Recently, our team completed a technical due diligence review on a proposed underground longwall extension designed to sustain metallurgical coal production from an established open pit operation. On paper, the project looked robust. The geology was well understood, the economics were competitive, and the development pathway appeared clear. But when we looked deeper, one issue stood out to the MEC technical team.
The complexity of dual-seam mining
The operation planned to extract two seams in sequence. This approach is becoming more common as companies seek to maximise resource recovery and extend mine life. However, dual-seam mining introduces geotechnical challenges that are often underestimated early in project development.
The interaction between seams, the influence of previous extraction on stress redistribution, and the variability of in-situ conditions can significantly change ground behaviour. Pillar stability, roof support requirements, subsidence, and long-term operational risk all become more complex.
In this case, the geotechnical design had been developed using established methodologies and had undergone peer review. But benchmarking against comparable operations revealed that the local conditions were not directly analogous to those used as reference points. Differences in stress regime, structural complexity, and depth meant that the assumed pillar sizing and support standards could either be overly conservative or, in some areas, insufficient. Both scenarios carry real consequences.
Overly conservative designs can reduce recovery and erode project value. Underestimating risk can result in operational delays, higher support costs, or safety concerns once production begins.
Quantifying the impact
Rather than treating this as a theoretical issue, we translated the geotechnical uncertainty into project value. Our review identified that optimisation of pillar sizing and seam interaction had the potential to increase coal recovery and deliver an uplift of approximately AU$30–35 million in project value. At the same time, technical uncertainty associated with dual-seam mining represented a potential downside of around AU$20 million if the upper seam could not be safely or economically extracted.
This clarity shifted the conversation from “is the design acceptable?” to “what is the value of getting this right?”
It also reinforced that geotechnical design is not just a safety and compliance function. It is a core driver of long-term value.
Moving beyond compliance
Rather than accepting the design at face value, we applied a structured due diligence approach. This included independent technical review, scenario testing, and alignment of geotechnical assumptions with the economic model.
A multidisciplinary team of geotechnical, mining, ventilation, and underground operations specialists worked together to challenge key assumptions. The focus was not only on whether the design met accepted standards, but whether it was robust under real operating conditions.
This process identified opportunities to optimise pillar sizing, improve recovery, and better align support design with expected ground conditions. It also highlighted areas where further drilling and modelling were required to reduce uncertainty ahead of final investment.
Most importantly, it translated geotechnical risk into quantified impacts on project value, schedule, and operational performance.
Most importantly, it translated geotechnical risk into quantified impacts on project value, schedule, and operational performance.
Why this matters now
Across the Bowen Basin and other major coal regions, the industry is moving into deeper, more complex deposits. Dual-seam mining, greater structural variability, and increased scrutiny on safety and ESG performance mean that traditional design approaches are no longer enough.
Projects that succeed will be those that integrate geotechnical thinking early, challenge assumptions, and treat ground behaviour as a strategic driver of value rather than a compliance exercise.
This is where experience matters. Ben Smedley, Paul Buddery, Neil Alston, our underground coal team, have worked across some of the most complex underground coal operations in Australia and globally. From concept through to operations, we focus on practical, experience-led solutions that improve safety, recovery, and long-term performance.
If you are assessing a new underground project, considering a seam extension, or reviewing your current design assumptions, it’s worth asking a simple question: Are your geotechnical assumptions creating risk, or unlocking value?