可液化场地碎石桩复合地基地震动力响应分析
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摘要
采用砂土液化大变形弹塑性本构模型分析可液化砂土,采用模量随应力与应变变化的等效非线性模型增量形式分析碎石桩,应用FLAC~(3D)有限差分软件对地震动力作用下可液化场地碎石桩复合地基进行三维动力响应分析。模拟分析了在地震作用下碎石桩刚度效应和排水效应对加固处理可液化场地的抗液化效果,从初始小变形到液化后大变形的变形发展,超静孔压累积与消散,及桩与土的变形与应力分配变化等。结果表明,所用模型与方法可合理描述可液化场地碎石桩复合地基在地震作用下场地的动力响应特性和抗液化效果;在地震作用下可液化场地中桩周土体与碎石桩体的竖向应力与水平向剪切应力向碎石桩体集中,竖向有效应力比可降至约1/6～1/3;桩周土体与桩体为非协调变形,剪应变比可达7～10;碎石桩抗液化影响范围约为2.5～3倍桩径,对超过3.5倍桩径范围影响较小;碎石桩与砂土渗透系数比大于100时对降低砂土中超静孔隙水压影响明显;碎石桩对场地的加密效应可显著降低超静孔隙水压力,而碎石桩刚度则对超静孔隙水压力变动影响较小,但有助于减低地面加速度响应峰值。
With the application of a plasticity model for large post-liquefaction deformation of sand to model the liquefiable soil and an equivalent nonlinear incremental model to model stone columns(SC), three-dimensional dynamic responses of stone columns composite foundation in liquefiable soil are numerically investigated using finite difference code FLAC~(3D). The analysis investigates the effect of the SC's high stiffness and improved drainage on soil liquefaction mitigation, the excess pore water pressure(EPWP)build-up and dissipation, the deformation process of the liquefiable soil from small to large deformation in the pre-and post-liquefaction regimes, and the variation of stress distribution between SC and surrounding soils. The results show that the model and the program can reasonably reproduce the seismic response of stone columns composite foundation in liquefiable soils and its effect of liquefaction mitigation. The vertical stress and horizontal shear stress gradually concentrate to SC during earthquake shaking and vertical effective stress ratio may decrease to 1/6-1/3, the deformation in soil and SC is incompatible and the ratio of shear strain in the soil and SC may reach 7-10. A ratio of SC permeability to soil permeability larger than 100 significantly decreases the EPWP,while the stiffness of SC slightly decreases EPWP but helps reduce the surface peak acceleration.
With the application of a plasticity model for large post-liquefaction deformation of sand to model the liquefiable soil and an equivalent nonlinear incremental model to model stone columns(SC), three-dimensional dynamic responses of stone columns composite foundation in liquefiable soil are numerically investigated using finite difference code FLAC~(3D). The analysis investigates the effect of the SC's high stiffness and improved drainage on soil liquefaction mitigation, the excess pore water pressure(EPWP)build-up and dissipation, the deformation process of the liquefiable soil from small to large deformation in the pre-and post-liquefaction regimes, and the variation of stress distribution between SC and surrounding soils. The results show that the model and the program can reasonably reproduce the seismic response of stone columns composite foundation in liquefiable soils and its effect of liquefaction mitigation. The vertical stress and horizontal shear stress gradually concentrate to SC during earthquake shaking and vertical effective stress ratio may decrease to 1/6-1/3, the deformation in soil and SC is incompatible and the ratio of shear strain in the soil and SC may reach 7-10. A ratio of SC permeability to soil permeability larger than 100 significantly decreases the EPWP,while the stiffness of SC slightly decreases EPWP but helps reduce the surface peak acceleration.
引文
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[18]邹佑学,王睿,张建民.砂土液化大变形模型在FLAC3D中的开发与应用[J].岩土力学,2018,39(4):1525-1534.ZOU You-xue,WANG Rui,ZHANG Jian-min.Implementing a plasticity model for large post-liquefaction deformation of sand into the FLAC3Dprogram[J].Rock and Soil Mechanics,2018,39(4):1525-1534.
[19]WANG R.Single piles in liquefiable ground:seismic response and numerical analysis methods[D].Beijing:Tsinghua University,2014.
[20]WANG R,FU P,ZHANG J M.Finite element model for piles in liquefiable ground[J].Computers and Geotechnics,2016,72:1-14.
[21]王睿,张建民.可液化地基中单桩基础的三维数值分析方法及应用[J].岩土工程学报,2015,37(11):1979-1985.WANG Rui,ZHANG Jian-min.Three-dimensional elastic-plastic analysis method for piles in liquefiable ground[J].Chinese Journal of Geotechnical Engineering,2015,37(11):1979-1985.
