The retired Battery Street Tunnel, where almost 100,000 people made a farewell walk in February, is now merely a forbidden cave.

Contractors have almost completely filled and blocked the north portal with Alaskan Way Viaduct rubble. The entire passageway will be filled with viaduct fragments to a depth of seven feet, then topped by an equal layer of low density concrete grout, pumped inside.

In a novel strategy, Kiewit Infrastructure West scrapped its initial plan for conveyor belts and chose a simpler method to pour the rubble directly into the defunct tunnel, from above. Side-dumping trucks are pouring the debris through a steel funnel where workers cut open a former sidewalk at Borealis Avenue, next to Elephant Car Wash. The deposit takes less than a minute.

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As the filling moves southwest, the dump trucks will stop and pour rubble into existing daylight vents between the lanes of Battery Street itself, said Ian McPherran, Kiewit construction manager for tunnel decommissioning and north-side roadwork.

Sidewalks above shiver from the movement of heavy loading equipment below. Noisy, high-power tunnel fans continue to hum, to keep the dusty air circulating for workers inside.

Just to the north, other workers broke the last of the barrier wall around the north tunnel portal. The low base of Aurora Avenue North, now renamed Seventh Avenue North, has been filled and topped by concrete, raising the level of Seventh to match the other South Lake Union streets. That way, the road grid can be reconnected by next year, so John and Thomas streets will cross the former Aurora Avenue between Seattle Center and South Lake Union.

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Along the Seattle central waterfront, the viaduct removal is gaining momentum. Kiewit now expects to smash the central part from the ferry terminal to Seattle Aquarium by “the first week of June,” said Phil Wallace, senior operations manager. That would mean the team regained a week or two, after a slow start in late February around the cramped Columbia Street onramp.

Demolition teams with giraffe-necked munching jaws have now moved far enough north, almost to Union Street, that they appear in the Washington State Department of Transportation’s demo-cams.

After the viaduct’s girders, decks and steel rebar fall, the pieces are trucked to Terminal 25 next to the West Seattle Bridge, where the concrete is pulverized to 3 inches diameter or smaller, before being dumped into the decommissioned tunnel. A WSDOT video posted Wednesday shows the process, which will require some 2,400 truckloads.

Rubble relocation started in earnest last week, said Wallace, after crews spent several weeks washing away toxic soot and cleaning or moving utility lines inside Battery Street Tunnel.

Down at Marion Street, columns for a new, temporary steel bridge are being built from First Avenue to Colman Dock, winding along Western Avenue. The bridge should be done by June 30, then connected soon after to the ferry terminal that is being rebuilt. The crossing is to be replaced by a parklike overlook walk around 2023.

The old viaduct closed permanently Feb. 1, replaced by the two-mile Highway 99 tunnel, which at 57 1/3 feet is the widest and longest single-bore tunnel in North America. The shallow Battery Street Tunnel, originally called the Battery Street Subway in 1954, connected the viaduct to Aurora Avenue.

Many residents hoped to keep the old tunnel as a bus or car shortcut, while some suggested a park or bikeway. WSDOT rejected those ideas in favor of long-standing mobility plans, back to 2004, that reconnect the South Lake Union streets. Government officials also argued millions would be needed to make safety retrofits for any reuse.

Filling the tunnel with rubble is more convenient for contractors, instead of paying extra to take it to a landfill or recycle it. Battery Street Tunnel decommissioning makes up $35 million of the total $94 million viaduct demolition contract.

A contractor walks up a mound of crushed viaduct rubble during a media tour inside the Battery Street Tunnel on Wednesday.   (Ken Lambert / The Seattle Times)
A contractor walks up a mound of crushed viaduct rubble during a media tour inside the Battery Street Tunnel on Wednesday. (Ken Lambert / The Seattle Times)