Read more on the Big Dig materials failure and see appalling aftermath photos and diagrams at Design News' Big Dig coverage page.

The company suspected of supplying the substandard concrete used in Boston’s Big Dig has agreed to pay $42 million to settle civil and criminal investigations, according to an article in today’s Boston Globe.

Six managers from Aggregate Industries NE Inc. were indicted in federal court in May 2006, on conspiracy charges they knowingly delivered at least 5,000 truckloads of substandard concrete for use in building the Big Dig’s tunnels, ramps and bridges between 1999 and 2003.

Last July, a portion of a ceiling collapsed inside a Big Dig tunnel, killing a 39-year-old woman when the car in which she was a passenger was crushed. Her husband survived.

Earlier this month the National Transportation Safety Board determined the probable cause of the July 10, 2006 ceiling collapse in the D Street portal of the Interstate 90 connector tunnel in Boston was the use of an epoxy anchor adhesive with poor creep resistance – the epoxy formulation was not capable of sustaining long-term loads. The recent release of shocking photos of the ceiling panel collapse, along with all the world-wide coverage has engineers talking.

Prosecutors alleged in a 135-count indictment that of the 135,000 truckloads of concrete, a “web” of falsified documents were used to cover up a conspiracy where at least 5,000 truckloads – 1.2 percent of the concrete used – did not meet specifications.

According to the indictment, suppliers recycled concrete that was rejected because it had not been used within 90 minutes of being mixed (per the project’s specifications). In some cases, they double billed for the loads. Workers also falsified documentation to project inspectors to show the concrete was fresh. While some rejected batches were sent back to the Big Dig, other partially used batches were mixed with fresh concrete. Water or other materials were added to some batches which, while making the mix appear fresh, weakened the concrete. But tainted concrete was allegedly shipped with forged records intended to trick Big Dig inspectors into accepting the loads.

The faulty concrete was used in walls and roof slabs in the I-93 tunnel, parts of the I-90 tunnel and the sea walls of the Fort Point Channel, among other locations within Boston’s Big Dig project.

The Globe reports that of the $42 million, $27 million would go to a special fund to pay for future maintenance and repairs on the project and the remaining $15 million would be split between the federal and state governments to settle the mater for Aggregate, which is one of the region’s biggest concrete supplier.

Full terms of the settlement are expected to be announced later today by federal and state prosecutors.