an engineering geological characterisation of tropical clays - GBV

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160 Liquid limit (LL) variation (< 0,5 m) 36°55É LL (%) 1°19´S Profile distance (m) West 1°21.5´S 36°49É LL% 88 87.5 87 86.5 86 85.5 85 84.5 84 83.5 83 82.5 82 81.5 81 80.5 80 79.5 79 78.5 South Profile distance (m) Fig. 8.4a. Block diagram showing distribution and variation of liquid limit values at depths of less than 0,5m in black clays. A contoured representation of the distribution is shown in Figures (8.4a & b) in which isolated patches of relatively low liquid limits correspond to zones of more lateritic clays and/or swampy environments. On the whole, however, there is a slight tendency of liquid limit values to increase with depth. This could be attributed to the relatively higher organic matter content of black clays for depths of less than 0,50m, and which has the effect of inhibiting the plasticity of soils. As a result, soil depths of less than 0,50m show median, mode and mean liquid limit values of 84%, 85%, and 84%, respectively, as well as standard deviation of 3,30 and variance of 10,90; while soil depths of 0,50m and greater, exhibit relatively larger median, mode and mean values of 87%, 89% and 86%, respectively. The latter soil depths are also characterised by standard deviation of 4,11 and variance of 16,86. On the whole, however, the two sets of data at the two different depth intervals are generally comparable and in good agreement, this being indicated by a covariance of 8,28 and a fairly strong correlation of 0,63 (Table 8.1).
161 Liquid limit (LL) variation (> 0,5 m) 36°55É 89 88 87 Profile distance (m) LL% 90 LL (%) South 84 85 86 83 82 1°19´S 81 80 Profile distance (m) West 1°21.5´S 36°49É Fig. 8.4b. Block diagram showing distribution and variation of liquid limit values at depths of more than 0,5m in black clays. 76 77 78 79 Liquid limit values obtained for the red soils in this study are comparatively lower, and range from 48% to 57%. 8.3 Plasticity index The variation of plasticity index of soils along the five field profiles of this study is represented diagrammatically in Figures (8.5a & b), for depths of less than 0,50m and those of 0,50m and greater, respectively.
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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
Page 121 and 122: 109 Table 7.10. Distribution and/ o
Page 123 and 124: 111 illustrated in Figures 7.6, 7.7
Page 125 and 126: 113 Black clays Cohesion c´ (kN/m
Page 127 and 128: 115 7.4 Oedometer consolidation tes
Page 129 and 130: 117 The compound coefficient, K/ρw
Page 131 and 132: 119 Primary consolidation is a time
Page 133 and 134: 121 where w (%) = moisture content
Page 135 and 136: 123 Relationships between values of
Page 137 and 138: 125 Plate 7.8. Oedometer consolidat
Page 139 and 140: 127 Cumulative log-time/settlement
Page 141 and 142: 129 Ranges of values of coefficient
Page 143 and 144: 131 is most probably due to the ten
Page 145 and 146: 133 The results of correlation show
Page 147 and 148: 135 by differences in lithology, mi
Page 149 and 150: 137 Black clays and red soils Swell
Page 151 and 152: 139 Testing procedure involved cutt
Page 153 and 154: 141 Black clays Swelling pressure S
Page 155 and 156: 143 Black clays: P (kPa) vs S (%) P
Page 157 and 158: 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: 159 Liquid limit variation; 0,50m a
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 and 210: 197 The swelling capability in term
Page 211 and 212: 199 Free swell/ clay fraction Free
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
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211 References Abebe, S. T., 2002.
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213 Galster, R.W., 1977. A system o
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215 Mitchell, J.K., 1993. Fundament
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217 ------,1964. Long term stabilit
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Appendix A: Oedometer consolidation
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Table A7. Consolidation parameters
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Results of swelling tests on black
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Appendix D Distribution/ variation
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4000 3000 2000 Distance (m) 1000 We
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4000 3000 2000 1000 Distance (m) We
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4000 3000 2000 Distance (m) 1000 We
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4000 3000 2000 Distance (m) 1000 We
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4000 3000 2000 Distance (m) 1000 We
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4000 3000 2000 Distance (m) 1000 We
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4000 3000 2000 Distance (m) 1000 We
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4000 3000 2000 Distance (m) 1000 We
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4000 3000 2000 Distance (m) 1000 We
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4000 3000 2000 Distance (m) 1000 We
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Appendix E Geotechnical soil map of
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an engineering geological characterisation of tropical clays - GBV

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