o a d i n g i s t o reduce the s t a b l e 71. slope angle; t h e r e f o r e the angle of repose i s the upper bound f o r the angle of the subaqueous slopes. C a r r i g y (1970)presented the r e s u l t s of a study cn tha angles of repose of v a r i o u s g r a n u l a r m a t e r i a l s . He d e f i n e s two angles of repose f o r each m a t e r i a l . The " c r i t i c a l angle of repose", a c , i s the maximum slope which a m a t e r i a l can have before i t s l i d e s and the "angle of r e s t " , a^, i s the angle a t which the m a t e r i a l comes to r e s t when the s l i d i n g f i n i s h e s . The c r i t i c a l angle of repose i s always g r e a t e r than the angle of r e s t . The angles of r e s t measured by C a r r i g y f o r three sands i n water were 32.1, 32.4 and 31.4 degrees. As p r e v i o u s l y s t a t e d i n the geology s e c t i o n , the subaqueous slopes average 1 1/2 degrees but exceed 23 degrees i n a few p l a c e s . F i g . 16 shows two s e c t i o n s (the l o c a t i o n s of which are shown on F i g . 17) each p l o t t e d from the 1967 Swan Wooster survey and the 1974 Canadian Hydro-graphic survey c h a r t No. 34 80 " A c t i v e Pass t o B u r r a r d I n l e t . " These s e c t i o n s were chosen to represent the steepest c o n d i t -ions e x i s t i n g other than a t the mouths of major channels. The p l o t s from the two sources were superimposed f o r the purposes of comparison; and although reasonable care was taken i n attempting to l o c a t e the s e c t i o n s i d e n t i c a l l y on the two source c h a r t s , which were drawn to very d i f f e r e n t s c a l e s , the two sets of p r o f i l e s do not c o i n c i d e . Some of the discrepancy may be due t o d e p o s i t i o n and e r o s i o n i n the seven years between the two surveys but i t i s f e l t t h a t most of the discrepancy i s due t o the d i f f i c u l t y of g e t t i n g an exact l o c a t i o n a l match f o r the p l o t t e d s e c t i o n s . ! i i i : •' • ' i 1 i ! M i ! I . i j j. ! | .1. I . . L . L ! . . , . . _ . .. . . , ,-• .• I P r o f i l e plotted If r.OmjSw^ 1967 ;•; ;: P r o f i l e p l o t t e d from ; Canadian Hydrographic Survey chart #3480 -I._L.i_I.'. i i l l l i ! • • • l-l- -!-•-•!• Fig.16 Two Sections of the 'subaqueous Slope Plotted to natural scale ; . i .. . i I ;. to 73 . F i g . 17 L o c a t i o n o f c r o s s s e c t i o n s S and R. The l i n e used f o r the l e a d i n g edge of the banks on t h i s drawing i s the lowest normal t i d e l e v e l . The surveys which have thus f a r been c a r r i e d out on the subaqueous slopes have found no evidence of mass wasting other than the p r e v i o u s l y discussed slump s t r u c t u r e s . Based on the data a v a i l a b l e up to 1962, Mathews and Shepard (196 2) discussed the p o s s i b i l i t y t h a t the deep g u l l i e s found o f f the mouths of the major d i s t r i b u t a r i e s might be r e l a t e d to mass wasting. The g u l l i e s , and i n p a r t i c u l a r the system of g u l l i e s and canyons o f f the mouth of the main channel, run downslope to a maximum depth of 90 fathoms. Mathews and Shepard compared these g u l l i e s to l a n d -s l i d e g u l l i e s o f f the M i s s i s s i p p i D e l t a and c o n t r a s t e d them with the t u r b i d i t y c u r r e n t g u l l y i n the Rhone D e l t a i n Lake Geneva, l e a v i n g the impression t h a t they favor l a n d s l i d i n g as the geomorphic process i n v o l v e d i n the formation of the g u l l i e s . To i l l u s t r a t e t h e i r argument they presented c h a r t s showing subaqueous contours of the M i s s i s s i p p i and Rhone d e l t a s . The c h a r t of the M i s s i s s i p p i D e l t a shows numerous w e l l developed g u l l i e s along w i t h a great confusion of i r r e g u l a r topography throughout the same area as the g u l l i e s . The subaqueous topography of the Rhone R i v e r D e l t a shows prominent levees on the s i d e s of the t u r b i d i t y c u r r e n t g u l l y and i t i s s t a t e d t h a t the g u l l y bottom sediments are sand and the levees are mud (presumably c l a y and s i l t ) . The i r r e g u l a r topography of the M i s s i s s i p p i D e l t a i s c o n s i s t e n t w i t h mass wasting, as the s l i d e s w i l l develop wherever the f a c t o r of s a f e t y drops below 1.0. S l i d e m a t e r i a l t r a v e l l i n g downslope i s probably o f t e n d i v e r t e d i n t o the s l i d e scar of a previous s l i d e and c e r t a i n p r e f e r e n t i a l g u l l i e s 75. become e s t a b l i s h e d a n d . d e e p e n e d . On t h e F r a s e r D e l t a we f i n d . a few w e l l d e v e l o p e d g u l l i e s , b u t t h e c o n f u s i o n o f i r r e g u l a r t o p o g r a p h y i s m i s s i n g . The s u r v e y s made up t o 1962 d i d n o t i n d i c a t e t h e p r e s e n c e o f any l e v e e s on F r a s e r D e l t a g u l l i e s a n d t h e l o n e s a m p l e o b t a i n e d f r o m t h e b o t t o m o f a g u l l y h a s l e s s s a n d t h a n d i d s a m p l e s f r o m t h e a d j a c e n t s l o p e s . E c h o - s o u n d i n g r e c o r d s f r o m a 197^ C a n a d i a n H y d r o g r a p h i c S e r v i c e s u r v e y o f t h e F r a s e r D e l t a s l o p e ( L u t e r n a u e r , 1976) show what a p p e a r t o be s u b d u e d l e v e e s a d j a c e n t t o t h e g u l l i e s c r o s s e d by t h e s u r v e y . The S t r a i t o f G e o r g i a , i s t i d a l , as o p p o s e d t o n o n - t i d a l L a k e G e n e v a , a n d i f t h e g e o m o r p h i c p r o c e s s o p e r a t i n g on t h e s l o p e s o f t h e F r a s e r D e l t a was a t t e m p t i n g t o f o r m l e v e e s , t h e t i d a l c u r r e n t s w o u l d p r o b a b l y i n t e r f e r e w i t h t h i s p r o c e s s . I t i s c o n c e i v a b l e t h a t when t h e r i v e r i s i n f l o o d t h e s a l t w a t e r wedge c o u l d be s p l i t t i n g t h e f l o w s u c h t h a t t h a t p o r t i o n w h i c h . i s d e n s e r t h a n t h e s e a w a t e r f l o w s down-s l o p e , a n d t h a t p o r t i o n w h i c h i s l e s s d e n s e f l o w s o u t on t h e s u r f a c e o f t h e s a l t w a t e r . The p o r t i o n f l o w i n g d o w n s l o p e w o u l d f l o w i n t h e e s t a b l i s h e d g u l l i e s , much l i k e t u r b i d i t y c u r r e n t s , b u t i t c o u l d a l s o i n v o l v e s l i d i n g o f t h e a c c u m u l a t e d g u l l y b o t t o m s e d i m e n t s ( T e r z a g h i , 1 9 6 2). The c o m p o s i t i o n o f t h e s e d i m e n t s a m p l e s p r e v i o u s l y m e n t i o n e d c o u l d be a f u n c t i o n o f t h e t i m e o f s a m p l i n g a n d t h e s e a s o n a l v a r i a t i o n o f t h e F r a s e r R i v e r s e d i m e n t a t i o n . E f f e c t o f S u r f a c e Waves S u r f a c e waves c r e a t e m o v i n g z o n e s o f p r e s s u r e w h i c h a r e a l t e r n a t e l y h i g h e r a n d l o w e r t h a n t h e mean p r e s s u r e a t t h e 76. s e a b e d . H e n k e l (1970) d i s c u s s e d a number o f t h e p o s s i b l e e f f e c t s o f s u r f a c e wave p r e s s u r e z o n e s on t h e s t a b i l i t y o f u n d e r w a t e r s l o p e s . The most r e a d i l y a p p a r e n t e f f e c t i s i l l u s -t r a t e d by F i g . 18 , w h i c h d e p i c t s a f r e e b o d y d i a g r a m o f t h e f o r c e s a c t i n g on a c i r c u l a r a r c s l i c e o f a s u b a q u e o u s s l o p e . The f o r c e s h a v e b e e n d e p i c t e d a t t h e p r e c i s e t i m e when t h e t r a n s i t o r y wave p r e s s u r e i s a l i g n e d s u c h a s t o m i n i m i z e t h e s t a b i l i t y o f t h e . s l i d i n g mass a g a i n s t f a i l u r e . The s h e a r i n g r e s i s t a n c e o f t h e s o i l , w h i c h a c t s t a n g e n t i a l t o t h e a r c b a s e s u c h as t o r e s i s t any u n b a l a n c e d f o r c e s , h a s n o t b e e n shown on t h e f r e e b o d y d i a g r a m . I f t h e s t a b i l i t y o f t h e f r e e b o d y s l i c e i s c o n s i d e r e d by summing t h e moments a r o u n d t h e c e n t e r o f r o t a t i o n , C, i t c a n be s e e n t h a t t h e n o n - h y d r o s t a t i c wave p r e s s u r e a t t h i s i n s t a n t i n t i m e c o n t r i b u t e s t o t h e c l o c k w i s e ( o v e r t u r n i n g ) moment. The o t h e r e f f e c t s o f t h e t r a n s i t o r y n o n - h y d r o s t a t i c wave p r e s s u r e s a r e a s s o c i a t e d w i t h t h e r e s p o n s e o f t h e s e a b e d m a t e r i a l t o t h e t r a n s i t o r y wave p r e s s u r e s . . The m o v i n g p r e s s u r e z o n e s , r e g u l a r l y a l t e r n a t i n g h i g h e r a n d l o w e r t h a n t h e mean s e a b e d w a t e r p r e s s u r e , i n e f f e c t , s u b j e c t t h e s e a b e d t o a c y c l i c p r e s s u r e l o a d i n g . Two p o s s i b l e e f f e c t s o f t h e c y c l i c p r e s s u r e l o a d i n g a r e a b u i l d u p o f n o n - h y d r o s t a t i c p o r e w a t e r p r e s s u r e s i n t h e s e a b e d , a n d a g r a d u a l r e m o u l d i n g o f s o f t c o h e s i v e s e d i m e n t s r e d u c i n g t h e s h e a r s t r e n g t h o f t h o s e s e d i -m e n t s . I n v e s t i g a t i o n o f t h e s e two p o s s i b l e e f f e c t s i s b e y o n d t h e s c o p e o f t h i s t h e s i s , a n d t h e y w i l l n o t be f u r t h e r p u r s u e d . A s i m p l e c o m p u t e r p r o g r a m f o r a n a l y s i n g t h e s t a b i l i t y o f c i r c u l a r a r c p o t e n t i a l f a i l u r e s u r f a c e s by t h e m e t h o d o f NOTE: The s o i l shear s t r e s s e s a c t i n g around the s l i p a r c are not shown on t h i s freebody. C = Center of s l i p a r c and r o t a t i o n R = Radius of s l i p a r c W = Weight of freebody 6 = Angle of s l o p e w i t h h o r i z o n t a l p = S i n u s o i d a l n o n - h y d r o s t a t i c water p r e s s u r e F i g . 