On-site Monitoring And Numerical Simulation Analysis Of Deep Foundation Pit Excavation

In the process of urban construction and development in our country,a large number of deep foundation pit engineering problems have arisen,and the size and depth of foundation pits have also continuously increased and deepened.The resulting geotechnical environment and geotechnical problems have also led to the design of underground structures.Construction has become a key issue in engineering construction.In Nanjing,because of the urban construction on the banks of the Yangtze River,the geological conditions of the Yangtze River tidal flat are relatively complex,and the high-rise buildings on the surface are complex.The underground pipe network is intricate and complicated.It is relatively difficult and risky to carry out the excavation construction of deep and large foundation pits.Therefore,the research on the safety and stability of the supporting system and the displacement of the surrounding soil during the excavation of deep foundation pits are the key factors to ensure the safety of deep foundation pit construction.In this paper,a deep foundation pit project located in Jianye District of Nanjing City is taken as an example.A large number of on-site observations have been carried out on the force of the supporting structure during the excavation of the foundation pit and the displacement of the soil around the pit,and the excavation of the actual project has been carried out.The finite element analysis was performed on the stress and deformation of the support system during the process.The main work and results of this article are as follows:Firstly,through the analysis of monitoring project data such as settlement of pile tops,horizontal displacement of supporting pile tops,horizontal displacement of deep soils,support column settlement and axial force of reinforced concrete horizontal support,the displacement of deep foundation pits is discussed.The reason for the change and the effect of the deformation on the support structure.The results show that the deformation of the deep foundation pit supporting structure is continuously increased during the excavation process of the foundation pit,and the rate of change is different under different working conditions;The effect of soil excavation speed,temperature on the deformation of support structure can not be ignored.Secondly,we can use the F-SPW software to calculate the internal forces of the supporting structure and compare it with the measured results:the calculation results of internal forces and displacements show that the elastic method calculation results are larger than the classical method,but the maximum displacement does not exceed the warning value,so the calculation of the elasticity method is more conservative and safer.The measured values of the axial forces in all layers are all greater than the design values.This is mainly due to the fact that the design values cannot take into consideration various sudden conditions encountered in the construction process,such as the steep rise or steep fall of the weather,and a large number of piles are piled on the supports,steel tubes and other external loads.Thirdly,using the Mohr-Coulomb model as the soil constitutive model,the FLAC3D finite element software was used to comprehensively consider the effects of layer excavation and horizontal support on the foundation pit,and then a two-dimensional model of the deep foundation pit was established and analyzed.Under the condition of parameters,the deformation and rule of deep foundation pit support:The stiffness of supporting structure,soil parameters,etc.have a great influence on the deformation of the support structure,and thedepth of the soil in which the support pile is too small may cause deformation of the support structure too big or even collapsed.Finally,in the sixth chapter,through the three-dimensional simulation and prediction analysis of a deep foundation pit in Hefei,the deformation of the retaining structure and the internal force that may occur during the excavation of the deep foundation pit are discussed,and the adjacent buildings may be adjacent to the excavation process.The impact wasanalyzed briefly.