Simulation of track settlement in railway turnouts-An iterative approach

In this thesis, a methodology for simulation of track settlement in railway turnouts (switches andcrossings, S&C) is presented. The methodology predicts the accumulated settlement for a given setof traffic loads using an iterative and cross-disciplinary procedure. The different modules of theprocedure include (I) simulation of dynamic vehicle–track interaction in a turnout applying avalidated software for multibody vehicle dynamics considering space-dependent track properties,(II) calculation of load distribution and sleeper–ballast contact pressure using a detailed finiteelement model of a turnout that includes all of the rails (stock rails, switch rails, closure rails,crossing nose, wing rails and check rails), rail pads, baseplates and sleepers on ballast, (III)prediction of track settlement for a given number of load cycles and (IV) calculation of accumulatedtrack settlement at each sleeper and the resulting vertical track irregularity along the turnout whichis used as input in the next step of the iteration. The iteration scheme is demonstrated by calculatingtrack settlement at the crossing when the studied turnout is exposed to freight traffic in the facingmove of the through route. Due to the design of the crossing panel and the character of the impactloads induced by the transfer of wheels between wing rail and crossing nose, the load transferredinto the track bed is not uniform and the resulting spatially varying (differential) settlement leads tovertical irregularities in track geometry.In the first paper of this work, track settlement is predicted using a discrete empirical model thatgives the local vertical settlement based on the number of load cycles and the prescribeddistribution of sleeper–ballast contact pressure. Such a model does not account for the materialbehaviour in, or the interaction between, different regions of the track substructure. In the secondpaper, a computationally efficient method for predicting long-term settlement in genericconfigurations of track (various combinations of track superstructure and substructure and nonsymmetricloading conditions) using a constitutive model accounting for the multi-axial stressstraincondition in the track substructure is developed. A key ingredient of the method is that theselected constitutive model evaluates track settlement in the cycle domain. The constitutive modelis adopted for both the ballast and the sub-ballast but with different parameter sets. The dimensionsof the three-dimensional finite element model of the track substructure and the number of sleepersthat need to be included to obtain accurate settlement at the crossing are investigated. To predict areliable distribution of settlement under a given sleeper, it is concluded that the loading on at leasttwo sleepers on either side of the sleeper must also be included in the model