an engineering geological characterisation of tropical clays - GBV

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198 FSmeasured = 0,99FSPI (10.24) and FSmeasured = 0,98FSLS (10.25) These relationships serve to support the reliability with which laboratory free swell; and therefore swelling capability of soils could be estimated from laboratory determined Atterberg limits and linear shrinkage. Measured/ calculated free swell Measured free swell (%) 200 150 100 50 0 n = 91 FSmeas. = 0,99FSPI FSmeas. = 1,01FSLL FSmeas. = 0,98FSLS 0 50 100 150 200 FS (meas.) vs FS (LL) FS (meas.) vs FS (PI) FS (meas.) vs FS (LS) Calculated free swell (%) Figure 10.10. A correlation between calculated and laboratory determined free swell values of black clays and red soils. 10.5 Clay fraction and linear shrinkage, free swell Relatioships between clay fraction and linear shrinkage and/ or swelling capability of black clays and red soils are generally poorly defined, being characterised by very weak correlations of less than 0,3 (Figs. 10.11 and 10.12). Linear shrinkage/ clay fraction Linear shrinkage LS (%) 35 30 n = 87 25 20 15 R 2 = 0,0363 10 5 0 10 20 30 40 50 % clay LS vs % clay Figure 10.11. Correlation between laboratory measured values of linear shrinkage and clay fraction of black clays and red soils.
199 Free swell/ clay fraction Free swell FS (%) 200 n = 87 150 100 R 2 = 0,0207 50 0 10 20 30 40 50 % clay FS vs % clay Figure 10.12. Correlation between laboratory measured values of free swell and clay fraction of black clays and red soils. Figures (10.11) and (10.12) illustrate a slight general increase of linear shrinkage and free swell values with increasing clay content. The broad spread of results, however, points to the possible influence of other factors such as soil fabric and/ or structure and clay mineralogy on activity and engineering behaviour of the soils.
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AN ENGINEERING GEOLOGICAL CHARACTER
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i Contents Page Acknowledgements Su
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iii Chapter 8. Distribution of inde
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v 7.29 - 7.33 Correlation between s
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vii 136 139 7.13 Compressibility cl
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ix Acknowledgements I would like to
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1 Chapter 1 Introduction 1.1 Scope
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Figure1.1 Map of Nairobi region sho
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5 Plates 1.2 (a) & (b) Strong shrin
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7 Available literature in the form
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9 slopes. The northern boundary bet
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11 1.6 Climate The Nairobi area and
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13 marked daily range of relative h
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15 Chapter 2 Previous works 2.1 Sum
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17 Table 2.1 Stratigraphic correlat
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19 Chapter 3 Geology 3.1 Introducti
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21 metamorphic minerals sillimanite
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25 and prismatic apatite occur as a
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27 Table 3.2 Chemical analyses of s
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29 caused by partial segregation of
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32 could otherwise lead to erroneou
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34 The red soils in this study occu
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36 17 16 15 14 13 12 11 10 9 8 7 6
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38 4.4 Vane test 4.4.1 Introduction
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40 Table 4.1 Classification of soft
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42 The variation of vane shear stre
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44 And thirdly, the field vane appa
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46 horizon, most probably a result
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49 The red friable clays on the who
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51 Results of chemical analyses of
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53 Results of previous soil classif
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55 neighbouring metamorphic areas a
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57 Table 5.10. Profile description
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59 The presence of BaO in the red a
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61 resulted most probably from supp
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63 800 Impulse 700 600 500 SC 17 -5
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65 sericite and chlorite (see next
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67 Q: Quartz (1%) H: Haematite K: K
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69 Plate 6.3. K-feldspar phenocryst
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71 The trachytes generally show a r
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73 Plate 6.16. Organic matter (rema
