Effects of Drying-Wetting Cycles on the Microstructure and Mechanical Properties of Granite Residual Soils

To examine the effect of drying-wetting cycles on the damage patterns of microstructural and mechanical properties of granite residual soils, nuclear magnetic resonance scans, triaxial shear tests and scanning electron microscopy measurements were performed on undisturbed samples. The correlation between pore distributions and shear strength parameters were then examined and the microscopic mechanism of the drying-wetting cycles was revealed. The pore volume distribution curve of granite residual soil showed a major peak and a secondary peak, which represented micro pores and macro pores, respectively. As the number of drying-wetting cycles increased, the distributed proportions of micro pores remained almost constant, whereas those of macro pores increased dramatically. The NMR-based porosity was nonlinearly related to drying-wetting cycles in a positive manner. Moreover, the weakening trend of mechanical properties evolved synchronously with the development of microstructure damage during continuous drying-wetting cycles. The damage patterns of microstructure and mechanical properties of soils were attributed to expansive forces in pore walls and losses of fine clay particle due to periodic drying-wetting cycles.