Experimental Study on Mechanical Properties and Micromechanisms of Cement‐Improved Granite Residual Soil

To enhance the engineering properties of granite residual soil for subgrade filling, cement is incorporated to improve the soil. Through compaction tests, direct shear tests, and scanning electron microscope (SEM) tests, the influence of adding different doses of cement on the shear strength, residual strength, and microstructure of granite residual soil is investigated. The experimental results show that the maximum dry density increases and the optimal moisture content decreases with increasing cement content up to 7%. The shear strength is significantly enhanced with the increase in cement content. This effect is mainly attributed to the significant improvement in soil cohesion due to the addition of cement. When the cement content exceeds 7%, the shear strength index still increases with the cement content, but the rate of change slows down significantly. The failure mode of improved soil exhibits brittle failure, with residual strength remaining unchanged after cement content reaches 3%. At lower stress levels, the residual strength of the improved soil is similar to the shear strength of the undisturbed granite residual soil; while at higher stress levels, the residual strength of the improved soil is inferior to the shear strength of the undisturbed granite residual soil. SEM images reveal that cement hydration products gradually fill pores, forming a continuous spatial network structure. Considering both effectiveness and economic factors, the optimal cement content is approximately 5%. These findings contribute to a deeper understanding of the engineering properties of cement‐improved granite residual soil and provide guidance for related engineering construction.