Collapse of a Deep Excavated Foundation Pit in the Soft Soils by 3-D FEM
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摘要
In view of the collapse of a deep excavated foundation pit of the Xianghu subway underground station in Hangzhou of China,the main features of the accident are analyzed,and the induced factors of the accident are summarized. Then,a 3-D FEM analysis model is created to demonstrate the soil-support structures interaction system,and the effect of the main factors,such as the volume replacement ratio of the bottom soil reinforcing,the asymmetric ground overload,the embedded depth of the diaphragm wall,the shear strength of the bottom soils disturbed by the construction,and the excessive excavation of the bottom soil,are analyzed and compared. The results show that the ineffective original reinforcement plan for the bottom soft soil is the most prominent factor for the accident,and the disturbance effect of the deep excavation on the shear strength of the bottom soft soil is another significant factor for the accident. Meanwhile,if the reinforcement of the bottom soft soil is canceled,an appropriate extension of the diaphragm retaining walls to the under lying harder soil layer can also effectively prevent the collapse of the deep excavated foundation pit. In addition,the partly excessive excavation in the process has a great influence on the axial force of the most nearby horizontal support but few effect on the stability of the diaphragm wall. Thus,the excessive excavation of the bottom soils should not be the direct inducing factor for the accident. To the asymmetric ground overload,it should be the main factor inducing the different damage conditions of the diaphragm walls on different sides. According to the numerical modeling and actual engineering accident condition,the development process of the accident is also identified.
In view of the collapse of a deep excavated foundation pit of the Xianghu subway underground station in Hangzhou of China,the main features of the accident are analyzed,and the induced factors of the accident are summarized. Then,a 3-D FEM analysis model is created to demonstrate the soil-support structures interaction system,and the effect of the main factors,such as the volume replacement ratio of the bottom soil reinforcing,the asymmetric ground overload,the embedded depth of the diaphragm wall,the shear strength of the bottom soils disturbed by the construction,and the excessive excavation of the bottom soil,are analyzed and compared. The results show that the ineffective original reinforcement plan for the bottom soft soil is the most prominent factor for the accident,and the disturbance effect of the deep excavation on the shear strength of the bottom soft soil is another significant factor for the accident. Meanwhile,if the reinforcement of the bottom soft soil is canceled,an appropriate extension of the diaphragm retaining walls to the under lying harder soil layer can also effectively prevent the collapse of the deep excavated foundation pit. In addition,the partly excessive excavation in the process has a great influence on the axial force of the most nearby horizontal support but few effect on the stability of the diaphragm wall. Thus,the excessive excavation of the bottom soils should not be the direct inducing factor for the accident. To the asymmetric ground overload,it should be the main factor inducing the different damage conditions of the diaphragm walls on different sides. According to the numerical modeling and actual engineering accident condition,the development process of the accident is also identified.
In view of the collapse of a deep excavated foundation pit of the Xianghu subway underground station in Hangzhou of China,the main features of the accident are analyzed,and the induced factors of the accident are summarized. Then,a 3-D FEM analysis model is created to demonstrate the soil-support structures interaction system,and the effect of the main factors,such as the volume replacement ratio of the bottom soil reinforcing,the asymmetric ground overload,the embedded depth of the diaphragm wall,the shear strength of the bottom soils disturbed by the construction,and the excessive excavation of the bottom soil,are analyzed and compared. The results show that the ineffective original reinforcement plan for the bottom soft soil is the most prominent factor for the accident,and the disturbance effect of the deep excavation on the shear strength of the bottom soft soil is another significant factor for the accident. Meanwhile,if the reinforcement of the bottom soft soil is canceled,an appropriate extension of the diaphragm retaining walls to the under lying harder soil layer can also effectively prevent the collapse of the deep excavated foundation pit. In addition,the partly excessive excavation in the process has a great influence on the axial force of the most nearby horizontal support but few effect on the stability of the diaphragm wall. Thus,the excessive excavation of the bottom soils should not be the direct inducing factor for the accident. To the asymmetric ground overload,it should be the main factor inducing the different damage conditions of the diaphragm walls on different sides. According to the numerical modeling and actual engineering accident condition,the development process of the accident is also identified.
