大光包滑坡滑带岩体碎裂特征及其形成机制研究
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摘要
大光包滑坡是"5·12"汶川地震触发的最大规模滑坡,滑坡南侧暴露长约1.8 km顺层滑带,其岩体高度碎裂,引起广泛关注,6 a来对此开展了持续研究。在前期工作基础上(工程地质测绘、坑槽探及浅孔钻探(钻孔声波)等),对滑带岩体的碎裂特征进行了充分的揭露和系统的描述,结果表明,滑带发育的地质基础是滑前坡体内部发育的层间剪切错动带。强震过程中,由于靠近发震断层的强烈垂向地震动,从而导致坡体沿相对软弱的层间错动带分离,并产生垂向振冲或夯击效应,导致层间错动带的进一步碎裂化。对滑带的细观分析表明,这种强震滑带碎裂化现象不仅存在,而且还表现出伴随碎裂过程的扩容效应。采用物理模拟和PFC数值模拟,进一步验证了强震过程中滑带的碎裂和扩容过程,揭示其产生的内在机制。研究表明,滑带岩体碎裂化及扩容现象具有特殊的工程地质和岩体力学意义:一方面滑带岩体的进一步碎裂、细粒化从物理上降低了滑带的摩阻力;另一方面,也是更为重要的是,由于滑带的夯击扩容,地下水将强力挤入扩容空间,从而可能激发水击作用机制,导致孔隙水压力激增,滑带抗剪能力急剧降低,从而促使滑坡骤然启动,产生高速滑动。
Daguangbao landslide is the largest landslide triggered by "5·12" Wenchuan earthquake. The exposed sliding zone with a length of 1.8 km and highly ruptured rock mass occurred on the south side of the landslide,which attracted great attention across the world and was a focus in the past 6 years. The engineering geological mapping and exploration in the past made the cataclastic characteristics of rock mass in sliding zone to be well revealed. The sliding zone was found to be bedding on a fault zone of the slope. Because of the strong vertical ground motion near the seismogenic fault,the slope was separated along the bedding fault zone which was the relatively weaker interlayer. Vertical impacting or tamping within the weaker layer occurred leading to the further fragmentation. Mesoscopic analysis of sliding zone confirmed the existence of the earthquake induced fragmentation in sliding zone and revealed the dilation effect in the process of fracture,which was further verified with the physical simulation and PFC numerical simulation. The rock mass fragmentation and dilation of sliding zone were thus concluded to be very significant. Firstly,the further fragmentation and fine grains of the rock mass reduces the friction of sliding zone. Secondly,what is more important,because of the tamping and synchronous dilation within the sliding zone,groundwater will be strongly squeezed into the dilated space,which may stimulate the water hammer with the rapid increase of pore water pressure and the sharp reduction of shear resistance and as a result,causes initiation of the landslide suddenly with high traveling speed.
Daguangbao landslide is the largest landslide triggered by "5·12" Wenchuan earthquake. The exposed sliding zone with a length of 1.8 km and highly ruptured rock mass occurred on the south side of the landslide,which attracted great attention across the world and was a focus in the past 6 years. The engineering geological mapping and exploration in the past made the cataclastic characteristics of rock mass in sliding zone to be well revealed. The sliding zone was found to be bedding on a fault zone of the slope. Because of the strong vertical ground motion near the seismogenic fault,the slope was separated along the bedding fault zone which was the relatively weaker interlayer. Vertical impacting or tamping within the weaker layer occurred leading to the further fragmentation. Mesoscopic analysis of sliding zone confirmed the existence of the earthquake induced fragmentation in sliding zone and revealed the dilation effect in the process of fracture,which was further verified with the physical simulation and PFC numerical simulation. The rock mass fragmentation and dilation of sliding zone were thus concluded to be very significant. Firstly,the further fragmentation and fine grains of the rock mass reduces the friction of sliding zone. Secondly,what is more important,because of the tamping and synchronous dilation within the sliding zone,groundwater will be strongly squeezed into the dilated space,which may stimulate the water hammer with the rapid increase of pore water pressure and the sharp reduction of shear resistance and as a result,causes initiation of the landslide suddenly with high traveling speed.
引文
[1]黄润秋,裴向军,李天斌.汶川地震触发大光包巨型滑坡基本特征及形成机理分析[J].工程地质学报,2008,16(6):730–741.(HUANG Runqiu,PEI Xiangjun,LI Tianbin.Basic characteristics and formation mechanism of the largest scale landslide at Dagungbao occurred during the Wenchuan earthquake[J].Journal of Engineering Geology,2008,16(6):730–741.(in Chinese))
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[12]裴向军,黄润秋,崔圣华,等.大光包滑坡岩体碎裂特征及其工程地质意义[J].岩石力学与工程学报,2015,34(增1):3 106–3 115.(PEI Xiangjun,HUANG Runqiu,CUI Shenghua,et al.The rock mass cataclastic characteristics of daguangbao landslide and its engineering geological significance[J].Chinese Journal of Rock Mechanics and Engineering,2015,34(Supp.1):3 106–3 115.(in Chinese))
[13]张倬元,王士天,王兰生,等.工程地质分析原理[M].北京:地质出版社,2009:278–296.(ZHANG Zhuoyuan,WANG Shitian,WANG Lansheng,et al.Principles of engineering geological analysis[M].Beijing:Geological Publishing House,2009:278–296.(in Chinese))
[14]CHO N,MARTIN C D,SEGO D C.A clumped particle model for rock[J].International Journal of Rock Mechanics and Mining Sciences,2007,44(7):997–1 010.
