Tunnel excavation for the Central Puget Sound Regional Transit Authority (Sound Transit) University Link Extension (U-Link) was completed in 2012 and tunneling for the Northgate Link Extension was completed in 2016 in Seattle, Washington. In both cases, the twin bore tunnels were advanced under the University of Washington (UW) main campus, and there was concern that the vibration could be detected at nearby buildings and potentially interfere with sensitive research activities. This paper will describe a field vibration measurement program and compare the predicted and measured TBM vibration at the ground surface above the tunnel alignment. The over-consolidated glacial till that underlies much of the region is a particularly efficient transmission medium for low frequency vibration. The predictions were based on available data collected in advance of the TBMs reaching the campus. Measurements were conducted outside and within the buildings. The U-Link and Northgate Link tunnel construction used a total of four 21-foot diameter Earth Pressure Balance TBMs. The TBMs were refurbished and relaunched multiple times to complete a total of about 13 miles of tunnel. The U-Link tunnel construction used small diesel mining locomotives on rails to supply the TBMs which were found to produce significant vibration at the surface. Rubber tired supply vehicles were subsequently used during construction of the Northgate Link tunnels to minimize vibration through the UW central campus.
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