Crews to resume pit-digging in Seattle's stalled tunnel project

[December 17, 2014]  SEATTLE (Reuters) - Washington state transportation officials said digging was expected to resume on Tuesday on a pit needed to salvage a $3.1 billion roadway overhaul in Seattle, deciding the excavation effort was not causing buildings and a rickety highway to sink.

Parts of the Alaskan Way Viaduct and the earth around it have sagged as crews pump groundwater from a deep pit near the highway, clearing the way for repairs to a massive tunnel-boring machine, nicknamed Bertha, which overheated and broke down a year ago.

The Department of Transportation said in a statement on Tuesday that they have not confirmed the extent to which groundwater pumping has contributed to the sinking, but added that excavation was not a factor.

It said digging was expected to resume on Tuesday evening.

The excavation was halted on Friday, days after officials said some 30 buildings in an historic downtown neighborhood would be inspected for damage because they sit in a wider area that has sagged roughly an inch since October.

While the sinking poses no immediate threat to public safety, officials worry that so much subsidence - or "settlement", as officials term it - in so brief a time might cause stress-induced cracks and other damage to the highway, buildings and public utilities in the area.

"Our experts are still analyzing data and conducting daily inspections of the viaduct, but to date, no significant settlement has been observed beyond the initial settlement we reported publicly on Dec. 5," the department said.

Local media reported that business owners have complained of cracks appearing in their buildings and that utility managers have said they may need to dig up and replace a water main.

The contractor aims to resume tunneling by late March 2015, with the goal of opening the underground expressway to traffic in late 2016, despite a year fraught with delays, state transportation officials said. The project is part of a broader $3.1 billion roadway overhaul.

The machine, nearly 60 feet in diameter, was brought in to dig an underground expressway to replace the aging waterfront highway, which was damaged in a 2001 earthquake.

(Reporting by Eric M. Johnson in Seattle; Editing by Curtis Skinner and Paul Tait)

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