To simulate the rockburst process of deep circular cavern under three-dimensional (3D) stress conditions

the granite material with extremely strong rockburst tendency was used for testing. True-triaxial compression tests were conducted on the cubic granite sample (100 mm×100 mm×100 mm cube granite sample with a diameter of 50 mm through circular hole) by using a self-developed TRW-3000 true-triaxial rock electro-hydraulic servo mutation testing machine. In the experiment

an initial stress environment of 1 000 m depth was simulated. Then

the stress in the vertical direction was increased gradually

and the hole wall was monitored with a real-time micro-camera and acoustic emission (AE) device. The results show that failure process can be divided into four stages

i.e.

calm stage

pellet ejection stage

rock exfoliation stage and rockburst stage. The middle parts of the circular hole have the highest stress concentration factor and the damage is initiated. Then cracks develop along the radial direction to the deep part of the tunnel

and ultimately form two symmetrical V-shaped notches. Three typical loading points reflecting the failure states of the hole wall are in line with the statistical relationship of the far field stress state and failure mode of deep circular roadway without support. Four kinds of rockburst criteria are also applied to analyse failure states of the hole wall under different loading conditions

and the results are consistent with the failure states recorded in the testing process. The failure of the wall is accompanied by an increase of AE count and AE energy. The more severe the rockburst is

the more active is the AE.