Manholes near collapse
Rehabilitation of manholes near collapse
Glynn County Engineering Services, Brunswick, GA – Robert Bowen, Engineer III
St. Simons Island, Georgia
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.
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.”
Upper Left: Photo reveals severe deterioration and complete failure of a rehab coating. According to Bowen, “Utility contractors judged these manholes to be beyond repair and in need of immediate replacement.”
Upper Right: The photo of the finished product shows a monolithic cured structural liner now protecting the interior surfaces, structurally restored and working like new.
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.”