an engineering geological characterisation of tropical clays - GBV

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cv = (0,1036/t50)* (H'/2)²
or cv = 0,026(H')²/t50 (m²/year) (7.32)
where H' (mm) = mean specimen height during the load increment
t50 (min) = time for 50% primary consolidation
A square-root time analysis using t90 corresponding to U = 90% primary consolidation and T90
= 0,848 (Table 7.11) transforms Equation (7.30) into
cv = (T90/t90)* h²
= 0,848 * (h²/t90) mm²/min, or
cv = (0,848 * (h/1000)²)/(t90/(60*24*365,25))
= 0,446* (h²/t90) m²/year (7.33)
In terms of mean height of specimen, H',
cv = (0,446*(H'/2)²)/t90, or
cv = 0,112 * H'²/t90 (m²/year) (7.34)
where t90 (min) = time for 90% primary consolidation for a given load increment
H' (mm) = mean specimen height during this load increment
In practice, however, cv is usually calculated from t50 rather than t90 because the middle
section of the laboratory settlement curve is the portion which agrees most closely with the
theoretical curve (Head, 1988).
Typical values of coefficient of consolidation (Lambe and Whitman, 1979) obtained from
laboratory oedometer tests on specimens of uniform soil are related to their approximate
plasticity ranges in Table (7.14). Values of cv obtained for black clays and red soils in this
study have also been related to their plasticity, and included alongside for comparison
purposes.
7.4.3.2 Voids ratio
Voids ratio, e, is the ratio of the volume of voids occupied by water and/ or air; to the volume
of solid particles in a mass of soil.
Voids ratio in a consolidation test is defined by
Voids ratio e = (Gs/ρo) –1 (7.35)
where Gs = specific gravity of solid particles
ρ0 = dry density of soil (Mg/m³)
Voids ratio, e, is related to degree of saturation, S, through the relation
S (%) = (w * Gs/e) * 100 (7.36)