Settlement response of fibre reinforced railway ballast

Ballasted track is the prevalent track form worldwide and with good design and maintenance can satisfy high performance demands including those of high speed lines. However, increasingly onerous loading is being placed on existing ballasted track networks in many parts of the world by more frequent, longer, faster and heavier trains. This leads to reduced windows of time for maintenance activities while simultaneously increasing maintenance needs. Therefore there are potential advantages if ballasted track could be modified to increase durability both in terms of intervals between maintenance interventions, e.g. tamping, and overall life cycle. This paper presents an assessment of the potential for randomly reinforced ballast, a mixture of ballast and fibres of selected dimensions and properties, to increase the durability of railway track. Compared with other types of reinforcement, fibres have potential advantages of: isotropy (avoiding the formation of weak planes); the possibility of using recycled plastic material; and expected compatibility with normal maintenance procedures. A series of full size tests has been conducted in the Southampton Railway Testing Facility (SRTF) to evaluate the resilient and plastic response of reinforced ballast to vertical cyclic loading. The testing apparatus represents a slice of single track extended to the shoulders and including one sleeper. A vertical load, representing a 20 tonne train axle, was applied by a hydraulic actuator with a frequency of 3Hz to 3 million cycles. Tests carried out thus far demonstrate the importance of selecting an appropriate fibre width as a function of the average particle size of the ballast to be reinforced. Appropriately selected fibres are shown to reduce ballast vertical permanent deformations by about 25%.