field and laboratory investigations of the effective contact surface between sleeper and ballast particles in railway tracks

Ballast is a porous layer that reduces the effective contact surface between sleeper and ballast. also, the sleeper does not have a smooth bottom surface, which causes a reduction of the contact surface between the sleeper and ballast particles. at field experiments, by installing sensitive papers under the sleepers of a track, the cyclic load was imposed by passing trains, and after passing a certain amount of loads, the sensitive pressure paper was removed, and the contact surface was measured while in the laboratory investigation, the ballast box test was used to achieve a similar goal. the values obtained for the contact surface showed that the 200 kn axle load contact area is about 4.9% for concrete sleepers and about 8.1% for wooden sleepers, and this value increases with increasing axle load and load cycle. the average contact area for ballast type 1 was 4.6%, for ballast type 4 was 5.5%, and for the sample of ballast from the field test site was 5.3%. two types of soft and stiff under sleeper pads (usp) were used. the results showed that the effective contact area between sleeper and ballast was 21.6% and 15.9% for soft and stiff usp, respectively.