超固结土三轴率敏性特性及影响因素分析
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摘要
为建立超固结土的弹黏塑性本构模型并预测其长期变形,研究土体不同应力历史的时间相依变形特性,采用土体率敏性三轴试验,对预加800k Pa有效应力历史的饱和黏土开展不同加载速率下的三轴剪切试验,并通过改变有效围压(50,100,200和400kPa)、细砂含量(占比0%,10%和20%)和加载速率(0.5625%/min,0.037 5%/min和0.002 5%/min)等方式,深入探讨超固结比、黏性以及应变速率对土体变形特征的影响,引入能通过试验测定的应变率参数ρ来表征黏土率敏性大小。试验结果表明:归一化不排水抗剪强度随超固结比(OCR)单调递增;随着OCR的增大,土体剪胀软化越明显;应变速率与土体的抗剪强度呈半对数线性关系;随着含砂的降低,土体的黏性增大,剪胀软化也越明显;率敏性随超固结比的增大而增强,土体黏性越大率敏性就越显著。
In order to establish an elasto-viscoplasticity constitutive model and predict its long-term deformation of over-consolidated clay, their time-dependent deformation characteristics with different stress history needed to be investigated by the rate-dependent triaxial shear test, which is a very effective method to measure timedependent deformation. The undrained triaxial shear compression tests were performed on saturated clay with an effective stress history of pre-stressing confining pressure of 800 kPa, and the influence of over-consolidated ratio, strain rate, and viscosity on mechanics characteristics of saturation remolded clay was investigated by changing confining pressure of 50, 100, 200, and 400 kPa, and sand content of 0%, 10%, and 20%, and strain rate of 0.562 5%/min, 0.0375%/min and 0.002 5%/min, respectively. The strain rate parameter ρ determined by the tests was chosen to indicate the strain rate sensitivity. The experimental result shows that: normalized undrained shear strength increases monotonously with over-consolidation ratio; dilatancy and softening property of clay becomes more obvious with the increase of over-consolidated ratio; strain rate shows a half logarithm linear relationship with shear strength of clay; when viscosity of clay increases with the decrease of sand content, dilatancy and softening property of clay also becomes more obvious; rate sensitivity of clay is enhanced with the increase of over consolidation ratio, and it also becomes more obvious with higher viscosity.
In order to establish an elasto-viscoplasticity constitutive model and predict its long-term deformation of over-consolidated clay, their time-dependent deformation characteristics with different stress history needed to be investigated by the rate-dependent triaxial shear test, which is a very effective method to measure timedependent deformation. The undrained triaxial shear compression tests were performed on saturated clay with an effective stress history of pre-stressing confining pressure of 800 kPa, and the influence of over-consolidated ratio, strain rate, and viscosity on mechanics characteristics of saturation remolded clay was investigated by changing confining pressure of 50, 100, 200, and 400 kPa, and sand content of 0%, 10%, and 20%, and strain rate of 0.562 5%/min, 0.0375%/min and 0.002 5%/min, respectively. The strain rate parameter ρ determined by the tests was chosen to indicate the strain rate sensitivity. The experimental result shows that: normalized undrained shear strength increases monotonously with over-consolidation ratio; dilatancy and softening property of clay becomes more obvious with the increase of over-consolidated ratio; strain rate shows a half logarithm linear relationship with shear strength of clay; when viscosity of clay increases with the decrease of sand content, dilatancy and softening property of clay also becomes more obvious; rate sensitivity of clay is enhanced with the increase of over consolidation ratio, and it also becomes more obvious with higher viscosity.
引文
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[2]Casagrande A,Wilson S D.Effect of rate of loading on the strength of clays and shales at constant water content[J].Geotechnique,1951,2(3):251-263.
[3]Bjerrum L.Engineering geology of Norwegian normally consolidated marine clays as related to settlements of buildings[J].Geotechnique,1967,49(5):83-118.
[4]Vaid Y P,Campanella R G.Time-dependent behavior of undisturbed clays[J].Journal of the Geotechnical Engineering Division,ASCE,1977,103(7):693-709.
[5]姜洪伟,赵锡宏.剪切速率对各向异性不排水抗剪强度的影响分析[J].同济大学学报(自然科学版),1997,25(4):390-395.JIANG Hongwei,ZHAO Xihong.Analysis of the shearing rate effect on anisotropic undrained strength of clays[J].Journal of Tongji University(Natural Science),1997,25(4):390-395.
[6]Graham J,Crooks J H A,Bell A L.Time effects on the stress-strain behavior natural soft clays[J].Geotechnique,1983,33(3):327-340.
[7]Adachi T,Oka F.Constitutive equations for normally consolidated clay based on elasto-viscoplasticity[J].Soils and Foundations,1982,22(4):57-70.
[8]Tint K S,Kim Y S,Seo I S,et al.Shear behavior of over consolidated nakdong river sandy silt[J].Journal of Civil Engineering,2007,11(5):233-241.
[9]Askarani K K,Pakbaz M S.Drained shear strength of over consolidated compacted soil-cement[J].Journal of Materials in Civil Engineering,2016,28(5):1-7.
[10]武朝军,叶冠林,王建华.上海莲花路浅部土层超固结特性试验研究[J].上海交通大学学报,2016,50(3):331-335.WU Chaojun,YE Guanlin,WANG Jianhua.Experimental study of overconsolidation behavior of the upper Shanghai clays in Lianhua road[J].Journal of Shanghai Jiaotong University,2016,50(3):331-335.
[11]王智超,金刚,吴晓峰,等.非饱和压实土率相关变形特征与时效模型[J].岩土力学,2016,37(3):719-727.WANG Zhichao,JIN Gang,WU Xiaofeng,et al.Ratedependent deformation characteristics and timedependent constitutive model of unsaturated compacted clay[J].Rock and Soil Mechanics,2016,37(3):719-727.
[12]Mitachi T S,Tago S.Change in undrained shear strength characteristics of saturated remouded clay due to swelling[J].Soils and Foundations,1976,16(1):45-58.
[13]Ladd C C,Foott R.Stress-deformation and strength characteristics[C]//In Proceedings of the 9th International Conference on Soil Mechanices and Foundation Engineering,Tokyo,1977,2:421-494.
[14]Alberoo J,Santoyo E.Long term behavior of Mexico City clay[C]//Proceedings of the 8th International Conference on Soil Mechanics and Foundation Engineering,Moscow,1973,1:1-9.
[15]ZHU J G,YIN J H.Strain-rate-dependent stress-strain behavior of over consolidated Hongkong marine clay[J].Canadian Geotechnical Journal,2000,37(6):1272-1282.
[16]李建中,彭芳乐.描述黏土黏塑性的新参数[J].岩石力学与工程学报,2005,24(5):859-863.LI Jianzhong,PENG Fangle.New parameters to describe viscoplastic property of clay[J].Chinese Journal of Rock Mechnics and Engineering,2005,24(5):859-863.