Walk through any opencast coal or ore mine and the machine that stands out is the dump truck. Shovels and draglines get the attention, but it is the trucks that decide how much material actually reaches the dump yard or the crusher every shift. If the trucks are badly matched or badly planned, even the best loading machine ends up waiting.
In this post we will go through the basics of dump trucks in mining: what their capacity really means, what makes up the cycle time and how to work out production and the number of trucks needed. At the end there is a complete worked example, which is exactly the kind of numerical you can expect in mining engineering exams like GATE.
What Is a Mining Dump Truck?
A mining dump truck is a heavy-duty haulage vehicle that carries overburden, coal, ore or waste from the loading point to the dumping point. The most common type in large opencast mines is the rigid-frame rear dump truck. Smaller mines and some quarries also use articulated dump trucks, which handle softer and steeper ground better.
In a typical shovel-truck operation, a shovel or excavator loads the truck in a few passes, the truck hauls the load along the haul road, dumps it and returns empty for the next load. The whole job is a loop, which is why we measure it as a cycle.
Dump Truck Capacity
When people say "a 60-tonne truck", they usually mean its rated payload, the weight of material it is designed to carry safely. Capacity can be described in a few different ways, and it helps to keep them separate:
- Payload (tonnes): the weight of material the truck can carry. This is the figure used most often for planning.
- Struck capacity (m³): the volume of the body when it is filled level with the sides.
- Heaped capacity (m³): the volume including the heap above the body. Manufacturers usually quote it at a standard heap slope (for example 2:1).
- Gross vehicle weight (GVW): the weight of the empty truck plus its payload. Overloading beyond the rated limit damages the truck and is unsafe.
Two practical points matter a lot in real mines:
- Fill factor: trucks are rarely filled to exactly 100 percent of their rated volume. If a truck is loaded to 90 percent, the fill factor is 0.9.
- Swell: material that is loosened by blasting or digging takes up more volume than it did in place. Production is often reported in bank cubic metres (BCM), while the truck carries loose cubic metres (LCM).
Passes needed to fill a truck = Truck payload ÷ Bucket payload. A good match is often around 4 to 6 passes. Fewer passes can mean the truck is too small for the shovel and gets overfilled or spilled, while many more passes make loading slow.
Cycle Time and Its Components
Truck cycle time is the total time a truck takes to complete one full loop. It is made up of five parts:
- Spot time at the loader: positioning the truck beside the shovel.
- Loading time: time for the shovel to fill the truck (number of passes × shovel cycle time).
- Haul (loaded travel) time: travelling to the dump point.
- Dump time: manoeuvring at the dump and tipping the load.
- Return (empty travel) time: going back to the loading point.
Cycle time = Spot + Loading + Haul + Dump + Return
Travel time depends on distance and speed:
Travel time (min) = Distance (km) ÷ Speed (km/h) × 60
Loaded trucks go slower, especially on uphill haul roads, so the haul time is normally longer than the return time over the same distance.
Production Calculation
Once the cycle time is known, the rest follows in a few simple steps:
- Trips per hour = Working minutes per hour ÷ Cycle time (min)
- Production per truck per hour = Trips per hour × Payload per trip
- Production per shift = Production per hour × Working hours in the shift
The "working minutes per hour" figure accounts for real-life delays such as waiting, shift change, refuelling and breaks. A common way to write this is an efficiency factor. For example, a 50-minute working hour means an efficiency of 50 ÷ 60 = 0.83.
If you need the answer in BCM, convert as follows:
Load per trip (BCM) = Truck volume (LCM) × Fill factor ÷ (1 + Swell)
For instance, a truck with a heaped capacity of 35 m³, filled to a factor of 0.9, carries 31.5 LCM. With 30 percent swell, that equals 31.5 ÷ 1.3 = about 24.2 BCM per trip.
Worked Example
Find (a) the cycle time, (b) production per truck per hour and per shift and (c) the number of trucks needed to keep the shovel fully busy.
