Fleet Saturation Simulator

Simulation method

This simulator runs a Monte Carlo simulation — hundreds of randomised iterations per data point — to model how trucks arrive at each digger under realistic conditions. Truck cycle times are drawn from a normal distribution controlled by the variance slider, then disruption events are layered on top. The result is a probabilistic picture of fleet behaviour, not a single deterministic calculation.

Because the simulation uses random sampling, changing any input re-runs the Monte Carlo. This can produce subtle differences in numbers between runs even with identical settings — that is normal behaviour, not an error. The more iterations, the more stable the results, but small fluctuations are inherent to the method and reflect the real-world variability being modelled.

What the saturation curves mean

Theoretical (grey dashed) is the perfect world. Every truck runs the exact same cycle time, arrives perfectly spaced, and nothing ever goes wrong. Production scales linearly with truck count until the digger is fully saturated.

System (blue) is the fleet running with no interruptions — no digger moves, no refuelling stops, no crib breaks — just the natural variability of truck cycle times. Road conditions, operator differences, and traffic mean trucks don't run identical cycles. Some arrive back-to-back (causing queue), others leave gaps (causing hang time). This curve shows the cost of variance alone.

Isolated (orange) is trucks running locked in their assigned cycle with no dispatch intervention. Each truck runs its loop — load, haul, dump, return — regardless of what is happening at other diggers. Disruptions hit and nobody reallocates. This is what production looks like without a dispatcher or FMS making cross-allocation decisions.

Fleet Dispatch (green dashed) is the best the dispatcher can achieve by cross-allocating trucks between diggers during disruptions. When one digger is down, trucks go somewhere useful. This only works when disruptions are uneven across diggers — if every digger goes down at once, there is nowhere to send the trucks.

Truck queue and digger hang time

Truck Queue is the average time each truck waits at the digger before being loaded. It increases when the fleet is oversaturated (too many trucks for the digger's capacity) or when variance bunches trucks together. High queue time means trucks are spending time idling at the face instead of hauling.

Digger Hang Time is the average time the digger sits idle waiting for the next truck to arrive. It increases when the fleet is undersaturated or when disruptions pull trucks out of sequence. High hang time means the most expensive asset on the bench — the digger — is not digging.

Queue and hang are two sides of the same coin. A well-matched fleet minimises both. The ideal operating point sits just below 100% saturation: enough trucks to keep hang time low without creating excessive queues.

Dispatch priority

Each digger can be assigned a dispatch priority (Balanced, Priority 1, 2, or 3). When priorities are set, the dispatch algorithm redistributes recovery effort — a Priority 1 digger receives a larger share of the cross-allocation benefit during disruptions, at the expense of lower-priority diggers. This models how real-world dispatch systems favour high-value faces (high grade, critical path, or production targets) when allocating trucks from a shared fleet.

Priority also affects queue and hang time. A higher-priority digger sees slightly more truck traffic (dispatch sends trucks there first), increasing its queue time but reducing hang time. Lower-priority diggers see the opposite effect.

When all diggers are set to Balanced, priorities have no effect and the simulator behaves as an equal-weighted fleet.

Fleet saturation chart

The fleet saturation chart shows combined production across all enabled diggers as total fleet truck count increases. Trucks are distributed proportionally to each digger's requirement. This chart reveals the fleet-wide saturation knee — the point where adding more trucks yields diminishing returns across the whole operation, not just a single digger.

What the controls model

Natural Variance (CV%) controls how much truck cycle times spread around the average. At 0%, every truck runs the same cycle. At 20% (typical for an open-pit operation), a 30-minute cycle might range from 24 to 36 minutes. Higher variance means more bunching and more hang time, even with zero disruptions.

Digger Disruption is time the digger is simply not available. Short moves, face cleanups, waiting for a dozer pushup, grade control holds, cable moves. 4–5 minutes per hour is common. When the digger stops, every truck assigned to it queues or gets cross-allocated.

Event Delays is how often individual trucks get hit by delays. Refuelling, pre-starts, tyre checks, crib breaks, changeovers, slow traffic. At 30%, roughly one in three truck cycles cops a delay. These don't stop the digger, but the late truck throws out the spacing for everyone behind it.

Event Duration is how long each delay event costs. The impact compounds because a truck that is late in one cycle is still out of position for the next. A 5-minute refuelling stop doesn't just cost 5 minutes of production.

The planning/supervision gap

Most sites measure queue time and hang time to judge dispatcher performance. But those numbers carry two jobs: they measure dispatch effectiveness AND they absorb supervision failures. A dispatcher cannot fix a refuelling bay that mine planning put in the wrong place, a face cleanup that supervision hasn't scheduled, or crib breaks that all hit at the same time.

The gap between the system curve (blue) and the dispatch curve (green) is the planning/supervision gap. That is production loss that no amount of truck allocation can recover. It only closes when the events themselves are addressed: better infrastructure placement (planning), proactive scheduling, and operational discipline (supervision).

If you are measuring your dispatcher against the theoretical line, you are holding them accountable for losses they cannot control.