Hydro-mechanical Behavior Of Expansive And Laterite Soils

As two kinds of special soils, expansive and laterite soils are widely distributed in China. Affected by the external environment, these special soils often lead to different degrees of engineering problems in related engineering. At present, many research results on expansive and laterite soils are achieved in the fields of mineral composition, origin, microstructure, cementation, physical and mechanical properties, disaster management and the practical application. However, the knowledge of expansive and laterite soils cannot meet the needs in engineering practice.In this paper, the water-retention and deformation characteristics of Nanyang expansive soil during wetting-drying cycles were studied by the vapor equilibrium method using saturated salt solution and the digital image processing, and the strength of compacted Guilin laterite soil and its prediction were studied by consolidated direct shear tests at different initial moisture contents. The mainly following conclusions are obtained.1. Water-retention and deformation characteristics of Nanyang expansive soil(1) With the increasing of wetting-drying cycle(1 to 3), water content decreases, void ratio increases, average skeleton stress and water retention capacity decreases. But the changes in the above mentioned behavior become less with increasing the cycle(3 to 6).(2) With the increasing of wetting-drying cycle, the shrinkage and crack areas after oven-dry increase, but the increases gradually reduced and tend to be stable. The shrinkage turns to stable faster.(3) The radial deformation of compacted expansive soil due to wetting or drying is greater than that in the height direction.2. Strength of compacted Guilin laterite soil and its prediction(1) Bishop formula for predicting the shear strength of unsaturated laterite soils cannot properly predict the strength of unsaturated Guilin laterite.(2) A macroscopic degree of saturation is defined by taking away the microscopic degree of saturation from the degree of saturation, and is substituted to the parameter χ in the Bishop formula, the predicted strength by the new formula is more closer to the measured one. Although it cannot be fully used, but it has a certain reference value to practical application.(3) The contribution of microscopic pore water to the shear strength of laterite soil cannot be fully ignored. More tests were needed to measure how the strength of unsaturated laterite soil is affected by the microscopic pore water.