地震P波和S波耦合的变围压动三轴试验模拟
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摘要
地震发生时,尤其是直下型地震发生时,P波对场地土体的作用不可忽略。通过变围压动三轴设备施加的特殊应力路径,模拟了P波和S波耦合对饱和软黏土动力特性的影响,即循环剪应力和循环正应力耦合对饱和软黏土动力特性的影响。试验结果表明:变围压动三轴试验得到的包括循环剪应力和循环正应力的应力路径可以较好地模拟P波和S波的耦合作用;循环剪应力和循环正应力的相位差对饱和软黏土的动强度有较大的影响,当相位差为180°时,土体的动强度最低,当相位差为0°时,动强度最高;随着循环正应力幅值的增大,土体的动应变发展速度与常规恒定围压动三轴试验下的动应变发展速度相比,差距逐渐增大。这些发现一方面表明强震过程中P波的作用不可忽略,另一方面表明,在某些情况下,常规恒定围压动三轴试验高估了饱和软黏土的动强度,对抗震设计不利。
In the earthquakes with high intensities,the effects of P-waves on the soil layers cannot be ignored.The coupling effects of S-waves and P-waves are simulated by the specific stress paths in the cyclic triaxial tests with cyclic confining pressure.The influences of the phase differences and ratios between cyclic shear stress and cyclic normal stress on the behavior of cyclic strain are studied.It is found that the specific stress paths which are composed of both cyclic shear stresses and cyclic normal stresses are appropriate to simulate the coupling effects of S-waves and P-waves.The phase difference strongly influences the cyclic strength of saturated clays,i.e.,when the phase angle is 180°,the cyclic strength is the lowest,and when the phase angle is 0°,the cyclic strength is the highest.With the increasing ratios,the development speeds of cyclic strain are becoming more different from the results of conventional cyclic triaxial tests.These findings indicate that the effects of P-waves are significant,and in some cases the conventional cyclic triaxial tests may overestimate the cyclic strength of saturated clays,which is adverse for aseismatic design.
In the earthquakes with high intensities,the effects of P-waves on the soil layers cannot be ignored.The coupling effects of S-waves and P-waves are simulated by the specific stress paths in the cyclic triaxial tests with cyclic confining pressure.The influences of the phase differences and ratios between cyclic shear stress and cyclic normal stress on the behavior of cyclic strain are studied.It is found that the specific stress paths which are composed of both cyclic shear stresses and cyclic normal stresses are appropriate to simulate the coupling effects of S-waves and P-waves.The phase difference strongly influences the cyclic strength of saturated clays,i.e.,when the phase angle is 180°,the cyclic strength is the lowest,and when the phase angle is 0°,the cyclic strength is the highest.With the increasing ratios,the development speeds of cyclic strain are becoming more different from the results of conventional cyclic triaxial tests.These findings indicate that the effects of P-waves are significant,and in some cases the conventional cyclic triaxial tests may overestimate the cyclic strength of saturated clays,which is adverse for aseismatic design.
引文
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[11]ISHIHARA K.Soil behavior in earthquake geotechnics[M].Oxford:Oxford Science Publications,1996.
[12]BOULANGER R W,SEED R B.Liquefaction of sand underbidirectional monotonic and cyclic loading[J].Journal ofGeotechnical Engineering,ASCE,1995,12:870-878.
[13]施明雄.多向振动下砂土动力特性试验研究[D].杭州:浙江大学,2005.(SHI Ming-xiong.Sand response tomulti-way dynamic loading[D].Hangzhou:ZhejiangUniversity,2005.(in Chinese))
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[15]HEYMSFIELD E.Two-dimensional scattering of SH wavesin a soil layer underlain with a sloping bedrock[J].SoilDynamics and Earthquake Engineering,2000,19(7):489-500.
[16]尤红兵,赵凤新,荣棉水.地震波斜入射时水平层状场地的非线性地震反应[J].岩土工程学报,2009,31(2):234-240.(YOU Hong-bing,ZHAO Feng-xin,RONG Mian-shui.Nonlinear seismic response of horizontal layered site due toinclined wave[J].Chinese Jounal of GeotechnicalEngineering,2009,31(2):234-240.(in Chinese))
[17]RASCOL E.Cyclic properties of sand:dynamic behavior forseismic applications[D].Lausanne:Swiss Federal Institute ofTechnology in Lausanne,2009.
[18]丁浩.地震波作用下饱和沙土动力特性研究[D].杭州:浙江大学,2010.(DING Hao.Experimental study of thedynamics of saturated sand subjected to incident seismicwaves[D].Hangzhou:Zhejiang University,2005.(in Chinese))
[19]SCHROEDER W L,SCHUSTER R L.Laboratory simulationof seismic activity in saturated sands[J].Vibration Effects ofEarthquakes on Soils and Foundations,ASTM,1968,450:57-58.
