Chattanooga integrates pavers with urban design
Planners in Chattanooga, Tenn., regard their downtown as the city’s “living room.” Consequently, the city of 153,000 has worked hard to restore and expand its downtown area by developing attractions including parks, gardens, museums, theaters, a zoo, a convention center and an aquarium.
The city has installed more than 350,000 square feet of interlocking concrete pavers (ICPs) over the past several years in an effort to unify downtown’s attractions and tie together the miles of sidewalks. ICPs, which use interlocking segmental units fitted tightly together over a granular base, date back more than 5,000 years. Romans built transportation systems with segmental paving technology, and, centuries later, the British used interlocking Yorkshire stones for roadways in many cities and towns.
“The ability of concrete pavers to be replaced after repairs to underground utilities was a key consideration for sidewalks and crosswalks,” says Stroud Watson, Chattanooga’s planning and design director. He says the pavers can reduce costs because expensive equipment is not required for removal, the pavers can be reinstated after the repair, and traffic interruptions and delays are minimized. Further, removing ICPs causes no damage to surrounding units, and the pavers leave no visible patches to detract from the aesthetics.
Scott Copley, an engineer with Chattanooga’s Engineering Division, has researched studies on the structural contribution of interlocking concrete pavement to the entire pavement cross section. He says pavers and underlying materials respond as a flexible pavement, distributing loads to the base and soil subgrade in a manner similar to that of asphalt, albeit without the hot weather softening and rutting of asphalt.
Those qualities are important to Chattanooga, he adds, since most of its major streets handle from 15,000 to 20,000 vehicles per day, between 5 and 10 percent of them trucks. Because the city is located in a river valley, the soils in the downtown area are slow-draining, silty clays. The latest intersection design included 3-inch-thick pavers, 1 inch of bedding sand and a 4-inch drainage layer of open-graded asphalt, all on top of a 12-inch layer of 5 percent cement-stabilized base.
American Association of Street, Highway and Transportation Official design guidelines emphasize that drainage of the pavement and the soil subgrade can extend pavement surface life. Consequently, Copley has incorporated drainage into Chattanooga’s latest intersection designs to reduce the need for future repairs and stretch the taxpayers’ investment.