Creep damage evolution and instability induction mechanism of rock under impact disturbance

In order to study the creep damage mechanism of composite coal rock mass under impact disturbance, based on the creep equation model under complex stress and considering the heterogeneity of coal and rock materials, a creep damage constitutive model which can describe the whole process of coal and rock creep was constructed in combination with Weibull distribution, and the sensitivity analysis of parameters was carried out. Furthermore, the influence of impact disturbance on rock creep failure under different initial creep stresses and different impact energy was analyzed. The impact disturbance failure of composite coal rock mass in the creep process was simulated and analyzed. The instability inducing mechanism of creep damage under different initial angles was discussed. The results show that the creep damage constitutive model based on the damage mechanics theory, with the maximum tensile strain criterion and the molar Coulomb criterion as the damage criterion, can describe the three-stage creep characteristics of coal rock well. In the creep model, the influence of parameters A, m₀ and n₀ on the creep characteristics of coal rock is mainly manifested as that the larger the parameters are, the more likely the coal rock is to have accelerated creep failure. Under creep loading, the instantaneous elastic strain increases obviously with the increase of axial loading stress. When the creep stress is the same, the larger the impact load is, the more likely the coal rock is to creep and thus the more likely it is to fail. When the impact load is the same, the failure time of coal rock will decrease obviously with the increase of creep stress. For the composite coal rock mass, the strain rate increases obviously when the initial creep stage is impacted. When the creep is in the stable stage, the strain rate amplitude is smaller, and finally the composite coal rock mass accelerates creep until it becomes unstable. With the increase of joint angle, the creep time firstly decreases and then increases. When the joint angle is 90°, the maximum creep time of coal mass reaches 75 h.