多向地震荷载对砂土震陷的影响
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摘要
利用有限元数值方法模拟不同类型砂土在多向地震荷载输入条件下的动单剪试验,采用弹塑性边界面模型,通过室内动单剪试验实测结果确定模型参数,选取包括大震、中震、近场、远场以及不同土质条件的148组具有完整记录的多向地震荷载时程对不同类型砂土试样进行单向和多向加载,分别进行应力和应变控制式动单剪试验,计算分析震级、震中距以及砂土特性不同的条件下多向地震荷载对砂土震陷问题的影响。结果表明:多向地震荷载对砂土震陷的影响具有较大的不确定性,多向和单向水平地震荷载引起的砂土竖向应变比与震级、震中距和砂土特性密切相关,震级越大,竖向应变比越大;震中距越大,竖向应变比越小;砂土相对密度越大,竖向应变比越大。另外,在应力控制和应变控制荷载试验条件下,多向和单向水平地震荷载引起的砂土竖向应变比差异较大,前者比值大于后者。
Dynamic simple shear tests on different types of sand under multidirectional earthquake loading are simulated by means of the finite element method.The reduced order bounding surface model is employed and its parameters are determined based on the results obtained from laboratory dynamic simple shear tests.148 groups of ground motions with multi-components from far and/or near fields of moderate and/or strong earthquake events at different site conditions are used as input motions for strain controlled and stress controlled dynamic simple shear tests.Effect of multidirectional earthquake loading on seismic compression of sand for different earthquake magnitudes site-to-source distances and properties of sand is studied.The results show that the ratio of vertical strain induced by multi-components of seismic loading and that induced by one component of seismic loading are greatly associated with earthquake magnitude,site-to-source distance and properties of sand,the ratio of vertical strain increases with the increasing earthquake magnitude and relative density of sand,and decreases with the increasing site-to-source distances.Great limitation exists in the method considering the effect of multidirectional earthquake loading on seismic compression proposed by Pyke et al(1975) due to its lack of considering the effect of characteristics of seismic loading and properties of sand.Also,the ratios obtained from stress controlled and strain controlled simple shear tests are greatly different and the mean ratios from the former are larger than those from the latter.
Dynamic simple shear tests on different types of sand under multidirectional earthquake loading are simulated by means of the finite element method.The reduced order bounding surface model is employed and its parameters are determined based on the results obtained from laboratory dynamic simple shear tests.148 groups of ground motions with multi-components from far and/or near fields of moderate and/or strong earthquake events at different site conditions are used as input motions for strain controlled and stress controlled dynamic simple shear tests.Effect of multidirectional earthquake loading on seismic compression of sand for different earthquake magnitudes site-to-source distances and properties of sand is studied.The results show that the ratio of vertical strain induced by multi-components of seismic loading and that induced by one component of seismic loading are greatly associated with earthquake magnitude,site-to-source distance and properties of sand,the ratio of vertical strain increases with the increasing earthquake magnitude and relative density of sand,and decreases with the increasing site-to-source distances.Great limitation exists in the method considering the effect of multidirectional earthquake loading on seismic compression proposed by Pyke et al(1975) due to its lack of considering the effect of characteristics of seismic loading and properties of sand.Also,the ratios obtained from stress controlled and strain controlled simple shear tests are greatly different and the mean ratios from the former are larger than those from the latter.
引文
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[17]吴世明.土动力学[M].北京:中国建筑工业出版社,2000.(WU Shi-ming.Soil dynamics[M].Beijing:China Building Industry Press,2000.(in Chinese))
[18]LI X S,WANG Z L,SHEN C K,et al.A nonlinear procedure for response analysis of horizontally layered sites subjected to multi-directional earthquake loading[R].Davis:Department of Civil Engineering,University of California,1992.
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[21]WANG Z L.Bounding surface hypoplasticity model for granular soils and its application[D].Davis:University of California,1990.
[22]孟凡超,袁晓铭,孙锐.加速度峰值不对称性特征及其影响[J].自然灾害学报,2008,17(1):191–196.(MENG Fan-Chao,YUAN Xiao-ming,SUN Yue.Study on characteristics and effect of asymmetry of peak ground acceleration[J].Journal of Natural Disasters,2008,17(1):191–196.(in Chinese))
[23]BYRNE P M.A cyclic shear-volume coupling and pore pressure model for sand[C]//Second International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics,St.Louis,1991.
[2]NAGASE H,ISHIHARA K.Liquefaction-induced compaction and settlement of sand during earthquakes[J].Soils and Foundations,1988,28(1):65–76.
