基于流动性的饱和砂砾土液化机理
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摘要
砂砾土的地震液化至今仍存较大的争议,相应的液化机理解释主要沿用传统的砂土液化分析思路和方法。利用动态圆柱扭剪仪开展了100 mm直径、3组典型级配(含砾量分别为37%,45%和60%)的饱和砂砾土试样循环动三轴实验。基于实验得到的应力–应变率关系曲线,定义了反应饱和砂砾土流动性的平均流动系数和流动性水平。实验发现,初始动应力比对不同含砾量下的平均流动系数–孔压比关系曲线无影响;相对密度越大、含砾量越大,饱和砂砾土的流动性水平越低;有效固结压力对饱和砂砾土平均流动系数–孔压比关系曲线的影响与含砾量相关。推测饱和砂砾土在循环荷载下的流动性由其粗粒接触状态和数量决定;粗粒间的接触在高孔压状态下不能顺利解除是饱和砂砾土与饱和细粒土抗液化性能的本质区别。提出的基于流动性的饱和砂砾土液化机理较好地解释了以上现象。
There is still much controversy over earthquake liquefaction of gravelly soils,and the mechanism explanation about earthquake liquefaction of saturated gravelly soils is similar to that of sand liquefaction. The cyclic dynamic triaxial experiments on some saturated gravel samples with 3 groups of typical gradations(gravel contents of 37%,45% and 65%) and the diameter of 100 mm are carried out by employing the dynamic hollow cylinder apparatus. Based on the relationship curves of the shear stress-strain rate from experimental results,an obvious phenomenon is discovered that the saturated gravelly soils possess the similar curve characteristics with the saturated sands. The curve shape is altered from the elliptical shape under low pore water pressure state to the dumbbell one under high pore water pressure state. According to this phenomenon,the average flow coefficient and fluidity level describing the flowing property of the saturated gravelly soils are defined. The influences of the initial dynamic stress ratio,effective consolidation pressure,relative dense and gravel content on the relationship curves between the average flow coefficient and the pore water pressure ratio are discovered and discussed. The experimental results show that the initial dynamic stress ratio has little effects on the relationship between the average flow coefficient and the pore water pressure ratio. The flow level of saturated gravelly soils decreases as the relative density or gravel content increases. The influences of effective consolidation pressure on the relationship curves between the average flow coefficient and the pore water pressure ratio are relative to the gravel content. It is conjectured that the fluidity of saturated gravelly soils under cyclic loading should be determined by the contact state and the scale between gravels in the soils. It might be the fundamental distinction between the anti-liquefaction performance of saturated gravelly soils and sands that the contact state between gravels can not be released favorably under high pore water pressure. A new mechanism of the liquefaction of the gravelly soils is proposed and used to interpret those phenomena mentioned above.
There is still much controversy over earthquake liquefaction of gravelly soils,and the mechanism explanation about earthquake liquefaction of saturated gravelly soils is similar to that of sand liquefaction. The cyclic dynamic triaxial experiments on some saturated gravel samples with 3 groups of typical gradations(gravel contents of 37%,45% and 65%) and the diameter of 100 mm are carried out by employing the dynamic hollow cylinder apparatus. Based on the relationship curves of the shear stress-strain rate from experimental results,an obvious phenomenon is discovered that the saturated gravelly soils possess the similar curve characteristics with the saturated sands. The curve shape is altered from the elliptical shape under low pore water pressure state to the dumbbell one under high pore water pressure state. According to this phenomenon,the average flow coefficient and fluidity level describing the flowing property of the saturated gravelly soils are defined. The influences of the initial dynamic stress ratio,effective consolidation pressure,relative dense and gravel content on the relationship curves between the average flow coefficient and the pore water pressure ratio are discovered and discussed. The experimental results show that the initial dynamic stress ratio has little effects on the relationship between the average flow coefficient and the pore water pressure ratio. The flow level of saturated gravelly soils decreases as the relative density or gravel content increases. The influences of effective consolidation pressure on the relationship curves between the average flow coefficient and the pore water pressure ratio are relative to the gravel content. It is conjectured that the fluidity of saturated gravelly soils under cyclic loading should be determined by the contact state and the scale between gravels in the soils. It might be the fundamental distinction between the anti-liquefaction performance of saturated gravelly soils and sands that the contact state between gravels can not be released favorably under high pore water pressure. A new mechanism of the liquefaction of the gravelly soils is proposed and used to interpret those phenomena mentioned above.
引文
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[10]TADASHI H,TAKAJI K,RYOUSUKE H.Undrained strength of gravelly soils with different particle gradations[C]//Proceeding of 13th World Conference on Earthquake Engineering.Vancouver,B.C.,Canada,2004.
[11]XENAKI V C,ATHANASOPOULOS G.A.Dynamic and liquefaction resistance of two soil materials in an eathfill dam-laboratory test results[J].Soil Dynamics and Earthquake Engineering,2008,28(8):605–620.
