Slab track performance under heavy haul revenue condition and its remediation method

Many types of slab tracks have been installed on high-speed passenger corridors in recent 2 decades in western European and Northeast Asian countries. And in last decade, some special designed slab-tracks have been tested for heavy axle load freight revenue condition in North America. Slab tracks have been successfully shown their advantages in track maintenance, such as high-stability and integration, high quality of track geometry, low maintenance and low life-cycle cost, etc. Hence, it has been acknowledged as one of the feature of modern railway system. Australian railway authorities are the pioneers to try the slab track structure on their heavy haul freight lines. As early as 1986, a nearly 600m concrete slab track section has been installed on the Up and Down tracks of Coal Line at Hanbury Dive of Hunter Valley Corridor, NSW. The Coal Line is one of the major heavy haul freight networks in Australia, working together with the Main Line which is parallel each other, the annual freight traffic is higher than 200Mt, and the freight train’s axle load is 30t. As a very earlier design, its structure is featured as the concrete slab is 350mm thick, using 35MPa strength concrete. Rails are supported by low profile concrete blocks at spacing of 600mm, with 2 anchor bolts and 2 Pandrol e-clips in each fastener plate used to anchor the rails to the slab. The slab track is constructed by top-down method. The track resilience and damping are provided primarily through rubber pads installed between the fastener plates and the slab surface. The whole structural design is similar to the American “Direct Fixation Slab Track (DFST)”, which has been tested at Transportation Technology Center (TTC), USA. After near 20 years’ service under heavy haul traffic, the condition of the slab track has been reported as deteriorated. The major defects including cracking of concrete slab, damage and failure of concrete support, and the fastening system failed. And these have resulted to issues with track stability, gauge widening and drainage problem. Since the slab track installed in 1980s, its conditions have been continually monitored, and in 2006 and 2012 the performance of the system was systematically studied. After assess the fastening system and associated factors that may lead to accelerated failure of the fasteners, a remediation strategy is made. It is included using the Alt 1 Delkor Baseplates with a 4 bolt connection to base slab to rectify the ongoing failure of the fastening system, and a special designed two-pot epoxy resigns material is used to rebuild the support and install the new fastening system. From 2006 until May of 2014 more than 700 fastening systems have been replaced. In this paper, both the recorded condition of the DFST slab track under heavy axle freight traffic and the remediation method are presented