Effectiveness of Soft Baseplates and Fastenings to Mitigate Track Dynamic Settlement at Transition Zones on Railway Bridge Approaches

Railway bridge approaches or bridge ends often suffer from a combination of dynamic wheel/rail interaction and poor formation compaction due to construction difficulties, resulting in an initial short-wavelength track settlement at the first few sleeper bays near the bridge over a short period under revenue services. This settlement then further induces impact loading that aggravates the differential settlement, causing downtime or restricted railway operation; and importantly more frequent maintenance, which is costly and time-consuming. Principally, the stiffness transition zones can be optionally designed to either: (1) provide a gradual increase in the stiffness of ballasted track to match that of the stiffer track (stiffness ramping); or (2) equalise the stiffness and rail deflection, usually by controlling the resilience of rails on the stiffer track, or by adding more resiliency to the stiffer track.

This paper demonstrates an application of special soft baseplates and fastening systems to isolate the dynamic conditions transferring from the transom steel bridge to the ballasted track at the bridge ends. The method appears to be useful for both green- and brown-field maintenance approaches. The soft baseplates can filter dynamic impact content from the aggressive loading conditions and provide longer-wavelength load redistribution over the railway track infrastructure. The field trail was conducted at a railway bridge in New South Wales, Australia. This paper presents the field performance and the dynamic behaviour and responses of railway bridge ends improved by the soft baseplates and fastenings. Based on the vibration measurements, the new bridge end improvement method can well suppress vibrations at the bridge ends. The data shows that the lesser vibrations are transferred to the ballast layer. In addition, the track geometry data from the track inspection vehicle 'AK Car' shows a slower deterioration process at the bridge end.