Effect of suction stress on critical state of compacted silty soils under low confining pressure

The critical-state behavior of an unsaturated dilative specimen under low confining pressure from 0 to 50 kPa was examined by conducting a constant water content-compression (CWCC) test on unsaturated compacted silty soil. Trends in the compressive strength and deformation of specimens were measured from each testing condition. The experimental results were analyzed by assuming that the effective confining stress can be calculated through the use of suction stress, which is defined as the product of the effective degree of saturation and the matric suction. It was found that the postpeak shear-strength states are arranged on the critical-state line for saturated conditions by considering the suction stress as a stress component in the (p_net + p_s, q) plane. The state boundary surface was observed in the relationship between the stress ratio [q/(p_net + p_s)], considering the suction stress, and referential specific volume (ν_λ). It can be concluded, therefore, that the existence of a critical state for an unsaturated dilative specimen under low confining pressure is verified through these results.