Experimental investigations of hydraulic and mechanical properties of granite residual soil improved with cement addition

•The pore structure of soil can be accurately assessed by X-ray CT.•The cement can improve the distribution of soil pore structure.•The cement reduces the connectivity of pores and increases isolated pores.•6% cement content can increase the strength of soil and decrease permeability. Granite residual soil is widely distributed in southeastern China. Notably, this soil easily softens when exposed to water and is easily damaged when subjected to stress, and these characteristics are not conducive to engineering construction and underground space development. In this study, computed tomography(CT), mercury intrusion tests, XRD and SEM techniques are used to examine the improvement of granite residual soil in the Shenzhen area through the addition of cement. The soil micropore structure, saturated permeability coefficient and soil strength characteristics for improved soil specimens with different cement contents (2%, 4%, 6% and 8%) and curing durations (3 d, 5 d and 8 d) are examined. The results show that the pore distribution of granite residual soil has a bimodal structure. In the cement-improved soil, the large pores are eliminated, connectivity of pores is decreased, and number of isolated pores increases. Moreover, the unconfined compressive strength of the improved soil is higher than that of the granite residual soil. The introduction of cement contents of 6% can effectively increase the strength of granite residual soil while decreasing the permeability.