Numerical Study of the Effect of Soil Water Response on Track Degradation at Transition Zones

The performance evaluation of a railway track transition zone is vital to ensure adequate track geometry and avoid excessive material deterioration that could in turn lead to an increase in maintenance requirements and frequent disruptions to freight and passenger services. While several different engineering solutions have been proposed in the past to address the stiffness variation and differential settlements observed in transition zones, the importance of soil water response is not commonly considered in the design and construction of transition zones. However, the consideration of the impact of a seasonal change in moisture that takes place in transition wedges is critical in view of more extreme climate patterns associated with climate change. This paper explores the role of water content and water retention on the stiffness of an engineered wedge transition zone using a numerical model developed in Plaxis 3D while using the Barcelona Basic Model (BBM) constitutive model. Two types of simulations were conducted. First, a rainfall event was simulated using transient flow analysis and then the vertical displacement associated with traffic load (InterCity Express rolling stock) was calculated using a pseudo-dynamic analysis. The results indicate that for the same rainfall event, the wedge engineered materials having a higher initial suction remain in partially saturated conditions for longer periods and hence the vertical deformation during loading is reduced. This implies there is an opportunity to reduce track degradation by engineering granular materials incorporated in the transition wedges, particularly in terms of their water retention capacity.