an engineering geological characterisation of tropical clays - GBV

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128 Consolidation curves of e/log p Voids ratio (e) 1,501 1,401 1,301 1,201 1,101 1,001 0,901 0,801 0,701 0,601 0,501 0,401 0,301 0,201 0,101 0,001 10 100 1000 10000 Pressure on log scale (log P (kPa)) RD1-30cm: red soils RD1-100cm: red soils RD1-400cm: red soils SA2-70cm: black clays SA37-50cm: black clays SB1-70cm: black clays SB42-50cm: black clays SC17-50cm: black clays SC29-50cm: black clays Figure 7.18. Voids ratio/ log Pressure (e/ log p) curves for black clays and red soils. Results of oedometer consolidation tests in terms of voids ratio, compression coefficients and/ or indices as well as permeability over the loading range of 25-800 kPa are summarised in Table (7.12). Complete results for the loading and unloading stages of black clays and red soils are tabulated in Appendix A. Table 7.12. Derived parameters from results of oedometer consolidation tests for the loading range of 25-800 kPa in this study. Sample t50 Cv No. E (%) e av (m²/kN) (min) (m²/year) K (m/s) Cc Cs Cα mv (m²/MN) SA2-70cm 0,31-11,11 0,52-0,70 0,000052-0,00045 0,03-0,26 1,00 - 60 0,07-5,08 2,6E-12 - 4,8E-11 0,3 0,07 0,0002-0,009 SA37-50cm 1,84-27,68 0,52-1,06 0,0003-0,0033 0,18-1,62 2,90-55 0,05-1,73 2,94E-12 - 3,94E-10 0,4 0,075 0,003-0,017 SB1-70cm 1,85-19,46 0,65-1,01 0,000148-0,0015 0,09-0,74 0,48-18 0,19-2,36 5,11E-12 - 1,2E-9 0,29 0,043 0,0002-0,006 SB42-50cm 8,02-29,11 0,23-0,59 0,0003-0,0014 0,22-0,80 9,5-50 0,06-0,494 3,92E-12 - 1,23E-10 0,34 0,03 0,005-0,024 SC17-50cm 1,74-20,64 0,37-0,7 0,00028-0,0010 0,17-0,60 9,0- 50 0,07-0,56 1,67E-12 - 3,0E-11 0,44 0,04 0,006-0,016 SC29-50cm 3,33-18,24 0,56-0,84 0,00026-0,0008 0,16-0,44 2,5 -35 0,104-1,97 5,03E-12 - 2,03E-10 0,38 0,065 0,003-0,13 RD1-30cm 10,98-32,07 0,74-1,28 0,00035-0,0047 0,19-2,0 0,35-1,85 1,38-11,85 7,99E-11 - 7,33E-9 0,42 0,03 0,003-0,004 RD1-100cm 7,35-39,01 0,59-1,42 0,00036-0,0074 0,21-2,94 0,98-1,75 1,18-4,67 7,57E-11 - 4,26E-9 0,4 0,03 0,005-0,008 RD1-400cm 3,09-19,60 0,74-1,1 0,00029-0,0024 0,16-1,11 0,40-1,30 2,71-12,14 1,32E-10 - 4,19E-9 0,39 0,02 0,002-0,007
129 Ranges of values of coefficient of volume compressibility, mv, obtained for black clays and red soils are given in Table (7.13), where they have been used to classify the soils based on compressibility. Ranges of values of mv for other types of soil are also included for comparison purposes. Results in Table (7.13) show that black clays would generally exhibit medium to high compressibility over the normal loading range of 25-800kPa; however, cases of low to medium compressibility are also to be expected. The red soils would be characterised by medium to very high compressibility over the same loading range. Comparatively, therefore, the red soils tend to be more compressible than the black clays. This difference could be attributed to the generally loose and friable nature of the red soils giving rise to higher porosities, as evidenced by voids ratios (e) of 0,59-1,42 (Table 7.12). Lower compressibility of the black clays could be attributed to lower porosities (e = 0,23- 1,06), a most probable result of the cohesive nature and dense compact structure of these clays. Table 7.13. Compressibility classification of black clays and red soils in this study. Coeff. of volume Category Clay type/ Sample No. compressibility mv (m²/MN) Compressibility classification Typical Very organic alluvial clays > 1,5 very high examples (after and peats Lambe & Whitman Normally consolidated 0,3-1,5 high -1979) alluvial/ estuarine clays Fluvio-glacial clays and 0,1-0,3 medium lake clays Boulder clays 0,05-0,1 low Heavily overconsolidated < 0,05 very low boulder clays SA2-70cm 0,03-0,26 very low to medium This study: SA37-50cm 0,18-1,62 medium to very high Black clays SB1-70cm 0,09-0,74 low to high SB42-50cm 0,22-0,80 medium to high SC17-50cm 0,17-0,60 medium to high SC29-50cm 0,16-0,44 medium to high RD1-30cm 0,19-2,0 medium to very high This study: RD1-100cm 0,21-2,94 medium to very high Red soils RD1-400cm 0,16-1,11 medium to high Ranges of values of coefficient of consolidation, cv, obtained for the black clays and red soils are given in Table (7.14). Typical ranges for other inorganic soils are included for comparison purposes. From the results, the red soils would undergo medium to high rates of consolidation –settlement when externally loaded in the range of 25-800 kPa. The rates of consolidationsettlement for the black clays would be generally low over the same loading range. The high rates of consolidation by the red soils could be attributed to their relatively high porosity and high permeability (K = 7,57*E-11 to 7,33*E-9 m/s ) which facilitate faster drainage and rapid dissipation of pore water pressures. On the other hand, the black clays are characterised by relatively lower porosity and permeability (K = 1,67*E-12 to 1,2*E-9 m/s) so that drainage and dissipation of pore pressures on external loading would be less rapid, causing slower consolidation –settlements.
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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
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 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: 127 Cumulative log-time/settlement
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 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
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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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