Deformation Characteristics And Control Measures Of Jacking Construction Of Box Culvert Under Longhai Railway

With the continuous increase of cross-projects such as crossing the existing railway under the box culvert in our country,most of them strengthen the upper existing lines to achieve the excavation of the lower soil and the jacking of the box,while ensuring the normal operation of the existing lines.However,it is inevitable that the surrounding soil will be disturbed during the construction,resulting in large deformation of the upper reinforcement structure,which poses a security threat to the operation of the upper line.At present,there are few studies on the track and the upper reinforcement system for the box culvert underpass the existing line.Especially when the jacking of the box culvert is large and the upper soil layer is thin,it is worth further study whether the trains can safely pass through the construction area.For this reason,this paper is based on the construction of the box culvert of the Longhai Railway underpass the highway,the stress and deformation characteristics of railway,box culvert and upper reinforcement system are analyzed comprehensively,and the corresponding deformation control measures are optimized.The main work completed in this article is as follows:(1)By comparing the measured results and the simulated results of the track settlement during the jacking of the box culvert,it is found that the maximum deviation between the measured results and the simulated results of the track settlement does not exceed 10%.and the presented law is basically consistent,which can better reflect the settlement change law of the existing track during the jacking construction.(2)The article studies the deformation law of the track,box culvert and upper reinforcement system in the process of jacking construction under the four kinds of traffic conditions of the existing line.The structural deformation characteristics are similar under all working conditions,in which the track settlement presents a "U" shape;the two sides of the box culvert bottom and the side wall are mainly under pressure,and the box top is mainly under tension;the vertical displacement of the upper reinforcement system is the largest at the central axis.Compared with the four kinds of traffic conditions,the deformation of each structure under the double-line traffic is the most serious,in which the maximum settlement value of the track is 7.50 mm.The research conclusion has certain reference value for similar projects.(3)By simulating the combination of different train speeds and different jacking lengths,the settlement and deformation characteristics of the upper reinforcement system and the existing track during the jacking process of the box culvert under the most unfavorableconditions are compared and analyzed.At the same jacking length,for every 15km/h increase of the train speed,the maximum settlement of the the upper existing track increases by an average of 8.36%;at the same speed,for every increase of 0.5m in the jacking length,the maximum settlement of the track surface increases by an average of 14.25%.The conclusion shows that the length of jacking has a greater impact on the existing railway track and upper reinforcement system than the upper train operating speed.(4)Based on the comprehensive analysis of the range of track early warning value and alarm value under different jacking step length and different traffic speed,the selection level of control measures for jacking construction of box culvert crossing Longhai railway is divided into three levels: recommended selection,carefully considered selection and not recommended selection.In this project,the maximum jacking length should not exceed 1m,and the maximum train speed shall be limited to 45km/h.