18 Freebody diagram of c i r c u l a r s l i p a r c showing n o n - h y d r o s t a t i c water p r e s s u r e from wave l o a d i n g . 78. s l i c e s , w i t h n o n - h y d r o s t a t i c p r e s s u r e l o a d i n g s a n d p o r e p r e s s u r e r e s p o n s e s , p r e p a r e d by N e i l Wedge o f t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , was m o d i f i e d and u s e d f o r a s e r i e s o f a n a l y s e s o f t h e assumed maximum s l o p e o f t h e b a n k s . A F o r t r a n l i s t i n g o f t h e p r o g r a m u s e d h a s b e e n I n c l u d e d as A p p e n d i x 2. The p r o g r a m makes a s t a t i c a n a l y s i s o f s t a b i l i t y u s i n g a s i n u -s o i d a l p r e s s u r e d i s t r i b u t i o n f o r t h e wave p r e s s u r e s , w h i c h i s s t r i c t l y a p p r o p r i a t e f o r deep w a t e r waves o n l y ( d e p t h o f s t i l l w a t e r g r e a t e r t h a n o n e - f i f t h t h e wave l e n g t h ) . The u s e o f a s t a t i c a n a l y s i s g i v e s an u p p e r b o u n d s o l u t i o n f o r t h e s t a b i l i t y , as t h e d y n a m i c e f f e c t - i f any - w o u l d be t o r e d u c e t h e s t a b i l i t y . The p r o g r a m c e n t e r s t h e s i n u s o i d a l wave p r e s s u r e d i s t r i -b u t i o n o v e r t h e m i d p o i n t o f t h e segment o f s l o p e b e i n g a n a l y s e d , w i t h t h e g r e a t e r p r e s s u r e on t h e u p s l o p e h a l f o f t h e s u r f a c e , t h u s m a x i m i z i n g t h e e f f e c t o f t h e wave p r e s s u r e . The n o n -h y d r o s t a t i c p r e s s u r e c h a n g e s a t t h e s u r f a c e o f t h e s e a b e d r e s u l t i n c h a n g e s i n t h e s e d i m e n t p o r e p r e s s u r e s . S l e a t h (1970) p r e s e n t e d t h e r e s u l t s o f a l a b o r a t o r y s t u d y , w h e r e i n t h e p r e s -s u r e d i s t r i b u t i o n i n a b e d o f s a n d b e i n g s u b j e c t e d t o wave p r e s s u r e l o a d i n g was m e a s u r e d . T h i s s t u d y i n d i c a t e d t h a t t h e s e d i m e n t p o r e p r e s s u r e s r e s p o n d i n p h a s e w i t h t h e p a s s i n g wave p r e s s u r e s , a n d t h a t t h e m a g n i t u d e o f t h e r e s p o n s e i s dampened w i t h d e p t h i n t h e s e a b e d . The p r o g r a m i n c l u d e s t h e d a m p i n g e f f e c t r e p o r t e d by S l e a t h (1970) a s w e l l a s t h e d a m p i n g o f t h e wave p r e s s u r e s w h i c h o c c u r w i t h d e p t h i n t h e w a t e r c o l u m n . P r o f i l e s o f t h e f o r e s l o p e i n d i c a t e a maximum s l o p e o f on t h e o r d e r o f 23 d e g r e e s , t h e r e f o r e , a s l o p e o f 25 d e g r e e s 79-was a n a l y s e d as t h e assumed maximum s l o p e u s i n g t h e m o d i f i e d p r o g r a m . I n o r d e r t o d e t e r m i n e t h e a p p r o p r i a t e wave l o a d i n g t o a p p l y t o t h e a n a l y s i s , d a t a f r o m w a v e - r i d e r , b u o y s ( w h i c h i s d i s c u s s e d i n a n o t h e r s e c t i o n ) was s t u d i e d . The maximum r e c o r d e d p e a k t o t r o u g h wave h e i g h t a t t h e b a n k s was on t h e o r d e r o f 9 f e e t a n d t h i s wave h a d a p e r i o d o f a p p r o x i m a t e l y 7 s e c o n d s . By a p p l y i n g t h e a p p r o x i m a t e deep w a t e r r e l a t i o n s h i p s C = 3T and X = CT ... ( 7 - 1 , 7 - 2 ) w h e r e C = v e l o c i t y i n k n o t s , T = p e r i o d i n s e c o n d s a n d A = wave l e n g t h , I t was c a l c u l a t e d t h a t t h i s wave w o u l d h a v e b e e n a p p r o x -i m a t e l y 250 f e e t l o n g . The mean s t i l l w a t e r d e p t h a t t h e m i d -p o i n t o f a l l s e c t i o n s b e i n g a n a l y s e d was c h o s e n t o be 100 f e e t p r i m a r i l y t o e n s u r e deep w a t e r c o n d i t i o n s e v e n a t t h e u p s l o p e edge o f t h e assumed f a i l u r e s u r f a c e s . A r e v i e w o f a l l t h e a v a i l a b l e d a t a on t h e b a n k s ' s e d i -m e n t s ( r e p o r t e d a n d d i s c u s s e d e l s e w h e r e i n t h i s t h e s i s ) i n d i c a -t e d t h a t t h e s t a b i l i t y a n a l y s i s s h o u l d be p e r f o r m e d f o r a p u r e l y f r i c t i o n a l m a t e r i a l . The c o h e s i o n was a s s i g n e d a v a l u e o f z e r o , t h e a n g l e o f i n t e r n a l f r i c t i o n was g i v e n a v a l u e o f 30 d e g r e e s a n d t h e m a t e r i a l was a s s u m e d t o h a v e a b o u y a n t u n i t w e i g h t o f 59 l b / f t 3 . A s e r i e s o f p o t e n t i a l f a i l u r e a r c s w i t h h o r i z o n t a l l e n g t h s r a n g i n g f r o m 125 f e e t t o 250 f e e t was a n a l y s e d . The d e p t h o f t h e p o t e n t i a l f a i l u r e a r c was v a r i e d f r o m 5 f e e t t o 55 f e e t f o r e a c h c h o s e n f a i l u r e l e n g t h . The l o w e s t f a c t o r o f s a f e t y , f o r any o f t h e p o t e n t i a l f a i l u r e s u r f a c e s c o m p u t e d by t h e p r o g r a m , was 1.2 f o r t h e s h o r t e s t , s h a l l o w e s t p o t e n t i a l f a i l u r e s u r f a c e (1.25 f e e t , 5 f e e t ) . I n a l l c a s e s , t h e f a c t o r o f s a f e t y 80. i n c r e a s e d a s t h e d e p t h o f f a i l u r e i n c r e a s e d a n d a s t h e l e n g t h o f f a i l u r e i n c r e a s e d . T h i s a n a l y s i s i n d i c a t e s t h a t e v e n t h e s t e e p e s t s l o p e f o u n d on t h e b a n k s i s s t a b l e d u r i n g l o a d i n g by n o n - h y d r o s t a t i c p r e s s u r e s i n d u c e d by w a t e r w a v e s . The a n a l y s i s a l s o i n d i c a t e s t h a t , i f t h e r e a r e any f a i l u r e s , t h e y w i l l be v e r y s h a l l o w f a i l u r e s a n d s h o u l d n o t c o n s t i t u t e a c a t a s t r o p h i c d a n g e r t o e n g i n e e r i n g i n s t a l l a t i o n s e x c e p t as a f o r m o f p r o g r e s s i v e e r o s i o n . I f t h i s p r o b l e m i s r e c o g n i z e d i t c a n be d e a l t w i t h i n much t h e same manner a s o r d i n a r y e r o s i o n . The s e d i m e n t s on t h e s l o p e s o f R o b e r t s Bank a n d S t u r g e o n B a n k a r e c o n s i d e r e d t o be s u f f i c i e n t l y c o a r s e t h a t w i t h t h e r e l a t i v e l y l a r g e p e r i o d s o f o s c i l l a t i o n i n v o l v e d (7 s e c o n d s a n d g r e a t e r ) d i s s i p a t i o n o f p o r e p r e s s u r e s w i l l be r a p i d a n d e x c e s s p o r e p r e s s u r e s due t o c y c l i c wave l o a d i n g w i l l n o t be l i k e l y t o b u i l d u p. E f f e c t o f E a r t h q u a k e M o t i o n s T h e r e a r e two b a s i c e f f e c t s o f e a r t h q u a k e m o t i o n s w h i c h must be d i s c u s s e d w i t h r e s p e c t t o s l o p e s t a b i l i t y c o n s i d e r a -t i o n s . F i r s t , t h e a c c e l e r a t i o n s o f t h e e a r t h q u a k e m o t i o n c r e a t e s i n e r t i a l f o r c e s i n t h e s l o p e s e d i m e n t s a n d any com-p o n e n t s o f t h e s e f o r c e s a c t i n g o u t w a r d f r o m t h e s l o p e become p a r t o f t h e d r i v i n g f o r c e a t t e m p t i n g t o c a u s e f a i l u r e . S e c o n d , t h e o s c i l l a t o r y n a t u r e o f t h e e a r t h q u a k e m o t i o n s s u b j e c t t h e s e d i m e n t s t o r e v e r s i n g s h e a r s t r e s s e s w h i c h , a s was d i s c u s s e d e l s e w h e r e , c a n l e a d t o a b u i l d u p o f e x c e s s p o r e w a t e r p r e s s u r e s . T h i s c a n h a v e a s i g n i f i c a n t e f f e c t on t h e s t r e n g t h o f p r i m a r i l y g r a n u l a r s o i l s . S arma (1973) p r e s e n t e d a m e t h o d o f s l o p e s t a b i l i t y 81. a n a l y s i s w h i c h i n c o r p o r a t e s a h o r i z o n t a l a c c e l e r a t i o n i n t h e a n a l y s i s . A l t h o u g h t h i s m e t h o d u s e s t h e c o n c e p t o f a h o r i z o n -t a l a c c e l e r a t i o n . I t i s a s t a t i c a n a l y s i s i n w h i c h t h e h o r i -z o n t a l a c c e l e r a t i o n i s c o n v e r t e d i n t o an i n e r t i a l d r i v i n g f o r c e a n d d y n a m i c e f f e c t s a r e n o t c o n s i d e r e d . Sarma (1973) u s e s t h e s y m b o l K t o r e p r e s e n t t h e h o r i z o n t a l a c c e l e r a t i o n ' a s a d e c i m a l f r a c t i o n o f g r a v i t y i n h i s a n a l y s i s . E q u a t i o n s a r e t h e n s e t up f o r t h e c o n d i t i o n o f l i m i t e q u i l i b r i u m ( f a c t o r o f s a f e t y e x a c t l y e q u a l t o 1.0) and t h e v a l u e o f K w h i c h s a t i s f i e s t h e s e e q u a t i o n s i s t h e c r i t i c a l a c c e l e r a t i o n , K . Sarma s u g g e s t s t h a t t h e v a l u e o f K c c a n be u s e d d i r e c t l y as a n i n d i c a -t i o n o f t h e s t a t i c f a c t o r o f s a f e t y o r t h e n o r m a l s t a t i c f a c t o r o f s a f e t y c a n be a r r i v e d a t by an a l t e r n a t e p r o c e d u r e . The a l t e r n a t e p r o c e d u r e i n v o l v e s r e d u c i n g t h e s t r e n g t h p a r a m e t e r s o f t h e m a t e r i a l a l o n g t h e s l i p s u r f a c e s u c h t h a t t h e c a l c u l a t e d c r i t i c a l a c c e l e r a t i o n i s j u s t e q u a l t o z e r o . The f a c t o r by w h i c h t h e s t r e n g t h p a r a m e t e r s must be r e d u c e d t o a c h i e v e t h i s c o n d i t i o n i s t h e s t a t i c f a c t o r o f s a f e t y . To i n c o r p o r a t e t h e p o s s i b l e d y n a m i c e f f e c t s o f e a r t h -q u a k e l o a d i n g i n t o t h e a n a l y s i s , Sarma . ( i n t e r n a l r e p o r t w r i t t e n f o r a p r o j e c t w h i l e w o r k i n g as a R e s e a r c h A s s o c i a t e a t U.B.C.) i n c l u d e d a p o r e p r e s s u r e f a c t o r i n t h e a n a l y s i s w h i c h he r e l a t e d t o i n c r e a s e s i n p o r e p r e s s u r e due t o c y c l i c l o a d i n g . He d e f i n e d t h e c h a n g e i n p o r e p r e s s u r e , Au, as Au = A n K Y h ... (7-3) where A^ = t h e p o r e p r e s s u r e p a r a m e t e r , K = t h e h o r i z o n t a l i n e r t i a c o e f f i c i e n t , y = t h e s a t u r a t e d u n i t w e i g h t o f t h e s o i l and h = t h e d e p t h o f t h e p o i n t f r o m t h e s u r f a c e o f t h e s l o p e . 