Study of a damage constitutive model for water-bearing coal measures sedimentary rock with nonlinear deformation during compaction stage

The problem of repeated immersion-induced fatigue damage in engineering coal measures sedimentary rock, including coal-rock pillars, reservoir bank slopes, and water-rich tunnels at the boundary of coal mine underground reservoirs, has profound implications for their stability, safety, and operation, and can even lead to geological disasters. To address this issue, this paper aims to construct a constitutive model that accurately captures the comprehensive process of deformation and failure in water-bearing coal measures sedimentary rock. It explores the deformation characteristics of these formations and provides a theoretical foundation for numerical simulations of geological disasters induced by water-rock interaction. This study integrates the deformation mechanisms of void and matrix deformation in coal seam sedimentary rocks, while considering the influence of immersion cycles. Subsequently, it formulates a segmented constitutive model to depict the entire process of deformation and failure in cyclically immersed water-bearing coal measures sedimentary rock under uniaxial compression. The proposed model's accuracy and rationality are validated through comparisons with experimental research findings and existing theoretical curves from similar models. The results demonstrate the model's effectiveness in describing the deformation behavior of non-dense water-bearing coal measures sedimentary rock under uniaxial compression or low confining pressure before reaching peak stress, although further refinements may be necessary to precisely capture post-peak deformation characteristics. Model parameters, including the deformation caused by voids (γ₀) between voids, increase exponentially with immersion times, while the elastic modulus (E_v) of voids and the parameter (F₀) related to the average strength of microelements decrease exponentially. The homogeneity degree (m) exhibits no discernible pattern. These research outcomes provide valuable insights for the stability control of engineering coal measures sedimentary rock under water-rock interaction and the mitigation of related geological disasters.