The construction of deep high-stress tunnels can face various problems such as rockbursts, rib spalling, and tunnel collapse. The 2 400 m deep China Jinping Underground Laboratory (CJPL-II) is currently the world's largest buried laboratory. The construction of this group of tunnels included field monitoring and numerical analyses of the mechanical response of the rock around the tunnels, such as the deformation, stresses and microseismic events. The complex geological conditions are analyzed to predict tunnel disaster characteristics and the long-term in-situ mechanical response of the rock. The results show that the surrounding rock mass deformation is larger on the north side walls of laboratory 1# and laboratory 4# with a maximum deformation of 83.7 mm. The maximum rock bolt stress is 530 MPa. The rock mass deformation tended to become stable about three months after completion of the excavation. The excavation damage zone revealed by elastic waves and a borehole camera is generally 0.8~3.5 m. The results also show that the internal fractures in the surrounding rock mass evolve with the excavation with zonal disintegration. The high strength, good integrity rock has a small fracture zone while the low strength, poor integrity rock has a large fracture zone. The results also show that there is more micro-seismic activity in the completed rock mass tunnel and the area around the fault. The intensity of the microseismic activity in each laboratory tunnel during excavation was highest for 8# and decreased to 8#, 7#, 4#, 3#, 5#, 6#, 1#, 2# and 9# as the lowest. After excavation, the microseismic activity in each tunnel gradually decreased. The CASRock software analysis showed the high stresses and large relaxation depth of the southern arch shoulder and sidewall after excavation and unloading that created high-risk areas. The results provide direct support for disaster warning system development, stability assessments, dynamic designs, and long-term safe tunnel operation for safe construction of high-stress, deep tunnels with similar geological conditions.
[1] BETTINI A. Underground laboratories[J]. Nuclear Instruments and Methods in Physics Research Section A:Accelerators, Spectrometers, Detectors and Associated Equipment, 2011, 626-627(S1):S64-S68.
[2] COCCIA E. Underground laboratories in Europe[J]. Journal of Physics:Conference Series, 2006, 39:134.
[3] 程建平, 吴世勇, 岳骞, 等. 国际地下实验室发展综述[J]. 物理, 2011, 40(3):149-154.CHENG J P, WU S Y, YUE Q, et al. A review of international underground laboratory developments[J]. Physics, 2011, 40(3):149-154. (in Chinese)
[4] ZHENG M Z, LI S, ZHAO H, et al. Probabilistic analysis of tunnel displacements based on correlative recognition of rock mass parameters[J]. Geoscience Frontiers, 2021, 12(4):101136.
[5] 钟山, 江权, 冯夏庭, 等. 锦屏深部地下实验室初始地应力测量实践[J]. 岩土力学, 2018, 39(1):356-366.ZHONG S, JIANG Q, FENG X T, et al. A case of in-situ stress measurement in Chinese Jinping Underground Laboratory[J]. Rock and Soil Mechanics, 2018, 39(1):356-366. (in Chinese)
[6] ZHENG M Z, LI S J, YAO Z, et al. Core discing characteristics and mitigation approach by a novel developed drill bit in deep rocks[J]. Journal of Central South University, 2020, 27(10):2822-2833.
[7] 冯夏庭, 肖亚勋, 丰光亮, 等. 岩爆孕育过程研究[J]. 岩石力学与工程学报, 2019, 38(4):649-673.FENG X T, XIAO Y X, FENG G L, et al. Study on the development process of rockbursts[J]. Chinese Journal of Rock Mechanics and Engineering, 2019, 38(4):649-673. (in Chinese)
[8] 冯夏庭, 陈炳瑞, 张传庆, 等. 岩爆孕育过程的机制、预警与动态调控[M]. 北京:科学出版社, 2013.FENG X T, CHENG B R, ZHANG C Q, et al. Mechanism, warning and dynamic control of rockburst development processes[M]. Beijing:Science Press, 2013. (in Chinese)
[9] 黄晶柱, 冯夏庭, 周扬一, 等. 深埋硬岩隧洞复杂岩性挤压破碎带塌方过程及机制分析——以锦屏地下实验室为例[J]. 岩石力学与工程学报, 2017, 36(8):1867-1879.HUANG J Z, FENG X T, ZHOU Y Y, et al. Analysis of collapse process and mechanism of complex lithologic compressive rupture zone in deep buried hard rock tunnel:A case study of Jinping Underground Laboratory[J]. Chinese Journal of Rock Mechanics and Engineering, 2017, 36(8):1867-1879. (in Chinese)
[10] FENG X T, XU H, QIU S L, et al. In situ observation of rock spalling in the deep tunnels of the China Jinping Underground Laboratory (2400 m depth)[J]. Rock Mechanics and Rock Engineering, 2018, 51(4):1193-1213.
