Critical Softening Radius of a Development Heading Causing Rock Bursts

Abstract

Generally, prevention and control methods are adopted to reduce the possibility of regional stress-field-induced impact bursts in pressure relief engineering. However, such methods lack theoretical support and may inadvertently induce rock bursts owing to their improper implementation during the drilling process. Therefore, this paper proposes a method for calculating the critical softening radius of a development heading causing rock bursts under static load based on the theory of mutation, which is used to guide construction in local unloading engineering. According to the total potential energy principle, a cusp catastrophe model is established to determine the key-bearing ring instability of the surrounding rock; subsequently, a relationship between the softening radius and the stability coefficient of the key-bearing ring is deduced. Furthermore, a prediction model to determine the bearing ring stability is established. The stability criterion for the key-bearing ring of the surrounding rock is obtained, verified, and analyzed using calculation examples and actual engineering cases. The results demonstrate that the stability of the surrounding rock can be improved to a certain extent by degrading the strength of the coal rock mass. When the softening range exceeds a certain limit, the key-bearing ring becomes unstable owing to a nonlinear increase in the external load, thereby inducing rock bursts. Simultaneously, a surrounding rock with a higher hardness value exhibits a higher sensitivity to the pressure discharge; therefore, the softening radius of the area with a higher surrounding rock hardness value should be chosen more carefully. For the engineering cases, the upper limit of the critical softening radius calculated theoretically differed from existing theoretical calculation results by less than 15%. Similarly, the lower limit of the critical softening radius calculated theoretically differed from the stress peak position of the surrounding rock by less than 8%. These results verify the reliability and engineering application of the proposed method.