冻融循环作用下粉质黏土原位动剪切模量及其衰减特征
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摘要
根据深季节冻土区高速铁路周边土体实际工程状态,开展现场地震波扁铲侧胀试验和室内共振柱试验,结合现场土体刚度和室内刚度衰减规律,综合评价了冻融环境下粉质黏土原位刚度性状及衰减特征。结果表明:受冻融循环作用的影响,小应变条件下粉质黏土最大动剪切模量G_(max)由未经冻融时97.9 MPa降至53.6 MPa,最大衰减出现在冻融循环初期;经历循环后,土体归一化G/G_(max)-γ曲线出现上移,同等应变条件下,冻融循环后土体的G/G_(max)值较高;粉质黏土原位最大动剪切模量G_0显著高于室内最大动剪切模量G_(max)。说明取样、运输及制样等过程存在对土样的扰动作用,仅借助室内试验难于还原土体原位刚度特性;原位剪切模量随着冻融循环次数的增加而减小,冻融作用的影响随着应变的增大逐渐减弱,当应变超过工作应变γ_(DMT)时,可忽略冻融循环对土体动剪切模量的影响,根据工程实际应变范围和冻融作用合理选用土体刚度值是深季节冻土区工程设计的关键。
According to the actual soil state of geotechnical structures in deep seasonally frozen region, systematic in-situ seismic dilatometer tests and laboratory resonant column tests were conducted. The in-situ G-γ decay characteristics of silty clay were investigated based on the in-situ maximum shear modulus and laboratory decay characteristics. The results show that freezing and thawing cycles exert great impacts on the G-γ decay characteristics of silty clay. The maximum dynamic shear modulus G_(max) drops from 97.9 MPa to 53.6 MPa over successive freezing-thawing cycles. The maximum attenuation occurs in the prophase of cyclic freezing-thawing process. After several freeze-thaw cycles, the normalized G_(max)-γ curves shift upwards. The G/G_(max)-value of the specimens subjected to freezing and thawing cycles is relatively higher, which indicates that cyclic freezing and thawing can relieve the shear modulus decay. On the other hand, the in-situ dynamic shear modulus G_0 by in-situ SDMT was greater than the G_(max) from laboratory RCT. This is due to the soil disturbance during sampling and transportation, and suggests the necessity of in-situ tests. G_0 decreases with freezing and thawing cycles. Moreover, the influence of freezing and thawing decreases with shear strain and is negligible when the shear strain exceeds the working strain γ_(DMT). Rational selection of the value of soil modulus with the consideration of actual strain level and freezing-thawing is the key for the engineering design in deep seasonal frozen area.
According to the actual soil state of geotechnical structures in deep seasonally frozen region, systematic in-situ seismic dilatometer tests and laboratory resonant column tests were conducted. The in-situ G-γ decay characteristics of silty clay were investigated based on the in-situ maximum shear modulus and laboratory decay characteristics. The results show that freezing and thawing cycles exert great impacts on the G-γ decay characteristics of silty clay. The maximum dynamic shear modulus G_(max) drops from 97.9 MPa to 53.6 MPa over successive freezing-thawing cycles. The maximum attenuation occurs in the prophase of cyclic freezing-thawing process. After several freeze-thaw cycles, the normalized G_(max)-γ curves shift upwards. The G/G_(max)-value of the specimens subjected to freezing and thawing cycles is relatively higher, which indicates that cyclic freezing and thawing can relieve the shear modulus decay. On the other hand, the in-situ dynamic shear modulus G_0 by in-situ SDMT was greater than the G_(max) from laboratory RCT. This is due to the soil disturbance during sampling and transportation, and suggests the necessity of in-situ tests. G_0 decreases with freezing and thawing cycles. Moreover, the influence of freezing and thawing decreases with shear strain and is negligible when the shear strain exceeds the working strain γ_(DMT). Rational selection of the value of soil modulus with the consideration of actual strain level and freezing-thawing is the key for the engineering design in deep seasonal frozen area.
引文
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[12]蔡国军,刘松玉,童立元,等.基于SCPTU的软土最大剪切模量测试分析研究[J].岩土力学,2008,29(9):2556-2560.CAI Guojun,LIU Songyu,TONG Liyuan,et al.Evaluation of maximum shear modulus of soft clay from seismic piezocone tests(SCPTU)[J].Chinese Journal of Rock Mechanics and Engineering,2008,29(9):2556-2560.
[13]李晶晶,孔令伟,金磊.膨胀土原位剪切模量-剪应变衰减曲线与特征分析[J].岩石力学与工程学报,2017,36(4):1032-1039.LI Jingjing,KONG Lingwei,JIN Lei.In situ shear modulus and shear strain decay curves in expansive soils and the analysis of its characteristics[J].Chinese Journal of Rock Mechanics and Engineering,2017,36(4):1032-1039.
[14]周幼吾.中国冻土[M].北京:科学出版社,2000.
[15]LING X Z,ZHANG F,LI Q L,et al.Dynamic shear modulus and damping ratio of frozen compacted sand subjected to freeze-thaw cycle under multi-stage cyclic loading[J].Soil Dynamics&Earthquake Engineering,2015,76:111-121.
