EXPERIMENTAL STUDY ON THE DETERIORATION OF BASALT MECHANICAL PROPERTIES UNDER DRY-WET CYCLES IN DIFFERENT ACIDIC AND ALKALINE ENVIRONMENTS

The long-term exposure of slope rock masses to seasonal rainfall cycles leads to intensified weathering and deterioration of their mechanical properties, increasing their vulnerability to landslide hazards. This study conducted dry-wet cycle tests on basalt samples saturated in solutions with pH values of 2, 4, 7, 9, and 11,with the number of cycles ranging from 0 to 40,to investigate the impact of acidic and alkaline environments and cyclic drying and wetting on the mechanical characteristics of basalt. Through uniaxial compression tests and scanning electron microscopy(SEM)analyses, the degradation patterns of basalt's mechanical properties under dry-wet cycles across different pH conditions were examined. Furthermore, a damage constitutive model for basalt was developed based on statistical strength theory to quantitatively characterize its progressive deterioration. The results demonstrate that both the compressive strength and elastic modulus decreased sharply with increasing numbers of dry-wet cycles. Under acidic conditions, the uniaxial compressive strength decreased by 59.93% ~70.33%; under neutral conditions, by 56.93%; and under alkaline conditions, by 53.07% ~53.73% after 40 cycles. The reduction in elastic modulus was even more pronounced than that in compressive strength, with the severity of degradation following the trend: acidic>neutral>alkaline. However, as the number of cycles increased, the differences in degradation among the various environments gradually diminished. The failure morphology of the rock changed significantly with the increasing number of cycles. More severe fragmentation was observed under acidic conditions, while alkaline conditions did not exhibit a similar trend. SEM image analysis revealed distinct degradation mechanisms for different pH conditions: a three-stage evolution of defect distribution in acidic environments, a two-stage pattern in alkaline conditions, and a logarithmic trend in neutral environments. The damage constitutive model, constructed using the Weibull distribution and statistical strength theory, demonstrated a strong fit to the experimental data. These findings provide a scientific basis for evaluating the stability of basalt rock slopes and contribute to landslide hazard prevention and mitigation.