Payload
Open-pit payload management: applying the CAT 10/10/20 rule
The balance between tonnage and truck structural life
Maximizing shift payload is the continuous goal of pit supervisors, but chronic overloading destroys truck frames, overheats hoist cylinders, and shreds haulage tires. Conversely, chronic underloading starves production targets and forces redundant truck trips.
The mining industry's recognized standard for payload governance is Caterpillar's 10/10/20 policy: 1. No more than 10% of loads should exceed 110% of rated target payload. 2. No more than 10% of loads should fall below 90% of rated target payload. 3. Zero loads (0%) should ever exceed 120% of target gross machine weight.
Pass matching formulas and bucket fill factor
Payload ($P_{Truck}$) is the sum of metric tons delivered by each excavator pass:
Where $V_{Bucket}$ is nominal bucket capacity ($m^3$), $FF$ is bucket fill factor (typically 95% to 102% in well-blasted rock), and $\rho_{loose}$ is loose material density ($t/m^3$).
The sweet spot for open-pit pass matching is **3 to 5 passes per truck**. Two passes generates excessive suspension shock and tray structural fatigue, while six or more passes creates severe shovel bottlenecks, tying up the excavator for more than 150 seconds per truck load.
Financial impact of under-filling buckets
When an excavator operator averages an 85% fill factor due to poor penetration at the muckpile toe, the machine requires a 5th bucket pass to reach nominal truck payload. That single extra pass adds approximately 26 to 30 seconds of loading time ($t_{PassCycle}$) to every truck load.
Over an active 12-hour shift with 200 truck loads, that extra pass wastes up to 100 minutes of shovel loading capacity—equivalent to losing 15 to 20 full truck loads of production from the same fleet.
Audit steps for ground observers
To maintain payload compliance within the 10/10/20 envelope: - Conduct regular dipper fill audits across rock fragmentation zones. - Calibrate on-board truck payload pressure sensors against static weighbridge tickets weekly. - Coach shovel operators to place a level cushioning pass first, then center subsequent loads over the rear axle pivot to avoid chassis twist.
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