Deformation Behavior Of Divided Excavation Group In Shanghai Soft Deposit

Divided excavation group has become an effective method in large-scale deep excavation construction in soft soil area with the advantages such as good deformation control effect,construction organization flexibility and strong adaptability,and it has been developed rapidly and popularized in Shanghai recent years.In the design and research of deep excavation engineering,the most concerned problems are revealing deformation control mechanism,putting forward control measures and predicting its deformation.But as a new type of excavation group,there is a lack of systematic study on deformation characters.Because of the high complexity of excavation group engineering,the conventional method can not meet the needs of complex deformation behavior research.Therefore,three-dimensional nonlinear finite element method combined with statistical analysis of measured data of excavation groups in Shanghai was used to systematically study the deformation behavior of divided excavation group in soft soil area of Shanghai.The main contents include the following aspects:1.The commonly used analysis methods and numerical analysis software of excavation group were analyzed and compared,especially the numerical simulation of excavation engineering in FLAC3 D software has been of particular concern.In the field of numerical methods,the advantages,disadvantages and applicability of commonly used numerical analysis software ABAQUS,FLAC3 D and Plaxis are compared and analyzed in detail.In the analysis of surrounding environment influence of excavation group,the small strain stiffness of soil has an important influence on the results of numerical simulation.But there is no constitutive model which can reflect the small strain stiffness of soil in FLAC3 D.Based on the present situation,a small strain stiffness constitutive model based on Moore Kulun model was established by FLAC3 D method in the Fish language.The other technical problems of FLAC3 D in numerical simulation of foundation pit engineering were also analyzed.And the method has been verified by an engineering example,laying a solid foundation for subsequent calculations.2.Based on the FLAC3 D numerical analysis software,a basic analytical numerical model was established to study the deformation characteristics of the divided excavation group.The development rules of partition deformation,lateral deformation of retaining structure and settlement of soil behind excavation were analyzed in detail.The difference between the deformation of the underground wall and the ground surface settlement of different area were also analyzed and compared.For divided excavation groups,the average deformation of the underground wall of the partition zone is 0.09H% and the mean value of groundsurface settlement is 0.14H% which both are less than 0.18%H and 0.15H% of the first grade environmental protection grade foundation pit in the technical code of Shanghai foundation pit engineering.3.Based on the soil parameters of soft soil area in Shanghai,a three-dimensional nonlinear finite element method is adopted to analyze the deformation of divided excavation group by FLAC3 D software.The influence of partition method,foundation reinforcement,underground wall insertion ratio and construction method on the deformation of excavation group was studied.With consistent conditions,when the width of partition zone is equal to the excavation depth(B=H),the control effect of the partition zone is the best.When the partition zone reinforced by full reinforcement and the big excavations reinforced by skirt reinforcement,the groundsurface settlement reaches the minimum and compared with non reinforcement,the deformation can be reduced by more than 30%.Increasing the partition ratio of the wall will not only reduce the lateral deformation of the underground wall but also make the maximum deformation of the underground wall move deep.4.Based on field measured data of Shanghai Aviation Center excavation group,the deformation characteristics of divided excavation group were studied in detail.And the development rules of partition deformation,lateral deformation of retaining structure and settlement of soil behind excavation were also analyzed in detail,which were also compared with the deformation characteristics of traditional excavation engineering.In this project,the lateral deformation of underground wall near the metro line and groundsurface settlement were only 0.16H% and 0.14H% by setting the separation zone,which produced effective protection to adjacent the metro line.