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A Thesis Entitled Engineering Geology of the London Clay in The A Thesis Entitled Engineering Geology of the London Clay in the London and Hampshire Basins Submitted for the degree of Doctor of Philosophy in the Faculty of Science in the University of London by Alister Douglas Burnett Geology Department, February, 1972 Royal School of Mines, Imperial College. Abstract The aim of this study has been to investigate relationships between geological and geotechnical properties of the London Clay in the London and Hampshire Basins. This has been carried out on three scales, i.e. a laboratory or "one dimensional" scale; a single engineering site or cliff exposure, a "two dimensional scale"; and a regional scale from top to bottom of the deposit, i.e. "three dimensional scale." It was possible to relate the more factual geological information, thickness and structural contours, lithology and a sedimentqklgical and palaeontological biased zonation system of the London Clay to the detailed mineralogy of the clay. The mineralogy and lithological (mainly grading) characteristics were found to have close relationship to the mechanical properties of the clay and by this means geology and geotechnical properties were linked. The geological and geotechnical data was largely gathered from the literature either published or private, whereas the mineralogical data was accumulated by the writer on analysis of over 300 samples. The study has been corroborated and linked with strong sedimentological evidence which suggested a rhythmic pattern of clay deposition giving rise to regional lithological, palae- ontological and mineralogical variations both horizontally and vertically. These variations have been analysed and plotted using several techniques, both manual and computerised. Geo- technical property variations have been similarly plotted and comparison of the two sets of data reveals significant correlations at varying confidence levels. Regional plots of clay zonation, palaeogeography, structural contours and isopachytes and mineral distribution maps and plans are presented. Geological and: geotechnical depth profile sections are used to establish qualitative relations between lithology, zonation, mineralogy and geotechnics. The magnitude of influence of changes in lithology and mineralogy on soil properties has also been investigated by means of a series of laboratory experiments designed to simulate ii in-situ variations within the deposit. These experiments found the grading variations within the London Clay to account for some 14 percent of its plasticity variation whereas the minera logical distribution accounts for the complete plasticity variation range found throughout the London Clay of the London and Hampshire Basins. A testing programme to investigate the effects of weathering on London Clay produced results which indicated that this phenomena has played only a small role in soil property variations. iii Contents Page Abstract List of Figures vii List of Plates xi List of Tables xii Chapter 1 Introduction 1 Chapter 2 Geology of the London Clay Sea Basin 6 A. Regional Stratigraphy 6 B. Palaeogeography and Structure 0 C. Sedimentology 9 1)Principals and Early Views 9 2)Current Views and Regional Palaeogeography 11 D. Conclusions 18 Chapter 3 Review of the Chemistry and Mineralogy of Clay 20 Deposit Genesis A. Sedimentary Clay Mineral Environments 20 1)Chemical Aspects 20 2)Mineralogical Aspects 22 B. Sediment Deposition 25 1)Chemical Aspects 25 2)Mineralogy Aspects 25 3)Discussion 29 C. Diagenetic Processes 29 1)Chemical Aspects 29 2)Mineralogical Aspects 32 3)Discussion 33 D. Weathering 34 1)Chemical Aspects 34 2)Mineralogical Aspects 36 3)Discussion 38 Chapter 4 Processes Culminating in the Formation of the London 42 • Clair I. Geological History, Structure and Deposition 42 iv Page A. Palaeogeography and Strui:ture 42 B. London Clay Zonation 48 C. Depositional Characteristics 50 II. Mineralogy 54 A. Regional Mineralogy 54 B. London Clay Mineral Suite 58 C. The Vertical Relations between Lithology and 59 Mineralogy D. The Regional, 3 Dimensional, London Clay 61 Mineral Distribution 1) Puartz Distribution 62 7) Total Clay Mineral Distribution 63 3)1Caolinite Distribution 64 4)Illite Distribution 65 5)Montmorillonite Distribution 65 6)Cation Exchange Capacity Distribution 66 E. Regional London Clay Isopleth Distribution 67 1)Quartz Isopleths 67 2)Total Clay Mineral Isopleths 67 3)Ka1inite Isopleths 68 4)Illite Isopleths 69 5)Montmorillonite Isopleths 70 III. Environment of Deposition 70 Chapter 5 Geologica: :factors Influencing Engineering Properties 74 A. Fabric and Mineralogy 75 B. Void Itio 77 C. Permeability 78 D. Plasticity 79 E. Sensitivity 81 F. Compressibility and Consolidation 87 G. Shear Strength 84 Chapter 6 Experiments to Relate Geological