Softening mechanism and characteristics of mudstone after absorbing moisture

Mudstone is formed of weakly consolidated clay through moderate epigenesis. Its strength significantly deteriorates after absorbing moisture, which seriously impacts the safety and stability of engineering facilities. It is imperative to investigate the softening mechanism and characteristics of mudstone exposed to water for the infrastructure in mudstone strata. In this study, the softening mechanism of mudstone after absorbing moisture was revealed through mineral composition test and scanning electron microscopy (SEM), and the softening characteristics were analyzed by uniaxial compression test and a novel statistical damage constitutive model. The results show that dissolution and chemical reaction of the active chemical components and clay minerals are the internal factors of mudstone softening after absorbing moisture. The deterioration of mechanical property is attributed to the combined effects of water erosion and wedge, and water erosion and wedge action coexist and interact. The stress-strain curves of mudstone with different moisture contents under uniaxial compression are typical plastic-elastic-plastic curves, forming an S shape. As moisture content increases, the stress-strain curve becomes flatter, the failure mode shifts gradually from splitting failure to shear failure, and the plastic deformation degree increases. The statistical damage constitutive model based on the Drucker-Prager criterion and Weibull distribution can describe the entire softening and failure process of mudstone after absorbing moisture. The impact of moisture content on the stress-strain curve can be well reflected by the correlation equations between moisture content and the parameters of the constitutive model.