考虑围护结构强度折减的基坑坑底隆起稳定分析
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摘要
基坑坑底隆起稳定验算是基坑设计最重要的问题之一,坑底隆起失稳破坏伴随着土体和围护结构失效.然而目前基坑稳定常用的分析方法,强度折减有限元法,在已有研究和实践中却仅折减土体强度,未对围护结构强度进行折减,这与强度折减法的计算理念不统一,且与实际基坑的破坏模式有一定差异.因此本文提出同时折减土体抗剪强度和围护结构抗弯强度的强度折减有限元法.进而通过建立大量的数值模型,对比了考虑与不考虑围护结构抗弯强度折减的计算结果,并与圆弧滑动法进行了对比分析.最后基于实际工程案例分析了新方法的应用效果.分析结果表明,不折减围护结构抗弯强度将高估基坑的坑底抗隆起稳定安全水平,验证了采用强度折减有限元法时同时折减土体强度和围护结构抗弯强度的必要性.
The evaluation on the basal-heave stability of excavations is one of the most important problems in excavation design.The instability of the basal-heave of excavations is accompanied by failure of soil and the retaining structures.Finite element method(FEM)with shear strength reduction is one of the commonly used methods for calculating the basal-heave stability of excavations;however,this method only reduces the shear strength of soil and ignores the flexural strength of the retaining structures,which is not only inconsistent with the concept of the method,but also differs from the failure mode of practical evaluations.Therefore,an improved FEM that simultaneously reduces the shear strength of soil and the flexural strength of the retaining structures is proposed in this paper.By establishing a large number of numerical models,the calculation results of the improved FEM with strength reduction and the traditional FEM with strength reduction were compared,and they were also compared with the slip circle method.Finally,based on practical engineering cases,the application effect of the improved FEM with strength reduction was analyzed.The analysis results show that the safety level of the basal-heave of excavations will be over estimated if the flexural strength of the retaining structures is not reduced when FEMs with strength reduction are used.The necessity of simultaneously reducing the strength of the soil and the flexural strength of the retaining structures when using FEMs with strength reduction is demonstrated.
The evaluation on the basal-heave stability of excavations is one of the most important problems in excavation design.The instability of the basal-heave of excavations is accompanied by failure of soil and the retaining structures.Finite element method(FEM)with shear strength reduction is one of the commonly used methods for calculating the basal-heave stability of excavations;however,this method only reduces the shear strength of soil and ignores the flexural strength of the retaining structures,which is not only inconsistent with the concept of the method,but also differs from the failure mode of practical evaluations.Therefore,an improved FEM that simultaneously reduces the shear strength of soil and the flexural strength of the retaining structures is proposed in this paper.By establishing a large number of numerical models,the calculation results of the improved FEM with strength reduction and the traditional FEM with strength reduction were compared,and they were also compared with the slip circle method.Finally,based on practical engineering cases,the application effect of the improved FEM with strength reduction was analyzed.The analysis results show that the safety level of the basal-heave of excavations will be over estimated if the flexural strength of the retaining structures is not reduced when FEMs with strength reduction are used.The necessity of simultaneously reducing the strength of the soil and the flexural strength of the retaining structures when using FEMs with strength reduction is demonstrated.
引文
[1]Hsieh P G,Ou C Y,Liu H T.Basal heave analysis of excavations with consideration of anisotropic undrained strength of clay[J].Canadian Geotechnical Journal,2008,45(6):788-799.
[2]Do T N,Ou C Y,Chen R P.A study of failure mechanisms of deep excavations in soft clay using the finite element method[J].Computers and Geotechnics,2016,73:153-163.
[3]Tan Y,Wei B.Performance of an Overexcavated metro station and facilities nearby[J].Journal of Performance of Constructed Facilities,2012,26(3):241-254.
[4]Chen R P,Li Z C,Chen Y M,et al.Failure investigation at a collapsed deep excavation in very sensitive organic soft clay[J].Journal of Performance of Constructed Facilities,2015,29(3):04014078.
[5]O’Rourke T D.Base stability and ground movement prediction for excavations in soft clay[C]//Retaining Structures.London:Thomas Telford,1993:657-686.
