When discussing sewer system improvement projects, it’s often the pipe relining rehabilitation work that gets the limelight. It’s easy to see why, as these tend to be high dollar projects and often in heavily trafficked areas. However, system owners over the years have come to understand the importance of looking at the doorways to the systems as part of these large projects.
By doorways to the system, we are referring to the manholes. These access points take a lot of abuse internally in the form of sewer gases and externally based on their proximity to the roadway and other aboveground structures. Because of this environmental abuse, the manhole is quite often a major source of inflow/infiltration (I/I) to the sewer system.
As with many aspects of the trenchless industry, the last decade has experienced growth in the manhole market as owners become more cognizant of the role the structures play in I/I. Repairs include a variety of linings and coatings, cast iron and composite manhole covers and good old-fashioned cleaning programs to keep sewers functioning as intended.
In October 2020, the crews at Alberta Pipe Inspection Ltd. tackled two extremely deep manhole structures in the City of Edmonton as part of a larger deep sewer structural lining program. The manholes in question were 15 and 26 m deep and the work was completed in temperatures approaching -12 C.
For the repairs, Alberta Pipe Inspection, a Canadian licensee of McNeil Technologies’ Triplex Liner System, opted to use a cured-in-place (CIP) approach.
“The problem with these structures was sewer gas deterioration and ground water infiltration into the sewer system,” says Ron McNeil, inventor of the Triplex Liner System. “These structures were in streets and deep in the City of Edmonton. Removing and replacing could easily have cost 10 times as much or more to accomplish. It may have even been impossible in this location. Also, to remove that size structure would have taken major excavation in the street and would have traffic blocked for the entire duration of the excavation, replacement and repaving of the street.”
Because manholes – especially those of an older vintage – are often hand constructed, it’s imperative that a successful rehabilitation start with a good inspection to gain critical field knowledge. Such was the case in Edmonton, where prior to the work beginning, the manhole structures were inspected, and measurements taken so that a custom Triplex Liner could be fabricated.
In addition to good field data in advance of fabricating the liners, it is just as important to prep the structures. Like a sewer pipe CIP project, the manholes need to be thoroughly cleaned and any major sources of water intrusion be sealed with grout before the liner can be inserted and steam cured.
“Cured-in-place liners provide total resistance to sewer gases and a halting of further infiltration and deterioration. There is also the benefit of minimal disruption of traffic which is much less inconvenient to the public,” says McNeil. “These are very large structures, and the city chose a more permanent solution in this very corrosive environment. Other spray- and hand-applied methods are less permanent. Additionally, these structures are so large that the danger for personnel entry into the depths of the structure [for a hand-applied repair] is great.”
Because of the design of the Triplex Liner System, man-entry into the manhole structure was not needed. McNeil, along with his son Ryan McNeil, mechanical engineer and CTO of McNeil Technologies, were on-hand to help Alberta Pipe Inspection with this complex install.
Each install took one workday. The liner was wet-out with a proprietary epoxy resin and lowered into the manhole structure. In this case using a crane. Once in place, the liner was inflated using an internal inflation bladder and steam cured. The McNeil team used a dual pulley system with a 2,500-lb. test line to put the bladder into place and to remove the bladder when the liner was cured.