A forensic engineering firm hired by the Massachusetts Turnpike Authority after a traffic-snarling Interstate 93 tunnel slurry wall panel leak in mid-September is reviewing project work records to determine other potential problems. The move could presage extensive repairs while another independent review may prompt cost recovery actions against contractors and the project consultant.

The I-93 tunnel box may have more problem slurry wall panels. (Photo courtesy of BigDig/Matt Poirier)

Mueser Rutledge Consulting Engineers, New York City, has reviewed installation records for defective panel EO-45 and is now reviewing other potential problem panels that may be cause for concern. While the tunnel box remains structurally sound repairs to EO-45 could cost $250,000 and take months to complete. "This is unacceptable and the taxpayers and tollpayers will not pay for it," says Matthew J. Amorello, MTA chairman, which oversees the $14.6 billion Central Artery/Tunnel project. Another team led by Lemley Associates, Boise, Idaho, is also reviewing records for possible cost recovery efforts. Project consultant Bechtel/Parsons Brinckerhoff has identified at least six to ten other panels as having similar potential problems and another 400 smaller leaks, which contractors had been repairing as part of their punch list work.

Construction on the 3-mile $6.6 billion I-93 roadway, which includes a cable-stayed bridge and 1.5 miles of mainline tunnel, started in 1995 with some utility work. Serious tunnel slurry work started in 1997 with the northbound lanes opening in early 2003 followed by the southern lanes last December (ENR 12/29/03 p. 14). The tunnel runs under and replaces a six-lane 50-year-old viaduct that was supported by the tunnel walls and demolished this year. The tunnel contains some 2,000 slurry wall panels, each about three ft thick by eight ft wide and extending in length from 60-ft to 180-ft deep. Each panel sits between steel soldier piles and contains a rebar cage. About 1,400 slurry panels were also used on ramp connections.

Panel EO-45, which blew out flooding the shoulder and one lane of the northbound roadway with groundwater, is located at the eastern interface between two construction contracts awarded to Cambridge-based Modern Continental Construction Co, Inc and the Framingham-based Perini/Kiewit/Cashman joint venture. According to the MRCE report, submitted by George J. Tamaro, the PKC work preceded Modern’s and the leak occurred in the adjacent Modern wall just north of the PKC end stop beam. The 27-ft long sand, stone and debris filled defect varies up to 12-in wide and was caused by several factors including a PKC overpour, Modern’s apparent failure to remove it and other debris plus the rebar cage stopped about 18-in shy of the pile flanges instead of behind them. The field engineer noted the slurry did not meet specs, that the crew had difficulty placing the tremie pipe and that the cage shifted during the pour. The defect was noted and covered with shotcrete.

The panel has been temporarily capped with a steel plate and back-grouted on both sides but permanent repairs will also require installation of a temporary dewatering system, removal of non-conforming materials, extending the cage and placing a steel wall stiffener between piles. Knowledgeable sources speculate that the area, which had long been dewatered to support other construction projects now completed, was finally feeling full hydrostatic pressure. A Modern spokesperson issued the following statement; "A cooperative investigation with all involved parties for the cause of the CA/T leak is still ongoing. We are confident the results of the investigation will confirm that Modern’s workmanship was in accordance with contract plans and specifications."

There is a drainage gallery between the inside slurry wall and the six-in thick tile tunnel finishing panels that was designed to handle normal slurry wall weeps and seeps and channel it to pump stations. Also the CA/T is still closing roof penetrations caused by underpinning beams used to support the elevated artery that still allow rain and ground water into the tunnel. The pump system is functioning as designed but pushed about 26 million gals as opposed to a planned 3 million per year and will continue to pump extra water until all openings are sealed.