土体弱化等级及其与地震动关联性初探
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摘要
本文采用统一观点,以地震下土体剪应变衰减为出发点,对土体弱化程度进行整体等级划分,采用简化理论模型,初步研究了土体不同弱化程度与地震动特征相对变化的关系。研究表明,土体的弱化程度可划分为低弱化、中等弱化、强弱化和流动破坏(液化)四个等级,土体低弱化和中等弱化状态下地表加速度的高频成分占优,而土体在强弱化和液化状态下地表加速度长周期成分显著占优;与未弱化相比,低弱化PGA变化很小,中等和强弱化的PGA增大,且强弱化下增大显著,而液化下PGA变化则不定;与未弱化相比,土层弱化下低频放大和高频滤波作用同时存在,但二者比例关系则依土体弱化程度和输入波而定;中等弱化下低频放大和高频滤波效应大略相同,强弱化低频放大作用大于高频滤波作用,而液化下对低频丰富输入波低频放大则十分显著;相对未弱化,土体弱化对高频滤波和低频放大比例关系的影响与对PGA放大效应的影响趋势一致。
Based on the shear strain attenuation under seismic loading,the subsoil softening extent is classified in a comprehensive view.Meanwhile,the correlation between soil softening classification and ground motion characteristics was preliminarily studied by using a theoretical model.The analytical results show that subsoil softening can be classified into low softening,medium softening,high softening and flow failure(liquefaction);high-frequency components predominantly exist in ground motions when the soil is low and medium softening;long-period components,by contrast,in ground motions are considerably dominating when soil is high softening or flow failure(liquefaction);comparing to non-softening,PGA changes little with respect to low softening subsoil,but increases with increasing extent of soil softening till high softening;PGA under liquefaction is unpredictable;comparing to non-softening,long-period amplification and high-frequency de-amplification effects both exists in ground motion,nevertheless their proportional relationship depends on the products of soil softening class and input seismic ground motions;long-period amplification effect is comparable to high-frequency de-amplification effect in medium softening soil but greater than high-frequency de-amplification effect in high softening soil;liquefaction can remarkably amplify long-period motion;comparing to non-softening,the influence of soil softening on the proportional relationship of long-period amplification effect and high-frequency de-amplification effect is consistent with that on PGA amplification effect.
Based on the shear strain attenuation under seismic loading,the subsoil softening extent is classified in a comprehensive view.Meanwhile,the correlation between soil softening classification and ground motion characteristics was preliminarily studied by using a theoretical model.The analytical results show that subsoil softening can be classified into low softening,medium softening,high softening and flow failure(liquefaction);high-frequency components predominantly exist in ground motions when the soil is low and medium softening;long-period components,by contrast,in ground motions are considerably dominating when soil is high softening or flow failure(liquefaction);comparing to non-softening,PGA changes little with respect to low softening subsoil,but increases with increasing extent of soil softening till high softening;PGA under liquefaction is unpredictable;comparing to non-softening,long-period amplification and high-frequency de-amplification effects both exists in ground motion,nevertheless their proportional relationship depends on the products of soil softening class and input seismic ground motions;long-period amplification effect is comparable to high-frequency de-amplification effect in medium softening soil but greater than high-frequency de-amplification effect in high softening soil;liquefaction can remarkably amplify long-period motion;comparing to non-softening,the influence of soil softening on the proportional relationship of long-period amplification effect and high-frequency de-amplification effect is consistent with that on PGA amplification effect.
引文
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[8]陈龙伟,袁晓铭,孙锐.水平场地地表位移简化理论解答[J].岩土力学,2010,31(12):3823-3828.CHEN Longwei,YUAN Xiaoming,SUN Rui.A simplified theoretical solution of displacement in horizontal liquefiable soil strata[J].Rock andSoil Mechnics,31(12):3823-3828.(in Chinese)
[9]陈龙伟,袁晓铭.求解液化土表位移两种简化理论模型的比较研究[J].地震工程与工程振动,2010,30(6):141-147.CHEN Longwei,YUAN Xiaoming.Comparison between two simplified theoretical models for calculating surface displacement on liquefiable sites[J].Journal of Earthquake Engineering and Engineering Vibration,2010,30(6):141-147.(in Chinese)
[10]廖振鹏.工程波动理论导引[M].北京:科学出版社,1996.
[11]Pease J W,O’Rourke T D.Seismic response of liquefaction sites[J].Journal of Geotechnical and Geoenvironmental Engineering,1997:37-45.
[2]Trifunac M D,Todorovska M I.Nonlinear soil response-1994 Northridge,California,Earthquake[J].Journal of Geotechnical Engineering,1996:725-735.
[3]Idriss I M.Earthquake ground motions at soft soil sites[C]//Proceedings:Second International Conference on Recent Advances in GeotechnicalEarthquake Engineering and Soil Dynamic,March,1991,St.Louis.
[4]Yu G,Anderson J G,Siddharthan R.On the characteristics of non-linear soil response[J].Bulletin of Seismological Society of The American,1994(83):218-244.
[5]Youd T L,Carter B L.Influence of soil softening and liquefaction on spectral acceleration[J].Journal of Geotechnical and GeoenvironmentalEngineering,2005:811-825.
[6]孙锐,袁晓铭.液化土层地震动特征分析[J].岩土工程学报,2004,26(5):684-690.SUN Rui,YUAN Xiaoming.Analysis on feature of surface ground motion for liquefied soil layer[J].Chinese Journal of Geotechnical Engineer-ing,2004,26(5):684-690.(in Chinese)
[7]孙锐,袁晓铭,陈龙伟,等.液化土层对地表位移谱的影响[J].世界地震工程,2009,25(3):1-7.SUN Rui,YUAN Xiaoming,CHEN Longwei,et al.Effect of liquefied soil layers on surface displacement spectra[J].World Earthquake Engi-neering,2009,25(3):1-7.(in Chinese)
[8]陈龙伟,袁晓铭,孙锐.水平场地地表位移简化理论解答[J].岩土力学,2010,31(12):3823-3828.CHEN Longwei,YUAN Xiaoming,SUN Rui.A simplified theoretical solution of displacement in horizontal liquefiable soil strata[J].Rock andSoil Mechnics,31(12):3823-3828.(in Chinese)
[9]陈龙伟,袁晓铭.求解液化土表位移两种简化理论模型的比较研究[J].地震工程与工程振动,2010,30(6):141-147.CHEN Longwei,YUAN Xiaoming.Comparison between two simplified theoretical models for calculating surface displacement on liquefiable sites[J].Journal of Earthquake Engineering and Engineering Vibration,2010,30(6):141-147.(in Chinese)
[10]廖振鹏.工程波动理论导引[M].北京:科学出版社,1996.
[11]Pease J W,O’Rourke T D.Seismic response of liquefaction sites[J].Journal of Geotechnical and Geoenvironmental Engineering,1997:37-45.
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