C-CORE is helping ensure the safe and timely construction of a rapid transit corridor in the heart of the nation’s capital.
Planning for the O-Train Confederation Line segment of the Ottawa Light Rail Transit (OLRT) project, began in 2013 and is scheduled for completion in the Fall of 2018. This segment will provide rapid east–west transit across the city. To alleviate downtown traffic congestion and ensure optimal service, the 12.5km, 13-station system includes a 2.5km tunnel and four underground stations. It is the largest infrastructure project in Ottawa’s history and constitutes the first phase of the city’s Transportation Master Plan.
C-CORE’s role is to provide an overview of the OLRT corridor and to monitor for ground movement during excavation/construction. Using satellites 800km above the Earth, we are measuring, with an accuracy of 3 5mm, any ground deformation resulting from tunneling. The goal is to identify issues during excavation/construction, allowing constructors and city representatives to mitigate the project’s potential long-term impacts on infrastructure within the corridor.
Shallow bedrock underlies the route downtown, with areas where the bedrock is much deeper (5–25 metres). The area also includes notable geologic features: differing combinations of sensitive silty clay, glacial till and sand, which have substantial groundwater issues and at least three faults that cross the tunnel in the downtown core. These features are stable, but could potentially impact the overall bedrock quality and hydro-geological regime, leading to differing patterns of deformation along the corridor.
The baselining and monitoring use satellite-based SAR interferometry (InSAR), which is well suited to cover large areas that are difficult to either access or instrument (for example, unstable slopes near transport corridors, building tops or remote regions). The increasing number of radar satellites enables more frequent coverage of an area of interest and a greater aerial density of measurement, providing wider and more uniform spatial coverage than the sparse point measurement available through standard geodesy techniques.
The baseline overview was derived from a dataset of 20 Cosmo-SkyMed satellite scenes of the corridor, processed through a Persistent Scatterer Interferometry (PSI) technique and aligned to a single reference image enhanced by a digital terrain model to scale displacement and a 3D model of buildings in the corridor to correctly simulate their radar response. The baseline overview is visualized in a GIS-compatible deformation map.
Frequent Cosmo-SkyMed satellite scenes are being collected for the duration of the project to provide ongoing monitoring of the entire corridor and updates to displacement maps.