Property Owner Information

SR 99 Tunnel Project - Information for Property Owners


The SR 99 Tunnel Project is one of the largest excavation projects in the history of our state. The project’s five-story-tall tunneling machine will remove approximately one million cubic yards of soil by the time it finishes digging the tunnel. The ground naturally experiences movement over time, but digging underground can cause additional movement.

While we do not anticipate significant levels of settlement, as a precaution, we have implemented a comprehensive program to monitor and mitigate any effects of tunneling. The following information is intended to be a guide for property owners above and near the SR 99 tunnel route.


If you have questions, please email us at or call our hotline at 1-888-AWV-LINE (298-5463).

Common Questions for Property Owners


When will the tunneling machine be near my building?

The tunneling machine began its journey under downtown Seattle in summer 2013. In December 2013, Seattle Tunnel Partners, our contractor for the tunnel project, stopped excavation approximately 1,000 feet into the dig after measuring increased temperatures in the tunneling machine. While investigating the cause of the high temperatures, STP discovered damage to the machine’s seal system and contamination within the main bearing.

STP is now building a 120-foot-deep pit that will allow crews to access and repair the machine, which is stopped about 60 feet underground between South Jackson and South Main streets. When the pit is complete, the machine will tunnel forward into it. Crews will then partially disassemble the machine, and make repairs and enhancements. STP plans to resume tunneling by the end of March 2015. After tunneling resumes, we will contact you to let you know when the machine will be close to 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, noise and vibrations would last less than one week as the machine passes beneath.

Will my building be damaged during tunneling?

It is unlikely that your building will be damaged during tunneling. The machine was designed specifically for the soil and groundwater conditions beneath Seattle. As a result, we do not anticipate significant levels of settlement from tunnel construction. If any damage occurs as a result of tunnel construction, we will be responsible for repairs.

How is WSDOT protecting structures along the tunnel route?

While we do not anticipate significant levels of settlement, as a precaution, we have implemented a comprehensive program to monitor and mitigate any effects of tunneling. As the tunneling machine pushes forward through the earth, crews will measure the soil it removes while also tracking any ground movement above its path.

Buildings, utilities and streets located above and near the tunnel route will be monitored before, during and after construction. Each building was surveyed prior to construction to document its interior and exterior condition. Monitors installed on the buildings by our crews will be checked against data from before construction, as well as data from monitors installed outside the monitoring area. If damage does occur to buildings, utilities or streets as a result of tunnel construction, we will be responsible for costs associated with repairs.

What types of monitoring equipment are installed on buildings?

Crews have installed monitoring equipment on buildings along the tunnel route. Automated survey machines on rooftops rotate and take readings of small monitoring points on nearby buildings every few seconds to measure any movement. They also use lasers to take measurements of reference points on the ground. Information from these machines is transmitted and recorded around the clock and 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.

What happens if damage occurs to my building during tunnel construction?

If we receive a report of damage to buildings or infrastructure, we will assess the damage and determine the cause. We will be responsible for repairing damage that occurs as a result of tunnel construction.  Our staff in the Seattle project office will work with property owners to address claims. 

Crews have conducted pre-construction surveys that document each building’s interior and exterior condition prior to tunneling. This survey will help building owners and our structural experts quickly determine if any damage occurred as a result of tunnel construction.   

To report property damage or discuss any concerns during tunneling, please contact us at 1-888-AWV-LINE (298-5463) or The hotline is answered 24 hours a day, seven days a week.