Plots of land are rarely flat enough, high enough or big enough to build on and that's where the retaining wall comes in. Creating a buildable plot while holding back tons of dirt is what retaining walls do.
Joseph Walker, president of Walker Risk Management in the City of Fairfax, knows the retaining wall industry. With some walls measuring over 20 feet tall and hundreds of yards long, it's no longer a matter of putting up a few railroad ties battened down with rebar. Weight, pressure and drainage have to be considered. That requires engineers, soil tests and inspectors.
"There's a lot of work that has to come together," Walker said. "It's more engineering and common sense."
A wall in Fairfax Corner extends over 100 yards, building up a plateau to the Wegman's grocery store site. The wall was built by Metroplex Walls Inc. of Leesburg. Bob Kelly of Metroplex has faith in his wall.
"They don't move," Kelly said. "We've never had any problems with any walls."
Metroplex Walls tested the soil first and then had its structural engineer in to finalize the plans. A structural engineer is a specialized position.
"They have to be certified in the state you're building in," said Kelly. "Engineering generally only takes a couple of weeks."
THE WALL in Fairfax Corner is fully grouted and outfitted with "weep" holes for drainage. Weep holes are a necessity in retaining walls, but they aren't the only way the water is prevented from building up behind the mason work. The land is piled slightly higher in the middle so the water flows off to the side.
"It's an engineered wall, generally the water dissipates or goes left or right," Kelly said.
Walker Risk Management specializes in unseen walls, which are out of sight, or timber tie retaining walls, or interlocking concrete blocks. They all have material anchoring the wall to the soil.
"The wall has to have a force to keep from coming out. They factor in the soil and loads on top of the soil. Virtual weights go down to the soil and shoot out at a 45-degree angle. All that's got to be considered," Walker said.
TECHNOLOGY PLAYS a factor in to today's walls. Walker's company has rebuilt old walls as well. Those walls didn't have the engineering that today's walls are required to have.
"Nearly every retaining wall done in the 1940s were done by Portuguese stone masons," Walker said.
A basement wall is a retaining wall to some extent, Walker added. A leaky basement is really a natural seep hole forming on its own.
"Water is definitely the main culprit in walls failing," Walker said.
In Fairfax County, if the differential elevation in a residential retaining wall is 2 feet or more, a building permit and inspection is required. The differential elevation is the difference between the desired plateau and the low point on the slope. Different criteria are in place for retaining walls in residential and commercial settings, said Steven Turchen of the Fairfax County Building Plan and Review Division.
"If they're permitted, then we'll inspect them," Turchen said.
The Fairfax County Web site (www.fairfaxcounty.gov) has guidelines on residential retaining walls.
"The county actually has some suggested designs," Turchen said.