Question 2 of 13: Shovel Production, Over-Trucking, and Spotting

Question 1.2: Shovel Production, Over-Trucking, and Spotting (6 marks, compulsory)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

1.2.1 – Shovel production vs. trucks assigned. With too few trucks the shovel is starved – it sits idle between arrivals – so production rises almost linearly as trucks are added. The curve then bends over and FLATTENS once the truck count reaches the theoretically matched fleet size (match factor $=1.0$, Question 3.1): beyond that point every additional truck simply queues, so shovel production is already at its ceiling (the shovel's own digging rate) and cannot rise further no matter how many more trucks are assigned.

1.2.2 – Doubling the theoretical fleet. The shovel is already saturated at the theoretical (matched) truck count, so doubling the fleet produces essentially zero additional production – the surplus trucks simply queue at the shovel, truck utilization collapses (each truck spends roughly half its cycle waiting instead of hauling), fuel/tyre/operator cost per tonne moved rises sharply, and congestion on the loading bench and haul road increases the accident risk, all for no tonnage gain. It is a pure loss of capital efficiency; the surplus trucks would be far better deployed on an under-trucked shovel elsewhere in the pit.

1.2.3 – Spotting, double back-up, drive-by. Spotting is manoeuvring an empty truck into the single loading position beside the shovel, requiring the shovel to pause digging while the truck backs in and positions – the simplest layout but the one with the most shovel-idle time between trucks. Double back-up provides two spotting positions, one on each side of the shovel, so a second truck can back in and be ready the instant the first pulls away loaded – this halves the shovel's exposure to spotting delay at the cost of a wider working pad and a blast pattern (typically a herringbone or double-row layout) that leaves enough muck-pile width for two truck positions side by side. Drive-by (drive-through) loading positions trucks so the next truck can pull straight into the loading position without reversing at all – the fastest of the three, but it requires a blast layout and muck-pile shape (a long, narrow single-row shot with a clear through-lane) that permits one-way, drive-through traffic; it is not achievable with a compact, boxy muck pile from a tight-pattern blast.