Railway Transition Zones

Abstract

Railway tracks are subjected to constant degradation in terms of geometry, and wear and tear of the track components (rails, sleepers, fasteners, trackbed layers, etc.). Over the years, trains have evolved immensely, but the track infrastructure has not kept pace. With rapid advancements in vehicle technologies, the design of rail infrastructure must cope with the challenges associated with the operation of railway tracks. In addition, railway transition zones (RTZs) degrade even faster (4-8 times) than normal tracks, leading to higher maintenance and operational costs. RTZs are areas where railway tracks cross stiffer structures (e.g., roads, bridges, culverts). The amplified degradation in RTZs is mainly attributed to abrupt changes in vertical stiffness and to differential settlement, resulting in amplified and non-uniformtrack responses. Even though the dynamic behavior of RTZs differs from that of normal tracks, the design of track components in these zones remains similar to normal tracks, with some modifications at the superstructure and/or substructure levels to mitigate the transition effects. There have been several attempts to mitigate the adverse effects of dynamic response amplification in RTZs, but they have proven either marginally effective or counterproductive. Therefore, a comprehensive design methodology for RTZs is needed that addresses the main degradation mechanisms leading to amplified degradation of these zones.

In this paper-based thesis, a novel methodology is proposed to design and evaluate railway transition zones. For this purpose, detailed analysis and design optimization is performed for a bridge-embankment transition using various two-dimensional and three-dimensional finite element models, different vehicle models, and surrogate models (using polynomial chaos expansion). Firstly, the proposed methodology establishes a robust design criterion to design and evaluate RTZs. The criterion relates the magnitude and uniformity (spatial and temporal) of the total strain energy in the trackbed layers to the permanent deformation of RTZs. This novel energy-based criterion is used to evaluate the most commonly used mitigationmeasures at the superstructure and substructure levels and to investigate the key phenomena governing RTZ design. Based on insights obtained from these analyses, a preliminary design of a novel transition structure called SHIELD (Safe Hull-Inspired Energy Limiting Design) is proposed. The second phase of the work is dedicated to identifying the most influential design parameters leading to optimized geometry of SHIELD and the desiredmaterial characteristics. The third phase involves the performance evaluation of optimized SHIELD subjected to critical loading conditions (e.g., critical and supercritical velocities, different directions of movement, hanging sleepers, non-straight rail) and SHIELD is shown to be a robust design solution for all conditions under study. In the end, the use of SHIELD is extended to another type of an embankment-bridge transition (with ballast running over the bridge) where it is shown to be equally (compared to embankment-bridge transition with no ballast layer over the bridge) efficient in mitigating the transition effects, and a laboratory experiment is designed to test the effectiveness of the proposed design criterion and methodology. A robust design methodology for RTZs is proposed in this work, which aims to minimize operation-induced degradation and can be adapted to different transition types and sitespecific conditions. A preliminary optimized design of SHIELD is proposed, which has been shown to be effective in mitigating dynamic amplifications in RTZs under both ideal and non-ideal conditions. The results and conclusions presented in this work demonstrate the promise of SHIELD as an intervention for railway transition zones, outline the next steps toward its practical implementation, and highlight the challenges that need to be addressed in future research.