Energy-driven mechanism of failure and instability of anchored surrounding rock in deep gob-side entry

Affected by the dynamic load induced by the fracture of lateral roof in the deep gob-side entry, the anchored surrounding rock is prone to produce large deformation, even failure and instability. Taking the tailgate of the 31120 working face in the Suncun Coal Mine as an engineering background, firstly, the development law of cracks in the anchored roof and the main failure mode of brittle tension crack were obtained by using the YTJ20 rock detection recorder. In addition, based on the similar material simulation test, the typical characteristics of three stages of lateral roof movement in the deep gob-side entry were obtained, and the fracture evolution and energy release law of anchored surrounding rock in different stages were analyzed. It is noted that the internal stress and deformation of anchored surrounding rock increase sharply, the cracks develop obviously and the energy is released significantly in the transitional movement stage, which has the greatest influence on the stability of anchored surrounding rock in the gob-side entry. Finally, the structural mechanical model of gob-side entry under lateral roof fracture movement was constructed, the quantitative calculation method of input and resistant energy of anchored surrounding rock were firstly provided, the energy-driven mechanism of failure and instability was revealed, and the instability energy criterion was defined, that is, when the energy applying on anchoring surrounding rock in gob-side entry is greater than the resistant energy of anchoring surrounding rock, the instability will occur. Accordingly, the instability risk classification method of anchoring surrounding rock and the corresponding strengthening control technology were put forward. The calculation results show that the instability risk level of anchored surrounding rock in the gob-side entry of the 31120 working face was medium risk. After strengthening the support, the deformation of roof and floor and the two sides of gob-side entry were reduced by 35.47% and 35.71%, respectively, the force of anchor cable was reduced by 23.43%, the deformation speed was obviously reduced, and the energy accumulation degree of anchoring surrounding rock was reduced.