Session: 02-08 DESIGN - Tools and Techniques

Paper Number: 133769

133769 - Performance of Terrain Mapping Estimation of Depth to Bedrock in Pipeline Construction Planning: A Case Study 

Abstract: 

Terrain mapping, the delineation of polygons with unique surficial geology, landforms and processes is often conducted at the start of a project to provide preliminary ground information, particularly in areas that have not been subject to significant development. Depth to bedrock, one of the attributes typically assigned to terrain mapping polygons, can be a key input in estimating rock excavation volumes through the Front-End Engineering and Design (FEED) phase of a project. In this case study, FEED-level depth to bedrock estimation for three short new pipeline alignments routed through southeastern British Columbia are compared to detailed ground condition observations collected through construction. Possible causes of discrepancies are then discussed, leading to a review of the approach to conducting FEED-phase estimates.  

Terrain mapping for the studied pipeline routes was completed at 1:20,000 scale for an average 500 m wide corridor using air photographs, lidar, satellite imagery and ground truthing. Ground truthing consisted of mapping of available natural exposures and road cuts, and logging of hand dug soil pits in areas with no exposures.  Data from drilling and test pitting is also incorporated where available.  Estimated depth to bedrock was organized in three classes: <1 m, 1 to 3 m and >3 m. During construction of the three sections of pipeline, visual and textural observations of the material encountered in the grade cuts and trench were made along the near entirety of the alignment length. These observations were compared to the FEED-phase terrain mapping to determine where the estimated depth to bedrock was correct and where it was incorrect. The data was then interrogated to define in which terrain unit types bedrock depth was most reliably estimated, and what type of data was primarily relied on to drive the estimate. This study finally investigates possible reasons for discrepancies and discusses modifications to practices that could optimize planning outcomes for future projects.

Presenting Author: Betsy Waddington BGC Engineering

Presenting Author Biography: Betsy Waddington is a principal geoscientist at BGC Engineering. She has been mapping surficial geology and terrain around North America for over 30 years.

Authors:

Betsy Waddington BGC Engineering
Luc Toussaint BGC Engineering
Rami Ghazali TC Energy
Alex Baumgard BGC Engineering