Experimental simulation investigation on rockburst induced by spalling failure in deep circular tunnels

Abstract

Spalling and rockburst are two common failure modes in deep hard-rock tunnels and they exhibit a strong correlation. In this paper, the process of rockburst induced by spalling is investigated. The uniaxial compressive strength and rockburst tendency of red sandstone are measured. Four different initial stress conditions are set up, and cubic red sandstone samples with a prefabricated hole are tested by a true-triaxial test system. During the experimental process, the failure of the hole sidewall is monitored and recorded in real time by a micro-camera. The process of rockburst induced by spalling damage in deep hard-rock tunnels is reproduced, and the mechanism by which spalling damage on induces rockburst is revealed. In addition, the evolution process and failure characteristics of rockburst induced by spalling damage are analysed. The experimental results indicated that the red sandstone has a moderate rockburst tendency, and its rockburst process can be divided into four periods: the calm period, the small grain ejection & spalling damage period, the slab buckling & fragment ejection period and the violent ejection period. The mechanism of spalling damage on inducing rockburst is mainly embodied in two aspects: promoting large buckling deformations (providing energy for rockburst) and to weakening the strength of the rock mass (creating conditions for the suddenly release of energy). The effect of lateral stress on spalling damage and rockburst is more obvious than that of axial stress, and the severity of rockburst can be significantly reduced by increasing the lateral stress. The diameter of the hole has a strength size effect on the sidewall damage, producing a certain inhibitory effect on the spalling damage and rockburst. Smaller lateral stress corresponds with greater depths of the V-shaped notch and much smaller width-to-length ratios in the rock fragments.