Effect of coarse content on shear behavior of unsaturated coarse granular soils

The effects of coarse content on the microstructure, soil-water characteristics, shearing behavior, and critical state characteristics of three types of unsaturated coarse granular soil with different coarse contents are investigated in an integrated manner through an extensive laboratory test program. The tests were performed on samples with the same void ratio of 0.62. As the coarse content increases, the pore-size distribution of the soil changes from unimodal to bimodal. Accordingly, the soil-water characteristic curve (SWCC) changes from unimodal to bimodal. The whole drainage process of the bimodal SWCC is divided into four stages based on the role of the pore water. The contribution of suction to the peak state parameters and critical state parameters, except for the intercept of the critical state line in the stress plane (μ(s)) of a bimodal soil, reaches its maximum in the first drainage region. The pore water in the two pore series of a bimodal soil contributes to the shear strength differently during the desaturation process. Hence, the variations of themaximumdilatancy and the shear strength parameters with degree of saturation are highly nonlinear and μ(s) shows bimodal features. The contributions of suction to the shear strength parameters decrease with increasing coarse content