Experimental study on the influence of intermediate principal stress on failure characteristics of strain rock burst for granite

During the excavation process of deep underground engineering, investigating the effect of the redistribution of radial surrounding rock stress field within roadway under various buried depths on rock burst characteristics is of great meaning. Hence, in this study, a series of true triaxial rock burst experiments under five intermediate principal stresses σ2 with 9.4, 18.8, 28.2, 37.6, and 47 MPa (σ2 = 10%, 20%, 30%, 40%, and 50% of uniaxial compressive strength σuc) were conducted on granite. The experimental results indicate that with an increase in σ2, the evolution of damage severity within specimen exhibits a delaying and then accelerating trend; correspondingly, the peak strength σp of specimen also increases firstly and then decreases. With the development of σ2, the rock burst failure modes transform from tensile-shear failure to predominantly shear failure, and the released energy and the volume of rock burst pit arrive at maximum value when σ2 is 30%σuc. To verify the reliability of assumed critical stress status with σ2 = 30%σuc, the fractal dimensions of rock burst fragments were calculated from three kinds of views, i.e., the distribution of granularity, the surface morphology, and micro-cracks of fragments, respectively. When σ2 = 30%σuc, the obtained fractal dimensions from three kinds of views are minimum value. Combining above both aspects, σ2 = 30%σuc is determined as a critical stress status, and it symbols rock mass has greatest resistance for rock burst failure, the possibility of rock burst failure is least, and the intensity of rock failure is the most severe.