Abstract
Rockburst disaster is one of the prominent problems faced by deep underground engineering. Microseismic (MS) monitoring techniques can be used to warn of rockburst in tunnels to provide scientific basis for rock burst prevention and control measures. Described in this paper, is an MS monitoring system based on MS source location with hierarchical strategy implemented in the tunnel group of the Jinping II hydropower station in Sichuan Province, China. The spatiotemporal distribution of MS events was analyzed in the construction process and the size effect of rockburst risk discussed by statistical analysis and numerical calculation of rockburst in seven tunnels. The results show that the active period of microseisms and the high-incidence period of rockburst are within 1.5 h after the rock disturbance. The MS events within 1D from the tunnel wall are the most intensive and are mainly concentrated near the heading face, the side wall, and the left spandrel. At the construction site, the accuracy rate of rockburst prediction is 61.8%, of which the accuracy rate of the medium and strong rockburst is 80.3%. Based on field statistics of rockburst, the increase of the tunnel excavation section size can reduce the rockburst strength to a certain extent, which is consistent with the numerical simulation results.
Highlights
The increasing number of long and deeply buried tunnels has brought great challenges to the construction and operation of the project, in which rockburst is a prominent problem [1,2,3,4]
Warning of rockburst is of great significance and remains as a worldwide challenge in geotechnical engineering
Based on the MS monitoring system in the tunnel group of the Jinping II hydropower station of China, this paper analyzed the spatiotemporal distribution of MS events in the process of construction, and discussed in detail the size effect of Rockburst problems induced by high in-situ stresses are prominent during the construction of underground engineering
Summary
The increasing number of long and deeply buried tunnels has brought great challenges to the construction and operation of the project, in which rockburst is a prominent problem [1,2,3,4]. The phenomenon of rockburst is different due to the accumulation level of geostress, the characteristics of the rock and the shape of the underground engineering contour [6,7,8]. It is a kind of dynamic instability geological disaster in that the elastic strain energy of the surrounding rock can be released suddenly and produces burst release, exfoliation, ejection, and even throw in the rock mass caused by the brittle failure of the excavation unloading during or after the excavation of the underground engineering in the high stress zone [9,10].
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