Research On Differential Settlement Characteristics And Performance Evaluation Of Subgrade-culvert Transition Section Of Ballasted Track Of High-speed Railway

There is two orders of magnitude difference in stiffness between the ballasted track embankment subgrade and the culvert of the high-speed railway.In the high-speed railway subgrade section with a large number of culverts,when the train passes through the subgrade and culvert junctions at high speeds,the rigidity unevenness between the softer subgrade and the harder culvert will cause the vehicle-track-subgrade coupling system to produce a significant dynamic effect.At the same time,this dynamic action cyclically will form and aggravate the differential settlement of the subgrade surface at the junction of the road and culvert,resulting in obvious uneven deformation of the subgrade surface,which is finally mapped to the rail to form geometric irregularities of the track.The geometric irregularities caused by the dynamic action will continue to increase,which will react to the vehicle-track-subgrade coupling system,intensify the dynamic effect of the coupling system,and form a vicious circle.In severe cases,it may even threaten the safety of high-speed railways.In the design,construction,and maintenance of high-speed railways,great attention must be paid to the problem of the subgrade-culvert transition section.In view of this,this paper uses finite element simulation and partial least square regression analysis for ballasted track systems to study the control threshold and long-term evolution of the uneven settlement of the subgrade-culvert transition section,and to propose the evaluation index of the transition performance,which may provide theoretical basis and engineering application value for the design,construction and maintenance of high-speed railways.Basically,based on a wide range of relevant research results at home and ababroad,this paper selects the subgrade-culvert transition section of a ballast track of a high-speed railway as the research object.Based on the research data of the high-speed railway,the numerical simulation standard calculation conditions of the subgrade-culvert transition section are designed.And with the aid of the finite element analysis software ABAQUS,the differential settlement of the subgrade-culvert transition section was simulated and analyzed,and the law of uneven settlement of the subgrade-culvert transition section was studied from the perspective of statics.Then,based on the simulation results of the differential settlement of the subgrade-culvert transition section under different working conditions,the transition performance evaluation index of the subgrade-culvert transition section is proposed,that is,the representative value of the rail top bending angle caused by the differential settlement of the subgrade-culvert transition section— Maximum sliding slope of 2 m chord length.According to this index,an evaluation method for the transitional performance of the high-speed railway ballasted track subgrade-culvert transition section is proposed,and the rail top bending angle database is established at the same time.According to the rail top bending angle database,the cover soil thickness on the top of the culvert,the culvert width,and the culvert height are selected as single factors,and the single factor,single-factor second-order terms and the influence of the interaction on the rail top bending angle are comprehensively considered,according to the partial least squares multiple regression analysis principle combined with the SPSS software to performmultiple regression analysis on the rail top bending angle,and the partial least squares linear regression equation for the rail top bending angle is established.With the help of partial least squares regression analysis results,significant influencing items are selected.And the degree of influence of single factor,single factor second-order items and interaction on the control index of the subgrade-culvert transition section—rail top bending angle is obtained.Get the following conclusions:(1)At the junction of the subgrade and the culvert,when the thickness of the culvert top,the width of the culvert,and the height of the culvert body remain unchanged,compared with the structure without the transition section,the installation of the transition section structure will significantly reduce the size of the rail surface bending angle .And after setting the transition section structure,the most dangerous working conditions in this article(the thickness of the culvert top is 0 m,the width of the culvert is 6 m,and the height of the culvert is 5.5 m)also meets the requirements of the rail surface bending angle specification.(2)At the same time,within the analysis value range,the most unfavorable combination of factors corresponding to the control value of 1‰ of the track bending angle can be obtained by using the partial least squares regression equation.Under the premise that there is no transition section structure at the junction of subgrade and culvert,according to the combination of the most unfavorable factors,when the width of the culvert = 6 m and the height of the culvert = 5 m,if the thickness of the top of the culvert of a subgrade-culvert transition section is> 2.6 m,Initially meet the control index of rail bending angle θ<1‰.Therefore,it can be evaluated that the transition performance of the subgrade-culvert transition section is good.