TRENCHLESS | HDD
CHALLENGE IN CANADA HDD ELEVATION
A technically complex and high-risk crossing for a pipeline project in Canada saw HDD chosen for the excavation works. This is a short version of a paper to the No-Dig Show 2026 and is used, edited for space, with permission of the North American Society for Trenchless Technology (NASTT).
INTRODUCTION TC Energy required a pipeline crossing of the Simonette River in northern Alberta, Canada, and the HDD Intersection Method was employed for the installation, which more than 1190m long with an elevation change of over 70m between entry and exit locations. The crossing is part of the Grande Prairie Mainline Loop No.2 Project. The client retained the services of Blue Fox Engineering for engineering design, The Crossing Co for the HDD Installation, and CCI for installation, plus others contributed to the project’s success.
SITE AND GEOTECHNICAL CONDITIONS The river crossing project is about 90km southeast of Grande Prairie, Alberta, and passes under a 1,000m-wide valley which has an adjacent steep slope, to the south east side. Studies over 2019-2022 included geotechnical investigations, hydrology and scour analysis, landslide hazard assessments, and geophysical surveys. Boreholes were drilled along the alignment to help assess the open cut and trenchless excavation options. Based on the available geotechnical information, in the
northwest end of the alignment, the first 6m of bedrock was completely weathered and extremely weak to weak. In the southwest, site conditions near the HDD exit location consisted of about 12m to 16m of sandy silty clay, sandy clayey gravel, gravelly clayey sand with inferred cobbles and
boulders, and gravel with inferred cobbles. The gravel layer located just above the bedrock was more than 5m-thick vertically. Beneath the river and below the steep slope on the southeast side, the soils consist of silty clay, sandy silty clay, sandy silty gravel, and sandy gravel. The thickness of the soil layers ranged from 4m to 13m, and were firm and stiff to compact. Beneath, the bedrock mainly comprised of siltstone and mudstone, with some sandstone at depth.
HDD GEOMETRY AND DESIGN The HDD alignment was in bedrock materials and under the landslide hazard zone, and below the thick coal seams layer. Due to the length of the HDD and deep-seated gravel layer above bedrock at the top of the slope, a drill and intersect methodology was selected for construction. The resulting HDD geometry consisted of a 14° entry
angle, a 12° exit angle, and vertical curves with radii of 1400m. The resultant drill path is 1,191m long, with cover of 50.8m beneath the centreline of the river. The hydraulic fracture assessment for this crossing was performed using the Delft Geotechnics Method, per Appendix B of the Army Corps of Engineers 1998 Report CPAR-GL-98 and 2002 Report ERDC/GSL TR-02-9 and also TC Energy’s internal standards. A Factor of Safety of 2 was applied.
CONSTRUCTION AND CHALLENGES Due to the significant challenges involved in the works— including large elevation differences, pipe diameter, crossing length, and complex geotechnical conditions such as coal seams, zones of circulation loss, potential water ingress from the upper slope, and sections of the bore that could lack drilling fluid support—the HDD was classified as very high risk. Mitigations were implemented where possible and construction split over two seasons: Fall 2022 - Spring 2023; mid to end 2023. SMJV served as
Top: Figure 1:
Annular pressure – pilot hole from entry rig.
Bottom: Figure 2: Annular pressure – pilot hole from exit rig.
Right: Figure 3: Forward boring unit
30 | October 2026
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