A Solid Solution for a Lake Erie Cliff

By Karl Bremer, Versalok Retaining Wall Systems

The retaining wall was built behind the deck/stairway structure and begins at about 13 feet above the water level. It's 65 feet wide and 27 feet tall and was built in three tiers with a slight curve. Images courtesy of Versalok Retaining Wall Systems

Few retaining walls have been so complex or unique as keeping a towering cliff from crumbling into Lake Erie outside of Cleveland, and taking a million dollar home with it.

This shot is of the overall site. The top 8 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. 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, then the clay washes away and then large pieces of rock.''

About 3,000 retaining wall blocks in a blended pattern of 80 percent brown and 20-percent gray were used. A special conveyer belt system was designed to lower the blocks down the cliff face one by one; a chute alongside the conveyer was used to transport the backfill aggregate.

 


Work conditions on Lake Erie were brutal at times. Workers had to rappel down the cliff face at times to make adjustments to the conveyer that carried the blocks down. ''We had to adjust our system of transport the higher we went with the wall,'' says Andrassy. ''We had a little innovation going on. Everyone got a good workout. No matter how good you are at moving it, that's a lot of block.''

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 ''armor 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 that rose 13 feet out of the water from the base of the cliff.

''We didn't cover the rest of the cliff. We tried to get vegetation to grow but we couldn't get anything to sustain,'' says Norton. 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.

The existing seawall was used as the footing. The concrete wall extends upward for 13 feet and an 18-inch cap on top rests on a ledge chiseled out of the cliff face. The retaining wall rests on top of the cap. The seawall required about 600 cubic yards of concrete.

Andrassy started researching alternatives and determined that anchor bolts could be used to secure the geogrid to the bluff. Another course awaits geogrid, which will be tied to square steel tubing bolted to the wall face.

Using a 2.5-inch drill bit, holes were drilled 6 to 7 feet into the cliff face and anchor bolts cemented into the borings. Seventy-five holes were drilled. Then a steel bar was attached to the anchor bolts and the geogrid attached to the steel bar to secure the wall to the cliff face.

''I'd done different kinds of retaining walls-SRWs, sheetpile, seawall blocks-but 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.''

''Greg was careful about the drilling. He made sure he had plenty of depth, and in a lot of cases he probably over-drilled them. It was a pretty conservative design. Since you're dealing with some unknowns and with the nature of the rock-hard, competent rock to more crumbling rock-you've got to err on the side of caution.''

Once the footing was completed, a series of three decks was built that jutted out from the cliff and was connected to a pier on the water by zig-zagging stairways. ''With its flexible slot-and-hole pinning system, Versa-Lok was perfect for the application,'' says Norton. ''It looks awesome.''

''One of the biggest challenges of the job,'' Norton concludes, ''was explaining to people what it was going to look like when it was done. The other big challenge was getting the material down there. But I like the challenge. I don't like cookie-cutter designs.''

When you're looking at using a geogrid, you've got to have adequate space in your backfill to lock into,'' explains Andrassy. In this case, there was little room for geogrid, so a different type of anchoring system had to be used. Square metal bars were bolted into the cliff face and the geogrid was attached to them.

''The nature of the bluff face was such that the lower two-thirds was very steep, nearly vertical. The rock transitions to soil at the top, so it starts to fall back. That allowed us to bench into the existing face, so each segment has its own footing.'' Here, a workman is fabricating the steel tubing for attaching the geogrid to the bolts in the cliff face.

This was definitely not a cookie-cutter design. And it may not be the last such wall he designs, says Andrassy. ''There are all these million-dollar houses up here and none of them can get down to the water.'' That may change once the neighbors see this wall.

Project Details

Project Location: Shore of Lake Erie, OH
Contractor: NCS Construction, Brunswick, OH
Engineer: Andrassy Engineering, Bay Village, OH
Versa-Lok Manufacturer: 4D/Schuster's, Sheffield Village, OH