Study On The Mechanical Characteristics Of The Transition Section Of Sheet Pile Railway Bridge In Permafrost Region

As the key structure connecting road and bridge,the transition section of road and bridge is the key to ensure the smooth and safe passage of trains.However,due to the sudden change of stiffness between abutment and subgrade,the structure is prone to differential settlement disease,especially under the dynamic load after opening to traffic.According to the analysis of the survey data,the differential settlement disease of the transition section of the road and bridge along the Qinghai-Tibet railway is very serious.At present,the commonly used treatment method is to fill the ballast in the settlement difference cavity and re level it.This method has a certain effect in a short time,but the long-term landfill ballast is not conducive to the stability of the subgrade will lead to new diseases.At present,the research on the diseases of road bridge transition section in permafrost area is based on its temperature field and water field,and most of them are theoretical analysis or numerical simulation analysis.Based on the characteristics of permafrost active layer,this paper proposes the transition section structure of sheet pile road bridge from the perspective of stiffness difference to carry out the indoor simulation test.This test is mainly to observe the change rule of temperature field and displacement field of the transition section of sheet pile road bridge under the action of external cyclic temperature load and continuous external force load.The following conclusions are drawn:(1)The soil temperature at the center of the transition section of sheet pile road and bridge is slightly higher than that of the general transition section of road and bridge due to the higher thermal conductivity of pile foundation and the influence of double row pile foundation on it.However,the pile foundation can only affect the soil temperature within a certain range and will not affect the frozen line of frozen soil.(2)This indoor simulation test is more realistic to simulate the active layer of frozen soil,and the frozen soil simulated by the test has good frost heave and thaw settlement characteristics.Under the condition that the external environment temperature increases year by year,the active layer depth of the transition structure of road and bridge increases slightly,and the increase amplitude of the transition structure of sheet pile road and bridge is slightly larger.(3)Under the action of continuous external load and cyclic temperature load,the differential settlement of the transition section structure of sheet pile road bridge is greatly reduced compared with that of the general transition section structure.At the same time,thebending angle of the rail surface of the transition section structure of sheet pile road bridge is also greatly reduced compared with that of the general transition section structure,which shows that the existence of pile foundation greatly increases the rigidity of soil mass,which has a significant effect on reducing the differential settlement of the transition section of road bridge It has good effect and can ensure the safety and smoothness of train operation.(4)The long-term stability analysis of two kinds of road bridge transition structure is carried out by using ANSYS finite element software and numerical simulation method.Through the analysis and comparison of the temperature field and deformation field of the two structures,it is concluded that the sheet pile road bridge transition section structure has a good governance effect on the differential settlement of the road bridge transition section in permafrost area.