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.

To study the influence of dehydration conditions on the pore structure and the mechanical property of expansive soil, two experimental conditions with high-temperature drying (temperature 50 °C-humidity 10%) and high-temperature humid (temperature 50 °C-humidity 70%) were carried out. Taking the remolded expansive soil in the province of Anhui in China as the research object, this paper used mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) to analyze the pore size distribution and pore structure of remolded expansive soil samples under different dehydration conditions and duration. After these tests, their mechanical properties were further obtained by uniaxial compression tests. The results showed that the distribution of pore structure of expansive soil was various under different dehydration conditions. Under high temperature and dry environment, the volume of large pores decreased first and then increased with the time of dehydration, while the medium pore volume decreased until the dehydration was stable. Under high temperature and humid environment, the volume of large pore and medium pore both showed a trend of decrease until the dehydration kept stable. The pore volume of expansive soil did not change significantly under the two dehydration conditions. The uniaxial compressive strength (UCS) of remolded expansive soil samples in high temperature and dry environment reached the highest on the 5th day of dehydration, and then the soil strength decreased slightly until it stabilized. The UCS of remolded expansive soil reached the highest on the 15th day of dehydration under high temperature and humidity environment, and the soil strength changed little after continual dehydration. These tests showed that the UCS of dehydrated expansive soil samples under the condition of high temperature and humidity is higher than that of dehydrated expansive soil samples under the condition of high temperature and dry environment.