an engineering geological characterisation of tropical clays - GBV
an engineering geological characterisation of tropical clays - GBV
an engineering geological characterisation of tropical clays - GBV
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
120<br />
cv = (0,1036/t50)* (H'/2)²<br />
or cv = 0,026(H')²/t50 (m²/year) (7.32)<br />
where H' (mm) = me<strong>an</strong> specimen height during the load increment<br />
t50 (min) = time for 50% primary consolidation<br />
A square-root time <strong>an</strong>alysis using t90 corresponding to U = 90% primary consolidation <strong>an</strong>d T90<br />
= 0,848 (Table 7.11) tr<strong>an</strong>sforms Equation (7.30) into<br />
cv = (T90/t90)* h²<br />
= 0,848 * (h²/t90) mm²/min, or<br />
cv = (0,848 * (h/1000)²)/(t90/(60*24*365,25))<br />
= 0,446* (h²/t90) m²/year (7.33)<br />
In terms <strong>of</strong> me<strong>an</strong> height <strong>of</strong> specimen, H',<br />
cv = (0,446*(H'/2)²)/t90, or<br />
cv = 0,112 * H'²/t90 (m²/year) (7.34)<br />
where t90 (min) = time for 90% primary consolidation for a given load increment<br />
H' (mm) = me<strong>an</strong> specimen height during this load increment<br />
In practice, however, cv is usually calculated from t50 rather th<strong>an</strong> t90 because the middle<br />
section <strong>of</strong> the laboratory settlement curve is the portion which agrees most closely with the<br />
theoretical curve (Head, 1988).<br />
Typical values <strong>of</strong> coefficient <strong>of</strong> consolidation (Lambe <strong>an</strong>d Whitm<strong>an</strong>, 1979) obtained from<br />
laboratory oedometer tests on specimens <strong>of</strong> uniform soil are related to their approximate<br />
plasticity r<strong>an</strong>ges in Table (7.14). Values <strong>of</strong> cv obtained for black <strong>clays</strong> <strong>an</strong>d red soils in this<br />
study have also been related to their plasticity, <strong>an</strong>d included alongside for comparison<br />
purposes.<br />
7.4.3.2 Voids ratio<br />
Voids ratio, e, is the ratio <strong>of</strong> the volume <strong>of</strong> voids occupied by water <strong>an</strong>d/ or air; to the volume<br />
<strong>of</strong> solid particles in a mass <strong>of</strong> soil.<br />
Voids ratio in a consolidation test is defined by<br />
Voids ratio e = (Gs/ρo) –1 (7.35)<br />
where Gs = specific gravity <strong>of</strong> solid particles<br />
ρ0 = dry density <strong>of</strong> soil (Mg/m³)<br />
Voids ratio, e, is related to degree <strong>of</strong> saturation, S, through the relation<br />
S (%) = (w * Gs/e) * 100 (7.36)