Laboratory and Field Testings of the New Concrete Friction Sleeper

Abstract

In summer the temperature stresses in the rails may become very high and induce lateral distortion of the track with risk of derailment. In small radius curves (R < 300 m) there are restrictions on use of CWR due to the risk of track buckling. This requires fishplated rail-joints with their many drawbacks. To improve safety and reduce maintenance costs it was found essential to find a practical way of improving the lateral resistance of ballasted track with concrete sleepers. The new concrete Friction Sleeper was designed with cross-wise ridges at the under-side to form a coarse cogging with adequate dimensions to utilise more of the high internal friction potential of the crushed stone ballast. By lateral displacement of this sleeper a completely continuous layer of ballast material will be held fixed to the sleeper under-side by hooking, wedging and granular interlock, and give a very high friction resistance. In performed field tests the Friction Sleepers provided a considerably larger lateral displacement resistance than the standard concrete and wood sleepers. Based on the observation data in these tests, the track with Friction Sleepers obtained the highest absolute and relative lateral resistance values for all three axle load levels. A very important result was that the unloaded track with Friction Sleepers had a very high lateral resistance, 35 and 110 % higher than obtained by the track with the standard concrete and the wood sleepers respectively. Based on the field and laboratory test results the new concrete Friction Sleeper has a considerable potential to yield higher safety against rail buckling, increased use of CWR tracks and less strict requirements on ballast quality and ballast profile.