Adjustable risers keep manholes at-grade in Fairhope, Alabama

Manhole Risers Case Studies July 06, 2017
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Fairhope is a small city, just 15,000 residents, situated on the cliffs and shoreline of Mobile Bay in Alabama’s Gulf Coast. It can seem like Fairhope is a long way from anywhere, but people seem to like it—the city has been named one of the best small towns in the South by Southern Living magazine, and others. Infrastructure maintenance can be a challenge here for all the usual reasons, and one unusual one—the city has a history of devastation and flooding by hurricane, including Hurricane Frederic in 1979 and Hurricane Katrina in 2005.

 

But the city does not have a problem keeping manholes at grade after roadway resurfacing projects, not in recent years anyway. “Starting about 15 years ago, a salesman came to town and showed us this adjustable riser, and we’ve been using it ever since,” explains Dan McCrory, superintendent of Fairhope’s Water and Sewer Department. “They work perfectly for what we want to do, which is keeping our manholes precisely at grade. And if we don’t use them, we get big dips in our asphalt roads.”

 

For 15 years, Fairhope has been specifying the American Highway Products’ (AHP) Pivoted Turnbuckle Manhole Riser. About 25 are installed each year, mainly by contractors during paving operations. The AHP risers are sturdy, flexible rings made of galvanized steel. They can be ordered in precise diameters to match any manhole, and in precise (increments as fine as ¼ in.) thicknesses to match paving lifts. The “pivoting turnbuckle” is an adjustable linkage that allows the risers to be set loosely in an original utility rim, then expanded with a Phillips screwdriver (used as a lever) to seat tightly and securely. According to the company’s website, “A 60-lb. force applied 7 in. from the center of the pivoted turnbuckle exerts a 5,600-lb. tangential force in the Manhole Adjusting Riser Rings that will be bent to fit the out of round, worn manhole opening.”

 

Put another way, when leverage is used properly, it is an almost irresistible force. As applied in this riser, it forces a tight fit at the right height to match new paving, and provides a new, at-grade rim for the old manhole lid. “When we have a paving project coming up, we get with the engineer of record, and we encourage them to use these risers,” says McCrory. “Over 15 years, they have a very good record of reliability here.”

 

At-grade risers are better for roads in many ways, compared to concrete ring replacement. They do not set low, so water does not collect around the manhole lid, and they do not set high, so vehicle tires do not jar the lid and rim continually. And since risers are usually set just before paving runs, the newly raised manhole is surrounded by new, contiguous pavement, and that prevents water and freeze/thaw damage in the pavement around the manhole. 

 

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