[2]黄润秋,裴向军,张伟锋,等.再论大光包滑坡特征与形成机制[J].工程地质学报,2009,17(6):725–736.(HUANG Runqiu,PEI Xiangjun,ZHANG Weifeng,et al.Further examination on characteristics and formatiom mechanism of daguangbao landslide[J].Journal of Engineering Geology,2009,17(6):725–736.(in Chinese))
[3]殷跃平,成余粮,王军,等.汶川地震触发大光包巨型滑坡遥感研究[J].工程地质学报,2011,19(5):674–684.(YIN Yueping,CHENG Yuliang,WANG Jun,et al.Remote sensing research on daguangbao gigantic rock-slide triggered by Wenchuan earthquake[J].Journal of Engineering Geology,2011,19(5):674–684.(in Chinese))
[4]殷跃平,王猛,李滨,等.汶川地震大光包滑坡动力响应特征研究[J].岩石力学与工程学报,2012,31(10):1 969–1 982.(YIN Yueping,WANG Meng,LI Bin,et al.Dynamic response characteristics of daguangbao landslide triggered by Wenchuan earthquake[J].Chinese Journal of Rock Mechanics and Engineering,2012,31(10):1 969–1 982.(in Chinese))
[5]ZHANG Y,CHEN G,ZHENG L,et al.Effects of near-fault seismic loadings on run-out of large-scale landslide:a case study[J].Engineering Geology,2013,166(8):216–236.
[6]YANG C M,CHENG H Y,TSAO C C,et al.The kinematics and initiation mechanisms of the earthquake-triggered Daguangbao landslide[C]//EGU General Assembly Conference Abstracts.[S.l.]:[s.n.],2015:13 014.
[7]许向宁,李胜伟,王小群,等.安县大光包滑坡形成机制与运动学特征讨论[J].工程地质学报,2013,21(2):269–281.(XU Xiangning,LI Shengwei,WANG Xiaoqun,et al.Characteristics of formation mechanism and kinematics of Daguangbao landslide caused by Wenchuan earthquake[J].Journal of Engineering Geology,2013,21(2):269–281.(in Chinese))
[8]马艳波.强震条件下巨型滑坡滑带岩体损伤特性研究-以大光包滑坡为例[硕士学位论文][D].成都:成都理工大学,2012.(MA Yanbo.Study on damage features of the rock mass in the sliding belt of the giant landslide under the strong earthquake-A case of Daguangbao landlside[M.S.Thesis][D].Chengdu:Chengdu University of Technology,2012.(in Chinese))
[9]四川省地质矿产勘查开发局化探队.中华人民共和国区域地质图说明书[R].德阳:[s.n.],1995.(Geochemical Exploration Brigade of Geology and Mineral Resources Exploration and Development Bureau of Sichuan.Geological map specification of the People′s Republic of China[R].Deyang:[s.n.],1995.(in Chinese))
[10]黄润秋,张伟锋,裴向军.大光包滑坡工程地质研究[J].工程地质学报,2014,22(4):557–585.(HUANG Runqiu,ZHANG Weifeng,PEI Xiangjun.Engingering geological study on daguangbao landslide[J].Journal of Engineering Geology,2014,22(4):557–585.(in Chinese))
[11]许强,裴向军,黄润秋.汶川地震大型滑坡研究[M].北京:科学出版社,2009:53–91.(XU Qiang,PEI Xiangjun,HUANG Runqiu.Largescale Landslides Induced by the Wenchuan Earthquake[M].Beijing:Science Press,2009:53–91.(in Chinese))
[12]裴向军,黄润秋,崔圣华,等.大光包滑坡岩体碎裂特征及其工程地质意义[J].岩石力学与工程学报,2015,34(增1):3 106–3 115.(PEI Xiangjun,HUANG Runqiu,CUI Shenghua,et al.The rock mass cataclastic characteristics of daguangbao landslide and its engineering geological significance[J].Chinese Journal of Rock Mechanics and Engineering,2015,34(Supp.1):3 106–3 115.(in Chinese))
[13]张倬元,王士天,王兰生,等.工程地质分析原理[M].北京:地质出版社,2009:278–296.(ZHANG Zhuoyuan,WANG Shitian,WANG Lansheng,et al.Principles of engineering geological analysis[M].Beijing:Geological Publishing House,2009:278–296.(in Chinese))
[14]CHO N,MARTIN C D,SEGO D C.A clumped particle model for rock[J].International Journal of Rock Mechanics and Mining Sciences,2007,44(7):997–1 010.