Settlement, circumferential and radial cracking, holes, and asphalt separating from around poorly adjusted manhole frames were a way of life in Kelowna, British Columbia. The failures brought inflow and infiltration, and noise complaints from residents tired of hearing ka-lunk as vehicles drove over the manhole covers.
If conditions became bad enough, an Infrastructure Planning Department crew patched them; otherwise, maintenance was ignored.
Kelly Hanson, utility technologist, was curious about the extent of the problem. His drive-by survey revealed that half the manholes had asphalt failures or the adjustment elevation did not meet tolerance. Further investigation found causes such as chimney deterioration, settling, poor workmanship, unsuitable materials, and freeze-thaw cycles.
Contractors used rocks, sticks, and metal wedges to elevate the manhole frame to final slope and grade. Hanson questioned whether those materials provided the required H-20 loading factor. They didn’t. Even metal wedges and washers produced point loads on the concrete grade rings that cracked the asphalt.
Aware of the issues, construction superintendent Wayne Nadasde designed a support ring system for the city’s standard manhole cover and frame. He took his design to Terminal City Iron Works A.C.S. Inc. in Langley, British Columbia, for casting. The adjustable manhole frame with support ring, or AFSR, was born.
Kelowna and surrounding municipalities have used the AFSR exclusively since 2005. Many provincial engineering consulting firms have started specifying them.
Safe and simple
A retaining lip on the bottom of the support ring secures it inside the grade ring, stabilizing and centering the frame during construction. A centering groove in the top of the support ring accepts four setscrews in the frame. The setscrews adjust the frame’s elevation and camber. A 1-inch-tall riser above the support ring allows the worker to apply a minimum 1-inch-thick layer of concrete under the frame.
Before installation, the worker puts graphite lubricant on the setscrews or in the tapped holes. Using string line, straightedge, site level or survey equipment, he or she matches the frame rim to final grade and elevation by turning the setscrews with a 5/16-inch Allen head socket. The threads on the setscrews are protected by PVC caps.
“Our guys doubled the number of adjustments they do in a day, and with less physical effort and risk of injury,” says Hanson. “When doing repairs, the ease and speed of installation enables us to open roads sooner.”
Over several years, Nadasde and Hanson compiled information and test data to support the invention. In their manhole investigation report, they identified criteria for manhole frame adjustment products. They should be simple, safe, stable, reusable and cost-effective, as well as install quickly, support H-20 loading, and adjust to within millimeters. The investigation confirmed that the AFSR did all of the above.
“Initially, we had two people on the string line, another lifting the frame, and one man adjusting it,” says Hanson. “Lifting is heavy work and hard on backs. The AFSR needs two people on the string line and one adjusting with a ratchet.”
Money maker
The city’s major roads have two lifts of asphalt. After the base course is laid, crews adjust the manhole frames and wrap plastic sheets around them and the support rings. They then place asphalt or concrete around the outside of the plastic and just under the edge of the frame base.
“The AFSR meets H-20 load specification without concrete support,” says Hanson. “Once the second lift is applied, a worker knocks off the manhole’s surrounding material, pops the protective caps, and turns the setscrews to readjust the frame. We save a couple hundred dollars every time we do this.”
Crews used to pour concrete around the exterior of manholes, then return to grout the interior. The design of the AFSR allows a homogeneous pour around and between the frame and support ring that eliminates future I/I issues. “Placing the concrete directly after adjustment produces sound structures that eliminate maintenance problems,” says Hanson. “The pour also fills the voids, so we save time and it’s easy to do.”
Kelowna installed its first AFSR in 2004. Since then, the asphalt around the manholes remains secure. “Our citizens are happy that we’ve addressed our maintenance issues with a reusable product, and we’ve reduced the number of work-related back strains or injuries,” says Hanson.
