Abstract: To explore the environmental effect of crack evolution characteristics of expansive soils, an environmental chamber was employed to perform desiccating tests on saturated undisturbed expansive soils in varying humidity environments. The soil crack network was extracted using computed tomography (CT) to obtain relevant characteristic indexes. The results show that crack evolution characteristics of expansive soils can be quantitatively characterized by characteristic indexes, which are closely related to desiccating rate. An increased desiccating rate reduces soil shrinkage strain and causes significant fluctuations in the two-dimensional longitudinal porosity. From a 3D perspective, water loss causes the gradual extension of micro-scale cracks. An increased desiccating rate results in greater connected porosity, pore-throat volume, and average coordination number, indicating enhanced connectivity between pores. Most cracks in expansive soil are distributed horizontally. As the desiccating rate increases, cracks exhibit a three-stage distribution pattern: (i) horizontal cracks progressively connect, and oblique cracks gradually increase; (ii) the connectivity of horizontal cracks reaches its maximum, and the proportion of oblique cracks peaks; (iii) oblique cracks gradually connect, and horizontal cracks re-emerge. The evolution pattern of crack distribution mainly depends on the initial distribution state of primary cracks, with the desiccating rate being an important factor affecting crack scale and connectivity degree.

Key words: undisturbed expansive soil, humidity environment, crack evolution characteristics, characterization, connectivity