断层错动引发基岩上覆土层破裂过程模拟
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摘要
利用有限元方法对断层基岩错动引发上覆土层破裂过程进行数值模拟,展示场地土层破裂形成和扩展特征,以及场地地表出现破裂并不一定形成土层贯通破裂的地震现象。研究表明,土层破裂始于土层与基岩的交界面并向上扩展,而随着断层基岩错动量的增加,场地地表出现破裂(单个或两个)并向下扩展,在断层基岩错动量达到一定值时上下扩展的破裂在土层某一深度位置相连形成土层贯通破裂;不同的断层基岩错动量和覆盖土层条件将导致隐覆破裂、非贯通地表破裂和贯通破裂3类不同的场地地震破裂现象。研究进一步揭示土层厚度和特性对土层破裂特征的影响。当出现地表破裂时,土层越厚破裂带的宽度越大,砂土形成的破裂带宽度小于黏土;土层越硬,越易于形成贯通破裂;土层厚度和土质特性对土层破裂的破裂角影响不明显;对于逆冲断层,地表土层初始破裂出现所需的基岩位错量约为贯通破裂位错量的80%或更小,50m以内的覆盖土层产生贯通破裂的基岩位错垂直量小于上覆土层厚度的5%。
Earthquake fault dislocation-induced ruptures of soil layers are simulated by finite element method. The study demonstrates soil rupture propagation and characteristics,and also proves the observed earthquake phenomenon that a ground surface rupture failure does not mean a penetrating rupture failure. The simulation results indicate that the soil rupture starts at interface between soil and bedrock and expands upward. Furthermore, one or two ruptures appear at ground surface and extend downward with the increase of fault dislocation,and the ruptures from bedrock and ground surface meet somewhere in soils so that a penetrating rupture from bedrock to ground surface occurs if fault dislocation is large enough. Three kinds of soil ruptures including buried rupture, non-penetrating ground surface rupture and penetrating soil rupture are presented in case of different fault dislocations and soil conditions. The obvious effects of soil thickness and properties on characteristics of soil rupture are revealed. The ground surface rupture belt is enlarged due to the increase of soil thickness if a ground surface rupture occurs,and the rupture angle is almost not affected by soil thickness and properties. The width of rupture belt of sands is smaller than that of clays,and the penetrating rupture occurs more easily for harder soil than for softer soils. In condition of reverse fault,the value of bedrock fault dislocation for initial ground surface rupture occurring is 80% or less than that for a penetrating rupture occurring,and the vertical value of bedrock fault dislocation for a penetrating rupture occurring is 5%less than that of soil thickness for soil layer with thickness less than 50 m.
Earthquake fault dislocation-induced ruptures of soil layers are simulated by finite element method. The study demonstrates soil rupture propagation and characteristics,and also proves the observed earthquake phenomenon that a ground surface rupture failure does not mean a penetrating rupture failure. The simulation results indicate that the soil rupture starts at interface between soil and bedrock and expands upward. Furthermore, one or two ruptures appear at ground surface and extend downward with the increase of fault dislocation,and the ruptures from bedrock and ground surface meet somewhere in soils so that a penetrating rupture from bedrock to ground surface occurs if fault dislocation is large enough. Three kinds of soil ruptures including buried rupture, non-penetrating ground surface rupture and penetrating soil rupture are presented in case of different fault dislocations and soil conditions. The obvious effects of soil thickness and properties on characteristics of soil rupture are revealed. The ground surface rupture belt is enlarged due to the increase of soil thickness if a ground surface rupture occurs,and the rupture angle is almost not affected by soil thickness and properties. The width of rupture belt of sands is smaller than that of clays,and the penetrating rupture occurs more easily for harder soil than for softer soils. In condition of reverse fault,the value of bedrock fault dislocation for initial ground surface rupture occurring is 80% or less than that for a penetrating rupture occurring,and the vertical value of bedrock fault dislocation for a penetrating rupture occurring is 5%less than that of soil thickness for soil layer with thickness less than 50 m.
