既有建筑地下增层双层悬臂排桩承载性状及优化分析
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摘要
在既有地下室以下增设地下空间,常面临既有支护与新增支护构成双层支挡结构的开挖工况,这是传统开挖设计方法未涉及的新问题。基于室内模型试验结果,采用有限元分析该特殊支挡结构承载机理和破坏模式,以及既有-新增支护桩排间距、长度比等参数对基坑安全系数和支挡结构受力分担的影响。研究表明:随排间距减小,基坑安全系数不断增大,新增支护桩由主动区土置换体转变为主要受荷结构,双层支挡结构产生整体倾覆破坏;排间距较大时,既有支护桩单独发生倾覆破坏,土体滑移面被限制于排间土体,而新增支护桩及其桩背土体受影响较小。在一定长度范围内,新增支护桩桩长的增加可明显提升基坑安全系数及其受力分担效果,且排间距越小其作用越明显。通过对新增-既有两级支护桩的弯矩最大值差值、总和及支护安全系数的综合评价,得到新增支护桩布置的最优方案。
Underground space supplement by excavation beneath constructed basement usually encounters the situation that existing and newly-created retaining piles form a double-layered retaining structure. This is a new issue that traditional excavation design methods have not involved. On the basis of model-test results, a finite element analysis is carried out to investigate the bearing mechanism and the failure mode of such special retaining structure. The parametric studies involve the influence of the length ratio of the two-layer piles and the row spacing on the safety factor of excavation and the force sharing of the two retaining rows. The research shows that the safety factor increases with decreasing the pile-row spacing, leading the supplementary retaining piles transferred from replacement elements in the active soil to be the principal bearing elements and the overall overturning failure of the retaining structure. When the row spacing is relatively large, the overturning failure is caused by the existing piles alone, and soil slip surface is limited to the soil between the pile rows, while the newly-added support piles and the soil behind these piles have been little affected. Within a certain length range,increase of the length of the new support piles will effectively increase the safety factor of excavation and the force sharing effect. Such effect is more obvious for smaller spacing of the pile rows. The optimal solution for the arrangement of new support piles is obtained by comprehensively evaluating the maximum value of the bending moments of the new-existing two-stage support piles, the sum and the safety factor of the support.
Underground space supplement by excavation beneath constructed basement usually encounters the situation that existing and newly-created retaining piles form a double-layered retaining structure. This is a new issue that traditional excavation design methods have not involved. On the basis of model-test results, a finite element analysis is carried out to investigate the bearing mechanism and the failure mode of such special retaining structure. The parametric studies involve the influence of the length ratio of the two-layer piles and the row spacing on the safety factor of excavation and the force sharing of the two retaining rows. The research shows that the safety factor increases with decreasing the pile-row spacing, leading the supplementary retaining piles transferred from replacement elements in the active soil to be the principal bearing elements and the overall overturning failure of the retaining structure. When the row spacing is relatively large, the overturning failure is caused by the existing piles alone, and soil slip surface is limited to the soil between the pile rows, while the newly-added support piles and the soil behind these piles have been little affected. Within a certain length range,increase of the length of the new support piles will effectively increase the safety factor of excavation and the force sharing effect. Such effect is more obvious for smaller spacing of the pile rows. The optimal solution for the arrangement of new support piles is obtained by comprehensively evaluating the maximum value of the bending moments of the new-existing two-stage support piles, the sum and the safety factor of the support.
