By Caterpillar | Published March 31, 2022
Another consideration is the length of the haul and the percent of time a truck spends loading vs. hauling. If hauls are longer, then switching to a larger truck will mean more material is being carried along that longer distance — and the costs come down. With shorter distances, smaller trucks can compete as the lower-cost option.
Another consideration is the impact on overall pit dimensions. “In a really deep pit application, it may not make sense to go to a larger truck because of how much material you will have to push back in order to get to the width that’s required,” says Richards. The wider the roads, the lower the pit slope or angle. That means there must be more overburden stripped in order to get to the ore.
“There is a concept we call the ultimate pit cutoff,” explains John Ingle, Caterpillar large mining truck performance manager. “Break-even grade equates the cost of mining, milling and refining to the value of the block in terms of the recovered material and the selling price. You have to consider how much extra waste removal is needed to mine the ore.”
Most mines design their maintenance shops and wash bays around specific pieces of equipment, from the width of the bay doors to the height of the overall structure. Any change in equipment, especially when it’s larger, is going to have an impact on that infrastructure.
“Shops are expensive,” Ingle points out. “So once you’ve built one, you want to keep it.” Expanding and reconfiguring the shops for larger equipment requires a major investment. Larger trucks may also require the purchase of new cranes or specialized tools.
Bringing on any new piece of equipment is going to have an impact on employees. There can be significant costs associated with training them to work with new machines.
“You have to keep in mind the people side of the business,” says Richards. “For example, if your operators are used to driving a smaller truck, and your technicians are accustomed to maintaining it, it can be a big change to go to a new size. And it will take time and money to get them up to speed and working productively.”
While it’s true that larger trucks deliver higher productivity and overall lower cost per ton, it also costs more to operate them in terms of fuel usage, maintenance, etc. “If the mine is not optimized to use these trucks to their full efficiency, they can add costs rather than reduce them,” says Ingle.
The shovel is the major portion of a mine’s fleet investment. Mines choose the loading tool to meet mine parameters and production needs — and then trucks are matched accordingly.
Each shovel has a maximum output capacity and can only serve a maximum number of trucks. A larger truck can realize more shovel production with fewer units. As a result, high production costs less.
“But if the loading tool is not increased in size to match a change to larger trucks, the cost per ton for that loading tool will stay the same” Ingle points out. “The cost of the hauler is affected if the large truck must wait to be loaded. You’re paying money for it just to sit there.”
Also consider the impact of mixed fleets on the shovel. Different truck sizes impair the ability to load all the trucks with their optimal payload, especially when they are being loaded by a one-size shovel fleet. This creates problems such as out-of-range loading and improper load distribution in the truck.