自由场地液化响应特性的离心机振动台试验
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摘要
利用ZJU-400土工离心机振动台,对相对密度为40%的福建中细砂自由场地模型,进行5次动态加载的液化试验.分析试验中土的动力特性和地震动特性,得到土体不同深度范围内加速度、超静孔隙水压力随时间的发展规律,以及土体加速度、沉降与超静孔隙水压力增长之间的关系,增强了对地震过程中土体加速度、沉降与孔隙水之间相互作用的理解.结果表明:场地放大作用受超静孔隙水压力增长和土体软化的共同作用,液化破坏了土颗粒的联结强度和结构稳定性,再次沉积形成的结构不稳定易再次液化;峰值过后切应力对超静孔隙水压力增长仍起到不可忽视的作用;土体超静孔隙水压力增长和土体沉降是外荷由土颗粒到孔隙水再到土颗粒传递的结果;液化后固结完成,场地土体自振频率增加;基于剪切波速确定CRR曲线的方法是合理的.
A free-field model whose relative density is 40% with Fujian sand was constructed,and five dynamic loading liquefaction tests were performed in ZJU-400geotechnical centrifuge shaking table.By analyzing dynamic soil features and seismic motion character in the tests,the development and variation rules of acceleration,excess pore-water pressure(EPWP)with time were obtained at different soil depth for a few of seismic vibrations,as well as the relationship between soil acceleration,settlement and EPWP increasing,which help improving our comprehension of interaction of soil acceleration,settlement and pore-water during earthquake.Results are as follows:the site amplification depends on a combination of soil softening and EPWP increasing;liquefaction destroys connection strength and structural stability of soil grain,and resedimentation soil fabric isn't stable and is easy to liquefy again;effect of shear stress after peak on EPWP increasing can't be neglected;EPWP increasing and soil settlement is result of external load shift from soil grain to pore-water,and then to soil grain;site soil natural frequency increases when consolidation is finished after liquefaction;it's reasonable to determine cyclic resistance ratio(CRR)curve based on shear wave.
A free-field model whose relative density is 40% with Fujian sand was constructed,and five dynamic loading liquefaction tests were performed in ZJU-400geotechnical centrifuge shaking table.By analyzing dynamic soil features and seismic motion character in the tests,the development and variation rules of acceleration,excess pore-water pressure(EPWP)with time were obtained at different soil depth for a few of seismic vibrations,as well as the relationship between soil acceleration,settlement and EPWP increasing,which help improving our comprehension of interaction of soil acceleration,settlement and pore-water during earthquake.Results are as follows:the site amplification depends on a combination of soil softening and EPWP increasing;liquefaction destroys connection strength and structural stability of soil grain,and resedimentation soil fabric isn't stable and is easy to liquefy again;effect of shear stress after peak on EPWP increasing can't be neglected;EPWP increasing and soil settlement is result of external load shift from soil grain to pore-water,and then to soil grain;site soil natural frequency increases when consolidation is finished after liquefaction;it's reasonable to determine cyclic resistance ratio(CRR)curve based on shear wave.
引文
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[14]汪轩.瞬态振动法测地基土密实度[J].安徽建筑工业学院学报:自然科学版,2010,18(6):8-10.WANG Xuan.Determination of soil compactness tested by instant vibration method[J].Journal of Anhui Institute of Architecture and Industry:Natural Science Edition,2010,18(6):8-10.
[15]ZHOU Yan-guo,CHEN Yun-min,SHAMOTO Y.Verification of the soil-type specific correlation between liquefaction resistance and shear wave velocity of sand by dynamic centrifuge test[J].Journal of Geotechnical and Geoenvironmental Engineering,2010,136(1):165-177.
[16]周燕国.土结构性的剪切波速表征及对动力特性的影响[D].杭州:浙江大学,2007:97-117.ZHOU Yan-guo.Shear wave velocity-based characterization of soil structure and its effects on dynamic behavior[D].Hangzhou:Zhejiang University,2007:97-117.
[17]SEED H B,IDRISS I M.Simplified procedure for evaluating soil liquefaction potential[J].Journal of the Soil Mechanics and Foundation Division,1971,97(SM9):1249-1273.
[18]LIAO S S C,WHITMAN R V.Overburden correction factors for SPT in sands[J].Journal of the Geotechnical Engineering Divisions,1986,112(3):373-377.
[2]刘晶波,刘祥庆,王宗刚.离心机振动台试验叠环式模型箱边界效应[J].北京工业大学学报,2008,34(9):931 -937.LIU Jing-bo,LIU Xiang-qing,WANG Zong-gang.Boundary effect of laminar model box for shaking table tests on geotechnical centrifuge system[J].Journal of Beijing University of Technology,2008,34(9):931-937.
