循环荷载下砂土液化特性颗粒流数值模拟
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摘要
利用PFC2D常体积循环双轴试验条件,对砂土在不排水循环荷载作用下的液化特性进行了颗粒流数值模拟,数值模拟按等应力幅加荷方式进行。颗粒流数值模拟的优点在于得到试样液化宏观力学表现的同时,通过不同循环加荷时刻试样内细观组构参量(包括配位数、接触法向分布、粒间法向接触力、粒间切向接触力)的演化规律,分析砂土液化过程中细观组构变化与宏观力学响应之间的内在联系,从而可进一步探讨砂土液化的细观力学机制。数值模拟研究结果表明,砂土液化现象在宏观力学表现上反映为超静孔隙水压力的累积上升和平均有效主应力的不断减小,在细观组构上对应于配位数的累积损失和粒间接触力的不断减小。砂土液化细观机制分析表明,试样配位数的减少与循环加荷过程中组构各向异性滞后于应力各向异性有关。
Based on the constant volume cyclic biaxial test in particle flow code(PFC),PFC2D,the behavior of sand liquefaction under cyclic loading is simulated by PFC2D.The major advantage of PFC2D is the evolution regularity of microscopic fabric parameters including co-ordination number,contact normal,normal contact force,shear contact force,can be achieved together with the macroscopic liquefaction response.The micromechanism of sand liquefaction is further discussed.The results of numerical simulation indicate that the sand liquefaction is reflected by the accumulation of excess pore water pressure and progressive decrease in mean effective principal stress in macroscopic response;and on the other hand,corresponds to the cumulative loss of co-ordination number and continuous reduction of contact forces in microscopic fabric.The micromechanical research exposes that the loss of co-ordination is related to the lagging of fabric anisotropy behind stress anisotropy.
Based on the constant volume cyclic biaxial test in particle flow code(PFC),PFC2D,the behavior of sand liquefaction under cyclic loading is simulated by PFC2D.The major advantage of PFC2D is the evolution regularity of microscopic fabric parameters including co-ordination number,contact normal,normal contact force,shear contact force,can be achieved together with the macroscopic liquefaction response.The micromechanism of sand liquefaction is further discussed.The results of numerical simulation indicate that the sand liquefaction is reflected by the accumulation of excess pore water pressure and progressive decrease in mean effective principal stress in macroscopic response;and on the other hand,corresponds to the cumulative loss of co-ordination number and continuous reduction of contact forces in microscopic fabric.The micromechanical research exposes that the loss of co-ordination is related to the lagging of fabric anisotropy behind stress anisotropy.
引文
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[2]刘汉龙,余湘娟.土动力学与岩土地震工程研究进展[J].河海大学学报,1999,27(1):6-15.LIU Han-long,YU Xiang-juan.Advance in soil dy-namics and geotechnical earthquake engineering[J].Journal of Hohai University,1999,27(1):6-15.
[3]CUNDALL P A,STRACK O D L.A discrete numerical model for granular assemblies[J].Geotechnique,1979,29(1):47-65.
[4]周健,池永,池毓蔚,等.颗粒流方法及PFC2D程序[J].岩土力学,2000,21(3):271-274.ZHOU Jian,CHI Yong,CHI Yu-wei,et al.The method of particle flow coed and PFC2D code[J].Rock and Soil Mechanics,2000,21(3):271-274.
[5]周健,池永.砂土力学性质的细观模拟[J].岩土力学,2003,24(6):901-906.ZHOU Jian,CHI Yong.Mesomechanical simulation of sand mechanical properties[J].Rock and Soil Mechanics,2003,24(6):901-906.
[6]周健,张刚,孔戈.渗流的颗粒流细观模拟[J].水利学报,2006,37(1):28-32.ZHOU Jian,ZHANG Gang,KONG Ge.Meso-mechanics simulation of seepage with particle flow code[J].Journal of Hydraulic Engineering,2006,37(1):28-32.
[7]JENSEN R P,BOSSCHER P J,PLESHA M E,et al.DEM simulation of granular media-structure interface:effects of surface roughness and particle shape[J].International Journal for Numerical and Analytical Methods in Geomechanics,1999,23:531-547.
[8]ISHIHARA K,TATSUKA K,YASUDA S.Undrained deformation and liquefaction of sand under cyclic stresses[J].Soils and Foundations,1975,15(1):29-44.
[9]ODA M.Initial fabrics and their relations to mechanical properties of granular materials[J].Soils and Foun-dations,1972,12(1):17-36.
[10]ROTHENBURG L,BATHURST R J.Analytical study of induced anisotropy in idealized granular materials[J].Geotechnique,1989,39(4):601-604.
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