حميدرضا رفاهيت نيكو

The contact of sleeper and ballast is not same and flat. the presence of empty space between the ballast grains causes that reduces the effective of contact surface between the sleeper and ballast. an‎d as a result it can be reduction the toughness and ballast support. also sleeper itself don’t have smooth surface for creating the lateral resistance and it can reduce the surface between the sleeper and ballast and also this will reduce the stiffness and cracks in sleeper. Distribution of stress is not uniform under the sleeper .and there is a highest stress under the rails. The number of railway ballast particles in contact with a sleeper may be relatively small. The discrete and non-uniform nature of these contacts may cause fracture and abrasion. the target of this investigation and experimentation is to develop complete perception of the mechanical behavior of the sleeper and ballast surface contact. an‎d the variation can be loading according to the type of sleeper and the type of ballast grading; and the load cycle and amount loading. for the measure of the level contact between the sleeper and the ballast can have performed two laboratory and field method. In the field method for the installation of pressure paper the crib ballast was empty on the both side of sleeper .and the rail is slightly moved upwards so that the sensitive paper placed under the sleeper. after the installing the sensitive paper ballast has been replaced then the cyclical loading was performed on the rail and after loading the paper out the amount of the contact was recorded. It can be observed that the effective surface contact between the sleeper and ballast it dependent it the type of ballast and sleeper and loading amount and as well as related to the loading cycle. The values obtained for the contact surface showed that the contact surface for the concrete sleeper was about 4.9 percent and for the wooden sleeper was 8.1 percent. and this amount growth whit increasing axial load and cycle. also the ballast granulation was very effective on the contact surface. Keyword: contact surface between the sleeper and ballast, distribution of stress under the sleeper, empty spaces in the ballast, pressure paper.