[3]苏栋,李相菘.砂土自由场地震响应的离心机试验研究[J].地震工程与工程振动,2006,26(2):166-170.SU Dong,LI Xiang-song.Centrifuge modeling of seismic response of free sand ground[J].Earthquake Engineering and Engineering Vibration,2006,26(2):166-170.
[4]苏栋,李相菘.地震历史对砂土抗液化性能影响的试验研究[J].岩土力学,2006,27(10):1815-1818.SU Dong,LI Xiang-song.Centrifuge investigation on effect of seismic history on resistance of sand to liquefaction[J].Rock and Soil Mechanics,2006,27(10):1815-1818.
[5]章为民,日下部治.砂性地层地震反应离心模型试验研究[J].岩土工程学报,2001,23(1):28-31.ZHANG Wei-min,KUSAKBE O.Dynamic centrifuge model test of sandy layer[J].Chinese Journal of Geotechnical Engineering,2001,23(1):28-31.
[6]曹杰,韩黎明,冯昌明,等.软弱土层自由场动力离心模型试验[J].长江科学院院报,2012,29(2):78-82.CAO Jie,HAN Li-ming,FENG Chang-ming,et al.Dynamic centrifuge tests on free-field response of soft soil[J].Journal of Yangtze River Scientific Research Institute,2012,29(2):78-82.
[7]ELGAMAL A,YANG Zhao-hui,LAI Tao,et al.Dynamic response of saturated dense sand in laminated centrifuge container[J].Journal of Geotechnical and Geoenvironmental Engineering,2005,131(5):598-609.
[8]TABOADA-URTUZUASTEGUI V M,DOBRY R.Centrifuge modeling of earthquake-induced lateral spreading in sand[J].Journal of Geotechnical and Geoenvironmental Engineering,1998,124(12):1195-1206.
[9]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(2):193-211.
[10]ZEGHAL M,ELGAMAL A,ZENG Xiang-wu,et al.Mechanism of liquefaction response in sand-silt dynamic centrifuge tests[J].Soil Dynamics and Earthquake Engineering,1999,18(1):71-85.
[11]陈云敏,韩超,凌道盛,等.ZJU400离心机研制及其振动台性能评价[J].岩土工程学报,2011,33(12):1887-1894.CHEN Yun-min,HAN Chao,LING Dao-sheng,et al.Development of geotechnical centrifuge ZJU400 and performance assessment of its shaking table system[J].Chinese Journal of Geotechnical Engineering,2011,33(12):1887-1894.
[12]YOUD T L,IDRISS I M,ANDRUS R D,et al.Liquefaction resistance of soils:summary report from the1996NCEER and 1998 NCEER/NSF workshops on evaluation of liquefaction resistance of soils[J].Journal of Geotechnical and Geoenvironmental Engineering,2001,127(10):817-833.
[13]韩超,周燕国,凌道盛,等.液化判别应力折减系数分布特征研究[J].岩石力学与工程学报,2010,29(9):1833-1839.HAN Chao,ZHOU Yan-guo,LING Dao-sheng,et al.Study of distribution features of stress reduction coefficient in liquefaction evaluation[J].Chinese Journal of Rock Mechanics and Engineering,2010,29(9):1833-1839.
[14]汪轩.瞬态振动法测地基土密实度[J].安徽建筑工业学院学报:自然科学版,2010,18(6):8-10.WANG Xuan.Determination of soil compactness tested by instant vibration method[J].Journal of Anhui Institute of Architecture and Industry:Natural Science Edition,2010,18(6):8-10.
[15]ZHOU Yan-guo,CHEN Yun-min,SHAMOTO Y.Verification of the soil-type specific correlation between liquefaction resistance and shear wave velocity of sand by dynamic centrifuge test[J].Journal of Geotechnical and Geoenvironmental Engineering,2010,136(1):165-177.
[16]周燕国.土结构性的剪切波速表征及对动力特性的影响[D].杭州:浙江大学,2007:97-117.ZHOU Yan-guo.Shear wave velocity-based characterization of soil structure and its effects on dynamic behavior[D].Hangzhou:Zhejiang University,2007:97-117.
[17]SEED H B,IDRISS I M.Simplified procedure for evaluating soil liquefaction potential[J].Journal of the Soil Mechanics and Foundation Division,1971,97(SM9):1249-1273.
[18]LIAO S S C,WHITMAN R V.Overburden correction factors for SPT in sands[J].Journal of the Geotechnical Engineering Divisions,1986,112(3):373-377.
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