Retaining wall abutments shorten bridge span

By: Kevin Loe

When a development in Lenoir City, Tenn., required a new bridge, the owner wanted to do something different than a standard reinforced earth wall for the abutments.

“The owner needed a wall to contain the abutment fills so the bridge could be shortened to a single-span bridge. If retaining walls for the abutments had not been used, a much longer three-span bridge would have been needed,” explained Blalock Ready Mix’s Dale Dockery.

To shorten the span of the bridge, the general contractor proposed a precast, massive retaining wall system called Redi-Rock for the job. The developer liked the aesthetics and the design of the Redi-Rock system and chose it as an alternative to a conventional tie-back system or conventional concrete cantilever wall bearing on piles.

The retaining wall system utilizes massive, one-ton blocks to harness the power of gravity and build taller walls that often don’t require reinforcement, and even taller walls with reinforcement.

“There was a stream with an existing sewer line near the stream embankment that would have had to be moved if a conventional tie back or conventional concrete cantilever wall bearing on piles had been used,” Dockery said.

The blocks are available in three textures, including Limestone, Cobblestone and the new Ledgestone textures to give walls the “essence of natural rock” look. For this project, Limestone-textured blocks from Blalock Construction gave the abutments a polished look.

“The walls looked fantastic in comparison to the standard reinforced earth walls that are commonly used in bridge abutments. It was easy to install, it was easy to engineer and there are a lot of options for finishes,” explained Robert Saunders, P.E., of GEO Services LLC.

The retaining wall system is easy to install because crews simply use a piece of heavy machinery to stack the interlocking blocks like giant Legos.

“There are sections of this wall that were left gravity and the program (Redi-Rock Wall Analysis Software) definitely helped in engineering it. For the reinforced sections, we used the NCMA program (SRWall),” Saunders added.

The abutments were built using 28-in. blocks (measured from face of block to rear) and stand 16 ft high at the highest point, are 100 ft long and encompass a total of 5,700 sq ft. The sections of the walls that are reinforced utilize geogrid in every other course.

To install, the walls had to be excavated to the bottom of the wall elevation, then the abutment bearing piles had to be installed in the reinforcement zone behind the walls before the wall backfill and reinforcement could be placed.