Investigation On The Coupling Interaction Between Piled Bridge Foundation And Stabilizing Piles On Steep Slope

Many piled bridge foundations of high speed railway are constructed on steep slopes,and stabilizing piles have proven to be an effective means of stabilizing such projects.However,the coupling interaction between the piled bridge foundation and stabilizing piles is still unclear.How to stabilizing the slope against landslide,especially soils around the bridge foundation is still at an early stage.The design of piled bridge foundation on steep slope was mainly based on empirical method,assuming lateral loads were fully bear by the stabilizing piles constructed near the bridge foundation.The lateral load acting on the bridge foundation due to soil movements was not considered.But when the shear deformation of soils occurs,the bridge foundation and stabilizing piles are all affected and there is a coupling interaction between them.Ignoring the lateral load acting on the bridge foundation by soil movements will certainly overestimate the bridge structural safety.The coupling interaction between the piled bridge foundation and stabilizing piles and the optimum space between them should be studied in depth.Meanwhile,the criteria for tolerable horizontal movement of bridge foundation on steep slopes is not well established.To address the problems mentioned above,combined with scientific research project“Research to reinforcement technique of landslide(talus)and experiment on the impact of retaining structure on the piled bridge foundation(Z2012-061-1)” supported by the former Chinese ministry of railway,three typical sites are selected on the basis of investigation of lots projects,which give full consideration of the influence on piled bridge foundation by landslide types,the relative bridge foundation position in the slope,different ways of reinforcement.Some research methods,such as indoor model experiment,three-dimensional numerical simulation and theoretical study,are adopted for the further research of the coupling interaction between the piled bridge foundation and stabilizing piles,especially the lateral response of the bridge foundation under the shear deformation of soils.The main research contents of this paper include:(1)Experiment on the impact of stabilizing piles on piled bridge foundation on the steep slopeModel experiments,based on similarity theory,were designed and then carried out to investigate the mechanical properties of piled bridge foundation and the interaction between the piled bridge foundation and stabilizing piles throughout the experiments.The shear deformation of soils was assumed to be uniformly distributed perpendicular to the slip surface and loaded by the jack.Firstly,the horizontal displacement gauges were adopted to monitor the feature points on slope surface.The thin phosphor bronze plates were installed vertically in the soil with strain gauges attached symmetrically to monitor the horizontal displacement of soils around the bridge foundation.And the horizontal displacement fields of the slope-bridge foundation-stabilizing piles system were obtained.Secondly,the mini soil pressure sensors were adopted to monitor the soil pressure in front and at the back of piles,both bridge piles and stabilizing piles.The strain gauges were adopted to monitor the pile bending moment.The mechanical properties and load-sharing of the piled bridge foundation,the front-row and back-row stabilizing piles were obtained through comprehensive analysis of the test data from mini soil pressure sensors and strain gauges.Finally the failure process of the slope-bridge foundation-stabilizing piles system was reproduced by comprehensive analysis.The coupling mechanism among piled bridge foundation,stabilizing piles and soils was expatiated from the standpoint of load transfer and progressive deformation.(2)Three-dimensional numerical simulation on piled bridge foundation and stabilizing piles on the steep slopeA numerical method was proposed in which the landslide was triggered by reducing shear strength at the sliding surface to simulate the slope movement due to the strength reduction of sliding interface in severe cases.Three-dimensional numerical models were established.Results from model experiment were examined and used as a basis for verifying the proposed numerical models.Parametric analyses were performed to investigate the impact of parameters of piled bridge foundation and stabilizing piles on the behavior of bridge foundation.Specifically,numerous three-dimensional numerical simulations,with actual projects as prototypes,were carried out to investigate the impact of the relative bridge foundation position in the slope,pile head constraint,stabilizing piles and the space between piled bridge foundation and stabilizing piles on the behavior of bridge foundation.(3)Theoretical model of piled bridge foundation on the steep slopeA theoretical model of piled bridge foundation on the steep slope was proposed considering the inclined slip surface,in combination with the model experiment results.Three-dimensional numerical simulation was employed to access its feasibility and validity.Error analysis has been done qualitatively,then a coefficient to revise the approximate formula was proposed and the application scope was given.(4)Optimum design method for piled bridge foundation retaining with stabilizing piles on the steep slopeThe criteria for tolerable horizontal movement of bridge foundation on steep slopes was proposed.Then this paper also tries to explore the practicability of stabilizing piles with compressible material in such projects.Based on results of three-dimensional numerical simulations,principles of reinforcement of piled bridge foundation retaining with stabilizing piles on the steep slope were proposed,including the optimum location of bridge foundation in the slope and space between bridge foundation and stabilizing piles.Finally,the reinforcement technique for such projects was proposed preliminarily,with the tolerable horizontal movement of bridge foundation as a control condition.