Damage Characteristics and Degradation Mechanism of Silty Mudstone Under Wet–Dry Cycling

Silty mudstone distributed in southern China subjected to wet–dry cycling exacerbates the rock deterioration, posing significant challenges to slope stability. This study aims to investigate the damage characteristics and degradation mechanisms of silty mudstone after undergoing multiple wet–dry cycles. The specimen variation was simulated in laboratory under repeated cycles and the degree of specimen degradation across various cycle numbers (N) was evaluated using a combination of geotechnical tests (uniaxial compressive and split tensile tests) and microscopic observations via Scanning Electron Microscopy. Further, the fractal feature was characterized by Box-counting Dimension method implemented in MATLAB, and the damage evolution equation was obtained based on the damage theory. The findings reveal a pronounced decline in mechanical properties and a transition from brittle to shear failure modes with an increase in N, alongside an enhancement in cross-sectional integrity post-damage. Porosity changes notably, with an increased proportion of larger pores post-erosion. The fractal dimension escalates with rising N, with the damage variable and strength degradation rate initially increasing followed by stabilizing. A developed quadratic polynomial damage model exhibits universality for silty mudstone submitted to wet–dry cycling. The degradation mechanism is identified as resulting from cement dissolution and recrystallization, mineral surface hydration, and particle softening and disintegration.