Investigation of the Shear Strength of Unsaturated Soils over a Wide Suction Range

Unsaturated shear strength (τus) is a critical parameter in many geotechnical engineering designs, including embankment stability assessments and slope antiskid design. This paper investigates the hydromechanical behavior of unsaturated reconstituted clay by conducting suction-controlled triaxial shear tests. The results show a nonlinear increase in τus over a wide range of suction, as well as a nonzero τus value at high suctions. However, using existing strength equations to predict τus may result in an overestimation or underestimation in the residual zone. To address this limitation, a fitting-type strength model of unsaturated soils that takes the impact of void ratio into account is proposed based on the unified effective stress equation that separates capillary stress from adsorbed stress. The proposed model accurately describes various types of strength behaviors over a wide range of suction, such as nonlinear increasing strength type and peak strength type. Finally, the proposed model is evaluated against experimental results of the test soil in this study and different soils reported in other resources, showing that it can reasonably capture important features of the strength behavior of unsaturated soils over a wide range of suction.