The Influence Of Preloading On Piles Of Existing High Speed Railway Bridge In Soft Soils And Control Technologies

With the development of national economy,the high-speed railway construction has been in a stage of rapid growth.Some cities already have a number of operational high-speed rail,and due to the needs of urban development,it’s inevitably that there are construction projects near high-speed railway facilities.The soft soil has low shear strength and large thickness in coastal region,so the usually ground improvement is surcharge.According to the engineering experience,the soil will produce a large deformation under the preloading,and the vertical settlement value can reach a few meters,the level of deformation is also large.When the soil is soft,the horizontal deformation is bigger would be threat to the surrounding normal use of existing buildings,and sometimes lead to structural damage.And the normal operation of high-speed railways need better track smooth degree,so how to control the influence of large deformation of foundation of high speed railway has become the urgentthing.This paper is devoted to study heaping pre-compression projects near the bridge foundation of a coastal high-speed railway in Fujian,analyze its influence on surroundings,and put forward some improved schemes for the deformation control of the pile foundation of high-speed railway bridges.(1)The deformation of soil under the loadsand pile-soil interaction analysis method and the research status is summarized.The results based on experience or experimental data method are generally in line with the actual,but we should have extensive engineering data or field test;Calculation of soil deformation is based on the theory of elasticity and unsuitable for the deformation under the large load;Finite element soft show the results intuitively and is good at to study the factors analysis,but it has the higher requirements for the establishment of the model.(2)This article is based on an stack engineering in Fujian,to analyzethe settlement and horizontal displacement distribution of soft soil under the action of the large stack.And it points out that,vertical deformation of soil characterized by saddle type,and the larger settlement is located near the load boundary.Horizontal deformation is decreases in the direction away from the surcharge,the maximum is located in the slope foot,and with the increase of the distance from the stack,the deep horizontal displacement by triangle distribution to trapezoidal distribution.(3)The numierical simulation analysis of force and deformation of high-speed railway bridge pile foundation influence by loads is conducted.The results show that,under the effect of loads,the largest horizontal displacement of the pile head has reached 22 mm,beyond the limit of high speed railway request.Caps to deviate from the loads at the same time,the bridge deck transverse slope change.In the piles and pile caps points where a larger shear force and bending moment,the bending moment value in 400kN.m.(4)On the basis of predicting the horizontal displacement of soil and deformation characteristics of tip of piles,deformation and internal force of pile is calculated.Using two phase analysis method based on deformation of soil,considering of constraints on the top of the pile,the lateral deformation and internal force of the pile foundation which is impacted by loading is analyzed is caculated by the corresponding finite difference method to calculate program.The comparison of numerical simulation and two phase analysis results show that there is a small error,which is permission.Given two phase analysis method need the pile end constraint conditions,the finite difference method can be obtained easily,so it’s more convenient and effective in practical application.(5)Analyzing the loads characteristics(loads distance,and the size of loads,loading rate),soft soil properties(soil thickness,poisson’s ratio and elastic modulus of soil)which have influence on internal force and deformation of the adjacent pile foundation.Results show that linear relationbetween stack size and pile internal force or deformation,the additional internal force and deformation of the pile foundation is gradually increased with the loads increase.The logarithmic relation of deformation or force with the distance is shown,too.When foundation is close with the boundary of loading aero internal force and deformation of piles increase sharply,and in a far away place,with the increase of distance pile internal force and deformation changes smaller;the rate of loading influence on pile foundation during filling,and it has little influence on the final result.When poisson’s ratio is less than 0.4,the deformation and force of the pile is almost unchanged.When poisson’s ratio changed between 0.4～0.5,force and deformation of piles have a large variation.The thickness and elastic modulus of soil have a greater influence on pile foundation,the force and deformation increases with the thickness increases,and decrease with elastic modulus increase.(6)According to the deformation of the pile foundation of the high-speed railway bridge,the reinforcement measures are put forward:When satisfying the engineering requirements,changing stacking size and the stacking distance can be reduce the influence on the pile foundation.Or improving the soft soils by preloading with plastic drainboards and sand piles,to reduce the deformation of the pile foundation.And we can treat the soft soil between piles and preloading by concrete mixing pile and reinforced concrete grouting pile.