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75 Plate 6.24. Solution pores/ cavi
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77 Plate 6.29. Iron concretion with
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79 The CS-225 is a micro-processor
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81 The red soils generally exhibit
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83 Chapter 7 Laboratory soils index
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85 According to Johnson and Degraff
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87 Table 7.2. Results of index test
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89 Plate 7.2a. Apparatus for liquid
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91 Activity chart Plasticity index
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93 Table 7.3 (continued). Atterberg
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95 where 7.1.4.4 Results V = volume
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97 A standard classification of soi
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99 Table 7.6. Viscosity and density
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101 Table 7.7, continued. Results o
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103
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105 Plate 7.7a. Shear testing showi
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107 Shear stress / Displacement Cur
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109 Table 7.10. Distribution and/ o
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111 illustrated in Figures 7.6, 7.7
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113 Black clays Cohesion c´ (kN/m
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115 7.4 Oedometer consolidation tes
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117 The compound coefficient, K/ρw
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119 Primary consolidation is a time
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121 where w (%) = moisture content
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123 Relationships between values of
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125 Plate 7.8. Oedometer consolidat
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127 Cumulative log-time/settlement
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129 Ranges of values of coefficient
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131 is most probably due to the ten
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133 The results of correlation show
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135 by differences in lithology, mi
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137 Black clays and red soils Swell
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139 Testing procedure involved cutt
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141 Black clays Swelling pressure S
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143 Black clays: P (kPa) vs S (%) P
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145 The same relationship is repres
Page 159 and 160: 147 Alternatively, percentage swell
Page 161 and 162: 149 Combined sample results: S % vs
Page 163 and 164: 151 Black clays: Greek method P% =
Page 165 and 166: 153 partly produced by effects of w
Page 167 and 168: 155 Chapter 8 Distribution of index
Page 169 and 170: 157 the study area, respectively. R
Page 171 and 172: 159 Liquid limit variation; 0,50m a
Page 173 and 174: 161 Liquid limit (LL) variation (>
Page 175 and 176: 163 (8.6). The few isolated patches
Page 177 and 178: 165 Similarly, soil thicknesses of
Page 179 and 180: 167 Free swell variation; 0,50m dep
Page 181 and 182: 169 fraction at the two depth inter
Page 183 and 184: 171 Variation of fines (%), < 0,50m
Page 185 and 186: 173 %coarse % coarse fraction varia
Page 187 and 188: 175 1°19´S 22 Shear angle variati
Page 189 and 190: 177 9.2 Grain size distribution The
Page 191 and 192: 179 rapid dissipation of pore water
Page 193 and 194: Chapter 10 181 Correlation of index
Page 195 and 196: 183 Black clays; plasticity index/
Page 197 and 198: 185 On the other hand, laboratory m
Page 199 and 200: 187 Red clays; measured/ calculated
Page 201 and 202: 189 These two relationships could b
Page 203 and 204: 191 Diagram: PImeasured/ PIcalculat
Page 205 and 206: 193 Table 10.5, continued. Calculat
Page 207 and 208: 195 Table 10.6. Calculated and labo
Page 209: 197 The swelling capability in term
Page 213 and 214: 201 There has also been a decrease
Page 215 and 216: 203 PI = 1,88*LS A comparison of pl
Page 217 and 218: 205 cc = 0,0099(122-LL) for black c
Page 219 and 220: 207 Chapter 12 Recommendations Anal
Page 221 and 222: 209 cc = 0,0099(122-LL) for black c
Page 223 and 224: 211 References Abebe, S. T., 2002.
Page 225 and 226: 213 Galster, R.W., 1977. A system o
Page 227 and 228: 215 Mitchell, J.K., 1993. Fundament
Page 229 and 230: 217 ------,1964. Long term stabilit
Page 231 and 232: Appendix A: Oedometer consolidation
Page 233 and 234: Table A7. Consolidation parameters
Page 235 and 236: Results of swelling tests on black
Page 237 and 238: Appendix D Distribution/ variation
Page 239 and 240: 4000 3000 2000 Distance (m) 1000 We
Page 241 and 242: 4000 3000 2000 1000 Distance (m) We
Page 259 and 260: Appendix E Geotechnical soil map of
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