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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122<br />
Fig. 7.15a. Log-pressure/ voids ratio (e/ log p)<br />
curve .<br />
Fig. 7.15b. Determination <strong>of</strong> coefficient <strong>of</strong><br />
secondary compression cα.<br />
The coefficient <strong>of</strong> volume compressibility, mv, is the ch<strong>an</strong>ge in volume <strong>of</strong> soil test specimen<br />
per unit volume, per unit pressure ch<strong>an</strong>ge, as a result <strong>of</strong> consolidation due to that pressure<br />
ch<strong>an</strong>ge. It is a modulus <strong>of</strong> volume ch<strong>an</strong>ge <strong>an</strong>d serves to indicate the compressibility per unit<br />
thickness <strong>of</strong> soil under test, i.e.<br />
mv = av/(1+e1) = 1/(1+e1) * (- δe/ δp) m²/kN, or<br />
mv = 1000/(1+e1) * (- δe/ δp) m²/MN (7.40)<br />
where e1 = voids ratio at start <strong>of</strong> load increment δp (kN/m²)<br />
Typical values <strong>of</strong> mv for a number <strong>of</strong> types <strong>of</strong> clay are given in Table (7.13), alongside values<br />
<strong>of</strong> mv obtained for black <strong>clays</strong> <strong>an</strong>d red soils <strong>of</strong> this study, for comparison purposes.<br />
The compression index, cc, is a dimensionless number. It refers to the slope <strong>of</strong> the linear<br />
section <strong>of</strong> a consolidation curve <strong>of</strong> voids ratio, e, plotted against loading pressure, p (log<br />
scale). It is therefore the ch<strong>an</strong>ge in voids ratio for one log cycle <strong>of</strong> pressure ch<strong>an</strong>ge on the<br />
curve whose linear section is represented by the equation<br />
e = eo – cclog10 (po+ δp)/po (7.41)<br />
where eo <strong>an</strong>d po refer to initial conditions <strong>of</strong> voids ratio <strong>an</strong>d pressure.<br />
Skempton (1944), found cc to be related to liquid limit, LL, <strong>of</strong> <strong>clays</strong> to a reasonable degree <strong>of</strong><br />
approximation through<br />
cc = 0,009 (LL-10%) (7.42)<br />
for undisturbed clay, <strong>an</strong>d<br />
cc = 0,007(LL-10%) (7.43)<br />
for remoulded clay.