The success of any trenchless pipe rehabilitation project demands initiative and cooperation to foresee and resolve challenges. This has been especially true in 2020 with the onset of the global pandemic.
While no one could predict and prepare for COVID-19 in August 2019, it was then that Clean Water Works Inc. (CWW) was focused on finding cost-saving solutions in its bid – and subsequent contract award — for City of Toronto tender call No. 44-2019 for the Large Diameter (Non-Circular) Sewer Rehabilitation by CIPP. With AECOM and Robinson Consultants as contract administrator, the team was ready to start the project for Toronto Water in February 2020 with liner installations scheduled from March to May 2020.
Decisive actions from CWW management under the leadership of Paul McCarney, president and CEO, were crucial in keeping the project on track during these unprecedented times.
“At all levels, CWW quickly introduced and maintained measures to address the health & safety risks posed by COVID-19,” said McCarney. “While the world was shutting down, CWW understood the importance of essential work on critical infrastructure and we continued to move forward with the highest regards to safety.”
The accessible part of the project was completed on budget and ahead of schedule earning CWW an early-completion incentive. What sets this project apart is not only the challenging timing in which it was delivered but more so the multiple site challenges it presented. Versatility in CIPP methodologies was key in overcoming these challenges.
Coordination Is Key
Pipe access was a common issue with all 40 sewer sections and 2,286 m included for CIPP rehabilitation. Sewers were in downtown Toronto, within close sight of the iconic CN Tower and surrounded by high-rise condos.
“We anticipated the high level of coordination that would be required. It was important to plan each task carefully to minimize impacts to businesses and residents while respecting time constraints issued in road-occupancy permits,” said Amin Shojaei, CWW project manager. “The contract covered large sewers of egg-shape and oval profiles ranging in sizes from 500 by 750 mm to 1,050 by 1,500 mm. While the traditional method for CIPP lining of large diameter sewers is water-inversion and hot-water-cure, this option would require up to 48-hour around-the-clock and didn’t fit in our construction time windows. We opted instead for the air-inversion and steam-cure method for most liners thus minimizing our site occupancy.”
Quality control measures, including liner temperature monitoring during cure, enabled crews to proceed with the steam-cure alternative while ensuring the highest standard of quality during construction.
The cure method was not the only variable in selecting the best-suited lining method for each location. This project included other CIPP solutions such as “hybrid” liners, “blind-shot” liners and “transition” liners. But before any liner could be installed a significant amount of pipe preparation was needed.
Keats Ling, CWW Quebec general manager and his Montreal-based team jumped at the occasion to work in collaboration with Shojaei and the Toronto-based crews. “In the last nine years, we’ve completed approximately 15,000 to 20,000 m of man-entry sewer work yearly in the Montreal area,” said Ling. “Our crews’ expertise is unmatched, and we knew we could rise to the challenge in Toronto on similar work.”
Pipe CCTV footage showed heavy calcite that needed to be removed before liners could be installed. Man-entry crews crawled the pipes and tirelessly cut and removed the debris. Anchors were drilled-in at service connections for rapid re-instatement of services, voids were filled, infiltrations were grouted, and sewer walls were repaired in preparation for lining.
Material and Method Selection
Two CIPP material systems were employed – a conventional felt-resin liner system and a “hybrid” liner system. The “hybrid” liner, as CWW calls it, is a fiberglass-reinforced felt-inversion liner that offers enhanced mechanical properties. It blends the benefit of the felt’s flexibility needed for the inversion with the enhanced mechanical properties of fiberglass typically found in more rigid pull-in-place systems. A hybrid liner was ideal for an installation on Jarvis Street. This was the largest sewer section of the project – an egg-shape of 1,050 by 1,500 mm with a length of 155 m. A conventional felt-resin liner of 50-in. nominal diameter with a 42 mm thickness would have been required. A constructability issue was identified by CWW as the weight of the liner exceeded the limit that could be transported from wet-out plant to site. An over-the-hole wet-out was considered but ultimately the hybrid liner solution prevailed.
“With another contractor working on a site nearby, our window of opportunity was insufficient to set up a wet-out plant,” said Shojaei. “We opted for the hybrid liner because its superior mechanical properties resulted in a 31-mm thick liner design with a weight that could be transported to site.”
The term “blind-shot” describes a liner installed from one end with limited or no access to the other and the inversion can’t be seen. At two locations on this project, the downstream manhole was positioned in the middle of Toronto Transit Commission (TTC) tracks. To avoid interrupting the City’s public transportation, limited access was granted in proximity to the tracks.
“We were on Queen Street and John Street where lane occupation was very strict. A water shot was not an option due to the time needed for hot-water curing,” said Shojaei. Troy McCarney, CWW operations manager, was quick to find a solution. “A blind-shot is common with water, but not with steam yet that’s precisely what we did,” he says. “There are definitely some limitations to this technique due to the need to circulate steam through the entire liner and releasing it back from the same access point. As steam travels, it cools and condensates, so length is an important factor.”
Crews adapted the blind-shot lining method to air-inversion and steam-cure. With proper quality control, CWW successfully achieved the results expected from the more traditional water inversion blind-shot while public transportation went uninterrupted.
Brick Sewer Challenges
Brick sewers present additional challenges. Dimension changes are common, sewers bend and often tie into larger sewers downstream. Maintenance holes are typically brick chimneys and are rarely positioned directly at these connections or dimension changes. This is exactly why a section on Queen Street required another adapted CIPP solution.
This egg-shaped sewer section had a sweeping 90-degree bend followed by a diameter change before bending again and tying into another line with the nearest chimney 10 m downstream from the node.
“A transition liner was needed to accommodate a diameter of 30 to 39 in. The multiple bends further complicated the installation because the liner stretches differently in the inner and outer radius of the bends, so lining up the liner transition precisely with the pipe’s dimension change was challenging,” said Troy McCarney.
Armed with years of experience, the CWW team succeeded in adapting yet another CIPP solution to renew an oddly-configured brick sewer section.
Large diameter CIPP projects require a great deal of planning and no single CIPP solution is suitable for every application. When non-circular profiles and limited access to structures are also factored, the overlapping challenges can significantly increase the complexity of the project. Through initiative and collaboration, CWW displayed the versatility of CIPP solutions which ensured value and an overall successful delivery of this project to the City of Toronto.
Nicolas Brennan, B.A.Sc., is chief estimator and technical advisor at CWW.