Timeliness of damage and deterioration of mechanical properties of coal⁃rock combined body under water⁃rock interaction

The coal and rock mass under water⁃rich coal mine environment and the underground water⁃prevention coal and rock pillar will be affected by groundwater erosion， and the mechanical properties and damage of coal and rock mass under the action of water and rock will directly affect its stability and safety. Based on this，the uniaxi⁃ al compression tests of three kinds of coal⁃rock combined bodies including fine sandstone⁃coal ( FC ) ， coarse sandstone⁃coal(GC)and fine sandstone⁃coal⁃coarse sandstone(FCG)were carried out under different immersion times. The deterioration law of mechanical properties and acoustic emission damage characteristics of coal⁃rock combined body under water⁃rock interaction were studied，and the deterioration mechanism of coal⁃rock combined body was ana⁃ lyzed in detail. The results show that 1 With the increase of immersion time，the water content of the composite in⁃ creases gradually，but the increase rate decreases. At the same immersion time，the moisture content of GC composite is the highest，while that of FC composite is the lowest. When the combination is immersed in water for 40 days，it ba⁃ sically reaches the state of being saturated. 2 With the increase of immersion time， the compressive strength of the composite decreases gradually，and the total deterioration degree and stage deterioration degree of compressive strength show a certain time effect and non⁃uniformity. With the increase of immersion time，the deterioration effect de⁃ creases gradually. Under the same immersion time，the compressive strength of FC composite is the highest，while that of GC composite is the lowest. 3 With the increase of immersion time，the elastic modulus of three combinations de⁃ crease in varying degrees，and the total deterioration degree of elastic modulus increases. In the early stage of immer⁃ sion，the deterioration effect of elastic modulus is obvious，but in the later stage，the deterioration effect is weak. 4 With the increase of immersion time，the AE cumulative energy and cumulative number of the composite decrease in varying degrees，the energy storage capacity and strain energy release capacity of the sample decrease significantly， and the plasticity of the sample increases. 5 The damage model of the combination based on the immersion time is constructed. It is known from the model that with the increase of immersion time，the damage of the combina⁃ tion caused by water increases，but the increase rate decreases gradually. 6 The deterioration mechanism of coal⁃ rock combined body under the action of water and rock is analyzed in detail. The physical，chemical and mechanical effects of water on the coal⁃rock samples lead to the change of internal microstructure of coal⁃rock samples，which leads to the deterioration of mechanical properties such as compressive strength and elastic modulus. The deterioration effect of water⁃rock interaction on coal⁃rock combined body is a damage accumulation process from microscopic to macroscopic.