Abstract: Rockburst mechanism of surrounding rock masses in underground cavern group under high stress and strong unloading is a frontier subject, and needs to be studied and solved urgently at present. The rockburst process of the granite from the Shuangjiangkou underground caverns under various intermediate principal stresses was simulated through three-directions and five-sides true triaxial tests. The fracture surface of the specimens after rockburst was observed by scanning electron microscope and energy dispersive spectrometer. The strength and deformation characteristics, macroscopic failure modes, rockburst process and meso-fracture modes of main minerals of the specimens under various intermediate principal stresses were analyzed. The experimental results show that: 1) With the increasing intermediate principal stress, the macroscopic failure of the specimens after rockburst changes from tensile failure to shear failure. 2) With the increasing intermediate principal stress, the specimen rockburst types change from time-delayed rockburst to immediate rockburst, and the rockburst intensity first increases and then decreases. 3) Under each intermediate principal stress, the fracture pits of the specimen after rockburst are primarily shear fracture, while the fractures of the ejection debris are tensile fracture. 4) The meso-fracture mode of main minerals in the studied granite is independence on the intermediate principal stress: the probability of intergranular and transgranular fracture of quartz and K-feldspar is almost the same, while plagioclase and mica are more prone to transgranular fracture. The research results can provide technical support for rockburst prevention during subsequent excavations.

Key words: underground cavern group, deep buried granite, intermediate principal stress effect, strain rockburst, meso-fracture mode