An Application of Geotechnical Instrumentation Permanently Embedded in Railway Track

Researchers and engineers rely on information and data to study, operate, maintain, and improve transportation infrastructure. Measurement provides quantitative information and evidence for these purposes. Sensors for measurement can be embedded into the track system at a fixed location or vehicle mounted. This paper describes the design, deployment, and operation of a permanent measurement system that uses sensors embedded in the trackbed on an operational railway in the United Kingdom to monitor track deflection, stiffness, and pressures at key trackbed interfaces. The measurement systems comprise a longitudinal array of accelerometers fixed to sleeper ends; dynamically sampled total pressure cells placed at the ballast-subgrade interface; and total pressure cells, piezometers, and accelerometers buried in the subgrade. Permanent, fixed sensors provide large volumes of detailed but highly localized information, while multichannel sensor arrays produce data that describes performance along the track. Methods for data reduction are proposed for the acceleration measurement system that allows spatial and seasonal variation to be visualized along the instrumented site for different train types. This approach enables comparison with track geometry data from rolling (on-train) measurements. Locally, buried instrumentation provides evidence for variation in load transfer to the subgrade both along the line and across individual sleepers; illustrates how interaction between wheelsets varies with depth and by vehicle type; and how the pore water responds to train loading. The application of measurement for monitoring purposes permits an analytical approach to data interpretation where monitoring parameters are similar to those used for design and simulation.