Grade Adjustment Rings

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Definition - What does Grade Adjustment Rings mean?

Grade adjustment rings are circular or square shaped ring sections that are used to adjust the overall height of a manhole such that the manhole lid is flush with the roadway surface. These rings are usually constructed from steel or reinforced concrete and are available in specified thicknesses. Several grade adjustment rings may be vertically stacked to achieve the desired manhole lid elevation.

Grade adjustment rings are also known as adjustment rings or extension rings.

Trenchlesspedia explains Grade Adjustment Rings

Grade adjustment rings are ideal for increasing the elevation of manhole lids, especially during road resurfacing works. As the elevation of the road increases after resurfacing, additional adjustment rings can be added until the manhole lid and the finished road surface are at the same level.

Grade adjustment rings are considered to be the weakest part of the manhole structure. Increased traffic loading, freeze and thaw cycles, impact loading from vehicles, and other cyclic loadings can result in deterioration of the adjustment rings. This can eventually lead to the infiltration of soil and water through the ring interfaces which can result in settlement, cracking of the roadway surface, or structural failure of the manhole.

Several trenchless techniques are used to rehabilitate deteriorated grade adjustment rings. These include:

  • Cured-in-place pipe (CIPP) liners
  • Internal and external joint seals and wraps
  • Lid plugs and gaskets
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