Beginning Oct. 23, we are conducting an in-water test pile and noise reduction study. This work is done as part of the design work for the I-5 to Medina: Bridge Replacement and HOV Project.
We know that Portage and Union Bays are sensitive areas for surrounding neighbors and local fish and wildlife. This work will help us:
- Evaluate the noise effects of pile driving in Lake Washington and identify the best methods for minimizing noise that could affect people, fish and wildlife during construction.
- Determine the best pile installation methods and ensure that the Bridge Replacement and HOV Project stays on schedule.
This work will begin as early as Oct. 23, 2009, and is scheduled to occur during daylight hours only over the course of approximately 25 working days, weather conditions permitting.
Work is planned to occur Monday through Friday, but weekend work may be necessary. All work will be completed by Dec. 31, 2009.
What is the test pile and noise reduction study?
Crews will use a combination of vibratory and impact hammers to install a total of nine steel test piles at three locations shown in the map below. Each of these piles is between 40 and 120 feet long. The pile driving at each location will last for two to three days, followed by several days of load testing and monitoring.
Map of in-water drilling locations.
While each pile is being driven, we will study several kinds of noise abatement measures:
- "Bubble curtains" or walls of air bubbles that surround the pile underwater and mitigate the noise that could affect fish in this area.
- Hollow steel pile casings placed around the piles being driven, which are also designed to mitigate noise.
- A "noise shroud" or curtain of sound-attenuating fabric placed around the pile-driving equipment.
Once all testing and monitoring work is complete, the test piles will be removed using a vibratory hammer. If they cannot be removed, they will be cut off a minimum of 2 feet below the mud line.
What should residents expect to experience during the study?
The test pile and noise reduction study will be loud during periods of pile driving. Residents may hear a hammering sound as test piles are being installed. Because noise diminishes the further one is from the source, residents a greater distance from the pile driving should experience lower noise levels. Again, the work will take place during daylight hours only.
Additional questions about this work?
Please call our project hot line: 206-708-4657.
Photos of previous fieldwork
Nov. 17, 2008 - Land drilling on the Eastside
Oct. 29, 2008 - The smaller barge operating in the Montlake cut area.
Oct. 15, 2008 - The Seahorse barge in Lake Washington photographed from an SR 520 bridge camera
Oct. 7, 2008 - The Seahorse barge used for drilling in Lake Washington. Its dimensions are 40 feet wide by 110 feet long.
