Laboratory Study on Soil Shear Stiffness and Strength Under Unloading Conditions

Abstract In excavated earth structures (e.g., deep excavation, cut slope, and underground construction etc.) unloading is the most predominant factor that affects the behavior of soil mass. However in engineering practice, the influence of unloading factor has not been really considered. For example, the soil shear strength characteristics are often investigated from the conventional triaxial shear test, consequently it leads to some doubts when applying the shear strength properties under loading condition to analyze the stability and displacement problem of unloading cases. In this study, a comparison of soil shear deformation and strength between loading and unloading conditions was carried out, which was based on two series of tests for remoulded clay conducted on the Advanced Stress Path Triaxial Testing System. The test results showed that the unloading factor affects soil behaviour significantly. The differences in friction angle, collapsibility, excess pore-water pressure, and shear modulus during shear under unloading condition are remarkable from under loading condition.