Experimental study on the compression and shear deformation evolution of coal pillar dam samples.

To understand the mechanical properties and deformation failure patterns of coal pillar dams in gently inclined coal seam mine underground reservoirs, compression-shear coupling tests with variable angles were conducted on coal pillar dam samples under different saturation states. The digital image correlation (DIC) technique was utilized to obtain the deformation patterns of the displacement field throughout the compression-shear failure process of the samples. Numerical simulations were used to perform a comparative analysis and validation of the experimental results. The results indicated that the load-bearing capacity of the coal pillar dam samples decreased by 12.8-17.4% under water-saturated conditions. For every 5° increase in the inclination angle, the load-bearing capacity of the coal pillar dam samples decreased by an average of 3.53%. The normal stress and shear stress on the shear surface of the saturated samples were both lower than those of the natural samples, and both exhibited a linear variation with increasing inclination angle. The deformation evolution of the coal pillar dam samples under different test conditions exhibited similarity. The initial positive and negative displacement extremities in the horizontal direction were located at the lower right and upper left corners of the samples, respectively. Ultimately, the displacement field of the samples showed a pattern of smaller displacements at the top and larger displacements at the bottom, with negative values at the top and positive values at the bottom, distributed along the direction of the sample's bedding. The saturated state and the increase in inclination both had a weakening effect on the load-bearing performance of the samples but had a relatively small impact on the differences in the displacement field deformation patterns. The research results can provide a reference for the study of the stability of coal pillar dams under similar conditions.