Sammendrag
Fault-slip seismic waves could result in rockbursts in various scales depending on the power of the waves as well as the stressing and fracturing conditions of the rock mass surrounding the underground opening. In the case that the surrounding rock is highly stressed but not yet failed, a strain burst could be triggered by seismic waves combined with the in-situ static stresses. In the case of existence of a fracture zone in the surrounding rock, the seismic waves will be reflected and transmitted at the boundary of the fracture zone and at the tunnel contour as well. On one hand, the reflections would result in tensile fractures in the intact rock, leading to extension of the fracture zone. On the other hand, the broken materials in the fracture zone could be ejected by the waves transmitted into the zone, leading to a rockburst event. In the paper, wave reflections and transmissions at the boundary of the fracture zone and the tunnel wall are analyzed in detail with the help of an 1D model, assuming that the arrival pulse is a sine wave. The analysis shows that tensile fractures could be created both in the intact rock behind the fracture zone and in the fracture zone. The seismic energy transmitted into the fracture zone, together with the stored strain energy in the rock, could eject the rock, leading to a rockburst event. The ejection velocity of the rock is determined by the particle peak velocity (PPV) and the stored strain energy. The required energy absorption for rockbolts to avoid ejection can be estimated based on the ejection volume, the PPV and the stored strain energy in the rock.
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