Work filling in the decommissioned Battery Street Tunnel has reached the final stage. The Washington State Department of Transportation (WSDOT) said crews have started pouring a special type of concrete into the tunnel through ventilation grates and holes in the roof of the tunnel. The WSDOT said approximately 40,000 cubic yards of low-density cellular concrete (LDCC) will be used to fill in roughly nine vertical feet of space remaining in the tunnel.
During phase one of the project, workers poured and packed crushed rubble from the Alaskan Way Viaduct into the Battery Street Tunnel, King 5 reports. Crews then installed new utilities like sewer and electrical infrastructure in the decommissioned tunnel, instead of digging into existing streets. Controlled Density fill concrete was then poured around the new utilities during the spring and summer.
The WSDOT said LDCC is a lightweight material and will help protect the installed utilities from excess weight and allow “future crews to dig through it when required to reach those utilities.”
Contract crews started pouring LDCC at the tunnel’s north end near Denny Way using a series of hoses placed along the street. The work is expected to take several months to complete, and is expected to be finalized in 2021.