Study On Vibration Reduction Performance And Design Parameter Optimization Of Ballast Bed In Subway Tunnel

At present,monolithic track bed structure is widely used in subway tunnels,which has produced many problems in the operation process,such as excessive vibration and noise,rail corrugation,parts damage and so on.Ballast track bed has the advantages of low construction cost,fast construction speed,good elasticity and easy maintenance.It can provide vibration and noise reduction and adjust track deformation.However,there is no engineering example of large-scale application of ballast track bed in subway tunnel in China.This paper considered the application of gravel track bed in subway tunnel,carried out the dynamic response analysis of track,vehicle and tunnel structure,analyzed the vibration reduction performance of gravel track bed in subway tunnel,and analyzed the optimization of design parameters.Firstly,according to the relevant design specifications,this paper put forward the structural design parameters of ballast track bed in subway tunnel.Secondly,the coupling model of sleeper-ballast bed in the tunnel was established by the coupling method of discrete element and multi-body dynamics,and the mechanical properties of the ballast bed in the subway tunnel were studied.Then,combined with the field measurement,this paper analyzed the vibration reduction effect of ballast bed.The three-dimensional coupling model of vehicle-track-tunnel-soil was established by finite element method,this paper analyzed the vibration damping performance of ballast bed under different design parameters and combined with other vibration damping measures,and proposed the optimized design parameters of ballast bed in subway tunnel.The main contents and conclusions of this paper are as follows:(1)Combined with the subway tunnel gauge,relevant design specifications and engineering experience,it is proposed that the thickness of the ballast track bed in the tunnel was 350mm,the sleeper adopted the national railway Ⅱ concrete sleeper with the length shortened to 2.2m,and the ballast track bed in the tunnel adopted 60kg/m steel rail and elastic strip Ⅱ separate fasteners.The transverse resistance,longitudinal resistance and supporting stiffness of ballast bed in subway tunnel were 11.9k N/sleeper,15.1k N/sleeper and 131.3k N/mm respectively,meeting the design requirements of the code.The average contact force,velocity,angular velocity and kinetic energy between ballast particles decrease with the increase of track bed depth,indicating that the dissipation of vibration energy by ballast particles decreases gradually.The smaller the stiffness of the track bed,the greater the amplitude of the settlement of the track bed,and the longer the time to reach the relatively stable state,which is not conducive to the smoothness and stability maintenance of the line.The greater the stiffness,the denser the accumulation between ballast particles,and the smaller the overall energy loss of the track bed.(2)According to the field measurement,the tunnel wall acceleration of monolithic track bed and ballast bed were 1.18m/s~2 and 0.8m/s~2 respectively,the tunnel wall acceleration of gravel track bed was reduced by 32.20%,the total vibration level is86.35dB and 81.24dB respectively,and the insertion loss is 5.11 dB,and the ballast bed has good vibration damping performance.The simulation analysis results were consistent with the measured results.Compared with the monolithic track bed,the track structure displacement,wheel rail force and derailment coefficient of the ballast bed track were increased,the wheel load reduction rate was reduced,and all indexes were less than the safety limit,which will not affect the driving safety.In the process of increasing speed from 60km/h to 160km/h,the track dynamic displacement,wheel rail force,track and tunnel structure acceleration were increasing,and the vehicle safety index changes little,which can ensure the safe operation of the train.(3)The increase of the thickness of the track bed can effectively reduce the vibration transmitted from the track to the tunnel structure.Considering the vibration reduction demand and tunnel clearance,this paper suggested that the thickness of ballast bed in metro tunnel was 300～350mm.The closer the sleeper spacing,the smaller the vibration acceleration of track structure and tunnel structure,and the higher the safety of train operation.In combination with vibration control and engineering economic benefits,this paper suggested that the sleeper spacing of ballast bed in subway tunnel was 1680 pieces/km.Poor ballast grading would enlarge the vibration of track and tunnel structure and reduce the safety of train operation.This paper recommended adopting the first-class ballast standard in accordance with the relevant provisions of railway crushed stone ballast.(4)The insertion loss of sleeper pad ballast bed at 1.5m of tunnel wall is 8.39db.The sleeper pad effectively reduced the vibration of track bed and the vibration transmitted from track to tunnel structure.This paper suggested that the stiffness of sleeper pad was 40～60kN/mm.The insertion loss of ballast pad ballast bed at 1.5m of tunnel wall was 10.29db,and the vibration reduction effect of ballast pad decreases with the increase of ballast pad stiffness.This paper suggested that the surface stiffness of ballast pad was 80～120MPa/m.After polyurethane curing,the acceleration of tunnel structure significantly reduced.Considering the economic benefit and the demand of vibration reduction,this paper suggested that the top curing width of gravel bed should be 0.7-1.0m.