Arch Engineers Ltd. provided expert design and engineering services for over 250 trenchless crossings on the TransMountain and Coastal GasLink projects, tackling diverse geotechnical and environmental challenges across highways, railways, steep slopes, boulder fields, and marshlands. These trenchless crossings supported major pipeline infrastructure, ensuring safe and efficient pipeline installation beneath sensitive and high-traffic areas.
Our scope encompassed geotechnical analysis, structural design, and shoring systems for entry and exit pits, including solutions for HDD (Horizontal Directional Drilling), TBM (Tunnel Boring Machine), and casing removal operations. Pits often exceeded depths of 8.5 meters and required complex designs to accommodate large-scale equipment such as thruster machines and HDD units. Pits at the Clearwater River crossing exemplified the challenges faced, where boulders damaged sheet piles, causing gaps and deformation. Arch Engineers adapted with patch welding, additional walers, struts, and a soldier pile design to stabilize excavations and allow progress.
Dynamic site conditions and client-driven changes required rapid iteration, with some pits undergoing over eight design revisions. On one site, conflicting engineering approaches from adjacent contractors led to instability. Arch intervened, issuing a stop work order and designing a trench box system that stabilized the working area and enabled safe pipe hammering to resume. Additional designs included an aqua dam sheet pile wall for in-water isolation and alternative containment methods like sandbags and lock-blocks.
Throughout the projects, Arch Engineers demonstrated unparalleled flexibility, innovation, and commitment to safety. By delivering practical, tailored solutions under extreme time pressures, Arch successfully navigated complex geologies and operational challenges, ensuring safe, efficient, and compliant trenchless crossing installations.