引文
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[15]ZHANG Y S.Study on the deformation of deep foundation pit and its influence to lateral tunnel on deep soft site[D].Nanjing:Nanjing Tech University,2017.(in Chinese)
[16]HUANG S M,GAO D Z.Foundation and underground engineering in soft ground[M].2rd Edition.Beijing:China Architecture&Building Press,2005:639-690.
[17]CHANG S B,ZHANG S M.Engineering geology manual of China[M].4rd Edition.Beijing:China Architecture&Building Press,2007:823-867.
[2]JUANG C H,SCHUSTER M,OU C Y,et al.Fully probabilistic framework for evaluating excavation-induced damage potential of adjacent buildings[J].Journal of Geotechnical and Geoenvironmental Engineering,2011,137(2):130-139.
[3]SCHUSTER M,KUNG G T C,JUANG H C,et al.Simplified model for evaluating damage potential of buildings adjacent to a braced excavation[J].Journal of Geotechnical and Geoenvironmental Engineering,2009,135(12):1823-1835.
[4]ZHUANG H Y,WU X Z,QU Y J.Analysis on the construction deformation of the foundation pit excavated for metro station built in soft site[J].Journal of Railway Engineering Society,2011(5):86-91.
[5]REN J X,FENG X G,LIU H,et al.Research on the deformation law of supporting structure for deep foundation pit of metro station[J].Journal of Railway Engineering Society,2009(3):89-92.
[6]WANG W D,XU Z H.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):258-265.
[7]GUO H Z,ZHANG Q H,ZHU J W,et al.Application of soil coupled creep model to simulate foundation pit excavation[J].Rock and Soil Mechanics,2009,30(3):688-693.
[8]YOOA C,LEE D.Deep excavation-induced ground surface movement characteristics-A numerical investigation[J].Computers and Geotechnics,2008,35:231-252.
[9]LIKITLERSUANGA S,SURARAK C,WANA-TOWSKI D,et al.Finite element analysis of a deep excavation:A case study from the Bangkok MRT[J].Soils and Foundations,2013,53(5):756-773.
[10]LAW K H,OTHMAN S Z,HASHIM R,et al.Determination of soil stiffness parameters at a deep excavation construction site in Kenny Hill Formation[J].Measurement,2014,47:645-650.
[11]OU C Y,HSIEH P G,LIN Y L.A parametric study of wall deflections in deep excavations with the installation of cross walls[J].Computers and Geotechnics,2013,50:55-65.
[12]RAO M.Stability and deformation analysis of a rebuilt excavation engineering in soft clay in Hangzhou[D].Hangzhou:Zhejiang University,2012.(in Chinese)
[13]ZHANG K C,LI J M.Accident analysis for“08.11.15”foundation pit collapse of Xianghu Station of Hangzhou metro[J].Chinese Journal of Geotechnical Engineering,2010,32(S1):338-342.
[14]CHEN Y M,HU Q,CHEN R P.Soil disturbance by the collapse of retaining wall for a pit excavation and the induced additional settlement:A case study of Hangzhou Metro Xianghu Station[J].China Civil Engineering Journal,2014,47(7):110-117.
[15]ZHANG Y S.Study on the deformation of deep foundation pit and its influence to lateral tunnel on deep soft site[D].Nanjing:Nanjing Tech University,2017.(in Chinese)
[16]HUANG S M,GAO D Z.Foundation and underground engineering in soft ground[M].2rd Edition.Beijing:China Architecture&Building Press,2005:639-690.
[17]CHANG S B,ZHANG S M.Engineering geology manual of China[M].4rd Edition.Beijing:China Architecture&Building Press,2007:823-867.