As complex and heterogeneous materials, the mechanical properties of rocks are still in need of further investigation regarding the mechanisms of the effects of water. In engineering projects such as goaf foundation treatment and ecological restoration, it is particularly important to describe the fracturing process of non-uniform water-containing sandstone media. The study utilized the theory of continuum mechanics to adopt an elastoplastic strain-softening constitutive relationship and develop a numerical model for analyzing the uniaxial compressive strength and failure characteristics of non-uniform water-containing sandstone. The results indicate that, compared with the reference rock sample, the shorter the capillary path of water entering the rock sample’s internal pores or the larger the contact area with water, the shorter the time required for the rock sample to be saturated. Increasing the water content causes a rapid decline in the rock sample’s elastic modulus and intensifies its brittleness. Group D2 and D3 samples exhibited a decrease in average peak strength to 70.4% and 62.1%, respectively, along with a corresponding decrease in the elastic modulus to 90.78% and 76.55%, indicating significant strain softening. While the failure mode of the rock sample remains consistent across different water contents, the homogeneity of failure shows significant variation. Increasing volumetric water content raises the likelihood of interconnecting cracks between rock samples, resulting in a progressive decline in macroscopic mechanical properties such as peak strength, critical strain, and elastic modulus. This research is significant in advancing the theory and construction technology for ecological restoration in goaf areas.

The mechanical behavior and fracture evolution of overlying strata during thick-seam mining directly govern stope stability, mining-induced pressure, and surface subsidence. However, existing static structural models often fail to reconcile with the dynamic nature of mining processes. This study systematically investigates the formation and evolution mechanisms of load-bearing structures in the overlying strata of the Shendong Mining Area. Failure criteria for overlying strata structures are established and the formation mechanisms along with evolutionary processes are elucidated. Key findings include: (1) The stacked beam-arch (SBA) structure forms through three evolutionary stages—immediate roof collapse (L ≤ 40 m), fixed-end beam fracture (40 m < L ≤ 80 m), and arch stabilization (L > 80 m). (2) The critical span of the main key stratum is 105 m, 23% longer than predictions by key stratum theory, due to the flexural constraint of underlying sandstone layers. (3) The interdependence within the beam-arch dual structure is systematically analyzed. When beam failure occurs in the stacked beam-arch configuration, three distinct failure modes emerge based on depth-span ratios. This study formulating the basis for safety factor calculations of stope overburden structures and providing a unified framework for optimizing support design and subsidence control in similar geological settings.

The phenomenon of surface subsidence in mining areas is closely associated with the mechanical properties of rock movement, which are influenced by the complex diversity of mining geological factors and technical conditions. This study examines the overlying rock of a nearly horizontal coal seam as a case study to elucidate the evolutionary mechanism and fracture mechanics conditions of the overburden structure in goaf areas. The research findings reveal that the maximum principal stress value within the rock support beam is linearly related to the load (q) and Poisson’s ratio (µ), approximately following a quadratic function with the beam length (l), and showing an inverse proportional relationship with the beam height (h). The magnitude and direction of the principal tensile stress depend on the ratio of normal stress to shear stress within the beam, thereby influencing the beam’s failure mode. The span-to-height ratio of the beam impacts the final fracture mode of the rock mass, while the direction of the maximum principal stress within the beam and the internal friction angle of the rock mass are the primary factors influencing the fracture angle of the rock strata. Two types of “stacked beam” structural models are established, along with the corresponding mechanical conditions for failure.