82. T h i s d e f i n i t i o n o f t h e c h a n g e i n p o r e p r e s s u r e , Au, r e q u i r e s t h e a d o p t i o n o f t h e a s s u m p t i o n t h a t t h e c h a n g e i n p o r e p r e s s u r e a t any p o i n t i s p r o p o r t i o n a l t o t h e t o t a l s t r e s s a t t h a t p o i n t , w h i c h i s p r o b a b l y a r e a s o n a b l e a s s u m p t i o n . I n t h e s e c t i o n on l i q u e f a c t i o n p o t e n t i a l , i t was shown-' t h a t a c o m p l e x e a r t h q u a k e m o t i o n c a n be a p p r o x i m a t e d by two p a r a m e t e r s , K a n d N, w h e r e K i s t h e m a g n i t u d e o f a c c e l e r a t i o n and N i s t h e number o f c y c l e s o f s t r e s s . The c h a n g e i n p o r e p r e s s u r e , Au, a l s o d e p e n d s on b o t h t h e s e f a c t o r s . K e n t e r s d i r e c t l y i n t o e q u a t i o n ( 7 - 3 ) , t h e r e f o r e , t h e p o r e p r e s s u r e p a r a m e t e r A n must b e a r a r e l a t i o n s h i p t o ' t h e number o f c y c l e s o f s t r e s s , N. F rom f o r m u l a e p r o p o s e d by M a r t i n , F i n n a n d S e e d (1975) , Sarma p l o t t e d c u r v e s o f U/G^Q V S . T/O^Q ( w h e r e u = e x c e s s p o r e p r e s s u r e , x = s h e a r s t r e s s , and a' = i n i t i a l v e r -' 3 vo t i c a l e f f e c t i v e s t r e s s ) f o r d i f f e r e n t numbers o f c y c l e s o f s t r e s s . T h e s e c u r v e s a r e r e p r o d u c e d i n F i g . 19 a n d t h e d e r i -v a t i o n o f the" i n i t i a l f a i l u r e l i n e , shown a s a d a s h e d l i n e i n F i g . 19 , i s shown i n F i g . 20. T o . r e l a t e t h e c u r v e s t o t h e s l o p e s t a b i l i t y a n a l y s i s t h e p o r t i o n o f e a c h c u r v e f r o m z e r o o u t t o t h e i n i t i a l f a i l u r e l i n e i s a p p r o x i m a t e d by a s t r a i g h t l i n e . A s t r a i g h t l i n e a p p r o x i m a t i o n t o t h e s e c u r v e s g i v e s t h e e q u a t i o n u / a ' = A x/o' ... (7-4) v o n vo w h e r e A^ i s a c o n s t a n t f o r a f i x e d number o f c y c l e s o f s t r e s s , a n d i s e q u a t e d t o t h e p o r e p r e s s u r e p a r a m e t e r , A , o f t h e s l o p e s t a b i l i t y a n a l y s i s . The l i n e a r i z a t i o n o f t h e u / a ' v s . x / a ' c u r v e s c r e a t e s vo vo a u n i q u e r e l a t i o n s h i p b e t w e e n t h e p o r e p r e s s u r e p a r a m e t e r , A, • i-i- I 1 ' F i g . j i g j j R e l a t i o n s h i p 1 between excess Pore 'Pressure Jand -applied shear (stress i !-; ; ^various numbers o f c y c l e s o f s t r e s s . \ U...Ld--l'''' f o r •!- •!- i- t - j - XLJ CO LO 84. F i g . 20 D e r i v a t i o n of the f a i l u r e c r i t e r i o n used t o p l a c e the f a i l u r e l i n e on F i g . 19. 85. . i n t h e s l o p e s t a b i l i t y a n a l y s i s a n d t h e number o f c y c l e s t o i n i t i a l f a i l u r e , N, f o r l a b o r a t o r y c y c l i c l o a d i n g t e s t s . T h e r e a r e two r e a s o n a b l e ways t o p e r f o r m t h e l i n e a r i z a t i o n , t h e r e -s u l t s o f w h i c h h a v e b e e n p l o t t e d i n P i g . 2 1 . The u p p e r c u r v e shows t h e A n v a l u e s d e r i v e d by j o i n i n g t h e o r i g i n t o t h e i n t e r -s e c t i o n o f t h e f a i l u r e l i n e w i t h t h e c u r v e s f o r t h e v a r i o u s n umbers o f c y c l e s , N. The l o w e r c u r v e i s t h e A v a l u e s o b t a i n e d ° 3 n by a p p r o x i m a t i n g t h e a v e r a g e s l o p e s o f t h e F i g . 19 c u r v e s . The u p p e r c u r v e i s f a v o u r e d by t h i s w r i t e r b e c a u s e i t l e a d s t o h i g h e r p o r e w a t e r p r e s s u r e s a n d i s , t h e r e f o r e , t o be c o n s i d e r e d more c o n s e r v a t i v e . The d e r i v a t i o n o f t h e i n i t i a l f a i l u r e l i n e i s b a s e d on an i n i t i a l p r i n c i p a l s t r e s s r a t i o , Ko, o f 0.5 a n d t h e a s s u m p t i o n t h a t t h i s r a t i o r e m a i n s c o n s t a n t d u r i n g t h e c y c l i c l o a d i n g . The c u r v e s p r e s e n t e d i n F i g . 19 a r e b a s e d on t h e r e s u l t s o f v a r i o u s c y c l i c l o a d i n g t e s t s on a s o i l d e s c r i b e d a s " c r y s t a l s i l i c a s a n d " a t r e l a t i v e d e n s i t i e s r a n g i n g f r o m 45 t o 60 p e r c e n t . A l t h o u g h t h e c o m p o s i t i o n o f t h e b a n k s ' s e d i m e n t s i s n o t t h e same as t h e m a t e r i a l t e s t e d , t h e A v s . N c u r v e s d e r i v e d f r o m ' n t h e t e s t r e s u l t s s h o u l d p r o v i d e a r e a s o n a b l e f i r s t o r d e r a p p r o x i -m a t i o n o f t h e number o f c y c l e s t o f a i l u r e . I f r e f i n e m e n t o f t h e A v s . N c u r v e s was f e l t t o be d e s i r a b l e t h e n a t e s t i n g p r o -gram c o u l d be u n d e r t a k e n u s i n g t h e b a n k s ' s e d i m e n t s , w i t h t h e t e s t s c o n d u c t e d u n d e r c o n d i t i o n s w h i c h m a t c h e d t h e i n s i t u c o n d i t i o n s . Sarma f u r t h e r m o d i f i e d , h i s m e t h o d o f a n a l y s i s t o i n c l u d e n o n - h y d r o s t a t i c wave p r e s s u r e l o a d i n g s i n c o n j u n c t i o n w i t h t h e e a r t h q u a k e l o a d i n g . A s e r i e s o f p o t e n t i a l f a i l u r e s u r f a c e s 37. on t h e s t e e p e r p o r t i o n s o f t h e s u b a q u e o u s s l o p e s , as r e p r e -s e n t e d by t h e u p p e r p o r t i o n o f p r o f i l e S i n F i g . 16, w e r e a n a l y s e d f o r s t a b i l i t y u s i n g t h e Sarma m e t h o d . The a n a l y s e s w e r e p e r f o r m e d f o r a s o i l w i t h z e r o c o h e s i o n , an a n g l e o f i n t e r n a l f r i c t i o n o f 30 d e g r e e s and a t o t a l u n i t w e i g h t o f 1 2 4 . 8 p . c . f . Wave p r e s s u r e l o a d i n g c o r r e s p o n d i n g t o a s i n u -s o i d a l wave w i t h a wave h e i g h t o f 9 f e e t a n d a wave l e n g t h o f 250 f e e t was i n s e r t e d I n t o t h e a n a l y s e s . The s e c t i o n a n a l y s e d and t h e i n p u t wave l o a d i n g a r e shown I n F i g . 22. To i l l u s t r a t e t h e p r o c e d u r e and t h e k i n d o f r e s u l t s t h a t may be o b t a i n e d , f i v e p o t e n t i a l f a i l u r e s u r f a c e s w e r e a n a l y s e d , f o r a f i x e d c h o r d l e n g t h , and t h e two s u r f a c e s w h i c h g a v e t h e l o w e s t c r i t i c a l a c c e l e r a t i o n , K , f o r f a c t o r s o f s a f e t y , FS .= 1, a r e shown i n F i g . 22. The a n a l y s e s w e re p e r f o r m e d w i t h t h e a i d o f a c o m p u t e r p r o g r a m w h i c h I s l i m i t e d t o t h e c a s e o f a homogeneous m a t e r i a l . T h i s l i m i t a t i o n i s n o t c o n s i d e r e d t o be r e s t r i c t i v e i n t h i s i n s t a n c e , s i n c e t h e f i e l d d a t a a v a i l a b l e i n d i c a t e s t h a t a homogeneous r e p r e s e n t a t i o n o f t h e u p p e r s e d i -m e nts i s r e a s o n a b l e . A F o r t r a n l i s t i n g o f t h e p r o g r a m u s e d i s p r e s e n t e d i n A p p e n d i x 3-The l o w e s t c r i t i c a l a c c e l e r a t i o n , K , o b t a i n e d f r o m t h e a n a l y s e s was 0.124g f o r s u r f a c e 5. a n d t h e c r i t i c a l a c c e l e r a -t i o n i n c r e a s e d as t h e d e p t h o f t h e p o t e n t i a l f a i l u r e s u r f a c e I n c r e a s e d . T h i s i s c o n s i s t e n t w i t h t h e p r e v i o u s a n a l y s i s w h e r e t h e f a c t o r o f s a f e t y i n c r e a s e d a s t h e d e p t h o f t h e s u r f a c e i n c r e a s e d . F i g . 23 shows t h e K c v s . A c u r v e s d e v e l o p e d f o r s u r f a c e s 4 and 5- P o t e n t i a l f a i l u r e s u r f a c e 5 g i v e s a K o f 0.019g when • ; 88. F i g . 22 Slope a n a l y s e d by Sarma program,, showing ::Zfailure:.sur,f ac.es:^Zandl5_iaM:_the::::;:^ri;;::.. n o n - h y d r o s t a t i c wave data. - — i ~ , ,1 ; F i g . 2 3 R e l a t i o n s h i p between c r i t i c a l A c c e l e r a t i o n and Pore P r e s s u r e Parameter f o r s u r f a c e s 4 and 5. 90. A = 10 and t h i s c o r r e s p o n d s t o 8 t o 10 c y c l e s o f s t r e s s a c c o r d -i n g t o F i g . 