饱和砂土液化后大变形机制的离散元细观分析
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摘要
采用颗粒流软件模拟了饱和砂土在不排水条件下的循环剪切试验,研究了不同因素对液化的影响,并进一步分析了饱和砂土液化后宏观变形的基本规律。在此基础上,从孔隙分布角度解释了砂土液化后的大变形的细观物理机制。通过自编程序对颗粒排列和孔隙分布的演化过程进行定量描述,给出孔隙率标准差作为液化后体积收缩势的度量,并研究了孔隙率标准差与液化后大变形的关系。离散元细观数值模拟再现了室内试验中的宏观现象,证实了室内试验中饱和砂土液化后的有限剪切大变形是客观真实的材料响应。土体体积收缩势的累积所导致的孔隙均匀化以及土颗粒间自由空隙增大正是饱和砂土液化后循环剪应变逐渐增大的细观机制。孔隙率标准差作为孔隙均匀化的量化指标,与循环剪应变各周次幅值有良好的相关性。
The particle flow code(PFC) was adopted to simulate the cyclic shear test of saturated sand under undrained condition.The influence of different conditions of sand samples on liquefactions was studied. The meso-mechanism of the large limited post-liquefaction deformation was explained by pore distributions. A statistic code was developed to quantify the arrangement of particle and pore, and standard deviation of porosity was proposed to measure the post-liquefaction volume shrinkage potential. Then relationship between the standard deviation of porosity and the limited large post-liquefaction deformation was investigated. It was found that initial conditions have little effect on the ultimate state of post-liquefaction sample, while it only influences the cycle numbers of initial liquefaction. The large limited post-liquefaction deformation on saturated sand in laboratory test repetitively occurs during numerical simulations. The homogenization of pore and the increasement of distance between particles caused by the accumulation of sand volume shrinkage potential was the meso-mechanism of the generation of the large limited post-liquefaction deformation during cyclic shear. As a quantitative index of pore homogenization, standard deviation of porosity got a favorable correlation with the shear strain amplitude in each cycle.
The particle flow code(PFC) was adopted to simulate the cyclic shear test of saturated sand under undrained condition.The influence of different conditions of sand samples on liquefactions was studied. The meso-mechanism of the large limited post-liquefaction deformation was explained by pore distributions. A statistic code was developed to quantify the arrangement of particle and pore, and standard deviation of porosity was proposed to measure the post-liquefaction volume shrinkage potential. Then relationship between the standard deviation of porosity and the limited large post-liquefaction deformation was investigated. It was found that initial conditions have little effect on the ultimate state of post-liquefaction sample, while it only influences the cycle numbers of initial liquefaction. The large limited post-liquefaction deformation on saturated sand in laboratory test repetitively occurs during numerical simulations. The homogenization of pore and the increasement of distance between particles caused by the accumulation of sand volume shrinkage potential was the meso-mechanism of the generation of the large limited post-liquefaction deformation during cyclic shear. As a quantitative index of pore homogenization, standard deviation of porosity got a favorable correlation with the shear strain amplitude in each cycle.
引文
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[16]NG T,DOBRY R.Numerical simulations of monotonic and cyclic loading of granular soil[J].Journal of Geotechnical Engineering,1994,120(2):388-403.
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[19]KUHN M R,RENKEN H E,MIXSELL A D,et al.Investigation of cyclic liquefaction with discrete element simulations[J].Journal of Geotechnical&Geoenvironmental Engineering,2014,140(12):04014075.
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[21]WANG R,FU P,ZHANG J M,et al.DEM study of fabric features governing undrained post-liquefaction shear deformation of sand[J].Acta Geotechnica,2016,11(6):1321-1337.
[2]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.
[3]刘年平,王宏图,袁志刚,等.砂土液化预测的Fisher判别模型及应用[J].岩土力学,2012,33(2):554-557,622.LIU Nian-ping,WANG Hong-tu,YUAN Zhi-gang,et al.Fisher discriminant analysis model of sand liquefaction and its application[J].Rock and Soil Mechanics,2012,33(2):554-557,622.
