Crews Build Highest Geotech Retaining Wall East of the Mississippi

Thu May 03, 2007 - Northeast Edition
Construction Equipment Guide

Trumbull Corp. of Pittsburgh, Pa. has been acting as a subcontractor on a 125-acre (50.6 ha) commercial site development project in Washington County, Pa. since April 2006. The project site is located adjacent to U.S. Route 19 and just north of I-70 in South Strabane Township.

The project, a retail development known as “The Foundry,” involves moving some 2.4 million cu. yds. (1.83 million cu. m) of dirt and stone to establish commercial building and parking sites.

Trumbull Corp. reports to the site’s general contractor, Pepper Construction Inc. of Indiana. Trumbull’s responsibilities include earthmoving, site grading, establishing underground utilities, and constructing reinforced fabric retaining walls. Reportedly, the 95-ft. (23 m) high geotech retaining walls are the highest to be found east of the Mississippi River.

In constructing the reinforced fabric walls, the design called for placing crushed stone to a certain length and depth between each succeeding layer. The site specifications called for a minus 4-in. (10.2 cm) crushed stone base to be used. Various quantities of sandstone, limestone and shale were unearthed beneath top and sub soils in the site’s higher elevations.

Because the contract called for movement of this material, Trumbull Corp. petitioned the general contractor to crush it for use in the wall construction. Since it received approval, Trumbull has crushed approximately 320,000 cu. yds. (244,658 cu. m) of material.

Initially, the site subcontractor received quotes from outside sources to provide managed site crushing services. Trumbull Corp. had previous experience with portable screening activities but had only worked smaller portable crushing jobs.

When they reviewed the cost of hiring a subcontractor, they decided to give it a try, and, according to Trumbull Project Superintendent Charles Hickle they have “made the right decision.”

Hickle said, “We went into this looking at doing 150,000 or 200,000 cubic yards of crushed material, and now we have 300,000.”

Trumbull uses track-mounted crushing plants, fed by as many as three large excavators and discharging in a common line. The crusher product is dozed to a stock area for loading onto articulated haul trucks for transportation to the wall construction areas.

Jaw and impact crushers from four different manufacturers were represented and supplied by three area equipment dealers, but in the end, Trumbull pared down the equipment to two Metso/Nordberg portable track mounted crushers, supplied by Cleveland Brothers through its Construction Aggregate Division.

The earlier crushers were slower and operated only 70 percent of the time, said Trumbull Lead Estimator Rich Doyle. As the Metso crushers became available, Trumbull switched to them exclusively, because they operated 90 percent of the time, and Cleveland Brothers service was efficient and timely.

Both units, powered by Caterpillar diesel engines, are capable of producing site specification products well in excess of 250 tons (227 t) per hour.

“The two machines process the material quite a bit faster,” Doyle said. “When we brought the first Cleveland Brothers machine in, we were processing, loading, hauling, and placing, and basically, the guys on placing had to wait.”

Hickle said there were early lessons to be learned. He indicated that the key to making it work well was to match “right size loading equipment to the differing abilities of the remotely controlled crushing plants.” The other factor was “understanding the maintenance activities required to minimize the downtime experienced for each plant.”

“The crushers are high maintenance, and they take a beating,” Hickle added. “We just had better luck with the crushers we got from Cleveland Brothers as far as downtime. That’s the reason they’re still here. It keeps everything working.”

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