Design Approach, Inspection For Manhole Rehabilitation Technologies

3nd In A 3-Part Series
By Gerhard “Gerry” P. Muenchmeyer, P.E., NASSCO Technical Director | November 2011, Vol. 66 No. 11

Editor’s Note: This is the final installment of three articles focusing on the current state of manholes, manhole assessment and manhole rehabilitation. Parts one and two were published in the September and October editions of Underground Construction.

The design of manhole coating and lining systems must take into consideration a number of conditions in the manhole, both as a whole and as individual components. When evaluating the nature of the coating or lining that will work best, a number of conditions should be defined.

If the manhole is structurally sound but showing signs of infiltration or inflow, a combination of grouting, patching and joint seals, applied either internally or externally, might be one answer.

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If the manhole is brick and the mortar has deteriorated, the joints are leaking but display no real sign of corrosion, then a combination grout, patching, cementitious coating and joint seals might be one answer.

If the manhole is precast concrete, structurally sound but leaking at the riser joints, internal seals or grouting might be options.

If the manhole is precast concrete and the wall mortar has deteriorated and the steel cage is visible, then a wall build-back and a polymer top-coat or a cured-in-place liner might be the answer.

Many answers
There are a multitude of other scenarios that can be further illustrated but the point is, each individual manhole or group of manholes may require a specific selection of products, to accomplish a long-term rehabilitation of the structure.

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Further, it must be determined whether or not the manhole is in jeopardy of structural failure. Unlike a pipe which may go through various stages of failure leading to total collapse, a manhole is either extensively deteriorated but structurally okay, or it has collapsed. Also unlike a pipeline, a manhole is a vertical structure where the hydrostatic pressure, earth loading and live loading from the surface is constant at any specific elevation. Loads on the manhole will, however, increase at the deeper elevations.