USA: Northern Edge of Bored Tunnel, SR 99 Tunnel Project, Seattle, WA

360° panorama by Bill Edwards.
Click the image to open the interactive version.

This extraordinary view shows you where Bertha, the SR 99 tunneling machine, installs the curved concrete segments that form the walls of the tunnel. You can see the silver hydraulic jacks that retract to allow space for each segment. Directly overhead is Bertha’s red segment erector, which uses vacuum power to lift each segment and rotate it into place. Once a segment is in place, the jacks secure it. When all 10 segments have been placed together to form a ring, the jacks push forward six-and-a-half feet and start the process all over again. To the south, beyond Bertha’s 326 feet of trailing gear, is the light at the southern end of the tunnel.This 360-degree photo is part of a virtual tour of the SR 99 Tunnel Project in Seattle. Learn more about the Alaskan Way Viaduct Replacement Program at or follow Bertha, the SR 99 tunneling machine, on Twitter @BerthaDigsSR99.

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