Following reports of the Boston Central Artery Big Dig project developing a “big leak” in September, (T&TI, November, p14), the Bechtel/Parsons Brinkerhoff consortium that manages construction of the scheme has circulated a response to the incident and subsequent media coverage stating: “The Big Dig is structurally safe and sound.”.
Over six pages, the consortium addresses the waterproofing and sealing situation and also refute seven allegations that have appeared in news reports or been suggested by public figures. The response asserts that coverage has “vastly exaggerated the impact and significance of tunnel leaks” and as a result, “unjustified fears have been raised about the safety of the tunnels.”
Bechtel and Parsons Brinkerhoff maintain that conversely, the factual situation is that despite not yet being finished and signed off, the “tunnels already meet industry norms for water intrusion”. The leak sealing works are due to be finished within the next few months as opposed to the years of remedials and chasing suggested by some members of the press and the consortium maintained this work would be carried out at the contractors’ expense rather than from the project budget. The normal maintenance program will handle residual seepage.
Stressing that engineers would expect inflows during construction, the document also claims that the permanent drainage installations are handling the volumes that are continuing to decrease as finishing works progress. Some reports claimed that defective waterproofing designs were upgraded throughout the construction period. Bechtel and Parsons Brinkerhoff said this was merely an evolution of the designs as experience was gained with local conditions and materials performance, but that earlier designs were not in fact found to be defective.
Despite this, the consortium did admit that the mid-September incident, that resulted in a 200mm hole appearing in the eastern wall of the northbound tunnel, was a separate issue to seepage and was due to improper construction of a single wall bay. An investigation is currently underway to determine “why the construction error happened and why it wasn’t corrected earlier”. Repeating that the tunnel was structurally safe, the consortium described how issues of this type were rare, but then went on to announce that dependent upon the results of investigation and records review, four other bay walls may require remedial works.
The allegations comprehensively rebutted in the statement were: It is unacceptable that the completed tunnels continue to leak; water entering the tunnels makes them structurally unsafe or structurally unsound; fixing the tunnel leaks will take up to a decade; the September wall breach was indicative of tunnel leak problems; Bechtel/Parsons Brinkerhoff failed to correct wall construction problems, allowed poor waterproofing to go uncorrected and has not acknowledged the extent of the leak problem.
