PROJECT REPORT | TRENCHLESS
Top left: Partial Platform used for 3rd Drive.
Top right: Steel bypass flume.
Below top: Shaft 1-1 Final MTBM Retrieval with bypass in place and temporary benching removed.
The use of microtunnelling was envisioned early in the
design process as a way to mitigate project constraints while minimising impacts on the public, businesses and the environment. The project extends of almost 5200m, with the majority of the trunk being 2286mm and 2500mm in diameter, respectively. Near the treatment plant a box culvert (3m x 1.5m) was utilised to mitigate the shallow cover. Twin 1500mm-diameter inverted siphons of 400m lengths were required to cross under the Bow River. Following Value Engineering, the project was split into two phases of work which provided some construction relief to the local residents as well as a way to adjust the amount of capital dollars spent consecutively. Construction commenced on Phase One in January 2019
with the contract awarded to a local underground general contractor and Ward & Burke as tunnelling sub-contractor. Phase One was completed in late 2020. Following a three- year break, in December 2023, Phase Two commenced with Ward & Burke as both General Contractor and tunnelling contractor. Phase Two was completed in mid-2025, with the entire system then complete and fully operational. To maintain cleansing velocities, with current flows, only one barrel of the siphon is open; the second barrel is projected to be opened in 2039. The total construction costs were approximately
Can$100 million (US$72 million), split 70:30 between Phase One and Phase Two.
PROJECT HIGHLIGHTS Greenline light rail transit The design of the IST was completed in conjunction with a second major project proposed for the City of Calgary: a new light rail transit route called Green Line. Because of this, construction of Phase One of IST had to be meticulously coordinated in almost all shaft locations with the Green Line project team. The phasing was carefully managed by the City, Aecom and the contractors, resulting in zero delay claims.
Artpoint gallery building During a 450m-long curved drive, the IST project team had to tunnel approximately 6m (to top of pipe) under the corner of an art gallery building called Artpoint. The building was two-stories in height and did not have a basement. Coordination between the project team and the tenants of the building led to the building being unoccupied during tunnelling activities in March 2020. A vibration monitoring unit and a Building Monitoring Point (BMP)
were installed during tunnelling to monitor vibrations and settlements, with no vibration exceedances and settlements being recorded. During the week the tenants were asked to vacate, the City reimbursed the occupants per day as well as paid for 24-hour security during the period. Cost to the project was approximately Can$12,000 (US$8,800).
Sanitary main During the Fall of 2019, the project team was preparing for the longest drive of the project, approximately 860m of 2500mm-diameter pipe. The plan was to complete the drive in less than three months, finish before Christmas break. Two weeks prior to launch, Ward & Burke were completing measurements on an existing 900mm- diameter sanitary main that the new tunnel would cross, less than 3m from the face of the shaft and noted a discrepancy between the Issue for Construction (IFC) drawings and field measurements. Manhole surveys were completed by dipping the
manholes from the surface during design and indicated 400mm of clearance, which was detailed in the IFC drawings. However, on site the contractor, upon entering the manholes to verify the inverts, they found over 275mm of solid debris in the pipe not visible from the surface under flow, meaning in actuality there was only 125mm of clearance between the pipes. A risk mitigation session was held, and after reviewing
options the team chose to install a cured-in-pace pipe (CIPP) liner in the 900mm-diameter sanitary sewer. It was recommended that the CIPP liner be installed but not bonded to the concrete pipe to allow for greater pipe movement and to prevent any joint movement in the existing pipe reflecting through the liner. As an additional safety measure, the bypass used when installing the CIPP liner was left in operation while the micro-tunnel boring machine (MTBM) cleared the existing pipe and the existing pipe could be monitored. Construction monitoring and later a CCTV inspection confirmed no adverse impacts on the existing pipe. Unknown to the project team, the manhole located 5m
upstream of the crossing was constructed with a cold joint between the base and wall slabs which resulted in a frac- out in the manhole. Tunnelling operations were temporarily halted for three days while the manhole was cleaned and an additional concrete slab was poured to seal the joint. Tunnelling operations resumed with no further frac-outs at the location. Total claim for the frac-out and manhole repairs were approximately Can$46,000 (US$34,000).
June 2026 | 21
Below bottom: S MH 1-1 Phase One MTBM Reception after material removal. Existing trunk at back of image.
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