The Cost of Overbreak in Underground Mining: Why Design Deviation Matters 

OverbreakEnvironment
Written By Natasja Reicheld

In underground mining, every metre matters. Precision in design and execution is still regarded as a luxury, but we disagree. It is an essential to safety, efficiency, and profitability. Yet across the sector, one recurring challenge undermines this precision: overbreak. Defined as the unplanned excavation beyond the intended profile, overbreak is often dismissed as a by-product of blasting. In reality, it is a costly design deviation that carries far-reaching consequences for both operations and people. 

 

What Is Overbreak? 

Overbreak occurs when blasting removes more rock than the design specifies, enlarging an excavation unnecessarily. Research shows that it is a pervasive issue in drill-and-blast operations, with causes ranging from geological variability to inadequate blast design and execution (Maerz, Ibarra, & Franklin, 1996; Singh, Xavier, & Verma, 2004). 

Importantly, overbreak is not simply a technical nuisance. Each deviation from the design profile compounds across a project, creating a chain of cost, safety, and efficiency impacts (Overbreak prediction in underground tunnels, 2023). 

 

The Financial Cost 

The financial impact of overbreak is both direct and cumulative. Enlarged excavations require: 

  • Additional mucking and hauling of excess rock. 

  • Extra ground support, such as mesh, bolts, and shotcrete. 

  • Longer cycle times, which slow development. 

Studies demonstrate that overbreak volumes can inflate development costs significantly, particularly when reinforcement and scaling requirements escalate (Factors influencing overbreak volumes, 2020; Sjöberg, 1996). These costs don’t stop at development: overbreak shortens the effective life of mine infrastructure and increases long-term maintenance burdens. 

 

Safety and Stability 

Beyond cost, the safety implications are profound. Overbreak alters the intended geometry of excavations, redistributing stress in the surrounding rock mass and creating zones of instability (Hoek & Marinos, 2000). The larger voids expose more surface area to weathering, and in weak ground conditions, this can accelerate deterioration. 

Case studies highlight that uncontrolled overbreak increases fall-of-ground risks, forcing operators to allocate more resources to scaling and re-support (Orica, 2020). For mine workers, this means more exposure to hazardous environments and an elevated potential for incidents. 

 

Efficiency and Productivity 

Overbreak is also an efficiency drain. Excessive excavation adds unnecessary tasks — mucking, reinforcing, re-shaping — which slow production cycles. It also strains downstream systems such as ventilation and haulage, increasing operational inefficiencies (Singh & Xavier, 2012; Overbreak and underbreak in underground openings, 1996). 

In a sector where margins are tight, these inefficiencies ripple outward, delaying schedules and undermining project predictability. 

 

Why Design Deviation Matters 

At its heart, overbreak is a problem of design deviation — the gap between engineered intent and executed reality. Even small, repeated deviations accumulate into systemic inefficiencies and risks. Addressing overbreak is not only about saving money; it is about aligning operations with the discipline of design. 

By tightening the link between design and execution, operators can: 

  • Reduce direct excavation and support costs. 

  • Improve ground stability and worker safety. 

  • Enhance schedule reliability. 

  • Extend the life of mine assets. 

 

Towards a Solution 

Solutions exist at the intersection of technology and discipline. Advances such as 3D laser scanning now enable precise monitoring of excavation profiles in real time, improving feedback loops between design and execution (Cheng, Zhang, & Wu, 2019). Predictive modelling — including hybrid AI methods such as ANFIS-PSO — is increasingly being used to forecast overbreak and optimise blast parameters (Overbreak prediction in underground excavations, 2017). 

But technology alone is not enough. Success relies on a cultural shift: treating design adherence not as an aspirational target but as a non-negotiable standard. As case studies like MMG Golden Grove have shown, operational discipline combined with precision monitoring significantly reduces overbreak and the risks it carries (Orica, 2020). 

 

Conclusion 

Overbreak is not an unavoidable cost of doing business underground. It is a design deviation that can — and must — be managed. Its financial, safety, and efficiency consequences make precision more than a matter of engineering pride; they make it a strategic imperative. 

Every centimetre of rock excavated unnecessarily is a cost, a risk, and a deviation from the future we are capable of building. With the right tools, the right practices, and the right mindset, the industry can reclaim precision — and with it, resilience. 

 

References 

  • Maerz, N. H., Ibarra, J. A., & Franklin, J. A. (1996). Overbreak and underbreak in underground openings Part 1: Measurement using the light sectioning method and digital image processing. Geotechnical & Geological Engineering, 14, 307–323. https://doi.org/10.1007/BF00421946 

  • Singh, S. P., Xavier, P., & Verma, A. K. (2004). Causes, impact and control of overbreak in underground excavations. Tunnelling and Underground Space Technology, 19(1), 1–17. https://doi.org/10.1016/j.tust.2003.07.003 

Natasja Reicheld