Study On Deformation And Internal Force Of Braced Retaining Structure With Row Piles In Deep Foundation Pit

With the rapid development of urban subway,the development of deep foundation pit to the ultra deep and super large scale has brought great challenges to the engineering design.Taking the deep foundation pit of Chunxi Road Chengdu metro station as the background,the conventional design of deep foundation pit is carried out according to the actual excavation parameters,and the site monitoring of deep foundation pit is carried out.The three-dimensional model of deep excavation is established by the finite element software Midas/GTS,and the dynamic numerical simulation is carried out,and compared with the monitoring value and design value.On this basis,the influence of the physical and mechanical parameters of the steel support,the row of piles and the soil and rock mass on the deformation and internal force of the retaining structure is studied.The deformation and internal force of the retaining structure are summarized.Through the above work,the main results are as follows:(1)According to the characteristics of deep foundation pit,the inner support pile arrangement is selected,and the conventional design of deep excavation is carried out according to the actual excavation parameters.Through the analysis of monitoring data,it is found that the deformation of pile body is smaller and the deformation of pile bottom is larger before the installation of the first steel support,and the row of piles is linearly shifted to the foundation pit.After the construction of the second steel support,the deformation of the pile body is convex,and the displacement of the pile head is small,the displacement of the bottom of the pile is larger than the outside of the foundation pit,and the middle part of the pile is deformed to the pit.With the continuous excavation of the foundation pit and the support of third steel supports and pre axial forces,the deformation of the upper part of the pile is smaller,and the overall deformation of the lower part is larger than the pit.Among them,the first and second steel support shaft force is bigger,and the curve has bigger fluctuation,the third steel support shaft force is smaller,and the curve fluctuation is not big.(2)By Midas/GTS finite element software for deep foundation pit numerical simulation,and the simulation and design values of three were analyzed.The simulation results show that,with the excavation,pile foundation pit displacement has been to,but when combined with steel support,the deformation rate was under control,from the first steel support shaft deformation the force of back pile in foundation pit in slow deformation and design values,there is a big difference between the value of monitoring.Although both the monitoring value and the simulated value have different pile deformation,there is one point that the application of steel support controls the deformation of the row of piles to the foundation pit.The simulation value of the steel support axial force is close to the monitoring value,but the design value is rather large.The monitoring value of the bending moment and shear force of the pile row is in good agreement with the design results.(3)By changing the steel brace stiffness and pre axial force,pile rigidity,soil physical and mechanical parameters,found that the effect of factors on the internal bracing row pile supporting structure deformation and internal force of the steel support: increased stiffness and pre axial force and pile's stiffness,can effectively inhibit horizontal displacement of piles,but then increased to a certain range,the horizontal displacement of pile effect is greatly reduced.Increase of steel brace stiffness and pre axial force,although the control of the horizontal displacement of pile,but also resulted in the increase of pile internal force and steel support axial force,means to pay more,the project cost will increase accordingly.At the same time,increasing the rigidity of the row piles makes the row piles increase the bending moment,and the internal supporting axial force decreases gradually.It shows that the greater the rigidity of the pile is,the more force it bears,and the smaller the counterforce of the steel support.(4)In order to analyze the pile in the lower part to the pit deformation of mudstone,cohesion,internal friction angle,elastic modulus and Poisson's ratio influence factor analysis obtained: with the increase of mudstone cohesion,internal friction angle,elastic modulus decreases or Poisson's ratio,increase the middle and lower parts of piles will shift to a certain extent the.Among them,the mudstone Poisson ratio has the greatest influence on the horizontal displacement of the pile,followed by elastic modulus,cohesion and internal friction angle.Preliminary analysis of pile bottom to pit deformation reasons: pile surrounding soil rigidity is low,the pile process make the pile surrounding mudstone more broken,which leads to the impact characteristics more easily by the compression of the mudstone hole environment around the hole,numerical change of physical mechanics around the pile of mudstone Poisson ratio,elastic modulus the parameters,combined with steel support stiffness and pre axial force is bigger,will force the pile deformation to the pit,resulting in the lower row of piles to the pit deformation characteristics of the larger.