Multi-parameter assessment and integrated damage modeling of water-bearing mudstone under uniaxial compression

Mudstone commonly acts as an aquiclude in underground mines, and its water-induced degradation can promote fracture propagation, pore-water migration, and water-inrush hazards. Due to its strong water sensitivity, water-bearing mudstone exhibits distinct mechanical degradation characteristics compared with water-bearing sandstone, requiring lithology-specific damage characterization. In this study, mudstone specimens with different water saturation levels were subjected to uniaxial compression, while mechanical, acoustic emission, and electrical responses were monitored simultaneously. The temporal evolution of these parameters was analysed to identify the influence of water saturation on failure precursors and to establish empirical relationships among the monitored responses. Based on these multi-parameter responses, a segmented variable-weight integrated damage constitutive model was developed to characterize the progressive failure process by considering the stage-dependent contributions of different damage indicators. The results show that increasing water saturation markedly weakens the mechanical and energy-storage capacities of mudstone: peak stress, elastic modulus, cumulative acoustic emission energy, and initial electrical resistivity decrease by 47.67%, 52.84%, 87.65%, and 97.59%, respectively, while peak strain increases by 18.88%. The integrated damage model reproduces the measured stress–strain curves more accurately than single-variable damage models, with a coefficient of determination exceeding 0.99. This study provides an experimental-scale framework for multi-parameter damage characterization of water-bearing mudstone and offers a basis for further investigation of aquiclude stability.