an engineering geological characterisation of tropical clays - GBV

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94 Table 7.4. Free swell classification of clay soils (Gibbs & Holtz, 1956). FREE SWELL VALUE FS (%) FREE SWELL CLASSIFICATION POSSIBLE EXPANSIVENESS 200 very high very high Up to 2000 (e.g. bentonite) extremely high extremely high 7.1.4.2 Procedure About 50g of a selected soil sample was oven-dried (105 °C) overnight, cooled and passed through a 400 µm sieve. About 10 ml of the sieved dry soil powder was measured out into a dry 25 ml measuring glass cylinder, without compacting and/ or shaking it down. The soil powder was then steadily drizzled into 50 ml of distilled water contained in a 50 ml glass measuring cylinder. The main part of the solid particles was allowed to come to rest for a period of 30 minutes (Plate 7.3), when the total volume of settled solids was read off and recorded. Plate 7.3. Free swell determination of clay soils. 7.1.4.3 Calculation Free swell is the change in volume of the dry soil expressed as a percentage of its original volume; and is given by free swell (%) = ((V-Vo)/Vo)*100, or free swell (%) = ((V-10)/10)*100 (7.8)
95 where 7.1.4.4 Results V = volume of settled solid particles Vo = 10ml, i.e. original volume of dry soil Results of free swell test (FS %) obtained from the present study are given in Table (7.2), and are reported to the nearest whole number or 1%. Classification of soils based on swelling capabilitiy is summarised in Table (7.3). Black clays have high swelling capabilities, being characterised by free swell values of 100% and over. The red soils with free swell values of less than 50% (i.e. 15-20%) are classified as low swelling capability clays. Potential influence and/ or effects of these swelling capabilities on light constructed structures are discussed in the next chapter. 7.1.5 Linear shrinkage 7.1.5.1 Scope and procedure Linear shrinkage tests were carried out in this study according to British Standard testing procedure (BS 1377: 1975, Test 5). The tests usually serve to determine the percentage linear shrinkage of clays as well as soils of low plasticity such as silts (Head, 1984). In practice, the results of the tests serve to point to possible volumetric changes soils would undergo in situ during a change of seasons from rainy wet months to hot dry ones. In this study, the tests were performed on both the highly plastic black clays as well as the low plasticity silty red soils; and involved determination of linear or one-dimensional change in length of a semicylindrical bar sample of clay soil when dried out, starting from near the liquid limit. The apparatus and procedure are as summarised in Plate (7.4) in which a suitable amount of selected soil, previously dried (105 °C) and conveniently prepared, was mixed with distilled water to produce a homogeneous paste around its liquid limit. The paste, initially filled into a semi-cylindrical standard metal (brass) mould of 140 mm length and 25 mm diameter, was dried (105 °C) and the average length (Ld) of dried test specimen determined by measuring its top and lower surface lengths. Linear shrinkage, LS, was calculated as a percentage of the original length of the specimen, i.e. LS (%) = ((Lo-Ld)/Lo)*100 (7.9) where Lo = original length (140 mm) of semi-cylindrical bar sample of soil at about its liquid limit Ld = average length of dried specimen Results of linear shrinkage tests obtained for the soils in this study are presented in Table (7.2), and are reported to the nearest 1%. Black clays exhibit LS values of 21-29%, while red soils show relatively lower values of 10-11%.
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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
Page 56 and 57: 44 And thirdly, the field vane appa
Page 58: 46 horizon, most probably a result
Page 61 and 62: 49 The red friable clays on the who
Page 63 and 64: 51 Results of chemical analyses of
Page 65 and 66: 53 Results of previous soil classif
Page 67 and 68: 55 neighbouring metamorphic areas a
Page 69 and 70: 57 Table 5.10. Profile description
Page 71 and 72: 59 The presence of BaO in the red a
Page 73 and 74: 61 resulted most probably from supp
Page 75 and 76: 63 800 Impulse 700 600 500 SC 17 -5
Page 77 and 78: 65 sericite and chlorite (see next
Page 79 and 80: 67 Q: Quartz (1%) H: Haematite K: K
Page 81 and 82: 69 Plate 6.3. K-feldspar phenocryst
Page 83 and 84: 71 The trachytes generally show a r
Page 85 and 86: 73 Plate 6.16. Organic matter (rema
Page 87 and 88: 75 Plate 6.24. Solution pores/ cavi
Page 89 and 90: 77 Plate 6.29. Iron concretion with
Page 91 and 92: 79 The CS-225 is a micro-processor
Page 93 and 94: 81 The red soils generally exhibit
Page 95 and 96: 83 Chapter 7 Laboratory soils index
Page 97 and 98: 85 According to Johnson and Degraff
Page 99 and 100: 87 Table 7.2. Results of index test
Page 101 and 102: 89 Plate 7.2a. Apparatus for liquid
Page 103 and 104: 91 Activity chart Plasticity index
Page 105: 93 Table 7.3 (continued). Atterberg
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
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145 The same relationship is repres
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147 Alternatively, percentage swell
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149 Combined sample results: S % vs
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151 Black clays: Greek method P% =
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153 partly produced by effects of w
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155 Chapter 8 Distribution of index
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157 the study area, respectively. R
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159 Liquid limit variation; 0,50m a
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161 Liquid limit (LL) variation (>
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163 (8.6). The few isolated patches
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165 Similarly, soil thicknesses of
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167 Free swell variation; 0,50m dep
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169 fraction at the two depth inter
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171 Variation of fines (%), < 0,50m
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173 %coarse % coarse fraction varia
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175 1°19´S 22 Shear angle variati
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177 9.2 Grain size distribution The
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179 rapid dissipation of pore water
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Chapter 10 181 Correlation of index
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183 Black clays; plasticity index/
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185 On the other hand, laboratory m
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187 Red clays; measured/ calculated
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189 These two relationships could b
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191 Diagram: PImeasured/ PIcalculat
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193 Table 10.5, continued. Calculat
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195 Table 10.6. Calculated and labo
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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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