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Tough quarry

Oct. 15, 2010

The hard rock that Gorham Sand & Gravel must break up gets so hot from hydraulic hammering that any grease dripping onto it from the attachment starts on fire. These extreme underground construction conditions might leave you wondering what gets more punishment—the rock or the hammer?

By: Volvo Construction Company

When Gorham Sand & Gravel’s 12,000-lb hydraulic hammer burned out while working in the company’s quarry operations, company co-owner Jim Shaw knew he couldn’t afford downtime. So he turned to Chadwick-BaRoss Inc., the Portland, Maine, Volvo Construction Equipment dealer, which had just put 12 new Volvo hammers into its rental fleet.

At first, Shaw rented the Volvo HB3800 hammer, which delivers force of 12,000 lb/ft. It didn’t take long to decide to buy it.

“It has been night and day, the [new] hammer vs. the other hammer,” Shaw said. “It’s a lot faster. It hits a lot harder. It doesn’t take nearly as long to do the same job as the other hammer did. We really like it.”

The first job the hammer went on was installation of a drainage system for a new 1,000-space parking garage at the Portland airport. Gorham Sand & Gravel needed to lay 18-in. storm drains 28 ft below grade. After excavating 9 ft of overburden, Shaw’s crews had to dig out between 18 and 21 ft of solid Maine granite along a 300-ft-long trench.

“It’s a hard, blue-gray rock,” Shaw said. “It’s almost like glass. It breaks up like glass. It’s the hardest stuff we’ve ever worked with.”

Because the rock was so dense, simply using a hammer would not fracture it. Crews first had to drill 6-ft-deep pilot holes in the granite to create a “Swiss cheese” pattern. Then the Volvo HB3800 was brought in to break up the ledge. Every 2 ft or so, an excavator would dig out and remove the broken rock, and then the process would start over. The process was time-consuming and extremely hard on the equipment.

“We were hammering between eight and 10 hours a day out of a 12-hour work day, seven days a week,” Shaw said.

Shaw said because the hammer gets nearly constant use, durability, speed and performance are key issues. “If the hammer’s not working, the crew’s not working,” he said. “A lot of times, we’ll keep the hammer working all night so when the crew gets there in the morning, they have something to do.”

The Volvo HB3800’s low-noise design also is a big advantage, especially on urban jobsites where equipment noise levels are strictly regulated and monitored.

“It’s a lot quieter than other hammers we’ve used,” Shaw said. “That’s a big issue. If they come out with the decibel meter and you’re over the levels, you can’t use the hammer. But the hammer is compliant with even the strict Portland noise standard.”