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Seattle Tunnel Partners resumed mining today following a temporary stop to change tools on the cutterhead of Bertha, the SR 99 tunneling machine. As of lunchtime, crews were tunneling north approximately 170 feet below First Avenue, just north of Union Street.Crews replaced a total of 14 large cutting tools during the two-week maintenance period. Bertha has moved from clay to a mixture of sand and gravel that wears down cutting tools more quickly. A photo comparing a new cutting tool with a worn cutting tool is available in this post.The tools STP changed during this maintenance stop are the first parts of the cutterhead that contact the ground, making them crucial to the machine’s ability to excavate soil. STP will continue to inspect and replace these tools as needed during the course of mining. They are also planning Bertha’s next hyperbaric maintenance stop, the location of which is still being determined.The machine has tunneled more than 4,135 feet and is nearing the halfway point of its 9,270-foot-long journey. 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.Recent tunneling updates— more —
Seattle Tunnel Partners is continuing to change large cutting tools on the cutterhead of Bertha, the SR 99 tunneling machine. Crews have inspected 12 tools – replacing 10 of them – during the current maintenance stop. They could change up to four additional tools before they resume mining.This is a normal part of tunnel mining. Cutting tools wear down over time and must be replaced regularly. Bertha recently transitioned from soft clay to a more abrasive mixture of sand and gravel, resulting in greater tool wear.The tools STP is focused on during this maintenance stop are the first parts of the cutterhead that contact the ground, making them crucial to the machine’s ability to excavate soil. Replacing them now will preserve the cutterhead and keep the machine in good working order as it continues mining north beneath downtown.The current maintenance does not require crews to work in hyperbaric conditions, as they did during the previous two maintenance stops. That’s because the cutting tools along the spokes of the cutterhead can be accessed from within the machine, at regular air pressure. Crews performing the work must climb into tight quarters inside the spokes and use hoists and chains to remove the tools, which weigh up to 600 pounds.STP will resume mining when the tool replacement is complete, no sooner than next week. We’ll continue to provide updates as this work progresses.Crews are replacing worn cutting tools (left) with new ones (right).Recent tunneling updates— more —
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.
Recent tunneling updates— more —
Just a few days before the SR 99 tunneling machine started tunneling under the Alaskan Way Viaduct, the Washington State Department of Transportation flew a video-equipped drone through the SR 99 tunnel to show Seattle Tunnel Partners’ construction progress. There has been continued interest in seeing what has been built below ground and this video gives a glimpse of the tunnel as well as the nooks and crannies of the complex tunneling machine.
On an average day, the tunnel is … more
This week, at the south entrance to the bored tunnel, Seattle Tunnel Partners is pouring concrete for a section of the future southbound highway. On one hand, the pouring of concrete (also known as a "concrete placement”) is nothing extraordinary – it’s a common occurrence on a project that will use enough concrete to build nine football stadiums. But their frequency belies the complex choreography that goes into executing each pour successfully. Since concrete plays … more
Keeping the public informed about our work to replace the Alaskan Way Viaduct is an important part of what we do every day. Our goal is to give you as much access as possible to this amazing project, which is why we regularly post updates, photos and videos of our progress. We even offer walking tours from our information center, Milepost 31, to a viewing platform that overlooks the pit where tunneling began in summer 2013.
Unfortunately, there’s one frequently received request … more
As reported elsewhere on our website, work to access and repair the SR 99 tunneling machine is coming along. We’ve heard from some people that Seattle Tunnel Partners’ repair plan is hard to picture. Enter STP’s Chris Dixon, who was nice enough to narrate a video that explains what crews are doing to resume tunneling by March 2015. Watch it on YouTube or download a WMV file.
Seattle Tunnel Partners repair work plan (pdf 4.8 Mb) … more
We’ve been asking you to do your part to reduce congestion when SR 99 closes for four days starting Friday night, Aug. 22. That includes things like changing your commute habits and choosing an alternate way to get around.
But what are we, the agencies tasked with keeping traffic moving during this closure, doing to help? Quite a bit, actually. Here’s a roundup of some of the steps we’re taking to help you and your fellow commuters through the closure.
Washington … more
Less than three years ago, crews demolished the southern mile of the Alaskan Way Viaduct. When they did, they shifted traffic onto a new section of State Route 99 south of downtown Seattle.
Much of that new section of SR 99 is permanent, but the piece west of the stadiums is temporary. This curving stretch of road takes drivers around the SR 99 tunnel construction site and connects to the remaining section of the viaduct near South King Street. It’s nothing fancy, but it’s … more
Just in time for Bike Month, we opened a new permanent connection between the on-street bike lanes south of South Atlantic Street and the shared-use path from South King Street. Here’s a map that shows the improvements, which include:
A dedicated, 14-foot-wide shared-use path with improved paving.
A separate northbound and southbound path for more efficient navigation.
Signs warning of vehicles crossing the intersection of … more