Bridges

In recent years, there has been a significant growth in the new and extension of railway lines in Victoria. This has resulted in an increase need for rail viaducts due to narrow rail corridors in heavily built up suburban areas. Traditional railway tracks in Australia comprises ballasted track form made up of rails laid on concrete sleepers supported by ballast under the sleeper. Ballasted tracks have served well for train speeds up to 80 km/h. With the increased focus now on faster trains with speeds between 140 km/h to 200 km/h, ballast is known to degrade and pulverise at these high speeds due to higher vibration. Ballasted tracks require regular maintenance, and with the increasing rain frequencies and longer operational hours, it is becoming difficult to maintain.

To overcome the problems of ballasted tracks, slab track (ballastless track) is beginning to be introduced in Australia, which is better suited for high speed trains, relatively maintenance free and longer design life. Over 3000 km of slab tracks have been installed worldwide and have in operation since the early 1970s. The slab track comprises a concrete panel that replaces the standard sleeper and the 300 mm of ballast. The rail sits directly on this concrete panel. The Melbourne Airport Rail project has long rail viaducts and as a result, slab track option was explored and adopted in the reference design. As this slab track form will be increasingly used in Australia, this paper will discuss the common types of slab tracks used in Australia to introduce the concept widely amongst the practising bridge engineers; provides guidance in the selection of slab track; and addresses the loading and structural design of the fixity of the slab track onto the bridge deck.