Manholes Rehabilitation: Sometimes Misunderstood, Yet Key Infrastructure Solution

First In A Three-Part Series
By Gerhard “Gerry” P. Muenchmeyer, P.E. NASSCO Technical Director | September 2011, Vol. 66 No. 9

• Drop Inlet - Pipe Drop Inlets are special pipe systems that connect to the incoming pipe, turn 90 degrees downward to the bottom of the manhole, then turn horizontally into the manhole. These structures can be rehabilitated using available products.

Exploring the issue
As the nation’s collection system infrastructure continues to deteriorate at an accelerated rate, rehabilitation, renewal or reconstruction of the manhole component of the system become more urgent.

The nature and type of manhole defects must be evaluated to determine the best method of rehabilitation. Defects can occur in the form of structural, operation and maintenance, construction features and miscellaneous. Deterioration can be identified by a number of conditions including cracks and fractures, root intrusion, deteriorated mortar, loss of wall surface in concrete, water leakage through defects and failed joints, failed seals, poor pipe connections and more. The causes of deterioration can be from chemical or biological attack, poor maintenance, infiltration/inflow and in some cases, just old age.

Many rehabilitation technologies are available for rebuilding existing manhole structures without the need for excavation and replacement. These can include cementitious, polymer, cure-in-place, grouting, mechanical and more, for both internal and external coating, lining and sealing techniques.

The questions which arise frequently from industry professionals are: which system works best? And under what conditions and for how long? Most products and technology systems have verifiable histories of applications and longevity. Many products have been proven over time for rehabilitating specific defects, yet on occasion the installation does not perform as expected.

Questions are asked frequently about why a product has not performed as expected. Confidence in manhole rehabilitation technologies and products becomes questionable as perceived by the customer.

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