THE OUTER BANKS OF THE FRASER RIVER DELTA; ENGINEERING PROPERTIES AND STABILITY CONSIDERATIONS by STEVEN SCOTTON B.A. Sc., University of British Columbia, 1971 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCES in the FACULTY- OF GRADUATE STUDIES .- Dept. of Civil Engineering We. accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA MAY, 1977 © Steven Scotton, 1978 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Steven Scotton Department of Civil Engineering The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date February 6th, 1978 ii ABSTRACT Roberts Bank and Sturgeon Bank are the leading edges of the Fraser River Delta. In the past half century various aspects of the delta, and the banks, have been studied by geologists, geomorphologists and engineers. Published papers and reports of these studies form the primary data base for this thesis. The geology and geomorphology reports comple• mented the engineering data. Logs of 6 8 boreholes were found in the engineering reports made available for this 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 split 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 tests, triaxial tests and consolidation tests. The upper 80 feet of sediments, which is the zone of concern for strength and stability analyses, are primarily granular in nature. These sediments exist at a medium to loose density with a relative density as low as 40 percent suggested for large areas of the banks. Some of the deeper sediments are moderately compressible in nature and are presently normally consolidated. The nature of the surficial sediments is such that, in the existing seismic environment in which they are located, there is the possiblity of earthquake induced liquefaction. Methods of assessing the probability of liquefaction 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 in a few spots, are shown to be at least nominally stable with respect to mass wasting. There are some indications that these slopes could be subject to some erosional instability. The physical environment of the banks (wind, wave, temperature) is not particularly harsh, and presents no problems to engineering development. Certain aspects of the ecology of the banks, however, are of sufficient importance to warrant consideration as part of the design process for any project on the banks. TABLE OF CONTENTS Abstract Table of Contents List of Tables List of Figures Acknowledgements INTRODUCTION AREA OF STUDY SLUMP STRUCTURE ENGINEERING PARAMETERS Subsurface Sediments. Grain Size Distribution Relative Density Friction Angle Consolidation Parameters Atterburg Limits Compression Index Estimates SETTLEMENT CASE HISTORY PROBABLE EARTHQUAKE ACCELERATIONS LIQUEFACTION POTENTIAL OF THE BANKS Liquefaction Empirical Liquefaction Criteria Analytical Liquefaction Potential SUBAQUEOUS SLOPE STABILITY Erosional Instability Mass Wasting Effect of Surface Waves Effect of Earthquake Motions V ADDITIONAL DESIGN CRITERIA 9 7 Wind 9 8 Wave 99 Ecology 101 CONCLUSIONS 102 APPENDIX 1 APPENDIX 2 APPENDIX 3 vi LIST OF TABLES TABLE Page 1. Test Results 29 2. Historical Earthquakes 50 3. Earthquake Probability Analysis 51 4. Earthquake Duration 62 5. Cumulative Winds - 1953 to 1971 98 VI1 LIST OF FIGURES FIGURE Page 1. The Fraser Delta and the Strait of Georgia showing the location of Sturgeon Bank and Roberts Bank. 3 2. Photographs taken from a Pisces Submersible on March' 22 , 19 75. 5 3. Geologic Map of the Fraser River Delta .9 4. Interpreted Continuous Seismic Profile across the Slump Structures 11 5. Grain Size Distribution curves for the 3 surface samples taken on Sturgeon Bank 2 4 6. The Gibbs and Holtz and the Bazaraa curves of Relative Density vs. N - value 26 7. The de Mello relationship of jtfr vs. N - value 32 8. Possible relationship between the ratio of the Compression Index over the Void Ratio plus one (C /1+e), and the measured water contents - liquid limit and natural moisture content 41 9. Terminal of the Westshore Terminals Bulk Loading Facility showing the location of settlement Gauges 7 and 12 and the initial location of the coal stockpiles 44 10. Settlement of gauges 7 and 12 45 11. Extended settlement Record 48 12. Predicted maximum ground surface accelerations 52 13. Comparison of the Ohsaki and Kishida liquefaction criteria 56 14. Cumulative results of Standard Penetration Tests 59 15. Results of the Seed and Idriss Simplified Liquefaction analysis 64 16. Two Sections of the subaqueous slope plotted to natural scale 72 viii 17. Location of cross sections S and R 73 18. Freebody diagram of circular slip arc 77 19. Relationship between excess Pore Pressure and applied Shear Stress 83 20. Derivation of the failure criterion used to place the failure line on Fig. 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 Critical Acceleration and Pore Pressure Parameter for surfaces 4 and 5 89 24. Long deep section analysed to approximate the possible origin of the slump structures 91 25. Tracing of Hypsographic Profiles H, I and J 94 26. Location of Hypsographic Profile lines H, I and J 95 ix ACKNOWLEDGEMENTS / The names of all the people who have given me assist• ance with this thesis would fill another volume. As I am limited in space I would like to hereby thank everybody who lent assistance and request that you not take offence if your name is not specifically mentioned. In the Department of Civil Engineering I wish to thank Dr. W.D.L. Finn for his guidance during the research and his assistance during the writing of this thesis. Dr. P.M. Byrne and Dr. R.G. Campanella are to be thanked for their encouragement and assistance. Thanks are also due to fellow grad student Neil Wedge for shared research and work. Last but not least I wish to acknowledge the assistance of the secretaries, particularly Desi Cheung. Dr. J.W. Murray of the Department of Geology provided valuable assistance during the research and critical review during the writing, for which I thank him. The Vancouver Office of the Geological Survey of Canada, and in particular Dr. J.L. Luternauer, have been of great assistance to me In this thesis - assisting with the field excursion to Sturgeon Bank, tolerating my presence around their offices, allowing me access to their great store of literature and data -thank 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. Finally I would like to thank my wife Marika for her patience, for supporting me and for her help with the hard• est part of the thesis, the typing. Financial support for this thesis was kindly provided by the National Research Council (Grant 67-1498) and Energy Mines and Resources (Grant 65-1652) for which I am grateful. INTRODUCTION Roberts Bank and Sturgeon Bank, comprising some 90 odd square miles of tidal flats, have in recent years taken on great importance as potential locations for 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 Facility, and future expansions to many times the size of the present installations have been proposed. Also proposed is an extension of the Vancouver International Airport runway system out onto Sturgeon Bank. This may represent only a small fraction of the interest in Roberts Bank and Sturgeon Bank as potential sites for develop• ment. With the present and potential interest in the area, it appeared that a general investigation of the soils and engineering environment of Roberts Bank and Sturgeon Bank might be of value. In this thesis an attempt has been made to compile all existing data available for Roberts Bank and Sturgeon Bank, especially subsurface data. This data was used to determine characteristic soil parameters for use in various types of stability analyses. The data gathered and most of the analyses performed conform to standard practice in the engineering community. Where possible and practical supple• mentary information, such as listings of computer programs used in analyses, have been included in the appendices. 2. This thesis is concerned with general conditions at Roberts Bank and Sturgeon Bank and the kinds of engineering problems that may be faced during further developments. AREA OF STUDY Roberts Bank and Sturgeon Bank are located at approxi• mately 49° 00' to 49° 15' North Latitude and 123° 05' to 12 3° 15' West Longitude. This is the southwest corner of mainland British Columbia, Canada. These banks form the western (seaward) extremity of the delta of the Fraser River, and are the youngest part of the delta.