Wednesday, October 5, 2022

NJDOT to Look into Possible “Sudden Failure” of Route 80 Retaining Wall

As reported by Bruce A. Scruton in the New Jersey Herald –

A state Department of Transportation internal committee met this week to advance a project to study damage to a retaining wall that supports a raised section of Route 80 near the Delaware Water Gap, which may be “subject to sudden failure,” according to the meeting’s agenda.

The committee received approval for its request for $5.5 million in state funds to inspect the wall and come up with solutions to address the problem, which includes the deterioration of the wall and a minimum 12-inch-deep crack.

The estimated cost of the repairs to the wall’s crack and deterioration stands at $51 million.

The “failure” warning was included in the project description from the meeting’s agenda,  which also stated the retaining wall “does not meet current serviceability requirements due to its minimal reinforcement,” and that a failure “is a risk to the traveling public and could result in a closure of I-80.”

The retaining wall stretches for more than a quarter-mile around the base of Mount Tammany, an area known as the S-curves that was built in the 1950s.

This file photo from March 2022 shows the "erosion cave" repairs made to the retaining wall on I80 in the Delaware Water Gap. The photo also shows water stains of a leak (left of repair) through the wall and evidence of water coming from weep holes (right of repair) installed as part of the project.

The engineering study will take a look at the retaining wall issues that were discovered by crews making repairs to a nearby section of the wall that had been scoured or eroded by water coming down from Mount Tammany. The mountain is located on the New Jersey side of the Delaware Water Gap and is maintained by the NJDOT.

The scour, known by locals as the “erosion cave,” is at milepost 1.4 of the wall, which is 1,470 feet long, 13 to 18 feet tall and consists of 49 individual panels.

According to an NJDOT memo, “upon clearing vegetation west of this wall repair, additional wall deterioration, with a minimum 12-inch-deep crack adjacent to the wall shear key, was observed.” The memo also stated the wall “does not meet current serviceability requirements due to its minimal reinforcement. Due to the tied-back construction of the existing wall, it could be subject to sudden failure, which is a risk to the traveling public and could result in a closure of I-80.”

A video taken in 2020 by local residents as part of their effort to draw attention to the “erosion cave” and other problems with the 75-year-old road and wall, shows the crack existed at that time. 

When the wall was constructed, a drainage system was included that would collect and control the water flowing off the mountain to channel it into the river.

However, breaks and cracks in that system of mostly concrete pipes allowed water to get into the fill. The water, seeking a path to the river, pushed down to the bottom of the wall and eroded parts of it away.

Over the years, other breaks and cracks in the drainage system allowed water to get into the fill behind the wall that holds up the highway.   

A retired civil engineer who worked for public entities looked at the information that the engineering study will include and said he thinks the water has built up behind the wall, creating more pressure on the structure.

The S-curve on Route 80 west at the Delaware Water Gap Recreation Area.

The engineer, who asked that his name not be published, said the concrete, like a piece of chalk, can take a lot of pressure, but is also “brittle” and can break without warning.

As part of the repair project, the contractor drilled a series of “weep holes” in the retaining wall. Those holes are attached to perforated piping and provide a route for water trapped behind the wall to flow through the wall to reduce the pressure.

“However, that’s just a temporary measure,” the engineer said. “It’s a sign that there’s water back there.”

The engineer also said he thinks there was minimal steel used in building the wall and in anchoring it to the base of the mountain. 

While there are strict federal laws on how often inspections need to be conducted on bridge structures, there is no similar law on how often retaining walls need to be inspected.

The study is needed since the structure is likely nearing the end of its useful life and was built to standards of the 1950s, not modern standards, the engineer said. He added he does not think there is immediate danger, but a full inspection needs to be done.

Additional photos provided to the Ridge View Echo by Tara Mezzanotte. Follow up interviews will be conducted with State & County Officials on this matter.

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