Route 80 wall panel work begins, NJDOT estimates 5 months

KNOWLTON — A contractor began laying down concrete barriers along Interstate Route 80 in the Delaware Water Gap Thursday to create work space for the repair and possible replacement of four concrete panels which are part of the retaining wall which holds I-80 against the base of Mount Tammany.

Built in 1952, the wall is nearly 1,500 feet long and consists of 49 panels of varying heights. The space between the wall and the rocky surface of the mountain was filled in to create the base on which the interstate was built.

But the wall has deteriorated to the point where last year the New Jersey Department of Transportation contracted for an emergency inspection of the wall. The department said it found in 2020 the wall had cracks and spalling (parts of the concrete falling away) which put the wall in danger of failing.

Those DOT inspections came as it repaired an "erosion cave" at the base of a panel caused by water working under the bottom of the wall and washing out an area. Members of the public noted they had given the department pictures of of the case the previous year. It wasn't until pictures were made available to the media that the department began work on that panel, No. 44. Panels are numbered from west of east.

The emergency inspection found that many of the panels have problems and singled out panels 14-17 as needing immediate work. The two adjoining panels will also get repairs.

On Dec. 1, the DOT sent a letter to the National Park Service asking for talks about the first stage of work, which their schedule has beginning this month. The letter said the department "identified emergent structural needs which require the complete replacement of the retaining wall...from milepost (MP) 1.20 to MP 1.50."

The area of the proposed work all is within the boundaries of the Delaware Water Gap National Recreation Area, a unit of the National Park Service, which has strict oversight over projects within its boundaries.

Related:NJDOT committee approves study of Route 80 retaining wall 'subject to sudden failure'

Michael Baker International, Inc., which did the emergency inspection, identified the area of panels 14-17 to be an immediate concern because of "severe wide cracking, spalling and wall movement."

Last fall, DOT installed small barriers on the shoulder of the highway, shielding the panels from impacts with traffic because, as noted in the letter, "any impact load on the barrier may cause movement in the stem wall above the foundation, resulting in failure of these four wall panels."

Included with the three-page letter, was a package of engineering drawings of proposed fixes to the panels (13-18) of most concern and pictures of the panels.

The letter notes that to gain best access to make repairs, and to lessen impact on I-80 traffic, the engineers are proposing building a "trestle" which would hug the outside of the retaining wall and extend 15 feet toward the river. The structure would be held up on "micro piles."

"In-water work and bank stabilization activities are not proposed," the letter states, but also adds that the preliminary plans "are subject to change based on the contractor's 'means and methods'."

The trestle would end just to the east of a current underpass in the Kittatinny Point area of the park where the interstate has turned enough from the river to be held up by the land.

A drawing of that end of the trestle contains a note: "The contractor will access the worksite through the Kittatinny Point Visitor Center 'based on his needs and methods'."

The area where the additional barriers are being installed appear to match up with that entrance needed by the contractor to access the trestle.

The trestle shown in the drawings, only got through to the end of panel 19, but could extended along the wall to access the remaining 30 panels.

In a response to the New Jersey Herald, park spokeswoman Kathleen Sandt said the park "assembled an interdisciplinary team of subject matter experts to review the plans and we are in the process of doing that now." The local park also has regional and national NPS experts at their disposal.

Asked Thursday if there was any comment about Wednesday's meeting between DOT and NPS, Sandt only described the meeting as "long and detailed."

The engineering drawings show that wall panel work includes driving reinforcing rods into the face of Mount Tammany which would be connected to the new or reinforced panels.

DOT spokesman Stephen Schapiro has not responded to written questions from the Herald, including a cost for the current, four-panel emergency work. When the inspection was authorized, the cost of that work was put at $5.5 million.

At that time, DOT also estimated that the entire repair work would cost about $51 million, to be paid for from state funds.

DOT's Dec. 1 letter, stressed that this project to repair, replace and reinforce the wall is not part of the larger Rockfall Mitigation project which has become controversial.

Objections to that project are that before spending millions to prevent hazardous rockfalls, the DOT needs to show proof of just how prevalent rockfalls are, and should instead be focusing on efforts to prevent accidents within that area, known locally as the S-curves, where the highway curves around the cliffs of Mount Tammany.