an engineering geological characterisation of tropical clays - GBV

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148 The variation of so calculated percentage swelling (S%) with extent of external loading P% (i.e., load decrements, P kPa, expressed as a percentage of respective swelling pressure, SP kPa) is presented diagrammatically in Fig. (7.37a). The variation is also closely logarithmic with a very strong correlation (R = 0,98), i.e. P = -15,86Ln(S) + 29,84 (7.50) where P = extent of loading (%) S = cumulative swelling (%), derived w.r.t initial specimen height Ho This relationship is also represented as a straight line graph in Fig. (7.37b) where percentage swelling (S%) has been plotted on a logarithmic scale. The second relationship could also be possibly used to estimate and/ or anticipate percentage swelling (S%) and/ or swelling (S mm) that may arise from certain or chosen projected external loading conditions. For instance, choosing zero loading conditions implies P (kPa) and P% [i.e. (P/SP)*100] are also zero, so that from Equation (7.50), 0 = -15,86Ln(S) + 29,84 or Ln(S) = 29,84/15,86 = 1,88, so that S = e^ 1,88 = 6,55% Or for initial specimen thickness Ho of 11mm, S = (6,55/100) * 11 = 0,72mm On the average, therefore, the black clays would undergo a maximum percentage swelling of 6,55% (or swelling of 0,72 mm relative to the initial specimen thickness Ho of 11 mm), under zero external loading conditions. Other values of percentage swelling and/ or amount of swelling that may arise from selected external loading could be similarly calculated or just read off from the curves of Figs. (7.37a &b). The second relationship could also be possibly used for estimating the extent of external loading (P%) and/ or external load (P kPa) necessary to give chosen or allowable percentage swelling and/ or amount of swelling, as may be required by foundation designers. For instance, a selected average percentage swelling of S% = 2 (or S = 0,22 mm for Ho = 11 mm) would be exhibited by the clays when the extent of external loading P% is such that P% = -15,86 * Ln(2) + 29,84 = -(15,86 * 0,693) + 29,84, or P% = 18,85, and this is the same value given by the curve of Fig. (7.37) for S% = 2. For an average swelling pressure, SP = 50,29 kPa as calculated for tested samples of black clays in Table (7.23), the external loading pressure is given by P (kPa) = (P% * SP)/100 = (18,85 * 50,29)/100 or P (kPa) = 9,48
149 Combined sample results: S % vs P% (2nd method) 120 100 n = 25 Loading P (%) 80 60 40 P = -15,86Ln(S) + 29,84 R 2 = 0,96 Combined sample results 20 0 0,00 2,00 4,00 6,00 8,00 10,00 Swelling S (%) Figure 7.37a. Correlation between percentage swelling (derived w.r.t initial specimen height Ho) and extent of external loading for combined sample results of black clays. Combined sample results: S % vs P% (2nd method) 120 n = 25 Loading P (%) 100 80 60 40 P = -15,86Ln(S) + 29,84 R 2 = 0,96 Combined sample results 20 0 0,01 0,10 1,00 10,00 Swelling S (%) on log scale Figure 7.37b. Correlation between percentage swelling (derived w.r.t initial specimen height Ho) on log scale, and extent of external loading for combined sample results of black clays.
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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
Page 109 and 110: 97 A standard classification of soi
Page 111 and 112: 99 Table 7.6. Viscosity and density
Page 113 and 114: 101 Table 7.7, continued. Results o
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Page 117 and 118: 105 Plate 7.7a. Shear testing showi
Page 119 and 120: 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: 147 Alternatively, percentage swell
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 and 210: 197 The swelling capability in term
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199 Free swell/ clay fraction Free
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201 There has also been a decrease
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203 PI = 1,88*LS A comparison of pl
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205 cc = 0,0099(122-LL) for black c
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207 Chapter 12 Recommendations Anal
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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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