and Soil Index Parameters 86 A. Sedimentation Simulation 86 B. Removal of Overburden 91 C. Investigation into Weathering 92 1)Mineralogy 93 2)Chemistry 94 3)Cation Exchange Capacity 95 Chapte 7 Page Geotechnical Investigation of Principal Sites and 100 Lateral Trends I. Detail of Principal Sites 100 A. Ashford-Sunbury 101 B. Bradwell-Orford Ness 104 C. Streatham-Central London 108 D. Hoak-Hill 109 E. Herne Bay 110 II. Lateral Trends 113 Chapter 8 Regional Trends in the Engineering Index Properties 117 of the Deposit A. Liquid Limit 119 B. Plasticity Index 121 C. Dry Density 122 D. Undrained Shear Strength 124 E. Discussion 125 Chapter 9 Engineering Implications of London Clay Geology 127 A. Implications Drawn from Clay Deposit Literature 127 B. Implications of the Regional Geology lns C. 2tructural Implications 130 D. Depositional Implications 131 E. M.:--alogical Implications 132 F. Implications Drawn from the Experiments Conducted 134 G. atiwriag Tests Implications 136 H. Conclusions Drawn from Single Site Implications 136 I.Regional Trend Implications 138 Chaptcyr 10 Summary and Conclusions 141 A. Results of the Geological Literature Review 141 B. Structural and Sedimentological Development of 144 the London Clay Basin C. London Clay Mineralogy 145 D. Geotechnical Literature Review and Experimental 147 Results E. Studies at the Principal Sites and Regional 150 Geotechnical Trends F. Analytical Techniques 154 vi Cnapt, 11 ApperZliz 1 Page A. Choice of Analytical Techniques 157 B. Sampling and Sample Preparation and Treatment 162 1)Sampling 162 2)Sample Preparation 162 3)Sample Treatment 163 C. Interpretation and Quantification of X-Ray 165 Data 1)Whole Rock 165 2)Clay Fraction 167 3)Notes on the Calculation of Whole Rock 171 Mineral Percentages 4)Notes on the Calculation of Clay Fraction 174 Mineral Percentages D. Reproducibility of X-Ray Results 178 1)Diffractometer Characteristics 181 2)Metal Holder Characteristics 184 3)Porous DiSc Reproducibility 185 E. Accuracy 18C' 1)Quartz Determination 18C 2)Chlorite Determination 193 3)Cation Exchange Capacity 194 4)Carbonate Determination 196 5)Full Chemical Analysis 197 F. Summary and Conclusions 201 Ac~~nccvlo:~ tints 203 neferences 205 Appendix 2 Vol.II Mineralogic..71 124-,st Data Appendix 3 Vol.II Geotechnical Test Data vii List of FiLas Chapter 1 Figure No. 1.1 Location and General Geology Map Chapter 2 2.1 Diagramatic Representation of 3 Cycles of Deposition n n ea. /.3 Palaeogeography of the Lower Landenian Sea 2.3 Palaeogeography of the Upper Landenian Sea 2.4 Section through the N.W.Cent Area 2.5 Palaeogeography of the Basal Ypresian Sea 2.6 Palaeogeography of the Uppermost Ypresian Sea 2.7 Palaeogeography of the Upper Ypresian Sea 2.8 Palaeogeography of the Lower Lutetian Sea Chapter 4 4.1 Chalk Top Contours and Zonal Boundaries 4.2 Trend Surface Chalk Top Contours 4.3 That Bed Isopachytes 4.4 Wool'Ach and Reading Isopachytes 4.5 London Clay Computer Isopachytes 4.6 Computer London Clay Base Elevations 4 7 London Clay Lithology and Zonal Boundaries 4.8 Lower London Tertiaries Depth Grading Profiles 4.9 Vineral Distribution Within a Single Sample alum Bay London Clay Depth Profiles /,11 Lonclon Clay Quartz Distribution 4,12 London Clay Total Clay Minc..-al Distribution 4.:3 London Clrty Kaolinite Distribution 4.14 London Clay Illite Distribution 4.15 London Clay Montmorilionite Distribution 4.16 London Clay Cation Exchange Capacity Distribution 4.17A Upper London Clay cultrtz Distribution 4.17E Middle London Clay Quartz Distribution 4.17C Lower London Clay Quartz Distribution 4.18A Upper London Clay-Clay Mineral Distribution 4.18B Middle London Clay-Clay Mineral Distribution 4.18C Lower London Clay-Clay Mineral Distribution 4.19A Middle Londdn Clay Kaolinite Distribution 4.19B Middle London Clay Xaolinite and Chlorite proportion distribution viii 4.ncA Middle London Clay n.Ae Distribution 4.20B Middle London Clay Illite Proportion Distribution 4.21A Middle London Clay Montmorillonite Distribution 4.21B Middle London Clay Montmorillonite Ptoportion Distribution Chapter 5 5.1 Particle Orientation in Clays 5.2 Comparison of Activities of Clay Mixtures 5.3 Principal Types of e Log P Relationship for Cohesive Sediments 5.4 Correlation of Compression index with Percent Clay Fraction 5.5 Pressure-void Ratio Curves for Montmorillonite Xaolinite 5.6 Rate of Consolidation of Montmorillonite and Xaolinite 2 at 4 to 8 Tons/Ft. 5.7 Coefficient of Consolidation Versus Pressure 5.8 Preoure-Void Ratio curves for Hydrogen Clay Minorals 5.9 Li(1,'_dity Index Versus Shear Strength for Remouldt-c: Clay 5.10 Shear strength Versus Depth for normally Consolidated Clays showing surface drying Zone 5.11 Residual Shear Strength of Mineral Mixturos Chapter 6 Graded Cmartz added to London Clay 6.2 Liz.,'1.id Limit
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