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.

This study investigates the infiltration characteristics of expansive soil subjected to drying–wetting cycles under surcharge. Infiltration tests are conducted on undisturbed expansive soil over four drying–wetting cycles. Additionally, the permeability coefficient under loading is determined prior to any drying–wetting cycles. Within the context of this study, the sample heights after drying and after wetting are monitored to determine the natural swelling and shrinkage deformations. Experimental results show that the infiltration rate decreases as the pressure increases. The sample’s swelling–shrinkage deformation decreases with each progressive drying–wetting cycle, whereas the infiltration rate consistently increases. The infiltration curve under the drying–wetting cycle can be divided into three stages according to the infiltration characteristics, which is significantly different from the infiltration curve of the sample without the drying–wetting cycle. Moreover, the proposed model can fit the infiltration curves well, and its fitting parameters are described using dimensionless pressure and the number of drying–wetting cycles. The drying of the expansive soil produces cracks that are advantageous for infiltration. Additionally, the microscopic connection between aggregates reflects changes in the internal structure of the soil during successive drying–wetting cycles. As the number of drying–wetting cycle increases, small particles aggregate into large aggregates, and the contact relationship between the aggregate changes from face–face to point–point contact, reducing the swelling potential and increasing the porosity and infiltration capacity of the soil.

The strength damage and deformation failure of frozen soil–rock mixture (FSRM) often restrict the safety of the major engineering construction in cold areas or the spatial development of urban underground water-rich rock and soil masses. To investigate the uniaxial strength damage evolution and failure characteristics of FSRM under different loading rates (0.3, 0.6, 3, 6, 30, and 60 mm·min⁻¹) in the quasi-static range, resistivity monitoring and image recognition technology were used to study the time-stress-volumetric strain-resistivity changes. The results indicate that the peak stress, peak strain, initial yield modulus, and tangential modulus of FSRM increase rapidly before increasing slowly as the loading rate increases, and there are critical loading rates and post-peak failure phenomenon. Three distinct types of failure modes, bulge failure, oblique shear failure, and fragmentation failure were observed at low (0.3–0.6 mm·min⁻¹), medium (3–6 mm·min⁻¹), and high loading rates (30–60 mm·min⁻¹), respectively. The macroscopic failure of the FSRM at different loading rates arises from a combination of strain rate hardening of the strength and damage softening of the structure. To predict the stress-strain characteristics at various loading rates, a damage prediction model with a damage variable correction factor considering residual strength was employed based on the improved Duncan–Chang model and damage theory of electrical resistivity, and the predicted results were in good agreement with the experimental data.