液化场地自由场体系的数值分析及振动台试验验证
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摘要
应用有限差分法程序FLAC3D对液化场地自由场体系的地震响应进行三维完全非线性分析。与通常采用的等效线性法相比,完全非线性分析方法由于采用了弹塑性模型,可以自动计算永久变形;采用合理的塑性方程,使得塑性应变增量与应力相联系;结合孔隙水压力模型可以模拟地震作用引起的饱和砂土液化问题。计算模型考虑了土体非线性、孔隙水压力的变化以及模型边界条件的处理等。通过与液化场地自由场体系振动台试验结果的对比分析,方法的有效性得到验证。结果表明,砂土对地震动可起滤波和隔震作用;当加速度峰值到达时砂土层中的孔隙水压力比存在负值;震后土中孔隙水压力不一定随振动的停止而立即开始消散,短期内也可能继续增长。
3D fully nonlinear analysis of seismic response of free field in liquefiable site is carried out using the general finite difference program FLAC3D.Compared with the equivalent-linear method,the permanent and irreversible displacements can be modeled automatically in the fully nonlinear method.A proper plastic formulation is used in the soil nonlinear constitutive relation,whereby plastic strain increments are related to stresses.Combined with the pore water pressure model,soil liquefaction under the seismic excitation can be modeled.Soil nonlinearity,pore water pressure build-up process and boundary condition of the model are taken into account in the calculation model.A comparison between the results from the finite difference analysis and those from the shaking table tests is made to validate the effectiveness of the computational model.Numerical results demonstrate that the liquefied soil can filter and isolate vibration.The phenomena of transient minus pore pressure occurr in the test.Pore water pressure does not always dissipate in short time immediately after the excitations,but it may keep on increasing.
3D fully nonlinear analysis of seismic response of free field in liquefiable site is carried out using the general finite difference program FLAC3D.Compared with the equivalent-linear method,the permanent and irreversible displacements can be modeled automatically in the fully nonlinear method.A proper plastic formulation is used in the soil nonlinear constitutive relation,whereby plastic strain increments are related to stresses.Combined with the pore water pressure model,soil liquefaction under the seismic excitation can be modeled.Soil nonlinearity,pore water pressure build-up process and boundary condition of the model are taken into account in the calculation model.A comparison between the results from the finite difference analysis and those from the shaking table tests is made to validate the effectiveness of the computational model.Numerical results demonstrate that the liquefied soil can filter and isolate vibration.The phenomena of transient minus pore pressure occurr in the test.Pore water pressure does not always dissipate in short time immediately after the excitations,but it may keep on increasing.
引文
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[16]张之颖,吕西林,陈跃庆,等.黏性土覆盖层下土中超孔隙水压力的动力试验研究[J].岩石力学与工程学报,2003,22(1):131-136.(ZHANG Zhiying,LU Xilin,CHEN Yueqing,et al.Experimental study on excess pore water pressure of soils covered by clay layer[J].Chinese Jounal of Rock Mechanics and Engineering,2003,22(1):131-136.(in Chinese))
[17]凌贤长,王臣,王志强,等.自由场地基液化大型振动台模型试验研究[J].地震工程与工程振动,2003,23(6):138-143.(LING Xianzhang,WANG Chen,WANG Zhiqiang,et al.Study on large-scale shaking table proportional model test for free-ground liquefaction arisen from earthquake[J].Earthquake Engineering and Engineering Vibration,2003,23(6):138-143.(in Chinese))
[18]KAGAWA T,MINOWA C,MIZUNO H,et al.Shaking table testing on piles in liquefying sand[C]//Proceedings of the5th U.S.National Conference on Earthquake Engineering.Chicago:[s.n.],1994:107-116.
[2]凌贤长,王臣,王成.液化场地桩-土-桥梁结构动力相互作用振动台试验模型相似设计方法[J].岩石力学与工程学报,2004,23(3):450-456.(LING Xianzhang,WANG Chen,WANG Cheng.Scale modeling method of shaking table test of dynamic interaction of pile-soil-bridge structure in ground of soil liquefaction[J].Chinese Journal of Rock Mechanics and Engineering,2004,23(3):450-456.(in Chinese))
[3]张建民,王刚.考虑地基液化后大变形的桩-土动力相互作用分析[J].清华大学学报(自然科学版),2004,44(3):429-432.(ZHANG Jianmin,WANG Gang.Pile-soil dynamic interaction analysis considering large post-liquefaction ground deformation[J].Journal of Tsinghua University(Science and Technology),2004,44(3):429-432.(in Chinese))
[4]孟上九,刘汉龙,袁晓铭,等.可液化地基上建筑物不均匀震陷机制的振动台试验研究[J].岩石力学与工程学报,2005,24(11):1978-1985.(MENG Shangjiu,LIU Hanlong,YUAN Xiaoming,et al.Experimental study on the mechanism of earthquake-induced differential settlement of building on liquescent subsoil by shaking table[J].Chinese Journal of Rock Mechanics and Engineering,2005,24(11):1978-1985.(in Chinese))
[5]冯士伦,王建华,郭金童.液化土层中桩基抗震性能研究[J].岩石力学与工程学报,2005,24(8):1402-1406.(FENG Shilun,WANG Jianhua,GUO Jintong.Seismic resistance of pile foundation in liquefaction layer[J].Chinese Journal of Rock Mechanics and Engineering,2005,24(8):1402-1406.(in Chinese))
[6]BYRNE P M,PARK S S,BEATY M,et al.Numerical modeling of liquefaction and comparison with centrifuge tests[J].Canadian Geotechnical Journal,2004,41(3):193-211.
