Numerical simulation of effect of cleats on energy evolution of coal and rock in loading process

Energy is the essential factor leading to the failure of rock samples. Cleat is a remarkable feature of coal and rock. In order to analyze the influence of cleat on the energy evolution characteristics of coal and rock in loading process,three kinds of two-dimensional numerical models with different cleat quantities,different cleat densities and different cleat angles were used to carry out the numerical simulation of uniaxial compression in RFPA. The fractal di- mensions of numerical model were calculated by using MATLAB software to characterize the complexity of cleat structure. The influence of cleat quantity,cleat density and cleat angle on the energy-strain curve and the energy in failure point were investigated. The influence of cleat structure complexity on the energy evolution characteristics of coal and rock was discussed. The results show that the change of point elastic energy curve from “concave” to “convex” can be a dividing point and the highest point of stress curve or elastic energy curve (the failure location of specimen) can be another dividing point,then the whole loading process can be divided into three stages:energy accumulation,energy dissipation and energy release. Whether the distribution of cleats is uniform or not in coal samples,the total energy curve and elastic energy curve increase slowly with the increase of total cleat number in the sample during the loading process,the dissipated energy increases with the increase of axial strain at a similar rate,and the potential energy of e- lastic deformation of samples decreases,but the energy used to destroy the internal structure and generate heat and move rock remains basically unchanged. If cleat angle is 0°and 90°,the total energy and elastic energy increase fastest with the increase of axial strain. If cleat angle is 60°,the total energy and elastic energy increase slowest. There is no obvious law for the increase rate of dissipated energy under different cleat angles. With the increase of cleat angle,the total energy and elastic energy of the sample decrease firstly and then increase,showing an approximate “ U” shape. The dissipated energy keeps basically unchanged firstly,and then increases slightly. The total energy and elastic energy decrease with the increase of cleat structure complexity,while the dissipated energy has no significant change with the change of cleat structure complexity. The cleat angle of coal samples has the greatest impact on energy storage in com- pression process. The centralized distribution of cleats has more significant impact on energy storage than the uniform distribution of cleats.