[6]Ukritchon B,Whittle A J,Sloan S W.Undrained stability of braced excavations in clay[J].Journal of Geotechnical and Geoenvironmental Engineering,2003,129(8):738-755.
[7]Huang M S,Tang Z,Yuan J Y.Basal stability analysis of braced excavations with embedded walls in undrained clay using the upper bound theorem[J].Tunnelling and Underground Space Technology,2018,79:231-241.
[8]Japanese Society of Architecture.Guidelines of Design and Construction of Deep Excavation[S].Tokyo,Japan:Japanese Society of Architecture,1988.
[9]Taiwan Geotechnical Society.Design Specifications for the Foundation of Buildings[S].Taipei,China:Taiwan Geotechnical Society,2001.
[10]上海市勘察设计行业协会.DG/TJ08-61-2010基坑工程技术规范(上海)[S].上海:上海市勘察设计行业协会,2010.Shanghai Exploration&Design Trade Association.DG/TJ08-61-2010 Technical Code for Design of Excavation Engineering(Shanghai)[S].Shanghai:Shanghai Exploration&Design Trade Association,2010(in Chinese).
[11]郑刚,程雪松.考虑弧长和法向应力修正的基坑抗隆起稳定计算方法[J].岩土工程学报,2012,34(5):781-789.Zheng Gang,Cheng Xuesong.Basal stability analysis method considering arc length and normal stress correction[J].Chinese Journal of Geotechnical Engineering,2012,34(5):781-789(in Chinese).
[12]郑刚,程雪松,刁钰.无支撑多级支护结构稳定性与破坏机理分析[J].天津大学学报:自然科学与工程技术版,2013,46(4):304-314.Zheng Gang,Cheng Xuesong,Diao Yu.Analysis of the stability and collapse mechanism of non-prop and multistage retaining structure[J].Journal of Tianjin University:Science and Technology,2013,46(4):304-314(in Chinese).
[13]Goh A T C.Assessment of basal stability for braced excavation systems using the finite element method[J].Computers and Geotechnics,1990,10(4):325-338.
[14]Goh A T C.Estimating basal-heave stability for braced excavations in soft clay[J].Journal of Geotechnical Engineering,1994,120(8):1430-1436.
[15]Faheem H,Cai F,Ugai K,et al.Two-dimensional base stability of excavations in soft soils using FEM[J].Computers and Geotechnics,2003,30(2):141-163.
[16]Faheem H,Cai F,Ugai K.Three-dimensional base stability of rectangular excavations in soft soils using FEM[J].Computers and Geotechnics,2004,31(2):67-74.
[17]陈福全,吕艳平,刘毓氚.内撑式支护的软土基坑开挖抗隆起稳定性分析[J].岩土力学,2008,29(2):365-369.Chen Fuquan,LüYanping,Liu Yuchuan.Base stability of braced excavations in soft clays using FEM[J].Rock and Soil Mechanics,2008,29(2):365-369(in Chinese)
[18]Do T N,Ou C Y,Lim A.Evaluation of factors of safety against basal heave for deep excavations in soft clay using the finite-element method[J].Journal of Geotechnical and Geoenvironmental Engineering,2013,139(12):2125-2135.
[19]Goh A T C.Deterministic and reliability assessment of basal heave stability for braced excavations with jet grout base slab[J].Engineering Geology,2017,218:63-69.
[20]Sun Y Y,Zhou S H,Luo Z.Basal-heave analysis of pit-in-pit braced excavations in soft clays[J].Computers and Geotechnics,2017,81:294-306.
[21]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.
[22]李忠超,陈仁朋,陈云敏,等.软黏土中某内支撑式深基坑稳定性安全系数分析[J].岩土工程学报,2015,37(5):769-775.Li Zhongchao,Chen Renpeng,Chen Yunmin,et al.Factor of safety of a braced deep excavation in soft clay[J].Chinese Journal of Geotechnical Engineering,2015,37(5):769-775(in Chinese).
[23]Brinkgreve R B J,Broere W,Waterman D.Finite Element Code for Soil and Rock Analyses,Users Manual[M].Netherlands,2017.