[4]陈国兴,孔梦云,李小军,等.以标贯试验为依据的砂土液化确定性及概率判别法[J].岩土力学,2015,36(1):9-27.CHEN Guo-xing,KONG Meng-yun,LI Xiao-jun,et al.Deterministic and probabilistic triggering correlations for assessment of seismic soil liquefaction at nuclear power plant[J].Rock and Soil Mechanics,2015,36(1):9-27.
[5]颜可珍,刘能源,夏唐代.基于判别分析法的地震砂土液化预测研究[J].岩土力学,2009,30(7):2049-2052.YAN Ke-zhen,LIU Neng-yuan,XIA Tang-dai.Discriminant analysis model for prediction of sand soil liquefaction during earthquake[J].Rock and Soil Mechanics,2009,30(7):2049-2052.
[6]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.
[7]DE ALBA P A,SEED H B,CHAN C K.Sand liquefaction in large-scale simple shear tests[J].Journal of the Geotechnical Engineering Division,ASCE,1976,102(9):909-927.
[8]YASUDA S,MASUDA T,YOSHIDA N,et al.Torsional shear and triaxial compression tests on deformation characters of sands before and after liquefaction[C]//Proceedings of 5th US-Japan Workshop on Earthquake Resistant Design of Lifelines and Countermeasures Against Soil Liquefaction.[S.l.]:[s.n.],1994:249-265.
[9]SHAMOTO Y,ZHANG J M,GOTO S.Mechanism of large post liquefaction deformation in saturated sands[J].Soils and Foundations,1997,37(2):71-80.
[10]ZHANG J M,SHAMOTO Y,TOKIMATSU K.Moving critical and phase-transformation stress state lines of saturated sand under undrained cyclic loading[J].Soils and Foundations,1997,37(2):51-59.
[11]张建民,王刚.砂土液化后大变形的机理[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.
[12]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.
[13]张建民,王富强.饱和剪胀性砂土液化后流滑现象与机理[J].岩土力学,2010,31(9):2711-2715.ZHANG Jian-min,WANG Fu-qiang.Post-liquefaction flow failure of saturated dilative sands and its mechanism[J].Rock and soil Mechanics,2010,31(9):2711-2715.
[14]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.
[15]王刚,张建民.砂土液化大变形的弹塑性循环本构模型[J].岩土工程学报,2007,29(1):51-59.WANG Gang,ZHANG Jian-min.A cyclic elasto-plastic constitutive model for evaluation of large postliquefaction deformation of sand[J].Chinese Journal of Geotechnical Engineering,2007,29(1):51-59.
[16]NG T,DOBRY R.Numerical simulations of monotonic and cyclic loading of granular soil[J].Journal of Geotechnical Engineering,1994,120(2):388-403.
[17]SITHARAM T G.Discrete element modelling of cyclic behaviour of granular materials[J].Geotechnical and Geological Engineering,2003,21(4):297-329.
[18]刘洋,周健,付建新.饱和砂土流固耦合细观数值模型及其在液化分析中的应用[J].水利学报,2009,40(2):250-256.LIU Yang,ZHOU Jian,FU Jian-xin.Fluid-particle coupled model for saturated sand and its application to liquefaction analysis[J].Journal of Hydraulic Engineering,2009,40(2):250-256.
[19]KUHN M R,RENKEN H E,MIXSELL A D,et al.Investigation of cyclic liquefaction with discrete element simulations[J].Journal of Geotechnical&Geoenvironmental Engineering,2014,140(12):04014075.
[20]WEI J T,WANG G.Microstructure evolution of granular soils during liquefaction process[C]//Geomechanics from Micro to Macro-Proceedings of the TC105 ISSMGE.[S.l.]:[s.n.],2015.
[21]WANG R,FU P,ZHANG J M,et al.DEM study of fabric features governing undrained post-liquefaction shear deformation of sand[J].Acta Geotechnica,2016,11(6):1321-1337.