双向循环荷载下饱和软黏土变形特性的试验研究
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摘要
利用GDS双向振动仪进行不排水三轴试验。循环荷载分别被简化成单向(轴向)正弦波和双向(轴向和径向)正弦波形式。对比研究径向振动对萧山软黏土变形特性和循环强度的影响;给出不同轴向循环应力幅值和不同径向循环应力比(径向应力幅值与轴向应力幅值之比)情况下的轴向应力-振次曲线。研究表明:在变形发展初期,不同径向循环应力比的应变曲线比较接近;随着应变的增大,应变曲线之间的差别越来越大;且径向循环应力比越大,轴向应变发展越快;轴向循环应力越大,不同径向循环应力比的应变曲线之间的差异越大;将5%定义为破坏应变,给出不同径向循环应力比的动强度曲线;双向循环荷载作用下的循环强度曲线要比单向循环荷载作用下的曲线低,但是,当径向循环应力比超过0.5时,不同循环强度曲线之间的差别非常小;径向循环应力对最小极限循环强度的影响非常小,因此双向循环荷载作用下的最小极限循环强度值可以用单向循环荷载作用下的结果代替。
An undrained triaxial test was designed using GDS bidirectional dynamic testing system.The cyclic loading was simplified as unidirectional(axial) and bidirectional(axial and radial) sine wave.And the effect of radial cyclic loading on deformation behavior and cyclic strength of Xiaoshan soft clay was studied.The curves of axial strain against number of cycles for different axial cyclic stresses and radial cyclic stress ratios(the ratio of radial stress amplitude against axial stress amplitude) were presented.It is found that the strain curves for different radial stress ratios are close at the beginning of strain.But the difference between curves is bigger and bigger with the strain's increasing.The higher the radial cyclic stress ratio is,the faster the axial strain develops.And for a higher axial cyclic stress the difference between axial strain curves for different radial stress ratios is bigger.Taking 5% as the failure strain,the cyclic strength curves for different radial cyclic stress ratios were presented.It is shown that the cyclic strength curves under bidirectional cyclic loading are lower than that under unidirectional cyclic loading.But the difference between strength curves is small when the radial cyclic stress ratio is higher than 0.5.And its effect on the minimum limit cyclic strength is very weak;therefore the minimum limit cyclic strength under bidirectional cyclic loading can be substituted by that under unidirectional loading.
An undrained triaxial test was designed using GDS bidirectional dynamic testing system.The cyclic loading was simplified as unidirectional(axial) and bidirectional(axial and radial) sine wave.And the effect of radial cyclic loading on deformation behavior and cyclic strength of Xiaoshan soft clay was studied.The curves of axial strain against number of cycles for different axial cyclic stresses and radial cyclic stress ratios(the ratio of radial stress amplitude against axial stress amplitude) were presented.It is found that the strain curves for different radial stress ratios are close at the beginning of strain.But the difference between curves is bigger and bigger with the strain's increasing.The higher the radial cyclic stress ratio is,the faster the axial strain develops.And for a higher axial cyclic stress the difference between axial strain curves for different radial stress ratios is bigger.Taking 5% as the failure strain,the cyclic strength curves for different radial cyclic stress ratios were presented.It is shown that the cyclic strength curves under bidirectional cyclic loading are lower than that under unidirectional cyclic loading.But the difference between strength curves is small when the radial cyclic stress ratio is higher than 0.5.And its effect on the minimum limit cyclic strength is very weak;therefore the minimum limit cyclic strength under bidirectional cyclic loading can be substituted by that under unidirectional loading.
引文
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[2]陈云敏,陈仁朋,芦森.软土地基地铁施工及运营过程中的几个土力学问题[C]//城市地铁建设与环境岩土工程高级技术论坛论文集.杭州,2002:165-177(Chen Yunmin,Chen Renpeng,Lu Sen.Several soil mechanics problems inmetro construction and operation on soft clay foundation[C]//Proceedings of Seminar on Metro Construction andEnvironmental Geotechnical Engineering.Hangzhou,2002:165-177(in Chinese))
[3]黄茂松,李进军,李兴照.饱和软黏土的不排水循环累积变形特性[J].岩土工程学报,2006,28(7):891-895(Huang Maosong,Li Jinjun,Li Xingzhao.Cumulativedeformation behaviour of soft clay in cyclic undrained tests[J].Chinese Journal of Geotechnical Engineering,2006,28(7):891-895(in Chinese))
[4]Ishihara K.Soil behavior in earthquake geotechnics[M].New York:Oxford University Press Inc.,1996
[5]Wang Changjing,Chen Yunmin,Wen Shiyou.Train-induced cyclic loads in an elastic half-space[C]//Proceedingsof the 5th Asia-Pacific Conference on Shock and ImpactLoads on Structures,2003:361-368
[6]王常晶,陈云敏.列车荷载在地基中引起的应力响应分析[J].岩石力学与工程学报,2005,24(7):1178-1186(Wang Changjing,Chen Yunmin.Analysis of train-inducedstresses in ground[J].Chinese Journal of Rock Mechanicsand Engineering,2005,24(7),1178-1186(in Chinese))
[7]Chen Y M,Wang C J,Chen R P,et al.Characteristics ofstresses and settlement of ground induced by train[C]//Environmental Vibration Prediction,Monitoring andEvaluation.Okayama,2005:33-42
[8]王常晶.列车移动荷载作用下地基的动应力及饱和软粘土特性研究[D].杭州:浙江大学,2006
[9]TowhataI,IshiharaK.Undrained strength ofsand undergoingcyclic rotation of principal stress axes[J].Soils andFoundations,1985,25(2):135-147
[10]沈扬,周建,龚晓南,等.考虑主应力方向变化的原状软黏土应力应变性状试验研究[J].岩土力学,2009,30(12):3720-3726(Shen Yang,Zhou Jian,Gong Xiao-nan,et al.Experimental study of stress-strain properties ofintact soft clay considering the change of principal stressdirection[J].Rock and Soil Mechanics,2009,30(12):3720-3726(in Chinese))
[11]郭莹,栾茂田,何杨,等.主应力轴持续旋转条件下饱和松砂的振动孔隙水压力特性[J].地震工程与工程振动,2007,27(3):156-162(Guo Ying,Luan Maotian,He Yang,et al.Dynamic pore water pressure behavior forsaturated loose sand under condition of continuous rotationin principal stress direction[J].Journal of EarthquakeEngineering and Engineering Vibration,2007,27(3):156-162(in Chinese))
[12]蔡袁强,王军,海钧.双向激振循环荷载作用下饱和软黏土强度和变形特性研究[J].岩石力学与工程学报,2008,27(3):495-504(Cai Yuanqiang,Wang Jun,Hai Jun.Study on strength and deformation behaviors ofsoft clay under bidirectional exciting cyclic loading[J].Chinese Journal of Rock Mechanics and Engineering,2008,27(3):495-504(in Chinese))
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