[22]刘星,王睿,张建民.液化地基中群桩基础地震相应分析[J].岩土工程学报,2015,37(12):2326-2331.LIU Xing,WANG Rui,ZHANG Jian-min.Seismic response analysis of pile groups in liquefiable foundations[J].Chinese Journal of Geotechnical Engineering,2015,37(12):2326-2331.
[23]WANG Rui,LIU Xing,ZHANG Jian-min.Numerical analysis of the seismic inertial and kinematic effects on pile bending moment in liquefiable soils[J].Acta Geotechnica,2017,12(4):773-791.
[24]SEED H B,WONG R T,IDRISS I M,et al.Moduli and damping factors for dynamic analyses of cohesionless soils[J].Journal of Geotechnical Engineering,1986,112(11):1016-1032.
[25]ROLLINS K M,EVANS M D,DIEHL N B,et al.Shear modulus and damping relationships for gravels[J].Journal of Geotechnical Engineering,1998,124(5):396-405.
[26]Itasca Consulting Group Inc.Fast Lagrangian analysis of continua in 3 dimensions user's manual[M].version 5.0.Minneapolis:Itasca Consulting Group Inc.,2012.
[27]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 Yu-min,XU Ding-ping.FLAC/FLAC3Dfundamentals and engineering applications[M].Beijing:China Water&Power Press,2009.
[28]ARULMOLI K,MURALEETHARAN K K,HOSSAINM M,et al.VELACS:verification of liquefaction analysis by centrifuge studies,laboratory testing program,soil data report[R].California:The Earth Technology Corporation,1992.
[29]RAYAMAJHI D,SCOTT A A,BOULANGER R W,et al.Dense granular columns in liquefiable ground.II:effects on deformations[J].Journal of Geotechnical and Geoenvironmental Engineering,2016,142(7):1-10.
[30]TANG L,ZHANG X Y,LIANG X Z.Numerical simulation of centrifuge experiments on liquefaction mitigation of silty soils using stone columns[J].KSCEJournal of Civil Engineering,2016,20(2):631-638.
[2]ADALIER K,ELGAMAL A.Mitigation of liquefaction and associated ground deformation by stone columns[J].Engineering Geology,2004,72:275-291.
[3]HAUSLER E A.Influence of ground improvement on settlement and liquefaction:a study based on field case history evidence and dynamic geotechnical centrifuge tests[D].Berkeley:University of California,2002.
[4]GREEN R A,OLGUN C G,WISSMANN K J.Shear stress redistribution as a mechanism to mitigate the risk of liquefaction[C]//Proceedings of Geotechnical Earthquake Engineering and Soil Dynamics IV.Sacramento:American Society of Civil Engineers,2008:1-10.
[5]OLGUN C G,MARTIN J R.Numerical modeling of the seismic response of columnar reinforced ground[C]//Proceedings of Geotechnical Earth-quake Engineering and Soil Dynamics IV.Sacramento:American Society of Civil Engineers,2008:1-11.
[6]RAYAMAJHI D,NGUYEN T V,SCOTT A A,et al.Numerical study of shear stress distribution for discrete columns in liquefiable soils[J].Journal of Geotechnical and Geoenvironmental Engineering,2014,140(3):1-9.
[7]ELGAMAL A,LU J,FORCELLINI D.Mitigation of liquefaction-induced lateral deformation in a sloping stratum:three-dimensional numerical simulation[J].Journal of Geotechnical and Geoenvironmental Engineering,2009,135(11):1672-1682.
[8]ASGARI A,OLIAEI M,BAGHERI M.Numerical simulation of improvement of a liquefiable soil layer using stone column and pile-pinning techniques[J].Soil Dynamics and Earthquake Engineering,2013,51(1):77-96.
[9]FORCELLINI D,TARANTINO A M.Assessment of stone columns as a mitigation technique of liquefaction-induced effects during Italian earthquakes(May 2012)[J].The Scientific World Journal,2014,DOI:10.1155/2014/216278.
[10]PAPADIMITRIOU A,MOUTSOPOULOU M E,BOUCKOVALAS G,et al.Numerical investigation of liquefacton mitigation using gravel drain[C]//The 4th International Conference on Earthquake Geotechnical Engineering.Thessaloniki,Greece:[s.n.],2007:1-12.
[11]张艳美,张鸿儒.碎石桩设计参数对复合地基抗液化性能的影响[J].岩土力学,2008,28(5):1320-1323.ZHANG Yan-mei,ZHANG Hong-ru.Influence of stone columns design parameters on anti-liquefaction nature of composite foundation[J].Rock and Soil Mechanics,2008,29(5):1320-1324.
