武汉深基坑施工动荷载诱发软土塑性应变研究
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摘要
随着城市建设的高速发展,武汉市深基坑机械施工振动荷载诱发软土层过大地面沉降和塑性变形已成为亟待解决的关键问题。针对施工过程中机械振动荷载和往复交通荷载引起的淤泥和淤泥质黏土地基长期沉降问题,考虑到软土的结构特性、触变性和小应变特征,采用室内三轴试验、共振柱试验,现场剪切波速测试、地脉动测试和十字板剪切试验综合分析软土在机械振动荷载和往复交通荷载条件下的沉降、变形机理。论文得出如下结论:高灵敏度淤泥和淤泥质黏土的不固结不排水剪切强度主要是黏聚强度,在振动荷载下,触变性增加;共振柱试验中,随着剪应变的增加,淤泥的共振频率f随之增大,动剪切模量G随之减小,阻尼比λ变化不明显;而淤泥质黏土的共振频率f和动剪切模量G随之减小,阻尼比?有增大的趋势;场地的剪切波速随地层的结构、强度和土层分布而变化;现场地脉动测试3个方向的共振频率均远小于共振柱测试的共振频率;最后,基于机械振动波在淤泥和淤泥质黏土中峰值加速度放大效应,提出修正现有软土塑性应变计算公式的建议。
With the rapid development of urban construction, the problems of ground subsidence and plastic deformation of soft clay under dynamic loading of deep foundation construction in Wuhan are urgent to be solved. Considering the issue of long-term ground settlement in the layers of silt and silty clay due to machinery vibration loading and repeated loading as well as the characteristics of structure, thixotropy and small strain of soft clay, the static triaxial test, resonant column test, field shear wave velocity test, ground micro-tremor test and vane shear test are taken to comprehensively analyze the mechanisms of ground subsidence and deformation under the machinery vibration loading and repeated loading. The test results show that the unconsolidated and undrained shear strengths are determined by the cohesive strengths of high-sensitivity silt and silty clay.The resonant frequency of the silt has a positive correlation with shear strain, but the dynamic shear modulus has a negative one.The resonant frequency and dynamic shear modulus of silty clay has a negative correlation with shear strain, but the damping ratio has a positive one. The filed shear wave velocity is determined by the structure, strength and distribution of soil stratum.The resonant frequency of three directions monitored by the ground micro-tremor test is much smaller than that of the resonant columns test. Based on the amplification effect of vibration wave peak acceleration in silt and silty clay, the formula for plastic strain of soft clay is suggested to be modified.
With the rapid development of urban construction, the problems of ground subsidence and plastic deformation of soft clay under dynamic loading of deep foundation construction in Wuhan are urgent to be solved. Considering the issue of long-term ground settlement in the layers of silt and silty clay due to machinery vibration loading and repeated loading as well as the characteristics of structure, thixotropy and small strain of soft clay, the static triaxial test, resonant column test, field shear wave velocity test, ground micro-tremor test and vane shear test are taken to comprehensively analyze the mechanisms of ground subsidence and deformation under the machinery vibration loading and repeated loading. The test results show that the unconsolidated and undrained shear strengths are determined by the cohesive strengths of high-sensitivity silt and silty clay.The resonant frequency of the silt has a positive correlation with shear strain, but the dynamic shear modulus has a negative one.The resonant frequency and dynamic shear modulus of silty clay has a negative correlation with shear strain, but the damping ratio has a positive one. The filed shear wave velocity is determined by the structure, strength and distribution of soil stratum.The resonant frequency of three directions monitored by the ground micro-tremor test is much smaller than that of the resonant columns test. Based on the amplification effect of vibration wave peak acceleration in silt and silty clay, the formula for plastic strain of soft clay is suggested to be modified.
引文
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[18]CHAI J,MIURA N.Traffic-load-induced permanent deformation of road on soft subsoil[J].Journal of Geotechnical and Geoenvironmental Engineering,2002,128(11):907–916.
[19]战吉艳,陈国兴,刘建达.深软场地大地震远场地震动反应特性分析[J].岩土力学,2011,32(增刊1):507–514.(ZHAN Ji-yan,CHEN Guo-xing,LIU Jian-da.Seismic response characteristics analysis of deep soft site under far-field ground motion of great earthquake[J].Rock and Soil Mechanics,2011,32(S1):507–514.(in Chinese))
[20]陈继华.新近沉积土动力性能及深软场地地震效应研究[D].南京:南京工业大学,2004.(CHEN Ji-hua.Study on dynamic behaviors of recently deposited soils and characteristics of site seismic effect for deep soft sites[D].Nanjing:Nanjing University of Technology,2004.(in Chinese))
[21]战吉艳,陈国兴,刘建达,等.远场大地震作用下大尺度深软场地的非线性地震效应分析[J].岩土力学,2013,34(11):3229–3238.(ZHAN Ji-yan,CHEN Guo-xing,LIU Jian-da,et al.Analysis of nonlinear seismic effects of large-scale deep soft site under far-field large earthquake[J].Rock and Soil Mechanics,2013,34(11):3229–3238.(in Chinese))
[2]冯晓腊.论深圳淤泥类软土微观结构对工程性质的影响[J].中国地质灾害与防治学报,1996,7(3):34–39.(FENG Xiao-la.Study on the effect of mucky soil microstructure on engineering properties in Shenzhen[J].The Chinese Journal of Geological Hazard and Control,1996,7(3):34–39.(in Chinese))
[3]杨顺安,冯晓腊,张聪辰.软土理论与工程[M].北京:地质出版社,2000.(YANG Shun-an,FENG Xiao-la,ZHANG Cong-chen.Theory and engineering of soft soil[M].Beijing:Geological Publishing House,2000.(in Chinese))
[4]王超.内陆河湖相软土区划及鉴别指标研究[D].西安:长安大学,2012.(WANG Chao.Study on the regionalization and identification index of the inland fluvial-lacustrine soft soil[D].Xi'an:Chang'an University,2012.(in Chinese))
[5]胡聿贤.地震工程学[M].北京:地震出版社,2006.(HUYu-xian.Earthquake engineering[M].Beijing:Earthquake Press,2006.(in Chinese))
[6]ANDREASSON B.Deformation characteristics of soft,high-plastic clays under dynamic loading conditions[D].Sweden:Chalmers University of Technology,1979.