Step 1: Passes and loading time
Passes = 60 ÷ 12 = 5 passes
Loading time = 5 × 42 s = 210 s = 3.5 min
Step 2: Travel times
Haul time = 2.5 ÷ 20 × 60 = 7.5 min
Return time = 2.5 ÷ 30 × 60 = 5.0 min
Step 3: Cycle time
| Component | Time (min) |
|---|---|
| Spot at shovel | 0.5 |
| Loading | 3.5 |
| Haul (loaded) | 7.5 |
| Dump | 1.0 |
| Return (empty) | 5.0 |
| Total cycle time | 17.5 |
Step 4: Trips and production per truck
Trips per hour = 50 ÷ 17.5 = 2.86 trips/hour
Production per hour = 2.86 × 60 = about 171 tonnes/hour
Production per 8-hour shift = 171.4 × 8 = about 1,371 tonnes per truck
Step 5: Number of trucks needed
Number of trucks = Truck cycle time ÷ Loading time = 17.5 ÷ 3.5 = 5 trucks
You can cross-check this from the shovel side. The shovel can load 12 t × (3000 s ÷ 42 s) = about 857 t/hour in a 50-minute hour. One truck carries 171.4 t/hour, so 857 ÷ 171.4 = 5 trucks.
Answer: Cycle time = 17.5 min; production = about 171 t/h per truck (about 1,371 t per shift); trucks required = 5.
How Many Trucks Do You Need? The Match Factor
In real life, we check whether the number of trucks suits the shovel using the match factor (MF):
MF = (Number of trucks × Loading time per truck) ÷ (Number of shovels × Truck cycle time)
- MF = 1: perfect match, in theory neither the shovel nor the trucks wait.
- MF < 1: too few trucks, so the shovel waits for trucks.
- MF > 1: too many trucks, so trucks queue at the shovel.
In our example, 5 trucks give MF = (5 × 3.5) ÷ (1 × 17.5) = 1.0. With 4 trucks, MF = 0.8 and the shovel would sit idle part of the time. With 6 trucks, MF = 1.2 and trucks would be waiting in a queue. Real mines often keep MF slightly above 1 so that the shovel, which is the more expensive machine, is never starved.
What Affects Truck Productivity?
- Haul road condition and gradient: steep or rough roads slow trucks and increase fuel use and tyre wear.
- Haul distance: travel time grows directly with distance.
- Loading efficiency: shovel cycle time, bucket size and operator skill all change loading time.
- Queuing and bunching: trucks arriving together at the shovel or crusher waste time.
- Fill factor: underloaded trucks carry less per trip, while overloaded trucks damage the machine and are unsafe.
- Weather and visibility: rain, dust and fog reduce safe speeds.
- Maintenance and availability: a truck in the workshop produces nothing.
Frequently Asked Questions
What is the difference between struck and heaped capacity?
Struck capacity is the body volume filled level with its sides, while heaped capacity includes the heap above the body at a stated slope, such as 2:1.
How is dump truck cycle time calculated?
Add spot time, loading time, loaded haul time, dump time and empty return time. Travel time is distance divided by speed.
How do you calculate truck production per hour?
Divide the working minutes in an hour by the cycle time to get trips per hour, then multiply by the payload per trip.
What is a match factor in shovel-truck operations?
It is the ratio that shows whether the number of trucks suits the shovel. A value of 1 is a perfect match, below 1 means the shovel waits and above 1 means trucks wait.
Why is efficiency factor used?
Because trucks do not work for a full 60 minutes in every hour. Delays, breaks, waiting and shift changes reduce the real working time.
Final Words
Dump truck planning looks complicated at first, but it really comes down to three things: how much a truck carries, how long one loop takes and how many loops it can complete in an hour. Once you have those, production, shift output and fleet size follow naturally. Practise a couple of numericals with different distances and speeds and the method will stay with you.
For more notes and practice sets, visit the Indian Minerology homepage or test yourself with our Mining Safety MCQ Series.
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