Relating trackbed stiffness and behaviour with track performance and maintenance needs

Abstract

Differential settlement along the track is a significant concern for railways, especially but not exclusively at transitions onto or from hard substructures. Recent attempts to forecast its development have combined empirical or semi-empirical ballast settlement equations with dynamic vehicle track interaction (VTI) models. Such analyses may demonstrate a relationship between variations in loading and settlement and how track geometry deterioration onsets. However, a generally applicable settlement equation is inexistent, and current VTI simulations run for short track sections or in large steps with settlement predicted forward cycles for computational economy.
This study proposes a new track settlement model, named STAM, that accounts for load magnitude and history and the contribution of subgrade layers to the total permanent deformation. The model’s functions and parameters are determined using data from cyclic laboratory tests on a single sleeper and Finite Element (FE) analyses. STAM was then integrated into an in-house VTI model and acceleration algorithm to form a Vehicle Track Interaction Long-term Model (VTILM). The capability of VTILM to estimate the development of track differential settlement over 10,000 cycles was tested in two 65-m long track sections with variations in trackbed support conditions: a single-span railway bridge and a plain track section with a stochastic trackbed stiffness. The effect of track stiffness, train speed, earthwork materials and initial settlement profile on the performance of the single-span railway bridge was also evaluated in the short-term using a dynamic 2D FE model.
The model demonstrates that variations in track stiffness associated with changes in trackbed condition could onset track geometry degradation. The model can replicate three frequently observed track behaviours: the development of a bump/dip at the ends of transition zones, the increased maintenance needs for poor trackbed conditions, and a relation between the maximum settlement and maximum angular distortion.

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Identifiers

ORCID for Giacomo Ognibene: orcid.org/0000-0003-4620-2399

ORCID for William Powrie: orcid.org/0000-0002-2271-0826

ORCID for Louis Le Pen: orcid.org/0000-0002-4362-3895

ORCID for John Harkness: orcid.org/0000-0003-0908-0791

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