Thermal creep and stress relaxation of London clay

This paper investigates the effect of temperature variations on the creep and stress relaxation behaviour of clay samples from London Bank Station. The independent and coupled effects of strain-rate and temperature on one-dimensional stress-strain and stress relaxation responses were investigated based on a series of temperature-controlled constant rate of strain (CRS) compression-relaxation tests carried out at fast, intermediate, and slow displacement-rates and over a temperature range of 20 - 55°C. The temperature effect on creep index (C_α) was investigated based on a series of temperature-controlled multi-staged loading (MSL) oedometer tests. The results of CRS compression-relaxation tests showed that with the increase of temperature, the coefficient of stress relaxation (R_α) decreases for samples loaded at fast and intermediate pre-relaxation displacement-rates (υ ̇), but it increases for samples loaded at the slow pre-relaxation displacement-rate. A decrease in υ ̇ by a factor of 10, i.e. from 0.01 to 0.001 mm/min, causes the R_α values to reduce by 55 – 11% with temperature increase. The increase in temperature was found to generally cause an increase in C_α values obtained from the MSL tests. The maximum value of C_α increased by 18% for temperature change from 35°C to 45°C, and by 37% for temperature change from 45°C to 55°C. The temperature effects on other conventional parameters including preconsolidation pressure, compression and swelling indices (C_c and C_s) were found to be comparable with findings reported in the literature. Comparing the values of C_α obtained from the MSL tests, and R_α values obtained from the CRS tests supports the validity of R_α= C_α/C_c correlation for thermally influenced saturated reconstituted clays, and that the time-dependent soil parameters could be obtained from relatively fast CRS compression-relaxation tests as an alternative to conventional time-consuming oedometer tests