MECHANICAL PROPERTIES OF OVERCONSOLIDATED SILTY CLAY UNDER FAST SHEAR CONDITIONS

This paper employs a sophisticated ring shear apparatus and conducts a series of fast rate ring shear tests to quantify the mechanical properties of Changchun silty clay. The tests are carried out under overconsolidated and fast ring shear conditions. The test results are obtained under different preconsolidation pressures, shear rates and normal stresses. The effects of stress history and shear rate on the shear resistance of the over-consolidated silty clay are examined and discussed. It is found that the preconsolidation pressures and shear rates exert remarkable influences on the peak shear strengths and the following post-peak reductions in strength. The shear strengths became greater when the preconsolidation pressures were higher. The test results at different shear rates show that if the OCR values are the same, both the peak strength and the post-peak strength reduction become greater as shear rate increases. The soils with high shear rate are prone to have the strain softening. The faster shear rate tests are more favorable to development of slip surface that lead to the ultimate stable shear strengths. The variations of shear resistance under fast shear rate in ring shear tests are mainly due to the structural changes in the shear zone, while the influence of pore water during fast shearing is negligible.