Mechanical behavior for coal under true triaxial loading test connecting the effect of excavation- and mining-induced disturbances

Abstract Mining of underground resources is generally accompanied by frequent geological disasters. To understand the mechanical behavior of a stope, the stress conditions of the surrounding rocks after ventilation shaft excavation and the abutment stresses of the top coal mining layout were analyzed. In situ uniaxial stress monitoring tests were performed to understand field abutment pressure evolution, and the variation of stress concentration factor was studied, using a case of Tongxin Mine 8309 mining face of the TongMei Group, China. The loading model of coal rock under excavation- and mining-induced disturbances was proposed, and the stress path and experimental method were designed to investigate the high excavation damaged zone (HDZ), excavation damaged zone (EDZ), and undisturbed zone (UZ). The mechanical characteristics of the coal rock in different zones under site disturbance were obtained. The results indicated that the strengths of the UZ, EDZ, and HDZ samples declined gradually. The maximum principal strains of the HDZ and EDZ sample are 2.30 times and 2.21 times that of the UZ sample at the peak stress, respectively. The intermediate principal strains of the HDZ and EDZ samples are 0.91 and 0.88 times that of the UZ sample, respectively. The volume of the UZ sample continuously expanded, whereas the volumes of the EDZ and HDZ samples expanded when the peak stress was reached. The shear bands presented in all three samples resulted in failure. The stress path used in the laboratory with mining-induced stress throughout the stope could well reproduce in situ mining process, which is of significance for safe and efficient mining of deep resources.