[24]Wu S H,Ou C Y,Ching J Y.Calibration of model uncertainties in base heave stability for wide excavations in clay[J].Soils and Foundations,2014,54(6):1159-1174.
[25]郑刚,王凡俊,孙宏宾,等.软土地区CFG桩群孔效应引发的地表沉降[J].天津大学学报:自然科学与工程技术版,2017,50(8):796-805.Zheng Gang,Wang Fanjun,Sun Hongbin,et al.Surface Settlement Caused by Borehole Group Effect of CFG Piles in Soft Soil[J].Journal of Tianjin University:Science and Technology,2017,50(8):796-805(in Chinese).
[26]Ladd C C.Stability evaluation during staged construction[J].Journal of Geotechnical Engineering,1991,117(4):540-615.
[27]Su S F,Liao H J,Lin Y H.Base stability of deep excavation in anisotropic soft clay[J].Journal of Geotechnical and Geoenvironmental Engineering,1998,124(9):809-819.
[28]Ou C Y.Deep Excavation:Theory and Practice[M].Boca Raton,Florida,USA:CRC Press,2006.
[29]Whittle A J,Davies R V.Nicoll Highway Collapse:Evaluation of Geotechnical Factors Affecting Design of Excavation Support System[C]//International Conference on Deep Excavations.Singapore,2006.
[30]Ou C Y,Liao J T,Lin H D.Performance of diaphragm wall constructed using top-down method[J].Journal of Geotechnical and Geoenvironmental Engineering,1998,124(9):798-808.
[31]Rampello S,Tamagnini C,Calabresi G.Observed and predicted response of a braced excavation in soft to medium clay[C]//Predictive Soil Mechanics.London:Thomas Telford,1993:544-561.
[2]Do T N,Ou C Y,Chen R P.A study of failure mechanisms of deep excavations in soft clay using the finite element method[J].Computers and Geotechnics,2016,73:153-163.
[3]Tan Y,Wei B.Performance of an Overexcavated metro station and facilities nearby[J].Journal of Performance of Constructed Facilities,2012,26(3):241-254.
[4]Chen R P,Li Z C,Chen Y M,et al.Failure investigation at a collapsed deep excavation in very sensitive organic soft clay[J].Journal of Performance of Constructed Facilities,2015,29(3):04014078.
[5]O’Rourke T D.Base stability and ground movement prediction for excavations in soft clay[C]//Retaining Structures.London:Thomas Telford,1993:657-686.
[6]Ukritchon B,Whittle A J,Sloan S W.Undrained stability of braced excavations in clay[J].Journal of Geotechnical and Geoenvironmental Engineering,2003,129(8):738-755.
[7]Huang M S,Tang Z,Yuan J Y.Basal stability analysis of braced excavations with embedded walls in undrained clay using the upper bound theorem[J].Tunnelling and Underground Space Technology,2018,79:231-241.
[8]Japanese Society of Architecture.Guidelines of Design and Construction of Deep Excavation[S].Tokyo,Japan:Japanese Society of Architecture,1988.
[9]Taiwan Geotechnical Society.Design Specifications for the Foundation of Buildings[S].Taipei,China:Taiwan Geotechnical Society,2001.
[10]上海市勘察设计行业协会.DG/TJ08-61-2010基坑工程技术规范(上海)[S].上海:上海市勘察设计行业协会,2010.Shanghai Exploration&Design Trade Association.DG/TJ08-61-2010 Technical Code for Design of Excavation Engineering(Shanghai)[S].Shanghai:Shanghai Exploration&Design Trade Association,2010(in Chinese).
[11]郑刚,程雪松.考虑弧长和法向应力修正的基坑抗隆起稳定计算方法[J].岩土工程学报,2012,34(5):781-789.Zheng Gang,Cheng Xuesong.Basal stability analysis method considering arc length and normal stress correction[J].Chinese Journal of Geotechnical Engineering,2012,34(5):781-789(in Chinese).
