| Mountain ridges densely cover in Southwest China,and multiple environmetal sensitive areas and active fault zones are distributed in this area.To ensure the track regularity and reduce the influence of train operation on the surroundings,railways mostly adopt the form of long tunnel to across those areas including the situation where the railways are supposed to pass through active fault zones.When passing through those zones,the repeated impact of train-induced dynamic load can cause the tunnel structure to crack and expend,and even lead to the overall failure of tunnel structures.Moreover,vibration propagation in rock mass will disrupt the surroundings and promote fault dislocation.The possibility of these diseases has posed a severe threat on the safety of railway and tunnel structures.On the background of the project of Chengdu-Lanzhou railway crossing active fault zones,this paper conducted a series of static and dynamic researches on the basis of finite element method and wheel-rail coupling dynamics theory,aiming to select the proper vibration reduction track to reduce the negative effect of vibration.The main works and conclusions are as follows:(1)A spatial model for a track-tunnel-active fault zone system was established,and the mechanical and deformation characteristics of track structures under fault movement were analyzed based on quasi-static method.The results show that each layer of ballastless structures have gone through similar dislocation deformation under the condition of fault dislocation,and seams appeared between bed plate and tunnel.The maximum tensile stress of slab exceeds its tensile strength when the dislocation value amounts to 15mm,leading to the failure of slab.Under the condition of fault movement,ballasted track excels in stress state,structure failure situation and adjustment abilities of railway geometry in comparison to ballastless track,thus ballasted track is recommended in active fault zones.(2)A vehicle-ballasted track-tunnel coupling dynamic model was established.Based on the model,elastic sleeper and ballast mat’s influence on the dynamic characteristics of the system was analyzed from the perspective of driving safety,riding comfort and damping effect.It is concluded that laying elastic sleeper and ballast mat can ensure the running safety and stability of trains.After laying elastic sleeper,the vertical displacement of rail and sleeper increase significantly while dynamic response of ballast bed decrease.Laying ballast mat deteriorate the working condition of ballast bed while increase the track structure displacement.Elastic sleeper and ballast mat both exhibit excellent damping effect with maximum attenuation up to 26dB and 18dB.The using of elastic sleeper and ballast mat can slow down the trend of fault dislocation caused by wheel-rail impact.(3)Study on the effect of ballast mat’s surface stiffness and sleeper pad’s stiffness on dynamic response of vehicle and track,as well as damping effect.Referring to the results,a reasonable range of parameters are proposed.The principle of parameter setting is to control the deformation,vibration and force of the track structures,without weakening its damping effect.Through a systematic comparison,a range of ballast mat’s surface stiffness is suggested to be 100 to 150 MN/m3,and that of the sleeper pad to be 40 to 60 MN/m.(4)Put forward a new idea for vibration reduction of rubber concrete tunnel backfill,and conduct research on its damping effect and its influence on the dynamic responses of vehicle and track structures.The results have shown a significant damping capacity of rubber concrete tunnel backfill,which is manifested in all frequency with a maximum damping effect to be 10.3dB.The dynamic indexes of the vehicle and track structures are not changed before and after the backfill layer adopts rubber concrete.The adoption of rubber concrete tunnel backfill does not aggravate wheel-rail dynamic interaction or affect the running safety of trains. |
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