an engineering geological characterisation of tropical clays - GBV
an engineering geological characterisation of tropical clays - GBV
an engineering geological characterisation of tropical clays - GBV
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43<br />
V<strong>an</strong>e shear strength (kPa)/ bulk density (g/cm³)<br />
200,00<br />
c = 12597ρ 2 - 41512ρ + 34133<br />
180,00<br />
R 2 = 0,9366<br />
V<strong>an</strong>e shear strength c (kPa)<br />
160,00<br />
140,00<br />
120,00<br />
100,00<br />
80,00<br />
60,00<br />
40,00<br />
c = -4406,1ρ 2 + 13695ρ - 10461<br />
R 2 = 0,9714<br />
c = -3406,9ρ 2 + 10178ρ - 7533,1<br />
R 2 = 0,9996<br />
Kenya High<br />
School<br />
Arboretum<br />
Madaraka West<br />
Polynomial<br />
(Madaraka West)<br />
Polynomial<br />
(Arboretum)<br />
Polynomial<br />
(Kenya High<br />
School)<br />
20,00<br />
0,00<br />
1,2 1,4 1,6 1,8 2<br />
Bulk density ρ (g/cm³)<br />
Figure 4.8 Variation <strong>of</strong> field v<strong>an</strong>e shear strength with bulk density <strong>of</strong> soils for the<br />
s<strong>of</strong>t red friable <strong>clays</strong> <strong>an</strong>d s<strong>of</strong>t black <strong>clays</strong>.<br />
4.4.4 Applications<br />
In practice, determination <strong>an</strong>d knowledge <strong>of</strong> the values <strong>of</strong> low shear strength <strong>of</strong> s<strong>of</strong>t <strong>an</strong>d/ or<br />
weak soils to a reasonable degree <strong>of</strong> accuracy is essential, <strong>an</strong>d some <strong>of</strong> the applications are as<br />
mentioned below.<br />
First <strong>of</strong> all, the determined low shear strength could be useful in indicating the maximum safe<br />
bearing pressure which a stratum <strong>of</strong> very s<strong>of</strong>t soil could sustain initially, when external loads<br />
<strong>of</strong> constructed <strong>engineering</strong> structures are placed <strong>an</strong>d/ or imposed on them. This would in turn<br />
determine <strong>an</strong>d influence the designed thickness <strong>of</strong> such structures (emb<strong>an</strong>kments, etc.) which<br />
could be built <strong>an</strong>d placed as a first stage. Thereafter, subsequent consolidation would serve to<br />
increase the shear strength <strong>of</strong> the soil so that construction could proceed in stages, based on<br />
the shear strength criterion (Head, 1988).<br />
Secondly, the shear strength <strong>of</strong> s<strong>of</strong>t strata near the ground surface is usually used for the<br />
estimation <strong>of</strong> “negative skin friction” resulting from adhesion on piles driven down to a firmer<br />
stratum below (Lambe <strong>an</strong>d Whitm<strong>an</strong>, 1979). Infact, s<strong>of</strong>t soil deposits which have been<br />
extensively disturbed by the effect <strong>of</strong> driving <strong>of</strong> piles commonly end up exhibiting signific<strong>an</strong>t<br />
amounts <strong>of</strong> remoulded strength.
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