Physical Model Study on Brittle Failure of Pressurized Deep Tunnel with Support System

Severe instability disasters of hard rock often occur in pressurized deep tunnels with support systems. To investigate the deformation characteristics, brittle fracture process, failure mechanism, and collaborative effect of the rock and support system in a pressurized deep tunnel, physical model tests were designed and performed. An analog material preparation method is proposed for simulating the brittle failure of deep tunnels. The test results indicated that the brittleness and the strength of the developed analog material were significantly increased compared to those of previously reported analog materials, and its characteristics were similar to those of deep hard rock. The physical model tests realistically simulated the instantaneous process of brittle fracture of a pressurized deep tunnel, and the mechanical response laws of deformation, digital images, and acoustic emissions were captured. The strains of the surrounding rock, the lining, and the bolt were the largest in the shallow part of the sidewall and gradually decreased away from the tunnel. The brittle cracking paths of the shallow rock were along the direction of the internal pressure, whereas that of the interior rock mass were along the direction of the maximum principal stress. The brittle failure of a pressurized deep tunnel is caused by the incompatible tensile strain of the surrounding rock under the control of the anisotropic stress field. The bearing capacities of the surrounding rock, the lining, and the bolt decreased successively. Cyclic loading and unloading of internal pressure can reduce the bearing capacities of deep tunnels, whereas a constant internal pressure has a supporting effect.