引文
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[19]唐芬,郑颖人,杨波.双排抗滑桩的推力分析及优化设计[J].岩石力学与工程学报,2010,29(1):3162-3168(Tang Fen,Zheng Yingren,Yang Bo.Thrust share ratios and optimization design for two-row anti-slide piles[J].Chinese Journal of Rock Mechanics and Engineering,2010,29(1):3162-3168(in Chinese))
[2]Yu Feng,Xie Zheng Bin,Duan Nuo,et al.Performance of double-row piles retaining excavation beneath existing underground space[J].International Journal of Physical Modelling in Geotechnics,2018:1-14
[3]申永江,杨明,项正良.双排长短组合桩与常见双排桩的对比研究[J].岩土工程学报,2015,37(2):96-100(Shen Yongjiang,Yang Ming,Xiang Zhengliang.Comparative study on double-row piles with different lengths several common anti-slide piles[J].Chinese Journal of Geotechnical Engineering,2015,37(2):96-100(in Chinese))
[4]俞峰,刘念武,房凯.软黏土中双排微型桩围护结构的开挖过程性能分析[J].岩石力学与工程学报,2013,32(S2):4139-4148(Yu Feng,Liu Nianwu,Fang Kai.Excavation-induced behavior of retaining structure using double-rowed micropiles in soft clay[J].Chinese Journal of Rock Mechanics and Engineering,2013,32(S2):4139-4148(in Chinese))
[5]Simpson B,NicholsoN D,Banfi M,et al.Collapse of the Nicoll Highway excavation,Singapore[C]//Proceedings of the 4th International Conference on Forensic Engineering.London:Tomas Telford Press,2009
[6]唐德琪,俞峰,陈奕天,等.既有-新增排桩双层支挡结构开挖模型试验研究[J].岩土力学.2019,40(3):1-10(Tang Deqi,Yu Feng,Chen Yitian,et al.Model excavation tests on double layered retaining structure composed of existing and supplementary soldier piles[J].Rock and Soil Mechanics,2019,40(3):1-10(in Chinese))
[7]李大鹏,唐德高,闫凤国,等.深基坑空间效应机理及考虑其影响的土应力研究[J].岩土力学,2014,48(9):1632-1639(Li Dapeng,Tang Degao,Yan Fengguo,et al.Mechanics of deep excavation,spatial effect and soil pressure calculation method considering its influence[J].Rock and Soil Mechanics,2014,48(9):1632-1639(in Chinese))
[8]张雪峰,张蓓,覃小华,等.悬臂式围护桩受力性状与土压力试验研究[J].岩土力学,2015,36(2):340-346(Zhang Xuefeng,Zhang Bei,Qin Xiaohua,et al.Experimental investigation on force behavior and earth pressure of cantilever fender pile[J].Rock and Soil Mechanics,2015,36(2):340-346(in Chinese))
[9]徐中华,王卫东.敏感环境下基坑数值分析中土体本构模型的选择[J].岩土力学,2010,31(1):258-264(Xu Zhonghua,Wang Weidong.Selection of soil constitutive models for numerical analysis of deep excavations in close proximity to sensitive properties[J].Rock and Soil Mechanics,2010,31(1):258-264(in Chinese))
[10]Zienkiewicz O C,Humpheson C,Lewis R W.Associated and non-associated visco-plasticity and plasticity in soil mechanics[J].Géotechnique,1975,25(4):671-689
[11]Griffiths D V,LanE P A.Slope stability analysis by finite elements[J].Géotechnique,1999,49(7):653-654
[12]Dawson E M,Roth W H,Drescher A.Slope stability analysis by strength reduction[J].Géotechnique,1999,49(6):835-840
[13]赵尚毅,郑颖人,时卫民.用有限元强度折减法求边坡稳定安全系数[J].岩土工程学报,2002,24(3):343-346(Zhao Shangyi,Zheng Yingren,Shi Weimin.Slope safety factor analysis by strength reduction FEM[J].Chinese Journal of Geotechnical Engineering,2002,24(3):343-346(in Chinese))
[14]Brinkgreve R,Khoury R A,Bakker K J,et al.Plaxis 2Dversion 8 manual[M].Rotterdam:Balkema A A,2002
[15]Cai F,Ugai K,Toshiyuki H.Base stability of circular excavations in soft clay[J].Journal of Geotechnical and Geoenvironmental Engineering,2002,128(8):702-706
[16]Feheem H,Cai F,Ugai K.Three-dimensional base stability of rectangular excavations in soft soils using FEM[J].Computers and Geotechnics,2004,31(1):67-74
[17]钱明.双排混凝土灌注桩基坑支护的数值模拟分析[J].岩土工程学报,2014,36(2):136-139(Qian Ming.Numerical simulation of double-row bored concrete piles in foundation pits[J].Chinese Journal of Geotechnical Engineering,2014,36(2):136-139(in Chinese))
[18]浙江城建建筑设计院.浙江饭店翻扩建工程施工图[R].杭州:浙江城建建筑设计院,1996(Zhejiang Urban Construction and Architectural Design Institute.Design paper of Zhejiang Hotel expansion project[R].Hangzhou:Zhejiang Urban Construction and Architectural Design Institute,1996(in Chinese))
[19]唐芬,郑颖人,杨波.双排抗滑桩的推力分析及优化设计[J].岩石力学与工程学报,2010,29(1):3162-3168(Tang Fen,Zheng Yingren,Yang Bo.Thrust share ratios and optimization design for two-row anti-slide piles[J].Chinese Journal of Rock Mechanics and Engineering,2010,29(1):3162-3168(in Chinese))