Analysis On Reasonable Replace Thickness Of High Speed Railway Cutting Subgrade

High-speed railway is an important part for the development of the national economy.The subgrade structure,as an important underground line of the railway system,should have high strength and stability under the action of train loads,and must have good service performance to ensure the safety and comfort of the train.With the rapid development of high-speed railways,the high speed and high traffic density have increased the dynamic effect between the vehicle and the track,and the problems of safety and comfort caused by the vehicle have become more prominent.The cutting is a common form of railway subgrade.With the large number of high-speed railways in the mid-western low hill and hilly areas,their frequency of occurrence is getting higher.Therefore,it is necessary to conduct in-depth research on it.In the actual project,when the natural foundation can not meet the design requirements after excavation,it is often used to replace the high-quality filler and compact to the specified density.In general,high-quality fillers are used in the refilling process.Therefore,a reasonable refilling thickness is the key to the refilling process.In addition,in the previous design of the foundation bed structure,the embankment dy-namic coefficient often uses an empirical formula and is determined only by the type of rail and the speed of travel.This method of determination is convenient and quick for engineering applications.However,due to the differences between the data used to form the empirical formula and the actual conditions of the current high-speed railway,as well as the number of statistics and other issues,the dynamic coefficients determined by this method can not fully reflect the comprehensive effects of many factors such as the type of track structure,the con-dition of line irregularities,and the axle load of the vehicle.The emergence of vehicle-track coupling dynamics provides another way to study the dynamic characteristics of subgrade and determine the subgrade dynamic coefficient.Aiming at the characteristics of vehicle-track coupling dynamics system matrix,a method of quickly constructing and modifying system dynamics matrix is formed through system mod-ularization and object-oriented method.The vehicle-track system dynamic simulation was carried out for the ballastless track and ballastless track structures using the vehicle-track cou-pling dynamic analysis method.Aiming at the technical characteristics of high-speed railway subgrade,considering the cyclic deformation characteristics and time effects of typical filling materials,the basic bed structure design method based on structural dynamic strength,cyclic deformation,and long-term stability control principles is applied.The replacement thickness of the roadbed subgrade under high-speed railway ballast track and high-speed railway ballast-less track structure was discussed.And proposed the design standards for the filling thickness of high-speed railway ballast and ballastless subgrade.The main work and conclusions are as follows:1.Vehicle-track coupling dynamics modular implementationBased on the principle of vehicle-track coupling dynamics,component dynamics ma-trix and relational classification characteristics are analyzed,and modular and object-oriented techniques are used to modularize the assembly and modification of system dynamics matrix.According to the cause of the force in the equation of motion,the force of the component mo-tion equation can be divided into four categories.Based on the classification of component motion equation forces,the modular construction method of calculation program and the rapid formation method of system dynamics matrix are discussed.2.Subgrade coupling dynamics analysisUsing the vehicle-track coupling dynamics analysis method,considering vertical random irregularities,coupling dynamics simulations were performed on the high-speed railway bal-lasted track and the high-speed railway ballastless track,and the probability distribution char-acteristics of the subgrade surface dynamic coefficient were studied.The results show that with the increase of speed,the dynamic coefficient of the subgrade surface increases gradually and the discreteness increases.At the same speed,the dynamic coefficient of the subgrade surface can pass the K-S normality test and obey the normal distribution.Based on the proba-bility distribution characteristics of dynamic coefficients,the probability is distinguished,and the frequently encountered dynamic coefficients and limit dynamic coefficients of 300 km/h of high-speed railway ballast track and 400 km/h of high-speed railway ballastless track are proposed.3.Study on replacement thicknesses of soft rock cutting subgrade on high-speed rail-way ballast trackAiming at the technical characteristics of high-speed railway ballast track subgrade,to control the cumulative deformation of the subgrade bed in slow-steady state with weak time effect,based on the principle of subgrade structure design,the design technique to design re-placement thickness of soft rock road foundation bed in high-speed railway track is discussed.The results show that the bed replacement thickness of soft rock subgrade is not only related to the degree of weathering,but also affected by its anti-immersion water softening ability.The basic bearing capacity of soft rock decreases with the increasing degree of weathering and softening,and the filling thickness decreases with the increase of basic bearing capac-ity of soft rock.Aiming at the medium-soften soft rocky cutting subgrade,the suggestion of replacement thickness considering the weathering and hardness of rock under high-speed rail-way ballast track was put forward.That is,the macro-weathered soft rock with R_c≥20MPa can be treated as hard rock;the weakly weathered soft rock with 10≤R_c<20MPa need only be replaced with the surface layer;R_c<10MPa and R_c<5MPa for strongly,fully weathered soft rock,need to increase the replacement thickness to the bottom layer 0.5m and 1.0m.4.Study on subgrade replacement thickness of soil cutting subgrade on high-speed railway ballastless trackAiming at the technical characteristics of high-speed railway ballastless track,to control the cumulative deformation of the subbed in slow steady state of micro-time effect,based on the structural dynamic strength,cyclic deformation,and long-term stability design principles,the foundation bearing capacity as the basic design parameter,the design technique of the re-placement thickness of the soft rock road foundation bed for high-speed railway ballastless track was discussed.Based on the calculation results of different rail structure types and dif-ferent foundation bearing capacity,and taking into account the convenience of engineering application,a proposal is made for the replacement thickness of foundation bed of high-speed railway ballastless track.That is,hard weathered hard rock can be without replenishing treat-ment,but for soft rock,strong weathered hard rock and soil subgrade,when f_k≥330kPa,it only needs to replace the surface with 0.4m;As to 300≤f_k<330kPa,250≤f_k<300kPa,220≤f_k<250kPa,180≤f_k<220kPa,in addition to replacing the surface 0.4m,the bottom layer needs to be replaced by 0.6m,1.1m,1.6m,and 2.1m respectively.