2 1 . T h u s , t h i s a n a l y s i s i n d i c a t e s t h a t a c o n d i t i o n o f l i m i t e q u i l i b r i u m w i l l be r e a c h e d f o r t h e s h a l l o w p o t e n t i a l f a i l u r e s u r f a c e on t h e assumed s t e e p e s t s u b a q u e o u s s l o p e s on t h e b a n k s , w i t h a s i n g l e h o r i z o n t a l a c c e l e r a t i o n d i r e c t e d o u t -w a r d f r o m t h e s l o p e o f 0.124g, when c o m b i n e d w i t h t h e 9 f o o t wave l o a d i n g . I n c o n j u n c t i o n w i t h t h i s same wave l o a d i n g 8 t o 10 c y c l e s o f s t r e s s , w i t h a h o r i z o n t a l a c c e l e r a t i o n i n t o a n d o u t o f t h e s l o p e o f 0.02g, a r e s u f f i c i e n t t o a c h i e v e t h e c o n d i -t i o n o f l i m i t e q u i l i b r i u m . Somewhat g r e a t e r m a g n i t u d e s o f h o r i z o n t a l a c c e l e r a t i o n w o u l d be n e c e s s a r y t o a c h i e v e t h e c o n d i -t i o n o f l i m i t e q u i l i b r i u m i n c o n j u n c t i o n w i t h l e s s e r wave l o a d -i n g s o r i n t h e a b s e n c e o f wave l o a d i n g . The r e s u l t s o f t h e s e a n a l y s e s , i n . a g r e e m e n t w i t h t h e r e s u l t s o f t h e c i r c u l a r a r c a n a l y s e s , i n d i c a t e t h a t t h e s t e e p e s t o f t h e s u b a q u e o u s s l o p e s a r e s t a b l e e v e n d u r i n g s t o r m m a g n i t u d e wave l o a d i n g , i n t h e a b s e n c e o f d y n a m i c l o a d i n g . A s i g n i f i c a n t s e i s m i c e v e n t i s i n d i c a t e d a s n e c e s s a r y t o p r o d u c e s l o p e i n s t a -b i l i t i e s , w h i c h w o u l d t e n d t o be o f a s h a l l o w n a t u r e . To o b t a i n a n e s t i m a t e o f t h e m a g n i t u d e o f h o r i z o n t a l a c c e l e r a t i o n w h i c h w o u l d be n e c e s s a r y t o t r i g g e r a mass w a s t i n g on t h e s c a l e o f t h e s l u m p s t r u c t u r e s p r e v i o u s l y d i s c u s s e d , a v e r y l a r g e p o t e n t i a l f a i l u r e s e c t i o n 200 f e e t d e e p , a s shown i n F i g . 2 4, was a n a l y s e d . No n o n - h y d r o s t a t i c wave p r e s s u r e l o a d i n g was u s e d i n t h i s a n a l y s i s s i n c e t h e s e c t i o n b e i n g a n a l y -s e d was much t o o m a s s i v e a n d e x t e n s i v e t o be a f f e c t e d b y wave l o a d i n g . The a n a l y s i s y i e l d s a c r i t i c a l a c c e l e r a t i o n , K c , o f 0.24g t o p r o d u c e t h e c o n d i t i o n o f l i m i t e q u i l i b r i u m f o r t h e s e c t i o n a n a l y s e d n e g l e c t i n g c y c l i c l o a d i n g e f f e c t s . F i g . 12 . i n d i c a t e s t h a t a maximum h o r i z o n t a l a c c e l e r a t i o n o f 0.24g w o u l d be a s s o c i a t e d w i t h a s e i s m i c e v e n t w i t h a r e t u r n p e r i o d o f a b o u t 180 y e a r s . S u c h an e v e n t c o u l d be c l a s s i f i e d a s a r a r e e v e n t , w h i c h i s i n a g r e e m e n t w i t h t h e p r e v i o u s d i s c u s s i o n . The e a r t h q u a k e s t a b i l i t y a n a l y s i s i n d i c a t e s t h a t t h e b a n k s ' s e d i m e n t s c o u l d be l i q u e f i e d by an e a r t h q u a k e o f a m a g n i -t u d e a n d d u r a t i o n w h i c h i s w i t h i n t h e r a n g e o f p o s s i b l e s e i s m i c a c t i v i t y o f t h e a r e a . T h e r e a r e a number o f ways t o r e d u c e t h e l i q u e f a c t i o n p o t e n t i a l o f a p a r t i c u l a r s i t e o f f i n i t e s i z e , h o w e v e r , t h e e x p e n s e a n d t h e c o n s e q u e n c e s o f t h e s e m e t h o d s must be c a r e f u l l y c o n s i d e r e d . The two m e t h o d s w h i c h seem t o o f f e r t h e g r e a t e s t p o t e n t i a l f o r s u c c e s s f u l a p p l i c a t i o n a r e . t h e p l a c e -ment o f a f i l l l o a d i n g a n d t h e d e n s i f i c a t i o n o f t h e i n s i t u d e p o s i t s . D o c u m e n t e d e v i d e n c e o f t h e s u c c e s s o f t h e l a t t e r p r o c e d u r e i s c o n t a i n e d i n t h e s t u d y by O h s a k i (1970) f o l l o w i n g t h e T o k a c h i o k i e a r t h q u a k e . D e n s i f i c a t i o n i s t h e most d i r e c t and p o s i t i v e m e t h o d o f r e d u c i n g l i q u e f a c t i o n p o t e n t i a l . The a d d i t i o n o f s i t e f i l l i n c r e a s e s t h e o v e r b u r d e n e f f e c t i v e s t r e s s b u t i t a l s o i n c r e a s e s t h e s h e a r s t r e s s r a t i o d u r i n g t h e e a r t h q u a k e e x c i t a t i o n , w h i c h o f f s e t s t h e a d v a n t a g e s o f i n c r e a s e d e f f e c t i v e s t r e s s a n d may r e s u l t i n o n l y a m i n i m a l r e d u c t i o n i n e a r t h q u a k e r e s i s t a n c e . L u t e r n a u e r ( 1 9 7 6 ) s p e c u l a t e d t h a t t h e u n d u l a t i n g s u r f a c e o f t h e f o r e s l o p e b e l o w -70 m e t e r s , i n t h e a r e a b e t w e e n a p o i n t o p p o s i t e Canoe P a s s a g e a n d t h e W e s t s h o r e T e r m i n a l s b u l k l o a d i n g f a c i l i t y , c o u l d be r e l a t e d t o mass w a s t i n g . The u n d u l a t i o n s i n q u e s t i o n a p p e a r on t h r e e ( H , I a n d J ) o f a s e r i e s o f h y p s o g r a p h i c 93. p r o f i l e s o f t h e f o r e s l o p e t a k e n by t h e C a n a d i a n H y d r o g r a p h i c S e r v i c e i n 197*1 • The u n d u l a t i o n s a p p e a r t o h a v e a somewhat r e g u l a r w a v e - l i k e p r o f i l e , w i t h a w a v e l e n g t h o f a b o u t 300 f e e t and a p e a k t o t r o u g h wave h e i g h t o f a b o u t 5 t o 10 f e e t m e a s u r e d i n t h e p l a n e o f t h e s l o p e ; w h i c h a v e r a g e s 1.4 t o 1.5 d e g r e e s a t t h i s d e p t h a n d l o c a t i o n . T r a c i n g s o f t h e s u r f a c e o f t h e r e c o r d e d e c h o s i g n a l s o f h y p s o g r a p h i c p r o f i l e s H, I a n d J , b e t w e e n 60 a n d 100 m e t e r s d e p t h , h a v e b e e n p r e s e n t e d i n F i g . 25 and t h e l o c a t i o n s o f t h e p r o f i l e s i s shown I n F i g . 26. No s c a l e was p u t on F i g . 25 s i n c e t h e h o r i z o n t a l s c a l e i s d e p e n d e n t u p o n t h e a c t u a l h o r i z o n t a l m o t i o n o f t h e - s u r v e y s h i p ; h o w e v e r , n a v i g a t i o n a l p o s i t i o n i n g i n d i c a t e s t h a t t h e h o r i z o n t a l s c a l e f o r t h e s e p r o f i l e s i s a p p r o x i m a t e l y 1 i n c h t o 300 m e t e r s . The d i s t o r t i o n c r e a t e d by t h e v e r y l a r g e r a t i o o f h o r i z o n t a l t o v e r t i c a l s c a l e t e n d s t o mask t h e w a v e - l i k e n a t u r e o f t h e u n d u -l a t i o n s b u t c l o s e i n s p e c t i o n r e v e a l s t h a t t h e s e l o n g s h a l l o w wave f o r m s a p p e a r t o be a s y m e t r i c a l w i t h t h e l o n g g e n t l e s l o p e r u n n i n g d o w n s l o p e and t h e s h o r t e r s t e e p e r s l o p e r u n n i n g . o u t f r o m t h e g e n e r a l s l o p e . I n t h e l a t t e r p a r t o f J u l y , 1976, t h e G e o l o g i c a l S u r v e y o f C a n a d a d i d some s i d e - s c a n s o n a r o f t h e f o r e s l o p e o f R o b e r t s B ank. The t r a c k l i n e s f o l l o w e d by t h e s u r v e y s h i p w e r e s u b -p a r a l l e l t o t h e s t r i k e o f t h e s l o p e when m a k i n g s i d e - s c a n s o n a r r e c o r d s , a n d a number o f t h e t r a c k l i n e s p a s s e d t h r o u g h t h e a r e a c o v e r e d by p r o f i l e s H, I a n d J . A l t h o u g h t h e a n a l y s i s o f t h e s u r v e y r e s u l t s i s n o t c o m p l e t e , D r . L u t e r n a u e r made t h e s i d e - s c a n s o n a r r e c o r d s a v a i l a b l e f o r i n s p e c t i o n . The r e c o r d s show many a r e a s w i t h o r d e r l y r o w s o f m e g a - r i p p l e s w i t h r e m a r k a b l y F i g . 25 T r a c i n g o f Hypsographic P r o f i l e s H, I and J from 60 t o 100 meters below sea l e v e l . ROBERTS •' i BANK S T R A I T OF GEORGIA ' CANADA .U.S.A. Galiano Island r Active Pass Mayne Island SCALE 1:98,842 H, I, J - Hypsographic p r o f i l e l i n e s Mean Low T i d e Depth Contour i n Fathoms F i g . 26 L o c a t i o n o f hypsographic p r o f i l e l i n e s H, I and J . 96. r e g u l a r s i z e , s h a p e a n d s p a c i n g on t h e f o r e s l o p e o f c e n t r a l R o b e r t s B a n k . T h e s e m e g a - r i p p l e s a r e o f a n a s y m e t r i c s h a p e s i m i l a r t o t h e s h a p e o f s a n d d u n e s . The m e g a - r i p p l e s a r e p r e v a l e n t on a l l t h e r e c o r d s t a k e n on t h e f o r e s l o p e o f c e n t r a l R o b e r t s B a n k . No r e c o r d s w e r e t a k e n s o u t h o f t h e b u l k l o a d i n g f a c i l i t y , b u t some r e c o r d s w e r e t a k e n on n o r t h R o b e r t s B a n k , r i g h t t o t h e m a i n c h a n n e l o f t h e F r a s e r , w h i c h show s u b d u e d by s t i l l r e c o g n i z a b l e m e g a - r i p p l e s . By p l o t t i n g t h e t r a c k l i n e o f t h e s h i p on a c h a r t t h e G e o l o g i c a l S u r v e y o f C a n a d a h a s b e e n a b l e t o t r a n s f e r t h e o r i e n t a t i o n o f t h e m e g a - r i p p l e s t o t h e c h a r t . I n some p l a c e s t h e m e g a - r i p p l e s a p p e a r e d d i s t u r b e d o r j u m b l e d b u t t h e r e was a l w a y s a n o v e r a l l r e c o g n i z a b l e o r i e n t a t i o n t o t h e r i p p l e s . The o r i e n t a t i o n o f t h e r i p p l e s a s t r a n s f e r r e d t o t h e c h a r t i s p a r a l l e l t o s u b -p a r a l l e l t o t h e d i p o f t h e s l o p e , a n d t h e s t e e p s l o p e s o f t h e s e a s y m e t r i c wave f o r m s a r e f a c