The smell of rain and diesel broke the stiff humid air over Placerville, Calif., on Nov. 4, 2008. Construction of the new Holiday Inn Express Gateway hotel on Highway 50 was just underway amidst the rain that began pummeling the western Sierra foothills. Richard MacFarlene, owner of Catamount Construction, began preparing the jobsite for mud. The project had been running on schedule and would have to be halted until the downpour subsided.

The large-block gravity wall design allows faster and sturdier construction compared with smaller block configurations.

The wet season returned in Northern California with a vengeance, dumping 4 inches of rain in one day on the red, drought-stricken clay soil. And more bad weather was forecast. When the skies finally cleared, a retaining wall on the south end of the development awaited construction. It was a race against time to get started before the next storm. Luckily, MacFarlene wouldn’t be pouring and curing shotcrete in the rain this year.

"Originally, we were going with shotcrete rock around the property, but I couldn’t see using a wall that looked like a freeway underpass next to the nice hotel," Brian McCommas, developer and owner of Smith Flat Construction, said. "We chose to use Jensen Precast Redi-Rock for this project. I was familiar with its architectural design, working with Richard on another job."

McFarlene credits Jensen Precast for helping make the process simple. McFarlene had purchased Jensen Precast stormwater and sewer products before knowing they were also licensed manufacturers and consultants for the Redi-Rock product.

"On my previous job, the blocks showed up and I had to wing it," MacFarlene said. "A lot of information was left out. I took the wall up and down three times working on a job in Colfax. I like these blocks, and then found out [that] Jensen Precast manufactured Redi-Rock. They took care of the planning and logistics and made sure we had the right stuff."

Had McFarlene decided not to call Jensen Precast, shotcrete would have been the retaining wall at the Gateway Hotel project. Shotcrete, a mechanically fastened retaining wall method where concrete is sprayed (shot) and reinforced by conventional steel rods, requires excavating soil, drilling, and tying reinforcements back into the earth. Brandon Shimizu, geotechnical engineer at Youngdahl Consulting Group, believes that the process used to design and build Redi-Rock walls saves contractors money and minimizes rain delays compared with shotcrete.

"Besides the aesthetic appearance, Redi-Rock helped the owners skip the additional step of hiring structural help," Shimizu said. "We could design a wall and get it approved by the city quicker using the Redi-Rock engineering software. We were trying to beat the rains, and [shotcrete] would’ve taken additional time. If the design was shotcrete, it would’ve had to be covered—you can’t place it [in the rain]."

Jeff Friedman of Jensen Precast helped coordinate the project for the Gateway Hotel. By introducing the free online engineering software to Shimizu, a variety of construction details, downloadable PDF files, and CAD drawings provided all the structural calculations required to move the design phase forward rapidly. The design software addresses seismic conditions for gravity walls, providing pre-structural calculations for a variety of soil conditions and wall heights for both gravity and reinforced walls. Technical consulting assistance was all provided in-house through Jensen Precast.

Higher gravity walls
Each Redi-Rock wall configuration can be manufactured in different sizes and shapes that weigh 1,800 to 3,400 pounds. This weight combines with a specialized interlocking system to allow walls as tall as 15 feet without using geogrid. The Redi-Rock walls are capable of greater heights using less geogrid and in shorter lengths than competitive systems, according to the manufacturer.

"Each wall has its own natural fit," Shimizu said. "This wall will be roughly 16 feet [tall]. We are only cutting back about 5 feet [for geogrid]. The size of the blocks allows you to maximize gravity wall height too. There were savings in excavation."

The weight of the Redi-Rock blocks and a specialized interlocking system combine to allow walls as tall as 15 feet without using geogrid.

Depending on soil types and requirements, alternative segmental retaining wall systems and natural rock are available but can require more excavation, and smaller blocks take longer to place. The large-block gravity wall design allows a faster and sturdier construction compared with smaller block configurations. Walls can be built much closer to property lines and installation costs are lower.

"The key thing is placing that bottom block and getting that grade," MacFarlene said. "The planner blocks make this wall work—you get the height. It all boils down to logistics and planning."

Specifications and quality control
Jensen Precast delivered the Redi-Rock block system to the Gateway Hotel site ready to be constructed. Using wall layout software, blocks were first designed then manufactured according to the construction schedule. The blocks, which have several variations, were loaded onto multiple trucks and sequenced in the manner that the contractor requested.

"The wall specifications were for 60-inch block," Friedman said. "We began the process pouring 40 blocks in one day to exact specifications. Manufacturing tolerances on the product must be exact."

Redi-Rock blocks are manufactured under controlled and consistent conditions at Jensen Precast’s National Precast Concrete Association-certified, Sacramento, Calif., plant. All Redi-Rock blocks use a minimum of 4,000-pound-per-square-inch concrete and do not have separate connecting pins that must be placed during the installation. With 5.75 square feet of face on each block, Redi-Rock requires minimal manual labor to install. By utilizing heavy equipment and larger blocks, walls will go up much faster than if using smaller blocks, saving time and money.

"It accented what was already being done with the hotel," McCommas said. "Building a shotcrete wall would have taken twice the time to build. The cost was 75 percent of a shotcrete wall. And all the engineering data is already done and on the Internet."

Jensen Precast currently manufactures Redi-Rock in the cobblestone natural rock texture, and offers coloring methods using cast-in dyes, as well as post-installation stains, to match the natural environment or customized designs.

This article was provided by Jensen Precast, based in Sparks, Nev. The company operates 12 precast concrete plants in Arizona, California, Hawaii, and Nevada.