Larger than the Pentagon - Telebelt TB 105 Helps Contractor Backfill Nearly 5,000 Tons of Rock a Day July 1999

Equipment turns estimated month-long project into three-day job

The task wasn't complicated – backfill an excavation that contained a utility tunnel with two different types of aggregate. The problem was time, manpower and an enormous amount of material.

This wasn't a typical utility tunnel. And it wasn't connected to a typical office building. It was Texas-sized.

The backfill project was for a new six-story, million-square-foot addition to the USAA headquarters in San Antonio. When the addition is completed, it will give the company a total of more than 4-million-square-feet of office space, making it larger than the Pentagon. According to the insurance and finance company, USAA has outgrown its current facility – which holds more than 12,000 employees.

So when USAA built a utility tunnel for the addition, it was big. The finished tunnel contains 250 tons of rebar and 2,500 cubic yards of concrete. When the addition is completed, the 20x30, 330-foot-long tunnel will carry the building's water, electric, telephone lines and more. Large enough to drive semi-trucks through, the tunnel will also provide service access for the six-story office addition that will rest on top.

The problem with the recently completed backfill job was that the contractor was falling behind schedule using a bucket on a crane. That's why Olmos Construction called Concrete Pumps of Texas to lend a hand with its Putzmeister TB 105, a telescopic conveyor the company purchased just a few months earlier.

"In just three 10- to 11-hour days, we moved 15,000 tons of backfill. That's about 5,000 tons a day," said Mike Schultz, sales manager for Concrete Pumps of Texas. "We only stopped because the crews that were waterproofing the concrete walls couldn't keep up." With a maximum output of 360 cubic yards an hour, the Telebelt® TB 105 outpaced any other piece of machine that could have been used. "It would have taken a crane forever," added Tony Tye, owner of Concrete Pumps.

Using a pair of wheel loaders and the Putzmeister conveyor, the company placed 17 feet of 1 1/2-inch washed limestone over 3 feet of 3/8-inch washed river rock on both sides of the tunnel.

At the surface, the backfilled trenches were 30 feet wide, and they tapered down to 3 feet wide at the base of the structure. The engineers also used French drains to relieve water pressure from the sides of the tunnel.

Tye also said it was a very busy job site because machines could only access the excavation from one side. "The Telebelt's 105-foot reach was ideal for this job," explained Tye. "We only had to move the truck a couple of times. It would have been a fiasco without it."

"What we did in three days would have taken the crane and skid steer about a month to do," said Schultz. This was by far the largest material-placing job Concrete Pumps of Texas had tackled with the conveyor –and everyone was very pleased with the results. He also explained that because of the speed of the TB 105, it took fewer people less time to do the job. "We saved the customer a lot of money and time because we had the right equipment for the job," he said.

Construction of the USAA addition began in November 1998, and the company anticipates completion in the summer of 2001.