ABSTRACT
Track transitions are known for poor geometry and unwanted track-vehicle dynamic forces, resulting in high vehicle accelerations and poor riding quality. Various methods and products have been developed to address the rapid change in substructure stiffness between normal ballast track and ballastless track structures encountered in tunnels and on bridges, among others. These methods and products have been successful to some degree, but recent research has demonstrated that track transition design should firstly be aimed at reducing differential settlement and secondly at gradual stiffness transitioning. The paper discusses a series of monotonic and dynamic laboratory tests carried out to characterize the behaviour of rigid polyurethane foam reinforced ballast as a possible solution to the differential settlement problem. The tests include the testing of unreinforced, partly reinforced and fully reinforced ballast in two different ballast box configurations as well as unconfined compression tests on reinforced ballast. The use of rigid polyurethane foam as ballast reinforcement is suitable for reducing settlement in track structures. Rigid polyurethane foam reinforced ballast settled 60% less than conventional unreinforced ballast, and reinforcing only 50% of a ballast layer lead to a reduction in settlement of 42% compared to that of conventional unreinforced ballast.
