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Manholes Rehabilitation: Sometimes Misunderstood, Yet Key Infrastructure Solution
First In A Three-Part Series
Editor’s Note: This is the first of three articles focusing on the current state of manholes, manhole assessment and manhole rehabilitation. Part two will be published in the August.
The nation’s failing sewer collection system infrastructure encompasses main pipelines, lateral sewers and manholes. There exist over 20 million manholes in the U.S. of which over four million are older than 50 years and over five million are 30 to 50-years old. The manhole is a key element of the collection system, as it provides access to the pipeline infrastructure for maintenance, inspection, evaluation, renovation and testing.
Manholes have been constructed since the 19th century from a variety of different materials including brick, concrete block, concrete, fiberglass and other materials. In addition to different materials, manholes have been configured in a variety of shapes, configurations and depth to meet specific location requirements.
A manhole, also referred to as a person hole, utility hole or maintenance hole, is the access point to an underground utility including sewer, telephone, electricity, storm drains and gas pipes.
Typically sealed by a cover or grate, a manhole is designed to prevent accidental or unauthorized access to the utility system. The interiors of a manhole can be constructed with metal or plastic steps or ladders installed in the inner side of the wall to allow access by maintenance personnel. As the main access point to the collection system, a manhole must be accessible from the ground surface, and must extend from the ground surface to the wastewater pipe connections.
A manhole must be structurally sound to resist earth and groundwater pressures at various depths and be capable of resisting damage as a result of mowing equipment and other machinery, withstand constant traffic in street installations, and must be resistant to a variety of weather conditions including ground frost heave in colder climates.
Perhaps the most important requirement of a manhole is that it must be watertight, not allowing the entrance of inflow from surface runoff or infiltration from groundwater into the sewer system. In addition, the interior of a manhole must also be resistant to powerful deterioration mechanisms such as erosion, abrasion, hydrogen sulfide induced corrosion and other corrosive chemicals that occur naturally or may be introduced into the system from businesses or industries.