大埋深高地应力关山隧道围岩变形破坏分析
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摘要
甘肃省关山隧道是一条受高地应力影响的大埋深硬脆性闪长岩铁路隧道,位于青藏高原东北缘,构造活跃,运动速率较大,且方向变化显著的六盘山挤压隆升构造区。在隧道开挖过程中围岩变形破坏现象明显,围岩等级低于前期岩体质量分级,表现出强烈的岩体质量劣化和各向异性。针对该问题,除了采用矿物成分和微结构分析寻找原因,还通过现场结构面统计分析对围岩质量劣化和各向异性进行描述,同时运用自行研发的钻孔电视进一步分析开挖前后一定时间间隔内围岩的渐进式变形和破坏。钻孔电视试验结果表明,尽管闪长岩作为一种硬脆性岩体,单轴抗压强度(UCS)高于现场地应力值,但其变形和破坏却普遍发生,开挖过程中新生裂隙迅速发育,原先在高地应力下闭合的裂隙也会重新张开和发展,围岩劣化,稳定性降低。为了进一步分析围岩的变形破坏过程,设计了变压力大小和方向的单轴抗压试验,试验中闪长岩的单轴压力值低于单轴抗压强度,试验结果与钻孔电视试验观测结果吻合,证明了在开挖引起的地应力剧烈变化条件下硬脆性闪长岩结构劣化,存在变形破坏的可能性。在大埋深高地应力条件下,除了岩体的各向异性,地应力的变化也是硬脆性围岩稳定性的重要考量因素。
Guanshan railway tunnel, located in Gansu Province, China, is a deep tunnel in hard and brittle diorite rock mass under high in situ stress. Meanwhile, this tunnel is also located in the Liupan Mountain, which is an active tectonic region of the compression uplift with a high horizontal movement rate and significantly changes of movement direction on the northeastern margin of Qinghai-Tibet block. On the contrary of the good rock mass classification predicted in investigation stage, the real situation after excavation shows a great change of rock mass parameters and structure, revealing not only the degradation of rock mass quality also the significant anisotropy of rock mass. The degradation and anisotropy of rock mass is described and analyzed based on the statistic analysis of the rock structural plane in field. Meanwhile, self-developed borehole camera is adopted to further observe the progressive deformation and failure of rock mass in an interval after excavation. As one of the hard and brittle plutonite, the uniaxial compressive strength(UCS) of diorite is a relatively high index on investigation stage, which is obviously larger than the in situ stress. However, the deformation and failure of diorite rock mass happened prevailingly. As the evidence obtained by borehole camera, the micro fracture or closed rock structural plane under high in situ stress will re-open and develop quickly after the excavation, which degraded the stability and quality of rock mass structure. To figure out the deformation and failure process, an angle rotation of uniaxial compressive test is designed. The uniaxial pressure is lower than the uniaxial compressive strength of diorite. This test has good agreement with the borehole camera test results, fully presents degradation of rock mass structure, induced by stress field change after excavation and proves the feasibility of the progressive deformation and failure process of hard and brittle diorite rock mass during the strongly stress field change after excavation. Besides anisotropy of rock mass, stress field change is always a significant consideration factor in deep excavation project under high in situ stress.
Guanshan railway tunnel, located in Gansu Province, China, is a deep tunnel in hard and brittle diorite rock mass under high in situ stress. Meanwhile, this tunnel is also located in the Liupan Mountain, which is an active tectonic region of the compression uplift with a high horizontal movement rate and significantly changes of movement direction on the northeastern margin of Qinghai-Tibet block. On the contrary of the good rock mass classification predicted in investigation stage, the real situation after excavation shows a great change of rock mass parameters and structure, revealing not only the degradation of rock mass quality also the significant anisotropy of rock mass. The degradation and anisotropy of rock mass is described and analyzed based on the statistic analysis of the rock structural plane in field. Meanwhile, self-developed borehole camera is adopted to further observe the progressive deformation and failure of rock mass in an interval after excavation. As one of the hard and brittle plutonite, the uniaxial compressive strength(UCS) of diorite is a relatively high index on investigation stage, which is obviously larger than the in situ stress. However, the deformation and failure of diorite rock mass happened prevailingly. As the evidence obtained by borehole camera, the micro fracture or closed rock structural plane under high in situ stress will re-open and develop quickly after the excavation, which degraded the stability and quality of rock mass structure. To figure out the deformation and failure process, an angle rotation of uniaxial compressive test is designed. The uniaxial pressure is lower than the uniaxial compressive strength of diorite. This test has good agreement with the borehole camera test results, fully presents degradation of rock mass structure, induced by stress field change after excavation and proves the feasibility of the progressive deformation and failure process of hard and brittle diorite rock mass during the strongly stress field change after excavation. Besides anisotropy of rock mass, stress field change is always a significant consideration factor in deep excavation project under high in situ stress.
