Study On Optimization Design Of Deep Foundation Pit Combined Support Structure

With the development of human society,the trend of urbanization and the accumulation of population have caused the shortage of urban land resources and the demand for the development of underground space resources.In order to meet the needs of the city's operations,and the population's demand for space,more and more cities have become more efficient in the use of underground space.This has also led to more and more requirements for the design of foundation pits.Therefore,how to optimize the selection of foundation pit's scheme is very important.The optimized design of the foundation pit scheme is divided into two parts: the choice of design of foundation pit and parameter optimization.The paper adopts the concept of fuzzy set into the choice of foundation pit project,establishes a multi-objective fuzzy comprehensive evaluation model.By using Fuzzy Comprehensive Evaluation and Analytic Hierarchy Process and combining with engineering examples,the paper selects preferably among three supporting projects: unprotected open cut excavation,pile and inner support,underground diaphragm wall,pile and anchor rod.The supporting project with comprehensive evaluation value are 0.5604,0.1932,0.3642,that is the unprotected open cut excavation,pile and inner support is selected finally.In this paper,Plaxis was used to optimize the foundation pit's scheme,mainly adjusting the pile diameter and the depth of embedment of the pile.Through the simulation result,it can be conclude that when the pile diameter is 0.8m,it is most suitable.And the embedded depth of the pile to maintain the design of the most suitable 9m.In this paper,X-ray powder diffractometer is used to analyze the phase of the powdered clay in the foundation pit site.It is concluded that the main composition of the soil sample is quartz,and the content of other minerals is low,the soil layer have a bit of expansibility.