Several types of equipment will be used to monitor building movement during the tunnel project. All building exteriors within the construction monitoring area (pdf 720 kb) will be outfitted with instruments. A limited number will require additional equipment inside, typically in the basement.
Tiltmeters:
3-inch by 12-inch device typically fastened to an interior wall with bolts or brackets. Electronically transmits any building movement to the project team.
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Monitoring points:
6-inch by 6-inch, 3-D prisms mounted on building exteriors with a screw. Additional monitoring points are as small as the head of a nail.
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Liquid level sensors:
6-inch by 3-inch device connected to a half inch diameter tube filled with water, mounted on interior walls with bolts and brackets. Electronically transmits any building movement to the project team.
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Survey machines monitor building movement by continuously scanning these points on buildings and in the street.
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Crack gauges:
Small instruments placed on walls to monitor any changes in the size of existing building cracks.
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Automated survey machine:
A 1-foot by 6-inch machine, usually placed on the exterior or rooftop of an adjacent building. |
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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.