Strain-rate effect on consolidation behaviour of Ariake clay

A total of 114 constant rate of strain (CRS) consolidation tests and 15 incremental loading (IL) consolidation tests were conducted for undisturbed Ariake clay samples from three boreholes in the Saga Plain, Kyushu, Japan, to systematically investigate the strain-rate effect on the consolidation behaviour of Ariake clay. The test results show that the consolidation yield stress (p_c) of Ariake clays increased by about 15–16% with a tenfold increase in strain rate, and no clear correlation exists between the strain-rate effect and the clay content or plasticity index I_p of the samples. For a given strain level, the strain rate does not influence the compression index C_c, which implies that an isotach model is applicable to Ariake clay. It has been newly found that, under a given effective vertical stress, the coefficient of consolidation c_v increases with increase of the strain rate, resulting mainly from the increase of hydraulic conductivity k with strain rate. Linear regression gives about a 33% increase in c_v with a tenfold increase in the strain rate. For the Ariake clay tested, the p_c and c_v values of CRS tests with a strain rate of 0·02%/min are comparable with those of IL tests.