Research On Optimization Of Supporting Schemes For Deep Foundation Pit In Soft Soil And Construction Risk Prevention

With the development and utilization of underground space,the technical challenges and risks of excavation and support of deep foundation pits in cities are increasing,especially those of deep foundation pits in soft soil.The excavation and support of soft soil deep foundation pit are easy to cause soil slippage,pile displacement,bottom heave,support and retaining structure leakage,foundation pit instability and other damages,which have a great impact on the security of the surrounding environment in the construction process.At the same time,the supporting scheme of foundation pit engineering is not necessarily unique,and the cost of foundation pit construction is different.Therefore,it is necessary to carry out technical and economic comparison for the selection of foundation pit support schemes in soft soil environment based on the analysis of specific problems.On the basis of literature reading and practical investigation,this paper firstly sorts out and summarizes the feasible scheme for deep foundation pit support in soft soil area,and carries out technical screening for the preliminary scheme of deep foundation pit support in soft soil area.Secondly,the deep foundation pit support case of block b-2 project of hongqiao block 46 of Shanghai dongyuan group was selected as the research object.Based on the detailed analysis of the surrounding environmental conditions,engineering geological characteristics,support safety and deformation control levels of the foundation pit project,three feasible primary schemes were selected in combination with the previous studies.Among the feasible schemes of foundation pit support,the value engineering theory is applied to compare the advantages and disadvantages of three primary schemes,which are consistent with the practical scheme of foundation pit support.Function analysis is the core part of value engineering.In the function analysis,the paper innovates to use entropy method and OWA operator weighting method to calculate the function weight,and then combines the subjective and objective evaluation to make the function weight more scientific and reasonable.In addition,the risk evaluation and prevention of the selected final scheme are studied.The fault tree method is used to identify and analyze the risk factors of the supporting scheme of deep foundation pit in soft soil,and the rough set theory is used to reduce the factors,so as to form a representative risk index system.Then the risk evaluation of the preferred scheme is carried out based on the catastrophe theory,and the risk measures and risk monitoring plan are made according to its risk level.The thesis research provides a convenient,feasible and easy-to-operate path for the comparison and selection of deep foundation pit support schemes in soft soil areas.The proposed risk assessment method for foundation pit support schemes can provide a reference for practical cases.