Increasing loading frequency: Effects on railway platform materials

The aim of this paper is to present the influence of increasing train speed on the behaviour of conventional railway lines interlayer (ITL). In France, there are more than 30,000 kilometers of operational conventional lines in use. The main characteristic of these lines lies in the existence of an intermediate layer over the subgrade soil and under the ballast layer. This coarse soil is mainly the product of the interpenetration of ballast and subgrade soil. In some of the conventional lines, problems of stability could be expected if the train speed is increased. These problems are characterised by significant displacements of platforms. The behaviour of this interlayer soil has been studied using a large-size cyclic triaxial set up (300 mm diameter specimens). An appropriate method of sample fabrication is proposed. Then, typical results are presented corresponding to a triaxial test carried out on an ITL soil, in which the loading frequency has been increased. To simulate an increase of train speed, different loading frequencies have been used (corresponding to speeds of about 80 km/h - 160 km/h - 220 km/h). The vertical load applied on the specimen simulates the "M" load produced by the bogies of the carriages.