地下增层开挖时单桩竖向沉降的近似解析方法
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摘要
地下增层开挖会对既有桩基的承载性能产生影响,既包括上部土体挖除的影响,又会受到土体强度参数变化的作用。本文从上述两方面分别考虑增层开挖对土体的影响,应用Mindlin解获得开挖前后桩周土体的有效应力,再基于修正剑桥模型得到开挖前后土体的不排水抗剪强度,对于桩侧和桩端采用双曲线荷载传递模型,基于荷载传递法得到考虑土体强度参数变化的桩基荷载-沉降曲线,与现场试桩和有限元结果对比验证。针对增层开挖深度和宽度等因素进行参数分析,结果表明:相比于开挖宽度,桩基承载力对开挖深度更为敏感。
Excavation under existing building will affect the bearing capacity of the existing pile foundation,including the influence of the excavation of the upper soil and the change of the strength parameters of the soil.In this paper,the effects of excavation are considered from the above two aspects.The effective stress of the soil around the pile before and after excavation is obtained by Mindlin solution.Then the undrained shear strength of the soil before and after excavation is obtained based on the modified Cambridge model.For the pile side and pile end,the hyperbolic load transfer model is adopted.Based on the load transfer method,the pile foundation load-settlement curve considering the change of soil strength parameters is obtained,which is compared with the field test pile and finite element results.The parameters are analyzed for the factors such as depth and width of the layered excavation.The results show that the bearing capacity of the pile foundation is more sensitive to the excavation depth than the excavation width.
Excavation under existing building will affect the bearing capacity of the existing pile foundation,including the influence of the excavation of the upper soil and the change of the strength parameters of the soil.In this paper,the effects of excavation are considered from the above two aspects.The effective stress of the soil around the pile before and after excavation is obtained by Mindlin solution.Then the undrained shear strength of the soil before and after excavation is obtained based on the modified Cambridge model.For the pile side and pile end,the hyperbolic load transfer model is adopted.Based on the load transfer method,the pile foundation load-settlement curve considering the change of soil strength parameters is obtained,which is compared with the field test pile and finite element results.The parameters are analyzed for the factors such as depth and width of the layered excavation.The results show that the bearing capacity of the pile foundation is more sensitive to the excavation depth than the excavation width.
引文
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[17] Duncan J M.Nonlinear analysis of stress and strain in soils[J].Journal of Soil Mechanic and Foundation Engineering Division,ASCE,1970,96(5):1629-1653.
[18] 房凯.桩端后注浆过程中浆土相互作用及其对桩基性状影响研究[D].杭州:浙江大学,2013.Fang Kai.Study on the interaction of slurry and soil during post-grouting of piles and its influence on pile foundation characteristics[D].Hangzhou:Zhejiang University,2013.(in Chinese)
[19] Terzaghi K.Theoretical soil mechanics[M].New York:Wiley and Sons,1943.
[20] 郑刚,刁钰,吴宏伟.超深开挖对单桩的竖向荷载传递及沉降的影响机理有限元分析[J].岩土工程学报,2009,31(6):837-845.Zheng Gang,Diao Yu,Wu Hongwei.Finite element analysis of influence mechanism of ultra-deep excavation on vertical load transfer and settlement of single pile[J].Chinese Journal of Geotechnical Engineering,2009,31(6):837-845.(in Chinese)
[21] D′appolonia J.Floating foundations for control of settlement[C].Proc ASCE,1971,97:1508-1511.
[22] 中华人民共和国建设部.JGJ 106—2003 建筑基桩检测技术规范[S].北京:中国建筑工业出版社,2014.Ministry of Construction of the People’s Republic of China.JGJ 106—2003 Technical Specification for Detection of Building Foundation Piles[S].Beijing:China Architecture and Building Press,2014.
