Research on the damage laws and failure characteristics of sandstone in coal seam roofs under different rich-water conditions

There is a water seepage phenomenon in the sandstone of the coal seam roof in Pingdingshan mining area, and there is a risk of collapse. To study the damaging effect of water on sandstone and provide a theoretical basis for prevention and control measures in water-rich areas, this paper conducts experimental research on sandstone under different water-bearing conditions. The results show that the strength of sandstone decreases with the increase of water saturation, and the trend changes from rapid decline to slow decline. Compared with the dry condition, the compressive strength of sandstone under the different water conditions decreases by 16.98%, 30.54% and 39.46%, respectively. The tensile strength decreased by 18.67%, 31.35% and 41.16%, respectively. After the sand from drying to saturated water, the compressive deformation modulus decreased by 33.22%, the tensile deformation modulus decreased by 30.08%. The damage variables under tensile and compressive loads increased to 0.34 and 0.4. The increase of water content reduces the deformation modulus and brittleness index of sandstone, increases the damage of sandstone, and leads to the deformation and failure of sandstone more easily. Compared with dry and natural water conditions, the energy damage rate of sandstone increases faster and the time of damage occurs earlier under unsaturated water conditions. With the increase of water content, sandstone is gradually dominated by tensile failure and is more prone to failure. The research results further highlight the importance of groundwater control and monitoring as well as maintaining the stability of surrounding rocks.