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Questions raised over use of Big Dig anchors

News

US INVESTIGATORS were this week 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 is believed to have 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 earlier last month (NCE 20 July).

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 had been 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, specied 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 lambasted it for poor design specication, inadequate management of construction, improper load testing and unauthorised deviations from specication.

Among Cerasoli's host of concerns, he pinpointed that bolts were drilled through rebar, cut short to avoid rebar and that 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.

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 rms would comment.

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

MTA has been under intense pressure from state governor Mitt Romney to hand over the lead investigation role to Romney's department. Romney has accused MTA of having con cting interests, as both operator and accident investigator.

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