桩基动刚度影响因素分析
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摘要
动刚度是桩基动测分析中一个重要指标,研究动刚度的影响因素有着现实的工程意义。为了分析完整桩和缺陷桩单桩动刚度的变化规律和影响因素,推导并求解了竖向简谐荷载作用下考虑两个变截面桩的导纳响应解析解。利用测试数据验证了该模型能有效计算导纳共振频率值和动刚度值。同时,对513根相同型式桥桩进行机械阻抗法测试,并对其动刚度进行统计分析。研究表明:(1)桩端支撑刚度和桩长对动刚度影响较大,端承桩动刚度随桩长增加而降低,纯摩擦桩情况与之相反。摩擦桩在桩长较长时其动刚度可能大于端承桩。(2)桩身缺陷体积改变量与动刚度变化成正相关。(3)动刚度对桩身缩颈缺陷敏感度较高,在一定程度上可以用于判断桩身完整性和承载能力。
Dynamic stiffness is an important index in pile dynamic measurement and analysis. In practice it is important to analyze and identify the factors that influence the dynamic stiffness of pile foundation. To analyze the dynamic stiffness of the intact and defected piles, an analytical model of admittance response under vertical harmonic loads is developed and solved. In this model, two variable cross sections are considered. The measured results show that the model can be effectively used to calculate the values of resonance frequency and dynamic stiffness. Moreover, 513 bridge piles of the same type are measured using mechanical impedance method. The dynamic stiffness for all piles is analyzed statistically. It is shown as follows.(1) the supporting stiffness of pile tip and the pile length significantly effect dynamic stiffness; the dynamic stiffness of end-bearing pile decreases with its length, whereas that of pure friction piles increases with the pile length. If friction pile has a longer length, its dynamic stiffness may exceed that of end-bearing pile.(2) For defected piles, the volumetric change has the positive relation with the variation of dynamic stiffness.(3) Dynamic stiffness is very sensitive to necking defection, which can be used to estimate the pile integrality and bearing capacity to some extent.
Dynamic stiffness is an important index in pile dynamic measurement and analysis. In practice it is important to analyze and identify the factors that influence the dynamic stiffness of pile foundation. To analyze the dynamic stiffness of the intact and defected piles, an analytical model of admittance response under vertical harmonic loads is developed and solved. In this model, two variable cross sections are considered. The measured results show that the model can be effectively used to calculate the values of resonance frequency and dynamic stiffness. Moreover, 513 bridge piles of the same type are measured using mechanical impedance method. The dynamic stiffness for all piles is analyzed statistically. It is shown as follows.(1) the supporting stiffness of pile tip and the pile length significantly effect dynamic stiffness; the dynamic stiffness of end-bearing pile decreases with its length, whereas that of pure friction piles increases with the pile length. If friction pile has a longer length, its dynamic stiffness may exceed that of end-bearing pile.(2) For defected piles, the volumetric change has the positive relation with the variation of dynamic stiffness.(3) Dynamic stiffness is very sensitive to necking defection, which can be used to estimate the pile integrality and bearing capacity to some extent.
引文
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[2]RAUSCHE F.Non-destructive evaluation of deep foundations[C]//The 5th International Conference on Case Histories in Geotechnical Engineering.New York:[s.n.],2004:1-9.
[3]LIANG L,BEIM J.Effect of soil resistance on the low strain mobility response of piles using impulse transient response method[C]//The 8th International Conference on the Application of Stress Wave Theory to Piles.Lisbon:IOS Press,2008:435-441.
[4]羊建勋.瞬态激励确定基桩动刚度及承载力的初步研究[J].中国铁道科学,1994,15(1):104-115.YANG Jian-xun.Determination of dynamic stiffness and bearing capacity of pile-soil system by transient impact[J].China Railway Science,1994,15(1):104-115.
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[8]王奎华.桩材料阻尼对动测曲线的影响研究[J].岩土力学,1998,19(4):57-62.WANG Kui-hua.A study on the influence of material damping of pile on dynamic testing[J].Rock and Soil Mechanics,1998,19(4):57-62.
[9]胡昌斌,王奎华,谢康和.考虑桩土耦合作用时弹性支承桩纵向振动特性分析及应用[J].工程力学,2003,20(2):146-154.HU Chang-bin,WANG Kui-hua,XIE Kang-he.Soil-pile interaction in vertical vibrations of a pile with elastic bottom boundaries and its applications[J].Engineering Mechanics,2003,20(2):146-154.
[10]冯世进,陈云敏,刘明振.成层土中黏弹性桩纵向振动分析及工程应用[J].中国公路学报,2004,17(2):59-63.FENG Shi-jin,CHEN Yun-min,LIU Ming-zhen.Analysis and application in engineering on vertical vibration of viscoelasticity pile in layered soil[J].Chinese Journal of Highway and Transport,2004,17(2):59-63.
[11]吴京荣.单桩导纳曲线拟合与小应变桩基无损检测[J].振动、测试与诊断,1995,15(1):33-38,51.WU Jing-rong.Fitting admittance curve and the non-destructive vibration detecting of pile in condition of the low strain[J].Journal of Vibration,Measurement&Diagnosis,1995,15(1):33-38,51.
