Abstract
Rockburst is one of the most difficult problems encountered in the pilot tunnels of the Jinping II hydropower station, where the rock cover is up to 2,500 m. Some typical characteristics of the rockburst events are summarized. These events indicate the intrinsic reason of rockburst is energy release. In order to understand the outburst mechanism, a new energy index, the Local Energy Release Rate (LERR), is put forward to simulate the conditions causing rockburst. By tracking the peak and trough values of elastic strain energy intensity before and after brittle failure, the LERR was developed to help understand rockburst from the viewpoint of energy release. To test its reliability, the brittle breakage of Mine-by tunnel rock in Canada and two rock bursts in the Jinping pilot tunnels were simulated. The results showed that LERR can satisfactorily predict the intensity of a rockburst and the depth of the outburst pit. Although it is not yet possible to determine thresholds at which rockbursts will occur, the study indicates the potential of LERR for evaluating rockbursts in deep underground excavations.
Résumé
La décompression violente est l’un des plus difficiles problèmes rencontrés dans les galeries de reconnaissance de la station hydroélectrique de Jinping I ou la hauteur de recouvrement est de 2,500 m. Quelques caractéristiques typiques des événements de décompression violente sont résumées. Afin de comprendre le mécanisme de décompression, un nouvel indice d’énergie, le taux de dissipation locale d’énergie (LERR) est proposé pour représenter les conditions favorisant la décompression violente. Le LERR a été développé à partir de l’analyse de la valeur de pic et la valeur minimale de l’intensité d’énergie de déformation élastique avant et après la rupture fragile, aidant ainsi à comprendre la décompression violente du point de vue de la dissipation d’énergie. Afin de tester sa fiabilité, la rupture fragile de galeries minières au Canada et deux décompressions violentes dans les galeries de reconnaissance de Jinping ont été simulées. Les résultats ont montré que le LERR peut prévoir de façon satisfaisante les intensités de décompression violente et la profondeur où elle peut apparaître. Bien qu’il ne soit pas encore possible de déterminer les seuils pour lesquels les décompressions violentes apparaîtront, l’étude précise l’intérêt du LERR pour évaluer ces phénomènes dans les excavations souterraines profondes.
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Acknowledgments
The work is financially supported by National Special Funds for Major State Basic Research Project under Grant No. 2010CB732006 and Natural Science Foundation of China under Grant No. 40902090. In particular we wish to thank J. Hou, Q. H. Zhou, C. Q. Zhang, and S. L. Huang for their contributions to this paper.
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Jiang, Q., Feng, XT., Xiang, TB. et al. Rockburst characteristics and numerical simulation based on a new energy index: a case study of a tunnel at 2,500 m depth. Bull Eng Geol Environ 69, 381–388 (2010). https://doi.org/10.1007/s10064-010-0275-1
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DOI: https://doi.org/10.1007/s10064-010-0275-1