New Linkage Project to better understand ‘mud pumping’ in our rail networks

 The new LIEF funded test facility under construction. Photo courtesy: Cholachat Rujikiatkamjorn

University of Wollongong's SMART Railway Laboratory undergoing further modernisation. 
Image courtesy: Cholachat Rujikiatkamjorn

The Australian railway network is the world's seventh longest network, stretching more than 40,000km. It enables everything from commuter trains for workers through to heavy-haul trains for moving cargo, such as agricultural produce and mining materials.

Threatening this network, and costing rail companies millions in repairs every year, is the liquefaction of soil beneath the tracks when subjected to the repetitive force of a train—a process known in the industry as ‘mud pumping’. The vibration of a large heavy-haul train travelling above certain critical speeds can affect the ground just like an earthquake, softening the foundation soil, creating holes and contaminating the overlying ballast with the soft mud slurry—destroying the integrity of the track.

One of the first recipients of funding through the Australian Research Council’s newly operating continuous Linkage Projects scheme, Distinguished Professor Buddhima Indraratna, will be leading a research team at the University of Wollongong to determine the underlying causes of this highly destructive process.

“We have seen extensive mud holes and mud pumping. Sometimes we observe severely contaminated ballast and gaps beneath the concrete sleepers, and the soil in those areas makes the track behave like a sponge when the moisture level is high.  At times, one can even see gaps opening up while the train is going over— the repairs can be extensive and it’s a continuing problem,” said Professor Indraratna.

Having obtained significant additional cash and in-kind support from five partner organisations, Professor Indraratna is hoping to address two major issues of concern to industry in this project. How do we identify the areas vulnerable to mud pumping across Australia?, and, once recognised: How do we improve this sub-grade soil with proper drainage and treatment so that we reduce the risk of mud pumping?

Professor Indraratna has been actively seeking solutions to this problem for many years, and received a $900,000 ARC Linkage Infrastructure, Equipment and Facilities (LIEF) grant in 2014 to establish an internationally first-of-its-kind facility for the cyclic testing of high-speed rail. 

“Our prototype test facility is currently being built on a large piece of land near the university’s main campus. It was a major undertaking for the LIEF grant and I think that, including the industry contributions thus far, we have now attracted close to $2 million in total for this unique national facility.”

“Our Vice Chancellor was kind enough to get a ten-year lease for this piece of land so that we can set up this facility. You certainly can imagine it is a massive testing yard and expected to be a bit noisy—it can simulate heavy-haul trains going up to 120–130 km/h.  So you can’t conduct lectures in the main campus with this operating close by!”

“This is an iconic piece of equipment, that the Australian railway industry has been needing for a long time. It will allow us to do the testing at 1:1 scale without having to use real live tracks, so we don’t interfere with everyday railway traffic.”

Professor Indraratna says that due to his research there is an increasing understanding among track engineers and the companies that bid to construct new tracks, that the design must take account of the actual conditions of the soil over which the track is built. In Australia, we have some of the weakest and the softest soil deposits, from erodible silts to highly compressible estuarine clays.

“If you look at Australian railway track design in general—the design of the track for many kilometres is almost homogeneous. There is not much change from one location to another and, in the future, tracks have to be designed more comprehensively according to the terrain. The properties of the terrain have to be more critically evaluated and where there are mud pumping problems, the tracks have to be custom-made for that particular issue.”

“The Australian Rail Track Corporation (ARTC) and Sydney Trains have been very proactive in this area of research and development, and the Australasian Centre of Rail Innovation (ACRI) has also been proactive in facilitating the inclusion of the rail industry.”

With this new injection of ARC funding, Professor Indraratna hopes to attract young researchers to his rail geomechanics team at the University of Wollongong. “We desperately need to train more skilled people to serve the rail industry in design, construction and maintenance; we need to train our young engineering groups to become masters of the art of rail track design, to be competitive and to provide robust track infrastructure.”

“Looking to the future, before we can focus on high speed passenger and freight rail, we must first examine the foundations it uses—the ground it is built on.”