[7]WOODS R D.Measurement of dynamic soil properties[C]//From Volume I of Earthquake Engineering and Soil Dynamics-Proceedings of the ASCE Geotechnical Engineering Division Specialty Conference.Pasadena,California,1978.
[8]ANDERSON D G,RICHART JR F E.Effects of stratining on shear modulus of clays[J].Journal of Geotechnical and Geoenvironmental Engineering,1976,102(GT9):975–987.
[9]周燕国.土结构性的剪切波速表征及对动力特性的影响[D].杭州:浙江大学,2007.(ZHOU Yan-guo.Shear wave velocity-based characterization of soil structure and its effects on dynamic behavior[D].Hangzhou:Zhejiang University,2007.(in Chinese))
[10]周锡元,王广军,苏经宇.场地分类和平均反应谱[J].岩土工程学报,1984,6(5):59–68.(ZHOU Xi-yuan,WANG Guang-jun,SU Jing-yu.Site classification and average response spectra[J].China Journal of Geotechnical Engineering,1984,6(5):59–68.(in Chinese))
[11]孙锐,袁晓铭,刘晓键.动剪切模量比与剪切波速对地震动影响及等量关系研究[J].岩土工程学报,2009,31(8):1267–1274.(SUN Rui,YUAN Xiao-ming,LIU Xiao-jian.Effects of dynamic shear modulus ratio and velocity on surface ground motion and their equivalent relations[J].Chinese Journal of Geotechnical Engineering,2009,31(8):1267–1274.(in Chinese))
[12]李进军,黄茂松,王育德.交通荷载作用下软土地基累积塑性变形分析[J].中国公路学报,2006,19(1):1–5.(LI Jin-jun,HUANG Mao-song,WANG Yu-de.Analysis of cumulative plastic deformation of soft clay foundation under traffic loading[J].China Journal of Highway and Transport,2006,19(1):1–5.(in Chinese))
[13]李西斌,贾献林.交通荷载作用下软土路基沉降有限元分析[J].福州大学学报(自然科学版),2008,36(4):604–609.(LI Xi-bin,JIA Xian-lin.Finite element analysis of the settlement of the soft roadbed under traffic load[J].Journal of Fuzhou University(Natural Science),2008,36(4):604–609.(in Chinese))
[14]CUI X,ZHANG N,ZHANG J,et al.In situ tests simulating traffic-load-induced settlement of alluvial silt subsoil[J].Soil Dynamics and Earthquake Engineering,2014,58:10–20.
[15]MONISMITH C L,OGAWA N,FREEME C R.Permanent deformation characteristics of subgrade soils due to repeated loading[J].Transportation Research Record,1975(537):1–17.
[16]LI D,SELIG E T.Cumulative plastic deformation for fine-grained subgrade soils[J].Journal of Geotechnical Engineering,1996,122(12):1006–1013.
[17]唐大雄.对我国统一土质分类的建议[J].长春地质学院学报,1990,20(1):79–88.(TANG Da-xiong.A proposal concerning unified classification system of soil in China[J].Journal of Changchun University of Earth Science,1990,20(1):79–88.(in Chinese))
[18]CHAI J,MIURA N.Traffic-load-induced permanent deformation of road on soft subsoil[J].Journal of Geotechnical and Geoenvironmental Engineering,2002,128(11):907–916.
[19]战吉艳,陈国兴,刘建达.深软场地大地震远场地震动反应特性分析[J].岩土力学,2011,32(增刊1):507–514.(ZHAN Ji-yan,CHEN Guo-xing,LIU Jian-da.Seismic response characteristics analysis of deep soft site under far-field ground motion of great earthquake[J].Rock and Soil Mechanics,2011,32(S1):507–514.(in Chinese))
[20]陈继华.新近沉积土动力性能及深软场地地震效应研究[D].南京:南京工业大学,2004.(CHEN Ji-hua.Study on dynamic behaviors of recently deposited soils and characteristics of site seismic effect for deep soft sites[D].Nanjing:Nanjing University of Technology,2004.(in Chinese))
[21]战吉艳,陈国兴,刘建达,等.远场大地震作用下大尺度深软场地的非线性地震效应分析[J].岩土力学,2013,34(11):3229–3238.(ZHAN Ji-yan,CHEN Guo-xing,LIU Jian-da,et al.Analysis of nonlinear seismic effects of large-scale deep soft site under far-field large earthquake[J].Rock and Soil Mechanics,2013,34(11):3229–3238.(in Chinese))
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