Failure Evolution Characteristics and Resistivity Damage Model of Expansive Clay with Filled Fissures under Uniaxial Compression

The fissure in expansive soil is an important factor to control the failure and stability of expansive soil foundation, slope, and underground engineering. This study utilizes the uniaxial compression–resistivity testing system to investigate the damage evolution of expansive clay with filled fissures by evaluating the stress–strain–resistivity curves of filled fissures with inclination angles of 0°, 15°, 30, 45°, and 60°. Within the study context, the samples were continuously photographed and observed during the test, and the local strain was analyzed using digital image correlation technology. Moreover, a mechanical damage model of fissured expansive soil was proposed based on the resistivity testing data. Generally, the test results have shown increasing the inclination angles of fissures decreases the strength linearly and changes the stress–strain behavior from hardening to softening. The failure modes of various fissure morphologies are classified into three main types: compressive fracture failure (0°), slip-fracture coupling failure (15° and 30°), and slip failure (45° and 60°). The development characteristics of local strains with different fissure inclination angles are significantly different. Moreover, the soil’s effective conductivity and strain have shown significance when developing damage models. This study provides a reference for understanding fissured soil’s failure process and applying comprehensive resistivity testing technology in fissured soil mechanics.