Study On Mechanical Behaviors And Calculation Method Of U-groove With External Counterforts In High Railway Embankments

The U-groove with external counterforts is a new type of subgrade structure used for high embankment on soft soil.It can effectively control the settlement and deformation of foundation and meet the requirement of bearing capacity,but the theory of relevant design calculation is not yet mature.Therefore,this dissertation relies on the high embankment project of the railway line of the Bengma bridge in Bangladesh.Based on theoretical analysis and numerical simulation,the stress mechanism and calculation method of the embankment structure of U-groove with external counterforts are systematically studied.The main research work and results are as follows:(1)The stress mechanism of the U-groove structure with external counterforts is revealed.The lateral compressive stress generated by the surface load on the vertical arm is more prominent in the middle part of the vertical arm,and it has the characteristics of local centralization distribution,and its relative soil weight is less affected.The lateral compressive stress generated by the soil weight on the vertical arm is close to the triangle distribution.(2)A simplified load model of the U-groove structure with external counterforts is established,that is,the lateral pressure on the vertical arm of the surface load can be approximately spread according to the angle of 45~0+φ/2 to form a local trapezoid distribution mode.The side pressure of the triangular side of the filling arm is distributed,and the vertical pressure of the bottom plate is uniformly distributed.The effect of the strip load on the surface of the filling surface can be neglected.(3)A simplified theoretical calculation model for the U-groove structure with external counterforts is established.Taking the middle and middle section of adjacent buttress as a calculating unit,The vertical arm is equivalent to two two-way rectangular plates with two adjacent sides fixedly supported and two adjacent sides free with positive symmetry about the buttress.The middle vertical arm and the buttress are equivalent to the variable cross section beam,and the bottom plate is equivalent to the elastic foundation beam model.The formula for calculating the internal force and displacement of the structure is derived.(4)Example analysis shows that the bending moment and deflection of the vertical arm and the bottom plate obtained by theoretical calculation and three-dimensional ANSYS numerical simulation are all close to each other,and the relative error of the maximum bending moment of the arm is less than 20%.The result of the simplified theoretical analysis model is relatively safe.The bending moment of the vertical arm of the buttressed joint is significantly smaller than the other parts,which indicates that the buttress can effectively reduce the bending moment of the vertical arm.(5)The influence of vertical arm height,vertical arm thickness,buttress thickness,buttress spacing,foundation coefficient and earth friction angle on the internal force and deformation of the U-groove structure with external counterforts is given.The internal friction angle and foundation coefficient of the filling soil are negatively correlated with the deflection and bending moment of the structure,and the height of the boom is positively correlated with the deflection and bending moment of the structure.In this paper,the research results of the stress mechanism and simplified calculation method of the embankment structure of the U-groove structure with external counterforts can provide theoretical guidance and reference for the actual engineering design.