| Firstly,traffic has developed rapidly in recent years,urbanization process is accelerated,and more and more cities turn their development direction to the development and utilization of underground space.In addition,many cities did not consider the intersection with urban roads at the beginning of railway construction,resulting in inconvenient traffic and limited development on both sides of the railway.Therefore,it is urgent to build underground urban roads through both sides of the railway traffic and coordinate the development of both sides of the railway.As one of the ways to connect the traffic on both sides of the railway,the underpass railway has the advantages of less demolition,less traffic interference and short construction period.However,the urban road underpass railway frame bridge and culvert project is very complicated.Special consideration should be given to the impact of train vibration on the whole project when the train passes through the upper bridge structure.The existing calculation methods are faced with great challenges when dealing with the underpass problem of such a complex large-scale urban road interchange.Therefore,the study of train vibration load is of great practical significance to the mechanical response of trainbridge-foundation pit butting-soil coupling system.Based on a city road undercrossing railway bridge and culvert project,a coupling model of train-bridge-foundation pit butting-soil was established by finite element software,and its mechanical response under train vibration was analyzed.The main research methods and contents are as follows:(1)Using ABAQUS finite element software,combined with relevant theoretical methods,the train-bridge-foundation pit butting-soil coupling system model is constructed,and the effectiveness of the coupling model is verified.(2)A track unevenness model is established to study the dynamic response of each structure in the coupling system under the train vibration load when the train runs at a single speed and the axle load of the vehicle passes through the upper foundation pit bridge,and the mechanical response under the static load is compared and analyzed.(3)Under the excitation of track irregularity,the dynamic response law of each structure in the coupling system is studied under the train vibration load with different running speeds and different vehicle axle loads.Through the research and analysis of the above contents,the following conclusions are drawn:(1)In the bridge subsystem,the vertical displacement of longitudinal beam is the minimum,the vertical displacement of beam is the maximum,and the vertical displacement of rail is between the two.The longitudinal stress of longitudinal beam and rail is the largest,while the transverse stress of beam is the largest.The transverse stress,longitudinal stress,vertical stress,vertical displacement of longitudinal beam and vertical displacement of beam and rail increase with the increase of train speed.According to the calculation results,it is recommended that the maximum speed of train passing the bridge should not exceed 50 m/s.At the same time,the dynamic response of each structure in the bridge subsystem increases with the increase of the axle load of the train,and according to the calculation results,it is recommended that the maximum axle load of the train passing the bridge is not more than 117 t.(2)In the train subsystem,the transverse and vertical wheel-rail forces of the train are very large at the beginning of wheel-rail contact,which are in an unstable state and tend to be stable with the train running process;In addition,the derailment coefficient increases with the increase of train speed.At the same time,both lateral and vertical wheel-rail forces increase with the increase of axle load.(3)In the sub-system of foundation pit support and soil,the uplift deformation of soil in the excavation face under the action of train vibration load is significantly larger than that under the action of static load,and increases by 35.7%;The longitudinal horizontal displacement of foundation pit supporting pile under train vibration load is significantly larger than that under static load,and increases by 26.1%.The stress of prestressed bolt under train vibration load is also increased by 29.0% compared with that under static load.In addition,the dynamic response of foundation pit retaining pile does not change with the increase of train speed,but increases with the increase of train axle load.The above research results provide a reference for the future research of railway bridge and culvert problems,and have high engineering application value. |
