Contractors on the stalled project to dig a new tunnel under Seattle in the US now say it will open for traffic in 2018 after assessing the damage to "Bertha", a huge tunnel boring machine that got stuck.
The four-lane viaduct was originally scheduled to be open by the end of this year.
On 17 July the contractor Seattle Tunnel Partners (STP) said it had begun installing a new main bearing on Bertha, which overheated and stopped working in December 2013.
Fully disassembling and assessing the machine was always the key to determining how long the repairs would take– Chris Dixon, STP project manager
Bertha spent 15 months stuck underground before STP managed to lift its 2000-ton cutterhead out to assess the problem and repair it.
STP said tunnelling would resume in November when repairs are complete, according to the Washington State Department of Transportation (DOT).
The tunnel, called SR 99, is now scheduled to open to drivers in spring 2018, according to STP’s revised schedule.
STP and Bertha’s manufacturer, Hitachi Zosen, will perform extensive testing to ensure the machine is ready to bore the two-mile-long tunnel, which will take approximately one year.
Bertha had only completed around 1,000 feet of tunneling when it ran into problems.
Local media claimed Bertha had hit a steel pipe, but the DOT maintains that the cause of the damage has not been determined.
The DOT has taken a tough public line on the matter.
"The contractor’s schedule has changed, but the contract that governs their work remains the same," said Todd Trepanier, WSDOT’s Alaskan Way Viaduct Replacement Program administrator, in a statement.
"The state is a paying customer in this transaction, and we’re intent on getting what we contracted for. We will continue to protect taxpayers and hold the contractor responsible for their work as they deliver this vital project."
The DOT said responsibility for costs associated with the delay "will be determined through the process outlined in the tunnel contract".
Meanwhile, STP crews have been working to make Bertha stronger. They are installing a new seal system that will protect the bearing, and adding reinforcing steel, new monitoring systems and upgrades to the soil-conditioning system to prevent clogging.
The contractor said crews had to take the machine apart to find out how to avoid a repeat of the December 2013 mishap.
"Fully disassembling and assessing the machine was always the key to determining how long the repairs would take," said Chris Dixon, STP project manager.
"We want to reassemble the machine and resume tunneling as quickly as possible, but we also want to ensure the repairs are done right."
STP is a joint venture between New York-based Dragados USA, a wholly owned subsidiary of Dragados, S.A., the construction division of ACS Group of Spain, and Tutor Perini Corporation, based in California.
Photograph: Seattle Tunnel Partners crews use a milling machine to prepare the surface of Bertha’s bearing block prior to reassembly (Washington DOT)