土压缩指标的率相关特性试验研究——以兰州黄土为例
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摘要
黄土是一种特殊的率相关岩土材料,其压缩指标(如弹、塑性压缩系数和前期固结压力等)对加载速率的响应极为敏感.本文以兰州黄土为研究对象,开展了不同干密度和应力加载速率条件下的K_0加载试验.在此基础上基于不同压力条件下应变随时间的时程曲线分析了不同应变速率条件下的应力应变发展规律.结果显示,不同应变速率条件下兰州黄土进入塑性阶段的应力应变曲线为一系列平行线,且这些平行线的位置随着应变速率的增大而升高.对于应变速率相差一个数量级的平行线,其间距为常数.其物理意义为恒定荷载条件下应变与时间对数曲线的斜率.进一步分析表明,使用每级荷载作用下的最终应变得到的应力应变曲线与不同应变速率条件下的曲线大致平行,因而弹、塑性压缩系数以及前期固结压力可以通过最终应力应变曲线获取.其中,弹性压缩系数和前期固结压力与应力加载速率负相关,而塑性压缩系数和恒载应变速率参数受应力加载速率影响较弱.所以,在黄土场地动力学稳定性分析中,应充分考虑应力加载速率的影响,提高稳定性计算的准确性.
Loess is a special rate dependent geomaterial,and its compression index(such as elastic,plastic compression coefficient and pre-consolidation pressure)is extremely sensitive to loading rate.In this paper,Lanzhou loess was taken as study object and K_0 compression tests under different dry density and stress loading rates were carried out.Based on the duration curve of strain versus time under different pressure conditions,the law of stressstrain under different strain rates was analyzed.The results show that the stress-strain curves in plastic stage under different strain rates are a series of parallel lines,and the positions of these parallel lines move up with the increase of strain rate.For the parallel lines with strain rate difference of an order of magnitude,the space is constant.Its physical meaning is the slope of the strain versus time logarithmic curve under constant load conditions.Further analysis indicates that the stress-strain curves obtained by the final strain under each load are approximately parallel to the curves at different strain rate conditions,and thus elastic and plastic compressive coefficients and preconsolidation pressure can be obtained by the final stress-strain curve.Among them,the elastic compression coefficient and the pre-consolidation pressure are negatively correlated with the stress loading rate,while the influence of stress loading rate on plastic compression coefficient and the constant load strain rate parameter are not notable.Therefore,in the dynamic stability analysis of loess fields,the effect of stress loading rate should be fully considered to improve the accuracy of stability calculation.
Loess is a special rate dependent geomaterial,and its compression index(such as elastic,plastic compression coefficient and pre-consolidation pressure)is extremely sensitive to loading rate.In this paper,Lanzhou loess was taken as study object and K_0 compression tests under different dry density and stress loading rates were carried out.Based on the duration curve of strain versus time under different pressure conditions,the law of stressstrain under different strain rates was analyzed.The results show that the stress-strain curves in plastic stage under different strain rates are a series of parallel lines,and the positions of these parallel lines move up with the increase of strain rate.For the parallel lines with strain rate difference of an order of magnitude,the space is constant.Its physical meaning is the slope of the strain versus time logarithmic curve under constant load conditions.Further analysis indicates that the stress-strain curves obtained by the final strain under each load are approximately parallel to the curves at different strain rate conditions,and thus elastic and plastic compressive coefficients and preconsolidation pressure can be obtained by the final stress-strain curve.Among them,the elastic compression coefficient and the pre-consolidation pressure are negatively correlated with the stress loading rate,while the influence of stress loading rate on plastic compression coefficient and the constant load strain rate parameter are not notable.Therefore,in the dynamic stability analysis of loess fields,the effect of stress loading rate should be fully considered to improve the accuracy of stability calculation.
引文
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[5]栗润德,张鸿儒,白晓红,等.不同含水量下原状黄土动强度和震陷的试验研究[J].工程地质学报,2007,15(05):694-699.LI R D,ZHANG H G,BAI X H,et al.Dynamic shear strength and seismic subsidence of intact loess with different water contents from dynamic tri-axial testing[J].Journal of Engineering Geology,2007,15(05):694-699.
[6]王峻,王兰民,李兰.黄土场地震陷量的试验预测[J].西北地震学报,1997,19(2):62-66.WANG J,WANG L M,LI L.Laboratory prediction of seismic subsidence quantity on loess sites[J].Northwestern Seismological Journal,1997,19(2):62-66.
[7]王峻,石玉成,王兰民,等.不同地震荷载作用下黄土震陷特性的对比分析[J].岩土工程学报,2011,33(1):102-105.WANG J,SHI Y C,WANG L M,et al.Comparative analysis of characters of loess subsidence under different seismic load[J].Chinese Journal of Geotechnical Engineering,2011,33(1):102-105.
[8]徐舜华,王兰民,孙军杰,等.含水量对黄土震陷性定量影响研究[J].西北地震学报,2010,32(1):30-35.XU S H,WANG L M,SUN J J,et al.Study on the influence of water content to subsidence characters ofloess[J].Northwestern Seismological Journal,2010,32(1):30-35.
