Manhole Rehab in Fort Erie, Ontario

Manhole rehabilitation done by digging and replacing an entire structure, is an outdated and expensive process of the past. By determination, innovation and engineering, rehabilitation of a manhole in disrepair can be achieved by a true trenchless solution in many cases.

A problematic manhole near the Niagara River was in a state of disrepair and the town of Fort Erie, Ontario, was faced with finding a manhole rehab solution that would restore the manhole, extending its service life for many decades while limiting the impact on the surrounding environmentally sensitive area. The manhole in question was 14 ft deep, 48 in. in diameter and was tilted due to uneven ground settlement.

This structure was affected heavily by microbial induced corrosion and infiltration. Furthermore, it can be presumed that exfiltration was present due to the existence of infiltration. The manhole was located between a stream and river in proximity to the Niagara River. Its exact location within a quiet residential neighborhood, with overhead power lines, on land rich in vegetation, as well as its proximity to many bodies of water made it essential for the rehab to be as effective as possible with the least amount of disruption to both the environment and the residents in the area. Lastly, the location of the upstream manhole was on the opposite side of the river. If a bypass was required of that upstream manhole, this would be a difficult, disruptive and expensive procedure.

There was consideration of spray liners; however, this was not the best choice due to previous issues with failures and the need to ensure a long-term solution was implemented, mitigating the future risk of further damage to the sensitive environment. Other known rehab options considered were, for this project, in some way damaging or disruptive to the environment.

If there was such thing as a clean and quiet manhole rehabilitation option, Fort Erie was excited to learn about it. Link Utility Technologies Inc., heard of this problematic manhole and the Town’s concerns and advocated for PREDL’s trenchless manhole rehabilitation solution – FLEXLINER and CORPROTECT.

Link Utility Technologies was familiar with this option, having a fully customized solution for the base, riser and cone and the fact that this product becomes a part of the existing structure rather than laying on top of the existing structure. The rehab process was also known to Link Utility Technologies and it felt confident that this structure could be successfully rehabilitated without any disturbance to the residents or environment in this sensitive area.

Link Utility Technologies proceeded with obtaining a 3D laser scan of the manhole, as well as photos and videos of the infiltration in the structure. This data was shared with PREDL’s team of engineers to review the data and, in turn, provide a digitization of the manhole, showing how much structural loss had occurred due to corrosion, and included a recommendation on how to restore the manhole from invert to cone. Once approval from the Town was received, PREDL began the process of manufacturing the components necessary for rehabilitation based upon the scan data. With PREDL’s experience, advanced technology and engineering, the team created the exact baseliner required to restore the inverts to their original form, or better since benching was often originally performed by hand. PREDL created the riser and cone sections in the exact height and diameter required out of CORPROTECT, a durable Polypropylene liner.

With all components in hand, PREDL and Link Utility Technologies partnered with Titan Environmental to complete the rehabilitation of the manhole. The rehab process of the Fort Erie manhole is described below.

The pipes are plugged, and the manhole is prepped by pressure washing to remove loose debris; any remaining solids were also removed. The installer then chipped out a portion of the existing benching according to the drawings provided by PREDL. This is a necessary step to ensure the grout can flow in behind the liner and grip into the liner as well as the existing structure.

Now the FLEXLINER (baseliner) can be lowered into the manhole. This is achieved by folding the baseliner and wrapping it with a tie strap, which is then used to lower the section directly though the opening in the cone. The FLEXLINER was then unfolded and aligned with the existing pipes and secured in place. A rapid setting mortar was used to backfill the baseliner into place. After about 10 minutes, the grout was set, and installation of the riser section could be initiated. Flow was then restored to the manhole, while the remainder of the installation was completed. The flow was only required to be stopped for approximately three hours.

The CORPROTECT risers were then also folded and lowered through the cone, aligned with the FLEXLINER base and then affixed by extrusion welding of the horizontal seam. Braces are aligned to support the liner and then the first riser was backfilled. Within about 10 minutes, the crew could proceed to the next riser.
After all risers were installed, the CORPROTECT cone was installed, much like the riser sections. Once finished, the manhole was fully lined and structurally restored. The specialized grout used to backfill the entire liner is corrosion resistant and has a PSI of more than 7,200. This manhole was ready to be under load only 30 minutes after the installation was completed.

One final step was to install the stainless-steel expanding sleeves into the existing pipes. Once set and expanded, they provided a gastight and watertight connection.

Many were surprised at how quiet this operation was, as there was no need to use large diesel pumps or heavy equipment. Furthermore, the habitat surrounding the manhole was undisturbed and not contaminated with sprays or debris.

Ultimately, Fort Erie officials were extremely happy with the outcome and whilst it was acknowledged that this rehab option was more expensive than paying for a single spray liner application-it was also recognized that this solution was going to last them many decades to come and would ultimately save them much more money in the long run.

Jennifer Mabrey is business operations manager at PREDL Inc.