Abstract
Monitoring ballast support condition and improving current sub-structure and ballast maintenance strategies is critical to ensuring safe and efficient railroad operations. Researchers at the University of Illinois at Urbana-Champaign (Illinois) have developed a ballast support condition back-calculator, a non-destructive instrumentation method and corresponding analysis tool that quantifies ballast pressure distributions under concrete sleepers without interrupting revenue service train operations. This laboratory-validated non-intrusive method uses concrete sleeper bending moment profile and rail seat loads as inputs to back-calculate the reaction distribution using a Simulated Annealing optimization algorithm that incorporates Pareto Distribution as the random variable generator. In order to further understand in-service ballast support conditions, concrete surface strain gauges were installed on concrete sleepers at a revenue service field site to measure strains that could subsequently be converted into bending moments. This site is on a shared use rail corridor with traffic ranging from high speed passenger to heavy axle load (HAL) freight trains. Rail-mounted strain gauges were used to measure strains that were used to calculate the vertical wheel-rail loads to approximate rail seat loads. This paper quantifies the ballast pressure distributions beneath concrete sleepers under different types of rolling stock and evaluates how ballast support condition changes as a function of accumulated tonnage. A wide range of loads were observed at the field site, ranging from 4 to 35 kips (18–156 kN). Corresponding ballast pressures ranged from 14 to 175 psi (97–1,207 kPa), with sleeper-ballast contact area corresponding to 60% of the bottom of the sleeper area. The accumulation of 12.24 million gross tons (MGT) (12.44 million tons) did not generate a quantifiable change in ballast pressure values nor did it generate a change in the ballast support condition. The research results presented in this paper demonstrate the potential of the back-calculator to provide a stand-alone non-invasive method to quantify ballast support conditions, sleeper health, and sleeper bearing stress. Back calculator data will aid the rail industry in optimizing tamping cycles, enhancing safety, and developing more representative concrete sleeper flexural designs based on actual support conditions.
Highlights
The fourth industrial revolution, defined as the current trend of automation and data exchange in manufacturing technologies (Qian et al, 2019), has brought significant change to many sectors of today’s economy
Based on force equilibrium and the basic principles of statics, for a two-dimensional subject, only one combination of reaction forces can generate a given moment profile under a set of applied loads. Considering this principle, the concrete sleeper is simplified as a two-dimensional beam, and its ballast support condition can be back-calculated from the bending moments along the concrete sleeper and the corresponding rail seat loads, both of which can be quantified during experimentation (Qian et al, 2019)
This supports the hypothesis that this support condition would lead to increased demands at the rail seat, creating the potential for accelerated ballast deterioration at this location
Summary
The fourth industrial revolution, defined as the current trend of automation and data exchange in manufacturing technologies (Qian et al, 2019), has brought significant change to many sectors of today’s economy. Autonomous track geometry measurement systems (ATGMS) (Van Dyk, 2014; Saadat et al, 2018), unmanned aerial vehicles (UAVs) (Baniæ et al, 2019), and machine vision and laser-based inspection systems (Ye et al, 2019; Fox-Ivey et al, 2020) are being developed and deployed to provide actionable information about the overall state of the track’s health (Stuart et al, 2012; Saadat et al, 2014) Despite these encouraging advancements, more research is needed to develop and implement condition-based track maintenance strategies for individual components that make up the track structure. The specific focus of this paper will be the quantification of ballast pressures of concrete sleepers installed on a shared corridor with mixed intercity passenger trains and heavy axle load (HAL) freight traffic
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