Focused early investigation prices ground risk on a linear project, whoever forms the next government.
Sumas Prairie, Burnaby Mountain and the stretch between Merritt and Hope have one thing in common. Each appears by name in Trans Mountain Corporation’s March 2023 explanation of why its expansion would cost $30.9 billion (and come in at $34.2 billion in 2024): a water table on Sumas Prairie higher than planned, earthquake design standards for the Burnaby Mountain tunnel, difficult terrain from Merritt to Hope, and dense development between Sumas and Burnaby. On a line crossing two provinces, the causes the corporation named sat in a handful of British Columbia segments.
That pattern is common on linear projects, and it argues for a different way to spend investigation money. Boreholes at a fixed interval treat every kilometre of an alignment as equally uncertain. They are not.
The method below is written for owners and their engineers at the stage before a budget is fixed. None of it requires proprietary tools.
Segment the alignment by terrain class before any field work. Use surficial geology, floodplain mapping, LiDAR, historical landslide inventories and the as-built records of any parallel infrastructure. A corridor that follows an existing line, as Pacific Link would from Wabamun to Hope, inherits a record of what that line found. The terrain classes differ across the country: ice-rich permafrost on northern corridors such as the Mackenzie Valley Highway and the Grays Bay Road, sensitive marine clays in the Ottawa and St. Lawrence lowlands, peat and muskeg across the boreal, and floodplain soils like the Fraser Valley’s.
• Score each segment on the conditions that drive cost when they coincide: groundwater near surface, soft, sensitive or organic soils, ground ice, slope instability, seismic demand, watercourse crossings, and urban or utility density. One factor in a segment is usually manageable. Two or three in the same kilometre is where estimates fail.
• Investigate the top-ranked segments to detailed-design standard early and leave the low-ranked balance at a preliminary interval until later stages.
• Carry the result into the estimate as segment-specific contingency instead of one percentage across the job.
• Re-rank after every extreme weather season. The November 2021 floods on Sumas Prairie reset flood assumptions across the Fraser Valley in one event, and Trans Mountain Corporation cited B.C. flooding among its cost drivers.
The usual objection is timing. Owners are reluctant to fund intrusive investigation before funding is confirmed or a final investment decision is made, and on a 1,200 km corridor like Pacific Link’s, the reluctance is understandable. The Trans Mountain record answers it. Finance Canada’s 2020 explanation for the project’s jump from $7.4 billion to $12.6 billion was that the earlier estimate had not included final detailed engineering. Deferred investigation moves its cost to the point where a finding is most expensive to absorb.
Pacific Link offers a live test. Its conditions document is due by September 1, 2027, when construction can begin, and service is targeted for 2032-33, with a B.C. election three weeks after the listing and at least one federal election before first oil. Ground investigation done in the review year is the kind of work that holds its value whoever forms the next government: the soil does not change with the cabinet, and a corridor that is well understood is harder to stall and cheaper to restart.
A corridor budget is only as reliable as its worst-understood kilometre, and on most alignments that kilometre can be found from a desk, and investigated, before the next election.
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“In a changing climate and economy, resilient infrastructure is about fit for purpose engineering solutions tailored for now and tomorrow.”
Jesse Unke, P.ENG., PE, PMP, RMP, CMC
Vice President, Transportation & Infrastructure
jesse.unke@priengineering.com