Muddling Mud: EAIT's 3MT finalist talks about spoiled soil

17 Aug 2017

Timothy Vangsness is a PhD student at UQ's School of Civil Engineering; his research is focused on geotechnical engineering. Timothy was a finalist in the EAIT Faculty Three Minute Thesis (3MT) competition in 2017.

Timothy's academic supervisor is Professor David Williams and he has two industry supervisors, Adrian Smith from Pells Sullivan Meynink (PSM), and Leigh Bergin from BHP Billiton Mitsubishi Alliance (BMA).

His research looks at the strength characterisation of in-pit mud to improve low-wall stability, and is made possible due to support from BMA and the Australia Coal Association Research Program (ACARP).

EAIT's 3MT finalists Sean Johnston, Tim Vangsness and Edwin Davis.
Image: Timothy Vangsness (middle) from the School of Civil Engineering at the EAIT 3MT finals with finalists Sean Johnston (left) and Edwin Davis (right).

Muddling Mud

Imagine you are on the beach, playing in the sand.

You decide to dig a hole but you are a bit too close to the water’s edge.

Before you know it, the water starts to flood your hole, the walls cave in, and it disappears from sight.

As you can see by the poor kid in my slide (below), it is a pretty upsetting experience.

Fortunately, if this happens to you, you can take a few steps back and start again (or if you are smart, take a few more).

On a mine site however, when you are dealing with millions of cubic meters of soil, it can be a bit more serious.

The aim of an open-cut mine is to dig up the material in front of you to access the commodity, and place it either behind you in the pit, or somewhere outside the pit (much like how a dog digs a hole). Now this is all well and good, until water gets involved.

Large amounts of rainfall can cause mining pits to flood. This water causes the dug up material named spoil to degrade and lose strength, turning into mud.

When a decision is made to start mining again, something must be done about the formed mud. Either it is removed, costing millions, or it is left in place and spoiled upon.

The potential downside to this is that the weak material could act as a slip plane, and be the cause of slope instability, putting machinery, infrastructure, and lives at risk.

In 2009, at a mine site in India, weakened mud due to flooding caused 33.7 million cubic meters of soil to slide into an active mine, killing 14 people. The question is therefore, how could this be avoided?

Well that is the question I plan to answer. My topic is the shear strength characterisation of in pit mud to improve slope stability, and my research is going to make mine sites safer.

The key aspect of my research is investigations into the strength characterisation of in pit mud.

The aim of this is to quickly determine a materials strength without extensive testing.

A simple classification system was developed in 2004, basing the criteria on visual parameters such as particle size.

This is an excellent approach and has been used throughout the mining industry. It does however need improvement, and through further testing and analysis of geotechnical and hydrological material properties, more factors can be added into the equation, improving its reliability and accuracy.

Specifically, I will be looking at how different materials turn into mud, and how long it takes. By understanding how the material degrades over time due to water, we can then account for the associated reduction in strength in our calculations.

Through better spoil identification and design, millions of dollars, and many lives can be saved.

My research is going to make mine sites safer, so hopefully we can keep the tears to more trivial scenarios.

Slide from 3MT presentation 'Muddling Mud'
Image: The slide that accompanied Timothy's 3MT presentation, 'Muddling Mud'.

Never heard of the 3MT? Find out more about this global competition for PhD students at the 3MT website.