Integrated Structure And Its Working Properties Of Large Single Underground Structure And Deep Foundation Pit Enclosure

In the water environment treatment project of plain city,it is usual y necessary to build large-scale underground single structures such as primary rain regulating and storage pool,and the cost proportion of deep foundation pit retaining project is often very high.If we can analyze the mechanical response of the side wall of the foundation pit and put forward the integrated structure form of the underground structure and the deep foundation pit support,it will have significant economic benefits.In this paper,based on the urban water environment treatment project in Fuyang City,Anhui Province,the deformation and instability characteristics of different retaining structures in the process of excavation of deep foundation pit of single underground structure are studied by theoretical analysis,physical simulation test and numerical simulation.The main research work and achievements are as follows:(1)On the basis of summarizing and analyzing the changes of earth pressure,the upheaval of pit bottom,the deformation of retaining structure and the deformation of surrounding surface during the excavation of foundation pit,the integration method of underground single structure and retaining structure of foundation pit is put forward.According to the load acting on the composite retaining structure and the interaction between the structure and the soil,the calculation model of the earth pressure of the composite retaining structure is established,and the calculation formula of the earth pressure of the composite retaining structure is derived based on the calculation theory of the earth pressure of the inner supporting and double row pile retaining structure.(2)The model test method is used to simulate the excavation process of foundation pit step by step under four retaining conditions of single row piles,staggered double row piles,double row piles and "pile wall integration" composite structure.The results show that the top horizontal displacement and the lateral horizontal and vertical displacement of the retaining structure are closely related to the type and layout of the retaining structure.The "pile wall integration" composite retaining structure has obvious advantages in limiting the displacement of the top of the retaining structure and the displacement of the soil outside.(3)Using numerical simulation method,the influence of cantilever retaining structure on the excavation stability of deep foundation pit with and without internal support is calculated and analyzed,and the earth pressure distribution diagram,displacement distribution cloud diagram,foundation pit displacement diagram and retaining structure bending moment diagram of cantilever retaining structure are obtained.The results show that: without internal support,the retaining structure is in unilateral tension,and the bending moment value is large,and the horizontal displacement of the top and the horizontal and vertical displacement of the outer soil are also large;with internal support,the positive and negative bending moments of the retaining structure are evenly distributed,the maximum bending moment value is significantly reduced,the horizontal displacement is significantly reduced,and the excavation process of the foundation pit is safer.(4)This paper discusses the sensitive factors that affect the working performance of the integrated structure,analyzes the influencing factors of the excavation stability of the foundation pit,and puts forward the anti floating method of the integrated structure.This paper summarizes the waterproof measures in the process of excavation of foundation pit,obtains the calculation formula of buoyancy under different conditions in combination with the different position relationship between the main structure and aquifer,calculates the buoyancy resistance of underground single structure,and explains the anti buoyancy method of integrated structure.