Study On Mechanical Behavior And Analysis Method Of Box-type Embankment Structure In Highly Filled Railway Engineering

The box embankment structure is composed of hollow reinforced concrete box at the lower part and track bed at the upper part.It is a new type of embankment structure,which has the advantages of small area,low weight,large stiffness and high strength.It is suitable for limited land,large filling height and weak foundation.However,the related design calculation theory is not mature yet.In this paper,the vertical load transfer mechanism of box embankment structure is studied by means of numerical simulation,structural mechanics analysis method and elastic foundation beam theory based on the railway connection project of Bangladesh Padramar Bridge.The theoretical calculation method of the structure is established,and the influence characteristics of main factors on the internal forces of the structure and the optimal selection of the structure are discussed.The main results are as follows:(1)The vertical load transfer mechanism of box embankment structure is revealedUnder the action of on-line load and structure weight,the roof of box structure is subjected to direct stress,which is transmitted downward to the web and the middle partition,and then to the foundation plate,and then the base compressive stress is generated on the bottom surface of the foundation plate and transmitted to the foundation.In the vertical load transfer process of the trinity of superstructure,foundation plate and foundation,the members of the box structure produce internal forces and displacements.Because of the overall stiffness of the box structure,the members have good force transfer performance,and the internal force transfer has the characteristic of symmetry.The vertical stress at the junction point between the two webs and the foundation of the box embankment structure is non-uniform from the outside to the inside.The inner side of the common type and the outer side of the middle diaphragm type are the maximum respectively,which can be approximated as a four-section uniform distribution mode.(2)A theoretical analysis method of box embankment structure considering the interaction of superstructure-foundation and foundation is establishedFor single-track and double-track railway box embankment structure,the box structure is divided into upper frame structure and lower foundation plate,and the influence of structure self-weight is considered.The superstructure adopts the structural mechanics calculation method,the foundation plate adopts the Winkler elastic foundation beam calculation method,and the section uniform distribution pressure mode is adopted at the junction point of the middle baffle,web and foundation.The deformation coordination between the superstructure and the foundation plate is fully considered and the displacement of the foundation plate is introduced into the analysis of the superstructure as the displacement of the support.The example analysis shows that the relative deviation between the theoretical calculation and FLAC3 D numerical simulation results of the maximum bending moment in the middle span of the foundation slab is about 5%,13.5%,1% and 29%,respectively,for the single and double track railway common type and middle bulkhead type box embankment structure,and the theoretical calculation value is generally small.(3)The influence characteristics of the thickness of main components on the internal forces of single-line and double-line common box embankment are determinedFor ordinary structure,with the increase of the thickness of the roof and foundation plate,the maximum bending moment of the roof and foundation plate increases non-linearly and linearly while the bending moment of the diaphragm type roof changes little,and the maximum bending moment of foundation plate decreases linearly.With the increase of the thickness of web,the maximum bending moment of common and middle diaphragm foundation plates increases linearly and decreases linearly.The maximum bending moment of the foundation plate increases linearly with the increase of the thickness of the middle diaphragm.The example analysis shows that the maximum bending moment in the middle span of the roof and foundation plate of the box type structure is about 25% of that of the ordinary box type structure,which can significantly improve the force of the box type structure.(4)The optimal type of box embankment structure with a total height of 12 m is givenThe thickness of roof,foundation plate and web is 1.1m,1.2m,0.9m and 1.2m,1.2m and 0.9m respectively for the single and double wire common type.For single line and double line middle partition type,the thickness of roof,foundation,web and middle partition is 0.9m,1.0m,0.8m,0.8m and 1.0m,1.1m,0.8m and 0.8m.The research results of this paper on the theoretical analysis method of box embankment structure,the influence characteristics of main factors on the internal forces of the structure and the optimal selection of the structure can provide scientific basis and reference for the practical engineering,which has important theoretical significance and application value.