Based on the background of deep-buried tunnels project in Jinping II hydropower station, focusing on the prominent problems, such as casualties, equipment and facility damage caused by rockburst hazard, this paper attempts to provide a security risk assessment methodology during deep-buried tunnel excavation by drilling and blasting method. The results of previous research regarding the prediction of rockburst by means of real-time microseismic monitoring technique, in combination with the relevant statistical data from a large number of rockburst samples, have been used to propose the implementation procedures of dynamic risk assessment of rockburst during tunnel construction, which involves identifying and dividing risk region, analyzing the probability of risk, estimating the consequences of risk, determining the level of risk, evaluating and controlling the risk. Finally, one case study is given of the use of this method in the process of tunnel construction.

1 Introduction

In recent years, casualties, equipment and facility damage caused by rockburst have occurred more frequently, which requires our urgent attention. Can we accurately predict its likelihood before it occurs? How to anticipate the consequences of a possible rockburst? What measures should we take to avoid or minimize the occurrence of rockburst, and its negative consequences on workers, equipments, and facilities to an acceptable level? The problems associated with rockburst have attracted a great deal of attention of late, and although researches have been focusing on mechanism, prediction and control measures for rockburst, this still can't answer all of the above questions. Actually, this comes down to the research of security risk assessment. Since the 1970s, many scholars (Einstein, 1974; 1996; Schubert, 2011; Sousa et al., 2012; Huang, 2006) have made great contributions to the field of risk assessment in tunnel engineering. However, previous research mainly focused on road tunnels, subway tunnels and other shallow-buried tunnels. As for rockburst in deep-buried tunnels, the studies on risk assessment are quite few. Because of the specific peculiarities, such as concealed geologic conditions and high geostress, deep-buried tunnels are quite different from conventional tunnels. Present methods of risk assessment in tunnel engineering can not necessarily be applied to rockburst.

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