基于差异沉降和轴向刚度控制的竖向荷载作用下群桩基础优化分析
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摘要
目前在群桩设计中仍大多数采用均匀等长布桩的方法,这种方法在基础受力、变形等方面存在较大的缺陷。考虑增大群桩轴向刚度和减小群桩基础差异沉降的条件下,将群桩基础位移函数与桩长优化函数相结合,在对基础采取行变换、平面变换的方式下,通过设置不同的桩长比值ξ、连接曲率值η设定不同布桩方案,分析不同方案下群桩基础轴向刚度比、差异沉降比的变化规律;并利用数值模拟法对所得优化结果的可靠性进行验证。此外,针对不同桩土刚度比、不同桩间距对群桩基础的轴向刚度比和差异沉降比进行了参数分析。研究结果表明:不同群桩基础优化变换方式、不同桩长对群桩基础优化结果会产生不同的影响;当优化目的是为增加群桩基础刚度时,应主要考虑行变换的优化方式,当优化目的是为减小基础差异沉降时,应主要考虑平面变换的优化方式;基础轴向刚度比随着桩土刚度比的增加而增大,随着桩间距的减小而增大;基础差异沉降比随着桩土刚度比的增加而减小,随着桩间距的减小而减小。
At present, the method of uniform isometric piles is used in most group pile designs. This method has major defects in foundation stress and deformation. Considering the increase of group pile foundation stiffness and reducing the differential settlement of group pile foundation, the group pile foundation displacement function is combined with the pile length optimization function.Under the method of line transformation and squared transformation, different group pile designs are determined by setting different pile length ratio ξ and connection curvature η. The scheme is used to analyze the variation law of axial stiffness ratio and differential settlement ratio of group pile foundation under different schemes. The reliability of theoretical analysis results is verified by finite element method. In addition, parametric analysis of axial stiffness ratio and differential settlement ratio of pile group foundations are based on different pile-soil stiffness ratios and different pile spacings. The results show that the optimal transformation mode of different pile groups and different pile lengths have different effects on the optimization results of group pile foundations. When the optimization purpose is to increase the pile group foundation stiffness, the optimization method of line transformation should be chosen. When the optimization purpose is to decrease the differential settlement of pile group foundation, the optimization method of squared transformation should be chosen. The axial stiffness of pile group increases with the increasing of pile-soil stiffness ratio and the decreasing of pile spacing. The differential settlement ratio of pile group decreases with the increasing of pile-soil stiffness ratio and the decreasing of pile spacing.
At present, the method of uniform isometric piles is used in most group pile designs. This method has major defects in foundation stress and deformation. Considering the increase of group pile foundation stiffness and reducing the differential settlement of group pile foundation, the group pile foundation displacement function is combined with the pile length optimization function.Under the method of line transformation and squared transformation, different group pile designs are determined by setting different pile length ratio ξ and connection curvature η. The scheme is used to analyze the variation law of axial stiffness ratio and differential settlement ratio of group pile foundation under different schemes. The reliability of theoretical analysis results is verified by finite element method. In addition, parametric analysis of axial stiffness ratio and differential settlement ratio of pile group foundations are based on different pile-soil stiffness ratios and different pile spacings. The results show that the optimal transformation mode of different pile groups and different pile lengths have different effects on the optimization results of group pile foundations. When the optimization purpose is to increase the pile group foundation stiffness, the optimization method of line transformation should be chosen. When the optimization purpose is to decrease the differential settlement of pile group foundation, the optimization method of squared transformation should be chosen. The axial stiffness of pile group increases with the increasing of pile-soil stiffness ratio and the decreasing of pile spacing. The differential settlement ratio of pile group decreases with the increasing of pile-soil stiffness ratio and the decreasing of pile spacing.
引文
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[21]秋仁东,刘金砺,高文生,等.长群桩基础沉降性状的大比例尺模型试验研究[J].土木工程学报,2015,48(3):85-95.QIU Ren-dong,LIU Jin-li,GAO Wen-sheng,et al.Large scale model test study on settlement behavior of long pile group foundation[J].China Civil Engineering Journal,2015,48(3):85-95.
[22]中国建筑科学研究院.JGJ 94-2008建筑桩基技术规范[S].北京:中国建筑工业出版社,2008.China Academy of Building Research.JGJ 94-2008Technical specifications for building pile foundations[S].Beijing:China Architecture&Building Press,2008.
[2]SHEN W Y,CHOW Y K,YONG K Y.A variational approach for vertical deformation analysis of pile group[J].International Journal for Numerical and Analytical Methods in Geomechanics,1997,21(11):741-752.
[3]王伟,杨敏.基于变分原理的群桩位移计算方法[J].岩土工程学报,2005,27(9):1072-1076.WANG Wei,YANG Min.Calculation method of group pile displacement based on variational principle[J].Chinese Journal of Geotechnical Engineering,2005,27(9):1072-1076.
[4]张瑜,吴江斌,蔡永昌.考虑桩径和桩侧摩阻力分布的改进Geddes桩基沉降分析方法[J].岩土力学,2015,36(增刊2):406-412.ZHANG Yu,WU Jiang-bin,CAI Yong-chang.Improved settlement analysis method of Geddes pile foundation considering pile diameter and pile side friction resistance[J].Rock and Soil Mechanics,2015,36(Suppl.2):406-412.
