Characteristics of Failure and Deformation of an Unsaturated Silty Soil Experiencing Various Hydraulic Histories

Capillary hysteresis is an intrinsic phenomenon of the unsaturated soil.At the same matric suction,the degree of saturation of a soil with hydraulic histories is different,and the shear strength of the soil is also different.By conducting direct shear tests on the silty soil samples with different hydraulic histories,the result shows that,if the experimental data are represented by net stress,the effective cohesion decreases with degree of saturation and increases with matric suction,whereas the internal friction angle remains constant.If the experimental data are expressed using the effective stress,the shear strength curve can be normalized into a single line,independent of saturation and hydraulic history.Based on the modified Cam clay model,a hardening function of yield stress is developed,which treats the matric suction and saturated degree as internal variables.The proposed model is useful in analyzing the effect of antecedent rainfall on the stability of unsaturated soil slopes.