Aug. 31 project update: New soils, new tools for Bertha

Posted on Aug 31 2016 2:09 PM
After tunneling more than 1,000 feet since their last maintenance stop, Seattle Tunnel Partners has paused to inspect and replace some of the larger cutterhead tools on the front end of Bertha, the SR 99 tunneling machine. STP chose to check the tools – and change them as needed – because Bertha has moved from clay into a mixture of sand and gravel that will more quickly wear them down. Replacing the tools now will preserve the machine and ensure it continues to function well as it mines toward STP’s next planned maintenance stop. 
 
This work does not require crews to work in hyperbaric conditions as they did during the previous two maintenance stops. Still, their task is challenging. Crews must climb into tight quarters inside the spokes of the cutterhead and remove tools weighing up to 600 pounds with hoists and chains. Each tool can take 20 or more hours to remove, inspect and reinstall. 
 
Crews have inspected four tools since they stopped mining late last week, and they could inspect up to eight more in the coming days. STP will resume mining when tool replacement is complete, no sooner than next week.
 
The cutterhead is approximately 170 feet beneath First Avenue, near Union Street. The entire tunnel route, including descriptions of each of the 10 zones through which Bertha is mining, can be found on our Follow Bertha page. Tunneling statistics are updated on that page on Mondays and Thursdays. You can also track Bertha’s progress on Twitter @BerthaDigsSR99.
 
Cutting tools
 
 

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