Influence of Acidizing Reaction on Fracture Behavior of Hard Sandstone of Coal Mine Roof

Fracture properties and cracking mechanism of hard sandstone roof are of great significance to caving. Based on the idea of acidizing fracturing, this paper applied three-point bending loading on hard sandstone SCB samples soaked in 5%, 10% and 20% hydrochloric acid solution for 7 d and 14 d respectively, and the change characteristics of fracture toughness, fracture compression work and fracture morphology before and after acidizing reaction were obtained. The influence mechanism of acidification reaction on fracture behavior of hard sandstone roof in coal mine is preliminarily clarified. The results show that the displacement-load curve shows that the slope of sandstone sample at the post-fracture stage is large, indicating that the sandstone sample has significant brittleness. Acid concentration and reaction time have little influence on sandstone brittleness, but have influence on the curve morphology of sandstone before macro fracture. The fracture toughness of sandstone samples decreases with the increase of soaking acid concentration, and the slope decreases with the longer reaction time, and the damage effect is most significant at the initial reaction stage. The fracture compression energy decreases with the increase of acid concentration and the weakening of rock toughness. With the acidizing reaction, the fracture form of sandstone samples changes from single tensile fracture to tensile fracture and shear fracture, and the fracture efficiency of hard sandstone increases after acidizing. It is concluded that the acid solution corroded the micro-plagioclase and kaolinite in sandstone to form defects and destroy the bonding strength of the minerals. In this paper, it is considered that acidification can significantly reduce the energy consumption of hard sandstone fracture and rock crushing difficulty, which is beneficial to improve the efficiency of coal mine caving.