The District had a list of approximately 50 manholes that required attention. Using a traditional concrete grade ring system made this project look daunting for the District as the manholes were spread out amongst remote locations, off-road.
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Matt Pirrotta, technical sales for Martech Inc. met with District of North Vancouver utilities supervisor Chris Alexander to discuss the advantage of using the PRO-RING Manhole and Catch Basin Adjustment System over traditional concrete. Alexander saw an opportunity for the product and quickly gave the go-ahead for a demonstration on one of the District’s many manholes that required rehabilitation. The manhole was located in a residential area on Arborlynn Crescent in North Vancouver and tucked away in the back yard of a residence.
The PRO-RING system, from Cretex Specialty Products, of Waukesha, Wisconsin, consists of black expanded polypropylene (EPP) rings with a standard inner diameter of 609.6 mm and outer diameter of 914.4 mm. EPP is an engineered plastic that is lightweight and has a very high strength-to-weight ratio. PRO-RING can withstand repeated impacts without damage, resists water, most chemicals, and withstands temperature extremes from -35 C to 129.44 C. A traditional concrete grade ring would require up to four men to lift, while a 152.4-mm. thick PRO-RING unit weighs 6.35 kg – one man can install the system in a few minutes.
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The system features grade rings, finish rings and angle rings. Grade rings are used to raise the manhole to within an inch or two of the final elevation. A finish ring is applied in the final layer between the grade rings and the reinstalled manhole frame. Angle rings are used when the surrounding surface is sloped.
Grade rings have one deep and one shallow groove on the underside and a single corresponding tongue on the upper side. The tongue and groove fit together so that rings align precisely when they are stacked. Finish rings have only the grooves on the underside. The upper side is smooth to enable maximum surface contact, and therefore a maximum seal, with the underside of the manhole frame. There is also a groove on the top inner diameter of the finish ring and is designed to accept the angle ring. The entire ring system is assembled and bonded together using a construction adhesive to create a watertight, testable system.
The PRO-RING proved to be effective in this application, allowing crewmembers to handle the rings without any risk of injury. Aside from the obvious ergonomic benefit that the PRO-RING provides, the District crews spent less time on the job site, using fewer materials and a smaller crew.
With the positive outcome of this trial run, the District made the decision to go with the PRO-RING system instead of using traditional concrete. The key here was using a system that was ergonomically beneficial due to remote access of off-road manholes.
In addition to this, the District is now using a system that has a minimum design life of 50 years, which will outlast traditional concrete. The District of North Vancouver will complete the remainder of the project in the spring and summer of 2016.
Martech Inc. submitted this report.