Excavation Haul Cycle Optimizer

Method

How many trucks can one excavator keep busy?

This model has one loading station and identical trucks on a repeating cycle. Start with usable truck body volume V. If a payload limit is enabled, divide allowable material payload M by loose density ρ. Effective loose load q is the smaller of V and M/ρ.

Let P be the excavator’s productive loading rate in loose volume per hour, and e the spotting/exchange time in minutes. Loading time is 60q/P. Station service time S includes loading plus exchange; it is the shortest interval at which this station can serve consecutive trucks.

1. Effective truck load q = min(body volume, payload ÷ loose density), or body volume when payload checking is off
2. Loading time = 60 × q ÷ P
3. Loading-station time S = loading time + exchange
4. Unqueued truck cycle C = S + loaded travel + unloading/destination delay + empty return
5. Balance fleet = round C ÷ S up to the next whole truck

The balance fleet is the smallest whole fleet that avoids truck-starved loading in this idealized steady state. It does not establish the cheapest fleet or account for a separate unloading bottleneck.

Production, excavator waiting, and truck utilization

For N trucks, actual cycle time is the larger of C and N × S. When N × S exceeds C, the difference is the average loader queue per truck cycle in this deterministic model.

1. Loading-station capacity = 60 × q ÷ S
2. Fleet production Q = min(loading-station capacity, 60 × N × q ÷ C)
3. Excavator waiting for trucks = 60 × (1 − Q ÷ loading-station capacity) minutes per hour
4. Truck queue per cycle = max(0, N × S − C)
5. Truck cycle utilization = C ÷ max(C, N × S) × 100%
6. Equivalent steady-state work hours = total loose volume ÷ Q

Truck cycle utilization counts the entered loading, exchange, travel, and destination times; it excludes waiting added at the loader. It is not a payload fill percentage. Excavator waiting here excludes exchange time, breaks, and mechanical downtime.

Work hours are a production comparison, not a finite-job delivery schedule. Startup dispatch, last partial loads, and final delivery affect elapsed completion time. A small job with fewer trips than the balance fleet does not need that many trucks merely to match this steady-state balance point.

Worked example

Five, six, or seven trucks?

Suppose 1000 m³ of loose material must be hauled. Truck body capacity is 12 m³, allowable material payload is 16 metric tonnes, and loose density is 1600 kg/m³. Payload limits each load to 10 m³, so the job needs 100 loaded trips.

At 120 loose m³ per productive loading hour, each load takes 5 minutes. Add 1 minute of exchange time, 15 minutes of loaded travel, 3 minutes of unloading/destination delay, and 12 minutes of return travel. Station time is 6 minutes and the unqueued cycle is 36 minutes. The balance fleet is 36 ÷ 6 = 6 trucks.

• 5 trucks: 83.333 m³/h; excavator waits 10 min/h; no loader queue; equivalent work time 12 h.
• 6 trucks: 100 m³/h; no truck-starved loading or loader queue; equivalent work time 10 h.
• 7 trucks: still 100 m³/h, but each truck queues 6 minutes per cycle; truck cycle utilization falls to 85.714%.

These are illustrative values, not equipment specifications. A real fleet decision also needs costs, site constraints, and observed variability.

Keep all material quantities on a loose basis

Truck body capacity is loose volume, so the total quantity and loading rate must use the same material state. Use the Soil Swell and Shrink Calculator to convert bank excavation quantities before entering them here.

The Trench Bedding, Backfill and Spoil Calculator reports remaining spoil as loose volume. That quantity can be entered as total loose material here without applying swell a second time.

Assumptions and limitations

• One excavator/loading station and identical trucks with constant capacity and cycle times.
• The loading rate represents productive loading only. Exchange is added separately; avoid counting it twice.
• Destination delay is an entered fixed time. No shared dump queue or additional bottleneck is simulated.
• Payload and density checking is optional; disabling it yields a volume-only calculation.
• No truck costs, fuel costs, stochastic traffic, shifts, breaks, or dispatch optimization.
• Fleet sizes up to 10,000 are supported; extreme inputs that exceed numeric limits are rejected.

Excavation haul cycle FAQ