i n g w e s t w a r d . F r o m t h e p l o t t e d s h i p s p o s i t i o n s a n d t h e t i m e m a r k s p l a c e d on t h e s i d e - s c a n r e c o r d s t h e G e o l o g i c a l S u r v e y o f C a n a d a h a s made an i n i t i a l e s t i m a t e ( v e r b a l c o m m u n i c a t i o n ) o f t h e s p a c i n g o f t h e m e g a - r i p p l e s o n t h e o r d e r o f 40 m e t e r s . P r e c i s e e c h o s o u n d -i n g r u n s i m u l t a n e o u s l y w i t h t h e s i d e - s c a n s o n a r I n d i c a t e s a p e a k t o t r o u g h wave h e i g h t f o r t h e m e g a - r i p p l e s on t h e o r d e r o f 2 m e t e r s . T h e s e m e g a - r i p p l e s a r e s u b - p a r a l l e l t o h y p o s o -g r a p h i c p r o f i l e s H, I and J and t h e i n t e r s e c t i o n o f t h e mega-r i p p l e s a n d t h e p r o f i l e s w o u l d be a t a s m a l l a n g l e . The r i p p l e s a s s e e n on t h e p r o f i l e s w o u l d a p p e a r t o h a v e a much g r e a t e r s p a c i n g t h a n 40 m e t e r s a n d I t i s q u i t e c l e a r t h a t t h e u n d u l a t i n g f e a t u r e s n o t e d i n p r o f i l e s H, I and J a n d t h e m e g a - r i p p l e s 97. r e v e a l e d by t h e s i d e - s c a n s o n a r a r e i d e n t i c a l f e a t u r e s . The m e g a - r i p p l e s h a v e a l l t h e c h a r a c t e r i s t i c s o f b e i n g a c u r r e n t r e l a t e d phenomenon. D r . L u t e r n a u e r h a s i n d i c a t e d ( p e r s o n a l comment) t h a t t h e f l o o d t i d e h a s t h e s t r o n g e s t e f f e c t on t h e f o r e s l o p e o f t h e b a n k s and t h a t t h e o r i e n t a t i o n a n d a s y m e t r y o f t h e m e g a - r i p p l e s a p p e a r t o be c o n s i s t e n t w i t h t h e d i r e c t i o n o f t h e f l o o d t i d e c u r r e n t s . Some o f t h e r e c o r d s w e r e t a k e n d u r i n g a f l o o d t i d e a n d some d u r i n g a n ebb t i d e b u t t h e o r i e n t a t i o n a nd t h e d i r e c t i o n o f t h e a s y m e t r y o f t h e mega-r i p p l e s a p p e a r s t o h a v e r e m a i n e d u n c h a n g e d . W h a t e v e r t h e r e l a -t i o n s h i p s b e t w e e n t h e m e g a - r i p p l e s , t h e t i d e s a nd t h e c u r r e n t s a r e , i t i s c l e a r t h a t t h e s e f e a t u r e s a r e n o t r e l a t e d t o mass w a s t i n g a n d , h e n c e , t h e q u e s t i o n o f s l o p e s t a b i l i t y c a n now be r e s o l v e d . Some e r o s i o n a l i n s t a b i l i t y i s i n d i c a t e d by t h e a r e a s o f r e t r e a t b u t t h e r e a p p e a r s t o be no i n s t a b i l i t y w i t h r e s p e c t t o mass w a s t i n g u n d e r s t a t i c l o a d i n g a n d f u l l s t o r m wave l o a d i n g . ADDITIONAL DESIGN CRITERIA The r e m a i n i n g f a c t o r s w h i c h must be c o n s i d e r e d t o p r o v i d e a c o m p l e t e d a t a b a s e f o r an e n g i n e e r i n g i n v e s t i g a t i o n o f t h e b a n k s a r e p r i m a r i l y e n v i r o n m e n t a l . T h e r e a r e two b a s i c a l l y d i s t i n c t a s p e c t s o f t h e e n v i r o n m e n t w h i c h must be c o n s i d e r e d . One a s p e c t i s t h e p h y s i c a l f o r c e s o f t h e e n v i r o n m e n t w h i c h w i l l be a c t i n g on any e n g i n e e r i n g s t r u c t u r e on t h e b a n k s . The m a j o r p h y s i c a l f o r c e s o f t h e e n v i r o n m e n t t o be c o n s i d e r e d a r e w i n d a n d wave. T e m p e r a t u r e s c a n a l s o p l a y a n i m p o r t a n t r o l e a t many l o c a t i o n s , b u t do n o t do s o h e r e a s t h e a v e r a g e J a n u a r y t e m p e r a -t u r e i s a b o u t 36°F a n d t h e a v e r a g e J u l y t e m p e r a t u r e i s a b o u t 9 8 . 62°F (Hoos and Packman, 1 9 7 4 ) . The other aspect of the environ -ment i s the b i o l o g i c a l environment, which has come to be known as the ecology. Wind Hoos and Packman ( 1 9 7 4 ) l i s t the maximum observed wind speeds i n the banks area as N..W. 5 5 miles per hour at Vancouver I n t e r n a t i o n a l A i r p o r t and S.E. 64 miles per.hour at Tsawwassen Ferry Terminal and they present a wind rose of the cumulative winds from 1 9 5 3 to 1 9 7 1 - Table 5 i s a summary of the informa-t i o n on that wind rose. Table 5 Cumulative Winds - 1 9 5 3 to 1 9 7 1 D i r e c t i o n Frequency % Mean Wind Speed mph N. 2 . 3 4 . 1 N.E. 1 2 . 3 7 - 3 E. 3 1 . 6 7 - 4 S.E. 1 0 . 5 8 . 9 S. 6 . 8 8 . 7 S.W. 7 - 0 7 - 9 W. 1 5 . 8 1 0 . 8 N.W. 5 . 6 7 . 8 Calm 8 . 1 % Swan Wooster ( 1 9 6 7 ) presented monthly wind roses of winds i n excess of 2 0 miles per hour i n terms of hours per month averaged over a 1 0 year p e r i o d . The Swan Wooster ( 1 9 6 7 ) data a l s o Included the average number of hours of wind per month i n excess of 3 0 miles per hour. January, October, November and December each have at l e a s t 1 hour per month of 3 0 + m.p.h.- winds from the N.W. wit h January having the most at 2 . 1 hours per month. November and December a l s o have winds i n excess of 3 0 m.p.h. from S. and S.W. f o r l e s s than 1 hour per month f o r each d i r e c t i o n . The only other months w i t h winds i n excess of 99. 30 m.p.h. a r e May and J u n e w i t h 1.1 and 1.5 h o u r s p e r m o n t h , r e s p e c t i v e l y , f r o m t h e West. A u g u s t h a s t h e l o w e s t t o t a l h o u r s o f w i n d i n e x c e s s o f 20 m.p.h. a t 13-7 and M a r c h h a s t h e h i g h e s t a t 44. Wave The M a r i n e E n v i r o n m e n t a l D a t a S e r v i c e c o l l e c t s a n d com-p i l e s wave r e c o r d s f r o m s u c h s o u r c e s a s W a v e r i d e r A c c e l e r o m e t e r B u o y s , two o f w h i c h w e re l o c a t e d o f f t h e b a n k s . S t a t i o n 102 was a bu o y l o c a t e d o f f S t u r g e o n Bank f r o m F e b r u a r y 7. 1974 t o A u g u s t 9, 1975 a n d S t a t i o n 108 was a buoy l o c a t e d o f f R o b e r t s Bank f r o m F e b r u a r y 7 , 1974 t o J u l y 31 , 1975- The R o b e r t s B a n k buoy ( S t a t i o n 108) was o u t o f c o m m i s s i o n f r o m t h e e n d o f O c t o b e r 1974 t o t h e end o f A p r i l 1975 and t h u s d i d n o t r e c o r d t h r o u g h t h e w i n t e r m o n t h s , w h i c h h a v e t h e g r e a t e s t p e r i o d s o f t h e s t r o n g -e s t w i n d s a nd t h e r e f o r e p o t e n t i a l l y t h e l a r g e s t w a v e s . F o r t h e few months when b o t h b u o y s were o p e r a t i n g s i m u l t a n e o u s l y , t h e r e c o r d s p r o d u c e d i n t h e f o r m o f t h e C h a r a c t e r i s t i c Wave H e i g h t v s . t h e Time i n Days p l o t s a r e v e r y s i m i l a r . T h i s i n d i c a t e s t h a t f o r t h e p u r p o s e s o f c h o o s i n g d e s i g n p a r a m e t e r s t h e S t u r g e o n B a n k d a t a s h o u l d be a p p l i c a b l e t o t h e w h o l e D e l t a f r o n t . When f u n c t i o n i n g p r o p e r l y t h e W a v e r i d e r b u o y s make a 20 m i n u t e wave r e c o r d e v e r y t h r e e h o u r s . The s i g n i f i c a n t Wave H e i g h t i s d e f i n e d a s f o u r t i m e s t h e s q u a r e r o o t o f t h e a r e a u n d e r t h e v a r i a n c e s p e c t r u m o f t h e w a t e r e l e v a t i o n . To f o r m a c o n t i n u o u s p l o t o f s i g n i f i c a n t wave h e i g h t w i t h t i m e when t h e wave r e c o r d i n t e r v a l i s t h e s t a n d a r d t h r e e h o u r s , t h e p l o t s a r e j o i n e d by l i n e a r i n t e r p o l a t i o n . Gaps i n t h e s e r e c o r d s i n d i c a t e m a l f u n c t i o n s w h i c h c a u s e d m i s s i n g r e a d i n g s . E n v i r o n m e n t 100. C a n a d a c o m p i l e s a l l t h e wave d a t a on c o m p u t e r s w h i c h p r o d u c e d e t a i l e d l i s t i n g s o f t h e I n d i v i d u a l wave r e c o r d s , m o n t h l y c u r v e s o f C h a r a c t e r i s t i c H e i g h t v s . T i m e , P e r c e n t a g e E x c e e d e n c e v s . Wave H e i g h t f o r t h e o b s e r v a t i o n p e r i o d , P e r c e n t a g e O c c u r -r e n c e v s . P e a k P e r i o d f o r t h e o b s e r v a t i o n p e r i o d a n d a s c a t t e r d i a g r a m o f s i g n i f i c a n t Wave H e i g h t v s . P e a k P e r i o d d u r i n g t h e p e r i o d o f o b s e r v a t i o n . The l a r g e s t s i g n i f i c a n t wave h e i g h t r e c o r d e d o f f S t u r g e o n B a n k was b e t w e e n 9 a n d 10 f e e t w i t h a p e a k p e r i o d b e t w e e n 6 and 7 s e c o n d s a n d o f f R o b e r t s B a n k was b e t w e e n 7 a n d 8 f e e t w i t h a p e a k p e r i o d b e t w e e n 5 a n d 6 s e c o n d s . S t u r g e o n B a n k r e c o r d e d t h e maximum wave h e i g h t w i t h z e r o p e r c e n t a g e e x c e e d e n c e a s 13 f e e t a n d R o b e r t s B a n k r e c o r d e d 10 f e e t . The f a c t t h a t t h e R o b e r t s Bank b u o y d i d n o t r e c o r d d u r i n g t h e w i n t e r m o n t h s e x p l a i n s why t h e S t u r g e o n Bank b u o y r e c o r d e d s i g n i f i c a n t l y l a r -g e r w a v e s . The a p p r o x i m a t e r e l a t i o n s h i p -H = 1.4 / f e t c h ... (8-1) w h e r e H = wave h e i g h t i n f e e t a n d f e t c h = t h e s t r e t c h o f o p e n w a t e r o v e r w h i c h a wave c a n b u i l d u p , i n m i l e s , was u s e d t o e s t i m a t e t h e maximum wave h e i g h t w h i c h c o u l d be b u i l t up d u r i n g g a l e f o r c e w i n d s ( w i n d s i n e x c e s s o f 35 m i l e s p e r h o u r ) . The maximum f e t c h l e n g t h I n t h e S t r a i t o f G e o r g i a t e r m i n a t i n g on t h e b a