Influence of contact loss underneath concrete underlayer on dynamic performance of prefabricated concrete slab track

Contact loss between the concrete underlayer and the subgrade caused by the differential settlement or stiffness of subgrade structure is a common distress, which deteriorates the mechanical properties of the track structure and adversely affects the safety and comfort for the operation on high-speed railway. The objective of this paper is to study the damage mechanism of prefabricated slab track subjected to such contact loss and to propose a critical value for the size of contact loss that would not jeopardize the safety of rail traffic and riding comfort of passengers. Thus, a vibration calculation model for the vertically coupled vehicle-J-slab track-subgrade system is established using finite element method, both of the short-wave irregularity and the German long-wave irregularity were taken into account to calculate the dynamic response of vehicle, track structure and subgrade with different contact loss areas and speeds scenarios. Based on the numerical simulation results, a critical value of contact loss area is proposed. When the actual contact loss area is smaller than the critical value, the welded joint irregularity is the dominant factor in the vehicle dynamic response; however, when the actual contact loss area is larger than the critical value, the track irregularity induced by contact loss under the concrete underlayer becomes the dominant factor. It is suggested that the contact loss area should be controlled under the critical value in order to ease or mitigate the dynamic response of the vehicle and track structure. The numerical simulation indicates the critical contact loss area is about 10m(2) for the short-wave irregularity case and 14m(2) for the long-wave irregularity case, thus it is suggested that the contact loss area underneath the concrete underlayer should not exceed 10m(2), which is consistent with the Swedish standard and the German standard on weak areas of subgrade compaction.