Frequently Asked Questions
Posted on Dec 17 2014 5:22 PM
We've received a number of questions about the ground settlement measured recently near the SR 99 tunnel access pit. Answers to some of these questions can be found below. We'll continue to update this post as new questions come in.
Updated Jan. 21
What is the timeline to finish this project?
Each month, Seattle Tunnel Partners provides us with an updated schedule. This schedule includes all of the extra work days STP believes they are entitled to as a result of the tunneling stoppage and other delays. The schedule submitted for October, for example, now shows that tunneling will resume in late April 2015, and the project will be open to traffic in August 2017 – long after the original December 2015 open to traffic date and also later than the November 2016 date STP has been targeting since the tunneling stoppage.
While STP provides us with a schedule each month, we cannot endorse a project completion date until the work is further along. This is very difficult work and certain construction activities have and will continue to take longer than anticipated. While we are confident the project will be completed, a schedule we can endorse will likely come into greater focus only after the access pit is complete and the tunneling machine has demonstrated it can successfully mine.
Because this is a design-build contract, STP and their machine manufacturer are responsible for developing and implementing the plan to fix the machine and resume tunneling. Any repairs, production issues, or schedule impacts as a result of their operations remain the obligation and responsibility of STP. The nature of this design-build contract protects Washington taxpayers.
Transparency is an obligation that we take very seriously. Construction schedules on large projects always change, which is why the contractor is obligated to provide a monthly update. We recognize that the resulting schedule changes might create confusion, and we’re committed to clarifying these changes. Moving forward, a summary version of STP’s monthly schedule will be posted here
What’s the latest regarding ground settlement near the SR 99 tunnel access pit?
We installed a state-of-the-art settlement monitoring system as part of the SR 99 Tunnel Project. In late November, Seattle Tunnel Partners surveyors detected over an inch of ground settlement near the pit crews are building to access and repair the SR 99 tunneling machine. We also saw similar settlement on the Alaskan Way Viaduct, with lesser settlement in the surrounding area.
We quickly took action to survey nearby buildings and structures, including the viaduct, to confirm that there was no risk to public safety. No significant settlement has been observed in the area since Nov. 24. We are continuing to monitor this situation closely, but the viaduct remains safe for use and this settlement does not pose any safety risks.
What’s causing the ground to settle?
The cause of the settlement is still being determined. We believe that recent dewatering by our contractor may be a contributing factor, but we do not yet know if there are other factors. We will share additional information about this as it becomes available.
Is the ground still settling?
According to recent survey data, no significant ground settlement has been observed since Nov. 24.
What kind of settlement monitoring are you currently doing?
Crews from WSDOT and Seattle Tunnel Partners are conducting ongoing surveys of the Alaskan Way Viaduct and ground near the SR 99 tunnel access pit. In general, the surveys include:
Twice daily manual measurements at the bottom of both the east and west columns of the viaduct.
Approximately every other day measurements of deep survey points. These are survey points more than 80 feet underground.
Ground surveys of sidewalks and streets from Alaskan Way to Second Avenue and from Yesler Way to South King Street. Some areas are surveyed twice a day; other areas are surveyed once every two to three days.
Surveys of some buildings. Data is collected both manually and automatically and monitored daily.
What are your next steps?
We will continue to conduct frequent surveys and analysis, and provide regular updates to the public. In the meantime, STP crews have resumed work at the access pit and construction is moving forward.
Did recent settlement damage a water main in Pioneer Square?
On Dec. 15, Seattle Public Utilities officials announced that a 16-inch water main beneath First Avenue may have been damaged. They suggested this damage was the result of the settlement measured recently near the pit STP is building to access and repair the tunneling machine. A memorandum of agreement we reached with Seattle Public Utilities details acceptable levels of settlement for SPU infrastructure. Based on our current data, settlement has not exceeded acceptable levels. Also, no leakage or damage to the pipe has been verified by SPU. We will continue to work with SPU and other utility owners to protect their infrastructure.
