Time-Dependency of Undrained Behavior of Natural Soft Clay with Different Pre-shearing Stress History Based on Laboratory Test

The time-dependency of undrained behavior of the tested natural soft clay as well as the influence of pre-shearing stress history on the studied subject was examined based on experimental data. The tested clay was characterized by high water content and high plasticity with slight organic debris. Triaxial undrained constant strain rate £¨UCSR£© tests were employed to study the strain-rate sensitivity of the undisturbed natural clay by using computerized testing system with stress-path controlled. The specimens were loaded to different stress state after re-consolidation with in-situ stress and pore pressure and before the UCSR tests were performed. The specimens were sheared at step-changing axial strain rates respectively to exclude the influence of instinctive heterogeneities of different specimens. The strain-rate dependent properties of undrained shear strength and effective stress path as well as the effect of pre-shearing stress history on the strain-rate dependent properties of the natural soft clay were examined based on triaxial UCSR experimental results. The results show that the undrained strength increases by 9.7 % in compression tests and 7.2 % in extension tests caused by the 10-times increased strain rates for the tested clay.