[16]常丹,刘建坤,李旭,等.冻融循环对青藏粉砂土力学性质影响的试验研究[J].岩石力学与工程学报,2014,33(7):1496-1502.CHANG Dan,LIU Jiankun,LI Xu,et al.Experiment study of effects of freezing-thawing cycles on mechanical properties of Qinghat-Tibet silty sand[J].Chinese Journal of Rock Mechanics and Engineering,2014,33(7):1496-1502.
[17]郑郧,马巍,邴慧.冻融循环对土结构性影响的试验研究及影响机制分析[J].岩土力学,2015,36(5):1282-1287.ZHENG Yun,MA Wei,BING Hui.Impact of freezing and thawing cycles on structure of soilsand its mechanism analysis by laboratory testing[J].Chinese Journal of Rock Mechanics and Engineering,2015,36(5):1282-1287.
[18]VUCETIC M.Cyclic threshold shear strains in soils[J].Journal of Geotechnical Engineering,1994,32(7):321.
[2]WICHTMANN T,TRIANTAFYLLIDIS T.Influence of the grain-size distribution curve of quartz sand on the small strain shear modulus Gmax[J].Journal of Geotechnical&Geoenvironmental Engineering,2009,135(10):1404-1418.
[3]JARDINE R J.Nonlinear stiffness parameters from undrained pressuremeter tests[J].Canadian Geotechnical Journal,2011,29(3):436-447.
[4]尹松,孔令伟,杨爱武,等.循环振动作用下残积土动力变形特性试验研究[J].振动与冲击,2017,36(11):224-231.YIN Song,KONG Lingwei,YANG Aiwu,et al.Tests for dynamic deformation characteristics of residual soil under cyclic loading[J].Journal of Vibration and Shock,2017,36(11):224-231.
[5]ATKINSON J H.Non-linear soil stiffness in routine design[J].Geotechnique,2000,50(5):487-508.
[6]李晶晶,孔令伟.应力历史影响下的膨胀土动力参数响应特征[J].振动与冲击,2017,36(12):181-188.LI Jingjing,KONG Lingwei.The influence of stress history on the dynamic parameters of expansive soils[J].Journal of Vibration and Shock,2017,36(12):181-188.
[7]ISHIHARA K.Soil behaviour in earthquake geotechnics[M].Oxford:Oxford Engineering Science,1996.
[8]LEHANE B,FAHEY M.Using SCPT and DMT data for settlement prediction in sand[C]//Proceedings of the 2nd International Conference on Site Characterization.Rotterdam:Millpress,2004.
[9]AMOROSO S,MONACO P,MARCHETTI D.Use of the seismic dilatometer(SDMT)to estimate in situ G-γdecay curves in various soil types[C]//Proceedings of the International Conference on Geotechnical and Geophysical Site Characterization 4.London:Taylor&Francis Group,2012.
[10]AMOROSO S,MONACO P,LEHANE B M,et al.Examination of the potential of the seismic dilatometer(SDMT)to estimate in situ stiffness decay curves in various soil types[J].Soils&Rocks,2014,37(3):177-194.
[11]PEPE G,COEN G,NAPOLEONI Q,et al.SDMT testing for the estimation of in situ G decay curves in soft alluvial and organic soils[C]//Proceedings of the 3rd International Conference on the Flat Diatometer.Rome:[s.n.],2015.
[12]蔡国军,刘松玉,童立元,等.基于SCPTU的软土最大剪切模量测试分析研究[J].岩土力学,2008,29(9):2556-2560.CAI Guojun,LIU Songyu,TONG Liyuan,et al.Evaluation of maximum shear modulus of soft clay from seismic piezocone tests(SCPTU)[J].Chinese Journal of Rock Mechanics and Engineering,2008,29(9):2556-2560.
[13]李晶晶,孔令伟,金磊.膨胀土原位剪切模量-剪应变衰减曲线与特征分析[J].岩石力学与工程学报,2017,36(4):1032-1039.LI Jingjing,KONG Lingwei,JIN Lei.In situ shear modulus and shear strain decay curves in expansive soils and the analysis of its characteristics[J].Chinese Journal of Rock Mechanics and Engineering,2017,36(4):1032-1039.
[14]周幼吾.中国冻土[M].北京:科学出版社,2000.
[15]LING X Z,ZHANG F,LI Q L,et al.Dynamic shear modulus and damping ratio of frozen compacted sand subjected to freeze-thaw cycle under multi-stage cyclic loading[J].Soil Dynamics&Earthquake Engineering,2015,76:111-121.
[16]常丹,刘建坤,李旭,等.冻融循环对青藏粉砂土力学性质影响的试验研究[J].岩石力学与工程学报,2014,33(7):1496-1502.CHANG Dan,LIU Jiankun,LI Xu,et al.Experiment study of effects of freezing-thawing cycles on mechanical properties of Qinghat-Tibet silty sand[J].Chinese Journal of Rock Mechanics and Engineering,2014,33(7):1496-1502.
[17]郑郧,马巍,邴慧.冻融循环对土结构性影响的试验研究及影响机制分析[J].岩土力学,2015,36(5):1282-1287.ZHENG Yun,MA Wei,BING Hui.Impact of freezing and thawing cycles on structure of soilsand its mechanism analysis by laboratory testing[J].Chinese Journal of Rock Mechanics and Engineering,2015,36(5):1282-1287.
[18]VUCETIC M.Cyclic threshold shear strains in soils[J].Journal of Geotechnical Engineering,1994,32(7):321.