Has settlement caused any damage?
The settlement did not cause any new damage to the Alaskan Way Viaduct. We continue to reach out to owners of approximately 30 buildings where the greatest settlement has occurred. By the end of Wednesday, Dec. 23, we had surveyed 50 buildings. This number includes surveys that were requested by property owners. Survey crews have found some cosmetic damage in a handful of buildings, but no structural damage has been discovered.
What percentage of the tunnel project is complete?
Our design-build contract with Seattle Tunnel Partners includes a number of elements. In addition to boring the tunnel and building the highway within it, STP is responsible for building highway ramps and other connections at the north and south ends of the tunnel. They are also constructing buildings at each tunnel portal to house lighting, ventilation and other systems needed to operate the tunnel. Approximately 70 percent of this work has been completed.
Because this figure is specific to our contract with STP, it does not include a number of major elements. Some of these elements, including the projects that replaced the southern mile of the viaduct, are already complete. Others, such as demolition of the viaduct and decommissioning of the Battery Street Tunnel, will be completed later.
If more funding is needed, where would that money come from?
Funding for the state’s portion of the viaduct replacement program comes from state, federal and local sources, as well as the Port of Seattle and tolls. The Legislature has capped state funding for the program at $2.8 billion, an amount that is expected to cover the costs associated with completing all elements of our work. Additional funding, if needed, would require action by the Legislature.
Is the viaduct still safe?
Our bridge experts have confirmed that the viaduct remains safe for day-to-day use. If we had any reason to believe it wasn’t, we wouldn’t hesitate to close it. It’s important to remember, however, that the day-to-day safety of the structure does not change the fact that the viaduct remains vulnerable to earthquakes. That’s why it’s being replaced.
All structures, the viaduct included, are designed to withstand some settlement. In fact, we were expecting the structure to settle some as Seattle Tunnel Partners built the tunnel project. It’s challenging to explain in general terms how any ground movement is acceptable. In the case of the viaduct, no one number represents an acceptable level; limits vary along the length of the viaduct based on ground conditions and the condition of the structure. How the ground settles is also important. A structure that settles uniformly is less likely to be damaged than a structure that settles unevenly.
What structural improvements have been made to the viaduct since the 2001 Nisqually earthquake?
Crews successfully completed a project to demolish and replace the southern mile of the viaduct in fall 2012. The remaining mile-long waterfront section of viaduct remains open today due to a number of important safety measures we have taken since the 2001 Nisqually earthquake.
Immediately after the quake, we repaired damaged portions of the viaduct to make it safe and functional. Additionally, vehicles weighing more than 105,500 pounds are prohibited and trucks and buses must travel in the right-hand lane only to limit the number of heavy vehicles on the viaduct in one location at one time. In 2008, we strengthened four viaduct foundations between Columbia Street and Yesler Way that had settled as much as 5 ½ inches since the earthquake.
As discussion about how to replace the waterfront section of the viaduct continued, we began work on a system designed to close the viaduct automatically in the event of a moderate to severe earthquake in the greater Seattle area. Completed in 2011, the automated closure system consists of traffic gates at all viaduct access points controlled by an earthquake detection system. If the system detects significant earthquake motion, it will simultaneously lower all nine traffic gates and safely close the viaduct in under two minutes.
How much has the viaduct settled since the 2001 Nisqually earthquake?
Viaduct settlement varies by location. The most significant settlement our crews have measured – 5 ½ inches – occurred between Columbia Street and Yesler Way, where crews have since strengthened some of the structure’s foundations.
Identifying the cause of settlement is challenging and in some cases impossible due to the many factors that can contribute to settlement. For example, it’s not unusual for the ground to settle long after an earthquake. As a result, much of the settlement measured along the viaduct could potentially be traced back to the Nisqually earthquake. Other potential factors include natural ground movement and vibration caused by traffic or nearby construction.
