Stabilisation of rail tracks and underlying soft soil formations

Construction of rail tracks requires appropriate improvement techniques for ballast and underlying soft formation soil, both of which deform and degrade progressively under heavy train loads. This paper aims to demonstrate and discuss some major aspects in relation to stabilisation of ballasted rail tracks overlaying soft formation soils. The use of geocomposites (i.e. bonded geogrid-geotextile layers) for enhancing the performance of rail tracks is described, with the aim of achieving reduced track settlement, increased resilient modulus and decreased ballast degradation. The effects of increasing the confining pressure on rail tracks in regard to particle breakage are studied using laboratory tests. The utilization of prefabricated vertical drains (PVDs) to improve soft subgrade and provide better drainage system is introduced. Finite element analysis using an equivalent plane strain conversion is employed to predict settlements, excess pore pressures and lateral displacements under rail tracks. Finally, the use of native vegetation to stabilise soft formations of rail tracks is discussed, with the aid of preliminary suction models based on evapotranspiration mechanics applied to tree roots.