Property Owner Information
SR 99 Tunnel Project - Information for Property Owners
The following information is for property owners along the SR 99 tunnel route. If you have questions, please email us at viaduct@wsdot.wa.gov or call our hotline 1-888-AWV-LINE (298-5463), which is answered Monday through Friday from 8 a.m. to 5 p.m.
- View monitoring handout (pdf 755 kb)
Common tunnel construction questions
Property owner meeting:
In February 2012, we held a meeting for property owners above or near the tunnel route, so they could learn how we plan to protect their buildings during construction. We described pre-construction surveys, building monitoring equipment, timing and access needs in more detail. Below are the materials from this meeting.
- Presentation (pdf 797 kb)
- Construction monitoring area map (pdf 2.9 Mb)
- Display boards (pdf 1.6 Mb)
Pre-construction surveys
This survey documents a building’s condition prior to tunnel construction. Although we do not anticipate damage to buildings during this project, the survey information will help owners and WSDOT quickly determine if damage occurred as a result of tunnel construction. A final report documenting a building’s existing condition will be provided to the property owner for review.
When will WSDOT need access to my property for the pre-construction survey?
In August 2011 crews began pre-construction surveys for several buildings near the tunnel portals. We will survey other buildings along the tunnel route from mid-2012 through 2013.
What does the survey include?
Three to four members of the project team, which includes WSDOT and our contractor Seattle Tunnel Partners, will conduct each pre-construction survey. Survey crews will take photos, video and measurements of interior and exterior areas. We may also install gauges to monitor any changes in the size of existing building cracks. Survey work may take from four to 16 hours, depending on the building’s size and condition. Work will be scheduled between 7 a.m. and 5 p.m.
What if I choose not to allow access to my building for the pre-construction survey?
The survey protects the property owner and makes it easier to establish a record of the building’s current condition. If it is determined that damage occurred as a result of WSDOT construction, WSDOT could then work with the owner to make repairs quickly. If you choose not to allow access to your property for the survey, it may be more difficult to evaluate a future claim for damage to your building.
Subsurface property rights
Where the SR 99 tunnel passes beneath private property, WSDOT will purchase a right to construct and operate the highway tunnel below the surface. The process to acquire this right includes:
- Describing the needed underground property area.
- Appraisals of the property rights to determine fair market value.
- A purchase offer to the property owners with a copy of their property’s appraisal.
How will the tunnel affect future development on my property?
For properties above the SR 99 tunnel route, the tunnel should not preclude development opportunities. There will be limits to the building load that can be constructed above the tunnel. This load limit, analyzed for each block of the alignment, is generally 7,000 pounds per square foot, as measured at the top of the subsurface parcel acquired for the tunnel. This is a conservative load limit that still makes it possible to develop substantially higher than current land use regulations. Importantly, it establishes an objective standard for land owners and WSDOT when evaluating future developments.
Load limit calculations for future development directly above the tunnel depend on several factors, including the size and design of the development, distance between the ground surface and the top of the tunnel’s subsurface parcel, the tunnel alignment below the property, and the subsurface depth of the development.
In addition to the load limit, permanent, private improvements below ground, such as a geothermal well or deep foundation systems, will not be allowed inside WSDOT’s subsurface parcel for the tunnel corridor. WSDOT staff are available to answer additional questions regarding property-specific load limits and future development above the tunnel.
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Common tunnel construction questions
How long will the tunnel boring machine be under my building?
We estimate the tunnel boring machine (TBM) will advance 30 feet per day on average. The rate may be slightly slower during the start-up phase. This rate means the TBM will take about 10 days to pass underneath one city block. This is a preliminary estimate and may be longer or shorter depending on specific ground conditions.
Tunnel boring will begin south of downtown and end in the north. It is expected to start near the stadiums in mid-2013, with the boring machine exiting north of Thomas Street near Sixth Avenue North in late 2014.
What kind of vibrations will people in my building feel from the tunnel boring machine?
Vibrations caused by the TBM are expected to be very slight and virtually undetectable at the ground surface. If perceptible, this slight amount of vibration would last less than one week as the TBM passes beneath a building, as described above.
Will WSDOT need access to my building?
To protect buildings along the SR 99 tunnel route, WSDOT established a construction monitoring area (pdf 2.4 Mb). Crews will install and maintain monitoring equipment to measure any building movement in this area during tunnel construction. For most buildings within the monitoring area, engineers will also conduct an extensive pre-construction survey of the building’s interior and exterior areas. We are working with property owners to acquire rights of entry for this work.
Will I have to retrofit my building before construction?
Buildings along the tunnel route are sufficiently sound to withstand expected settlement, and retrofits will not be required prior to tunneling. In the isolated cases where advanced precautions are needed, WSDOT will be responsible for building protection. Any work necessary for building protection will be closely coordinated with the affected property owner.
Will my building be damaged by the tunnel boring machine?
We take the issue of potential building settlement very seriously. While we do not anticipate significant levels of settlement, we are monitoring buildings as a precaution. Most of the tunnel boring will be in dense glacially-deposited soils. A number of tunnels in this region have been successfully excavated in similar ground conditions and experienced negligible settlement and only minor cosmetic building damage, if any. The SR 99 tunnel boring machine is being designed specifically for the soil and groundwater conditions along the tunnel alignment.
Who would be responsible if damage occurs to my building during tunnel construction?
WSDOT will be responsible for costs associated with building repairs for damage caused by tunnel construction. WSDOT and property owners will rely heavily on the pre-construction survey and monitoring data to evaluate the extent of construction-related damages. WSDOT staff in the Seattle project office will handle claims and work with property owners to repair damages. Alternatively, property owners can file claims under the state tort claims process found in RCW 4.92.100.
SR 99 Tunnel Project - Building monitoring
Several types of equipment will be used to monitor building movement during the tunnel project. All building exteriors within the construction monitoring area (pdf 2.4 Mb) will be outfitted with instruments. A limited number will require additional equipment inside, typically in the basement.
When will monitoring equipment be installed?
Tunnel boring will begin south of downtown and end in the north. It is expected to start near Seattle's stadiums in mid-2013, with the boring machine exiting north of Thomas Street near Sixth Avenue North in late 2014. We will begin installing exterior monitoring equipment in 2012, so we can collect at least six months of data before tunneling begins, and will continue monitoring for approximately one year after the boring machine finishes tunneling.
Installation may take one to several days, depending on the number and type of equipment. After installation, we will take readings remotely. Crews may need access periodically for equipment maintenance and in-person readings. All building surfaces will be restored after the equipment is removed.