下蜀土边坡地震稳定性的大型振动台试验研究(Ⅱ)——试验结果及分析
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摘要
选用天然下蜀土,设计并完成了一几何相似常数为20、坡高为0.5 m、坡角为45°的模型边坡1 g大型振动台试验,通过对模型边坡动力特性、动力反应及宏观变形等三方面的研究,揭示了下蜀土边坡的地震反应机理。试验结果表明,下蜀土边坡有着稳定的一、二阶自振频率和阻尼比,随着地震动加载幅值(PGA)逐渐增大,其一阶自振频率逐渐减小,一阶阻尼比逐渐增大;坡高范围内,PGA放大系数均大于1,且自下而上逐渐增大,并在坡肩处达到最大,其在坡脚处的值小于水平方向其他位置处的值,输入El Centro波(经时间相似常数4.47压缩)时的值分别大于输入El Centro原波和Kobe波(经时间相似常数4.47压缩)时的值;随着输入PGA的增大,土体非线性特征逐渐增强,边坡也逐渐趋于失稳破坏状态;震后模型边坡坡脚、坡顶等部位出现了不同程度的裂缝,说明边坡中出现了通过坡脚的(潜在)滑动面。
Using natural Xiashu loess,a 1g large-scale shaking table model test with a scaling factor of 20 for a model slope with a height of 0.5 m and slope angle of 45°was carried out,and the mechanism of seismic behavior of Xiashu loess slopes was studied by means of investigating the dynamic properties,dynamic responses,and macroscopic deformations of the model slope.The experimental results showed that stable first and second order mode fundamental frequencies and damping ratios existed in Xiashu loess slopes,and that the first order mode fundamental frequency decreased gradually,while the first order mode damping ratio increased progressively with increasing input peak ground acceleration(PGA).The PGA amplification factors near the toe of the model slope were less than those at other positions in the horizontal direction, and the values with 4.47 scaled El Centro earthquake record input were greater than those with full El Centro earthquake record and 4.47 scaled Kobe earthquake record.The PGA values were all greater than 1 in the range of the height of the model slope.Moreover,they gradually increased from bottom to top and approached the maximal magnitude at the crest.With the increase of the input PGA,the nonlin-earity of the soil gradually enhanced,and the slope also gradually tended to be the state of being out of safety.A few fissures and cracks occurred at toe and crest of the model slope after a series of seismic loading, which indicated that a(potential) slip surface,where the dynamic shear modulus of the soil was somewhat reduced,could have initiated in the soil through the toe of the model slope.
Using natural Xiashu loess,a 1g large-scale shaking table model test with a scaling factor of 20 for a model slope with a height of 0.5 m and slope angle of 45°was carried out,and the mechanism of seismic behavior of Xiashu loess slopes was studied by means of investigating the dynamic properties,dynamic responses,and macroscopic deformations of the model slope.The experimental results showed that stable first and second order mode fundamental frequencies and damping ratios existed in Xiashu loess slopes,and that the first order mode fundamental frequency decreased gradually,while the first order mode damping ratio increased progressively with increasing input peak ground acceleration(PGA).The PGA amplification factors near the toe of the model slope were less than those at other positions in the horizontal direction, and the values with 4.47 scaled El Centro earthquake record input were greater than those with full El Centro earthquake record and 4.47 scaled Kobe earthquake record.The PGA values were all greater than 1 in the range of the height of the model slope.Moreover,they gradually increased from bottom to top and approached the maximal magnitude at the crest.With the increase of the input PGA,the nonlin-earity of the soil gradually enhanced,and the slope also gradually tended to be the state of being out of safety.A few fissures and cracks occurred at toe and crest of the model slope after a series of seismic loading, which indicated that a(potential) slip surface,where the dynamic shear modulus of the soil was somewhat reduced,could have initiated in the soil through the toe of the model slope.
引文
[1]陈新民,沈建,魏平,等.下蜀土边坡地震稳定性的大型振动台试验研究(Ⅰ)——模型试验设计[J].防灾减灾工程学报,2010,30(5):497-502. Chen X M,Shen J,Wei P,et al.Large-scale shaking table test of seismic stability of Xiashu loess slopes (Ⅰ):design of model test[J].Journal of Disaster Prevention and Mitigation Engineering,2010,30(5): 497-502.
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[2]沈建.下蜀土边坡地震稳定性的振动台试验研究[D].南京:南京工业大学,2009. Shen J.Research on the shaking table model test of the seismic stability of the Xiashu loess slopes[D]. Nanjing:Nanjing University of Technology,2009.
[3]The Regents of the University of California.Pacific Earthquake Engineering Research Center:NGA Database[EB/OL].http://peer.berkeley.edu/nga/ index.html,2005.
[4]Bray J D.Simplified seismic slope displacement procedures [C]//Earthquake Geotechnical Engineering,4th International Conference on Earthquake Geotechnical Engineering-Invited Lectures.Dordrecht,The Netherlands:Springer,2007.327-353.
[5]邓学晶.城市垃圾填埋场振动台模型试验与地震稳定性分析方法研究[D].大连:大连理工大学,2007. Deng X J.Shaking table test on seismically induced deformation mechanism and seismic stability evaluation of municipal waste landfills[D].Dalian:Dalian University of Technology,2007.
[6]GEO-SLOPE International Ltd.Dynamic modeling with QUAKE/W 2007(Third Edition)[M].Calgary, Alberta,Canada:GEO-SLOPE International Ltd, 2008.
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