Masonry Magazine October 2010 Page. 32
HARDSCAPING CASE STUDY BY KARL BREMER
Retaining Wall Ends Erosion
Versa-Lok retaining walls have been called upon to solve a lot of erosion problems. But few have been as complex or unique as preventing a towering cliff from crumbling into Lake Erie, outside of Cleveland.
The project came to Greg Norton, owner of NCS Construction Services, by way of his father, who owned a home atop a 40-foot bluff overlooking Lake Erie.
"He had a million-dollar home up there but always wanted lake access," says Norton. The back of the house is positioned only 20 feet from the bluff. However, the cliff face was eroding away, and he was slowly losing his lakefront real estate. The top eight to 10 feet of the cliff is pure topsoil, Norton explains. Beneath that is about five feet of solid clay, which turns to shale as you go deeper.
"The softer shale flakes off but it gets harder as you go deeper," he says. "The lake eats away at the base of the cliff, but it's the groundwater at the top that does most of the destruction. First the soil, and then the clay, washes away, and then large pieces of rock."
Norton and Chris Andrassy, a civil engineer with Andrassy Engineering in nearby Bay Village, whose specialty is designing erosion-control structures on the big lake, first attempted to control the erosion in 2001. After securing the necessary permits from the Ohio Department of Natural Resources and U.S. Army Corps of Engineers several years ago, they placed large boulders called "amor stones" in the lake, 20 feet from the shore, to break the wave action.
When that didn't work, a couple of years later, a concrete seawall was poured, which rose 13 feet out of the water from the base of the cliff.
"We didn't cover the rest of the cliff," says Norton. "We tried to get vegetation to grow, but we couldn't get anything to sustain."
Still looking for a solution, Norton's father wanted to use a segmental retaining wall to cover the rest of the bluff face. So Norton contacted Andrassy again.
"I'd done different kinds of retaining walls - SRWs, sheet-pile, seawall blocks but on these kinds of walls, when you're looking at using a geogrid, you've got to have adequate space in your backfill to lock into," Andrassy says. In this case, there was little room for geogrid, so a different type of anchoring system had to be used.
Andrassy started researching alternatives and determined that anchor bolts could be used to secure the geogrid to the bluff.
"I'd been interested in that technology for awhile working on these bluffs. So I went through different literature, got some data on the bond strength and ways to distribute anchorage capacity across the wall," says Andrassy. "There are probably different types of anchorages we could have used. We did hydraulic ram tests on a couple of the anchors we selected to make sure they'd hold."
Using a 2.5-inch drill bit, holes were drilled six to seven feet into the cliff face and anchor bolts cemented into the borings. Seventy-five holes were drilled, 12 for each course of block.