Limitations of measuring c_v by oedometer in Hong Kong granitic soils

Over recent years in Hong Kong, engineers have become concerned over the very low c_v (coefficient of consolidation) as measured by oedometer for permeable granular soils. The aim of the present paper is therefore to explore the underlying reasons for such low c_v values and the validity of an alternative measurement by isotropic consolidation in a triaxial cell (IC). Starting from a hypothetical curve relating consolidation to square root time, it can be seen that, with existing testing standards requiring an accuracy of 1 s only in the time-measuring device, it is impossible for permeable soils with t₉₀ (90% consolidation time) of less than about 1 s to have any consolidation readings recorded for determination of t₉₀. The apparent t₉₀ determined from measurable records will be considerably higher, yielding c_v of the same order as those by oedometer. However, c_v from a hypothetically low t₉₀ is more realistic, being the same order as those from IC. The validity of measuring c_v by IC is justified, as the ratio of c_v measured by oedometer to that derived by IC is of the same order of magnitude from both experimental results and theoretical evaluation, for a linear elastic, isotropic and homogeneous soil.