[12]郑刚,程雪松,刁钰.无支撑多级支护结构稳定性与破坏机理分析[J].天津大学学报:自然科学与工程技术版,2013,46(4):304-314.Zheng Gang,Cheng Xuesong,Diao Yu.Analysis of the stability and collapse mechanism of non-prop and multistage retaining structure[J].Journal of Tianjin University:Science and Technology,2013,46(4):304-314(in Chinese).
[13]Goh A T C.Assessment of basal stability for braced excavation systems using the finite element method[J].Computers and Geotechnics,1990,10(4):325-338.
[14]Goh A T C.Estimating basal-heave stability for braced excavations in soft clay[J].Journal of Geotechnical Engineering,1994,120(8):1430-1436.
[15]Faheem H,Cai F,Ugai K,et al.Two-dimensional base stability of excavations in soft soils using FEM[J].Computers and Geotechnics,2003,30(2):141-163.
[16]Faheem H,Cai F,Ugai K.Three-dimensional base stability of rectangular excavations in soft soils using FEM[J].Computers and Geotechnics,2004,31(2):67-74.
[17]陈福全,吕艳平,刘毓氚.内撑式支护的软土基坑开挖抗隆起稳定性分析[J].岩土力学,2008,29(2):365-369.Chen Fuquan,LüYanping,Liu Yuchuan.Base stability of braced excavations in soft clays using FEM[J].Rock and Soil Mechanics,2008,29(2):365-369(in Chinese)
[18]Do T N,Ou C Y,Lim A.Evaluation of factors of safety against basal heave for deep excavations in soft clay using the finite-element method[J].Journal of Geotechnical and Geoenvironmental Engineering,2013,139(12):2125-2135.
[19]Goh A T C.Deterministic and reliability assessment of basal heave stability for braced excavations with jet grout base slab[J].Engineering Geology,2017,218:63-69.
[20]Sun Y Y,Zhou S H,Luo Z.Basal-heave analysis of pit-in-pit braced excavations in soft clays[J].Computers and Geotechnics,2017,81:294-306.
[21]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.
[22]李忠超,陈仁朋,陈云敏,等.软黏土中某内支撑式深基坑稳定性安全系数分析[J].岩土工程学报,2015,37(5):769-775.Li Zhongchao,Chen Renpeng,Chen Yunmin,et al.Factor of safety of a braced deep excavation in soft clay[J].Chinese Journal of Geotechnical Engineering,2015,37(5):769-775(in Chinese).
[23]Brinkgreve R B J,Broere W,Waterman D.Finite Element Code for Soil and Rock Analyses,Users Manual[M].Netherlands,2017.
[24]Wu S H,Ou C Y,Ching J Y.Calibration of model uncertainties in base heave stability for wide excavations in clay[J].Soils and Foundations,2014,54(6):1159-1174.
[25]郑刚,王凡俊,孙宏宾,等.软土地区CFG桩群孔效应引发的地表沉降[J].天津大学学报:自然科学与工程技术版,2017,50(8):796-805.Zheng Gang,Wang Fanjun,Sun Hongbin,et al.Surface Settlement Caused by Borehole Group Effect of CFG Piles in Soft Soil[J].Journal of Tianjin University:Science and Technology,2017,50(8):796-805(in Chinese).
[26]Ladd C C.Stability evaluation during staged construction[J].Journal of Geotechnical Engineering,1991,117(4):540-615.
[27]Su S F,Liao H J,Lin Y H.Base stability of deep excavation in anisotropic soft clay[J].Journal of Geotechnical and Geoenvironmental Engineering,1998,124(9):809-819.
[28]Ou C Y.Deep Excavation:Theory and Practice[M].Boca Raton,Florida,USA:CRC Press,2006.
[29]Whittle A J,Davies R V.Nicoll Highway Collapse:Evaluation of Geotechnical Factors Affecting Design of Excavation Support System[C]//International Conference on Deep Excavations.Singapore,2006.
[30]Ou C Y,Liao J T,Lin H D.Performance of diaphragm wall constructed using top-down method[J].Journal of Geotechnical and Geoenvironmental Engineering,1998,124(9):798-808.
[31]Rampello S,Tamagnini C,Calabresi G.Observed and predicted response of a braced excavation in soft to medium clay[C]//Predictive Soil Mechanics.London:Thomas Telford,1993:544-561.