If all goes well, more than five years of planning and three months of physical preparation to implode the Greenfield Bridge will culminate in about 10 seconds of action Monday morning.
That’s about how long it is expected to take for explosives planted by Dykon Explosives Demolition Corp. and Kesco Inc. to crumble the 94-year-old bridge onto a dirt pillow created on the Parkway East underneath it. The goal is to drop the bridge at 9 a.m. Monday without causing any damage to the interstate highway.
The work begins in earnest at 6 a.m. Sunday, when a stretch of Parkway East closes for five days. The closure allows for the implosion of the bridge and the removal of remnants, fencing and dirt hauled in to cushion the roadway. The project’s general contractor, Mosites Heavy Construction, has until 6 a.m. Friday to reopen the highway.
Mosites has a $17.5 million contract with Pittsburgh to remove and replace the existing bridge, which connects Schenley Park with the Greenfield neighborhood. The bridge closed in October. A new structure should be ready in about two years.
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The Parkway East detours will be similar to the two recent weekend closures to prepare for the demolition. Drivers leaving Downtown and headed eastbound toward Monroeville will use exit 72A at Oakland, re-entering the highway at 78A in Wilkinsburg. Drivers coming into the city, traveling westbound from Monroeville, will exit at 78B, go through Wilkinsburg and the East End, and re-enter the highway after passing through Oakland. Local traffic can stay on the inbound parkway to Swissvale, exit 77.
One difference from the previous weekend closures for local traffic: In the Greenfield area, the Beechwood Boulevard onramp to the Parkway, headed east toward Monroeville, will close at 6 a.m. Sunday and remain closed until the afternoon or early evening Monday. Once the area is secured after the bridge implosion, drivers will be able to enter the Parkway eastbound, right before the Squirrel Hill Tunnel.
Signs along the main detour route will tell drivers how to get to the Squirrel Hill commercial district. Some merchants reported a drop in business during the two previous Parkway East closures.
After the highway is closed Sunday morning, dozens of trucks will begin hauling dirt to the Parkway East drop area between the Squirrel Hill Tunnel and Oakland. In all, about 4,000 cubic yards of dirt will be brought to the site.
The demolition crew will drill 224 holes in the arches of the bridge to place 1,400 pounds of explosives. The plan is for the explosives to pulverize the concrete into small or dust-sized pieces that can be hauled away easily after the blast.
Mosites crews have worked since the bridge was closed in October to remove the deck and as much other material as possible from the structure, leaving a skeleton of one of the city’s only remaining concrete arch bridges.
Only a few things could delay the blast — very low cloud cover or dense fog, which could cause a potentially damaging concussion reverberation; a snowstorm, which is unlikely given the forecast for above-freezing temperatures; a computer glitch; or intruders.
Over the past few months, demolition representatives have visited with residents who live closest to the blast area to review the conditions of their homes and advise them on any steps they should take to protect their property. In most cases, homeowners don’t have to do anything because the blast is expected to do nothing more than rattle windows on buildings close to the bridge.
Demolition experts have set up an 800-foot safety perimeter around the bridge. Streets will be closed beginning at 7 a.m. Residents within the perimeter will have to remain indoors.
Drone hobbyists, take note: Air space is restricted 2,999 feet above ground and within a 0.5 nautical mile (about 3,000 feet) radius of the site. The restriction will end by 4 p.m. Monday.
City officials said they will close streets near the bridge to keep spectators out of the area, including Greenfield Road, Beechwood Boulevard, Saline Street and Prospect Drive.
Officials would prefer that people watch the implosion on TV, but anyone compelled to see it can go to Oval Drive in Schenley Park for an unobstructed view.
“The bottom line is, we don’t know what kind of crowd to expect,” said Guy Costa, the city’s chief of operations. “Mostly people should stay home because they can’t see it” from most locations.
The charges are expected to be activated at 9 a.m. There will be an air-horn warning three minutes before the blast and police sirens will sound one minute before. Once it is determined that there is no one outdoors in the safety perimeter, the bridge will be imploded.
After the bridge comes down, there is expected to be a 10-minute wait while officials determine whether all charges were detonated before an all-clear signal is sounded.
“The contractor has five days to get this done, but we’re hopeful they can have it cleaned up before 6 a.m. Friday,” Mr. Costa said.
The week between Christmas and New Year’s Day is the only time PennDOT will let the city close the highway because it has the lowest traffic all year.
Ed Blazina: eblazina@post-gazette.com.
First Published: December 27, 2015, 5:00 a.m.
