Design and performance of a permanent vibration monitoring system with exceedance alarms in train tunnels

Abstract

Sound Transit has installed nine permanent vibration monitors (VMS) to continuously monitor the revenue service train 1/3 octave vibration velocity in the University of Washington (UW) campus area. The monitors allow verification that the vibration levels generated from the newly opened University Link (U-Link) extension light rail operations are within the thresholds established in the Master Implementation Agreement (MIA) signed by UW and Sound Transit. There are also three wheel flat detectors located along the light rail alignment outside of the campus area to serve as an early warning system that allows Sound Transit operations to implement mitigation measures in real time before trains with wheel flats reach the vibration-sensitive zone in the University of Washington. This paper discusses the design of the vibration monitoring program and the functioning of the system during the first three months of U-Link revenue service. Some of the key results are that the system is functioning as designed and consistently records and notifies vibration events that exceed alarm thresholds. The vibration levels from train passbys have been well below the MIA thresholds and preliminary investigation indicates that the alarms are not caused by the trains. A surprising result, however, is that several non-train vibration sources that coincide with train recording sessions are generating alarms. Vehicular traffic on adjacent roadways and mechanical equipment such as sump pumps located in the vicinity of the VMS units are suspected as the potential sources of vibration alarms.