Study On Mechanical Behavior And Analysis Method Of A Railway Embankment Structure Composed Of U-type Groove With Box In Highly Filled Earthworks

The railway embankment structure composed of U-type groove combined with box via a shared plate in highly filled earthworks is a new type embankment structure.There are plenty of outstanding superiorities for the novel embankment structure with reinforced concrete structure as the main body,such as low weight,large stiffness,small compression deformation,excellent stability,remarkable waterproofing effect,good economic efficiency,and so on.It is suitable for situations of high filled,limited land and soft foundation.However,the mechanism and analytical theory of the structure is still not established,which restricts its extensive application to the engineering practice.Therefore,this dissertation aims at the question so as to establish the calculation theories for such structure.In this dissertation,upper-bound limit analysis method,limit equilibrium theory,twodimensional rigid frame theory,beam on elastic foundation theory and three-dimensional numerical simulation are used for single and double line railway embankment structure composed of U-type groove combined with box in highly filled earthworks.The ultimate bearing capacity of upper filled soil foundation,the earth pressure of the limited soil behind the vertical arm of the upper U-type groove,the internal force and displacement of the whole structure,and the optimal selection of structure are systematically studied.The main research results are as follows:(1)The calculation method of ultimate bearing capacity of strip foundation for filling soil in U-type groove combined with box is established.In order to determine its theoretical analysis method reasonably,two kinds of potential failure modes are put forward based on the upper-bound limit analysis theory and the Hill mechanism combined with the symmetry of the U-type groove structure.The balance equation between internal and external powers is derived and established,which can reflect the relationship between the bearing capacity of filled soil foundation and several independent variables.Considering the geometrical conditions and kinematic constraints of the failure mechanisms,a nonlinear programming solution of the bearing capacity is carried out via the Matlab programming optimization algorithm.(2)The mechanism of load transfer for U-type groove combined with box is revealed.For U-type groove combined with box,the single or double line load is transmitted downward at a certain diffusion angle in the filled soil foundation,and the vertical stress of the bottom plate in the upper structure for the external load transfer shows a large trend in the middle and a small trend at both ends.The external load is transferred to the foundation through the U-type groove combined with box.And the obvious stress concentration occurs near the foundation soil at both ends of the foundation plate in U-type groove combined with box.The vertical stress at the contact place between the foundation plate and the foundation soil shows a small trend in the middle and a large trend at both ends.(3)The stress modes of single and double line U-type groove combined with box are constructed,and the calculation method of internal force and displacement of U-type groove combined with box is established.Based on the limit equilibrium theory and the horizontal slice method,the calculation methods of the soil pressure in the upper groove and the additional stress of the pavement load under two kinds of embankment widths are derived.Then the U-type groove combined with box is decomposed logically into a foundation beam element and the rest member on it.The former can be regarded as a beam on elastic foundation solved by Winkler foundation model,while the latter can be simplified as a two-dimensional rigid frame solved by the force method of structural mechanics.During the analysis,deformation compatibility between the beam and the foundation is fully taken into account.The numerical simulation results show that the proposed theoretical solutions are basically consistent with the numerical ones,and the deviation between the theoretical and simulated values of the internal forces of the structure is about 2.7-19.3%.(4)Aiming at the single and double line schemes of the U-type groove combined with box,the influence characteristics of four main design factors,such as thickness of each component plate,height of web,extension length of the upper bottom plate and extension length of foundation plate,are analyzed.The optimal selection method of the U-type groove combined with box is established.In the structural design of the U-type groove combined with box,configuration of the structure can be optimized by possibly reducing thickness of the upper bottom plate,foundation plate and webs under the condition of meeting the requirements of crack resistance,adjusting height of the webs by minimizing the sum of the maximum bending moment of the upper bottom plate and foundation plate under meeting the requirement of reducing the dynamic impact effect of train load,as well as controlling the ratio of extension length of the upper bottom plate and foundation plate at each end over its basic length between the two webs to be about 30% to 40%.In this paper,the research results of the analysis method of ultimate bearing capacity of strip footing on the filling foundation in a U-type groove,the calculation method for internal force and displacement of the U-type groove combined with box,the optimization and model selection of the U-type groove combined with box can provide scientific basis and guidance for practical engineering,and have extremely important theoretical significance and application value.