[11] LI S J, FENG X T, WANG C Y, et al. ISRM suggested method for rock fractures observations using a borehole digital optical televiewer[J]. Rock Mechanics and Rock Engineering, 2013, 46(3):635-644.
[12] LI S J, FENG X T, LI Z H, et al. In situ monitoring of rockburst nucleation and evolution in the deeply buried tunnels of Jinping II Hydropower Station[J]. Engineering Geology, 2012, 137-138:85-96.
[13] LI S J, FENG X T, LI Z H, et al. Evolution of fractures in the excavation damaged zone of a deeply buried tunnel during TBM construction[J]. International Journal of Rock Mechanics and Mining Sciences, 2012, 55:125-138.
[14] 冯夏庭, 吴世勇, 李邵军, 等. 中国锦屏地下实验室二期工程安全原位综合监测与分析[J]. 岩石力学与工程学报, 2016, 35(4):649-657.FENG X T, WU S Y, LI S J, et al. Comprehensive field monitoring of deep tunnels at Jinping Underground Laboratory (CJPL-II) in China[J]. Chinese Journal of Rock Mechanics and Engineering, 2016, 35(4):649-657. (in Chinese)
[15] FENG X T, YAO Z B, LI S J, et al. In situ observation of hard surrounding rock displacement at 2400 m deep tunnels[J]. Rock Mechanics and Rock Engineering, 2018, 51(3):873-892.
[16] 戴峰, 李彪, 徐奴文, 等. 猴子岩水电站深埋地下厂房开挖损伤区特征分析[J]. 岩石力学与工程学报, 2015,34(4):735-746. DAI F, LI B, XU N W, et al. Characteristics of damaged zones due to excavation in deep underground powerhouse at Houziyan Hydropower Station[J].Chinese Journal of Rock Mechanics and Engineering, 2015, 34(4):735-746. (in Chinese)
[17] FENG X T, GUO H S, YANG C X, et al. In situ observation and evaluation of zonal disintegration affected by existing fractures in deep hard rock tunneling[J]. Engineering Geology, 2018, 242:1-11.
[18] FENG X T, CHEN B R, LI S J, et al. Studies on the evolution process of rockbursts in deep tunnels[J]. Journal of Rock Mechanics and Geotechnical Engineering, 2012, 4(4):289-295.
[19] CHEN B R, FENG X T, LI Q P, et al. Rock burst intensity classification based on the radiated energy with damage intensity at Jinping II Hydropower Station, China[J]. Rock Mechanics and Rock Engineering, 2015, 48(1):289-303.
[20] FENG G L, FENG X T, CHEN B R, et al. Microseismic sequences associated with rockbursts in the tunnels of the Jinping II Hydropower Station[J]. International Journal of Rock Mechanics and Mining Sciences, 2015, 80:89-100.
[21] XIAO Y X, FENG X T, FENG G L, et al. Mechanism of evolution of stress-structure controlled collapse of surrounding rock in caverns:A case study from the Baihetan Hydropower Station in China[J]. Tunnelling and Underground Space Technology, 2016, 51:56-67.
[22] PAN P Z, FENG X T, HUDSON J A. Study of failure and scale effects in rocks under uniaxial compression using 3D cellular automata[J]. International Journal of Rock Mechanics and Mining Sciences, 2009, 46(4):674-685.
