Influence of Water Content on Track Degradation at Transition Zones

This study aims to explore the role of water retention behaviour in the track degradation of the transition zone by examining the influence of water content variation. A model of railway bridge approach transition was built in the PLAXIS 3D to simulate the track degradation under diverse water content scenarios. A wedge-shaped backfill with unbound granular material (UGM) was simulated as a technical solution between the bridge abutment and open track. The most distinctive characteristic of the model is that the direct relationship between soil water content and soil displacement can be explored. To achieve this, the seasonal change in the soil moisture content of subsoil was simulated as the independent variable. The water content variation adopted mimicked the wet season (ω = 7.6%), as-compacted (ω = 5.6%) and dry season (ω = 3.6%) water content conditions. The results indicate that higher soil strains and displacements are obtained for high water contents. This indicates that there is a clear correlation between soil water retention and track displacements. In addition, the results suggest that a reduction in water content in the track substructure can be effective in mitigating in-service settlement as overall track stiffness increases as a result. However, this effect is more pronounced at the track level and becomes less important at higher depth in the formation layer. This study also shows that the bump from the bridge structure to backfill can be mitigated and smooth track geometry from the backfill and the open track can be achieved by manipulating the water content.