Why muddy rail lines can be a derailment danger

University of Wollongong Professor Buddhima Indraratna is researching the problem of "mud pumping", which can affect rail lines. Picture: UOW
University of Wollongong Professor Buddhima Indraratna is researching the problem of "mud pumping", which can affect rail lines. Picture: UOW

University of Wollongong research could improve the reliability of the South Coast rail line – especially in rainy weather.

A team of researchers, led by Professor Buddhima Indraratna from the university’s School of Civil, Mining and Environmental Engineering, has recently received a $675,000 federal government grant to look into the phenomenon of “mud pumping”.

This can damage the rails to such an extent that a derailment is a real danger.

It occurs when heavy freight trains travel on rails sitting on soft maritime soils.

The weight increases the water pressure in the soil and forces mud up through the ballast – the stones that the rails sit on.

The mud coats the stones and blocks surface water from draining away and it starts to pool on top.

“This is why sometimes when it is raining very hard the trains are abandoned and the commuters have to take the buses,” Prof Indraratna said.

“It happens in the low-lying areas all the time where the groundwater table is close to the surface and the railway embankments are not very high

“When the water content rises the track becomes much weaker and the track cannot withstand the weight of the train.

“You increase the risk of derailment if the water content is very high.”

Prof Indraratna said passenger trains did not cause mud pumping as they lacked the weight of heavy freight trains.

But they could be affected by it on lines like the South Coast line, which is shared by passenger and heavy freight trains.

“Because of that, once the track is affected by the mud that is contaminating the ballast that of course affects the passenger trains too,” he said.

“The passenger train isn’t necessarily causing the mud pumping, but once the event happens and the track is not maintained it will affect everything that is travelling on it.”

Prof Indraratna’s research could save some of the $1.5 billion a year spent on rail maintenance in NSW.

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