Study On Mechanical Properties Of Reinforced Soil For Railway Ballast

With the increase of population and rapid urbanization development leads to an increasing demand for railroad transport infrastructure development.Excessive and frequent cyclic loading by train axle weight accelerates the process of train track damage,deformation of the track base layer(mainly the bed layer)and its settlement,as well as particle spreading and fragmentation from the underlying bed structure layer,requiring frequent and expensive track maintenance to ensure its stability.The cyclic stresses applied by trains usually lead to vertical and lateral displacements of the railroad bed layers,which eventually lead to their vertical settlement and ballast particle fragmentation leading to track misalignment and possibly to a series of safety problems such as derailment.Therefore,it becomes especially important to study the dynamics and axial cumulative strain characteristics of railroad bed under cyclic loading.In order to reduce the track deformation caused by excessive axle weight of trains and cyclic loading,geogrid and scrap tire reinforced railroad bed layer reinforcement technology is proposed.The main research findings of this paper are as follows.(1)Firstly,the physical properties of ballast layer and sub-ballast layer materials are studied by measuring material parameters through indoor tests,including particle gradation sieving,appearance shape identification,optimum moisture content and maximum dry density of ballast layer and sub-ballast layer;meanwhile,the engineering technical indexes of waste tires and bi-directional geogrid are analyzed.(2)Through solidification without drainage static triaxial test,the strength characteristics of reinforced roadbed layer of geogrid and waste tire are analyzed at different positions.Compared with the unreinforced specimens,the reinforcement of geogrid and waste tire significantly increased the peak bias stress of the roadbed specimens.According to the analysis of the shear strength parameters of the roadbed specimens,it was concluded that the shear strength of the roadbed specimens with geogrid and waste tire reinforcement was significantly increased compared with the unreinforced specimens.(3)The reinforcement effect of geogrid arrangement under different surrounding pressure by solidification without drainage dynamic triaxial test: the axial cumulative strain of reinforced roadbed layer of geogrid gradually decreases as the surrounding pressure increases;the range of change of axial cumulative strain of specimens reinforced with waste tires is in accordance with the stability theory.When the circumferential pressure,dynamic stress amplitude and cyclic loading times are the same,the geogrid reinforcement effect is significantly different from that of the used tire,and the geogrid is more suitable for reinforcing the coarse granular material of the ballast.Geogrid reinforced specimen Psec decreases,resulting in permanent deformation also decreases.Under the scrap tire reinforced condition,the permanent strain rate decreased significantly after T2 reinforcement;after T5 reinforcement,the permanent strain rate increased significantly.The excessive tire reinforcement reduced the stiffness of the whole roadbed specimen,which caused the permanent strain rate and axial accumulated strain of the roadbed layer to increase rapidly with the increase of dynamic stress.The dynamic modulus of elasticity increased with the number of cyclic loading,and the addition of geogrid significantly enhanced the dynamic modulus of elasticity of the roadbed.The reinforcement in the middle of the two layers of the waste tire increases the dynamic elastic modulus of the specimen,while the reinforcement of all the tires leads to an increase in the elastic strain of the roadbed specimen and the dynamic elastic modulus is lower than that of the reinforced specimen in the middle.(4)From five kinds of permanent deformation prediction model to select two kinds of geosynthetic materials in line with the laying conditions of the model.Through the Monismith exponential function model and power function model in different surrounding pressure of geogrid and waste tire respectively in different forms of reinforced roadbed specimens for axial cumulative strain and cyclic loading sub-relationship curve fitting,the research results show that: Monismith exponential function model and power function model respectively for reinforced railroad roadbed,Monismith model can better The Monismith model can better fit the prediction of the axial cumulative plastic strain of two different reinforcement materials at different locations of reinforcement on the roadbed,and can more accurately reflect the relationship between the axial cumulative plastic strain of the specimen and the number of loading.