Dynamic mechanical constitutive model of combined coal-rock mass based on overlay model

In order to study the dynamic mechanical characteristics of combined coal rock under impact load,using a ϕ75 mm split Hopkinson pressure bar ( SHPB) experimental system for the different combinations of coal samples (sandstone:coal:sandstone,1 ∶ 1 ∶ 1,2 ∶ 1 ∶ 1,1 ∶ 1 ∶ 2,1 ∶ 2 ∶ 2),the impact loading experiments at different rates (4. 590-8. 791 m / s) were carried out. The dynamic stress-strain curves of the combined coal rock were obtained. Combined with the research results of coal and rock constitutive model and the principle of overlay model,the strain rate correlation and damage characteristics of combined coal-rock mass in dynamic failure were fully con-sidered,and the seven-parameter combined coal rock layer constitutive model was constructed. The results show that ① The elastic and plastic phases of coal rock with different combination ratios have different durations,and the stress-strain curves of different combinations have obvious nonlinearity in the early stage. ② The dynamic impact yield strength of the combined coal rock increases with the increase of the strain rate,and decreases with the increase of the proportion of coal. ③ The numerical fitting curve of the 7-parameter combination coal-rock layer constitutive model is well consistent with the measu-r1ed dynamic constitutive curve. The fitting parameter analysis finds the medium strain rate (110. 41-195. 49 s ) impact load. Under the action,the damage softening effect of the combined coal-rock mass exceeds the strain rate strengthening effect and becomes the dominant factor. ④ The fitting parameter range and the impact damage characteristics of the sample indicate that the main damage part of the combined specimen is mainly caused by coal damage,not affected by the combination mode. The research results provide a reference for further understanding the mechanism of coal-rock dynamic disasters such as rock burst and predicting preventive measures. Due to the limited experimental conditions of SHPB for the impact damage of combined coal rock,the influence of surrounding rock is not considered. The dynamic failure charac-teristics of combined coal under confining pressure need to be further studied by experimental and numerical simulation methods.