Ground Monitoring

Ground Monitoring Process

Approximately one million cubic yards of soil will be removed during SR 99 tunnel construction, making the project one of the largest excavations in the history of our state. The ground naturally experiences movement over time, but digging underground can cause additional movement. The project team has a program to monitor and mitigate any effects of tunnel construction. 

If you have questions, please email us at or call our 24-hour hotline at 1-888-AWV-LINE (298-5463). If immediate attention is required to prevent property damage or to reduce a safety risk, such as a broken water line or structural damage, you should take actions to address the problem. Document the damage with photos and/or video and keep copies of all repair receipts. 

The Washington State Department of Transportation is a public agency and is subject to the State of Washington’s Public Records Act (RCW 42.56). Therefore, public comments and questions may be made available to anyone requesting them for non-commercial purposes.


Construction monitoring area along the tunnel route (pdf 2.9 Mb)

Ground monitoring folio (pdf 6.5 Mb)


Common questions about SR 99 tunnel construction

How is WSDOT protecting structures during tunnel construction?

Before construction, we implemented a comprehensive program to monitor buildings, utilities and the ground above and near the tunnel route. WSDOT and its contractor, Seattle Tunnel Partners, regularly review data from this system.

Buildings along the tunnel route and in Pioneer Square were surveyed to document their interior and exterior condition. These survey results serve as a resource for both property owners and the project team by documenting the current condition of each building.     

What types of monitoring equipment are installed along the tunnel route?

Crews have installed monitoring equipment on structures above and near the tunnel route. Automated survey machines on rooftops rotate and take readings of small monitoring points on nearby buildings and the ground to measure movement. Information from these machines is transmitted and recorded around the clock and regularly reviewed by the project team.  

When taking readings, the survey machines emit a red beam that is similar to a laser pointer. The beam may be briefly visible. Each reading takes less than one second and is not harmful if seen. The project team regularly surveys monitoring points on the ground and buildings. 

Underground monitoring equipment has been installed in the streets and sidewalks along the tunnel route. These instruments track movement below the ground surface. 

How would settlement affect a building?

You may notice new cracks or changes to existing cracks. You may also notice doors or windows that are sticking or do not open properly.  If the building settles more or less than the ground outside, utility services also could be affected. If you notice such changes in your building, please keep a list or take photos, and let the project team know at the contact information below.

When will the tunneling machine be near my building?

Visit our Follow Bertha page to track the tunneling machine's progress. We will contact you when the machine is near your property.  

Will I be able to hear or feel the tunneling machine?

It is possible that you may hear some noise or feel slight vibrations while the tunneling machine is near your building. If perceptible, we expect noise and vibrations would last less than one week as the machine passes beneath.

What should I do if I believe my building or property was damaged because of the SR 99 Tunnel Project? 

If you feel that your building or property has been damaged by the SR 99 Tunnel Project, please send an email to with the location and nature of the damage, your contact information and any photos that you may have. If you are a resident or tenant, please contact your property manager or building owner as well. You may also contact our 24-hour hotline at 1-888-AWV-LINE (298-5463).

If immediate attention is required to prevent further damage or to reduce a safety risk, such as a broken water line or structural damage, you should take actions to address the problem. Document the damage with photos and/or video and keep copies of all repair receipts. 

If you feel there has been damage caused by the SR 99 Tunnel Project and you are seeking compensation, you need to file a tort claim with the Washington State Office of Risk Management. More information and the tort claim form are available here: If you have questions about the form, you may contact the Office of Risk Management at 360-407-9199.

The tort claim form must be filed directly with the Office of Risk Management; however, we request that you provide a copy of the claim form to our program team as well at