2023 Trenchless Technology Project of the Year New Installation Winner – Malcolm Tweddle & Edith Rogers (MTER) Sewer Improvement Initiative
The Malcolm Tweddle & Edith Rogers (MTER) Sewer Improvement Initiative was completed in June 2023 amidst challenging conditions in Northern Alberta and a delayed construction schedule due to pandemic restrictions.
After multiple major flooding events over a 20-year period for the community of Millbourne, it became a priority for the City of Edmonton to advance flood mitigation measures in the area. The project was initiated with the objective of reducing the risk of flooding during high-intensity, low-frequency rainfall events.
Microtunneling was specified for this endeavor and proved to be the star of this project. Contractor Bothar Inc. completed a portion of the overall project that included installation of 1,257 m of 3,000-mm ID reinforced concrete jacking pipe (RCJP), 217 m of 800-mm ID of RCJP using Herrenknecht TBM systems, comprised of six individual tunnel drives, 10 manholes and a number of catch basins that collect and drain future stormwater to purpose-built dry ponds during major storm events. This portion of the project cost more than US$22 million.
EPCOR Utilities (EPCOR), Bothar Inc., AECOM and the City of Edmonton worked together to overcome trying and complex obstacles that included a highly-space restrictive project site, heavy congestion of existing underground utilities and complicated logistics — all of these were accomplished over two harsh construction winters with recorded temperatures at -40 C (-40 F). More importantly, the project was completed on grade and in alignment.
For all these factors and more, the MTER Sewer Improvement Initiative is the 2023 Trenchless Technology Project of the Year for New Installation.
“Personally, I am absolutely delighted [about this project being selected Project of the Year]. I put my heart and soul into the project and I am so proud of it,” says Bothar project manager Liam Ó Cuanacháin. “Speaking on behalf of Bothar, we are extremely grateful to the selection panel, to EPCOR, especially project manager Arjun Aryal, M.Eng., P.Eng., and the City of Edmonton. It’s a fantastic achievement and a credit to everyone who put a huge effort in over the several years. It took a huge team of professionals to execute a quality project like we did.”
“A lot of hard work has gone into this project over the past eight years and success wouldn’t have been possible without the collaboration between the owner (EPCOR), engineer (AECOM) and contractor (Bothar),” says Kristin St. Louis, P.Eng, AECOM senior water resources engineer for water in Western Canada. “Such a high level of cooperation and coordination is a testament to the teams’ shared dedication in achieving the project’s objectives. The MTER project serves as an inspiring example for the industry and showcases how infrastructure development can be seamlessly integrated into establishing urban settings for the greater benefit of the community.”
Project Background
Millbourne is a relatively small residential community within the City of Edmonton, located outside of its central business district. The area is populated with homes and businesses, as well as its school district, among others. During 2004 and 2012, extremely heavy rainfall events occurred, overpowering the existing overtaxed stormwater infrastructure, forcing the water into the residents’ and businesses’ basements, as well as other damage. City officials were determined to provide a solution to mitigate future catastrophic flooding events.
AECOM was hired in 2015 and tasked with designing this project. St. Louis explains that during a one in 100-year rainfall event, an estimated 250 homes within the project area were at risk of future flooding, with ponding up to 1.75 m on an arterial roadway. Stormwater infrastructure needed to be able to convey the water away from those homes and properties and stored until the downstream system capacity could handle the excess flow. Options were limited.
“A large diameter overflow sewer was required to convey the stormwater to dual-use dry ponds in the school park [located 1 km west of the arterial roadway],” St. Louis says. “The system can accommodate a peak flow rate of 20 m3/s, while providing a safe play area for the schools and community. There were numerous constraints, including congested utilities, storm and sanitary sewers in a common trench, a pipeline corridor and ongoing light rail transit (LRT) construction.”
Ó Cuanacháin says that microtunneling was the only feasible option to design and construct the needed solution, citing two examples as to its criticality to installing the tunnels at the required depth. “The first drive we did was 835 m in length and it followed the profile of the road that was directly above it. With 9 m of cover from the road to the top of our tunnel, that’s 12 m to the invert of the pipe,” he says. “There’s no way you could open cut at that depth and under the road. We would have been blocking everyone’s local access. That would have been impossible.”
His second example of why microtunneling was selected was the third drive that crossed under a pipeline right of way and seven high-pressure pipelines. Proximity agreements were needed from all the pipeline owners to move forward with the drive. Ó Cuanacháin says those owners would not permit open cut near those pipelines.
