A Mine of Information

Tim Cartledge had a fascination for rocks and a mindset for maths long before he ever heard about geotechnical engineering.
So when a school careers day introduced him to the profession that combined both his passions, the die was well and truly cast.

“On the science side, it’s fascinating because nothing is an exact answer,” he explains of a role that has taken him around the world. “You have to look at all the elements and come up with a solution. And with maths, I really enjoy being able to use numbers to tell the story.”

In his earlier days, Tim worked for some of the industry’s major names, but found himself frustrated by their lack of flexibility. The Global Financial Crisis (GFC) also proved an eyeopener, with subcontracting work drying up. “So it was basically a case of: ‘If you aren’t able to find me work, I will find a way to do it myself. And I did. It took a few months, but I won my first job on a mine site and it went from there.”

Path to success

Since those initial days, Cartledge Mining and Geotechnics (C&MG) has driven success through core values centred on delivering the best solutions for clients through practical, quality advice.

With clientele based around the world, it’s a truly global consultancy, although Tim reflects on his favourite job so far as sitting fairly close to home.

“Papua New Guinea has probably been my most enjoyable work, mostly because it’s been the biggest challenge,” he explains. “It’s a fascinating environment that’s so different to the big mines.

“I started doing work there in 2007, and went back a few years ago, just after it reopened from Covid, so it’s been fascinating to see the progress on the site back from before it was even a mine.”

In terms of the challenges PNG offers, Tim says they vary in complexity.

“Location is an obvious one, especially in terms of access, and also the availability of things we might usually take for granted, such as equipment or tools,” he says.

“It’s also an environment where it rains almost twice a day, every day, so logistics can be challenging.

“The people there also don’t have the same education and work standards as us, or the same opportunities, but I find it enjoyable to train them up.”

Beyond the bottom line

It’s a commitment to empowerment and education that serves as a “real driver” for Tim, as seen through measures such as launching Friction to offer guidance and an overview of industry movements and give back to geotechnics.

It was also the inspiration for C&MG’s 2023 Geotechnical Symposium, where Tim was one of the presenters. His topic, focusing on a coal mine in central Queensland, was A Case Study in the Use of Softwalls to Mitigate Geotechnical Risk.

C&MG became involved when it was asked to work on the expansion of an existing pit, which had to be reoriented from being mined south to north, to west to east. This involved a new 3.5km diversion drain and new 2.8km levee that had to be safely positioned.

Because it wasn’t a simple site, the work couldn’t be tackled with traditional coal mining techniques such as pre-split designs. Softwalling was adopted when slope failures occurred during the initial cut. Softwall is used in coal mining to disrupt unfavourably oriented geological structures.

This involves overblasting to disrupt contained structures contained within the wall, preventing them from failure. The wall is then cut at an angle of 45 degrees.

Other factors that came into consideration included two faults running parallel to the pit walls and the distinct risk of the levee being undermined due to movement along these structures.

During the mining process, key behaviours included:

• Significant deformation was observed in the wall

• Peak deformation velocities were recorded at >60mm/hr

• There was up to 10m of vertical subsidence and >20m horizontal displacement

• Dynamic alarm thresholds increased from 10mm/hr to 120m/2hr, in response to changes in slope behaviour

Tim said no geotechnical incidents were recorded during mining of the softwall, the levee wasn’t breached and all budgeted coal was recovered.

These helped cement two key takeaways.

“Firstly, softwalls are highly effective at sustaining significant deformation without failure,” he said. Secondly, they are a highly effective solution to mitigate geotechnical risk in complex geological conditions where issues such as thrust faults or small wedge failures can occur.”

Looking ahead

With an eye to the future, Tim is now excited to see what might happen with the opening of a new C&MG office in Perth.

“The main thing is to see the expansion of the business in opening up different markets and getting exposure to different jobs,” he says.

“As we grow and develop from there, we’ll have opportunities to get access to Africa, which is one of the expanding mining regions, and also out of Perth and Western Australia, where gold mines, lithium mines and iron ore drive their mining industry.

“Elsewhere on our team, senior principal Fernando Vieira has also spent a long time in South America, so he’ll be exploring that option.”

It’s a reference to geographical movement he recommends for geotechs generally.

“I think getting exposed to different places is very important, whether that’s local or international,” he says. “It’s about seeing how things materialise differently; not just the engineering side of it, but also how they operate and function. How cultures and processes can influence the way mines develop and how their problems can be solved.

“Every site is unique, so I think it’s very important to go out to different places – see how rock masses behave in different, challenging conditions.”

Something else he’d like to see is for the industry to address the way it sells itself.

“It does a poor job of communicating how enjoyable the mining industry is, how critical it is, and what it’s doing for everybody,” he says.

Tied up with this is a failure to attract young people, which Tim notes as a looming issue.

“That is going to be the ticking time bomb in the next five or 10 years,” he explains. “There are literally no people coming through in the industry, yet we need to try and double the size of the industry, if not triple it, to meet demand.

“But how do we do that when most of the brainpower is either close to retirement, or retiring, and we don’t have young people coming through? It’s going to have a major impact and influence on the ability of the world to actually transition to renewables; whether it’s possible or not.”

Tim also points to the industry’s growing opportunities for women.

“There was once a boys’ club feel, but attitudes and behaviours have changed,” he says. “Nowadays there are a lot more women on every site and in every role. I know I’d like to hire more women, but it’s not easy to find female geotechs.

“I think the industry just has to sell the opportunities for women better.”

It’s great advice for the industry, prompting a reflection in turn on the best advice he’s ever received himself: “Sometimes you’ve just got to take the leap to try new things. You can’t be ultraconservative all the time.

Tim Cartledge - Principal Consultant