In Clearfield County, Penn., heavy trucks exploring natural gas formations had made Four Mile Road, an unpaved forestry arterial maintained by the Pennsylvania Department of Conservation and Natural Resources (DCNR), unsuitable for traffic. The project owner—an oil and natural gas company—needed an affordable way to restore the road and support year-round traffic volumes of up to 1,000 heavy vehicle trips per day.
Increased traffic, significant snowfall, “ice lensing” and soft subgrade soils (CBR=1.0) were causing the road to deteriorate during the annual spring thaw cycle. The project owner initially considered restoration strategies such as soil cement, a new 33-inch-thick aggregate top layer and a competing geogrid in combination with an aggregate top layer. These solutions were rejected due to concerns over environmental impact, cost and performance, respectively.
Instead, the Tensar TriAx Geogrid was used to create an unyielding, stable platform over 9.5 miles of weak access-road soils. The project owner selected the Tensar Geogrid option that incorporates one layer of Tensar TX7 Geogrid as the best solution for stabilizing the roadway for public and commercial use. This system allowed the contractor to bridge saturated and crumbling soils by placing the TriAx Geogrid directly on the existing grade.
“TriAx is our first solution for soft subgrade issues,” said Jeff Osburn, project manager for Glenn O. Hawbaker Inc. “It covers areas that can barely support equipment. It’s phenomenal how well it works.”
Osburn’s crew repaired the road crown where needed. They then covered all areas of the roadway with TX7 Geogrid and 16 to 30 in. of dense graded aggregate. Reducing the aggregate requirements saved the project owner an estimated $1.2 million in material and installation costs.
“TriAx has a high-rib profile and a unique hexagonal shape that gives 360-degree load distribution,” said Tensar International Corporation Regional Manager David Lipomi. “Its superior base confinement means you can use less aggregate and still bridge wet soil conditions.”
“The TriAx roads are holding up beautifully,” said DCNR assistant district forester Marty Lentz. “TriAx is affordable and goes in quickly, even when field conditions are terrible. It’s definitely my preferred system for upgrading the roads in our state forests.”