引文
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[2]WELLS D L,COPPERSMITH K J.New empirical relationshipsamong magnitude,rupture length,rupture width,rupture area,and surface displacement(incomplete)[J].Bulletin of the Seismological Society of America,1994,84(4):974–1002.
[3]ROTH W H,SCOTT R F,AUSTIN I.Centrifuge modeling of fault propagation through alluvial soils[J].Geophysics Research Letters,1981,8(6):561–564.
[4]郭恩栋,冯启民,薄景山,等.覆盖土层场地地震断裂试验[J].地震工程与工程振动,2001,21(3):145–149.(GUO Endong,FENG Qimin,BO Jingshan,et al.Seismic test of soil site rupture under fault displacements[J].Earthquake Engineering and Engineering Vibration,2001,21(3):145–149.(in Chinese))
[5]刘守华,董津城,徐光明,等.地下断裂对不同土质上覆土层的工程影响[J].岩石力学与工程学报,2005,24(11):1868–1873.LIU Shouhua,DONG Jincheng,XU Guangming,et al.Influence on different overburden soils due to bedrock facture[J].Chinese Journal of Rock Mechanics and Engineering,2005,24(11):1868–1873.(in Chinese))
[6]TANIYAMA H,WATANABE H.Deformation of sandy deposits by fault movement[C]//Proceedings of the12th World Conference of Earthquake Engineering.Tokyo:Mc Graw Hill,2000:1–6.
[7]SCOTT R F,SCHOUSTRA J J.Nuclear power plant sitting on deep alluvium[J].Journal of the Geotechnical Engineering Division,1974,100(4):449–459.
[8]LADE P V,COLE D A.Multiple failure surface over dip-slip faults[J].Journal of Geotechnical Engineering Division,1984,110(5):616–627.
[9]BRAY J D,SEED R B.Analysis of earthquake fault rupture propagation through cohesive soil[J].Journal of Geotechnical Engineering,1994,120(3):562–580.
[10]BRAY J D,SEED R B.Earthquake fault rupture propagation through soil[J].Journal of Geotechnical Engineering,1994,120(3):543–561.
[11]郭恩栋,邵广彪,薄景山,等.覆盖土层场地地震断裂反应分析方法[J].地震工程与工程振动,2002,22(5):122–126.(GUO Endong,SHAO Guangbiao,BO Jingshan,et al.A method for earthquake rupture analysis of overlaying soil site[J].Earthquake Engineering and Engineering Vibration,2002,22(5):122–126.(in Chinese))
[12]周庆,周本刚,冉洪流.不同土质条件下断层地表破裂对比研究[J].震灾防御技术,2006,1(3):51–59.(ZHOU Qing,ZHOU Bengang,RAN Hongliu.Comparative study on surface rupture of faults in different soil mass[J].Technology for Earthquake Disaster Prevention,2006,1(3):51–59.(in Chinese))
[13]董津城.发震断裂的安全距离规定简介[J].工程抗震,1999,(2):14–16.(DONG Jincheng.Brief introduction to the stipulations related safety distance from earthquake causative fault[J].Earthquake Resistant Engineering,1999,(2):14–16.(in Chinese))
[14]赵雷,李小军,霍达.断层错动引发基岩上覆土层破裂问题[J].北京工业大学学报,2007,33(1):20–25.(ZHAO Lei,LI Xiaojun,HUO Da.Problems of rupturing process of overlaying soil due to fault dislocation of bedrock[J].Journal of Beijing University of Technology,2007,33(1):20–25.(in Chinese))
[15]SEED H B,IDRISS I M.Soil moduli and damping factors for dynamic response analysis[R].EERC70–10,1970.
[16]SEED H B,WONG R T,IDRISS I M.Moduli and damping factors for dynamic analyses of cohesionless soils[J].Journal of Geotechnical Engineering Division,1986,112(11):1016–1032.
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