A Message from WSDOT Regarding Ground Settlement

BerthaGood afternoon,

I wanted to send a quick note to let you know the latest information about settlement in Pioneer Square.

We have told you about our settlement monitoring system that we installed as part of the SR 99 Tunnel Project. As we publicly announced last Friday, STP surveyors detected over one inch of ground settlement near the pit Seattle Tunnel Partners is building to access and repair the tunneling machine. We have also seen settlement on the Alaskan Way Viaduct and some of the buildings that we are monitoring; the amount of settlement lessens in the surrounding area.

Most of the settlement we’ve detected has been uniform, which usually means little to no damage to buildings and utilities. Engineers have been walking through the Pioneer Square neighborhood since we first learned of the new settlement. They have not seen any signs of new damage so far. An inspection team that includes an architect with historic building experience has been conducting interior building surveys since Monday and will continue over the next couple of weeks. If you have seen any recent changes in your building, such as new cracks or lengthening of cracks, sticking doors and windows or utility problems, please email us so we can set up an appointment.

Additionally, we have stepped up our monitoring frequency. Deep survey control points are checked approximately every other day and buildings and various points on the ground are surveyed once a day. Since Dec. 1, STP has not seen any appreciable change in settlement. Based on this, it appears that additional settlement is not occurring, though we will continue to closely monitor the situation.

At this time, Seattle Tunnel Partners is maintaining their dewatering system – and water levels remain static. However, they have stopped excavation until we can verify the new data. We will let you know when excavation resumes.

As for the crack in King Street, Seattle Tunnel Partners checked the site with ground-penetrating radar Thursday afternoon. While we are still awaiting the report, no voids were detected under the pavement.

If you have concerns about your building, property or utilities, please do not hesitate to call our hotline at 1-888-298-5463 or email us at viaduct@wsdot.wa.gov.




Todd V. Trepanier, PE
Alaskan Way Viaduct Replacement Program

Tunnel Project Update

BerthaWSDOT and Seattle Tunnel Partners conducted additional survey work early Sunday morning (12/7/2014) to further assess the amount and extent of settlement that recently occurred on and near the Alaskan Way Viaduct.

Some of the data was inconclusive and analysis is still underway; however, WSDOT observed that a small amount of differential settlement is occurring near the access pit. Differential settlement is when the ground settles unevenly over an area. When the ground settles evenly or uniformly over an area, there is less risk of damage.

The additional survey work did not find that the differential settlement has caused any new damage to the viaduct nor have we observed any damage to buildings or utilities in the surrounding area. On-the-ground surveys will continue this week by historic architects and structural engineers.

Public safety is our top priority and while we have not seen any damage, Seattle Tunnel Partners is taking the prudent step to stop dewatering. The contractor will work with its geostructural designer to stop the dewatering in a deliberate manner in order to ensure worker safety and the structural integrity of the access pit and surrounding structures.

Data analysis, collection and monitoring will continue and we will provide updates as we have new information to share.

Alaskan Way Viaduct Replacement Project Update – April 2014

Milepost 31 Events

April 19, 2014 events at Milepost 31First Thursday Speaker Series – Bertha and Progress on the SR 99 Tunnel Project

April 3, 2014
6 – 6:30 p.m.

You’ve been hearing a lot lately about our efforts to replace the State Route 99 Alaskan Way Viaduct. This is a big, complex undertaking. And as we all know, we’ve encountered some challenges. Join us this Thursday at Milepost 31 as speakers from WSDOT and our tunnel contractor, Seattle Tunnel Partners (STP), explain what’s being done to address these challenges and get Bertha, the SR 99 tunneling machine, moving again.


  • Matt Preedy, WSDOT’s deputy administrator for the Alaskan Way Viaduct Replacement Program
  • Chris Dixon, Seattle Tunnel Partners (STP) project manager

History Scavenger Hunt

April 19, 2014
1 – 4 p.m.

Join us at Milepost 31 for our monthly activity for kids. This month we’re hosting a scavenger hunt eggstravaganza  (pdf 371 kb) to discover Pioneer Square’s rich transportation history. Hop on down with your family and friends to explore historic icons and hidden gems in Seattle’s oldest neighborhood. Test your knowledge, check out cool new Pioneer Square locales, and enter to win a grand prize furnished by the Alliance for Pioneer Square. Pick up your scavenger hunt kit at Milepost 31 between the hours of 1 and 4 p.m.

And don’t forget you can find regular updates about Bertha on Twitter by following @BerthaDigsSR99.

Watch the Alaskan Way Viaduct Replacement Project on YouTube

The Washington State Department of Transportation has a YouTube channel dedicated to the big construction project that has dominated the Seattle Waterfront for the past couple of years. Here you’ll find animated videos of how Bertha the world’s largest tunnel boring machine works, loving goodbyes to the old viaduct which the new tunnel will replace, and milestones throughout the project. Above is a video showing Mario driving a go-cart through a simulation WSDOT originally posted of a temporary route for SR 99.

As we’re learning about what’s really blocking Bertha the Tunnel Boring Machine, you may want to get caught up on what Bertha is doing underneath Pioneer Square and why she’s digging a 2-mile tunnel underneath Downtown Seattle. Visit Milepost 31, the information center dedicated to the area’s history and the technology used in the tunnel boring machine. It’s located in Pioneer Square and tours of the nearby launch site are held regularly, as well as a Speaker Series on First Thursdays. There’s also a fabulous historical website called ViaductHistory.com through which visitors can explore the history of the SR 99 viaduct and surrounding neighborhoods. You can even follow Bertha on Twitter!