[2] 文颖文,胡明亮,韩顺有,等.既有建筑地下室增设中锚杆静压桩技术应用研究[J].岩土工程学报,2013,35(S2):224-229.Wen Yingwen,Hu Mingliang,Han Shunyou,et al.Application of the technology of adding static anchor piles in the basement of existing buildings[J].Chinese Journal of Geotechnical Engineering,2013,35(S2):224-229.(in Chinese)
[3] 胡琦,凌道盛,陈云敏,等.深基坑开挖对坑内基桩受力特性的影响分析[J].岩土力学,2008,29(7):1965-1970.Hu Qi,Ling Daosheng,Chen Yunmin,et al.Influence analysis of deep foundation pit excavation on mechanical behavior of piles in pit[J].Rock and Soil Mechanics,2008,29(7):1965-1970.(in Chinese)
[4] 伍程杰,龚晓南,房凯,等.增层开挖对既有建筑物桩基承载刚度影响分析[J].岩石力学与工程学报,2014,33(8):1526-1535.Wu Chengjie,Gong Xiaonan,Fang Kai,et al.Analysis of influence of layer excavation on bearing stiffness of existing building piles[J].Chinese Journal of Rock Mechanics and Engineering,2014,33(8):1526-1535.(in Chinese)
[5] 伍程杰,龚晓南,俞峰,等.既有高层建筑地下增层开挖桩端阻力损失[J].浙江大学学报(工学版),2014,48(4):671-678.Wu Chengjie,Gong Xiaonan,Yu Feng,et al.Resistance loss of piles in underground excavation of existing high-rise buildings[J].Journal of Zhejiang University (Engineering Science),2014,48(4):671-678.(in Chinese)
[6] 龚晓南,伍程杰,俞峰,等.既有地下室增层开挖引起的桩基侧摩阻力损失分析[J].岩土工程学报,2013,35(11):1957-1964.Gong Xiaonan,Wu Chengjie,Yu Feng,et al.Analysis of lateral friction loss of pile foundation caused by excavation of existing basement[J].Chinese Journal of Geotechnical Engineering,2013,35(11):1957-1964.(in Chinese)
[7] Lin C,Bennett C,Han J,et al.Scour effects on the response of laterally loaded piles considering stress history of sand[J].Computers and Geotechnics,2010,37(7):1008-1014.
[8] Liang F,Zhang H,Huang M.Influence of flood-induced scour on dynamic impedances of pile groups considering the stress history of undrained soft clay[J].Soil Dynamics and Earthquake Engineering,2017,96:76-88.
[9] 王士杰,张梅,张吉占.Mindlin应力解的应用理论研究[J].工程力学,2001,18(6):141-148.Wang Shijie,Zhang Mei,Zhang Jizhan.Application theory of mindlin stress solution[J].Engineering Mechanics,2001,18(6):141-148.(in Chinese)
[10] Mayne P W.K0-OCR Relationships in soil[J].Journal of the Geotechnical Engineering Division,ASCE,1982,20(1):851-872.
[11] Wood D M.Soil behaviour and critical state soil mechanics[D].Cambridge,UK,1991.
[12] Lin C,Han J,Bennett C,et al.Behavior of laterally loaded piles under scour conditions considering the stress history of undrained soft clay [J].Journal of Geotechnical and Geoenvironmental Engineering,2014,140(6):06014005.
[13] Seed H B,Reese L C.The action of soft clay along friction piles[J].Transactions of the American Society of Civil Engineers,1957,122:731-754.
[14] Clough G W.Finite element analyses of retaining wall behavior[J].Journal of Soil Mechanics & Foundation Engineering,1971,97(12):1657-1673.
[15] Randolph M F,Wroth C P.Analysis of deformation of vertically loaded piles[J].Journal of the Geotechnical Engineering Division,ASCE,1978,104(12):1465-1488.
[16] Hirayama H.Load-settlement analysis for bored piles using hyperbolic transfer functions[J].Journal of Soil Engineering Society,1991,30(1):55-64.
[17] Duncan J M.Nonlinear analysis of stress and strain in soils[J].Journal of Soil Mechanic and Foundation Engineering Division,ASCE,1970,96(5):1629-1653.
[18] 房凯.桩端后注浆过程中浆土相互作用及其对桩基性状影响研究[D].杭州:浙江大学,2013.Fang Kai.Study on the interaction of slurry and soil during post-grouting of piles and its influence on pile foundation characteristics[D].Hangzhou:Zhejiang University,2013.(in Chinese)
[19] Terzaghi K.Theoretical soil mechanics[M].New York:Wiley and Sons,1943.
[20] 郑刚,刁钰,吴宏伟.超深开挖对单桩的竖向荷载传递及沉降的影响机理有限元分析[J].岩土工程学报,2009,31(6):837-845.Zheng Gang,Diao Yu,Wu Hongwei.Finite element analysis of influence mechanism of ultra-deep excavation on vertical load transfer and settlement of single pile[J].Chinese Journal of Geotechnical Engineering,2009,31(6):837-845.(in Chinese)
[21] D′appolonia J.Floating foundations for control of settlement[C].Proc ASCE,1971,97:1508-1511.
[22] 中华人民共和国建设部.JGJ 106—2003 建筑基桩检测技术规范[S].北京:中国建筑工业出版社,2014.Ministry of Construction of the People’s Republic of China.JGJ 106—2003 Technical Specification for Detection of Building Foundation Piles[S].Beijing:China Architecture and Building Press,2014.