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Efficiency drives an earthmover's decision-making process. "The basic idea of successful mass excavation is to work as efficiently as possible," says Tim Doucette, marketing manager, Liebherr Construction Equipment. "The higher the efficiency, the higher the production and profitability. Machinery standing idle (i.e., excavators waiting for trucks), inefficient cycle times or trucks waiting to be loaded reduces production and profitability."

Size excavators to the task

Mining operations place a premium on sizing excavators to maximize production with each truck load. "In mining, three passes is optimal," says Mike Stec, hauler/loader sales engineer, Volvo Construction Equipment North America. "Construction markets may not be as critical, dissecting every single penny. Typically, four to six passes or under 90-second loading is acceptable."

The goal is to maximize the total cycle time. "The fewer passes that are made result in shorter cycle times, which in turn will increase your production," says Brad Van De Veer, field coordinator/senior application consultant, Caterpillar. "If you six pass, you increase cycle times and reduce production. The quicker you can get that truck loaded and on the road, the better — provided you have enough trucks.

"If you're limited on trucks and the excavator is waiting on trucks anyway, you can get away with six passes," says Van De Veer. "It also depends on the haul distance."

There are major downfalls to loading in too few or too many passes. "If loading is under four passes, you have an oversized bucket in proportion to the truck it is loading," says Carl Heggen, product manager, hydraulic excavators, Komatsu America Corp. "Dumping a large amount of material at one time can add more wear and tear to the truck. Under sizing the excavator (in excess of six passes per truck) can result in long-term loss of productivity due to increased total cycle time." This includes the time to load the truck, travel to the dump site, dump the load and return to the loading site.