Dynamic Response Analysis Of Subgrade Under Different Track Structures Of High-speed Railway

With the implementation of the “The Belt and Road” policy,the high-speed railway in western China ushered in a new round of development opportunities.It is well known that there is mainly loess areas in western China and the loess can not be used to fill subgrade of high speed railway directly.To date,studies on dynamic analysis of high-speed railway subgrade in loess areas are not adequate.On the basis of cement-improved loess subgrade the author's research group investigated,this thesis studies the dynamic response of improved loess subgrade under different forms of track structure,as well as analyzes the running performance of CRH2.This thesis aims at finding out the dynamic response rule of the improved loess subgrade under the different track structures and creating corresponding database,provided theoretical foundation for the construction of high speed railway in the loess area.This thesis carried out the modeling and simulation analysis of vehicle,track and improved loess subgrade of six track structures by numerical simulation.The main results are listed as follows:(1)This thesis models the CRH2 using the multi-body dynamics software UM,and introduces flexible track module to make wheel-rail contact more closer to actual situation;setting rail structure dynamic parameters and using Chinese track spectrum as high-speed railway irregularity spectrum.The vehicle is set to run at four different speeds(200km/h?250km/h?300km/h?350km/h)respectively to get the wheel-track force,rate of wheel load reduction,derailment coefficient,vertical and lateral acceleration of vehicles;by contrastive analysis of those indexes and standard values,the change rules of different parameters variation as speed changed can be obtained and fitted into formula.(2)This thesis conducts modeling and simulation analysis of ballast track subgrade using finite element simulation software MIDAS GTS NX;through exerting the force function of a bogie and two wheel sets on the rail,it gets the distribution of dynamic displacement,dynamic acceleration,and dynamic stress of different structure layers(surface layer of subgrade bed?bottom layer of subgrade bed ?embankment),that is,the three roughly distribute in the shape of a saddle along the horizontal,and dynamic response of rail reaches maximum.At the speed of 300km/h and below,the speed has little influence on the dynamic response of subgrade structure,but the dynamic response of subgrade structure obviously changed at the speed of 350km/h.The dynamic displacement rapidly reduces along the depth in the first 3 meters,with about 70% decrement.The dynamic stress rapidly reduces within one meter area with over 70% decrement;and dynamic stress in 3 meter only equals to 10%of the dynamic stress in the surface layer of subgrade.(3)The modeling and simulation analysis of improved loess subgrade in five ballastless track structures show that the dynamic response of ballastless track subgrade is significantly less than that of ballast track.The dynamic response increases as the increase of vehicle'srunning speed and distributes in the shape of a saddle along the horizontal.The stress concentration in the place of supporting layer's edge and surface layer of subgrade results the large dynamic response.The distribution of dynamic displacement's,acceleration's and dynamic stress' attenuation along depth of reduce is obtained to analyze the attenuation rule of dynamic response subgrade.(4)The comparative analysis of the subgrade's dynamic characteristics of different track structures shows that ballastless track apparently precedes ballast track in terms of the attenuation of dynamic response(dynamic displacement,acceleration,and dynamic stress).In ballastless track,double block ballastless track precedes plate ballastless track in terms of dynamic response reduction,among which the CRTS ? double block type is the best.In addition,CRTS ? plate ballastless track's the attenuation performance of precedes that of CRTS I and CRTS?plate ballastless track.(5)By comparing thesis' results with the previous research results,it is found that subgrade dynamic stress in this study is slightly less than previous research results,but more conforms to the data measured in the field.This thesis also conducts stress analysis of elastic materials like track slab and sleeper of supporting layer to determine the reinforcement scheme.