循环荷载下饱和软黏土的动骨干曲线模型研究
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摘要
通过饱和软黏土室内不排水动三轴试验,研究了循环周次和动应力幅值对土体动力特性的影响。结果表明,在循环荷载作用下,随着循环周次的增加,土体均存在不同程度的刚度软化现象。根据动应力幅值大小的不同,循环荷载作用下饱和软黏土的动应变发展形态可分为3种类型:稳定型、破坏型和临界型。根据动应力-应变关系曲线特点,提出了含动应力幅值、固结围压和循环周次等影响因素的动骨干曲线模型。该模型所得的拟合值与试验值比较吻合。与传统骨干曲线模型相比,该模型能够体现土体在循环荷载作用下的刚度软化特性,更加切合实际。
To investigate the influence factors of the soil dynamic properties under cyclic loading,a series of undrained dynamic triaxial tests are conducted at different cyclic stress levels,cycle numbers and confining pressures. The test results show that while being subjected to cyclic loading,the soil's stiffness softening occurs more or less when the cycle number increase. There are three types of double amplitude strain of saturated soft clay under cyclic loading with different dynamic stress levels,such as stable type,destructive type and critical type. A new backbone curve model concerning cycle number,confining pressure,and cyclic stress level,is constructed to consider the stiffness softening feature of remoulded soil subjected to cyclic loading. Compared with the traditional backbone curve model,the simulative results computed from the dynamic backbone curve model,which can reflect the phenomenon of stiffness softening feature of soil,agree well with the experimental data.
To investigate the influence factors of the soil dynamic properties under cyclic loading,a series of undrained dynamic triaxial tests are conducted at different cyclic stress levels,cycle numbers and confining pressures. The test results show that while being subjected to cyclic loading,the soil's stiffness softening occurs more or less when the cycle number increase. There are three types of double amplitude strain of saturated soft clay under cyclic loading with different dynamic stress levels,such as stable type,destructive type and critical type. A new backbone curve model concerning cycle number,confining pressure,and cyclic stress level,is constructed to consider the stiffness softening feature of remoulded soil subjected to cyclic loading. Compared with the traditional backbone curve model,the simulative results computed from the dynamic backbone curve model,which can reflect the phenomenon of stiffness softening feature of soil,agree well with the experimental data.
引文
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[2]吴世明,周健,杨挺.土动力学理论与计算[M].北京:中国建筑工业出版社,2001.
[3]YASUHARA K,MURAKAMI S,SONG B W,et al.Postcyclic degradation of strength and stiffness for low plasticity silt[J].Journal of Geotechnical and Geoenvironmental Engineering,ASCE,2003,129(8):756-769.
[4]MATSUI T,BAHR M,ABE N.Estimation of shear characteristic degradation and stress-strain relationship of satuarated clays after cyclic loading[J].Soils and Foundations,1992,32(1):161-172.
[5]周建,龚晓南.循环荷载作用下饱和软黏土应变软化研究[J].土木工程学报,2000,32(5):62-68.ZHOU Jian,GONG Xiao-nan.Study on strain soften in saturated soft clay under cyclic loading[J].China Civil Engineering Journal,2000,32(5):62-68.
[6]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 dynamics and geotechnical earthquake engineering[J].Journal of Hohai University,1999,27(1):6-15.
[7]HARDIN B O,DRNEVICH V P.Shear modulus and damping in soil measurement and parameter effect[J].Journal of the Soil Mechanics and Foundation Engineering Division,1972,98(6):603-624.
[8]RAMBERG W,OSGOOD W R.Description of stress strain curves by three parameters[R].Washington D C:National Advisory Committee for Aeronautics,Technical Note902,1943.
[9]唐益群,黄雨,叶为民,等.地铁列车荷载作用下隧道周围土体的临界动应力比和动应变分析[J].岩石力学与工程学报,2003,22(9):1566-1570.TANG Yi-qun,HUANG Yu,YE Wei-min,et al.Critical dynamic stress ratio and dynamic strain analysis of soils around the tunnel under subway train loading[J].Chinese Journal of Rock Mechanics and Engineering,2003,22(9):1566-1570.
[10]徐干成,谢定义,郑颖人.饱和砂土循环动应力-应变特性的弹塑性模拟研究[J].岩土工程学报,1995,17(2):1-12.XU Gan-cheng,XIE Ding-yi,ZHENG Ying-ren.Elastoplastic modeling for cyclic stress strain behaviour of saturated sands[J].Chinese Journal of Geotechnical Engineering,1995,17(2):1-12.
[11]TATSUOKA F.Some recant developments in triaxial systems for cohessionless soils[M].Philadelphia:ASTM Special Technical Publication,1988.
[12]中华人民共和国水利部.SL237-1999土工试验规程[S].北京:中国水利水电出版社,1999.
[13]周建.循环荷载作用下饱和软黏土特性研究[D].杭州:浙江大学,1998.
[14]张勇.武汉软黏土的变形特征与循环荷载动力响应研究[D].武汉:中国科学院武汉岩土力学研究所,2008.
[15]蔡英,曹新文.重复加载下路基填土的临界动应力和永久变形初探[J].西南交通大学学报,1996,31(1):1-5.CAI Ying,CAO Xin-wen.Study of the critical dynamic stress and permanent strain of the subgrade-soil under the repeated load[J].Journal of Southwest Jiaotong University,1996,31(1):1-5.
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