Don't pour a wall, spray it

Wonder what that hose is spraying on the new Remount Road off-ramp on Interstate 26?

It's a wall. A 100-ton concrete wall.

The retaining wall for the eastbound off-ramp by the Bank of America building is being built with Shock-crete, a new generation concrete application that uses air pressure and a pump to spread a congealing mass of the liquid stone.

It's a quicker way to set a wall than erecting forms and backing up the cement truck.

"You pump it and then blow it on," said Shane Garrett, supervisor for Wurster Engineering and Construction, the subcontractor building the wall. The process is a little messy, he concedes, but it gets the job done.

The wall is one of six types that will be built along the project's three-mile length, per S.C. Department of Transportation specifications.

That's an unusual variety for this size project and maybe a harbinger of the engineering to come as the busy metro stretch of I-26 becomes what observers say could well be the first real densely urban highway in the state.

The built-by-spraying structure is actually called a "soil nail" wall.

A series of 12-feet long rods, or nails, are driven into the dirt bank behind it, then the Shock-crete secures them.

The resistance between the two holds back the earthen bank. A brick face will be built over the wall.

"It's more efficient, more cost-effective and more cost-effective in long-term maintenance," said Greg Cook, vice president of U.S. Group, the construction company running the project.

"If you had a rigid concrete wall, it would crack and have to be repaired."

Other walls called for in the project include sheet pile walls that are driven section by section into the ground and a mechanically stabilized wall built to hold fill dirt using reinforcements in the dirt.

The work is part of a three-year, $66 million project to widen the interstate to eight lanes in a stretch from Interstate 526 to Ashley Phosphate Road, where rush-hour traffic routinely jams.