Another Highway 99 tunneling-machine update from WSDOT before the holiday: The video above shows the machine building the tunnel’s 160th ring. (The music you hear isn’t a holiday feature, WSDOT says, explaining in the YouTube caption that it’s a safety alert.) The full online update says in part:
… In all, Bertha has excavated 8 feet of tunnel since STP restarted the machine early Tuesday. STP crews – which have been working long hours in the weeks leading up to the machine’s restart – will take a break over the holidays before resuming tunneling in the first week of January.
When work resumes, crews will mine through the concrete wall of the access pit and into the native soils that will serve as the next stage of STP’s testing process. This section of the tunnel route – like the 1,091 feet that came before it – is protected by underground walls that were built to hold the ground in place while crews continue to test the machine.
Bertha will mine toward an underground block of concrete approximately 450 feet north of the access pit. This area is the third and final protected maintenance stop, or safe haven, that STP built prior to the start of tunneling. According to the STP’s most recent schedule, the machine will spend up to one month at the safe haven while crews perform maintenance and make final adjustments before tunneling beneath the Alaskan Way Viaduct. …
The update also includes a reminder of the two-weeks-or-so Viaduct closure planned when that happens.
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