循环剪切方向对饱和软黏土动静力特性的影响
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摘要
地震中土层运动是复杂的多维运动,土体遭受水平两方向的剪切作用,两方向剪切在大小和方向上相互耦合。针对上述问题,采用多向循环单剪系统(VDDCSS),研究循环剪切方向和剪应变幅值γ对软黏土剪切过程中剪切模量G和孔压u的影响。试验结果表明:由于土样的各向异性,不同方向的G是不同的;小γ下剪切作用会使下一次其他新方向的G稍微增大;大γ下剪切方向的变化会促进G的衰减(最多为单向剪切G衰减量的1.51倍),也会促进剪切过程中u的增大(最多为单向剪切u增加量的1.67倍);存在一个剪应变特征值γs,即当γ≤γs时,剪切作用会使其他新方向的G稍微增大,反之无此现象;剪切方向对G和u的影响程度随γ的增大而先增后减,剪切方向的变化极大地影响了循环孔压周期幅值uamp的发展;当0.1%<γ<2.0%时,再固结轴向变形△Hrc/H随γ的增大而增大,剪切方向使△Hrc/H在小γ下达到单向剪切时大γ时的值;当γ≥2.0%时,2种剪切方式下△Hrc/H趋于一致。
The ground motion in earthquake is a complex and multi-dimensional movement. The ground soil experiences the horizontal shearing in two directions with the shear directions and the magnitudes of the loading both coupling. The effect of cyclic shear direction and shear strain amplitude γ on the shear modulus G and the pore pressure u were therefore investigated to the saturated soft clay during the shear process and compression in the reconsolidation process with the VDDCSS system. The shear modulus G was found to be different in different directions due to the soil anisotropy. The shear test with small γ made G increased slightly in other directions. The changing of shear direction accelerated the declining of G(1.51 times of unidirectional attenuation of G) and promoted the development of u in the shear process(1.67 times of the increment of the unidirectional pore pressure u). The shear tests with γ greater than a value γs had no such phenomenon. The changing of shear direction influenced greatly the amplitude of pore pressure uamp. When 0.1%<γ <2.0%,the reconsolidation settlement △Hrc/H increased with the increasing of γ. The changing of shear direction promoted the △Hrc/H at the small γ and reached a value which was reached at the large γ in uni-directional shear;when γ ≥2.0%,the △Hrc/H under 2 kinds of shear-mode tended to be the same.
The ground motion in earthquake is a complex and multi-dimensional movement. The ground soil experiences the horizontal shearing in two directions with the shear directions and the magnitudes of the loading both coupling. The effect of cyclic shear direction and shear strain amplitude γ on the shear modulus G and the pore pressure u were therefore investigated to the saturated soft clay during the shear process and compression in the reconsolidation process with the VDDCSS system. The shear modulus G was found to be different in different directions due to the soil anisotropy. The shear test with small γ made G increased slightly in other directions. The changing of shear direction accelerated the declining of G(1.51 times of unidirectional attenuation of G) and promoted the development of u in the shear process(1.67 times of the increment of the unidirectional pore pressure u). The shear tests with γ greater than a value γs had no such phenomenon. The changing of shear direction influenced greatly the amplitude of pore pressure uamp. When 0.1%<γ <2.0%,the reconsolidation settlement △Hrc/H increased with the increasing of γ. The changing of shear direction promoted the △Hrc/H at the small γ and reached a value which was reached at the large γ in uni-directional shear;when γ ≥2.0%,the △Hrc/H under 2 kinds of shear-mode tended to be the same.
引文
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[18]王军,谷川,蔡袁强,等.动三轴试验中饱和软黏土的孔压特性及其对有效应力路径的影响[J].岩石力学与工程学报,2012,31(6):1 290–1 296.(WANG Jun,GU Chuan,CAI Yuanqiang,et al.Behavior of pore water pressure in dynamic triaxial tests of saturated soft clay and its effect on effective stress[J].Journal of Rock Mechanics and Engineering,2012,31(6):1 290–1 296.(in Chinese))
[19]LADE P V,KIRKGARD M M.Effects of stress rotation and changes of b-values on cross-anisotropic behavior of natural,K0-consolidated soft clay[J].Soils and Foundations,2000,40(6):93–105.
[20]VUCETIC M.Cyclic threshold shear strains in soils[J].Journal of Geotechnical Engineering,1994,120(12):2 208–2 228.
[21]HSU C C,VUCETIC M.Volumetric threshold shear strain for cyclic settlement[J].Journal of Geotechnical and Geoenvironmental Engineering,2004,130(1):58–70.
[22]HSU C C,VUCETIC M.Threshold shear strain for cyclic pore-water pressure in cohesive soils[J].Journal of Geotechnical and Geoenvironmental Engineering,2006,132(10):1 325–1 335.
