Workmanship and design of tunnel are called into question

Investigators unraveling how concrete ceiling panels cascaded onto a car in one of the Big Dig tunnels should focus on some basic, troubling questions about the way the tunnel ceiling was built, civil engineers and highway construction specialists said yesterday.

Officials from the Massachusetts Turnpike Authority suspect that the accident that killed Milena Del Valle began with the failure of a single steel hanger that helped hold up the concrete ceiling, setting off a chain reaction that caused other hangers to fail and send 12 tons of concrete to the highway surface as Del Valle's husband drove underneath.

Now, federal and state investigators are looking into the possibility that there was some defect in the way the hangers were manufactured or secured to the roof of the tunnel connecting the turnpike to the Ted Williams Tunnel. A 1998 report from the state Office of the Inspector General documented numerous problems with the bolts and glue used to secure the ceiling in the Ted Williams Tunnel, including the use of bolts that were too short and trouble with an epoxy used to glue the bolts into the concrete.

The inspector general's report was written before construction of the ceiling section that later collapsed, and it's not clear whether the same methods were used. However, Governor Mitt Romney said the report should have served as a warning.

``That would suggest to a layperson like myself that a very high degree of care should have been taken in inspecting that section of the ceiling, and I don't know whether that care was given or not," said Romney, referring to the I-90 connector tunnel at an afternoon press conference.

The tunnel section was inspected before it opened to the public in January 2003 and another inspection was ``in the process" when the accident happened, Turnpike Authority chairman Matthew J. Amorello said yesterday. He said turnpike records from Modern Continental, the company that built the tunnel, show that the hangers were individually inspected and tested when completed.

Big Dig officials say there is no indication of a link between the ceiling collapse and previous problems such as leaks and use of inferior concrete.

Civil engineers said the questions must go beyond the quality of workmanship to the tunnel's design: Why were the concrete panels so heavy, weighing 2 1/2 to 3 tons apiece? Why were they there at all, since there was already a higher tunnel roof? And why did the failure of a single steel hanger send six to 10 of the slabs crashing down?

Initial reports from eyewitnesses and investigators indicate the accident began with a loud snap as a steel hanger gave way and the other three holding up a 40-foot steel bar couldn't handle the extra weight.

``I can't imagine anybody signing off on a design of suspending 3-ton concrete panels such that the failure of any one hanger would lead to 12 tons of concrete coming down on the highway," said Steve Banzaert , who teaches a course in ``spectacular failures in engineering" at MIT.

A spokesman for Modern Continental said the company would not answer specific questions. The company issued a statement saying it promised to cooperate with the investigation, while defending its workmanship. ``We are confident that our work fully complied with the plans and specifications provided by the Central Artery Tunnel Project," read the statement, adding that Big Dig officials inspected and approved the tunnel ceiling.

Bechtel/Parsons Brinckerhoff, the consultant that managed the design and construction of the project for 20 years, also promised to work with the Turnpike Authority to determine the cause.

The ceiling that collapsed -- inside the eastbound lane of I-90 under South Boston -- is structurally similar to a drop ceiling, with a lower ceiling suspended from the original one. However, instead of the light fiber panels used in homes, the drop ceiling in the Big Dig tunnel is composed of 20-by-40-foot slabs of concrete. The slabs rest on 40-foot-long steel bars that are suspended from the original concrete ceiling by steel hangers. The hangers are connected directly to the upper ceiling by a combination of bolts and glue.

Although such drop ceilings were built elsewhere in Big Dig tunnels, a 200-foot stretch where the accident occurred and the Ted Williams Tunnel have ceilings constructed differently from those in the rest of the connector and the Interstate 93 tunnel, which were built later, Amorello said. In the I-93 tunnel, a beam with ready-made steel connection points was embedded inside the concrete when it was poured to make it easier to suspend the ceiling. But in the affected section, crews didn't install the drop ceiling until 2000, five years after the original ceiling was built, forcing them to use another approach.

``They used this system of drilling in bolts and bolting it in with epoxy, and that's what we're investigating," Amorello said.

Michael P. Lewis , the state Big Dig project manager, said at a morning press conference that this was ``an approved method."

``It was actually the method used in the entire Ted Williams Tunnel," he said. ``It's a well-known way of attaching anchors to concrete structures."

One state official who has been briefed about the investigation said one focus is on whether ``a cheaper, quicker" ceiling design was approved by Big Dig officials for the turnpike section without adequate consideration of the possible consequences. The official is not authorized to speak publicly about the investigation.

This isn't the first time that investigators have looked at the quality of Big Dig drop ceilings. In 1998, Inspector General Robert A. Cerasoli said the project wasted $800,000 attaching hangers to the ceiling of the Ted Williams Tunnel because designers hadn't foreseen the need to attach hangers to the original concrete ceiling.

Although Cerasoli was focused on the needless cost of drilling and redrilling holes, he said yesterday that he is also concerned that low-quality work generally could have compromised tunnel safety. During construction, Cerasoli's report says, the contractors had trouble with the epoxy -- workers didn't give it time to cure properly or improperly cleaned holes, and the epoxy's manufacturer suspected the contractor was not mixing it properly. In a first set of tests, eight bolts failed out of 50.

Peter Zuk , the former state Big Dig director, had promised in a written response to the report to use a better way of fastening the steel hangers in the future, but the letter didn't describe the changes, and it was unclear yesterday whether they happened. However, Modern Continental's contract was modified several times in 1999, at a cost of almost $600,000, to allow for changes in the installation of ``adhesive anchors for ceiling struts" in the I-90 tunnel, according to state records.

``They really ought to have an independent group come in and evaluate all of these tunnels," said Cerasoli, inspector general from 1991 to 2001.

One construction industry specialist said he questioned whether the drop ceiling in the turnpike tunnel was needed at all. Turnpike officials said yesterday that the drop ceiling was needed to improve the flow of fresh air into the tunnel and move exhaust fumes out. But the specialist, who is familiar with the connector tunnel design but asked not to be identified, said the drop ceiling was there mainly for aesthetic reasons, to hide fans. He said the section is vented by open air entrance ramps only about 200 feet away.

Amorello said engineers will consider reopening the tunnel without any panels in the section where the accident occurred. He said that, if ``we can do without it, then we are going to do without it."

Gareth Cook of the Globe staff contributed to this report.