Discrete Element Modelling of Geocell-Reinforced Railway Ballast and Experimental Examination of Geocell Failure Mechanisms

Abstract

Rail transport is one of the major means of conveyance of passengers and goods worldwide. Due to the cyclic impact of trains, breakage and rearrangement occurs to the ballast in the trackbed of a railway. As a result, the trackbed is prone to lateral creep and subsidence, which is deemed to undermine the serviceability of rail tracks, and likely cause catastrophic failure of the tracks. To gauge the serviceability of the tracks, a significant amount of expense is spent annually to maintain the serviceability of rail tracks. To minimise this expense, a variety of engineered methods have been suggested and attempted to reinforce the ballast of the trackbed, such as embedment of geosynthetics into the ballast layer. Of these geosynthetics solution, geocells are an emerging and promising option of reinforcing railway ballast. However, to date, the study of geocell-reinforced railway is much limited, possibly due to the high-cost involved in an experimental or field-testing program, and the difficulties of modeling railway ballast with the currently available simulation technics. To gain an insight of the geocell reinforcement, numerical studies have been carried out to examine the mechanical responses of geocell-reinforced railway ballast. This research adopts a commercially available Discrete Element Method (DEM) software package, Particle Flow Code (PFC) 3D to simulate the interaction between the geocell and the discrete particles of ballast. Both monotonic and cyclic loading environments are assessed, and ballast breakage is considered. Displacements and stresses at both micro- and macro-scales are assessed for control and reinforced scenarios. This study demonstrates that the geocell can effectively reduce settlement and ballast breakage. The geocell stiffens its embedded layer and reduces stress propagation into the underlying layer. The outcomes of this study seek to encourage likely reduction in trackbed thickness and width, to save construction cost and improve the sustainability of the railway trackbed. Furthermore, the presented study experimentally examines the responses of geocell junctions and cell-walls under various loading conditions. An extensive testing program has been undertaken to assess the geocell junctions and geocell walls. A ductility ratio is developed to measure the rapidness of failure under different short-term loading scenarios for both the cell-wall and junction. The observed failure patterns are presented and an evaluation of the implications of the practical uses of geocells is drawn.