THE EXPERIMENTAL DETERMINATION OF THE AXIAL AND LATERAL TRACK-BALLAST RESISTANCE

Abstract

The track must be able to cope with the lateral and longitudinal loads generated by the train traffic and by the thermal stresses developed in long welded rails. The theoretical studies of the problems involved, have not led to adequate solutions. Experimental studies have been carried out by many railroads to determine the lateral and axial resistance of the track. The purpose of this paper is to survey the used methods and the obtained results. The tests were made on unloaded and loaded tracks to study the influence of the track components (type and profile of the ballast, type of cross-tie, rail section, fasteners) on lateral resistance and to determine the performance of the track after maintenance operations (packing, tamping, compacting). Through these tests it has become apparent that the compactness of the ballast is one of the most important factors to be considered. Next, follows a description of the use of the “derailer wagon,”; a special vehicle designed to study the lateral resistance of the track under the load exerted by a moving vehicle. This test car has made it possible to carry out tests with a variable vertical load and to establish a law governing the development of the lateral track resistance L as a function of the axle load P: L = 1 + P/3. This law made it possible to determine, experimentally, the maximum permissible speed of a vehicle, taking into consideration the lateral forces developed by it. The study of the axial resistance of the track has enabled design criteria to be established for tracks fitted with long welded rails, such as limiting radii, frequency of maintenance operations, etc. The test results are given in a special table showing the relative influence of the various factors affecting the resistance of the track in the horizontal plane.