Numerical modelling of railway track transition zone dynamic

Railway track transitions are zones where there is an abrupt change in the track-ground structure which include changes between ballasted and slab track, bridge approaches, and tunnel entry/exits. They are often the location of rapid track deterioration, which means more frequent track maintenance is needed compared to plain line tracks. To mitigate these effects, this research aims to investigate the ability of auxiliary rails and earthwork solutions to enhance the dynamic track behaviour of transition zones, in both the short-term and long-term. To do this, a 3D finite element track model is developed using eight-node solid elements and a perfectly matched layer absorbing boundary condition. A dynamic moving train load is simulated using a rigid multi-body approach capable of accounting for train-track interaction. Three track analyses are proposed to address this aim and provide new insight into engineering track transition design.
The first analysis focuses on enhancing the dynamic characteristics of ballasted tracks at transitions using auxiliary rails. It is found that using two auxiliary rails widely spaced and placed close to the running rails is useful. The potential generation of additional mini-transition zones and practical construction constraints with this approach are highlighted.
The second analysis compares various earthwork solutions for embankment-bridge transition, emphasising the importance of the initial three meters from the transition zone entry. ‘Single’ and 'double' trapezoid configurations are studied to assess their effect on track dynamics. Ballasted and slab tracks are studied, and it is found the improvement is more pronounced for ballasted tracks due to their lower bending stiffness compared to slab tracks. In addition, higher train speeds are found to result in significantly greater stress increases in ballasted tracks.
The third analysis focuses on predicting track transition zone settlement by comparing earthwork solutions and auxiliary rails. A double trapezoid earthwork configuration with two materials of UGM and CBM proves most efficient in reducing settlement and minimising the development of mini transition zones, remaining superior to normal track behaviour for years after construction.