Exploration Of Design Technique On Substructure For 350km/h High-speed Railway Of Ballast Track

The railway development in the world has entered a high-speed era.Its orbital structure types mainly include orbital orbital structures and ballastless orbital structures.With the characteristics of high stability and high smoothness,ballastless track has become the main structural type of China's high-speed rail,and it has also been widely used in the world.However,the ballastless track has a very high requirement for settlement deformation of the roadbed,which increases the construction cost and the difficulty of construction of the track accordingly,and generates large noise and vibration during operation.The ballasted gravel track bed can alleviate the dynamic impact of the train.It has better elasticity than the concrete track plate,and has features such as low cost,convenient maintenance,short construction period,and small noise transmission range.Therefore,in the special regions such as the alpine and seismic belts,there is a more economical choice for the orbital structure.In order to ensure the safety and stability of the high-grade railway foundation bed structure,the surface-enhanced double-layer bed structure type was adopted in China,and the corresponding packing selection and technical standards were formulated based on theoretical analysis,engineering tests and construction experience.However,there are still problems such as the technical standards of the bed structure being single,failing to reflect the difference in functional requirements at different speeds and environments,the strict and empirical nature of the filler properties,and the failure to unify the technology and economics of the bed structure design.The design standards of the subgrade bed directly affect the overall quality of the line and coincide with the fact that China is building a high-speed rail from Beijing to Zhangjiakou,which is actually operating at 350km/h.There is no domestic design experience for such projects,so there are orbits for 350km/h high-speed rails.The research on design methods and technical standards of subgrade bed structure has practical significance.Through theoretical analysis,numerical simulation and other research methods,based on the dynamic response characteristics of high-speed rail subgrade subgrade bed under train loads,the cumulative deformation characteristics of typical fillers of coarse-grained soil are combined with the technical parameters of axial spacing of high-speed railway trains.Based on the three-parameter control principle of the bed structure design,the design method for the subgrade bed structure of a 350km/h high-speed railway subgrade has been studied and the corresponding technical standards have been proposed.The main research content is as follows:1)Analysis of the Effect of Train Load on Subgrades with Concrete TracksUnder the action of train load,the dynamic load amplitude of the subgrade is corresponding to the number of axes,and there is obvious load superposition phenomenon between the two axles of the same bogie.According to the current typical high-speed EMU bogie,the fixed wheelbase is much smaller than the adjacent bogies.Based on the characteristics of the wheelbase,the 2Z2400 EMU load behavior mode can accurately reflect the dynamic response characteristics of a rail subgrade.The quasi-static method is used to calculate the dynamic load of the train.The principle of each calculation principle of the bed structure design is analyzed.Design load effects to classify train load effects into two categories,ie,the maximum load the subgrade may be subjected to for dynamic strength verification p_{d j},corresponding to the limit load dynamic influence coefficient ₁?.The long-term stability check and cyclic deformation check use the most frequently encountered subgrade bearing the most frequent and most probable load p_dc,corresponding to the dynamic influence factor of the normal load ₂?.2)Analysis of Subgrade Dynamic Response under Track IrregularitiesBased on the technical parameters of the axle spacing and ballast track structure of the CRH380A EMU,a vertical dynamics model of vehicle-track-subgrade coupling was established.Combined with the high-low irregularity spectrum of low-interference orbit in Germany,the MATLAB software was used to simulate the conditions of track irregularities.The above models were run straight at different speeds for 80m,and the load on the roadbed of 134 fastener nodes was collected and analyzed.The calculation shows that under the condition of high or low track irregularity,the load subjected to the subgrade is subject to the normal distribution characteristics along the longitudinal direction of the line;if the coefficient of dynamic influence_k?^N??,?²?Characterizes the dynamic effects of the subgrade,when the operating speed v=350km/h,_k?N?1.436,0.253²?,corresponding to the limit load dynamic influence coefficient ₁?=??10?2?=1.94.Commonly encountered load dynamic influence coefficient ₂?=?=1.44.3)Design method for foundation bed structure of high-speed railway ballast track and technical standards at 350km/hBased on the relationship between time-dependent deformation characteristics and load level of typical fillers in coarse-grained soil under cyclic loading,considering the influence of confining pressure on the filler strength,the load threshold level and foundation coefficient K₃₀ representing the deformation state of fillers were established.The mathematic expressions of the equations clarified the concept of the time-dependent cumulative deformation zone where the base bed range is obvious,that is,the filling below the sub-bed is in a fast and stable time-free zone.The requirements for the design of a weak time-effect zone should be in a slow and steady state.To meet the design requirements of the bed structure with the dynamic strength and long-term stability of the filler and the cyclic deformation of the subgrade surface not exceeding the limit,a subgrade bed suitable for high-speed ballast track was established.The structural design method,and proposed a technical standard with a certain safety reserve for the design of the bed structure under 350km/h:K₃₀?110MPa/m A,B,and C groups of fillers,base bed thickness 2.6m;base bed usedK₃₀?130MPa/m A,B group filler,corresponding to the bed surface layerK₃₀?190MPa/m graded gravel only0.45m.