Abstract: This study examines the evolution of rockburst in hard surrounding rock of a deep-buried tunnel affected by structural planes. True triaxial rockburst model tests were conducted on cubic sandstone specimens with a circular tunnel, with and without structural surfaces. An acoustic emission system was used in the experiment to monitor the evolution process of rockburst. Results show that the structural planes significantly affect the position and intensity of rockburst, as well as the failure mode of cavern wall. The damaged zone is symmetrical on both sides of specimens without a structural plane. Several rock flakes form a shallow V-shaped notch in the sidewall of the circular tunnel. The failure position on both sides of specimen with a structural plane is asymmetrical. On the side distant from the structural plane, a large number of rock flakes peel off, forming a deep V-shaped notch. Near the structural plane, multiple cracks form, causing the rock mass between the tunnel and the structural face to tend to collapse into the tunnel space. The acoustic emission (AE) events in specimen with structural plane are much more active, with the average energy of a single impact being approximately 2.2 times that of the specimen without a structural pane. According to the evolution of cumulative impact count, the loading process before rockburst can be divided into three stages, including crack closure and linear elastic deformation, crack initiation and stable propagation, and crack unstable development. The crack initiation and stable propagation is earlier in specimen with a structural plane than that in specimen without a structural plane. All cracks generated during the failure process are tension-shear mixed pattern in both tested specimens. The proportion of shear cracks is larger in specimen with a structural plane compared to that without. The presence of structural plane changes the position of initial damage in specimen. The AE location in the experiment generally correspond to the failure pattern of circular tunnel.

Key words: structure-type rockburst, circular tunnel, V-shaped notch, true triaxial loading, acoustic emission (AE)