| With the advancement of China’s urbanization process,the development of urban underground space is moving from point-line to block-oriented and networked development,and it has become an inevitable development trend to build large-scale urban spaces with diverse shapes.When the construction scale and excavation depth of the foundation pit reach a certain level,the entire space is difficult to form at one time.Conventional foundation pit design and construction methods have not been able to meet the actual needs of the project.Partitioning and block construction have become more common The second excavation will cause multiple repeated disturbances to the stratum,and the increase in the excavation sequence will significantly increase the construction risk of the foundation pit.The circular enclosure structure of the foundation pit has spatial center symmetry,which can effectively use the structure’s own compression characteristics to resist external loads.It is being used more and more in engineering practice,but the circular enclosure structure is in ultra-deep and large foundation pits.The design and construction theories and methods have not been thoroughly studied,and further research and exploration are needed.Based on the national key research and development project "Coupling evolution mechanism and safety evaluation system of major risks in urban underground space construction"(National Key R&D Program of China(2018YFC0808701)),the project group defines urban underground space and underground excavation urban underground space,and establishes the objective factor risk evaluation system of underground excavation large space according to the analytic hierarchy process.Based on the national key research and development project "coupling evolution mechanism and safety evaluation system of major risks in urban underground large space construction"(2018yec0808701),combined with Wuhan Optics Valley Plaza complex project,taking the circular deep foundation pit excavated in different districts as the research object,through the use of historical accident case analysis,on-site monitoring data analysis and numerical simulation methods,the research is divided into three parts The deformation laws of surrounding strata and retaining structure are analyzed,and the deformation characteristics of circular deep foundation pit are revealed.Based on the finite element numerical model,this paper discusses the influence law of foundation pit excavation under two conditions of step-by-step and synchronous excavation.In order to control the deformation of foundation pit,some guiding principles suitable for the construction of circular deep foundation pit are obtained.The specific research contents are as follows(1)Case analysis and deformation theory research of foundation pit accident.Collected 288 cases of foundation pit accidents in China in recent years,statistically analyzed the occurrence rules of the accidents;used causality diagram analysis to identify the influencing factors of the foundation pit deformation that caused the accident,and summarized the common forms of foundation pit deformation,The elastic foundation beam theory is used to reveal the mutual influence mechanism of foundation excavation.(2)Research on deformation characteristics of circular foundation pits.Combined with the monitoring data and numerical calculation results of the optical valley plaza complex,the settlement law of the soil outside the pit during the excavation of the circular foundation pit,the lateral deformation law of the surrounding structure of each area and the support axial force distribution of each layer are analyzed The law reveals the deformation characteristics of the circular deep foundation pit.The deformation of each measuring point is compared with the deformation control standards of the foundation pit,and the applicability of the bored piles as a retaining structure in the circular deep foundation pit project is demonstrated.(3)Study on the influence of deep excavation of large and deep foundation pits.Based on the optimized finite element model,the deformation influence theory of the excavation sequence of the foundation pit was studied.The deformation of surrounding soil and the deformation of the surrounding structure are analyzed separately under the two excavation conditions of stepped and simultaneous excavation of the foundation pit.According to the deformation characteristics of each area of the foundation pit,guidance for economic and reasonable construction of deep and large foundation pits is proposed in principle. |
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