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Questions raised over type of Big Dig anchors used

US INVESTIGATORS are asking why epoxy resin grouted anchors were still being used on Boston's Big Dig up to five years after the client said it had a better solution.

Failure of epoxy resin bonded anchors caused 10, 3t suspended reinforced concrete panels to fall from the roof on the Big Dig's Interstate 90 (I90) Connector Tunnel, killing a woman in July.

The 3t reinforced concrete panels fell from the roof of the east bound tunnel of the I90 highway, which passes beneath Boston Harbour en route to Logan Airport, on Monday 10 July.

It smashed into a car in which Milena Del Valle was a passenger and crushed her to death.

In August 1998 client for the project, Massachusetts Highway Authority (MHA), said: 'As a result of roof drilling into the dense rebar network [encountered from 1994-96, while suspending a similar ceiling panel system in the adjoining Ted Williams Tunnel], we have identified a better way to make connections into the roof concrete.' Panels were suspended from rods attached to plates bolted to the tunnel's heavily reinforced concrete roof slab. The 16mm diameter bolts were grouted with epoxy resin into sockets cored from the concrete.

Investigators identied movement in more than 250 additional anchors in the week following the fatal collapse.

But it is unclear why designer of the ceiling panel system for the Connector Tunnel, Gannett Fleming, speci d epoxy resin grouted anchors, or why the client allowed them to be used.

Neither MHA or Gannett Fleming would comment.

MHA made a commitment to use an alternative system to Massachusetts inspector general Robert Cerasoli, who produced a scathing report on anchor installation in the Ted Williams Tunnel in December 1998.

Instead of epoxy bonded anchors MHA pledged to use 'a special [steel] insert that is embedded into the concrete into which anchors can be placed without the need to locate or drill through rebar. But it was not used throughout the I90 tunnel.

Cerasoli conducted his report after costs on the Ted Williams Tunnel anchor installation contract soared.

He criticised poor design specication, inadequate construction management, improper load testing and unauthorised deviations from specication.

Among Cerasoli's host of concerns, he pinpointed:

Failure of the designer to anticipate how the ceiling panels would be anchored to the tunnel roof. As a result the contractor hit rebar on half of all holes drilled.

When rebar was hit the contractor was ordered to drill in a new location, but investigations revealed that some anchor bolts had been cut to the depth of short holes, rather than re-drill.

After 12 months, project manager Bechtel/Parsons Brinckerhoff agreed that the contractor could core through rebar to save time.

But no engineering evaluation was carried out to assess the impact of severing rebar on the roof's structural integrity.

A high proportion of resin bonds initially failed. This was blamed on improper mixing of the resin's constituent parts and failure to allow adequate cure time before testing.

But Cerasoli noted that water ingress through drilled and cored holes was widespread. A high proportion of test failures occurred in wet holes.

There was no industry standard procedure for testing anchor bolts.

Contractor for anchor installation in the Ted Williams Tunnel was Walsh Construction.

It is understood that the rm responsible for anchor installation in the I90 Connector Tunnel was main contractor Modern Continental Construction.

Neither firms would comment.

Last month, Matthew Amorello, chairman of the tunnel's operator Massachusetts Turnpike Authority (MTA), tendered his resignation.

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