Digging of the new Alaskan Way Viaduct replacement tunnel will start Monday, officials with the Washington State Department of Transportation said Tuesday.

Initial plans called for the massive tunnel boring machine, nicknamed Bertha, to begin on Thursday. However, the contractor leading the project elected to wait.

The tunnel will stretch from Pioneer Square to South Lake Union and carve an underground path that is scheduled to take sixteen months to complete. Total cost for the project is $3.1 billion.

Most of the details and plans for the project are complete. WSDOT Engineer Manager David Sowers said Tuesday right-of-way purchases or permissions for tunnel construction are nearly finished.

Plans created in case ground movement beneath the surface is too great for the buildings above should be finalized this week, officials said.

If there s any changes to plaster, windows or doorways, we need to make sure repairs are made in an historically sensitive manner, said Allyson Brooks with the state Department of Archaeology and Historic Preservation.

Brooks office has worked with tunnel contractors and WSDOT throughout the process, particularly on ensuring old buildings in Pioneer Square are not adversely impacted by the work.

I m always worried on every construction project, Brooks said, It s because of the construction techniques of tunneling that we re working so hard to make sure we have plans in place.

Tuesday, crews were seen installing one of the last building monitoring devices downtown. WSDOT is placing more than 3,000 instruments on structures, creating a labyrinth of lasers and mirrors that can measure whether buildings are moved by the tunnel construction below.

We have an alert level, which is 3/4th of an inch (of building movement), Sowers explained, Maximum level is an inch.

Business owners in Pioneer Square are cautiously optimistic about the construction process. Most said they looked forward to completion, but were concerned about the effects on commerce.

When it s done, it s going to be beautiful, described Luigi DeNuzio, whose restaurant is directly across from where the tunnel starts, In the meantime, construction is like labor. Beautiful children, but the labor is tough.

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