Case Study - Manhole
Client
Glynn County Engineering Services, Brunswick, GA - Robert Bowen, Engineer III
Project
Rehabilitation of Manholes - Near Collapse
Location
St. Simons Island, Georgia
Description
Traffic on one of the island’s major streets was increased because of a major road realignment project. Robert Bowen
inspected manholes there and saw that they were on the verge of collapse. According to Bowen, “Time was a very important
factor and there was not a large budget for repairs/replacement. Because of new pavement and landscaping in the area,
disruption of pavement, traffic, grass or utilities was not possible. The manholes were on thirty (30) inch gravity main and
therefore by-pass pumping was not a viable option.” As with many low lying coastal areas, St. Simons Island’s sewer
collection system was attacked by sewer gases and infiltration. Bowen explained, “The major cause of manhole deterioration
is H2S corrosion from the inside, causing structural damage. This damage in turn allows intrusion from the high water table
to accelerate the damage and eventual failure of the structure.” He cited "high water table, low elevation, and salt environment"
as key issues that must be dealt with in maintaining such an environmentally sensitive area.
Benefit
Value engineering has both short and long term cost effectiveness. Bowen concluded, "Poly-Triplex liners allowed immediate
significant cost savings. Without this type of structural liner system and non-invasive installation method, Glynn County
would have had to by-pass pump a large gravity main into the wastewater treatment plant, dig and replace four manholes."
Photos
Comments
With many utilities strapped with aging infrastructure and limited budgets to provide preventive maintenance, choices in
rehab materials and methods are crucial. When asked his recommendations, Bowen advised, "Cheaper is not better. Spend your
manhole maintenance budget on quality products, because you do not want to have to fix the same hole twice."
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