Improved behaviour of railway track substructure using 2D (planar) and 3D (cellular) geo-inclusions
A sustainable growth of ballasted railway is crucial in Australia in view of growing demands of an increasing costal population and highly congested roads and highways. In spite of recent advances in railway geomechanics, an optimum choice of granular media such as ballast and sub-ballast is still considered a challenging task. This is because, these coarse aggregates undergo progressive breakage and fouling under heavy cyclic loading. Moreover, the high capital requirements owing to frequent track maintenance pose serious challenges. The application of geo-inclusions in railway track is therefore essential. The use of two-dimensional i.e. planar (geogrids, geocomposites and shockmats) and three-dimensional i.e. cellular (geocells) geo-inclusions can assist in curtailing such high maintenance costs and improve track capacity. Recently, a series of large-scale laboratory tests were conducted using process simulation triaxial apparatus designed and built at the Centre for Geomechanics and Railway Engineering (CGRE), University of Wollongong. These tests were performed in cyclic drained conditions in order to establish relationships between ballast degradation and train speed, interface shear strength and geogrids as well as lateral confinement and geocells. The test results show that deformation and degradation of ballast and sub-ballast increase with number of load cycles (N), magnitude (qmax,cyc) and frequency (f) of cyclic loading. The ability of planar geo-inclusions to reduce deformations is mainly governed by the shape and the size of apertures. The influence of shockmats to mitigate ballast deformations under large impact loads is dependent on the placement position and the type of subgrade. A geocell offers more confinement than a planar geogrid. It can be more effective at high frequencies (f ≥ 10 Hz) and at low confining pressure (σ3 ≤ 15 kPa). This paper provides an insight to recent advances in railway geomechanics through research conducted at CGRE, capturing the effects of particle degradation and the role of confinement through the use of planar and cellular geo-inclusions.
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