[7]LIU H B,SONG E X.Seismic response of large underground structures in liquefiable soils subjected to horizontal and vertical earthquake excitations[J].Computers and Geotechnics,2005,32(4):223-244.
[8]汪明武,李丽.液化场地浅埋钢筋混凝土结构物变形及动土压力分析[J].岩石力学与工程学报,2008,27(增2):3374-3380.(WANG Mingwu,LI Li.Analysis of deformations of shallow-buried reinforced concrete structures and dynamic earthquake pressure in liquefiable soils[J].Chinese Journal of Rock Mechanics and Engineering,2008,27(Supp.2):3374-3380.(in Chinese))
[9]黄雨,八嶋厚，沢田和秀,等.堤防地基地震液化的数值模拟[J].工程力学,2007,24(12):82-87.(HUANG Yu,YASHIMA A,SAWADA K,et al.Numerical modeling of earthquake liquefaction in earth embankment foundations[J].Engineering Mechanics,2007,24(12):82-87.(in Chinese))
[10]陈育民,徐鼎平.FLAC/FLAC3D基础与工程实例[M].北京:中国水利水电出版社,2009.(CHEN Yumin,XU Dingping.Fundamentals of FLAC and FLAC3D and case study[M].Beijing:China Water Power Press,2009.(in Chinese))
[11]MARTIN G R,FINN W D L,SEED H B.Fundamentals of liquefaction under cyclic loading[J].Journal of the Geotechnical Engineering Division,ASCE,1975,101(5):423-438.
[12]袁大军,黄清飞,王梦恕,等.水底液化地层大型盾构隧道地震响应分析[J].岩石力学与工程学报,2007,26(增2):3609-3615.(YUAN Dajun,HUANG Qingfei,WANG Mengshu,et al.Study on seismic response of large shield tunnel in submarine liquefiable strata[J].Chinese Journal of Rock Mechanics and Engineering,2007,26(Supp.2):3609-3615.(in Chinese))
[13]陈育民.砂土液化后流动大变形试验与计算方法研究[博士学位论文][D].南京:河海大学,2007.(CHEN Yumin.Laboratory study and calculation method of large spreading deformation induced by post-liquefied sand[Ph.D.Thesis][D].Nanjing:Hohai University,2007.(in Chinese))
[14]Itasca Consulting Group,Inc..Fast Lagrangian analysis of continua in3dimensions[R].Minneapolis:Itasca Consulting Group.Inc.,2002.
[15]李培振,任红梅,吕西林,等.液化地基自由场振动台模型试验研究[J].地震工程与工程振动,2008,28(2):171-178.(LI Peizhen,REN Hongmei,LU Xilin,et al.Shaking table test on free field considering soil liquefaction[J].Earthquake Engineering and Engineering Vibration,2008,28(2):171-178.(in Chinese))
[16]张之颖,吕西林,陈跃庆,等.黏性土覆盖层下土中超孔隙水压力的动力试验研究[J].岩石力学与工程学报,2003,22(1):131-136.(ZHANG Zhiying,LU Xilin,CHEN Yueqing,et al.Experimental study on excess pore water pressure of soils covered by clay layer[J].Chinese Jounal of Rock Mechanics and Engineering,2003,22(1):131-136.(in Chinese))
[17]凌贤长,王臣,王志强,等.自由场地基液化大型振动台模型试验研究[J].地震工程与工程振动,2003,23(6):138-143.(LING Xianzhang,WANG Chen,WANG Zhiqiang,et al.Study on large-scale shaking table proportional model test for free-ground liquefaction arisen from earthquake[J].Earthquake Engineering and Engineering Vibration,2003,23(6):138-143.(in Chinese))
[18]KAGAWA T,MINOWA C,MIZUNO H,et al.Shaking table testing on piles in liquefying sand[C]//Proceedings of the5th U.S.National Conference on Earthquake Engineering.Chicago:[s.n.],1994:107-116.
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