Whether poured or built, a retaining wall has to work well and look good.
Although they’re usually built for utilitarian reasons, retaining walls often surround prime parcels of real estate. The occupants of high-end condos or prestigious business complexes don’t want views of massive slabs of rough concrete—the likes of which are often seen around maximum security prisons. With that in mind, contractors and retaining wall manufacturers alike strive to create walls of both strength and beauty.
Creative Concrete
A simple poured concrete wall retains soil, but it’s not what one would call “scenic.” For a more pleasing appearance, contractors call upon San Clemente, CA’s Boulderscape, which covers the wall with shotcrete and then sculpts it to look like natural stone. In many cases, viewers have no idea they’re looking at a manufactured product; Boulderscape also creates zoo enclosures that satisfy even the pickiest rock-climbing creatures.
Human beings are wowed by Boulderscape, too. When Carlsbad, CA’s Baldwin Construction was called in to repair a wall next to a new Wal-Mart in Corona, CA, Boulderscape gave the wall a timeless look.
“This was actually a repair to an existing MSE [mechanically stabilized earth] wall that was failing,” explains President Jim Baldwin. “It had moved about a foot. We built a new concrete wall in front of it, using 300 80-foot-long tie-back anchors run through the wall.”
As hydrostatic pressure was believed to have caused the demise of the previous wall, Baldwin installed 45 hydroaugers to drain water out of the hillside. “The augers are permanent, installed 45 feet into the slope, so the soil will drain and the wall doesn’t suffer hydrostatic pressure.”
The 22-foot-high, 1,160-foot-long replacement wall took five months to complete.
“The structural concrete part of the wall is 12 inches thick,” Baldwin continues. “Boulderscape crews put on 2 to 6 inches more concrete, then carve it as they go, and then come back and color it. There’s real artistry in it—it now looks like real rock. We never put up mechanically stabilized earth structures; we just pour on concrete walls and Boulderscape does the finish.”
He adds that Boulderscape can create computer-generated samples to help customers envision what the finished wall will look like. “We use them all the time. As for our client, Wal-Mart is thrilled, and the City of Corona likes it, too. Boulderscape is really good at what they do. Their work is very visual and very realistic.”
What You MSE Is What You Get
Mechanically stabilized earth walls may be concrete, albeit in smaller doses. Instead of a large pour of liquid concrete that needs to cure, MSE systems are already “pre-cured” and ready to set up. The likely ancestors of these systems—dry-set or mortared stone walls—long ago served erosion control purposes, but their components were of inconsistent size and volume, they were very labor-intensive, and they were ineffective or useless after a certain height was attained.
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Photo: AIS Construction |
| Pre-construction slope stabilization |
However, with all its failings, stone had one thing going for it—it was “natural,” looking much like the surrounding landscape, and people admired it, as it gave them a sense of permanence and solidity. It’s no wonder that many manufacturers of MSE components give their systems stonelike facades.
For example, WestBlock Systems of Tacoma, WA, offers four styles of retaining walls. SahaleeStone, a multicolored block, is available in three sizes and features six faces and three setback settings. These blocks have handholds for ease of installation. Stonewall, a gray, one-sized block, contains a notched channel and is secured with rugged nylon pins, which allows workers to guide the block into place. GravityStone Modular, which works well in a tight residential site, can build structures up to 12 feet tall without geogrid reinforcement. GravityStone MSE, also called “Fat Face,” is a larger version for commercial applications and for walls up to 25 feet.
Soil Retention Products of Carlsbad, CA, also offers a variety of products, including the Verdura retaining wall system. Although it does not simulate a rock face, Verdura’s semicircular gray concrete block allows property owners to plant vegetation inside the block, adding beauty as well as extra soil retention. In time, many installations become lush and totally green—passersby might have no idea that solid Verdura is quietly doing its job in the background. The company’s Candura segmental retaining wall system, a gray, pebble-textured, slightly curved block, creates structures that almost appear to have been “woven.” Candura is also plantable, if desired. As it’s a four-part product system (block, capstone, cornerstone, and stake), Candura’s design allows it to incorporate stairs and seating surfaces.
Build It—and Backfill
For Summerlin, a four-story business complex in West Linn, OR (in the Portland metro area), Bedrock Excavation and Construction of Wilsonville, OR, called Lock+Load Retaining Walls of Vancouver, BC, to handle the wall work.
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Photo: Geobrugg |
| Stabilizing a steep slope with the Tecco mesh system, which can be color-matched to the surrounding soil or rock |
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Photo: Geobrugg |
“The project was on a steep hillside, which was terraced,” explains Bedrock’s Bob Carter. “My contract was all the dirt excavating and pipe work. Lock+Load subcontracted with us to make the different levels of parking. My company then did all the paving.
“There’s a Lock+Load office right across the street from us,” he notes. “There are a lot of Lock+Load walls around town. I like the system and have used it in the past.”
Lock+Load’s system consists of a rectangular stone-faced block panel, 15.75 by 31.75 by 3.5 inches, which is backed with a long, narrow leverlike anchor bound by a steel clamp to the stone face. When the system is put in place, the panel is at a 45-degree angle to the anchor; it’s then clamped into place, resulting in a 90-degree angle. Each block in the system weighs 155 pounds.
Creating different levels allowed for maximum use of the steep, nearly 7-acre Summerlin site. “It was brought to the property owners’ attention [Bill Wilt and Jeff Parker of BlackHawk LLC] that this system would work,” Carter says. “Although the Lock+Load installation went really well, we had some issues we had to deal with; there were some stairwells that had to be built, and the engineering firm wasn’t really familiar with the Lock+Load system, but I had a lot of involvement on how we changed the stairwells.”
