With cracks as sharp as the frozen Arctic air, a 1,357-ft steel communications tower in Port Clarence, Alaska, tumbled to the ground on April 28, the first step in the U.S. Coast Guard�s decommissioning of its network of LORAN radio navigation facilities across the country.
The 400-ton, 45-segment triangular steel tower is the largest man-made structure to be felled by explosives, according to Controlled Demolition Inc. (CDI), Phoenix, Md., which performed the operation as a subcontractor to Jacobs Field Services North America.
For nearly 50 years, the remote installation located 75 miles north of Nome was one of 24 land-based LORAN stations throughout the U.S. that broadcast low-frequency signals to help ships and aircraft determine speed and position. The increasing precision and reliability of GPS technology rendered LORAN obsolete. Its powerful transmitters were silenced in February.
The Coast Guard now has until Sept. 30 to determine the future of its LORAN installations, which include operational and support buildings, transmitters, towers, and, in some cases, full water and sewer systems.
While more remote facilities such as Port Clarence will be demolished, others may be repurposed within the Coast Guard and the U.S. Dept. of Homeland Security, or be transferred to other federal and state agencies.
“We’ve received approval to sell about one-third of the sites,” says Commander David Savatgy, commanding officer of the Coast Guard’s civil engineering unit in Juneau, Alaska. He adds that Coast Guard-owned properties such as the oceanfront LORAN station on Nantucket Island, Mass., may prove attractive to both public- and private-sector bidders.
“Any funds from property sales will be put back into the decommissioning program,” Savatgy adds. “In the case of facilities on leased land, we’re talking with landowners to see what they want to do.” But because it could be several years before some properties are transferred or demolished, the facilities will be hardened to BRAC Level III status, with no future reuse expected. “We’ll also assess the Coast Guard’s environmental liability at the sites,” he says.
Because of the Port Clarence tower’s deteriorated condition—three of the 21 oil-filled cylinders in its ceramic base insulator were cracked and empty—a controlled demolition was more cost-effective than manual dismantlement, which would have taken several weeks. And with the ground still frozen, Savatgy says it made sense to take down the tower before thawing turned the ground into a quagmire. “Otherwise, some of the fallen pieces might bury themselves up to 15 ft in the muck, complicating the clean-up work,” he adds.
CDI’s staged sequential detonation used 32 linear-shaped charge explosives, each weighing less than 10 lb, to differentially release the 1/2- and 3/4-inch-thick structural guy and top loading element (TLE) radial link plates, located just above the anchorages at grade. Forged bridge sockets were also charged at the radial locations.
The tower was felled in a folded method with 75% of its height released in a southerly direction, and the top restrained by the upper radial guys on the north side.
“Folding the top portion of the tower back on itself reduced the debris field without causing damage to a transmitter building containing friable asbestos located just 14 ft away,” says CDI President Mark Loizeaux.
Although the tower demolition was spectacular to witness, Savatgy admits that he and others feel a sense of loss at its demise. The Port Clarence station, with eight reinforced concrete buildings on foundations set in permafrost, was built in 11 months for $2.7 million. “It means the end of a mission that the Coast Guard has been doing for a long time,” he says.