an engineering geological characterisation of tropical clays - GBV

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136 Table 7.17. Classification of black clays and red soils based on coefficient of secondary compression. Coeff. of secondary compression Average Category Sample No. cα value cα Clay type Typical examples < 0,001 Overconsolidated clays of clays 0,005-0,02 Normally consolidated clays (after Lambe & 0,03 and over Very plastic clays and/ or Whitman –1979) organic clays SA2-70cm 0,0002-0,011 0,006 Normally consolidated clays This study: SA37-50cm 0,003-0,017 0,009 Normally consolidated clays Black clays SB1-70cm 0,0002-0,012 0,005 Normally consolidated clays SB42-50cm 0,005-0,024 0,014 Normally consolidated clays SC17-50cm 0,006-0,02 0,012 Normally consolidated clays SC29-50cm 0,003-0,014 0,008 Normally consolidated clays RD1-30cm 0,002-0,004 0,003 Slightly overconsolidated clays This study: RD1-100cm 0,003-0,008 0,006 Normally consolidated clays Red soils RD1-400cm 0,002-0,007 0,004 Slightly overconsolidated clays Results of swell index, Cs, obtained for black clays and red soils during unloading phase of oedometer tests are summarised in Table (7.18). The black clays generally exhibit higher swelling capabilities and/ or expansion tendencies (Cs = 0,03-0,075; mean value = 0,054) on unloading than the red soils (Cs = 0,02-0,03; mean value = 0,027). Correlations between swell indices and index properties (liquid limit, plasticity index, free swell) are generally poor (Figures 7.25, 7.26 & 7.27). This implies that uncertainties would be encountered in trying to assess and/ or predict soils swelling and/ or expansion tendencies based on results of index tests performed on disturbed and fractioned samples. Table 7.18. Results of swell indices for black clays and red soils correlated with Atterberg limits and free swell. Sample No. Load kPa Wn (%) LL (%) PI (%) FS (%) Cs SA2-70cm 100-2400 34 90 54 170 0,07 SA37-50cm 25-1600 22 83 44 115 0,075 SB1-70cm 50-2400 30 90 51 145 0,043 SB42-50cm 100-2400 21 91 47 145 0,03 SC17-50cm 100-2400 22 81 48 110 0,04 SC29-50cm 100-2400 20 80 43 110 0,065 RD1-30cm 12,0-2400 39 49 18 20 0,03 RD1-100cm 12,0-2400 24 51 21 15 0,03 RD1-400cm 12,0-2400 25 48 18 15 0,02 Correlations (R ) Black & red soils 0,61 0,64 0,63 Correlations (R ) Black clays only -0,34 -0,14 -0,06 Diagramatically, the generally weak correlations are reflected in terms of plot points which tend to be more spread out (Figures 7.25, 7.26 & 7.27).
137 Black clays and red soils Swell index Cs 0,08 0,07 0,06 0,05 0,04 0,03 0,02 0,01 0 n = 9 40 50 60 70 80 90 100 Liquid limit LL (%) LL vs Cs Figure 7.25. Correlation between swell index and liquid limit for black clays and red soils. Black clays and red soils Swell index Cs 0,08 0,07 0,06 0,05 0,04 0,03 0,02 0,01 0 n = 9 10 20 30 40 50 60 PI vs Cs Plasticity index PI (%) Figure 7.26. Correlation between swell index and plasticity index for black clays and red soils. Black clays and red soils Swell index Cs 0,08 0,07 0,06 0,05 0,04 0,03 0,02 0,01 0 n = 9 0 50 100 150 200 Free swell FS (%) FS vs Cs Figure 7.27. Correlation between swell index and free swell for black clays and red 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
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 and 106: 93 Table 7.3 (continued). Atterberg
Page 107 and 108: 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: 135 by differences in lithology, mi
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 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
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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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