[3]WHANG D,et al.Characterization of seismic compression of some compacted fills[J].Advances in Unsaturated Geotechnics,2000:180–194.
[4]孟凡超.液化地基上建筑物不均匀震陷机理初步研究[D].哈尔滨:中国地震局工程力学研究所,2006.(MENG Fan-chao.Primary study on mechanism of earthquake-induced differential settlement of buildings on liquefiable subsoil[D].Haerbin:Institute of Engineering Mechanics,China Earthquake Administration,2006.(in Chinese))
[5]SEED H B,SILVER M L.Settlement of dry sands during earthquakes[J].Journal of the Soil Mechanics and Foundations Division,ASCE,1972,98(4):381–397.
[6]SILVER M L,SEED H B.Volume changes in sands due to cyclic loading[J].Journal of the Soil Mechanics and Foundations Division,ASCE,1971,97(9):1071–1082.
[7]YOUD T L.Compaction of sands by repeated shear straining[J].Journal of the Soil Mechanics and Foundations Division,ASCE,1972,98(7):709–725.
[8]SHAHNAZARI H,TOWHATA I.Torsion shear tests on cyclic stress-dilatancy relationship of sand[J].Journal of the Japanese Geotechnical Society:soils and foundation,2002,42(1):105–119.
[9]WHANG D H,STEWART J P,BRAY J D.Effect of Compaction conditions on the seismic compression of compacted fill soils[J].Geotechnical Testing Journal,2004,27(4):371–379.
[10]STAMATOPOULOS C A,et al.Earthquake-induced settlement as a result of densification,measured in laboratory tests[C]//Proc 13th World Conf on Earthquake Engineering,Vancouver,2004.
[11]DUKU P M,STEWART J P,WHANG D H.Effect of post-compaction ageing on seismic compression of fine-grained soils[C]//Ground Modification and Seismic Mitigation,Shanghai,2006.
[12]DUKU P M,STEWART J P,WHANG D H,et al.Volumetric strains of clean sands subject to cyclic loads[J].Journal of Geotechnical and Geoenvironmental Engineering,ASCE,2008,134(8):1073–085.
[13]STEWART J P,YEE E,DUKU P.Volume change in unsaturated soils from cyclic loading[R].Restion:National Earthquake Hazards Reduction Program,External Research Program,2009.
[14]胡聿贤.地震工程学[M].北京:地震出版社,1998.(HU Yu-xian.Earthouake engineering[M].Beijing:Earthquake Press,1998.(in Chinese))
[15]PYKE R,SEED H B,CHAN C K.Settlement of sands under multidirectional shaking[J].Journal of Geotechnical Engineering,ASCE,1975,101(4):378–398.
[16]TOKIMATSU K,SEED H B.Evaluation of settlements in sands due to earthquake shaking[J].Journal of Geotechnical Engineering,1987,113(8):861–878.
[17]吴世明.土动力学[M].北京:中国建筑工业出版社,2000.(WU Shi-ming.Soil dynamics[M].Beijing:China Building Industry Press,2000.(in Chinese))
[18]LI X S,WANG Z L,SHEN C K,et al.A nonlinear procedure for response analysis of horizontally layered sites subjected to multi-directional earthquake loading[R].Davis:Department of Civil Engineering,University of California,1992.
[19]STEWART J P,WANG D H,MOYNEURM,DUKU P.Seismic compression of as-compacted fill soil with rariable levels of fines content and fiues plasticity[R].2004.
[20]蔡宏英,周健,李相菘.深厚覆盖软土地层多向地震动力反应分析[J].同济大学学报,2000,28(2):177–182.(CAI Hong-ying,ZHOU Jian,LI Xiang-song.Plasto-elastic dynamic response of horizontally layered sites under multi-directional earthquake shaking[J].Journal of Tongji University(Natural Science),2000,28(2):177–182.(in Chinese))
[21]WANG Z L.Bounding surface hypoplasticity model for granular soils and its application[D].Davis:University of California,1990.
[22]孟凡超,袁晓铭,孙锐.加速度峰值不对称性特征及其影响[J].自然灾害学报,2008,17(1):191–196.(MENG Fan-Chao,YUAN Xiao-ming,SUN Yue.Study on characteristics and effect of asymmetry of peak ground acceleration[J].Journal of Natural Disasters,2008,17(1):191–196.(in Chinese))
[23]BYRNE P M.A cyclic shear-volume coupling and pore pressure model for sand[C]//Second International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics,St.Louis,1991.
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