Deformation Monitoring
Real-time 24/7 automated deformation monitoring of bridge and train tracks to measure stability
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The Challenge
- Replace Gloucester drawbridge in 4 phases
- Demolish half the bridge while keeping trains running
The Massachusetts Bay Transportation Authority (MBTA) completed a four-year drawbridge replacement project in Gloucester, MA. The first two phases of the project involved demolishing half of the existing bridge while the other side remained opened to trains.
The Gloucester Drawbridge is used by Rockport Line trains to cross the Annisquam River in Gloucester, MA. The new drawbridge features two side-by-side moveable track bridges providing more resilient and reliable commuter rail service and eliminating bridge related speed restrictions.
The Solution
Geocomp provided automated rail track and bridge deformation monitoring for the stability of the existing bridge while trains continued to run over the remaining working half of the structure. Automated motorized total stations (AMTS) were installed to measure the position of survey prisms clamped to the rail tracks while other AMTS units monitored the drawbridge, timber trestle, and abutments during partial demolition of the bridge and adjacent construction activities.
Additionally, to help quantify the impact of removing the south half of the bridge, Geocomp was asked to measure the deflection of certain structural elements when a train passed above them. Readings were taken before and after the partial bridge demolition to ensure that the bridge structure and reinforcements were performing as designed. Geocomp also added monitoring points to measure the performance of the reinforcing system installed on the bridge that helps to stabilize the wooden trestle. The monitoring points were measured every 15 minutes, and text message alerts were triggered if movement exceeded a threshold value or if any sudden changes were detected from one reading to the next.
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