Progress and trend of experimental investigation on rate-dependent behavior of soft clays

Extensive laboratory tests and field observations show that soft clay exhibits significant rate-dependent behavior. Based on published data from the view of the rate dependencies of preconsolidation pressure and undrained shear strength. The rate- dependencies of soft clays under both 1D and 3D conditions are first studied. The applicability of five rate-dependency equations (two equations in exponential form and three equations in logarithmic form) in correlating the preconsolidation pressure and the undrained shear strength with strain-rate is then discussed. Rate parameters under both 1D and 3D conditions for various clays are estimated by using five rate-dependency equations and correlated with Atterberg limits. Furthermore, the rate-dependencies of soft clays under complex stress conditions including shear vane tests and pressuremeter tests are also analyzed. Then, the uniqueness of rate-dependency between 1D and 3D, between triaxial compression and extension, between different OCR (over consolidation ration) conditions is discussed. Finally, the influence of applied strain-rate on the stress-dilatancy of Hong Kong marine clay for triaxial compression and tension tests under different OCR conditions is investigated with some typical stress-dilatancy equations. The results show that the existing typical stress-dilatancy relationships need further enhancement (e. g., amount, anisotropy) for better describing the stress-dilatancy of soft clays.