Thermal Creep and Stress Relaxation of London Clay

This paper investigates the effect of temperature variations on the creep and stress relaxation behavior of clay samples from London Bank Station. The independent and coupled effects of strain rate and temperature on one-dimensional (1D) 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 20 degrees C-55 degrees C. The temperature effect on the creep index ( C alpha) was investigated based on a series of temperature-controlled multistage loading (MSL) oedometer tests. The results of the CRS compression-relaxation tests showed that with the increase in temperature, the coefficient of stress relaxation ( R alpha) decreases for samples that were loaded at fast and intermediate prerelaxation displacement rates ( upsilon ); however, it increases for samples loaded at the slow prerelaxation displacement rate. A decrease in upsilon by a factor of 10 (i.e., from 0.010 to 0.001 mm/min) causes the R alpha values to reduce by 55%-11% with the temperature increase. The increase in temperature caused an increase in C alpha that were obtained from the MSL tests. The maximum value of C alpha increased by 18% from 35 degrees C to 45 degrees C and by 37% from 45 degrees C to 55 degrees C. The temperature effects on other conventional parameters that included the preconsolidation pressure, and the compression and swelling indexes (Cc and Cs) were comparable with the findings reported in the literature. Comparing C alpha that were obtained from the MSL tests and R alpha that were obtained from the CRS tests supports the validity of R alpha = C alpha / 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.