Vibration Control at Sound Transit
Sound Transit is constructing a light rail transit system with twin bored tunnels through the University of Washington (UW) campus in Seattle, Washington, USA. Ground vibration impacts on the UW campus were extensively studied with long range vibration propagation modeling and testing, vehicle force density measurements, and dynamic modeling of the vehicle and track isolation system. The vibration level design criteria were specified in third octave band velocities ranging from 500 nm/s to 2,500 nm/s at frequencies ranging from 3.16 to 100 Hz, placing substantial demands on vibration isolation design. Vehicle vibration force density levels were measured at ballasted track and resilient direct fixation fastener track. Vibration reductions of the order of 10 to 15 dB at 40 to 80 Hz were observed after profile grinding of the rails at direct fixation track. Vibration isolation provisions include discontinuous floating slabs with design resonance frequency of 5 Hz and high compliance direct fixation fasteners. Limits for rail undulation were specified to control low frequency vibration. Rail grinding and wheel truing combined with vibration monitoring and wheel flat detection complete the vibration control design. A major design complication is the provision of a direct current traction power cable beneath the slabs to control magnetic fields induced on campus by the trains.
KeywordsNatural Rubber Vibration Control Vibration Isolation Ground Vibration Direct Fixation
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