n k s i s j u s t o v e r 72 m i l e s ( f r o m H o r n b y I s l a n d ) , w h i c h i n d i c a t e s a maximum wave h e i g h t on t h e o r d e r o f 12 f e e t . A t l e a s t one wave o f t h i s m a g n i t u d e was r e c o r d e d d u r i n g t h e 1.5 y e a r o b s e r v a t i o n p e r i o d , i n d i c a t i n g t h a t w a v e s o f t h i s m a g n i -t u d e w o u l d n o t be a r a r e e v e n t on t h e b a n k s . F o r d e s i g n p u r p o s e s t h e wave d a t a , w i n d d a t a a n d g e o g r a p h y 1 0 1 . must be c o n s i d e r e d t o g e t h e r . W i n d s f r o m t h e N o r t h West h a v e t h e most h o u r s p e r y e a r i n e x c e s s o f 30 m i l e s p e r h o u r , a n d t h e l o n g e s t f e t c h i s p r o v i d e d f r o m t h e N o r t h West. From t h i s i t i s c l e a r t h a t t h e most f r e q u e n t l a r g e w a v e s , a n d p o t e n t i a l l y t h e l a r g e s t w a v e s , w i l l come f r o m t h e N o r t h West. . T h i s i n f o r -m a t i o n c a n g u i d e t h e o r i e n t a t i o n o f s t r u c t u r e s , b r e a k w a t e r s a n d c a u s e w a y s a n d a i d t h e d e s i g n o f s l o p e w a s h p r o t e c t i o n f o r s u c h s t r u c t u r e s . E c o l o g y M e n t i o n o f t h e b i o l o g i c a l e n v i r o n m e n t h a s b e e n l e f t t o l a s t n o t b e c a u s e i t i s o f l e s s i m p o r t a n c e t h a n t h e f o r c e s o f t h e p h y s i c a l e n v i r o n m e n t b u t b e c a u s e i t c a n n o t be a s r e a d i l y d e f i n e d a s c a n t h e p h y s i c a l e n v i r o n m e n t . The i n t e r a c t i o n o f t h e p h y s i c a l e n v i r o n m e n t a n d t h e e n g i n e e r i n g p r o j e c t a r e f a i r l y w e l l u n d e r s t o o d a n d , i n most c a s e s , t h e e n g i n e e r i s d e s i g n i n g f o r t h e e s t i m a t e d w o r s t p r o b a b l e c o n d i t i o n s o f t h e p h y s i c a l e n v i r o n m e n t a c t i n g a g a i n s t t h e e n g i n e e r i n g s t r u c t u r e . T h e r e i s no p a r a l l e l when d i s c u s s i n g t h e b i o l o g i c a l e n v i r o n m e n t b e c a u s e , i n most c a s e s , t h e b i o l o g i c a l e n v i r o n m e n t d o e s n o t a c t a g a i n s t t h e e n g i n e e r i n g s t r u c t u r e , i t i s a f f e c t e d by i t a n d r e a c t s t o i t s p r e s e n c e . A d e t a i l e d l o o k a t t h e b i o l o g i c a l e n v i r o n m e n t i s o u t s i d e t h e s c o p e o f t h i s t h e s i s , h o w e v e r , i t i s n e c e s s a r y t o d i s c u s s i t v e r y b r i e f l y s i n c e t h e e n v i r o n m e n t a l i m p a c t o f a p r o j e c t ' must be one o f t h e f a c t o r s g o v e r n i n g i m p l e m e n t a t i o n a n d d e s i g n . The much r e f e r r e d t o w o r k by Hoos and Packman ( 1 9 7 4 ) c o n t a i n s a w e a l t h o f i n f o r m a t i o n on a l l t h e v a r i o u s f o r m s o f l i f e f o u n d i n t h e F r a s e r R i v e r E s t u a r y . T h e r e a r e two a s p e c t s o f t h e 102. b i o l o g i c a l e n v i r o n m e n t o f t h e b a n k s w h i c h c o u l d p o t e n t i a l l y be f a i r l y s e n s i t i v e t o c h a n g e s on t h e b a n k s , a n d w h i c h a r e o f m a j o r i m p o r t a n c e . P o r t i o n s o f t h e b a n k s a r e c r i t i c a l f e e d i n g , g r o w t h and s h e l t e r a r e a s f o r t h e F r a s e r R i v e r s a l m o n as t h e y make t h e t r a n s i t i o n f r o m r i v e r t o o c e a n . The b a n k s a r e a d j a c e n t t o , a n d f o r m p a r t o f , a v e r y i m p o r t a n t f e e d i n g , r e s t -i n g a n d w i n t e r i n g a r e a f o r t h e m i g r a t o r y w a t e r f o w l w h i c h f o l l o w t h e P a c i f i c F l y w a y . The b a n k s a r e , o f c o u r s e , i m p o r t a n t t o many o t h e r a s p e c t s o f t h e b i o l o g i c a l e n v i r o n m e n t ( f o r e x a m p l e , t h e y a r e a n i m p o r t a n t f e e d i n g and s p a w n i n g a r e a f o r t h e P a c i f i c H e r r i n g w h i c h i s a m a j o r s o u r c e o f f o o d f o r t h e s a l m o n ) a n d i t i s t h e i m p o r t a n c e o f t h e b a n k s t o t h e b i o l o g i c a l e n v i r o n m e n t w h i c h n e c e s s i t a t e s t h e i n c l u s i o n o f t h e e n v i r o n m e n t a s a d e s i g n p a r a m e t e r . CONCLUSIONS R o b e r t s Bank a n d S t u r g e o n Bank a r e c omposed o f g e o l o g i -c a l l y r e c e n t , n o r m a l l y c o n s o l i d a t e d , s e d i m e n t s . T h e s e s e d i m e n t s a r e many h u n d r e d s o f f e e t t h i c k . The s u r f a c e 80 f e e t o f s e d i -ment i s p r i m a r i l y g r a n u l a r i n n a t u r e , e x h i b i t i n g no s i g n i f i c a n t c o h e s i v e p r o p e r t i e s . The g r a n u l a r s e d i m e n t s a r e r e m a r k a b l y u n i -f o r m i n g r a d a t i o n f o r any s p e c i f i c s a m p l e , h o w e v e r , t h e r e i s no n o t i c e a b l e l a t e r a l c o n t i n u i t y t o t h e s e d i m e n t l a y e r i n g e v e n a t 700 f o o t s p a c i n g . The s e d i m e n t c o l u m n h a s many l a y e r s w i t h a h i g h s i l t c o n t e n t w h i c h a r e m o d e r a t e l y c o m p r e s s i b l e ; and p o t e n -t i a l s e t t l e m e n t s must be one o f t h e g o v e r n i n g d e s i g n c o n s i d e r a -t i o n s f o r a n y p r o p o s e d d e v e l o p m e n t . The b a n k s ' s e d i m e n t s a r e o f l o o s e t o medium d e n s i t y a n d h a v e a s i g n i f i c a n t l i q u e f a c t i o n p o t e n t i a l b a s e d o n a number o f 103-d i f f e r e n t a n a l y s e s . A l t h o u g h t h e r e i s no p r o v e n e v i d e n c e o f p r e v i o u s l i q u e f a c t i o n on t h e b a n k s o r on t h e F r a s e r D e l t a , t h e b a n k s a r e l o c a t e d i n a n a r e a w h i c h h a s a r e a s o n a b l y h i g h p r o -b a b i l i t y o f , a t some t i m e , e x p e r i e n c i n g a n e a r t h q u a k e o f s u f f i c i e n t m a g n i t u d e a n d d u r a t i o n t o c a u s e l i q u e f a c t i o n o f t h e s e d i m e n t s . The p r e d i c t e d 1 i n 100 a n n u a l p r o b a b i l i t y e a r t h q u a k e a p p e a r s t o be s u f f i c i e n t t o c a u s e t h e l i q u e f a c t i o n o f some a r e a s on R o b e r t s B a n k a n d S t u r g e o n B a n k . The s u b a q u e o u s s l o p e s a r e a t l e a s t n o m i n a l l y s t a b l e w i t h r e s p e c t t o mass w a s t i n g . Any mass w a s t i n g , o t h e r t h a n a c a t a s -t r o p h i c e v e n t t r i g g e r e d by a n e x t e r n a l f o r c e , w o u l d be o f a s h a l l o w s m a l l v o l u m e n a t u r e . S t u d i e s c o n d u c t e d , s o f a r , i n d i -c a t e t h a t e r o s i o n o f t h e s u b a q u e o u s s l o p e s i s p r e s e n t l y o c c u r -r i n g a t a number o f p o i n t s . F u r t h e r s t u d i e s a r e recommended t o l o c a t e and q u a n t i f y any e r o s i o n a n d d e t e r m i n e t h e c o n t r o l l i n g p a r a m e t e r s and t h e a c t i v e a g e n t s . . W i n d s , waves and t e m p e r a t u r e s e x p e r i e n c e d o n t h e b a n k s a r e f a r f r o m t h e e x t r e m e s f o u n d , a n d d e a l t w i t h i n many o t h e r p a r t s o f t h e w o r l d . T h e s e f a c t o r s a r e r e a s o n a b l y w e l l q u a n t i -f i e d f o r most d e s i g n p u r p o s e s . T h e r e i s , h o w e v e r , one - f a c t o r w h i c h i s n o t v e r y w e l l q u a n t i f i e d and o f w h i c h a b e t t e r u n d e r -s t a n d i n g i s n e e d e d ; t h e e c o l o g y o f R o b e r t s and S t u r g e o n B a n k s . S u f f i c i e n t d a t a w e r e a v a i l a b l e f r o m v a r i o u s s o u r c e s t o a l l o w a g e n e r a l o v e r a l l a p p r a i s a l o f t h e e n g i n e e r i n g p a r a m e t e r s a n d . r e l a t e d f a c t o r s f o r R o b e r t s B a n k and S t u r g e o n B a n k . Some f a c t o r s , s u c h as s u b a q u e o u s s l o p e e r o s i o n and t h e e c o l o g y , r e q u i r e f u r t h e r s t u d y t o d e f i n e t h e s i g n i f i c a n t f a c t o r s a t w o r k . o 104. BIBLIOGRAPHY Bazaraa, A., 1967, "Use of the Standard Penetration Test f o r Estimating Settlements of Shallow Foundations on Sand," Ph.D. Di s s e r t a t i o n , University of I l l i n o i s , C i v i l Engineering. Carrigy, M.A., 1970, "Experiments on the Angles of Repose of Granular Materials," Sedimentology, V o l . 14. Cook, P.M., 1967, "Preliminary S o i l Report, Sturgeon and Roberts Banks," prepared f o r SWAN WOOSTER Eng. Co. Cook, P.M., 1968, " S o i l s and Foundation Report, Roberts Bank Development," prepared for SWAN WOOSTER Eng. Co. • Cook, Pickering, and Doyle Ltd., 1974. " S o i l Report, Vancouver Airport Extension, A p r i l 1974, " prepared for the Department of Public Works. de Mello, V., 1971. "The Standard Penetration Test — A State-ofr-the-Art Report," 4th Pan Am Conf. on SM and FE, Puerto Rico, Vol. 1. Finn, W.D.L., D.J. Pickering and P.L. Bransby, "Sand Lique-f a c t i o n i n T r i a x i a l and Simple Shear Tests," Journal of the S o i l Mechanics and Foundations D i v i s i o n , ASCE, Vol. 92 , SM 6 , 1966. Gargett, A.E., 1976, "Generation of Internal Waves i n the S t r a i t of Georgia, B r i t i s h Columbia," Deep-Sea Research and Oceanographic Abstracts, Vol. 2 3 , No. 1. GIbbs, H.J. and W.H. Holtz, 1957. "Research on Determining the Density of Sands by Spoon Penetration Testing," 4th ICSMFE, London, Vol. 1. Henkel, D.J., 1970, "The Role of Waves i n Causing Submarine Landslides," Geotechnique, Vol. 20 , No. 1. Hoos, L.M. and G.A. Packman, 1974, "The Fraser River Estuary, Status of Environmental Knowledge to 1974 , " Report of the Estuary Working Group, Department of Environ-ment, Regional Board, P a c i f i c Region. Johnston, W.A., 1921, "The Age of the Recent Delta of Fraser River, B r i t i s h Columbia, Canada," American Journal of Science (1) . Kishida, H-, 1965. "Damage of Reinforced Concrete Buildings i n Niigata City with Special Reference to Foundation Engineering," S o i l s and Foundations, Vol. 6 , No. 1. 