Using the PUMA test to predict performance of stabilised ballasted trackbed

The main functions of ballast are to provide structural support to the rail superstructure and fast drainage. Ballast performance degrades during its service life due to deterioration caused by dynamic loads from passing trains and by environmental weathering, and eventually it becomes fouled. The structural integrity of fouled ballast can be compromised leading to track instability and accelerating geometry deterioration. Moreover the constant increase in volume, tonnage and speed on the rail system stresses the trackbed to levels never experienced before; thus in order to keep the stability and geometry of the track at standard comfort and safety levels, ever more frequent maintenance is needed, both ordinary (tamping) and extraordinary (renewal). Ballast maintenance costs are a great part of the maintenance costs and material consumption; therefore new methods of trackbed maintenance must be adopted to enhance performance and in turn durability of the infrastructure. The study, presented in this paper, investigates the potential for in-situ stabilisation of the ballast layer by providing it with bonding strength through the addition of a bitumen emulsion that acts at ambient temperature. The resulting bituminous mixture was tested by means of vertical cyclic compression to account for accumulated vertical deformation by means of the precision unbound material analyser test, developed partly at the University of Nottingham, by applying a dynamic load simulating traffic conditions. The results show that this equipment is a reliable, economical, repeatable and relatively simple solution to perform accelerated simulative tests of railway trackbed technologies.