The Bothar team proposed temporary launch and reception shafts be utilized as the permanent manhole structures. The circular segmental caisson shafts were significantly safer to install vs. conventional shafts, reduced the footprint required for excavation, limiting the overall impact to the public, which was particularly beneficial on this project as there were significant traffic restrictions at each shaft location.
Once the microtunneling work was completed, the shaft segments were utilized to support precast roof structures that in-turn supported the standard manhole riser, designed to carry the permanent traffic loads. This approach negated the need to construct a new manhole to full depth and backfill inside the already constructed shafts.
Launch, intermediate and reception shafts of varying sizes — 3.66-m ID, 6-m ID and 11.4-m ID — were constructed up to depths of 15 m to facilitate boring. Long dual curved drives followed the profile of the roads above. Bothar overcame the technical complexities of executing an 835-m long, 3,000-mm ID, 400- and 600-m radius curved tunnel drive by incorporating hydraulic joints between pipes.
Challenges
The hydraulic joints were designed specifically to match the MTER drive profiles, with unique volumes of internal fluid to match each individual tunnel radii. As the jacking pipes moved through alignment curves, the hydraulic joints conformed to ensure even dispersion of jacking load across the full thrust face without closing the hydraulic joint. Pressure sensors and length encoders were installed throughout the tunnels, which in collaboration with VMT’s TUNIS Navigation program, provided real-time feedback to the TBM operator allowing precise control to maintain line and level.
When it comes challenges, this project seemed to have one at every turn, including one right out of the gate with the global pandemic, which negated any in-person meetings between the parties involved during the design phase. Space constraints of the project location made the logistics of delivering over 400 pipe sections to the site and coordinating spoils disposal a massive undertaking.
“We had 414 pipe sections individually delivered to that site, each on a truck of their own. Each pipe was 3 m long, weighed 22 tons and had a 3.6-m OD,” Ó Cuanacháin says. “Plus, we had 80 tandem loads of spoil being removed from the site. That is a lot of coordination with the pipes going into this gate and spoils going out that gate. Coordination and planning were key.”
Space was the overwhelming challenge that had to be dealt with to get the project done. Ó Cuanacháin notes that Bothar had 10 shafts at nine different work site locations. That congestion was compounded by the large and heavy equipment required for the project; crews could only store up to eight pipe sections at a time onsite.
He also explains that the web of existing underground utilities, especially those that could not be relocated, impacted the size of the shafts, which in turn required intricate maneuvers to launch the tunneling machines. Bothar designed and engineered reverse thrust launch cylinders, whereby the Herrenknecht TBMs were effectively pulled rather than pushed into the ground to commence bidirectional tunneling. Working within a limited footprint, surrounded by the existing underground infrastructure, 6-m ID reception shafts had to be utilized. On three separate occasions, Bother crews successfully retrieved and safely removed the TBM, weighing 110 metric tons, with an outer diameter of 3.685 mm.
“That was probably one of the best achievements: the retrieval of the TBM from a 6-m shaft on three separate occasions,” Ó Cuanacháin says. “That was really, really something that took a lot of preplanning and coordination. That is something we are proud of.”
When asked what made the MTER project outstanding from her perspective, St. Louis points to that 835-m, 3,000-mm ID first microtunnel drive. “[Crews] had to follow the S-curvature of the adjacent road, with the launch shaft located in the LRT corridor actively under construction and the reception shaft situated between a condominium complex and a junior high school,” she says.
Ó Cuanacháin also cites the complexity of completing curved microtunnel drives in this project, even though they are becoming more and more common in the industry. “The fact that we did do curved microtunnels and followed the profile of the road was very important,” he stresses. “Curves are definitely an important part of most projects. The machines can do it and we have the guidance systems that can do it. You can now get from A to B and it can be a S-curve or a compound curve. Cities and clients know that and are incorporating them into their design plans to aid efficiency and effectiveness.”
Overall, Ó Cuanacháin is immensely proud of the entire project and the wider team, saying it’s not a given that everything will go right on such a complex project. “I genuinely believe that 1.5 km, six different tunnels, two different machines, each and every one of them successfully and safely launched, tunneled and retrieved from their intended locations and all six being on grade and aligned, that for me is what makes this project outstanding,” he says. “I know that is what we had to do and we executed it well. And we had no issues. People sometimes underestimate how easy it is for a project to go wrong. Here was an outstanding success from start to finish.”
Project Owner: EPCOR Utilities
Engineer: AECOM
Contractor: Bothar Inc.
Manufacturers/Suppliers: Herrenknecht, Kayden Industries, VMT/TUnIS Navigation, Jack Control, TCI, Lafarge
Value of Trenchless Project (US$): $22 million
Sharon M. Bueno is the editor of Trenchless Technology.
