Failure investigations into interspersed railway tracks exposed to flood and washaway conditions under moving train loads

In traditional railway networks globally, timber sleepers have been widely adopted since the advent of railway systems. After a certain period of time, timbers tend to degrade and it becomes more and more difficult to seek cost-effective replacement hardwood sleepers. To provide a short-term solution, many rail infrastructure managers use an interspersing method of track maintenance. The interspersed sleeper of railway tracks, which is a spot replacement of old timber sleeper with concrete or composite counterparts, is often utilised as a temporary maintenance measure for secondary railway tracks such as low-traffic lines, yards, balloon loops or siding. Reportedly, the performance of railway lines including the interspersed tracks can quickly deteriorate when the tracks are exposed to heavy rains and floods. In many cases, ballast washaway can be often seen. This study is the world first to demonstrate the effects of ballast washaway on the vulnerability assessment of interspersed railway tracks using nonlinear finite element simulations, STRAND7. Two sets of moving point loads representing a bogie along the rails have been established to investigate the worst-case, potential actions for impaired performance of sleepers and differential settlements of the track. In this study, the emphasis is placed on the effects of ballast washaway on the maximum displacement of rails and the relative track geometries (i.e. top and twist). The maximum bending actions causing the failures of the track components are also investigated. The new insights will help track engineers develop appropriate climate change adaptation methods and policies for operations of interspersed railway tracks facing extreme rainfall and flooding conditions.