Threading the Needle: Navigating a Century-Old Tunnel with Dual Transmission Mains
Suzanna Lewis (WSP Canada Inc.)
Originally constructed in the mid-1800s, the Peninsula Low and Intermediate Transmission Mains are critical feeds for the Peninsula of Halifax. Over several years, Halifax Water is completing phased upgrades to improve system capacity and reliability to further support growth and development.
Constructed in 2023, the Churchill Drive Corridor Transmission Main Upgrades project involved replacement of a 1km section of the transmission mains between Chebucto Road and Quinn Street. The cast iron mains were replaced with new ductile iron pipe, upsized from 375mm to 500mm and from 600mm to 750mm in diameter.
Following their initial installation in 1856 and 1862, infrastructure was constructed around the cast iron mains as the city grew.
The CN Rail was constructed in the early 1900s, including a concrete relieving arch system spanning across the mains.
Investigations using CCTV and 3D scanning uncovered curvature in the alignment of the pipes and arch system below the rail.
An electrical substation was later constructed adjacent the railway, with the existing mains traversing on a diagonal through its centre. Replacement of the watermains through these two sites presented unique challenges, including:
Trenchless installation of 60m of dual transmission mains on a curved alignment through the 100+ year old relieving arch.
Installation of a curved HDPE casing pipe, fused on site and pulled through the tunnel.
Specification of custom-length restrained pipe TR-Flex to meet required deflection of the curved alignment, pulled through the casing pipe, held in place by spacers.
Temporary shoring walls along the rail embankment to permit access to the arch while maintaining rail operations.
Disassembly and de-energization of a section of the electrical substation, involving strict timelines for construction.
Close coordination of pipe installation through the adjacent and confined sites, including collaboration with CN Rail and NSPI to minimize impact on operations of their respective systems.
