SR 520 Bridge – West Approach Bridge North | USA

Project summary

Service provided:  Geotechnical instrumentation during bridge replacement
Location:  Seattle, Washington - USA
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Client:  WSDOT (Washington State Department of Transportation)
Period of the service:  September 2014-December 2017
Sixense solutions used: 

Images of the project

SR 520 Bridge - West Approach Bridge North


The West Approach Bridge North Pro­ject is part of the SR 520 Bridge Repla­cement and HOV Program. It re­placed the existing west approach bridge, which was vulnerable to a severe earthquake, and was connected to the new SR 520 floating bridge, the longest floating bridge built in the world, to Seattle’s Montlake area.


SR 520 Bridge Monitoring Network

During the bridge replacement, Sixense performed geotechnical instrumentation for the structure. The instrumentation program consisted of installing 6 automatic total stations to monitor displacements on the existing bridge. It also included 22 vibration monitors on the existing bridge and adjacent on-land residential structures to monitor vibration levels.

A challenge for this project was installing most of the instruments off-land without a sustained power source. Sixense successfully provided a solution using Cyclops, their patented total station grouping technology to remotely control and manage the robotic total stations installed on special supports right above the water.

Vibration monitors were also installed on the pier caps of the existing bridge and were powered by solar panels delivering continuous vibration data at 1-minute intervals.

Lastly, real-time data acquisition and management services were provided to their client through the Geoscope web portal that assessed immediate influence from construction activities.


The New Bridge

Sixense’s monitoring solutions ensured the construction work was completed safely and once the new SR 520 Bridge was finished it provided many benefits. It was replaced by stronger structures designated to withstand a catastrophic earthquake. It also created congestion relief and fewer traffic backups thanks to wider shoulders that allow vehicles to pull over without blocking traffic.

Project Key figures

6 AMTS (Cyclops)
22 Vibration Monitors