Mechanical properties and damage constitutive model of coal with different water content based on energy principle

In order to explore the energy evolution law and damage evolution characteristics of coal and rock mass in the process of deformation and failure under different water content, the uniaxial compression test of coal and rock mass in Shuangma No.1 Coal Mine under different water content conditions was carried out. Based on the principle of energy calculation and minimum energy consumption, the energy dissipation characteristics and damage evolution mechanism of coal and rock mass under different water content were analyzed. The results show that the mechanical properties of coal and rock mass under different water content are different, and the peak strain are positive correlated with water content, compressive strength and elastic modulus are negatively correlated with water content. The higher the water content of the coal and rock mass, the smaller the elastic strain energy at the peak value and the total strain energy absorbed by the failure, and the higher the proportion of the dissipated energy to the total strain energy. The damage constitutive model based on the principle of minimum energy consumption shows that the damage threshold value gradually decreases with the increase of water content of coal and rock mass. In the dry state, the damage variables of coal and rock mass at the peak stress are 0.36 and 0.28, respectively.When the water content increases to the natural state, the damage variables of coal and rock mass at the peak stress decrease by 0.09 and 0.18, respectively.However, when the water content increases to the saturated state, the damage variables of coal and rock mass at the peak stress increase by 0.102 and 0.49, respectively, showing a trend of decreasing first and then increasing.The evolution model of damage strain energy release rate of coal rock with different water content is further established. The maximum damage strain energy release rate of low water content coal rock is significantly lower than that of dry coal rock, and the decrease is 45.61% and 31.29% respectively. With the increase of water content to saturated state, the maximum damage strain energy release rate changes gently, which is 3.08% and 8.80% respectively, indicating that the damage severity of coal rock does not increase significantly.