128 Consolidation curves <strong>of</strong> 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 <strong>clays</strong> SA37-50cm: black <strong>clays</strong> SB1-70cm: black <strong>clays</strong> SB42-50cm: black <strong>clays</strong> SC17-50cm: black <strong>clays</strong> SC29-50cm: black <strong>clays</strong> Figure 7.18. Voids ratio/ log Pressure (e/ log p) curves for black <strong>clays</strong> <strong>an</strong>d red soils. Results <strong>of</strong> oedometer consolidation tests in terms <strong>of</strong> voids ratio, compression coefficients <strong>an</strong>d/ or indices as well as permeability over the loading r<strong>an</strong>ge <strong>of</strong> 25-800 kPa are summarised in Table (7.12). Complete results for the loading <strong>an</strong>d unloading stages <strong>of</strong> black <strong>clays</strong> <strong>an</strong>d red soils are tabulated in Appendix A. Table 7.12. Derived parameters from results <strong>of</strong> oedometer consolidation tests for the loading r<strong>an</strong>ge <strong>of</strong> 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 R<strong>an</strong>ges <strong>of</strong> values <strong>of</strong> coefficient <strong>of</strong> volume compressibility, mv, obtained for black <strong>clays</strong> <strong>an</strong>d red soils are given in Table (7.13), where they have been used to classify the soils based on compressibility. R<strong>an</strong>ges <strong>of</strong> values <strong>of</strong> mv for other types <strong>of</strong> soil are also included for comparison purposes. Results in Table (7.13) show that black <strong>clays</strong> would generally exhibit medium to high compressibility over the normal loading r<strong>an</strong>ge <strong>of</strong> 25-800kPa; however, cases <strong>of</strong> 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 r<strong>an</strong>ge. Comparatively, therefore, the red soils tend to be more compressible th<strong>an</strong> the black <strong>clays</strong>. This difference could be attributed to the generally loose <strong>an</strong>d friable nature <strong>of</strong> the red soils giving rise to higher porosities, as evidenced by voids ratios (e) <strong>of</strong> 0,59-1,42 (Table 7.12). Lower compressibility <strong>of</strong> the black <strong>clays</strong> could be attributed to lower porosities (e = 0,23- 1,06), a most probable result <strong>of</strong> the cohesive nature <strong>an</strong>d dense compact structure <strong>of</strong> these <strong>clays</strong>. Table 7.13. Compressibility classification <strong>of</strong> black <strong>clays</strong> <strong>an</strong>d red soils in this study. Coeff. <strong>of</strong> volume Category Clay type/ Sample No. compressibility mv (m²/MN) Compressibility classification Typical Very org<strong>an</strong>ic alluvial <strong>clays</strong> > 1,5 very high examples (after <strong>an</strong>d peats Lambe & Whitm<strong>an</strong> Normally consolidated 0,3-1,5 high -1979) alluvial/ estuarine <strong>clays</strong> Fluvio-glacial <strong>clays</strong> <strong>an</strong>d 0,1-0,3 medium lake <strong>clays</strong> Boulder <strong>clays</strong> 0,05-0,1 low Heavily overconsolidated < 0,05 very low boulder <strong>clays</strong> SA2-70cm 0,03-0,26 very low to medium This study: SA37-50cm 0,18-1,62 medium to very high Black <strong>clays</strong> 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 R<strong>an</strong>ges <strong>of</strong> values <strong>of</strong> coefficient <strong>of</strong> consolidation, cv, obtained for the black <strong>clays</strong> <strong>an</strong>d red soils are given in Table (7.14). Typical r<strong>an</strong>ges for other inorg<strong>an</strong>ic soils are included for comparison purposes. From the results, the red soils would undergo medium to high rates <strong>of</strong> consolidation –settlement when externally loaded in the r<strong>an</strong>ge <strong>of</strong> 25-800 kPa. The rates <strong>of</strong> consolidationsettlement for the black <strong>clays</strong> would be generally low over the same loading r<strong>an</strong>ge. The high rates <strong>of</strong> consolidation by the red soils could be attributed to their relatively high porosity <strong>an</strong>d high permeability (K = 7,57*E-11 to 7,33*E-9 m/s ) which facilitate faster drainage <strong>an</strong>d rapid dissipation <strong>of</strong> pore water pressures. On the other h<strong>an</strong>d, the black <strong>clays</strong> are characterised by relatively lower porosity <strong>an</strong>d permeability (K = 1,67*E-12 to 1,2*E-9 m/s) so that drainage <strong>an</strong>d dissipation <strong>of</strong> 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