Study On Construction Stability Of Large Section Box Culvert Under Running Railway

It is one of the construction methods to connect the traffic on both sides of the railway that the frame box culvert undergoes the existing railway.The jacking construction of the large section and large angle skew frame box culvert crossing the complex busy multi strand trunk road has high safety risk and great difficulty.It has important application value to study the stability of the box culvert under different construction conditions.Relying on the overpass project of Xi’an Jingjiu Road Underpass Longhai Railway under construction,this paper studies the jacking force and the deformation and stress of box culvert structure under the influence of train dynamic load in the process of oblique jacking of large section box culvert underpass operating railway line by using the methods of theoretical calculation,numerical simulation and field monitoring,the main research work and achievements are as follows:(1)Based on the analysis of the engineering geological characteristics and construction requirements,this paper puts forward the overhead structure system of the frame box culvert construction under the jacking construction multi strand railway line,the implementation scheme of the underpass construction and the key and difficult points of the jacking construction.Based on the theoretical and empirical formula method,the expected jacking force value of box culvert jacking is given;according to the size characteristics of large section and large angle skew frame culvert,and based on the requirements of local compressive strength and size,the layout scheme of jacking hydraulic jack is proposed.(2)In the jacking construction stage of box culvert under the action of jacking force,four most unfavorable conditions of box culvert jacking stage are selected,including the empty pushing stage,the first broken pile jacking stage,the second broken pile jacking stage and the third broken pile jacking stage.The numerical simulation method is used to study the deformation and stress of box culvert in different jacking stages.The numerical analysis results show that with the increase of jacking stage,the displacement of jacking direction gradually decreases,and the maximum uplift and settlement of box culvert decrease;in terms of stress,the main stress of frame culvert reaches the maximum in the third pile breaking stage,and its maximum main stress is less than the standard value of concrete strength,so the stability of box culvert in different jacking stages is good.(3)In the jacking construction stage of the box culvert under the influence of the dynamic load of the operating train,the construction of the box culvert under the conditions of 30 km/h,45 km/h and 60 km/h is carried out The numerical simulation results show that the displacement and principal stress of the characteristic points of the box culvert reach the maximum in the third pile breaking stage under the action of dynamic load,and the response amplitude of the characteristic points in the middle of the box culvert roof span is more obvious;the displacement and stress analysis of the box culvert under different train speeds It can be found that the variation law of time history curve of characteristic points is basically similar,the vertical displacement value and principal stress of characteristic points increase with the increase of train speed,the maximum tensile and compressive stress values are within the requirements of relevant specifications,and the dynamic load of the train is not enough to cause damage to the frame box culvert in the most unfavorable three pile breaking stages.(4)In the actual project,when the train passes at a speed of 45 km/h,six measuring points are arranged under the roof of the third span of the frame culvert to monitor its vibration acceleration on site.Among them,No.1,No.2 and No.3 measuring points are respectively located at the rear end,middle and front end of the central axis,and No.4,No.5 and No.6 measuring points are respectively located at the rear end,middle and front end near the middle wall.The results show that the response value of vibration acceleration of measuring points 2 and 5 is relatively large,and the maximum value is at measuring point 2.The vibration acceleration of measuring point 5 is relatively small on the side with middle partition,and that of measuring points 4,5 and 6 is slightly less than that of measuring points 1,2 and 3 because the adjacent middle partition bears a certain vertical impact load.(5)According to the actual working conditions,the nodes corresponding to the actual monitoring position are set in the numerical model for numerical simulation and comparative analysis.The simulation results of the numerical model are basically consistent with the measured data in the vibration acceleration response law,which verifies the rationality of the model and further proves the stability of the box culvert under the jacking force and the vertical dynamic load generated by the train running It’s very good.