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| DEPTH OF FRACTURE AND DAMAGE IN DEEP-BURIED SURROUNDING ROCK AND BOLT LENGTH DESIGN |
| LIU Ning1，2，ZHANG Chunsheng1，CHU Weijiang1 |
(1. PowerChina Huadong Engineering Corporation，Hangzhou，Zhejiang 310014，China；
2. Pumped Storage Engineering Center of Zhejiang Province，Hangzhou，Zhejiang 310014，China) |
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Abstract In order to determine the reasonable bolt length for Jinping II deep buried tunnels，the statistical analysis to the failure mode of surrounding rock was carried out and the main problem in bolt design was identified. Because the crack development in the damaged zone led to the decrease of wave velocity，the distribution characteristics of the damaged zone were obtained through the summarization of the typical acoustic test results in the tunnels. The related parameters of particle flow code(PFC) were fitted with the field acoustic test results，and the buried depths of damaged zone at different depths were forecasted. The results showed that the depth of rock damage and the number of cracks were also increased slowly with the increase of buried depth. This feature was beneficial to the design of the bolt length. The calculated results with PFC showed the phenomena of localized damage and that the surrounding rock in the damage zone still had the bearing capacity. The bolt installation in the damage zone still had the effect of limiting the damage development，and met the requirements of the damage zone supporting.
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2015, Vol. 34 
