Stabilisation of ballasted rail tracks and underlying soft formation soils with geosynthetic grids and drains

Railway ballast deforms and degrades progressively under heavy cyclic loading. Ballast degradation is influenced by several factors including the amplitude and number of load cycles, gradation of aggregates, track confining pressure, angularity and fracture strength of individual grains. The degraded ballast is usually cleaned on track, otherwise, fully or partially replaced by fresh ballast, depending on the track settlement and current density. The use of composite geosynthetics at the bottom of recycled ballast layer is highly desirable to serve the functions of both drainage and separation of ballast from subballast. Construction of the rail track also requires appropriate improvement of the subgrade soils to achieve an adequately stiff surface layer prior to placing the ballast and subballast. Based on extensive research at University of Wollongong, it is found that the gradation of ballast plays a significant role in the strength, deformation, degradation, stability and drainage of rail tracks. Results from large-scale triaxial testing indicate that a small increase in confining pressure improves track stability with less ballast degradation. Bonded geogridsgeotextiles also decrease differential settlements of tracks, ballast degradation and lateral movement, and the risk of subgrade pumping. Stabilization of soft subgrade soils is also essential for improving the overall stability of track and to reduce the differential settlement during the operation of trains. This paper also highlights the effectiveness of using prefabricated vertical drains (PVDs) for improving the behavior of soft formations underlying rail tracks.