Performance improvement of rail track substructure using artificial inclusions – Experimental and numerical studies

Abstract Large and frequent loads from heavy freight and passenger trains often lead to the progressive track deterioration. The excessive deformation and degradation of ballast and unacceptable differential settlement of track and/or pumping of underlying soft subgrade soils necessitates frequent and costly track maintenance. However, artificial inclusions such as geogrids and shockmats can mitigate ballast degradation and improve track performance. A quantitative assessment of the influence of breakage, fouling, and the effects of artificial inclusions on the shear behaviour of ballast can be performed either experimentally or numerically. Numerical modelling can simulate these aspects subject to various types of loading and boundary conditions for a range of material properties so in this study, the stress–strain and degradation response of ballast was analysed through discrete element (DEM) and finite element (FEM) methods. In DEM, irregularly shaped ballast aggregates were simulated by clumping together spheres in appropriate sizes and positions. In FEM, a composite multi-layer track system was simulated and an elasto-plastic model with a non-associative flow rule was used to capture ballast degradation. These DEM and FEM simulations showed a good agreement with large-scale laboratory tests. This paper outlines the advantages of the proposed DEM and FEM models in terms of capturing the correct stress–strain and degradation response of ballast with particular emphasis on particle breakage and fouling, as well as applications of geosynthetic grids and shockmats.