Characterizing Suction Stress and Shear Strength for Unsaturated Geomaterials under Various Confining Pressure Conditions

This paper focuses on the theoretical representation of suction stress as an added confining pressure in evaluating the mechanical behavior of unsaturated soil under various confining pressure conditions. In general, the effect of the suction stress in interpreting the mechanical behavior of unsaturated soil under confining pressure up to 1 MPa is examined by using a triaxial compression test. The role of suction stress under low confining pressure conditions, however, has not yet been fully explained theoretically. The concept of the suction stress derived from the triaxial compression test results for unsaturated soil and examples of its application were described in this study. By adding suction stress to the confining pressure, the geometric relationship between the failure criteria of the unconfined compression test and existing theories on failure envelope for unsaturated soils was discussed. In addition, the unconfined compression test and constant water content compression test for silty soils were also carried out under different density conditions. By evaluating the results obtained in this study and the past results of silty soils, it was found that the interpretation of suction stress in terms of confining pressure is valid regardless of the density condition.