[5]HORIKOSHI K,RANDOLPH M F.A contribution to optimum design of pile rafts[J].Geotechnique,1998,48(3):301-317.
[6]KIM K N,LEE S H,KIM K S,et al.Optimal pile arrangement for minimizing differential settlements in piled raft foundations[J].Computers and Geotechnics,2001,28(4):235-253.
[7]LEUNG Y F,KLAR A,SOGA K.Theoretical study on pile length optimization of pile groups and piled rafts[J].Journal of Geotechnical and Geoenvironmental Engineering,2010,136(2):319-330.
[8]梁发云,陈海兵.基于cut-off方法刚性承台下群桩基础优化分析[J].岩土力学,2011,32(增刊1):61-65.LIANG Fa-yun,CHEN Hai-bing.Optimization analysis of pile group foundation under rigid pile cap based on cut-off method[J].Rock and Soil Mechanics,2011,32(Suppl.1):61-65.
[9]LIANG F,SONG Z.BEM analysis of the interaction factor for vertically loaded dissimilar piles in saturated poroelastic soil[J].Computers and Geotechnics,2014,62:223-231.
[10]NAKANISHI K,TAKEWAKI I.Optimum pile arrangement in piled raft foundation by using simplified settlement analysis and adaptive step-length algorithm[J].Geomechanics and Engineering,2013,5(6):519-540.
[11]刘金砺,邱明兵,秋仁东,等.Mindlin解均化应力分层总和法计算群桩基础沉降[J].土木工程学报,2014,47(5):118-127.LIU Jin-li,QIU Ming-bing,QIU Ren-dong,et al.Calculation of settlement of pile group foundation by Mindlin solution of uniformized stress stratification[J].China Civil Engineering Journal,2014,47(5):118-127.
[12]张忠苗,杨淼,房凯,等.考虑桩身压缩的综合系数法计算超长桩基础沉降[J].岩土力学,2012,33(3):793-798.ZHANG Zhong-miao,YANG Miao,FANG Kai,et al.Calculation of settlement of super-long pile foundation considering comprehensive compression method of pile compression[J].Rock and Soil Mechanics,2012,33(3):793-798.
[13]高盟,高广运,杨成斌,等.层状地基群桩沉降计算的剪切位移解析算法[J].岩土力学,2010,31(4):1072-1077.GAO Meng,GAO Guang-yun,YANG Cheng-bin,et al.Analytical algorithm of shear displacement calculation for settlement of piles in layered soils[J].Rock and Soil Mechanics,2010,31(4):1072-1077.
[14]乔志炜,宰金珉,黄广龙.控制差异沉降的复合桩基优化设计方法[J].地下空间与工程学报,2006,2(5):818-821.QIAO Zhi-wei,ZAI Jin-min,HUANG Guang-long.Optimization design method of composite pile foundation for controlling differential settlement[J].Chinese Journal of Underground Space and Engineering,2006,2(5):818-821.
[15]LEUNG Y F A,KLAR A,SOGA K,et al.Superstructure-foundation interaction in multi-objective pile group optimization considering settlement response[J].Canadian Geotechnical Journal,2017,54(5):1408-1420.
[16]GHALESARI A T,CHOOBBASTI A J.Numerical analysis of settlement and bearing behaviour of piled raft in Babol clay[J].European Journal of Environmental and Civil Engineering,2016,2(3):132-140
[17]SAMANTA M,BHOWMIK R.3D numerical analysis of piled raft foundation in stone column improved soft soil[J].International Journal of Geotechnical Engineering,2017,12(1):43-50.
[18]林智勇,戴自航.由单桩载荷试验推算群桩沉降的互作用系数法[J].岩土工程学报,2016,38(1):155-162.LIN Zhi-yong,DAI Zi-hang.Calculation of interaction coefficient method for group pile settlement by single pile load test[J].Chinese Journal of Geotechnical Engineering,2016,38(1):155-162.
[19]张武,迟铃泉,高文生,等.变刚度桩筏基础变形特性试验研究[J].建筑结构学报,2010,31(7):94-102.ZHANG Wu,CHI Ling-quan,GAO Wen-sheng,et al.Experimental study on deformation characteristics of piles with variable stiffness piles[J].Journal of Building Structures,2010,31(7):94-102.
[20]刘金砺,黄强.竖向荷载下群桩变形性状及沉降计算[J].岩土工程学报,1995,17(6):1-13.LIU Jin-li,HUANG Qiang.Calculation of deformation behavior and settlement of pile groups under vertical loads[J].Chinese Journal of Geotechnical Engineering,1995,17(6):1-13.
[21]秋仁东,刘金砺,高文生,等.长群桩基础沉降性状的大比例尺模型试验研究[J].土木工程学报,2015,48(3):85-95.QIU Ren-dong,LIU Jin-li,GAO Wen-sheng,et al.Large scale model test study on settlement behavior of long pile group foundation[J].China Civil Engineering Journal,2015,48(3):85-95.
[22]中国建筑科学研究院.JGJ 94-2008建筑桩基技术规范[S].北京:中国建筑工业出版社,2008.China Academy of Building Research.JGJ 94-2008Technical specifications for building pile foundations[S].Beijing:China Architecture&Building Press,2008.