[12]牛琪瑛,刘建君,刘少文,等.碎石桩与水泥土桩加固液化地基的数值模拟研究[J].岩土工程学报,2011,33(增刊1):481-484.NIU Qi-ying,LIU Jian-jun,LIU Shao-wen,et al.Numerical simulation of liquefiable sandy ground reinforced by gravel piles and soil-cement piles[J].Chinese Journal of Geotechnical Engineering,2011,33(Suppl.1):481-484.
[13]张建民.砂土动力学若干基本理论探究[J].岩土工程学报,2012,34(1):1-50.ZHANG Jian-min.New advances in basic theories of sand dynamics[J].Chinese Journal of Geotechnical Engineering,2012,34(1):1-50.
[14]张建民.砂土的可逆性和不可逆性剪胀规律[J].岩土工程学报,2000,22(1):12-17.ZHANG Jian-min.Reversible and irreversible dilatancy of sand[J].Chinese Journal of Geotechnical Engineering,2000,22(1):12-17.
[15]张建民,王刚.砂土液化大变形的机理[J].岩土工程学报,2006,28(7):835-840.ZHANG Jian-min,WANG Gang.Mechanism of large post-liquefaction deformation in saturated sand[J].Chinese Journal of Geotechnical Engineering,2006,28(7):835-840.
[16]ZHANG J M,WANG G.Large post-liquefaction deformation of sand,part I:physical mechanism,constitutive description and numerical algorithm[J].Acta Geotechnica,2012,7(2):69-113.
[17]WANG Rui,ZHANG Jian-min,WANG Gang.A unified plasticity model for large post-liquefaction shear deformation of sand[J].Computers and Geotechnics,2014,59:54-66.
[18]邹佑学,王睿,张建民.砂土液化大变形模型在FLAC3D中的开发与应用[J].岩土力学,2018,39(4):1525-1534.ZOU You-xue,WANG Rui,ZHANG Jian-min.Implementing a plasticity model for large post-liquefaction deformation of sand into the FLAC3Dprogram[J].Rock and Soil Mechanics,2018,39(4):1525-1534.
[19]WANG R.Single piles in liquefiable ground:seismic response and numerical analysis methods[D].Beijing:Tsinghua University,2014.
[20]WANG R,FU P,ZHANG J M.Finite element model for piles in liquefiable ground[J].Computers and Geotechnics,2016,72:1-14.
[21]王睿,张建民.可液化地基中单桩基础的三维数值分析方法及应用[J].岩土工程学报,2015,37(11):1979-1985.WANG Rui,ZHANG Jian-min.Three-dimensional elastic-plastic analysis method for piles in liquefiable ground[J].Chinese Journal of Geotechnical Engineering,2015,37(11):1979-1985.
[22]刘星,王睿,张建民.液化地基中群桩基础地震相应分析[J].岩土工程学报,2015,37(12):2326-2331.LIU Xing,WANG Rui,ZHANG Jian-min.Seismic response analysis of pile groups in liquefiable foundations[J].Chinese Journal of Geotechnical Engineering,2015,37(12):2326-2331.
[23]WANG Rui,LIU Xing,ZHANG Jian-min.Numerical analysis of the seismic inertial and kinematic effects on pile bending moment in liquefiable soils[J].Acta Geotechnica,2017,12(4):773-791.
[24]SEED H B,WONG R T,IDRISS I M,et al.Moduli and damping factors for dynamic analyses of cohesionless soils[J].Journal of Geotechnical Engineering,1986,112(11):1016-1032.
[25]ROLLINS K M,EVANS M D,DIEHL N B,et al.Shear modulus and damping relationships for gravels[J].Journal of Geotechnical Engineering,1998,124(5):396-405.
[26]Itasca Consulting Group Inc.Fast Lagrangian analysis of continua in 3 dimensions user's manual[M].version 5.0.Minneapolis:Itasca Consulting Group Inc.,2012.
[27]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 Yu-min,XU Ding-ping.FLAC/FLAC3Dfundamentals and engineering applications[M].Beijing:China Water&Power Press,2009.
[28]ARULMOLI K,MURALEETHARAN K K,HOSSAINM M,et al.VELACS:verification of liquefaction analysis by centrifuge studies,laboratory testing program,soil data report[R].California:The Earth Technology Corporation,1992.
[29]RAYAMAJHI D,SCOTT A A,BOULANGER R W,et al.Dense granular columns in liquefiable ground.II:effects on deformations[J].Journal of Geotechnical and Geoenvironmental Engineering,2016,142(7):1-10.
[30]TANG L,ZHANG X Y,LIANG X Z.Numerical simulation of centrifuge experiments on liquefaction mitigation of silty soils using stone columns[J].KSCEJournal of Civil Engineering,2016,20(2):631-638.