[12]刘东甲.不均匀土中多缺陷桩的轴向动力响应[J].岩土工程学报,2000,22(4):391-395.LIU Dong-jia.Dynamic axial response of multi-defective piles in nonhomogeneous soil[J].Chinese Journal of Geotechnical Engineering,2000,22(4):391-395.
[13]王腾,王奎华,谢康和.变截面桩速度导纳的解析解[J].岩石力学与工程学报,2002,21(4):573-576.WANG Teng,WANG Kui-hua,XIE Kang-he.Analytical solution on velocity mobility of a pile with variable sections[J].Chinese Journal of Rock Mechanics and Engineering,2002,21(4):573-576.
[14]强建科,雷林源,宁立波.缺陷端承桩稳态动测导纳响应的正演模拟[J].工程勘察,2003,(6):64-66.QIANG Jian-ke,LEI Lin-yuan,NING Li-bo.Simulation to admittance response of end-bearing fault piles by constant dynamic method[J].Geotechnical Investigation&Surveying,2003,(6):64-66.
[15]雷林源.桩基动力学[M].北京:冶金工业出版社,2000.
[2]RAUSCHE F.Non-destructive evaluation of deep foundations[C]//The 5th International Conference on Case Histories in Geotechnical Engineering.New York:[s.n.],2004:1-9.
[3]LIANG L,BEIM J.Effect of soil resistance on the low strain mobility response of piles using impulse transient response method[C]//The 8th International Conference on the Application of Stress Wave Theory to Piles.Lisbon:IOS Press,2008:435-441.
[4]羊建勋.瞬态激励确定基桩动刚度及承载力的初步研究[J].中国铁道科学,1994,15(1):104-115.YANG Jian-xun.Determination of dynamic stiffness and bearing capacity of pile-soil system by transient impact[J].China Railway Science,1994,15(1):104-115.
[5]郑灿堂,王扬,许尚杰,等.稳态机械阻抗法动测单桩承载力[J].水利水电技术,1997,28(8):50-52.
[6]陆培毅,李忠献,顾晓鲁.低应变测桩承载力的理论与应用[J].地震工程与工程振动,1998,18(2):134-139.LU Pei-yi,LI Zhong-xian,GU Xiao-lu.Low strain dynamic testing of piles[J].Earthquake Engineering and Engineering Vibration,1998,18(2):134-139.
[7]王奎华,谢康和,曾国熙.有限长桩受迫振动问题解析解及其应用[J].岩土工程学报,1997,19(6):27-35.WANG Kui-hua,XIE Kang-he,ZENG Guo-xi.Analytical solution to vibration of finite length pile under exciting force and its application[J].Chinese Journal of Geotechnical Engineering,1997,19(6):27-35.
[8]王奎华.桩材料阻尼对动测曲线的影响研究[J].岩土力学,1998,19(4):57-62.WANG Kui-hua.A study on the influence of material damping of pile on dynamic testing[J].Rock and Soil Mechanics,1998,19(4):57-62.
[9]胡昌斌,王奎华,谢康和.考虑桩土耦合作用时弹性支承桩纵向振动特性分析及应用[J].工程力学,2003,20(2):146-154.HU Chang-bin,WANG Kui-hua,XIE Kang-he.Soil-pile interaction in vertical vibrations of a pile with elastic bottom boundaries and its applications[J].Engineering Mechanics,2003,20(2):146-154.
[10]冯世进,陈云敏,刘明振.成层土中黏弹性桩纵向振动分析及工程应用[J].中国公路学报,2004,17(2):59-63.FENG Shi-jin,CHEN Yun-min,LIU Ming-zhen.Analysis and application in engineering on vertical vibration of viscoelasticity pile in layered soil[J].Chinese Journal of Highway and Transport,2004,17(2):59-63.
[11]吴京荣.单桩导纳曲线拟合与小应变桩基无损检测[J].振动、测试与诊断,1995,15(1):33-38,51.WU Jing-rong.Fitting admittance curve and the non-destructive vibration detecting of pile in condition of the low strain[J].Journal of Vibration,Measurement&Diagnosis,1995,15(1):33-38,51.
[12]刘东甲.不均匀土中多缺陷桩的轴向动力响应[J].岩土工程学报,2000,22(4):391-395.LIU Dong-jia.Dynamic axial response of multi-defective piles in nonhomogeneous soil[J].Chinese Journal of Geotechnical Engineering,2000,22(4):391-395.
[13]王腾,王奎华,谢康和.变截面桩速度导纳的解析解[J].岩石力学与工程学报,2002,21(4):573-576.WANG Teng,WANG Kui-hua,XIE Kang-he.Analytical solution on velocity mobility of a pile with variable sections[J].Chinese Journal of Rock Mechanics and Engineering,2002,21(4):573-576.
[14]强建科,雷林源,宁立波.缺陷端承桩稳态动测导纳响应的正演模拟[J].工程勘察,2003,(6):64-66.QIANG Jian-ke,LEI Lin-yuan,NING Li-bo.Simulation to admittance response of end-bearing fault piles by constant dynamic method[J].Geotechnical Investigation&Surveying,2003,(6):64-66.
[15]雷林源.桩基动力学[M].北京:冶金工业出版社,2000.
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