| The U-groove embankment has the advantages of large overall stiffness,good waterproof performance and small floor area,which is suitable for areas with limited embankment grading,weak foundation and rich groundwater.In this dissertation,numerical simulation,limit equilibrium theory,elastic foundation beam theory and other means are used to reveal the load transfer mechanism of U-groove embankment structure,establish the calculation method of earth pressure acting on the vertical arm and establish the analysis method of U-groove structure considering the arm-soil deformation compatibility.The influence of main factors on the earth pressure behind the arm and the internal force and displacement of the U-groove structure are analyzed,and the structural optimization selection is given with an example.The main results are as follows:(1)The vertical load transfer mechanism of high fill U-groove embankment structure under railway train load is revealed.The unit weight of filling soil produces dead weight stress field,and the top train load produces additional stress field,which together constitute the stress field of filling soil in Ugroove.The lateral deformation of the fill is restrained by the vertical arm,resulting in the earth pressure behind the vertical arm.The vertical additional stress gradually diffuses downward in a band,and its diffusion range is limited by the width of the U-groove,which may reach the floor when the U-groove width is large to an extent;When the width of the Ugroove is relatively small,the additional stress diffusion is limited by the vertical arm.Under the combined action of the earth pressure behind the vertical arm,the vertical compressive stress of the floor and the ground constraint,the U-groove structure produces mechanical response,and the compressive stress of the base is transferred to the foundation.(2)The calculation method of the limit earth pressure of the finite soil behind the vertical arm of U-groove is established.Based on the symmetry characteristics of U-groove embankment structure and the assumption of two-stage polyline slip surface,the formula of active earth pressure of finite soil under limit state is derived by limit equilibrium method,which quantitatively reflects the influence factors such as unit weight,internal friction angle and cohesion of the soil,soil-arm interface friction angle and cohesion,width and height of the U-groove,and strip load on the top surface of the embankment.Analysis results of examples show that the proposed earth pressure is about 20%-30% higher than those by related existing methods but obviously smaller than Coulomb’s active earth pressure for semi-infinite soil,and internal friction angle of the fill soil,soil-arm interface friction angle and width of the vertical arms have non-linear effect on the earth pressure.(3)The theoretical calculation method of displacement-dependent earth pressure of rigid retaining wall rotating around the base of the wall is established.Based on the definition of shear strain,the expression of shear strain on the potential logarithmic spiral slip surface is derived.Combined with Duncan-Chang hyperbolic model,the variation characteristics of internal friction angle along the depth under non-limit state are obtained,Then,the horizontal slice method is used to calculate the distribution of earth pressure and the variation curve of earth pressure with displacement under non-limit state.Analysis results of examples show that the method is in good agreement with the experimental results,and the relative error is between 5% and 10%.The profile of the displacementdependent earth pressure under the active and passive non-limit states are concave outward and inward to the wall.The two ultimate displacements are decreasing as the internal friction angle increases,while the active one is decreasing but the passive one is not almost changed with the increase of the cohesion.Also,the passive one is slightly increasing with the wallsoil friction angle,but the angle does not influence the active one.(4)A U-groove structure analysis method considering the arm-soil deformation compatibilty is established.Based on the theory of displacement-dependent earth pressure,the displacement related earth pressure behind the vertical arm is determined,and then the vertical arm and the floor of U-groove embankment structure are individually calculated as the cantilever beam and the elastic foundation beam on Winkler foundation,and the internal force and displacement of the two are continuous at their joints.Analysis results of examples show that the earth pressure,shear resistance,bending moment and deflection of the vertical arm considering arm-soil deformation compatibilty are larger than those without considering deformation compatibility(classical Rankine active earth pressure theory),and the maximum deflection of the vertical arm considering deformation compatibilty is about 60% larger than that without considering deformation compatibility.(5)Considering the internal forces,displacement and crack resistance requirements of Ugroove structure,the optimal selection of U-groove structure is carried out.The case analysis of embankment with 8 m filling height shows that the reasonable structure type of U-groove embankment should meet the following requirements: the height of vertical arm is less than12.1 m,the section thickness of vertical arm is more than 0.97 m,the length of floor is less than 13.6 m,the section thickness of floor is more than 1.25 m,the relative length of overhanging is between 0.08 and 0.19,and the bottom of vertical arm adopts the variable section type of expanding angle.The research results in this paper of the limit earth pressure of the finite soil behind the vertical arm of U-groove,the displacement-dependent earth pressure of the rigid retaining wall rotating around the base,and the structural analysis method of U-groove considering the armsoil deformation compatibility can provide scientific basis and guidance for practical projects,which has important theoretical significance and application value. |
