The Seattle waterfront will feature a new look when demolition of the Alaskan Way Viaduct moves into the mop-up stages by the end of September. 

As the Washington State Dept. of Transportation and contractor Kiewit erase the double-decker viaduct’s concrete from the waterfront, the project that started in February has hit the final phases, now more than 80 percent complete. 

WSDOT expects the bulk of demolition to move away from the waterfront by the end of summer, although some additional work in early fall will include demolition of the viaduct above South Dearborn Street and near Pike Place Market over the BNSF tracks. The work in that area, which has no public impact, includes extremely limited work windows due to train traffic. 

Crews are already removing the last large piece of remaining viaduct in Pioneer Square and cutting and picking the western girders that are less than 2 ft. from a building full of glass windows at 450 Alaskan Way. 

As the viaduct comes down, unveiling fresh perspectives of the city skyline — and new views for buildings tucked behind the concrete highway for 50-plus years — the decommissioned Battery Street Tunnel fills up. The tunnel, no longer needed with the removal of the viaduct and opening of the new State Route 99 tunnel under downtown Seattle, is getting filled to about half its height with crushed concrete rubble from the viaduct. 

The first phase included crews pouring in processed concrete rubble from demolished pieces of the viaduct from vents in Battery Street above the tunnel and compacting it down with vibratory rollers. This cycle of pouring and packing continued until the tunnel was filled to about 7 ft from the ceiling. In all, the tunnel took on 74,000 tons of rubble

Before the next phase of work in the tunnel, crews will build utilities in the tunnel. Instead of digging into existing streets, crews can layer in vaults, duct banks and sewer lines in the space available in the tunnel before then filling in the space around them. When the utility works wraps up, crews will then being phase two, likely in 2020, that includes pouring low-density cellular concrete into the tunnel from the surface. The flowable concrete will fill in the gaps throughout the interior top of the tunnel. 

Already, more than two-thirds of the viaduct has come down and been cleared, including the vast majority of the central waterfront area. Work started near the middle of the viaduct in the central waterfront, so crews have moved north and south as they continue the sometimes-delicate work just 5 ft from buildings. When all said, WSDOT expects to clear 60,000 cu yds of rubble, with about 7,000 tons of rebar heading for recycling. 

Follow Tim Newcomb on Twitter at @tdnewcomb