Snags drive up cost of new span’s construction
TSTAFF WRITER he cost of the new Harrison Avenue Bridge nearly doubled from original estimates because state engineers’ initial designs proved flawed and unforeseen circumstances cropped up during construction.
State Department of Transportation engineers pegged construction at $13.47 million, but so far construction costs for the project are $25.37 million. PennDOT officials do not expect major additional costs, if any.
Overall, the cost stands at about $30.8 million after factoring in the cost of designs, engineering, inspections and purchases of homes to make way for the new bridge.
The bridge should open next month right next to the existing bridge, but with a different alignment connecting Scranton’s Hill Section to South Scranton.
The miscalculations also delayed completion.
Once expected to wrap up by July, the project won’t fully end until at least the spring, according to PennDOT. Crews still must demolish the current bridge and restore about 250 feet of inbound Central Scranton Expressway, among other things.
To avoid a repeat of what happened, PennDOT added an engineer to projects to review whether designed plans can actually be carried out, officials said.
“We have taken steps to move forward in a different direction with that,” said Carmen J. DiPietro, the construction management supervisor whose team uncovered the design shortcomings. “During the design process, I don’t think they had a clear picture of how this was going to be constructed. And, it really came back to bite us in construction.”
The project looked complicated from the outset. Designers and contractors had to deal with obstacles such as railroad tracks that carry the Electric City trolley, the Laurel Line tunnel the trolley travels through, Steamtown National Historic Site trains, high-tension power lines and the Central Scranton Expressway.
The realization the new bridge would cost more than expected dawned on construction officials early.
In October 2014, PennDOT awarded Minichi Inc. of Dupont a $17.72 million construction contract. That put the project $4.25 million over the original estimate.
Minichi and PennDOT construction managers quickly realized the design flaws.
“When we got here, the way they had proposed it would not work,” said Tom Bailey, Minichi’s project manager. “Access to get to both these piers was a challenge.”
Plans called for a bridge pier on both ends to support the new bridge, which sits about 140 feet above Roaring Brook.
The design assumed crews would build two platforms into surrounding hillsides about 40 feet above the surface where the piers would stand. Massive cranes, with steel bits eight feet wide, would sit on the platforms and bore holes into solid rock for the piers on either side of Roaring Brook.
Minichi and PennDOT construction management officials realized that wouldn’t work. The drills had to sit next to where the holes would start. DiPietro said the cranes also stood so tall they might have touched high-tension power lines crossing the bridge.
PennDOT’s plans lacked proper access roads for equipment to reach the land where the platforms would be built, according to a PennDOT document and DiPietro. The contractor had to build access roads on both sides of Roaring Brook. That included tearing out about 250 feet of the two inbound lanes of the Central Scranton Expressway for the access road for the southern pier job.
PennDOT found another problem on the northern, Hill Section side — a buried Scranton Sewer Authority sewage overflow pipe under a 100-year-old stone arch. If Minichi rolled heavy equipment over that, the arch could crumble, blocking water flow and spurring flooding in neighborhoods.
PennDOT added construction of a concrete causeway over the arch for the equipment to travel.
Building the access roads also required reinforcing the hillsides to avoid rock slides, which could affect the expressway and the Steamtown train tracks. The retaining walls alone cost about $2.1 million.
Engineers envisioned demolishing the old bridge differently, too. They thought cranes on the bridge could take it apart gradually starting in the middle, then pulling back and removing the arched sections from either side. Little debris would fall into Roaring Brook.
Minichi and the engineers concluded removing each section could weaken the remaining structure supporting the removal cranes, leading to potential collapses that dropped bridge debris and the cranes into the brook below.
“Nobody felt comfortable approving any kind of drawings and putting any kind of heavy equipment on that bridge and removing the deck,” DiPietro said.
The best way, they decided, will be to implode the bridge, but that meant debris could drop into the brook, affecting flow.
They plan to build a rock causeway in the brook to catch debris and divert water flow through a culvert for a few days until the debris is removed.
The demolition entailed another potential problem never accounted for in original plans. Right next to the existing bridge, PPL Electric Utilities had a huge steel pole carrying major east-west power lines along the brook and over the bridge. PPL removed that pole and installed a new one upstream farther away from the bridge.
A project review during construction found the mathematical model used to design the new bridge’s girders was “inaccurate.” Girders span the piers and form the base on which the road deck sits. The miscalculation forced a girder redesign that added “stiffeners” to make them sturdier.
Then there was the stuff that no engineer could have foreseen.
After drilling 46-foot deep holes for the piers, Minichi found unstable rock. That required drilling another 9 feet to reach stable rock, DiPietro said.
Minichi also found unstable earth where the bridge abutments — the concrete foundations on either end that support the bridge — would go. That required digging deeper and adjusting the bridge’s concrete footers’ construction.
PennDOT also had to account for unforeseen vibration monitoring, winter maintenance, catch basin reconstruction and other lesser factors.
Scranton Mayor Bill Courtright said he was unaware of the project’s cost overruns and the delay in finishing the project. He credited construction officials with keeping the city aware of closures during construction.
“I didn’t realize it was a year behind,” he said. “I know people want it open, the sooner the better.” Contact the writer: firstname.lastname@example.org; 570-348-9147; @BorysBlogTT on Twitter
Construction continues on the Harrison Avenue Bridge in Scranton.
An access road used during construction of the new Harrison Avenue Bridge in Scranton.
Construction continues on the Harrison Avenue Bridge in Scranton.