How much settlement would it take to close the viaduct?
If the viaduct were unsafe, we wouldn’t hesitate to close it. WSDOT has closed bridges in the past due to safety concerns, including the Murray Morgan Bridge in Tacoma. Because settlement limits vary along the length of the viaduct, there is no single threshold for determining when settlement would be significant enough to require further mitigation or closure of the structure.
Our contract with STP allows up to two inches of viaduct settlement before mitigation is required. Should it be necessary, a number of techniques could be used to strengthen the viaduct and keep it open to traffic until the new SR 99 corridor is completed. These techniques could include strengthening columns or other areas of the structure to provide additional support. We could also reinforce the viaduct’s foundation as we did in 2008.
If it became necessary to close the viaduct, what is the city's plan for traffic around downtown, Ballard, and West Seattle?
Our expectation is that the viaduct will remain in service until the SR 99 tunnel opens to traffic. Ground settlement levels have stabilized near the access pit, and no significant settlement has been measured since Nov. 24. Should it be necessary, a number of techniques could be used to strengthen the viaduct and keep it open to traffic while we complete the new SR 99 corridor. These techniques could include strengthening columns or other areas of the structure to provide additional support. We could also reinforce the viaduct’s foundation as we did in 2008. WSDOT and the Seattle Department of Transportation jointly developed an Emergency Closure Plan
that includes basic strategies for managing traffic in the event of a viaduct closure. This plan is currently being updated.
Does this new settlement increase the seismic risks facing the viaduct?
A few people on Twitter asked whether this settlement makes the viaduct more vulnerable to earthquake damage. The short answer is no. While any kind of ground movement has the potential to damage structures like the viaduct, ground settlement poses different risks, from a structural standpoint, than earthquakes. The main difference is that earthquakes cause lateral movement, while ground settlement causes structures to sink. These differing movements create different strains on the structure that aren’t related. In other words, settlement, if severe enough, has the potential to weaken a structure, but not necessarily in a way that makes it more likely to be damaged in an earthquake. How the ground settles is also an important factor. A structure that settles uniformly is less likely to be damaged than a structure that settles unevenly. This recently measured settlement was uniform.
Bertha repair effort
Has Seattle Tunnel Partners stopped work?
STP is continuing work on the project, including excavation of the access pit. We temporarily required them to stop excavation while we analyzed ground settlement data. Because no significant settlement has occurred since Nov. 24, and because there is no link between excavation and recent ground settlement, excavation was resumed on Dec. 16. Public safety remains our top priority as our contractor moves forward with their work.
How viable now is the plan to get Bertha restarted?
We’re disappointed with STP’s progress to date, and we can’t guarantee they will meet their schedule milestones. A preliminary review showed their plan to restart Bertha would likely work, but an expert technical team is awaiting more information from the contractor once the machine is brought to the surface to provide us with feedback on the plan.
How much more excavation is needed for the access pit to be completed?
The pit, which will be 120 feet deep when complete, is currently 90 feet deep.
What is the schedule for resuming tunneling?
The timeline will become clearer after the tunneling machine has been fully examined by the manufacturer and the contractor submits a full list of necessary repairs. A summary version of STP’s monthly schedule is posted here
What are the other options, if the 120-foot pit cannot be dug without destabilizing the viaduct?
There are other ways for STP to access the machine, both through the pit and through the tunnel. At its core, this is an engineering problem, one that can no doubt be solved. The current plan was chosen by STP. If they change course, deciding the best path forward — and assuming the risk associated with that choice — will be up to them.
What is the state’s financial exposure in this tunnel contract?
The answer to this question goes back to the way this contract is structured. Traditional design-bid-build contracts leave design up to the owner of the project – in this case WSDOT – but design-build contracts leave final design and construction up to the contractor. This gives the contractor greater opportunities for reward if things go well, but it also requires them to take on a greater share of the risk. As a result, the contract is perhaps the most important tool we have on this project. It can’t bore a tunnel or build the highway within it, but it can perform the project’s most vital function: setting the terms for completing the project safely while protecting taxpayers’ interests.
