| At present,the construction of modern metropolitan area has become a national strategy.Metropolitan rapid rail transit can greatly shorten the commuting time,realize the interconnection within the metropolitan area,and promote the coordinated development of the region,which has become an important leader in the construction of the metropolitan area.Due to the high design speed,heavy train axle and long distance between stations,the impact of trains on the track structure increases,which is bound to cause serious vibration problems of rail transit,thus affecting the safe and green operation of urban trains.As a special vibration reduction measure,steel spring floating slab track has been widely used in metro lines,but it is rarely used in emerging urban express lines,so the research on laying steel spring floating slab track is still blank.Therefore,it is urgent to study the dynamic characteristics of the steel spring floating slab track and its environmental vibration law,so as to provide theoretical support for its application in the urban express line.In this paper,based on the theory of vibration generation and propagation,a refined train-floating slab track-tunnel-soil integrated analysis model was established,and the dynamic characteristics of the steel spring floating slab track system were analyzed in detail when the train is running at 160km/h.Based on the field test,the transmission characteristics of track structure vibration were analyzed,and the propagation law and influence factors of vibration in the stratum were studied.Based on the case study of a large-scale construction project to be built,the paper evaluated the vibration impact of metropolitan rapid rail transit operation on adjacent buildings.The specific conclusions are as follows:(1)Based on the research and summary of metropolitan rapid rail transit and related technical standards,the target speed of line in this paper was determined to be 160km/h,and the steel spring floating slab track line with urban D-type vehicle was taken as the research object.Based on the rail-fastener-floating slab-isolator finite element modal analysis model,the influence of the main design parameters of floating slab track on modal analysis was analyzed.The influence rules are as follows:increasing the mass of floating slab track bed can reduce the natural frequency of the system,the first two order frequency decreases with the increase of slab thickness,and the third order frequency increases with the increase of slab thickness;larger material density can reduce the natural frequency of the whole system.The stiffness and spacing of the isolators have significant influence on the low order modes.Reducing the stiffness of the spring isolators or increasing the spacing of the isolators will greatly reduce the natural frequency of the system.(2)The integrated dynamic analysis model of train-floating slab track-tunnel-soil was established,and the dynamic index distribution law of steel spring floating slab track was obtained.The influence law of running speed,floating slab thickness,isolator stiffness and isolator spacing on track dynamic characteristics was studied.The rail head is the most disadvantageous position on its cross section,while the rail in and at the end of the floating slab is the most disadvantageous section on the track;the two ends of the floating slab,especially the front end which bears the train load first,are the most disadvantageous position of the floating slab track bed.With the increase of train speed,the vertical displacement of the system increases slowly,while the acceleration of the system increases significantly.In the process of increasing from 100km/h to 160km/h,the rail acceleration increases by 147.5%,and the vehicle dynamic index meets the requirements.With the increase of the thickness of the floating slab,the vertical displacement of the system decreases obviously,and the acceleration of the floating slab and the tunnel structure decreases obviously,which can improve the dynamic characteristics of the whole system.Increasing the stiffness of the isolator can significantly control the displacement of the system,but at the same time weaken the vibration reduction effect of the track structure.(3)Field test was carried out to study the transmission characteristics of track vibration,and the whole vibration transmission process of the system before and after optimization was compared to study the propagation law of ground vibration and the influence of soil quality and tunnel depth.The measured results show that the vibration attenuates rapidly from rail to tunnel,and the main frequency of vibration decreases gradually.The optimization scheme makes the vertical displacement of the structure meet the requirements of the code,and further improves the vibration characteristics of the system.The vibration gradually attenuates along the rail,floating slab,base,tunnel wall and soil,but increases when it spreads to the surface soil.The results show that the surface vibration increases in a fluctuating manner in the propagation distance from40m to 72m,especially the vibration level at 72m is basically the same as that at 0m,and the peak acceleration is 0.038m/s~2.When the vibration propagates from the buried depth to the surface,the vibration level is close to or even beyond the buried depth.The results show that the overall vibration level of harder soil is smaller,and the vibration amplification area is closer to the center line of the line;the vibration amplification amplitude of sandy soil near the surface is much larger than that of clay and silt.With the increase of tunnel depth,the soil vibration acceleration basically decreases,and the vibration amplification phenomenon gradually weakens.(4)Taking a large building near the X line of rapid rail transit as an example,the vibration impact analysis was carried out.Analysis results:the vibration caused by the steel spring floating slab track has little impact on the building,only a few positions exceed the standard limit,and the vibration of the proposed building basically meets the requirements.Due to the special structure of the proposed building,the vibration of the underground floor is less than 60d B,while the vibration of the ground floor is larger.The maximum Z vibration level of the first floor interlayer and the third floor exceeds the limit by 70d B.In order to ensure the actual use effect of the building,through the comparison and selection of vibration isolation measures,it is suggested to set row piles for vibration isolation relying on retaining piles,and the building vibration can meet the requirements after the implementation of single row piles for vibration isolation. |
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