ROADWAY DESIGN, CONSTRUCTION, & MAINTENANCE

Expanding possibilities

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Each year, repaving projects require Fairfax, Va., to raise and grade 25 to 50 of its 1,900 manholes.

The city's utilities department used to dig out the old rim, raise it with precast concrete rings, rebury and compact, and finish it with concrete or asphalt — still a common regrading method. Eventually the operation switched to adjustable manhole risers, but with mixed results.

“We've tried versions of expandable riser rings from several manufacturers and experienced several types of problems,” says Water and Sewer Distribution Superintendent Steve Walls, citing loose-fitting warped frames and fragile expansion mechanisms that broke or seized.

Through persistent experimentation, his team found the inclined pivoted turnbuckle manhole riser made by American Highway Products Ltd. When edge-milling removes pavement at the curb but not in the middle of a road, the riser raises and tilts the lid to match the road's crown. A flexible, galvanized steel frame outfitted with a turnbuckle, for expanding and contracting riser diameter, sets directly into the manhole rim. The turnbuckle enables the riser to squeeze inside rims and fit so tightly that rattling is eliminated. Risers can be custom-ordered according to desired thickness and diameter.

“The fact that a manhole hook and a screwdriver are usually the only tools needed is a big plus,” says Walls.

With other expandable rims, Walls had come to expect a failure rate of one or two per every 20 risers installed. None of the turnbuckle risers, however, have come loose or been broken.

“Every one we've installed in 18 years is still there,” he says.

Product: Turnbuckle manhole riser
Manufacturer: American Highway Products Ltd.
Headquarters: Bolivar, Ohio
www.ahp1.com


Stabilizing roads and budgets

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Thanks to triangular openings that create the snowshoe-like effect of evenly distributing stress to surface areas, TriAx Geogrid is able to reinforce paved or unpaved roads. Punched from a single polypropylene sheet into a grid with thick, square-edged ribs, the grid traps aggregates to create a stiff composite layer for stabilization.

In 2010, the Macomb County (Mich.) Road Commission saved $500,000 on restoring an 0.8-mile segment of a north-south artery in the Detroit metropolitan area. Situated over soft claysubgrade with no subsurface drainage, the aging pavement was rapidly deteriorating from alkali silica reaction. In addition to replacing that section, commission officials decided to turn afour-way intersection into a roundabout. This meant they also had to find a way to prevent the asphalt from rutting or shoving from constant left-hand turns.

At $1.1 million, full reconstruction wasn’t feasible. So they considered two options:

  • Patching the concrete and installing a 3-inch asphalt overlay with no base stabilization
  • Partially crushing (“rubblizing”) the concrete into a recycled aggregate base to be used with a reinforcing grid. By eliminating future reflective cracking, this option would extend service life by an estimated 20 years.

Not surprisingly, they went with the second option. A 12-inch base of recycled concrete was placed over the grid to create a mechanically stabilized layer and topped with a 7.5-inch layer of hot-mix asphalt. “We realized a sharp increase in the load-bearing capacity of the new road at no additional cost to the project,” says Project Engineer Heidi Flateau. “We now have a full-depth asphalt road with an expected service life equivalent to full reconstruction.”

To generate recommendations and cost comparisons for flexible pavements and unpaved roads, download the manufacturer’s free SpectraPave software and enter your project details. An application for use on any laptop or mobile device is available this month.

With other expandable rims, Walls had come to expect a failure rate of one or two per every 20 risers installed. None of the turnbuckle risers, however, have come loose or been broken. “Every one we’ve installed in 18 years is still there,” he says.

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Product: Turnbuckle manhole riser
Manufacturer: American Highway Products Ltd.
Headquarters: Bolivar, Ohio
www.ahp1.com