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[13]徐斌,孔宪京,邹德高,等.饱和砂砾料液化后应力与变形特性试验研究[J].岩土工程学报,2007,29(1):103–106.(XU Bin,KONG Xian-jing,ZOU De-gao,et al.Laboratory study on behaviour of static properties of saturated sand-gravel after liquefaction[J].Chinese Journal of Geotechnical Engineering,2007,29(1):103–106.(in Chinese))
[14]ISHIHARA K.Soil behavior in earthquake geotechnic[M].New York:Oxford University Press Inc,1996.
[15]王志华,周恩全,陈国兴,等.循环荷载下饱和砂土固-液相变特征[J].岩土工程学报,2012,34(9):1604–1610.(WANG Zhi-hua,ZHOU En-quan,CHEN Guo-xing,et al.Characteristics of solid-liquid phase change of saturated sands under cyclic loads[J].Chinese Journal of Geotechnical Engineering,2012,34(9):1604–1610.(in Chinese))
[16]陈国兴.岩土地震工程学[M].北京:科学出版社,2007.(CHEN Guo-xing.Geotechnical earthquake enigneering[M].Beijing:Science Press,2007.(in Chinese))
[2]刘惠珊,乔太平,王承春,等.场地的液化危害性[J].地震工程与工程振动,1984,4(4):69–78.(LIU Hui-shan,QIAO Tai-ping,WANG Cheng-chun,et al.Liquefaction risk evaluation during earthquakes[J].Earthquake Engineering and Engineering Vibration,1984,4(4):69–78.(in Chinese))
[3]YEGIAN M K,GHAHRAMAN V G,HARUTIUNYAN R N.Liquefaction and embankment failure case histories,1988Armenia earthquake[J].Journal of Geotechnical Engineering,ASCE,1994,120(3):581–596.
[4]HATANAKA M,UCHIDA A,OH-OKA H.Correlation between the liuefaction strengths of saturated sands obtained by in-situ freezing method and rotary-type triple tube method[J].Soils and Foundations.1995,35(2):67–75.
[5]袁晓铭,曹振中,孙锐,等.汶川8.0级地震液化特征初步研究[J].岩石力学与工程学报,2009,28(6):1288–1296.(YUAN Xiao-ming,CAO Zhen-zhong,SUN Rui,et al.Preliminary research on liquefaction characteristics of Wenchuan8.0 earthquake[J].Chinese Journal of Rock Mechanics and Engineering,2009,28(6):1288–1296.(in Chinese))
[6]BEZERRA F H R,DA FONDECA V P,VITA-FINZI C,et al.Liquefaction-induced structures in Quaternary alluvial gravels and gravelly sediments,NE Brazil[J].Engineering Geology,2005,76(3/4):191–208.
[7]KRINITZSKY E L,HYNES M E.The Bhuj,India,earthquake:lessons learned for earthquake safety of dams on alluvium[J].Engineering Geology,2002,66(3/4):163–196.
[8]EVANS M D,ZHOU S P.Liquefaction behavior of sand-gravel composites[J].Journal of Geotechnical Engineering,1995,121(3):287–298.
[9]HATANAKA M,UCHIDA A,OHARA J.liquefaction characteristics of a gravelly fill liquefied during the 1995Hyogo-Ken Nanbu Earthquake[J].Soils and Foundations,1997,37(3):107–115.
[10]TADASHI H,TAKAJI K,RYOUSUKE H.Undrained strength of gravelly soils with different particle gradations[C]//Proceeding of 13th World Conference on Earthquake Engineering.Vancouver,B.C.,Canada,2004.
[11]XENAKI V C,ATHANASOPOULOS G.A.Dynamic and liquefaction resistance of two soil materials in an eathfill dam-laboratory test results[J].Soil Dynamics and Earthquake Engineering,2008,28(8):605–620.
[12]王昆耀,常亚屏,陈宁.饱和砂砾料液化特性的试验研究[J].水利学报,2000(2):37–41.(WANG Kun-yao,CHANG Ya-ping,CHEN Ning.Experimental study on liquefaction characteristics of saturated sandy gravel[J].Journal of Hydraulic Engineering,2000(2):37–41.(in Chinese))
[13]徐斌,孔宪京,邹德高,等.饱和砂砾料液化后应力与变形特性试验研究[J].岩土工程学报,2007,29(1):103–106.(XU Bin,KONG Xian-jing,ZOU De-gao,et al.Laboratory study on behaviour of static properties of saturated sand-gravel after liquefaction[J].Chinese Journal of Geotechnical Engineering,2007,29(1):103–106.(in Chinese))
[14]ISHIHARA K.Soil behavior in earthquake geotechnic[M].New York:Oxford University Press Inc,1996.
[15]王志华,周恩全,陈国兴,等.循环荷载下饱和砂土固-液相变特征[J].岩土工程学报,2012,34(9):1604–1610.(WANG Zhi-hua,ZHOU En-quan,CHEN Guo-xing,et al.Characteristics of solid-liquid phase change of saturated sands under cyclic loads[J].Chinese Journal of Geotechnical Engineering,2012,34(9):1604–1610.(in Chinese))
[16]陈国兴.岩土地震工程学[M].北京:科学出版社,2007.(CHEN Guo-xing.Geotechnical earthquake enigneering[M].Beijing:Science Press,2007.(in Chinese))
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