Research On Dynamic Characteristics Of Subgrade Transition Zone For Ballastless Tracks On High Speed Railway

It is requested to paved by ballastless tracks on the whole line ofWu-Guang express railway engineering, compared with common railwayof ballast tracks, it is stricter in deformation of the subgrade. Thesettlement of post construction on high-speed railway is required less than30 mm, even of road foundation no settlement. The subsidence differencemust not exceed 20 mm with any 20 m in length section of the subgrade.Making an angle must not exceed 1/1000 within a railway-bridge(ortunnel, or culvert) transition section or the settlement of any two sectionssubgrades. Stagger for subsidence difference must not exceed 5mm. Thus,it's the key of subgrade design to control the stiffness discrepancy and thesubsidence difference and the bending of the track, which reduces greatlythe safety and ride comfort of the train in motion. With the rapiddevelopment of the high-speed railway in our country, the question oftransition zone come into view obviously than before. The dissertationcombines the research projects supported by National Doctor ScienceFund and railway ministry, it generalizes the previous achievements, andreviews the advanced development of the transitional sections, thedynamic analysis model of the railway-bridge-tunnel transition under theballastless tracks, with theory analysis and indoor test and site test andnumerical simulation, was studied thoroughly, and some originalconclusions are obtained as following:(1) A analysis model of semi-infinite tri-dimensional spatial finiteelements has been founded for the ballasfless track-bridge-tunneltransition system, based on weak variational form of the equilibriumequations for the transitional section in D'Alembert method and wholeLagrangian form. In the model, the track structure and the transitionsystem are dispersed to different elements and infinite element method isapplied to eradicate boundary effects. There is relative restricted couplingbetween contact interfaces of various materials of the system. It canprovide dynamic responses of the system with changes of wheel load,vehicle velocity, frequency and irregularities of the track, and distribution of dynamic responses in the subgrade can be given, also beused to select parameters, optimize designs and forecast dynamicproperties of the system, etc.(2) Based on Timoshenko beam and geostatic theory, couplingrestricted equations of various finite elements are founded. The restrictedequations have been dealt with by Lagrangian enlarging multipliers. Bythis way, the difficult problem of the coupling between the contactinterfaces of various materials of the ballastless track-bridge-tnnneltransition has been solved effectively.(3) Based on deformation characteristics of materials, the dissertationadopts analysis models, such as linear, nonlinear elasticity,Drucker-Prager, reinforced concrete elastic-plasticity constitutive model,etc. The coupling between vehicles system and the ballastless track-bridge-tunnel transition is affected by putting external simplified force onthe plane of the track vertically. The matrices equations as a whole havebeen solved, using implicit time integration of Newmark. Because thereare many restricted equations in the dynamic model, frontal solution isadopted to the modal analyses, and reduced solution is adopted totransient dynamic analysis.(4) Based on cone-shaped distributing of railway bed load and amass-spring-damper model, the equivalent stiffness and variogramstiffness thresholds of the system are acquired, which have something todo with the material properties of its oneself, besides the effects of thevertical amplitude and wavelength and irregularities of the track and thevehicle moving velocity on the system.(5) Based on wavelet theory and analysis of the time domain andfrequency domain with a great deal of field test data, and study oncharacteristics of the roadbed surface dynamic stress, vibrationacceleration, dynamic coefficient of the dynamic-stress speed, a "criticalspeed"conception is advanced, and it will influence the change trend onthe dynamic response of railway roadbed. At one time, a design idea isadvanced that "appropriate excess height"of roadbed can reduce thedifferential settlement and the dynamic response of transition sectionroadbed. (6) Test analyses on various function of stable graded crushed stoneslayer of cement additives have been accomplished, it is fit with thegraded crushed stones doped in adaptive 5%～5.5% cement additivesamount, can satisfy to transfer an each kind of function of the transition.It is advanced that critical value of dynamic stress exists in gradedcrushed stones. At one time, it is biggest for dynamic modulus ofelasticity in the graded crushed stones.(7) Applying the system dynamic model above-mentioned, theinfluences of wheel load, vehicle velocity, irregularity, materialparameter, stiffness and subsidence discrepancy on the dynamicresponses of the system were studied systematically. As for the furtherresearch on the same work and on the optimizing design of thetransition system, such a work may provide a helpful reference.