循环荷载下饱和砂土固-液相变特征
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摘要
基于南京饱和细砂动三轴试验发现,循环荷载下饱和砂土应力-应变率曲线形状随孔压累积由"椭圆形"渐变为"哑铃形"。"哑铃形"关系曲线的出现表明饱和砂土具有低抗剪性和流动性。定义了反映循环荷载下饱和砂土流动性的平均流动系数以及反映流动性随振次变化的流动曲线,发现流动曲线具有明显的三阶段特征。给出了相对密度、有效固结压力和循环应力比对流动曲线的影响规律。提出以平均流动系数急速增长初始点作为饱和砂土由固态向液态转变的临界点,据此定义平均流动系数急速增长初始点对应的孔压比为相变孔压比。试验发现,各工况的平均流动系数与孔压比关系曲线基本一致,相对密度、有效固结压力和循环应力比对相变孔压比几乎无影响,各工况相变孔压比均在0.8左右。
Based on the dynamic triaxial tests on the saturated Nanjing fine sand,an obvious phenomenon is discovered that the relationship curves of the shear stress-strain rate are altered from an elliptical shape to a dumbbell one with the build-up of the pore water pressure.The relationship curve with the dumbbell shape demonstrates that the saturated sand possesses low shear resistance and fluidity.The average flow coefficient and the flow curve describing the fluidity of the saturated sand under cyclic loading are defined.It can be found apparently that the three-phase characteristics exist in the flow curves.The influences of the relative dense,effective consolidation pressure and cyclic stress ratio on the flow curves are discussed.It is presented that the initial sharply-increasing point for the average flow coefficient is taken as the critical point of the saturated sand changing from the solid state to the fluid one.The pore water pressure ratio corresponding to the initial sharply-increasing point is defined as the pore water pressure ratio of phase change.The tests show that the relationship curves of the average flow coefficient and the pore water pressure ratio under various loading conditions are similar in shape.In addition,the pore water pressure ratios of phase change for the saturated Nanjing fine sand under various test conditions are about 0.8.The relative dense,effective consolidation pressure and cyclic stress ratio have few influences on the pore water pressure ratios of phase change.
Based on the dynamic triaxial tests on the saturated Nanjing fine sand,an obvious phenomenon is discovered that the relationship curves of the shear stress-strain rate are altered from an elliptical shape to a dumbbell one with the build-up of the pore water pressure.The relationship curve with the dumbbell shape demonstrates that the saturated sand possesses low shear resistance and fluidity.The average flow coefficient and the flow curve describing the fluidity of the saturated sand under cyclic loading are defined.It can be found apparently that the three-phase characteristics exist in the flow curves.The influences of the relative dense,effective consolidation pressure and cyclic stress ratio on the flow curves are discussed.It is presented that the initial sharply-increasing point for the average flow coefficient is taken as the critical point of the saturated sand changing from the solid state to the fluid one.The pore water pressure ratio corresponding to the initial sharply-increasing point is defined as the pore water pressure ratio of phase change.The tests show that the relationship curves of the average flow coefficient and the pore water pressure ratio under various loading conditions are similar in shape.In addition,the pore water pressure ratios of phase change for the saturated Nanjing fine sand under various test conditions are about 0.8.The relative dense,effective consolidation pressure and cyclic stress ratio have few influences on the pore water pressure ratios of phase change.
引文
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[3]HUWANG J I,KIM C Y,CHUNG C K,et al.Viscous fluidcharacteristics of liquefied soils and behavior of pilessubjected to flow of liquefied soils[J].Soil Dynamics andEarthquake Engineering,2006,26(2/4):313-323.
[4]SAWICKI A,MIERCZYNSKI J.On the behaviour ofliquefied soil[J].Computers and Geotechnics,2009,36(4):531-536.
[5]TOWHATA I,VARGAS M,ORENSE R P,et al.Shaking tabletests on subgrade reaction of pipe embedded in sandyliquefied subsoil[J].Soil Dynamics and EarthquakeEngineering,1999,18(5):347-361.
[6]UZUOKA R,YASHIM A,KAWAKAMIC T,et al.Fluiddynamics based prediction of liquefaction induced lateralspreading[J].Computers and Geotechnics,1998,22(4):243-282.
[7]DUNGCA J R,KUWANO J,TAKAHASHI A,et al.Shakingtable tests on the lateral response of a pile buried in liquefiedsand[J].Soil Dynamics and Earthquake Engineering,2006,26(2/4):287-295.
[8]陈国兴.岩土地震工程学[M].北京:科学出版社,2007.(CHEN Guo-xing.Geotechnical earthquake enigneering[M].Beijing,Science Press,2007.(in Chinese))
[9]SEED H B,LEE K L.Saturated sands during cyclic loading[J].Journal of Soil Mechanics and Foundation EngineeringDivision,ASCE,1966,92(SM6):105-134.
[10]CASAGRANDE A.Liquefaction and cyclic deformation ofsands:a critical review[C]//Proceedings of the 5thPan-American Conference on Soil Mechanics and FoundationEngineering.Buenos Aires,Argentian,1975.
[11]POULOS S J,CASTRO G,FRANCE J W.Liquefactionevaluation procedure[J].Journal of GeotechnicalEngineering,ASCE,1985,111(6):772-792.
[12]凌贤长,唐亮,于恩庆.可液化场地地震振动孔隙水压力增长研究的大型振动台试验及其数值模拟[J].岩石力学与工程学报,2006,25(增刊2):3998-4003.(LINXian-zhang,TANG Liang,YU En-qing.Large scale shakingtable test and its numerical simulation of research on build-upbehaviour of sesimically-induced pore water pressure inliquefiable site[J].Chinese Journal of Rock Mechanics andEngineering,2006,25(S2):3998-4003.(in Chinese))
[13]陈育民,沙小兵,林奔,等.饱和砂土液化前高孔压状态流动特性试验研究[J].世界地震工程,2010,26:267-272.(CHEN Yu-min,SHA Xiao-bing,LIN Ben,et al.Theflow characteristics of pre-liquefied sand under high excesspore pressure[J].World Earthquake Engineering,2010,26:267-272.(in Chinese))
[14]陈国兴,朱定华,何启智.DSZ-1型动三轴试验机研究与性能试验[J].地震工程与工程振动,2002,22(6):71-75.(CHEN Guo-xing,ZHU Ding-hua,HE Qi-zhi.Developmentand test of DSZ-1 cyclic triaxial testing system[J].Earthquake Engineering and Engineering Vibration,2002,22(6):71-75.(in Chinese))
[15]陈文芳.非牛顿流体力学[M].北京:科学出版社,1984.(CHEN Wen-fang.No-newtonian fluid mechanics[M].Beijing:Science Press,1984.(in Chinese))
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