Underhill contributed a number of survey services in the construction of twin 7.4 km water tunnels connecting Capilano Reservoir and the Seymour filtration plant, north of Vancouver. Initially, Billfinger Berger Canada contracted Underhill to provide a check survey of the GVRD’s GPS control network. Further services included establishing azimuth baselines for gyrotheodolite calibration. The GVRD then brought Underhill in to perform a plumbing check survey on the 180 m Seymour shaft. Results confirmed that the (original) contractor’s work was within a few millimeters. Subsequent to this, we provided quality control and review of the contractor’s survey work and results.
The next phases of the project included conducting precise survey control surveys and making as-built cross-sections for over 8 km of the bored tunnels. A precise 3D double-run control survey was run through both tunnels to provide the next contractor with accurate survey control. Portions of the tunnel were scanned using the Trimble GX 3D Scanner and cross-sections were extracted at various intervals from the point cloud directly. This survey allowed for the comparison of the existing tunnel with the original design to ensure project specifications were met. Data was processed in Trimble Realworks Survey Advanced 6.2.0. Over 200 cross-sections were extracted from the point cloud and overlaid against the original design.
Underhill then provided data reduction processing and adjustment services on the check data. Most recently, we provided precise (1mm) as-built surveys on 3 m diameter pipes prior to their installation in the tunnels.