(1. State Key Laboratory of Geomechanics and Geotechnical Engineering，Institute of Rock and Soil Mechanics，Chinese Academy of Sciences，Wuhan，Hubei 430071，China；2. China Three Gorges Project Corporation，Beijing 100038，China)
Abstract：The spalling of hard basalt is one of the serious geotechnical problems in the underground powerhouse of the Baihetan hydropower station. The paper presented the general inner cracking process captured by the digital borehole camera and the detailed in-situ failure proofs during the unloading excavation. These study showed that the spalling，with the sheet and plate shape，happened not only to the intact basalt，but to the basalt with a few joints. Further optical scanning and scanning electron microscope observations indicated that the break surface of the spalling rock was rough and belong to the tensional failure mode. The field digital borehole camera observation in the underground powerhouse indicated that the basalt spalling had the characteristics of spatial discontinuous distribution，time-dependent increase of cracking depth，increase and decrease of crack?s width，obvious restraining effect of rock bolt and anchor cable. What?s more，the case study also indicated that the inner crack and surface failure of basalt related to each other，namely，the surface failure happened when the inner cracks developed sufficiently. These knowledge about the basalt spalling provided us not only the visual picture of basalt's break，but also a guide for disaster warning and supporting optimization in the deep rock engineering.
江 权1，樊义林2，冯夏庭1，李 毅2，裴书锋1，刘国锋1. 高应力下硬岩卸荷破裂：白鹤滩水电站地下厂房玄武岩开裂观测实例分析[J]. 岩石力学与工程学报, 2017, 36(5): 1076-1087.
JIANG Quan1，FAN Yilin2，FENG Xiating1，LI Yi2，PEI Shufeng1，LIU Guifeng1. Unloading break of hard rock under high geo-stress condition：inner cracking observation for the basalt in the Baihetan?s underground powerhouse. , 2017, 36(5): 1076-1087.
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2017, Vol. 36 
