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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121<br />
where w (%) = moisture content <strong>of</strong> soil<br />
S (%) = degree <strong>of</strong> saturation, i.e. volume <strong>of</strong> water contained in the void space between<br />
soil particles expressed as a percentage <strong>of</strong> total voids<br />
The volume ch<strong>an</strong>ge which occurs during consolidation takes place only in the voids so that a<br />
ch<strong>an</strong>ge in height ∆H from <strong>an</strong> initial height Ho in the specimen corresponds to a ch<strong>an</strong>ge in<br />
voids ratio ∆e from <strong>an</strong> initial value eo. By proportion therefore,<br />
∆H/Ho = ∆e/(1+eo), so that<br />
∆e = ((1+eo)/Ho) * ∆H, or<br />
∆e = F∆H (7.37)<br />
Where F (mm¯¹) = ch<strong>an</strong>ge in voids ratio per unit height, with respect to initial conditions <strong>of</strong><br />
test specimen<br />
The ch<strong>an</strong>ge in height <strong>of</strong> specimen is used to give the voids ratio,e, at <strong>an</strong>y stage <strong>of</strong> a<br />
consolidation test through<br />
e = eo – ∆e (7.38)<br />
where eo = initial voids ratio <strong>of</strong> test specimen<br />
7.4.3.3 Coefficient <strong>of</strong> compressibility (av), coefficient <strong>of</strong> volume compressibility (mv)<br />
<strong>an</strong>d compression index (cc)<br />
These coefficients are derived from consolidation tests <strong>an</strong>d are indicative <strong>of</strong> the<br />
compressibility <strong>of</strong> soils. They serve to give estimates <strong>of</strong> the amount <strong>of</strong> settlement due to<br />
primary consolidation.<br />
The coefficient <strong>of</strong> compressibility, av, <strong>an</strong>d the coefficient <strong>of</strong> volume compressibility, mv, are<br />
usually calculated for each load increment while the compression index, cc, is derived from <strong>an</strong><br />
e/ log p curve obtained by plotting voids ratio, e, against applied pressure, p, (log scale), i.e.<br />
(Fig. 7.15a). In practice, mv is applied to overconsolidated <strong>clays</strong> <strong>an</strong>d cc to normally<br />
consolidated ones. The swell index, cs, gives <strong>an</strong> indication <strong>of</strong> exp<strong>an</strong>sion <strong>of</strong> a soil on<br />
unloading.<br />
The coefficient <strong>of</strong> compressibility, av, is the ch<strong>an</strong>ge in voids ratio, δe, per unit pressure<br />
ch<strong>an</strong>ge, during a given load increment, due to consolidation caused by that incremental<br />
pressure δp, i.e.<br />
av = (e2 – e1)/ δp<br />
= - δe/ δp (m²/kN) (7.39)<br />
where e1 <strong>an</strong>d e2 = voids ratios at start <strong>an</strong>d end <strong>of</strong> consolidation under the load increment<br />
δp in kN/m²<br />
The negative sign indicates decrease <strong>of</strong> e as p increases.