105. Lambe, T.W. and R.V. Whitman, 1969, " S o i l Mechanics," Series i n S o i l Engineering, John Wiley & Sons, Inc. Lee, K.L. and J.A. P i t t o n , 1969, "Factors A f f e c t i n g the C y c l i c Loading Strength of S o i l s , " V i b r a t i o n E f f e c t s of Earthquakes on S o i l s and Foundations, ASTM STP -450, American Society for Testing and Materials, 1969. Luternauer, J.L. and J.W. Murray, 1973, "Sedimentation on the Western Delta-Front of the Fraser River, B r i t i s h Columbia," Can. Journal Earth Science 10_ (11 ) . Luternauer, J.L., 1974, "The Fraser Ri'ver Estuary, Status of Environmental Knowledge to 1974, Geology," Report of the Estuary Working Group, Department of Environment, Regional. Board, P a c i f i c Region. Luternauer, J.L., 1976, "Fraser Delta Sedimentation, Vancouver, B r i t i s h Columbia," Report of A c t i v i t i e s , Part A, Geological Survey of Canada, Paper 76-1A, pp. 213-219-Martin, G.R., W.D.L. Finn and H.B. Seed, 1975, "Fundamentals of Liquefaction Under C y c l i c Loading," Journal of the Geotechnical D i v i s i o n , ASCE, Vo l . 101 , No. GT5, May 1975. Mathews, W.H. and F.P. Shepard, 1962, "Sedimentation of the Fraser River Delta, B r i t i s h Columbia," B u l l . Amer. Assoc. P e t r o l . Geol. 4i5 ( 8 ) . Mathews, Fyles and Nasmith, 1970, " P o s t g l a c i a l Crustal Move-ments i n Southwestern B r i t i s h Columbia and Adjacent Washington State," Canadian Journal of Earth Science, V. 7 , PP. 690-702. Mayers, I.R., 1968, "Analysis of the Form and Origin of the Fraser River Delta's Subaqueous Slump Deposits," B.Sc. Thesis, Dept. of Geophysics, University of B r i t i s h Columbia. Milne, W.G., I 963 , "Seismicity of Western Canada," Contribu-tions from Dominion Observatory, Ottawa, V. 5 , No. 13-Ohsaki, Y., 1970, "Effects of Sand Compaction on Liquefaction During the Tokachioki Earthquake," S o i l s and Foundations, Vol. X, No. 2. Sarma, S.K., 1973, " S t a b i l i t y Analysis of Embankments and Slopes," Geotechnique, Vol. 23 , No. 3 . Schmertmann, J.H., 1975, "The Measurement of I n s i t u Shear Strength," a State-of-the-Art presentation at the ASCE Specialty Conference on I n s i t u Measurement of S o i l Pro-p e r t i e s , Raleigh, N. Carolina. 106. Seed, H.B., I.M. I d r l s s and Kiefer, 1969. " C h a r a c t e r i s t i c s of Rock Motions During Earthquakes," Journal of the S.M. and P.D., ASCE, Vol. 95, No. SM5, September 1969. Seed, H.B. and I.M. I d r i s s , 1971, "Si m p l i f i e d Procedure for Evaluating S o i l Liquefaction P o t e n t i a l , " Journal of the SM and FD, Proceedings, ASCE, September 1971. Sleath, J.F.A., 1970, "Wave Induced Pressures i n Beds of Sand," Journal of the Hydraulics D i v i s i o n , ASCE, Vol. 96, No. HY2, February 1970. SWAN WOOSTER ENGINEERING CO.. LTD., 19.67, "Planning Study f o r Outer Port Development at Vancouver, B.C." Taylor, D.W., 1948, "Fundamentals of S o i l Mechanics," John Wiley & Sons, Inc. Terzaghi, K. and R.B. Peck, 1948, " S o i l Mechanics i n Engineer-ing P r a c t i c e , " Second E d i t i o n , John Wiley & Sons, Inc. Terzaghi, K., 1962, "Discussion, Sedimentation of the Fraser River Delta, B r i t i s h Columbia," B u l l . Amer. Assoc. P e t r o l . Geol. 4(5 ( 8 ) . T i f f i n , D.L., 1969, "Continuous Seismic P r o f i l i n g i n the S t r a i t of Georgia, B.C.," Ph.D. Thesis, University of B r i t i s h Columbia. T i f f i n , D.L., J.W. Murray, I.R. Mayers, and R.E. Garrison, 1971, "Structure and Origin of Foreslope H i l l s , Fraser Delta, B r i t i s h Columbia," B u l l . Can. Pet r o l . Geol. 19 (3). APPENDIX 1 L o c a t i o n P l a n o f Continuous S e i s m i c P r o f i l e s , B a thymetric P r o f i l e s , North Continuous S e i s m i c P r o f i l e , South Continuous S e i s m i c P r o f i l e , T r a n s v e r s e Continuous S e i s m i c P r o f i l e . 108. LOCATIONS OF THE CONTINUOUS SEISMIC PROFILES TAKEN ACROSS THE SLUMP STRUCTURES BATHYMETRIC P R O F I L E S I N AREA OF SLUMP STRUCTURES no. N O R T H P R O F I L E SOUTH PROFILE • 0 3 S TRANSVERSE PROFILE 117. APPENDIX 2 F o r t r a n L i s t i n g o f computer program f o r a n a l y s i n g c i r c u l a r a r c p o t e n t i a l f a i l u r e s u r f a c e s . $L I ST UWSLOPES • 1 C I F IT=NO. FA ILURE ARCS ; E= FA I LURE ARC SLOPE LENGTH/2 2 C D= IN IT IAL FA ILURE DEPTH;DMAX=MAX FA ILURE DEPTH 3 r i ^ O U Y A N T WEIGHT ;B=SLCPE ANGLE ; F= IN I T i AL TRY F OF S 4 C PH I=FR ICT ICN ANGLE;C=COHESION 5 C N=NO. SL ICES;J=N+1; ITMAX=MAX. U ITERATIONS 6 C IFPR=1 FOR NONHYDRQSTATIC; GW=UN IT WEIGHT WATER. 7 REAL D X . 5 0 ) f T A N T ( 5 0 ) , T ( 5 0 ) , X M { 5 0 ) W ( 5 0 ) , F 1 ( 5 0 ) , F 2 ( 5 0 ) , F 3 C 5 0 ) 8 REAL P P ( 5 0 ) . X 1 5 0 ) , T M ( 5 0 ) . D E P I 5 0 ) » H W ( 5 0 ) , U T { 5 0 ) ,UB(50) 9 REAL UX.LX:', R . DMAX ,DD 10 INTEGER N , K , J t I T M A X » P R » I F D A , I F I T 11 707 CCNTINUE 12 10 F O R M A T ( 8 F 1 0 . 3 . 13 R E A D ( 5 , 2 0 ) I F I T 14 READ. 5 ,10 ) E , D , D M A X , G , B , F , P H I , C 15 R E A D . 5 , 20) N . J , i t "NAX, IFPR,GW 16 20 F O R M A T . 4 1 5 , F 1 0 . 3 ) 17 WRITE ( 6 , 1 0 0 ) C t P H I t G 18 100 F O R M A T . ' 1 * , « C G H E S I C N = » v F 7 o 3 , ' P H I = » , F 7 . 3 B O U Y A N T UNIT WT. = » , F 7 . 3 ) 19 W R I T E ( 6 . 2 0 0 ) B 20 200 FORMAT { 11 SLOPE ANGLE=' . F 7 . 3 » 9 D E G R E E S ' . 21 IF( I F I T . L T . 1 . 0 0 ) IFIT= 1 22 B=B/57 .28 23 PH I=PH IZ57.28 24 Z = TAN(B ) . . . . . . . 25 Y=CCS<B) 2.6 - V = TAJMi-RHI 1 ' 27 DO 881 I 1=1. I F IT 28 R = ( D * D + E * E ) / ( 2 . D 0 * D ) 29 W R I T E ( 6 ? 3 0 C ) R.D 30 300 FORMAT (//•RA'D". "in- FT_T_T~CTKUL'E="•, F9 . 3, ! DEP TH 0 F PfcNE IR AI I U N - ' , F / . J J 31 ' l F i N . L T . 0 . 0 0 ) GOTO 1 32 A -FLOAT{N ) E = S O R T ( R * R - ( R - D ) * K R - D ) ) 34 D X S = 2 . D 0 * E * C 0 S . B ) / A 35 X l l ) = - E * C O S . B ) + (R-D.)*S IN.B) 36 X (N -H )=E *COS (B ) + CR -DJ * SIN-IB) 37 DX{15=DXS 38 C GET END POINTS AND WIDTH OF SL ICES IF THEY ARE TO BE GENERATED ""DO 2 I = 2 ,N ~ — -A - F L O AT ( I ) X ( I ) = X ( 1) + ( A - 1 ,.D0_)*pXS_ _ , a| DX{ I )=OXS 2 C O N T I N U E GOTO 17 : 1 C O N T I N U E I F ( I I . G T o l . O ) GOTO 17 I F S L I C E E N D P O I N T S ARE T O BE READ I N , READ THEM  DO 3 1 = 1 , J P E A D ( 5 , 3 0 ) X U ) 3 0 FORMAT I F 1 0 . 3 ) 3 C C N T I N U E I F S L I C E E N D P O I N T S HERE READ I N , G E T S L I C E W IDTHS N=-N DO 4 I = 1 , N D X { I ) = X ( I + 1 ) - X U ) 4 C C N T I N U E 1 7 C C N T I N U E CO 5 1=1,N U X = X { 1 + 1 ) L x=xm XM i I ) = ( U X + L X ) / 2 . D Q C A L C U L A T E T H E S L O P E OF T H E F A I L U R E S U R F A C E AT S L I C E M I D P O I N T T A N T ( I ) =XM 11 ) *1 o D O / S Q R T ( R * " R - X M I I )"*XM( I ) ) T „ „ „ T „ T C A L C U L A T E T H E S L O P E A N G L E OF T H E F A I L U R E S U R F A C E A T S L I C E M I D P O I N T T d ) =AT AN J T A N T { I ) J "CTTCULATE THE WEIGHTS OF THE SL ICES , n j „ , , nni U X P = { U X * U X / 2 . D 0 ) * Z - ( R - D ) * U X / Y + ( U X / 2 . D 0 ) * { S Q R T { R * R - U X * U X ) ) + l R * R / 2 . D 0 ) * f l^ ' i 'L X> 10 \~. T f H ^ Z ^ ~ D T ^ X 7 Y f T I X 7 2 .D 0 j * IS QRT { R *R - LX * L X > ) + R* R / 2 .DO * * A R S I N l L X / R ) \il I , = G * I U X P - L X P ) C O N T I N U E DO 8 1 = 1 » N i t j DEP { I ) IS T H E H E I G H T OF T H E S L I C E AT I T S M IDPO INT « U T I I ) = 0 3 D 0 U E ( I ) = 0 . D O 7 8 P P U ) = 0 . D 0 '•»MM*WJ.wJ,A'{JI"lt(. 7 9 8 C O N T I N U E \ 1 8 0 I F U F P R . E Q . O J G O T O 70 . . 81 I F f l l . G f . l . O J GOTO 7 71 j 8 2 8 3 C PR=1 C I FDA FOR A U T O M A T I C P R E S S . G E N E R A T I O N = 1 FOR D A M P I N G , 0 FOR NO DAMP ING ANYWHERE i 8 4 C I F B T =1 FOR D A M P I N G IN S O I L , 0 FOR NONE 85 R E A D ( 5 , 9 0 Q 0 ) P R , I F D A , I F 8 T 1 86 9 0 0 0 F 0 R M A T 1 3 I 5 ) i £ 7 I F i P R . N E . 0 ) GOTO 6 0 0 i i 88 89 DO 80 I = l t N C U T C 1 ) ^ P R E S S U R E T O P OF S L I C E ; U 8 { I ) = P R E S S . BOTTOM 3 •i 9 0 P. F A D ( 5 , 5 0 0 ) U T ( I ) , U B ( I ) •!91 5 0 0 F C R M A T ( 2 F 1 0 . 3 I 92 80 C O N T I N U E i 9 3 9 4 GOTO 7 0 C WN=WAVE N G . ( 2 * P I / L ) ; D C = M E A N S T I L L WATER D E P T H •] 9 5 C WL = WAVE LENGTH*,WH = WAVE H E I G H T — 'j 9 6 C DSB= T H I C K N E S S P E R M E A B L E S E A B E D I 9 7 6 0 0 R E A 0 ( 5 , 9 0 > W N , D C , W L , W H , D S B 1 9 8 90 F C R M A T i 5 F l 0 . 3 ) 9 9 7 7 1 C C N T I N U E 1 0 0 101 1 0 0 0 1 U T E ( 6 , 1 0 0 0 ) F ' r RMAT ( * * * * * * * WAVE DATA * * * * * * « ) ,~ .-.a 1 0 2 1 0 3 2 0 0 0 V.f I T E ( 6 , 2 0 0 0 ) WN F C R M A T { » W A V E NUMBER = » , F 1 0 . 3 ) 1 0 4 WR ITE I 6 , 3 0 0 0 ) WL .' 1 0 5 3 0 0 0 F O R M A T I * WAVE L E N G T H = ' , F 1 0 . 3 ) 1 0 6 1 G 7 4 0 0 0 W R I T E 1 6 . 4 0 C O ) WH F C R M A T { ' W A V E H E I G H T = » , F 1 0 . 3 ) 1 C 8 1 0 9 5 0 0 0 W R I T E ( 6 , 5 0 0 0 ) DC F O R M A T ( ' M E AN S T I L L WATER D E P T H = * , F 1 0 . 3 ) 1 1 0 111 6 0 0 0 F O R M A T ( ' T H I C K N E S S OF P E R M E A B L E S E A BED - « , F 1 0 . 