Study On Deep Foundation Pit Supporting Technology Of Middle-Down-Top And Side-Top-Down Construction In Complex Environment

With the development of urban construction in China,a large number of ultra-large deep excavations have emerged.In order to ensure that the safety of adjacent buildings and their own structures is not affected during the construction and excavation of deep foundation pits,appropriate supporting measures must be taken for deep foundation pits.Therefore,the selection of retaining structure,structural analysis,scheme optimization and field monitoring have become an important task of foundation pit engineering.This paper mainly explores the combined support method of central island structure and support system,and provides reference for similar engineering cases.(1)Taking the foundation pit support project of a commercial center plaza project in Foshan City,Guangdong Province as an example,the super-large foundation pit support scheme for the construction of the central island building in the same direction and the surrounding buildings in the reverse construction was studied.According to the serious and difficult problems encountered in the project,after the comparison of different schemes,a new method of joint support with the central island structure and supporting piles is proposed,and the built buildings in the foundation pit are used as the inner support of the foundation pit support.bearing system.Through theoretical analysis,numerical simulation and on-site monitoring,it is shown that the new support system can reduce the structural deformation of the foundation pit,save the construction period,and meet the relevant specifications.(2)The beamless floor of the central island structure that has been built in the down-top area is used as the horizontal support system,and the column piles and structural columns are used as the vertical support system.The node displacement of the inner support structure is analyzed in the case of symmetrical construction or asymmetrical construction.When the structure is constructed symmetrically,the interlayer displacement value of the structure can meet the requirements of the relevant specifications;when the construction is asymmetrical,the horizontal displacement of the structure is large,and the lateral displacement requirements can be met by increasing the support between the columns.(3)In order to study the influence of different construction schemes on the supporting structure,a model is established according to the layered,partitioned and symmetrical excavation,and the influence of different excavation methods on the deformation of foundation pit retaining structure and surrounding strata is analyzed.According to the analysis results,the construction scheme of deep and large foundation pit under complex environmental conditions is optimized.Layered,partitioned and symmetrical excavation can effectively reduce the deformation of foundation pit retaining structure,and symmetrical excavation can reduce the deformation of soil inside and outside the foundation pit.(4)The combined support of internal support and central island structure is beneficial to control the horizontal and vertical deformation of the supporting structure by using the advantages of large lateral stiffness and strong integrity of the existing building structure.The horizontal load of the inner support can be borne by the central island structure,and the horizontal inner support connecting the supporting piles can directly act on the central island structure.Symmetrical layered excavation can further improve the stress and deformation of the internal support structure.