Balancing trade-offs: Optimising loader productivity, rehandle, and delays
As mine planner, you are constantly trying to strike the right balance between efficiency, costs and ultimately get more ore to surface. Our first article in this series, Balancing trade-offs: Using simulation to optimise load & haul underground explores the tipping point between adding trucks and adding loaders in underground load and haul. The analysis looked at total ore hauled and highlighted a key trade-off.
“Getting more ore to surface often meant sacrificing truck efficiency”
In this article, we dive deeper into the simulation study using our advanced simulation software, idoba.sim to explore how loader performance, rehandle, and delays change the equation.
Two configurations – More than just extra loaders
With idoba.sim, our team was able to configure the study within minutes and delve into two distinct operational setups to examine how they influence both loader performance and operational efficiency.
Phase one - Single level operation
One production level
One stope
One stockpile
One loader
Phase two - Dual level operation
Two production levels
Two stopes producing simultaneously
Two stockpiles (one per level)
Two loaders working independently
In the dual-level case, the extra loader came with an entire second production stream — a structural change to mine execution strategy, not just an equipment upgrade.
Primary tonnes – The real pace setter
Primary tonnes are ore moved from the stope draw point — the first time it’s touched. Clearing the stope faster shortens the production cycle, accelerating time to backfilling, and moving to the next ore source sooner.
Single-level: Starts high (~1,190 t/loader) with one truck, peaks around ~1,840t at three trucks, then plateaus.
Dual-Level: Starts lower (~950 t/loader) with one truck, but climbs steadily with truck numbers, reaching ~1,730t at seven trucks without the mid-scenario stall.
Initial insights from idoba.sim
When primary tonnage plateaus, the truck fleet is over-supplied relative to loader capacity.
The loader is working at (or near) 100% utilisation, so it cannot increase its output, regardless of how many trucks are added. This situation is often referred to as being loader-limited (or loading capacity constrained). This is most prevalent in a single-level scenario.
Adding a second production front, and additional loader, distributing the truck fleet brings the system in balance.
Rehandle – Useful but double handling
Rehandle is the processes of moving ore from a stockpile to truck. Stockpiles help in low-truck situations by letting the loader clear the stope faster, but every tonne rehandled adds time and costs.
Single-Level: Rises to ~880t/loader at five trucks, then drops when the loader spends all its time on primary work.
Dual-Level: Rises more gradually, peaking at ~600t/loader at seven trucks, with capacity for both stockpile drawdown and primary loading.
Insight: Dual-level setups provide flexibility for rehandle without impacting primary output.
Rehandle insights from idoba.sim
Dual-level setups can maintain flexibility for rehandle without sacrificing primary output.
Loader wait-times – A hidden waste
Loader wait times (minutes per shift without a truck to load) reveals underutilisation.
Single-Level: Drops rapidly with more trucks — near zero by three trucks.
Dual-Level: Starts high (>300 min) with low truck counts, falling steadily as trucks are added, but still some idle time even at seven trucks.
Simulation insights from idoba.sim
In dual-level scenarios, balancing truck allocation is critical. In low truck scenarios, stockpiles are filled within the shift, driving increasing loader delays as loaders idle waiting on trucks due to an emergent bottleneck on the level.
Figure 1 Shows the primary and rehandle tonnes per loader (stacked bars) in a 1 stope/level and 2 stope/level scenario with associated loader delays waiting on trucks.
Scaling by layout, not just fleet size
By using an advanced simulation software like idoba.sim, we’ve rapidly evaluated multiple scenarios side-by-side to uncover the results that adding capacity to the same bottleneck has limits.
Using that adding capacity to the same bottleneck has limits. A bigger step-change comes from duplicating the production system — more levels, more stopes, more stockpiles, and more loaders.
The dual-level scenario sustained higher primary tonnes across the full truck range, smoothed rehandle patterns, and created headroom for growth — all while revealing where extra trucks or process changes could fill utilisation gaps.
By linking to the findings, in Balancing trade-offs: Optimising load & haul underground, you can see the full optimisation challenge: truck haul efficiency (TKM), primary tonnes, and ore to surface are all important, and the “best” solution depends on how much each matters for the mine’s current, and sometimes competing, objectives.
Optimising loader productivity with simulation software
Using a cutting-edge simulation software tool like idoba.sim, offers mining engineers several benefits including;
Easy to use - Designed for engineers, idoba.sim is easy to use and delivers high-impact insights without the need for deep simulation expertise.
Fast scenario analysis – With idoba.sim users can quickly evaluate scenarios side-by-side to identify the potential impacts of new trade-offs to optimise mine layout and resource allocation.
Reporting – At a glance monitor key performance metrics such as ore tonnes, truck tonnes, primary loader tonnes, TKM’s, and equipment delays in comprehensive reports, and charts.
Ready to unlock more from your underground mine operations?
If you are ready to see first-hand how idoba.sim can provide you with actionable insights, that can significantly reduce costs and improve performance underground, then request a demonstration.
David Andrews, Product Manager 20+ years experience
A geology and engineering professional with over 20 years of mining experience, integrating the technical disciplines at underground mine sites to ensure enterprise risk mitigation and enterprise value optimisation are completed at the design stage. As Product Manager for idoba.sim and an avid user of the software, Dave is passionate about strategic thinking, business transformation and finding simplicity on the other side of what can be extremely complex, vertically integrated value chains in the mining industry.