Study On Influencing Factors Of Deep Foundation Pit Deformation In Open Cut Tunnel

With the development of urbanization in China,high-rise buildings and rail transit projects are constantly emerging,and the safety of deep foundation pit projects is crucial to the smooth construction of underground projects.Because there are often dense buildings and pipelines around the foundation pit,the requirements for the deformation of the foundation pit are more stringent,combined with the complex geological conditions and engineering economic requirements,the foundation pit support has the characteristics of high risk and difficulty Therefore,the research on the deformation law and control of foundation pits has received extensive attention,and its results have important engineering application value.The thesis is based on the deep foundation pit project of the No.2 tunnel of Yu'an,a newly built intercity railway connection line,and studies the deformation law and influencing factors of the foundation pit.The main contents and conclusions are as follows:1.Based on the field monitoring data of the project,combined with the site construction conditions,the displacement of the pile and the axial force of the steel support are analyzed.The results show that: with the excavation of the foundation pit,the deformation mode of pile body gradually changes from forward inclination to arch shape,and the maximum horizontal displacement is located between the third support and the base.The axial force of the support increases overall with the excavation of the soil.After the lower support is installed,the growth rate of the axial force of the adjacent upper support slows down.When the earthwork is excavated to the basement,the axial force of each support tends to be stable.2.The software FLAC3D is used to conduct numerical simulation of the step-by-step excavation and support of the foundation pit,and the cloud diagram of the displacement of foundation pit and internal force of the supporting structure under various working conditions is obtained,and their variation with working conditions is analyzed.The simulation results are compared with the monitoring data,which proves that the analysis model is reliable.3.On the basis of the above work,a numerical analysis method is used to study the influence of various factors on the deformation of the foundation pit,including the parameters of the retaining pile,the pre-loaded axial force of the support,the location of the support arrangement,the width of the foundation pit,and overexcavation,etc.The results show that the appropriate supporting pre-applied axial force is 40% ? 70% of the designed axial force,which can effectively reduce the deformation of the foundation pit and prevent the bending moment of the retaining pile from being significantly increased due to the excessive pre-applied axial force;The position of the three supports is moved down properly,which can reduce the maximum horizontal displacement and bending moment of the retaining piles,which is conducive to the stability of the foundation pit.The width of the foundation pit has an obvious effect on the deformation of the foundation pit.For the foundation pit with a narrow width,the self-stability of the foundation pit can be fully utilized for optimal design.The overexcavation of the first layer of soil has a significant effect on the horizontal pile-top displacement and the shape of the deformation curve of the pile.The maximum deformation of the retaining pile is the most sensitive to the overexcavation of the third layer.The deformation of the foundation pit is affected by the overload from large to small order is: ground settlement,horizontal displacement of retaining pile,and heave of base.The maximum ground settlement and the displacement of the retaining pile increase approximately linearly with the increase of the overload value.