Elastoplastic analysis and stability investigation of water-rich mudstone roadway surrounding rock based on true triaxial loading tests

Due to geological constraints and engineering layout requirements, many mine roadways must be excavated in soft rock strata such as mudstone. Under the influence of groundwater, the mechanical properties of mudstone deteriorate significantly, seriously compromising roadway stability. To address this issue, true triaxial loading tests were first conducted on mudstone specimens with varying moisture contents. The results indicate that water saturation induces a transition of mudstone from brittle to ductile failure, with its strength behavior well described by the Mogi-Coulomb criterion. On this basis, an elastoplastic analysis model was developed by comprehensively considering the effects of moisture content and the dilatancy characteristics of the surrounding rock, with particular emphasis on the plastic flow characteristics and the Mogi-Coulomb strength criterion of water-rich mudstone. The approximate analytical solutions were derived for the displacement, failure zone radius, and plastic zone radius of the surrounding rock in a water-rich mudstone roadway under a non-uniform stress field. The parametric analysis based on an engineering case indicates that a higher moisture content markedly promotes surrounding rock deformation and the expansion of both the plastic and failure zones; variations in the lateral pressure coefficient alter the distribution patterns of deformation and failure zones at the roadway roof and sidewall, with roof conditions deteriorating as the coefficient increases and the sidewall conditions showing an opposite trend; in addition, enhanced support pressure can suppress overall roadway deformation and the development of failure zones to a certain extent. This study can provide a theoretical reference for the stability assessment and support design of similar water-rich mudstone roadways under comparable geological conditions.