[2]高玉峰,范昭平.多点、多向地震作用下非圆弧滑面边坡稳定分析通用条分法[J].岩土力学,2010,31(12):3 816–3 822.(GAO Yufeng,FAN Zhaoping.Generalized slice method for stability analysis of slope with non-circular slide face under multipoint and multidirection seismic ground motions[J].Rock and Soil Mechanics,2010,31(12):3 816–3 822.(in Chinese))
[3]柔洁,艾买提·乃买提.2005年2月15日新疆乌什6.2级地震的地震环境及强震加速度记录[J].国际地震动态,2005,(3):19–22.(ROU Jie,Aimaiti·Naimaiti.Seismic environment and acceleration record about the earthquake with Ms 6.2 in Wushi of Xinjiang,China on Feb.15,2005[J].Recent Developments in World Seismology,2005,(3):19–22.(in Chinese))
[4]张振斌,唐丽华,王宝柱.新疆伊犁州2次6级地震加速度记录特征对比分析[J].防灾科技学院学报,2013,14(4):84–91.(ZHANG Zhenbin,TANG Lihua,WANG Baozhu.Comparative analysis of seismic acceleration record characteristics of two earthquake in Yili,Xinjiang[J].Journal of Institute of Disaster Prevention,2013,14(4):84–91.(in Chinese))
[5]PYKE R M.Settlement and liquefaction of sands under multi-directional loading[Ph.D.Thesis][D].Berkeley:University of California,1973.
[6]PYKE R M,CHAN C K,SEED H B.Settlement of sands under multidirectional shaking[J].Journal of the Geotechnical Engineering Division,1975,101(4):379–398.
[7]ISHIHARA K,YAMAZAKI F.Cyclic simple shear tests on saturated sand in multi-directional loading[J].Soils and Foundations,1980,20(1):45–59.
[8]ISHIHARA K,NAGASE H.Multi-directional irregular loading tests on sand[J].Soil Dynamics and Earthquake Engineering,1988,7(4):201–212.
[9]BOULANGER R W,SEED R B.Liquefaction of sand under bidirectional monotonic and cyclic loading[J].Journal of Geotechnical Engineering,1995,121(12):870–878.
[10]LI X S.Rotational shear effects on ground earthquake response[J].Soil Dynamics and Earthquake Engineering,1997,16(1):9–19.
[11]KAMMERER A M,SEED R B,WU J,et al.Pore pressure development in liquefiable soils under bi-directional loading conditions[C]//Proceedings of the 11th International Conference of Soil Dynamics and Earthquake Engineering and the 3rd International Conference of Earthquake Geotechnical Engineering.NOGAMI T,SEED R B ed.Berkeley:[s.n.],2004:697–704.
[12]KAMMERER A,WU J,RIEMER M,et al.Shear strain development in liquefiable soil under bi-directional loading conditions[C]//Proceedings of the 13th World Conference on Earthquake Engineering.[S.l.]:[s.n.],2004:2 081.
[13]KAMMERER A M,PESTANA J M,SEED R B.Behavior of Monterey 0/30 sand under multi-directional loading conditions[C]//Geomechanics Testing,Modeling and Simulation,ASCE.[S.l.]:[s.n.],2005:154–173.
[14]DEGROOT D J,LADD C C,GERMAINE J T.Undrained multidirectional direct simple shear behavior of cohesive soil[J].Journal of Geotechnical Engineering,1996,122(2):91–98.
[15]MATSUDA H,SHINOZAKI H,OKADA N,et al.Effects of multi-directional cyclic shear on the post-earthquake settlement of ground[C]//The 13th World Conference on Earthquake Engineering.[S.l.]:[s.n.],2004:2 090.
[16]MATSUDA H,NHAN T T,ISHIKURA R.Excess pore water pressure accumulation and recompression of saturated soft clay subjected to uni-directional and multi-directional cyclic simple shears[J].Journal of Earthquake and Tsunami,2013,7(4):1250027-1–1250027-21.
[17]王军,蔡袁强,海钧.双向激振对饱和软黏土应力应变循环刚度软化的影响[J].水利学报,2008,39(9):1 083–1 091.(WANG Jun,CAI Yuanqiang,HAI Jun.Stiffness degradation of saturated soft clay under the action of bidirectional cyclic loading[J].Journal of Hydraulic Engineering,2008,39(9):1 083–1 091.(in Chinese))
[18]王军,谷川,蔡袁强,等.动三轴试验中饱和软黏土的孔压特性及其对有效应力路径的影响[J].岩石力学与工程学报,2012,31(6):1 290–1 296.(WANG Jun,GU Chuan,CAI Yuanqiang,et al.Behavior of pore water pressure in dynamic triaxial tests of saturated soft clay and its effect on effective stress[J].Journal of Rock Mechanics and Engineering,2012,31(6):1 290–1 296.(in Chinese))
[19]LADE P V,KIRKGARD M M.Effects of stress rotation and changes of b-values on cross-anisotropic behavior of natural,K0-consolidated soft clay[J].Soils and Foundations,2000,40(6):93–105.
[20]VUCETIC M.Cyclic threshold shear strains in soils[J].Journal of Geotechnical Engineering,1994,120(12):2 208–2 228.
[21]HSU C C,VUCETIC M.Volumetric threshold shear strain for cyclic settlement[J].Journal of Geotechnical and Geoenvironmental Engineering,2004,130(1):58–70.
[22]HSU C C,VUCETIC M.Threshold shear strain for cyclic pore-water pressure in cohesive soils[J].Journal of Geotechnical and Geoenvironmental Engineering,2006,132(10):1 325–1 335.
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