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Step 2: Excavation and Tunneling
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Click image for larger version of map |
Burke Gilman Trail and Montlake Blvd. workIn early 2010 Sound Transit's contractor installed the infrastructure for an electrical ductbank that will provide power to the UW Station construction site and ultimately additional high voltage service to the University of Washington campus. The work is scheduled during UW's winter break to minimize impacts on trail users. While the work is underway, pedestrian and bicycle traffic along the Burke Gilman Trail (BGT) will be re-routed for a short distance at the south end of the UW campus.
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The construction site for the UW light rail station will change over time. The site will start at two acres, and eventually grow to six acres as the construction effort gets under full swing.
The Flash illustration below shows how the site changes over time.
One of the first tasks the contractor will undertake is to construct a portion of the walls that will surround the construction site for the next 6 years. The wooden walls will vary between 8 feet high facing Montlake and up to 22 feet high on the south end of the job site. Mesh-covered chain link fences will secure the site on the other sides. The walls and fences will help to keep the dust, dirt and noise from the construction inside the job site. Sound Transit is working with the UW to design graphics for some of the exterior wall surfaces.
At first the walls will encompass only a portion of the site. As the project progresses, the construction area will grow, and the walls will expand to enclose the entire site.
The driveways that currently provide access through the southwest parking lots for Husky Stadium pass through the area that needs to be excavated for the station and TBM tunneling. Once the first section of the construction walls are in place, Sound Transit will build new roads and sidewalks that will allow cars and pedestrians to go around the construction area and maintain access between the remaining parking lot and the rest of campus. The road and pedestrian walkway construction will take place in several phases.
After the access roads are in place, the walls and fencing will be modified and the construction site will expand to the full six acres. During this phase the contractor will grade the construction site to make it level, and begin digging out the area for the station. The excavation for the station and crossover tracks is approximately 800 feet long, 100 feet wide, and 120 feet deep.
All of that dirt (also known as spoils) will need to be hauled away in trucks. The trucks will travel along the haul route identified by the City of Seattle - south on Montlake, over the bridge, onto SR520, and off to the final disposal site (determined by the contractor).
In order to minimize the traffic impact of the trucks hauling away dirt, the trucks are not allowed to operate on Montlake Boulevard between 7-10 and 3-7 pm. Because of these restrictions, much of the truck hauling will happen during the nighttime hours.
Once the excavation reaches the bottom of the station (approx. 120 feet), it's time to begin digging the two tunnels to Capitol Hill. Two tunnel boring machines will be launched from the bottom of the station excavation about 1 month apart. The TBM's will excavate an average of approximately 44 to 50 feet of tunnel per day. As they travel through the earth, the TBM's also place the concrete rings that form the exterior structure of the tunnel. Dirt from the excavation travels through the machine and onto a conveyance system which brings it back out to the surface to be hauled away.
For safety reasons, the tunneling operations must continue around the clock. Sound Transit has applied for a variance from the nighttime noise restrictions in order to continue operating the tunnel boring machine and the associated topside support equipment at night. For more information about the noise ordinance and variance process, please visit the City of Seattle Web site.
After the tunnel boring machines get underway, a second contractor will join the tunneling contractor to begin construction of the station (which includes completion of the station box excavation, floors, stairs, mezzanines, elevators, etc.) and the above ground entrance to the station.
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Click image for larger version of site plan |
Pedestrian BridgeOne of the final stages of construction will be building a pedestrian bridge approximately 600 feet long that connects the station entrance with the main campus. LandscapingAs the station construction draws to an end, the contractor will restore the trees, shrubs, lighting and other landscaping around the station. Sound Transit will plant over 200 new trees adjacent to Husky Stadium. |
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Wilbert Santos
Community Outreach Coordinator
University Link
206/370-5516 desk
wilbert.santos@soundtransit.org
Andy Casillas
Project Manager
University of Washington Capitol Projects Office
University Facilities Building
Box 352205
Seattle, Washington 98195-2205
(206) 685-9055
casillas@u.washington.edu
