Research On The Influence Of Construction Of New Bridge Pile Foundation On Additional Settlement Of Existing High-Speed Railway Box Culvert

At present,China's high-speed railways,highways,urban subways,urban corridors and other large-scale infrastructure construction are in the process of rapid development,and limited construction land has become the primary problem restricting the development of urban construction.Under this development trend,building buildings next to existing buildings and making full use of the upper space and underground space has become the only way for the development of urbanization in China.Therefore,the study of the interaction between the pile foundation of the newly-built building and the adjacent existing structure has become the difficult and hot spot that the geotechnical engineering community urgently needs to pay attention to.And most of the current research is about the interaction between pile foundation and adjacent buildings,most of which will focus on the impact of new tunnels,foundation pits,etc.on the pile foundation of existing buildings.There is very little research on existing high-speed railway box culverts on newly built pile foundations.It can be said that the impact of a newly built bridge group pile foundation on the adjacent existing high-speed box culvert is accompanied by the entire life of the entire pile foundation.From the initial construction stage to the subsequent superstructure construction stage and the later normal operation stage,each stage needs attention to the impact of the adjacent existing high-speed box culvert.Therefore,this paper uses the MIDAS/GTS finite element program to establish a three-dimensional model to study the effect of pile foundation load on existing high-speed box culverts.And consider the impact of the pile foundation on the box culvert structure in three stages:1.Pile foundation construction;2.Superstructure construction;3.Operation and use stage.In addition,the additional settlement of the box culvert structure under various influencing factors is considered.Finally,the structural deformation,additional settlement and control measures of the high-speed railway box culvert under pile foundation load are summarized.The details are as follows:?1?Using the three-dimensional finite element program MIDAS/GTS,a three-dimensional numerical model of the true relative position is established to study the influence of the pile foundation construction stage,the cap pier column construction stage,and its superstructure construction and operation stage on the adjacent existing railway box culvert structure.The changes of the additional settlement of the box culvert structure,the settlement of the track position of the box culvert floor and the settlement of the overlying strata with the construction of the bridge structure are analyzed.The research shows that due to the post-construction settlement of the box culvert structure and the additional settlement caused by the construction of the new bridge,the total post-construction settlement generated by the box culvert structure will most likely exceed the allowable value of 15mm required by the code.During the construction process,some isolation and protection measures are needed to avoid or reduce the impact on the adjacent existing box culvert structure.?2?According to the background engineering,three dimensional numerical simulation is carried out for different pile foundation lengths and the net distance between pile foundation and box culvert structure.The effects of different parameters?length of pile foundation?the net distance between pile foundation and box culvert structure?on the additional settlement of existing box culvert structures are summarized.According to the numerical simulation calculation of the five conditions of the bridge span arrangement,the analysis and comparison of the results show that the bridge span arrangement in the fourth condition?The distance S₁between pile foundation and box culvert is 10m;S₂ is 8 m?has the greatest influence on the additional settlement of the box and culvert structure.In the third working condition?The distance S₁ between pile foundation and box culvert is 9m;S₂ is 9 m?,the bridge span position arrangement has the least influence on the additional settlement of box and culvert structure.The numerical simulation is carried out according to five working conditions of bridge pile foundation length.The results show that the additional settlement of box culvert structure decreases with the increase of pile length.Therefore,appropriately increasing the length of bridge pile foundation can effectively control the settlement.Too long the value of pile length will also cause waste to a certain extent.?3?The blocking effect of the length of the isolation pile,the location of the isolation pile and the number of isolation pile rows on the additional settlement of the box culvert structure at the final stage is analyzed.In this paper,a total of 9 shielding schemes for bored piles are designed,and the numerical simulation of the isolation effect is carried out.The main analysis shows that when the isolation pile length is less than the length of the bridge pile foundation,it cannot block the additional settlement of the box culvert.When the isolation pile is longer than or equal to the length of bridge pile foundation,the blocking effect on box culvert structure will become more and more obvious with the increase of the isolation pile length.However,after increasing to a certain length,continue to increase the length of the isolation pile,the improvement of the blocking effect will gradually decline.The study on the number of isolated pile row shows that the additional settlement blocking effect of box culvert structure will be increased by increasing the number of row.However,if the number of isolation piles is increased after reaching a certain number of rows,the increase of blocking effect will be reduced.So in the setting of isolation,must pay attention to the isolation pile row number is not the more blocking effect is better.The number of pile rows should be selected reasonably according to the net distance between the new building and the existing structure.The net distance between isolated pile and box culvert is studied by numerical simulation.It is found that the larger the net distance between the isolation pile and the box culvert is,the larger the percentage reduction of additional settlement of the box culvert structure will be,and the more obvious the blocking effect will be.That is to say,the smaller the distance between the isolation pile and the bridge pile foundation is,the more obvious the barrier effect on soil displacement is,and the smaller the maximum value of additional settlement of box and culvert structure will be.