Particle flow simulation on mechanical behavior of coal specimen under triaxial cyclic loading and unloading

Based on the experimental results of coal samples under conventional triaxial compression,a set of micro- scopic parameters in particle flow code ( PFC) reflecting the macroscopic mechanical behavior of coal samples were obtained. And the cycle loading-unloading experiments of the coal samples under different confining pressures in PFC were carried out to analyze the macroscopic parameters and microcrack propagation of sandstone to find the connec- tions. Through the analysis of the change law of elastic modulus and irrecoverable strain with axial strain,it is found that the elastic modulus increases first before a decrease and the irrecoverable strain grows steadily then changes rapid- ly with axial strain,which prove it is workable to simulate the circulated load-reload process with PFC. Then the whole process was analyzed,which indicates the non-memorial behavior of the crack is reinforced and the micro-crack after peak is mainly occurred due to the mutual friction between the macro-cracks. Considering the crack development with- in the templates,the occurrence of shear section is the main cause resulting in the change of elastic modulus and irre- coverable strain,and thus the whole propagation of the sample under cyclic loading-reloading is better understood.