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

In order to understand the mechanical behavior of a stope and analyse the stress conditions of surrounding rocks after ventilation shaft excavation and the abutment stresses of the top coal mining layout. In situ uniaxial stress monitoring tests were performed to understand the field abutment pressure evolution. Furthermore, the variation of the stress concentration factor was studied using the Tongxin Mine 8309 mining face of the TongMei Group, China, as a case study. A 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). Moreover, the mechanical characteristics and failure characteristics of coal rock in different zones under site disturbance were obtained and the mesoscopic analysis is carried out by acoustic emission test. The results indicated that the strengths of the UZ, EDZ, and HDZ samples declined gradually. The volume of the UZ sample continuously expanded. However, the volumes of the EDZ and HDZ samples were compressed first and then expanded. Furthermore, the shear bands presented in all three samples resulted in failure. The cubic triaxial tests performed without considering mining-induced pressure produced higher strengths and less damage compared with the results of the true triaxial tests. The stress path used in the laboratory with the mining-induced stress throughout the stope could optimally reproduce the in situ mining process, which is significantly safe and efficient for the mining of deep resources.