Keywords: dual gauge turnout, FEM model, ballast degradation, discrete element method (DEM), track stiffness, dynamic behaviour.

Railway turnouts represent one of the most critical components of railway infrastructure due to the presence of geometric and mechanical discontinuities, which generate high dynamic loads at the wheel–rail interface. This issue is particularly pronounced in dual-gauge tracks, and especially in dual-gauge turnouts. Dual-gauge turnouts extend the concept of dual-gauge track to the realm of track switching. These devices must cater to the operational requirements of both gauges, ensuring that trains of differing specifications can safely merge, diverge, or cross paths without compromising performance. The complexity stems from the need to maintain proper alignment, flangeway gaps, and clearances for both track types. Thus, this research focuses on analysing the dynamic behaviour of dual-gauge turnouts, with particular focus on ballast and sub-ballast degradation induced by dynamic loads generated by passing rolling stock. A methodology based on hybrid numerical models is employed, combining the Finite Element Method (FEM), applied to track superstructure elements (rails, sleepers, and fastening systems), with the Discrete Element Method (DEM), used for detailed simulation of ballast and the sleeper–ballast contact interface. The analysis is supported by experimental data obtained from in-situ measurements on the through route of the turnout, allowing the evaluation of key aspects such as ballast particle displacement, force distribution, and stress propagation under different dynamic load scenarios associated with the turnout's geometry and stiffness. The findings of this study provide technical guidelines for the optimisation of dual-gauge turnout design and maintenance, contributing to improved structural integrity of the railway infrastructure, reduced maintenance costs, and extended track service life.

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