Induced Mechanism of Stope Roof Rockbursts in Underground Excavation

Abstract

ABSTRACT A rockburst is defined as a sudden and violent disruption of rock in underground excavation. Rockbursts have been regarded as the least understood and the most feared mining disasters. Excavation-induced stress redistribution may lead to slippage of some pre-existing faults or even a new faulting in the near field of an underground opening. Both fault slippage and faulting generate seismic waves that propagate from the hypocenter outward in the rock mass. It was observed that rockbursts are induced by a seismic event when the seismic waves arrive at the free surface of the underground opening. This paper is aimed to study the mechanism of stope roof rockbursts induced by seismic waves using the dynamic buckling theory. The roof is regarded as a beam on elastic foundations under axial seismic waves. The seismic wave is modelled as an excitation with multiple frequencies. A new numerical algorithm is proposed to construct rockburst (instability) diagrams. Our study shows that the amplitude and frequency of the seismic wave play a critical role in the occurrence of roof rockbursts in terms of the mechanisms of perturbation effect and parametric resonance. Based on the mechanism analysis, insights are provided to alleviate the hazard of roof rockbursts. INTRODUCTION In Ontario, Canada, more and more underground mines are operating at depths approximately 3000 meters. With the increase of mining depth, underground mines are generally more prone to ground instability incidents. In underground mines in Ontario, ground instability has been one of the main claims of fatalities. According to statistics, nearly 50 workers were critically injured, and 10 workers died due to rock falls of ground or rockbursts in underground mines in Ontario between 2000 and 2019. A rockburst is defined as a sudden and violent disruption of rock or disturbances of roof or walls in underground excavation, which is caused by or accompanied by a "shock" or tremor (seismic event) of sufficient magnitude, to cause obvious damage to support and excavations, or widespread simultaneous fall of rock. Rockbursts can be classified in terms of the source mechanism and the damage mechanism (Durrheim 1999).