In burstprone ground, sudden and violent failure of hard brittle rock dynamically loads and deforms ground support. Failure of underground excavations comprises two processes: bulking of stress-fractured rock and shape changes of the excavation in response to the fracturing process. For demonstration purposes, a case with a stress ratio k < 1 is examined. Brittle failure of sidewalls occurs if induced stresses exceed the crack propagation stress level, leading to a rupture process and rock mass convergence in which the bulking rock moves rapidly toward the excavation. At the same time, the roof and floor converge rapidly induced by the sudden shape change due to wall rupture. This article presents estimates of kinetic energy demands that would be imposed on support by self-induced strainbursts and associated sudden and violent shape change. The effects of confining pressure at the tunnel surface on the violence of this process are explored using FLAC.
Deeper underground mining activities and higher production rates increase the challenges of providing a safe and productive environment for mining production as well as the development of supporting infrastructure (e.g., extraction, haulage, transport and ventilation tunnelling). Higher stresses at depth and higher production rates increase the challenges of providing a safe and productive environment. Environments at greater depths are inherently more fragile due to the increase in the stress gradient, which leads to higher differential stress (Kaiser & Moss, 2021).
A self-induced strainburst is a type of rockburst whereby part of a highly stressed volume of rock suddenly fails and causes rapid bulking deformation into the excavation without the influence of energy radiation from a distant seismic event (e.g., slip-type bursts) (Kaiser & Malovichko, 2022). The strainburst is part of the seismic source and has an implosive seismic moment tensor component (ISO), and it is referred to as a crush-type event (Malovichko, 2020).
During a self-induced strainburst, unsupported floors may also suddenly lift, and rock blocks may detach from the roof, particularly at locations experiencing low confinement or even tangential tension. These failure processes induce rapid elastic and bulking displacements with related velocities and energy flux. These velocities are not generated by ground motions from a distant seismic event, but rather by the excavation failure process with a commonly neglected implosive (rapid closure) elastic deformation and inelastic bulking components. A well-designed rock support system must be able to survive these displacements and related kinetic energy demands.
