Cracking characteristics of granite surrounding rock under TBM edge cutter fragmentation
WANG Chunping1,2,MA Hongsu1,2,CHEN Liang1,2,ZHAO Xingguang1,2,LIU Jian1,2,LIU Jianfeng3,LI Xiang1,2
(1. Beijing Research Institute of Uranium Geology,Beijing 100029,China;2. CAEA Innovation Center for Geological Disposal of High-Level Radioactive Waste,Beijing 100029,China;3. College of Water Resource and Hydropower,Sichuan University,Chengdu,Sichuan 610065,China)
Abstract:Beishan underground research laboratory(URL) is the first URL in China for the research and development of geological disposal technology of high-level radioactive waste. The ramp in Beishan URL is excavated by full section tunnel boring machine(TBM),namely“Beishan–1”. This paper takes the cores drilled from the ramp as the research object,and studies the cracking characteristics of granite surrounding rock under TBM edge cutter fragmentation,by CT scanning,electron microscope scanning and fluorescence imaging tests. The experimental results indicate that,the cracking rate induced by TBM edge cutter is very low,about 0.13%–0.35%,and most of them are microcracks with equivalent diameter less than 120 μm. The cracks induced by TBM edge cutter fragmentation are mainly distributed directly below the groove of the cutter. The central main cracks at the bottom of the adjacent grooves are almost not connected,especially the crack concentration areas under the neighboring grooves are far apart. Most of the cracks in the rock propagate through the mineral particles. However, in the vicinity of quartz particles with higher strength that are far away from the excavation surface,the fractures preferentially propagate along the direction with less energy consumption at the mineral boundary. The crushing zone and crack intensive zone induced by edge cutter are asymmetrically conical distribution,and the inclination angle of the central main crack is related to the installation angle of edge cutter. The crack propagation depth caused by edge cutter is less than 1.60 cm measured by the three methods,among which the electron microscope scanning test has the highest accuracy. The test accuracy of CT scanning and fluorescence imaging is close,but the contrast between fracture and intact rock in fluorescence imaging test is higher,which is more conducive to fracture extraction and measurement.
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