From the "heaving" soils of the Fayetteville shale to sinkholes in the karst terrain around Eureka Springs, what's underground should be considered before building aboveground in Northwest Arkansas, two experts said.

"Pay me now or pay me later," said Thomas Aley, president of the Ozark Underground Laboratory in Protem, Mo., a consulting firm that does groundwater tracing studies. "I don't think you save money by ignoring potential problems."

Aley said people don't always take the subterranean features into consideration when projects are planned.

"The desirable thing would be to design with the land rather than construct structures and then during the construction, or later, discover that they create a problem that you have to try and repair," Aley said. "It often gets missed in regions of the country where planning and zoning is not very strong, where you don't have regional planning entities or not enough development going on to learn that 'Hey, these things can bite you and we ought to take care of them.'"

Stephen Boss, director of the Environmental Dynamics Program at the University of Arkansas at Fayetteville, agreed.

Many buildings in Fayetteville have cracks in their foundations because clay in the soil expands and contracts, Boss said. Buildings on concrete foundations probably have fewer problems than those with a basement, he said.

"Structures built on expansive soils commonly heave, displaying differential movements that result in simple cracking as well as vertical and horizontal displacement," according to a paper by Boss and two colleagues published in the Journal of the Arkansas Academy of Science in 2001.

Also, soil is slowly sliding downhill, Boss said. It's a phenomenon known as "downslope creep" and is common across the country in hilly towns with shale underneath.

On a recent tour of the Hyland Park subdivision in east Fayetteville, Boss pointed out the leaning light poles.

"They weren't leaning like that when they were put in," he said.

Across Fayetteville, many retaining walls are leaning because the earth they're attempting to retain is trying to slide. An example is a large concrete retaining wall on the west side of College Avenue, just north of Prospect Street.

While Fayetteville and Springdale have distinct personalities above ground, the differences underneath the adjoining cities may be even more dramatic, said Boss.

Springdale is built on a plateau that is part of an underground limestone formation, which stretches north and east through Northwest Arkansas.

Erosion of limestone can cause subterranean karst features such as springs and caves, according to the U.S. Geological Survey.

By contrast, Fayetteville was built on the Fayetteville shale, which got its name because it's visible in the college town. The shale can be seen jutting from a hillside behind businesses along the east side of College Avenue. From there, the shale is deeper underground across much of Arkansas.

Walter Jennings, a Fayetteville architect, said his firm encourages clients to have a geotechnical report done before beginning construction.

"This can identify problems early, but even then you are limited in the amount of bore holes you dig," Jennings said via email. "Sometimes problems lie between the investigations."

Almost all of the projects done by Maurice Jennings + Walter Jennings Architects PLLC have geotechnical reports before construction begins, he said. Walter is Maurice's son.

"That lets us know if we have any surprises, and it reassures us that the bearing capacity of the soil is suitable for our design," Walter Jennings said. "Several of our projects are on hillsides and/or close to rock outcroppings. These conditions can pose problems, so that is another reason we have geotechnical reporting done."

The pros and cons of such studies are discussed with clients, and so far all have opted to get a geotechnical report, Jennings said. Having a geotechnical study on a residential lot costs about $2,000, he said.

Philip Taldo, co-owner of Weichert Realtors-The Griffin Co. in Springdale, said developers in Northwest Arkansas usually have soil tests done before streets and utilities are put in.

"Normally, before anybody does a subdivision, you go out and do soils tests," he said, referring to a geotechnical report. "You see what kind of soil there is, what kind of challenges there may be to doing the construction and building the streets. ... Basically, by the time it gets to be a lot, it's been pretty well checked out."

Taldo said he's familiar with problems that can crop up from underneath.

"It's seldom a problem, but when it is a problem, it's a big problem," he said.

Concerning the Hyland Park neighborhood in Fayetteville, most of the houses there are built with pier-and-beam construction instead of on slabs, Taldo said.

"Most of the time those houses have drilled-down piers and beams to hold it up and keep it from sliding down the hill," he said.

Taldo said it's not uncommon to have cracks in the foundation of houses in Fayetteville. Such things should be checked by a building professional, but structures are often sound even if they have some foundation cracks, he said.

Aley did a study in 1998 and 1999 of water flowing underneath Hobbs State Park Conservation Area in Benton County. Based in part on the study, the park decided to move the location of one maintenance building on War Eagle Road, said Mark Clippinger, the park superintendent.

Aley will be speaking on the topic of tracing and protecting underground water at the Hobbs State Park visitors center at 2 p.m. today. Admission is free.

NW News on 05/19/2014