引文
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[2]HOEK E,BROWN E T,HOEK E,et al.The Hoek-Brown failure criterion——a 1988 update[J].Journal of Heuristics,2010,16(2):167-188.
[3]HAJIABDOLMAJID V,KAISER P K.Brittleness of rock and stability assessment in hard rock tunneling[J].Tunnelling and Underground Space Technology,2003,18(1):35-48.
[4]MARTIN C D.Seventeenth canadian geotechnical colloquium:The effect of cohesion loss and stress path on brittle rock strength[J].Canadian Geotechnical Journal,1997,34(2):255-272.
[5]丁国瑜.中国岩石圈动力学概论[M].北京:地震出版社,1991.DING Guo-yu.Introduction to lithospheric dynamics of China[M].Beijing:Seismological Press,1991.
[6]李天文,梁伟锋,等.基于GPS的青藏块体东北缘近期地壳水平运动与变形研究[J].干旱区地理,2007,30(5):637-645.LI Tian-wen,LIANG Wei-feng.Crustal horizontal movement and distortion of northeastern margin of Qinghai-Tibet block based on GPS[J].Arid Land Geography,2007,30(5):637-645.
[7]汪素云,许忠淮.中国东部大陆的地震构造应力场[J].地震学报,1985,7(1):17-32.WANG Su-yun,XU Zhong-huai.Seismo-tectonic stress field in East China[J].Acta Seismologica Sinica,1985,7(1):17-32
[8]江在森,马宗晋.青藏块体东北缘水平应力场与构造变形分析[J].地震地质,2001,23(3):337-345.JIANG Zai-sen,MA Zong-jin.Analysis of recent horizontal crustal strain field and tectonic deformation in the northeast margin of Qinghai-Tibet Block[J].Acta Seismologic Sinica,2001,23(3):337-345.
[9]中国地震局地壳应力研究所.天平铁路关山隧道2#斜井正洞(施工阶段DK76+070)钻孔地应力测量分析报告[R].北京:中国地震局地壳应力研究所,2014.The Institute of Crustal Dynamics,State Seismological Bureau.Measurement report of drilling hole crustal dynamics on#2 inclined and main tunnel(DK76+070under construction stage)in Tianping railway Guanshan tunnel[R].Beijing:The Institute of Crustal Dynamics,State Seismological Bureau,2014.
[10]伍法权.统计岩体力学原理[M].武汉:中国地质大学出版社,1993.WU Fa-quan.Principle of statistic rock mass mechanics[M].Wuhan:China University of Geosciences Press,1993.
[11]胡秀宏,伍法权.岩体结构面间距的双参数负指数分布研究[J].岩土力学,2009,30(8):2353-2358.HU Xiu-hong,WU Fa-quan.Research on two-parameter negative exponential distribution of discontinuity spacings in rock mass[J].Rock and Soil Mechanics,2009,30(8):2353-2358.
[12]长江科学院.GB 50218-94工程岩体分级标准[S].北京:中国计划出版社,1995.Yangtze River Scientific and Research Institute.GB50218-94 Standard for engineering classification of rock maseees[S].Beijing:China Planning Press,1995.
[13]DEERE D U.Rock quality designation(RQD)after 20years,U.S.Army Corps Engrs Contract Report GL-89-1.Vicksburg,MS:Waterways Experimental Station.
[14]WINES D R,LILLY P A.Measurement and analysis of rock mass discontinuity spacing and frequency in part of the Fimiston Open Pit operation in Kalgoorlie,Western Australia:a case study[J].International Journal of Rock Mechanics&Mining Sciences,2002,39:589-602.
[15]孙广忠.岩体结构力学[M].北京:科学出版社,1988.SUN Guang-zong.Rock structural mechanics[M].Beijing:Science Press,1988.
[16]GOODMAN R E,SHI G H.Block theory and its application to rock engineering[M].Englewood Cliffs:Prentice Hall,1985.
[17]BARTON N,CHOUBEY,V.The shear strength of rock joint in theory and practice[J].Rock Mechanics,1977,10(1):1-54.
[18]HUDSON J A,PREST S D.Discontinuity frequency in rock mass[J].International Journal of Rock Mechanics and Mining Sciences&Geomechanics Abstracts,1983,20(2):73-89.