[9]徐舜华,王兰民,袁中夏.黄土震陷初判指标的界定研究[J].西北地震学报,2006,28(2):140-143.XU S H,WANG L M,YUAN Z X.Study on initial judging criterions of loess seismic subsidence[J].Northwestern Seismological Journal,2006,28(2):140-143.
[10]邓津,王兰民,张振中.黄土显微结构特征与震陷性[J].岩土工程学报,2007,29(4):542-548.DENG J,WANG L M,ZHANG Z Z.Microstructure characteristics and seismic subsidence of loess[J].Chinese Journal of Geotechnical Engineering,2007,29(4):542-548.
[11]孙军杰,王强,王兰民.非饱和黄土震陷力学机制与主导影响因素[J].西北地震学报,2011,33(增刊):71-76.SUN J J,WANG Q,WANG L M.Study on the physical-mechanical mechanism and dominant influence factors of unsaturated loess subsidence under seismicloading[J].Northwestern Seismological Journal,2011,33(Sup):71-76.
[12]孙俊杰,王兰民,邱仁东,等.基于物理力学机制的黄土震陷数学估算模型[J].工程力学,2012,29(5):53-60.SUN J J,WANG L M,QIU R D,et al.A mathematical estimation model for seismic subsidence of loess based on physical-mechanical mechanism[J].Engineering Mechanics,2012,29(5):53-60.
[2]谢定义.试论我国黄土力学研究中的若干新趋向[J].岩土工程学报,2001:23(1):3-13.XIE D Y.Exploration of some new tendencies in research of loess soil mechanics[J].Chinese Journal of Geotechnical Engineering,2001:23(1):3-13.
[3]王兰民,张振中.地震时黄土震陷量的估算方法[J].自然灾害学报,1993,2(3):85-94.WANG L M,ZHANG Z Z.A method of estimating the quantity of seismic subsidence in loess deposits during earthquakes[J].Journal of Natural Disasters,1993,2(3):85-94.
[4]陈永明,王兰民,刘红玫.剪切波速预测黄土场地震陷量的方法[J].岩石力学与工程学报,2003,22(增2):2834-2839.CHEN Y M,WANG L M,LIU H M.Prediction method of seismic subsidence of loess ground with shear wave velocity[J].Chinese Journal of Rock Mechanics and Engineering,2003,22(Sup.2):2834-2839.
[5]栗润德,张鸿儒,白晓红,等.不同含水量下原状黄土动强度和震陷的试验研究[J].工程地质学报,2007,15(05):694-699.LI R D,ZHANG H G,BAI X H,et al.Dynamic shear strength and seismic subsidence of intact loess with different water contents from dynamic tri-axial testing[J].Journal of Engineering Geology,2007,15(05):694-699.
[6]王峻,王兰民,李兰.黄土场地震陷量的试验预测[J].西北地震学报,1997,19(2):62-66.WANG J,WANG L M,LI L.Laboratory prediction of seismic subsidence quantity on loess sites[J].Northwestern Seismological Journal,1997,19(2):62-66.
[7]王峻,石玉成,王兰民,等.不同地震荷载作用下黄土震陷特性的对比分析[J].岩土工程学报,2011,33(1):102-105.WANG J,SHI Y C,WANG L M,et al.Comparative analysis of characters of loess subsidence under different seismic load[J].Chinese Journal of Geotechnical Engineering,2011,33(1):102-105.
[8]徐舜华,王兰民,孙军杰,等.含水量对黄土震陷性定量影响研究[J].西北地震学报,2010,32(1):30-35.XU S H,WANG L M,SUN J J,et al.Study on the influence of water content to subsidence characters ofloess[J].Northwestern Seismological Journal,2010,32(1):30-35.
[9]徐舜华,王兰民,袁中夏.黄土震陷初判指标的界定研究[J].西北地震学报,2006,28(2):140-143.XU S H,WANG L M,YUAN Z X.Study on initial judging criterions of loess seismic subsidence[J].Northwestern Seismological Journal,2006,28(2):140-143.
[10]邓津,王兰民,张振中.黄土显微结构特征与震陷性[J].岩土工程学报,2007,29(4):542-548.DENG J,WANG L M,ZHANG Z Z.Microstructure characteristics and seismic subsidence of loess[J].Chinese Journal of Geotechnical Engineering,2007,29(4):542-548.
[11]孙军杰,王强,王兰民.非饱和黄土震陷力学机制与主导影响因素[J].西北地震学报,2011,33(增刊):71-76.SUN J J,WANG Q,WANG L M.Study on the physical-mechanical mechanism and dominant influence factors of unsaturated loess subsidence under seismicloading[J].Northwestern Seismological Journal,2011,33(Sup):71-76.
[12]孙俊杰,王兰民,邱仁东,等.基于物理力学机制的黄土震陷数学估算模型[J].工程力学,2012,29(5):53-60.SUN J J,WANG L M,QIU R D,et al.A mathematical estimation model for seismic subsidence of loess based on physical-mechanical mechanism[J].Engineering Mechanics,2012,29(5):53-60.