In this research, Discontinuous Deformation Analysis (DDA) is extended to analyze shear characteristics of unsaturated soil by separately considering capillary suction and adsorption suction at micro-scale. First, the developed matric suction model is validated by comparing simulation results with the analytical solution. Then, the shear characteristics of unsaturated cohesionless soil are simulated and compared with experimental results. The “peak effect” of the shear strength is reproduced, and it is quantitively explained by the proposed micro parameter CSN (number of the capillary bridge). Further, in the high suction range of cohesive soil, adsorption suction is the dominant factor for apparent cohesion. As the contact area of the clay layer decreases slightly in the high suction range, adsorption suction controls shear strength, therefore, there is seldom a “peak effect” of the shear strength for cohesive soil. The extended DDA provides an innovative approach to analyze the micro mechanism of matric suction in a wide suction range.
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