Using CT to test the damage characteristics of the internal structure of expansive soil induced by dry–wet cycles

Damage to the internal structure of expansive soil under dry–wet cycles is the key factor for engineering damage to expansive soil. The expansive soil in Nanyang, Henan Province, China, is taken as the research object, and the damage characteristics of the internal structure of the expansive soil under dry–wet cycles are discussed. Computed Tomography (CT) images of the internal cracks of the expansive soil after zero to eight dry–wet cycles under different initial moisture contents were obtained using a CT machine, and the development of the internal structural cracks of the expansive soil was analyzed. The damage variable of the expansive soil defined by the ME value of CT and the relation between the damage variable, the number of dry–wet cycles, and the initial control moisture content are described. An empirical nonlinear damage model of the internal structure of expansive soil is established. Finally, the rationality of defining the damage variable by the ME value of CT is verified by the test results of the low-stress shear strength of the expansive soil. The results show that the first to fourth dry–wet cycles have great influence on the microstructure of the expansive soil and that internal microcracks are noticeably developed. With the increase in dry–wet cycles, the SD value increases gradually, and the anisotropy of the expansive soil becomes more significant. The dry–wet cycles result in the weakening of the connection between the particles of the expansive soil and in the damage of the internal structure, which is a nonlinear cumulative process. The ME value can be used to describe the damage evolution characteristics of expansive soil after dry–wet cycles.