Stress-strain-time function of clay

Undrained creep of clay may cause significant displacement near an excavation site. To investigate the potential undrained creep, two series of constant-stress undrained creep tests were conducted on specimens from tube samples taken near an excavation site. Results from these creep tests performed by both lateral extension and axial compression are presented in this paper. Test results indicate that the characteristics and the amount of creep strain induced by lateral extension are similar to that induced by axial compression. However, pore pressure response of the lateral extension-induced creep is distinctly different from the pore pressure response of the axial compression-induced creep. Based on an extensive review of reported stress-strain-time functions, an alternative creep function that explicitly considers the effects of overconsolidation is developed. Predicted results are in good agreement with the experimental results and results reported in the literature. This study also shows that the creep function developed herein can be adopted to give reasonable predictions of the stress-strain relationship of constant-rate-of-strain tests. However, the present model does not account for strain softening.