Research On The Effect On The Stability Of The Main Bridge Pile Foundation Brought By The Construction Of Auxiliary Road In Deep Soft Foundation Area

Due to the rheological properties of soft soil,the long-term accumulation of deformation of engineering structures in deep soft soil area during construction period and after construction will lead to structural failure and endanger the safety of structures,which has attracted more and more attention from the engineering field.The road construction work near the existing bridge pile foundation and the subsequent traffic load will have a significant influence on the long-term stability of the bridge pile foundation and increase the safety risk of the bridge pile foundation over time..In this paper,an engineering case of adding a urban road under a viaduct bridge of a expressway in coastal area is taken as the research object,and the critical bearing capacity and displacement/stress of the existing bridge pile foundation are systematically studied with the methods of literature research,theoretical research and numerical simulation after the filling of the auxiliary road in the deep soft foundation area.The main research contents include the following aspects:Firstly,according to the theories of rheology and viscoelastic mechanics of soft soil,a variety of viscoelastic constitutive models were selected to fit the creep test data of soft soil samples taken from the site selection area of the project.Burgers model was selected as the constitutive model of soft soil for subsequent theoretical research and numerical simulation.Secondly,based on the hypothesis of Winkler foundation,the mechanical model of the elastic medium constrained elastic rod with fixed bottom and free top was established,and the critical force of the compressive rod was obtained by using Rayleigh-Ritz method,and the critical force of the elastic bending rod subjected to both axial force and local horizontal distributed load under the same supporting conditions was extended.According to the elasticviscoelastic correspondence principle,the viscoelastic medium around the rod is assumed to be the elastic medium in which the ground reaction coefficient changes with the depth in the image space,and an example of the deflection solution of an elastic rod in a viscoelastic medium of Kelvin under the second trigonometric series is given by means of inverse Laplace transform.The viscosity coefficient in the solution is set to 0 and the solution is reduced to an elastic solution,which verifies the correctness of the theoretical derivation process.Then,the deflection solution of the elastic bar in viscoelastic medium of Burgers was obtained by inverse Laplace numerical transformation,and the long-term influence of the values of axial force,bar length and stowing strength on the stability of the bar was studied.Thirdly,based on the engineering application,the finite element calculation model of pile group foundation,pile cap and soil under three dimensional conditions with different ground slopes was established,and the displacement field distribution of soil around the pile,the displacement and stress time history of pile group foundation and pile cap are analyzed.The differences of the long-term effects on the structural stress and displacement of pile foundation and cap are investigated when the roadbed is filled with one side of pile foundation upstream,one side of pile foundation downstream and two sides of pile foundation.Finally,set the engineering of the construction of a new urban road under an expressway bridge in coastal area as the prototype,the finite element model of pile group foundation,pile cap and soil with different angle between urban road and main bridge is established.The time history of displacement of pile group foundation is analyzed respectively while the left and right halves of the road are located on one side of the pile foundation or symmetrically separated on both sides of the pile foundation,and the relationship between the relevant results and the the angle between bridge and road is studied.The results show that it is beneficial to the safety and stability of pile group foundation to divide the left and right half-width roads symmetrically on both sides or to arrange the left and right half-width roads with a large bridge-road angle on one side of pile foundation.