What is the plan if the tunneling machine breaks down again?
Our contract with Seattle Tunnel Partners requires that they have plans for repairing the tunneling machine at any point along the tunnel drive. Should the machine require repairs at a location that is inaccessible from the surface, crews would complete these repairs from within the tunnel. The current plan, which includes digging a pit to access the machine from the surface, was chosen by STP.
How many more setbacks can STP afford before it abandons the project?
Seattle Tunnel Partners is comprised of firms that have completed major projects all over the world. Like WSDOT, these firms have a lot at stake in this project. Despite the struggles they are currently facing, STP has given us every indication that they are committed to the successful completion of the project.
If the contractor does pull out, what's the state's backup plan?
All state projects make contingencies for a range of scenarios, including contractor default. The SR 99 Tunnel Project has a $500 million construction bond to cover the cost of hiring a new contractor and completing the balance of the $1.35 billion design-build contract. To date, the work included in the contract is approximately 70 percent complete.
Protecting infrastructure in Pioneer Square
What kind of settlement has WSDOT seen near the access pit and in Pioneer Square?
In late November, Seattle Tunnel Partners surveyors detected a little over an inch of ground settlement near the pit crews are building to access and repair the SR 99 tunneling machine. We have also seen similar settlement on the Alaskan Way Viaduct; the amount of settlement lessens in the surrounding area. Settlement levels in the area have remained stable since Nov. 24, but we continue to closely monitor the area. The investigation into the source of this settlement is continuing.
Have buildings been damaged in Pioneer Square?
We have worked with property owners and managers to complete approximately 50 visual assessments of buildings in areas of greater ground settlement. During these assessments, an architect with expertise in historic buildings checked portions of each building to look for signs of recent damage that might require immediate attention. So far, a small amount of recent cosmetic cracking has been noted in some buildings. Most buildings have shown no signs of recent settlement.
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 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 follow the contact information below.
What should I do if I see new damage in my building?
If you are a resident or tenant, please contact your property manager or building owner. Building owners should contact the Alaskan Way Viaduct Replacement Program (1-888-AWV-LINE or firstname.lastname@example.org) to report any settlement-related concerns. A WSDOT representative will contact you to arrange for a mutually convenient time to inspect your building. If you have photos, please share them with our staff.
How do I file a claim if I have building damage?
If you feel your building has been damaged as a result of ground settlement caused by the project, you can contact us at 1-888-AWV-LINE or email@example.com
What is WSDOT doing to monitor buildings?
We implemented a comprehensive program to monitor ground movement during SR 99 tunnel construction. Crews are currently analyzing data from this system and conducting extensive surveys near the work zone.
For buildings closest to the tunnel route, crews previously conducted pre-construction surveys that incorporated photo and video to document each building’s interior and exterior condition. We will be conducting similar building condition surveys for additional buildings within Pioneer Square. These survey results will serve as a resource for both property owners and the project team by documenting the current condition of each building.
Can WSDOT expand the monitoring program to include more buildings?
Our monitoring system was designed to measure ground movement during tunneling. As part of that system, monitors were installed both in the ground and on structures. The most significant recent settlement has occurred in areas that already include both ground and building monitors. However, some settlement has been observed in areas that are not actively monitored. As a result, we do not have specific settlement data for some of these buildings.
Structural engineers and surveyors are inspecting buildings and infrastructure in all areas where settlement was detected. Decisions about expanding the scope of the monitoring program will be made after that analysis is completed.
Does WSDOT have a plan if settlement continues?
Settlement levels in the area have remained stable since Nov. 24, but we continue to closely monitor the area. Protecting people and infrastructure is our top priority. Protocols are in place to address a range of potential issues that could arise as a result of ground settlement.