Railway track performance study using a new testing facility

This paper presents results from full-scale laboratory research on railway tracks using the geopavement and railway accelerated fatigue testing (Graft) facility at Heriot-Watt University. A typical ballast depth of 300 mm has been considered, overlying subgrade soil (a typical situation on site). Sub-ballast has not been used, to ensure that only ballast and subgrade behaviour are investigated. The influence of load level and subgrade stiffness for a typical UK track is presented, and from the results a new railway track settlement equation is proposed that fits the measured data in Graft well. The proposed equation can predict track settlement in Graft after a number of cycles for any applied load, and for the clay and subgrade Young's modulus considered in this paper. The threshold stress concept used in fine-grained subgrade materials, granular materials and within railway track design processes has been considered, and a new track parameter (t) within the track settlement equation has been proposed to account for this. The equation has been compared with other previously published equations with different parameters that are based on both laboratory and field measurements, and similarities have been found. This paper demonstrates how the Graft facility can accurately simulate the railway track response.