[2]THIERS G R,SEED H B.Cyclic stress-strain characteristicsof clays[J].Journal of Soil Mechanics and Foundations,1968,94(2):555-569.
[3]李小军.非线性场地地震反应分析方法的研究[D].哈尔滨:中国地震局工程力学研究所,1993.(LI Xiao-jun.Nonlinearmethod research of the earthquake response[D].Harbin:Institute of Engineering Mechanics of China EarthquakeAdministration,1993.(in Chinese))
[4]廖山河,陈清军,徐植信.SH波斜入射时土层的非线性响应分析[J].同济大学学报,1994,22(4):517-522.(LIAOShan-he,CHEN Qing-jun,XU Zhi-xin.Nonlinear responseanalysis of soils subjected to inclined SH waves[J].Journal ofTongji University,1994,22(4):517-522.(in Chinese))
[5]李山有,廖振鹏.地震体波斜入射情形下台阶地形引起的波形转换[J].地震工程与工程振动,2002,22(4):9-15.(LIShan-you,LIAO Zhen-peng.Wave-type conversion causedby a step topography subjected to inclined seismic bodywave[J].Earthquake Resistance Engineering,2002,22(4):9-15.(in Chinese))
[6]HARDIN B O,DRNEVIEH V R.Shear modulus and dampingin soils:design equations and curves[J].Journal of SoilMechanics and Foundation Division,ASCE,1972,98(SM7):667-692.
[7]ISHIHARA K,LYSMER J,YASUDA S,et al.Prediction ofliquefaction in sand deposits during earthquakes[J].Soils andFoundations,1976,16(1):1-15.
[8]ISHIHARA K.Simple method of analysis for liquefaction ofsand deposits during earthquakes[J].Soils and Foundations,1977,17(3):1-17.
[9]AMINI F,SAMA K M.Behavior of stratified sand-silt-gravelcomposites under seismic liquefaction conditions[J].SoilDynamics and Earthquake Engineering,1999,18:445-45.
[10]SEED H B,LDRISS I M.Simplified procedure for evaluatingsoil liquefaction potential[J].Journal of Soil Mechanics andFoundation Division,ASCE,1971,97(9):1249-1273.
[11]ISHIHARA K.Soil behavior in earthquake geotechnics[M].Oxford:Oxford Science Publications,1996.
[12]BOULANGER R W,SEED R B.Liquefaction of sand underbidirectional monotonic and cyclic loading[J].Journal ofGeotechnical Engineering,ASCE,1995,12:870-878.
[13]施明雄.多向振动下砂土动力特性试验研究[D].杭州:浙江大学,2005.(SHI Ming-xiong.Sand response tomulti-way dynamic loading[D].Hangzhou:ZhejiangUniversity,2005.(in Chinese))
[14]李山有,马强,韦庆海.地震体波斜入射下的断层台阶地震反应分析[J].地震研究,2005,28(3):277-281.(LIShan-you,MA Qiang,WEI Qing-hai.Seismic responseanalysis of fault step subjected to obliquely incident bodywaves[J].Journal of Seismological Research,2005,28(3):277-281.(in Chinese))
[15]HEYMSFIELD E.Two-dimensional scattering of SH wavesin a soil layer underlain with a sloping bedrock[J].SoilDynamics and Earthquake Engineering,2000,19(7):489-500.
[16]尤红兵,赵凤新,荣棉水.地震波斜入射时水平层状场地的非线性地震反应[J].岩土工程学报,2009,31(2):234-240.(YOU Hong-bing,ZHAO Feng-xin,RONG Mian-shui.Nonlinear seismic response of horizontal layered site due toinclined wave[J].Chinese Jounal of GeotechnicalEngineering,2009,31(2):234-240.(in Chinese))
[17]RASCOL E.Cyclic properties of sand:dynamic behavior forseismic applications[D].Lausanne:Swiss Federal Institute ofTechnology in Lausanne,2009.
[18]丁浩.地震波作用下饱和沙土动力特性研究[D].杭州:浙江大学,2010.(DING Hao.Experimental study of thedynamics of saturated sand subjected to incident seismicwaves[D].Hangzhou:Zhejiang University,2005.(in Chinese))
[19]SCHROEDER W L,SCHUSTER R L.Laboratory simulationof seismic activity in saturated sands[J].Vibration Effects ofEarthquakes on Soils and Foundations,ASTM,1968,450:57-58.
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