Rockburst simulation tests on structural plane of deep high-stress circular tunnels: A true triaxial test study on several different hard rocks

After deep rock excavation, rockbursts can easily occur. The structural plane and rock properties play important roles in controlling rockbursts. To study the role of structural planes and rock properties in controlling rockbursts in the peripheral rocks of tunnels, five different brittle and hard rocks (Red sandstone, Gray sandstone, Granite,Marble, and Limestone) were tested, and cubic specimens with round holes (100 mm*100 mm*100 mm, Φ = 50 mm) and prefabricated fissures were used to simulate the structural plane. A high-speed camera system and an acoustic emission system were used to monitor the damage and microfracture processes of the surrounding rock. The damage process, acoustic emission characteristics, and damage patterns of five brittle rocks with and without specimens with structural planes during loading were comparatively analyzed. The main conclusions were as follows. (1) The presence of structural planes in the rock mass changed the stress and energy propagation paths in the rock mass, resulting in stress concentration; the structural planes in the five brittle rocks could not store energy, hence increasing the propensity for rockbursts. Structural planes in the Marble had the most obvious effect on the promotion of rockbursts. However, structural planes in the Gray sandstone had the weakest effect on the promotion of rockbursts. (2) The presence of structural planes significantly increased the rockburst intensity. In the Marble, regardless of the presence of structural planes, the damage mode of the surrounding rock was mainly shear flexural damage. However, the fine particle contents of specimens with structural planes were significantly higher than those without structural planes. Thus, the rockburst intensities of specimens with structural planes were greater than those without structural planes. For the Red sandstone, Gray sandstone, Granite and Limestone, the surrounding rock specimens with structural planes experienced mainly violent shear ejection damage. (3) The distribution of RA and AF and the number of ruptures in the specimens with and without structural planes were obviously changed, and the numbers of rupture events in the Red sandstone, Gray sandstone, and Granite specimens obviously increased because of the presence of structural planes. The numbers of rupture events for Marble and Limestone specimens significantly decreased due to the presence of structural planes. Gray sandstone and Granite had the most rupture events. (4) Different brittle rock specimens with structural planes had different sizes. The degrees of damage were observed to significantly increase for a period. In addition, the rock body experienced additional internal shear rupture, which intensified due to the structural planes and the tunnels between the rock columns. The ruptures were caused by the destruction of the structural planes during rockburst, and they served as predictions and early warnings, thus providing a certain reference basis. (5) In the Marble during rockbursts, there were structural planes that underwent flexural strain and slip strain. In the Red sandstone, Gray sandstone, and Granite during rockbursts, there were structural planes that underwent compression shear strain and slip strain. The disaster chain was introduced to understand and discuss the mechanism of slip strain for the development of rockburst in structural planes, which should be the final damage form. The disaster chain was a series of rockbursts caused by compression shear and slip of specimens with structural planes. The development of rockbursts in specimens with structural planes occurred sequentially. The final damage pattern was the end result of the development of a series of rockbursts in specimens with structural planes.