Field Test Analysis And Processing Effect Assessment On The Influence Of Construction Load Of T-Pattern Bridge On High Speed Railway Subgrade

This paper aims at studying the influence of construction load of T-pattern bridge of the major structure of newly-constructed flyover of Chengdu Second Ring Expressway on the Chengdu-Du Jiangyan Express Railroad that the second ring expressway crosses and studying the control efficiency of on-spot shelter piles measures by site test method analysis. Firstly, this paper gives detailed introduction of researches on influence of pile foundation construction on nearby buildings, researches on pile and pile group foundation settlement theory by collecting related research findings. Besides, this paper takes T-pattern steel-constructed bridge of Chengdu Second Ring Expressway that crosses Chengdu-Du Jiangyan Express Railroad as background project, makes field monitoring on foundation settlement deformation through arranging all kinds of settlement observation instruments at the spot site and makes analysis on the data gained from the spot site. Combined with field monitoring result, the theoretical analysis and numerical modeling and so on, this paper makes further research on additional impact of T-pattern steel-constructed construction load on subgrade of Chengdu-Du Jiangyan Express Railroad and verifies the control efficiency that shelter pile project can reduce the subgrade settlement and lateral displacement of on-operation high speed railway.Through field monitoring, theoretical analysis and numerical modeling, the following conclusions are made:The heavier the construction load is, the stronger the subgrade settlement is. After the construction, the subgrade surface becomes stable and the transformation of subgrade construction can be described as superposition produced by transformation of two major piers37#and40#. The real-time monitoring result from subgrade settlement of A-A, B-B section indicates that the additional settlement and differential settlement that the turned pile foundation load put on high speed railway are controllable both during the construction time and after the construction time, the existing subgrade construction is safe and the normal operation of Chengdu-Du Jiangyan Express Railroad is guaranteed.During the construction of turn bridge, the pile settlement at different layers increases as the times goes on; during the period of bridge fold, vertical load does not increasing and all depth settlement values restrain, becoming stable; the ratio of the up-pile soil settlement to the ratio of the down-pile soil settlement is about1:1.5; through actual measurement, it turns out that shelter pile project decreases the influence of pile foundation load on nearby subgrade construction transformation, obtaining obvious strengthening and isolation effect and ensuring the subgrade construction safety and stability of on-operation railway. The horizontal displacement of the soil around piles which is produced by group piles load and changes with depth change presents S-pattern with two obvious inflection points on this curve and one neutral point whose lateral displacement is0. On the upside of the foundation, the lateral displacement is likely to be dragged to the group piles while the soil under the foundation is likely to be extruded outward. Through the monitoring result, it can be concluded that shelter pile has certain restraint function on soil lateral deformation produced by group piles load.The soil around the piles produces settlement subsider under group piles load. The settlement around pile cap is most obvious with22mm. The further it is away from the file foundation, the less obvious the settlement is. The decreasing amplitude of the settlement is steeper within20m and beyond20m, it becomes stable gradually, until about50m (three times of the diameter of pile cap) the settlement is just1mm which can be ignored. This can be considered as the influence region of group piles foundation and verifies Randolph Theory.The high speed railway settlement through numerical calculation and the lateral deformation rule at both right and left slope toe conform to the spot test result. By comparing with project without shelter piles, the shelter project has obvious control efficiency and it can be learned in the future similar projects.