3 ) 1 1 2 1 1 3 4<.:0 "WR ITE ( 6 , 4 0 0 ) ^ o _ o , F O R M A T ! * * * * * * * * * * * S L I C E I N F O R M A T I O N * * * * * * * * * * * * * ) 1 1 4 1 1 5 4 0 W R I T E t 6 * 4 0 S „ w „ - r . K , - r , % FORMAT I ' S L I C E ' , 8 X » 8 O X ' , 6 X , ' W E I G H T ' , 5 X , * U T * , 7 X , ' U B * , 8 X , ' T A N T « ) 1 1 6 1 1 7 XPM=XP( I ) - ( R - 0 ) * S I N ( B ) 1 118 1 1 9 H=DC -XPM*Z D P = G W * ( W H / 2 . 0 ) * C 0 S I 1 . 5 7 1 - X P M * W N . 1 1 2 0 I F U F D A . E Q . O ) GOTO 8 5 0 0 i 121 U T { I ) = D P / C O S H < WN*H) 122 I F { I F B T . E O . 0 ) GOTO 8 0 0 0 1 2 3 WNO=COSH.WN*DS8 ) 1 2 4 W N C = W N * ( D S B - D E P ( I ) ) 1 2 5 U B C I l = U T ( I | * C O S H C W N C . / W N D I 1 2 6 G O T O 7 0 0 0 1 2 7 8 5 0 0 UT< I .=DP '< 1 2 8 8 0 0 0 U 6 ( i ) = u u n 1 2 9 7 0 0 0 C O N T I N U E 1 3 0 7 0 C O N T I N U E 1 j 131 DO 6 1 = 1 V N 13 2 WR ITE I 6 , 5 0 ) I , D X ( I ) , W ( I ) , U T ( I ) , U B { I ) , T A N T . I ) i 133 50 F O R M A T ( • • , I 6 , 5 F 1 0 , 3 ) 1 3 4 6 C O N T I N U E i 1 3 5 DO 9 1=1,N 1 3 6 XM { I )= { XM! I ) / Y ) - ( R - D ) * Z .< : 1 3 7 F i l l )=C * D X { I ) 1 3 8 1 3 9 F 2 ( I ) = ( W ( I ) + U T ( I ) * D X ( I J - U B l I ) * D X ( I ) » * V f 3 ( I ) = W ( I ) * S I N { T I I ) ) * R + U T { I ) * D X ( I ) * X M ( I ) / < Y * Y > 1 4 0 9 C O N T I N U E 141 1 4 2 C K--0 B E G I N I T I E R A T I ON T O F I N D F A C T O R OF S A F E T Y 14 3 13 C O N T I N U E 1 4 4 1 4 5 DO 11 1 = 1 , N T M ( I ) = C O S ( T _ 1 3 1 * ( l . D O + T A N T C I ) # V / F ) 1 4 6 11 C O N T I N U E 1 4 7 F 4 = 0 . C 0 1 4 8 F 5 = 0 . D 0 1 4 9 DO 12 1=1 ,N 1 5 0 F 4 = F4 + ( F i t I ) + F 2 J I ) ) * U . D O / T M l I ) 3 1 5 1 F 5 = F 5 + F 3 ( I ) 1 5 2 12 1 5 3 FN==F4*R'./F5. 1 5 4 1 5 5 6 0 W R I T E ( 6 , 6 0 1 FN F O R M A T { * F A C T O R OF S A F E T Y = S , F 1 0 . 3 ) 156 I F < A B S ( F N - F ) . L T . 0 . 0 0 1 ) G C T O 14 — — 157 F= FN | 158 K=K«-1 i 1 5 9 I F { K . G T . I T MA X)GOTO 14 I 1 6 0 GOTO 13 1 161 14 C O N T I N U E 162 163 1 6 4 I F ( I I .GT.1 . 0 ) GOTG 6 6 1 X X = F L 0 A T 1 I F I T ) O O - i DMAX-D)/(XX—1.0) 1 6 5 6 6 1 C O N T I N U E 1 6 6 167 8 8 1 D=D+DD C O N T I N U E i 168 R E A D ( 5 , 7 7 ) IFMORE j 1 6 9 1 7 0 7 7 FORMAT I I 5) I F{ I F M O R E . N E . 0 ) GOTO 707 i 171 STOP i 1 7 2 END ! END OF F I L E , . ... - ' < > APPENDIX 3 F o r t r a n L i s t i n g of Sarma sl o p e s t a b i l i t y program. S L I S T SARMAS 1 D I M E N S I O N X S C 5 0 ) , Y S ( 5 0 ) , Y L { 5 0 ) , U T ( 5 0 ) , U 6 ( 5 0 ) , X K B A R ( 5 0 ) , W ( 5 0 > , 2 l W B A R t 50 3 , H ( 5 0 ) , 0 ( 5 0 ) , A H 5 0 ) , A 2 ( 5 0 ) , A 3 _ 5 0 ) , A 4 l 5 0 ) , A5{ 5 0 ) , A6( 5"0T7~" 3 2 A 7 < 5 0 ) » 0 D { 5 0 ) , A 8 ( 5 0 ) , A A C 2 0 ) 3 . 2 GO TO 191 4 111 C O N T I N U E , 4 . 2 P R I N T 192 4 . 4 192 F O R M A T ( / / » * # * * NEW P R O B L E M * * * • , / / ) 4 . 6 191 C O N T I N U E 5 R E A D 2 ,NS 6 C N S = N O . OF S L I C E S + 1 , X S = S U R F A C E X - C O O R D . Y S = S U R F A C E Y - C O O R D 7 8 R E A D 1, ( X S U ) ,1 = 1 ,NS3 R E A D 1, .YS i I ) , 1 = 1 , NS 3 i 8. 2 GO TO 1 9 3 9 1 1 2 C O N T I N U E i 9 . 2 P R I N T 1 9 4 9 . 4 1 9 4 F O R M A T . / / , 1 * * * NEW S U R F A C E * * * » , / / ) 9 . 6 " 1 9 3 C O N T I N U E 1 0 R E A D 1, ( Y H I 3 , 1 = 1 ,NS3 11 R E A D 1 , C U T { I ) , 1 = 1 , N S ) 12 13 R E A D 1, ( U B ( I ) ,1 = 1 ,NS3 R E A D 1 , ( X K B A R { 1 3 , 1 = 1 , N S ) 14 R E A D 1,PHI,C,GAMMA,GAMWTWL 15 R E A D 2 , J J 16 R E A D 1 , ( A A { I 3,1 = 1 , J J ) 17 c Y L = B A S E Y - C O O R D , U T = N G N H Y D R O S T A T I C T O P , U B = N O N H Y D R O S T A T I C BOTTOM 18 c XKB AR= A S S U M E D S H A P E OF F U N C T I O N FOR D E T E R M I N I N G I N T E R S L I C E 19 c F O R C E S , P H I = A N G L E OF F R I C T I O N , C = C O H E S I ON,GAMMA=SATURATED D E N S I T Y 20 ~ c GAMW=UN IT WEIGHT WAT E R , A A = PORE WATER P R E S S U R E F A C T O R f E A R T H Q U A K E ) 21 c WL=WATER L E V E L 22 2 F O R M A T ( 1 2 1 6 ) 23 1 F O R M A T { 1 2 F 6 . 3 3 24 P R I N T 12 25 26 P R I N T 4 » P H I , C ,GAMMA,G A M W,WL 4 F O R M A T ( 4 X , • P H I = « , F 6 . 3 , 2 X , « C = • , F 7 . 3 , 2 X , * G A M M A = ' , F 7 . 3 , 2 X , * G A M W = 8 27 1 , F 7 . 3 , 2 X ^ * W L = « , F 7 ' . 3 ) 28 P R I N T 12 29 P R I N T 101 30 101 FORMAT ( 3 X , 8 I ' , 8 X , ' X S V I B X T 1 VS"' , i i X T ^ Y L ' , I 3 X , 8 U T ' . 13 X , « UB • , 13 X , 3 1 1 ' X K B A R ' ) s 3 2 P R I N T 3 , ( 1 , X S ( I ) , Y S U ) , Y L U ) , U T ( I ) ,UB{ I J ,XKBAR I I I , I = 1 , N S ) 1 1 3 3 3 F O R M A T { 1 6 , 6 F 1 5 . 3 ) • j 3 4 P R P H I = P H I i 1 3 5 DO 4 4 J = 1 , J J i 1 3 6 SUMl=0o 1 3 7 S U M 2 = 0 . 3 8 S U M 3 = 0 . 3 9 S U M 4 = 0 . 4 0 SUM5=0. 4 1 S U M 6 = 0 „ 1 4 2 0 ( 1 1 = 0 . j 4 3 H ( l)=0c I 4 4 P H = 0 . 4 5 HH = 0 . 4 6 A = A A ( J ) 4 7 P R I N T 1 2 1 , A 4 8 1 2 1 F G R M A T ( / / , 2 X , ' P O R E P R E S S U R E P A R A M E T E R A = « , F 6 . 3 ) 4 9 P H I = P R P H I 5 0 P H I = P H I * 3 . 1 4 1 5 9 2 6 / 1 8 0 . 5 1 T A N P H I = T A N ( P H I ) 5 2 P R I N T 1 2 5 3 DO 5 1 = 2 , N S ; t 5 4 B = X S ( I ) - X S ( 1-1 ) 5 5 H ( I ) = Y S ( I ) - Y L ( I ) 5 6 A R E A = ( H ( I ) + H ( 1 - 1 ) ) * 0 . 5 * B 5 7 i: { I ) = A R E A* (GAMMA-GAMW ) 5 8 W B A R ( I ) = A R E A # G A M M A 5 9 I F ( YS ( I ) . L E . WL.) GO T O 6 6 0 H H = Y S ( I ) - W L 6 1 A R E A 1 = { H H + P H ) * 0 * 5 * B 6 2 AR E A 2 = A R E A - A R E A1 6 3 MlI ) = A R E A 1 * G A M M A + A R E A 2 * ( G A M M A - G A M W ) 6 4 P H = H H 6 5 6 C C N T I N U E 6 6 I F ( Y L U ) . G T . WL) W ( I 5 = W B A R ( I ) 6 7 A L P H = A T A N ( ( Y L ( I ) - Y L ( I - 1 ) ) / B ) 6 8 B E T A= AT AN { ( Y S I I ) - Y S I I - 11 )/B ) 6 9 P f O P = 0 « 5 * ( U T { I ) + 0T t I — l ) ) *B*GAMW/C'OS(BET A) - — J 70 P B G T = 0 . 5 * ( U B ( I ) + U 8 ( 1 - 1 ) ) * B * G A M W / C O S ( A L P H ) 71 G ( I ) = X K B A R ( I ) * { GAMMA-GAMW ) * H ( I ) * H ( I ) * 0 • 5+C*H' l I ) 72 F F = Q ( I ) -Q( 1-1 ) 73 T A N A = T A N ( P H I - A L P H ) 7 4 X G = X S < 1 - 1 ) + B * B / 6 . * ( ( G A M M A — G A M W ) * { H ( 1 - 1 ) + 2 . * H ( I } ) + G A M W * ( P H + 2 , * H H ) ) / j 75 1W( I > i 76 I F ( Y L ( I ) . G T . WL . C R . Y S ( I ) . L E . WL ) 1 7 7 1 X G = X S { I - 1 ) + B / 3 . * ( H U - 1 ) + 2 . * H ( I ) ) / ( H ( I ) + H ( I ~ 1 ) } i 78 Y G = { Y L ( 1 - 1 ) + 0 . 5 * H ( 1 - 1 ) ) * ( l . - ( X G - X S ( I - 1 ) ) /B )+ ( Y L l I ) +H< I j * 0 . 5) * S 79 1 1 X G - X S ( 1 - 1 ) J / B i i 80 XB=XG J 81 YB = YL ( 1 - 1 ) + ( X B - X S ( I - i n * ( Y L ( I j - Y L l I-lH/B 1 82 D I V = U T ( I ) + U T ( I - 1 ) J 83 X T = ( X S ( I ) + XS ( I - 1 » J * 0 . 5 84 I F I A B S I D I V I . L E . 1 . 0 E - 6 ) GO TO 14 i \ 85 XT = X S ( I — l ) + B / 3 . * ( U T ( I - 1 ) + 2 . * U T ( I ) ) / ( U T ( I ) + U T { 1 - 1 ) ) i 86 14 C O N T I N U E i 87 Y T = Y S i I - i ) + I Y S I I ) - Y S ( I-I J ) * ( X T - X S ' ( 1 -1 ) ) /B 88 Z = C O S ( P H I ) / C O S ( A L P H ) 8 9 0 = W ! I ) * T A N A + ( C * B * Z - P B O T * S I N ( P H I ) * P T O P * S I N ( P H I - A L P H + B E T A ) ) / • 9 0 I C O S ( P H I - A L P H ) 91 D D ( I ) = D 92 A 11 I ) = F F * T A N A 9 3 S U M l = S U M i + A i ( I ) 9 4 A 2 ( I 1 = X B - Y B * T A N A 95 A31 I ) = F F * A 2 ( 1 ) • 9 6 SUM3=SUM34-A3( I ) l 9 7 A 4 ( I ) = A * S I N ( P H I ) * Y B / ( C O S ( A L P H ) * C O S ( P H I - A L P H ) ) i 98 A 5 ( I ) = W B A R ( I ) * ( Y G + A 4 ( I ) ) 99 S U M 4 = S U M 4 + A 5 ( I ) 1 0 0 A 8 ( I ) = A 4 ( I ) / Y B 1 101 S U M 2 = S U M 2 + W B A R ( I ) * l l . + A8( I ) ) 102 SUM5=SUM5+D i 1 0 3 A 6 ( I ) = P T O P * C O S ( B E T A ) * ( X B - X T + ( Y B - Y T ) * T A N ( B E T A) ) i 1 0 4 A 7 ( I ) = D * Y B 1 0 5 S U M 6 = S U M 6 + A 6 ( ! j - D * Y B 106 A L P H = A L P H * 1 8 0 . / 3 . 1 4 1 5 9 26 1 0 7 B E T A = B E T A * 1 8 0 . / 3 . 1 4 1 5 9 2 6 108 I F ( I o G T . 2 J GO T O 102 1 0 9 1 1 0 P R I N T 1G3 1 0 3 F O R M A T ( 2 X ? « I 8 , 5X » 8 H ' , 7 X , * W • , 5 X , • W B A R ' , 4 X , ' P T O P « , 4 X , ' P 8 G T » , 4 X , 111 1 "I A_ PHI • "", 4X7 ' • B E T A 1 6 X , 8 Q * » 6 X i • F F % 5X » • T ANA • t 5 X 1 1 X 6 1 t 6 X » ' Y G * t 6Xt 112 2 ' X B ° , 6 X ,C Y B « , 6 X , « X T ' , 6 X , 8 Y T » ) 1 1 3 1 0 2 C C N T I N U E 1 1 4 P R I N T 1 0 , I , H U 3 ,W( 13 ,WBAR{ I ) , P T O P , P B O T , A L P H , B E T A , Q { I 3 , F F , TANA , 1 1 5 1 X G , Y G , X B , Y B , X T , Y T 1 1 6 10 F C R M A T U 4 , 1 6 F 8 . 1 ) 1 1 7 1 1 8 5 C C N T I N U E D I V = S U M 1 * S U M 4 + S U M 2 * S U M 3 119 ALAM=t S U M 2 * S U M 6 * - S U M 4 * S U M 5 ) / D I V 1 2 0 X K C = ( S U M 5 * S U M 3 — S U M 6 * S U M l ) / D I V 121 P R I N T 12 122 12 F O R M A T ( 1H0 , / / 9 H C O N T I N U E / / / ) , _ 1 2 3 1 2 4 P R I N T 1 0 4 1 0 4 F 0 R M A K 6 X , « A 1 » , 1 2 X , ' A 2 « , 1 2 X , 4 A 3 ' , 1 2 X , « A 4 • , 1 2 X , »A5« , 1 2 X , » A 6 ' , 1 2 5 1 1 2 X , « A 7 ' , 1 2 X ,8 D D * , 1 2 X , * A 8 » 3 1 2 6 P R I N T 1 1 , ( A l ( I J7X2TIT , " A 3 T D7 "A 4 ( 1 ) , A 5 ( I J , A 6 { 1 ) , A / 1 1 3 , U l ) ( l ) , A 8 t U i 1 2 7 1 , I = 2 , N S ) 128 11 F 0 R M A T ( 9 F 1 4 . 3 ) „ i 1 2 9 P R I N T 12 1 3 0 131 P R I N T 1 0 5 1 0 5 F O R M A T ( 5 X , « S U M 1 « , 1 0 X , » S U M 2 « , 1 0 X , • S U M 3 ' , 1 0 X , • SU N 4 ' , 1 0 X , « S U M 5 * , 132 1 3 3 1 1 0 X , • S U N 6 ' ) P R I N T 1 1 , S U M 1 , S U M 2 , S U M 3 , S U M 4 , S U M 5 , S U M 6 134 P R I N T 1 3 , A L A M , X K C 1 3 5 13 FORMAT ( 1 H 0 , 6 H L A M D A = , F 1 0 . 4 , 5 X , 12HCR I T . A ' C C L N . - , F 1 0 . 4 ) 1 3 6 1 3 7 4 4 C O N T I N U E C C H E C K FOP F U R T H E R F A I L U R E S U R F A C E S 138 R E A D 8 8 , N N 1 3 9 8 8 F O R M A T { 1 4 ) 1 4 0 I F ( N N . G E . 1) GO TO 1 1 2 . 141 C C H E C K FOP NEW P R O B L E M 1 4 2 R E A D 88 ,MM 143 I F ( M M . G E . 1) GO TO 1 1 1 1 4 4 STOP 1 4 5 END END OF i 

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