Mechanical properties and damage constitutive model of coal under the coupled hydro-mechanical effect

In order to explore the impact of moisture on the mechanical properties of coal, the triaxial compression tests of raw coal with different moisture contents are carried out by using the triaxial servo-controlled seepage equipment for thermal-hydro mechanical coupling in coal containing methane. Based on elastic damage mechanics, the damage variables of coal with different moisture contents are deduced, and the damage constitutive model of coal under hydro -mechanical coupling is established, the deformation characteristics of coal with different moisture contents are obtained. The results show that: (1) the deformation and failure process of coal under different moisture contents are similar, which can be divided into pre-peak stress stage, post-peak stress stage and residual stress stage; (2) as the moisture content increases, the peak stress, elastic modulus and brittleness of coal decrease, but the Poisson's ratio increases; (3) the damage constitutive model of coal can better represent the deformation characteristics of coal in the complete stress-strain process under different moisture contents, which is suitable for the analysis of the triaxial compressive stress-strain of coal under different moisture contents; (4) both the damage correction coefficient q and the damage constitutive coefficient n determine the curve shape of the damage constitutive model. The damage correction coefficient reflects the characteristics of residual deformation of coal, and the damage constitutive coefficient reflects different degrees of post-peak strain softening of the stress-strain curve.