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Photo: Keystone Retaining Wall Systems Inc. |
| Consider various facades and colors when choosing a retaining wall. |
Stairwells allow pedestrians to reach each parking level, as effective use of the site required a 10-foot rise to each parking lot. “The walls themselves were 20 to 21 feet high,” Carter says. Why didn’t he pour concrete walls? “A 20-foot concrete wall is fairly ugly,” he says. “The main reason Lock+Load was picked was the way the system looks. With their rock-faced panels, the lot looks very good.” To further dress up the site, planters were placed throughout the whole project.
Speed of construction was another advantage, according to Carter. “Yes, you can do a concrete wall with forms and patterns, but it’s expensive. Lock+Load can make nice straight runs of its system; the walls go up really fast. A concrete pour takes a lot longer, and it also has a longer cure time, so you have to wait before you can backfill. With Lock+Load, I can backfill right at the same time as they finish the wall. There are lots of advantages with this kind of system.”
Carter details some of the construction tasks. “Soil at the site was a diggable rocky soil. Lock+Load used a geogrid fabric that goes down every 4 feet, and so many feet back, depending upon how tall the wall is. Then they put crushed 0.75 minus gravel behind the wall, and then I backfilled. We also installed a drainpipe behind the wall, a flexi perforated pipe down the bottom of the wall, to catch runoff. Water runs into an onsite retention pond as required by the city. Here in Oregon, we must control the water that goes into our tributaries; it’s costly, but it’s working.”
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Photo: Keystone Retaining Wall Systems Inc. |
| Though typically constructed for their strength, retaining walls can be beautiful as well. |
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Photo: Keystone Retaining Wall Systems Inc. |
With the paving and wall building, Bedrock had to make allowances for runoff. “The system on this project has a swale where rainfall enters, and then there’s an overflow system underneath made of galvanized pipes. If the drainage system gets too much water at one time, it backs up into that overflow system. The drainage pipes are made of PVC, but the overflow system is heavy gauge galvanized steel, because it has to be watertight.”
In addition to commercial projects such as Summerlin, Bedrock does work on high-end residential sites, which sometimes have different requirements. “For example, in Lake Oswego, they don’t let the runoff go into the lake,” says Carter. “We’ve done a lot of the systems in the homes, creating swales and drainage systems, so runoff then leaches into the ground.”
The company is now working on a 10-acre project adjacent to the Summerlin site.
Grand-Scale Good Looks
Contech Construction Products Inc.’s Earth Stabilization Solutions division offers a wide variety of stone facades and colors. The Keystone 133Elite, with its 8- by 24-inch face, increases efficiency by reducing the number of units required for a job, and the components are scaled for larger-scale projects. Four finishes are available: the terra cotta–colored Ashlar, with both horizontal and vertical rectangular “stones” that resemble finished fieldstone; the Stone Face, with identically sized pieces; the Random Score, a horizontal motif with three block sizes; and the rough-cut Hewn Stone.
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Photo: Lock+Load |
| A stairwell-incorporated wall |
Keystone’s Half Century Wall, with a random-pattern appearance, resembles a natural stone wall. Three different-sized units (7, 11, and 18 inches wide) allow builders to create patterns of their own choosing. The Stonegate Country Manor features a smooth, weathered look; the peaked 24- by 24-inch KapStones, with the choice of flagstone, granite, or limestone texture, add a finishing touch to columns.
The company recently introduced a new “build-it-yourself” Landscape Series of products: Palazzo Stone, Verazzo Stone, Caprezzo Stone, and Potenzo Stone. Designed to be easy to install, the series utilizes Keystone’s molded fiberglass pin-connection system.
Over its 15-year history, Structures of Minneapolis, MN, has installed many Keystone products. “I’ve been using it since I started the company,” President Jeremy Banken says. “Before then, when I worked for someone else, Keystone was the block we used. I like the standard sizes and connections in the units. They stay aligned, and we get better production results than we do with other products.”
Structures works for a variety of clients on residential, commercial, and highway projects. “We use Keystone’s standard unit most of the time. We put up about 200 walls this year, and 80% of those were made from the standard unit. The tallest walls we’ve done are in the 30- to 35-foot range, and it works as well at that height as it does with shorter walls.”
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Photo: WestBlock Systems |
| Gray, one-size blocks for a standard look |
Emphasis on “Retaining,” Not “Wall”
If the solution really calls for rocks, Maccaferri gabions, rectangular wire mesh baskets filled with rock at the project site, are a method of choice for ERWS Inc. (Erosion and Retaining Wall Structures) of Lewisville, TX. Whether for temporary projects on commercial, industrial, and road projects or for permanent use, such as riverbank protection, gabions are flexible, permeable, and easily assembled onsite with no specialized labor needed. For sites that demand MSEs, ERWS also handles Eureka, CA’s Hilfiker Retaining Walls.
CMI (Crane Materials International) of Atlanta, GA, goes without concrete; its products are made from plastics and composites. CMI’s vinyl sheet pilings are often used at shoreline or canal sites; impervious to sea salts, the structures prevent tides from lapping nearby bluffs or hillsides away to sea. The vinyl sheet pilings also hold back and prevent those hillsides from washing over the beach.
Santa Fe, NM’s Geobrugg, the US subsidiary of a Swiss company, offers cable systems, rockfall netting, barriers, and fences. Its slope stabilization mesh system, Tecco, consists of a high-tensile, alloyed steel wire in diamond-shaped meshes that are matched to the strain conditions prevailing in the slope. Lightweight steel spike plates and compression claws are used to connect the mesh sheets. For soil or rock nails, grouted anchor bar products can be used with the Tecco system.
To stabilize steep slopes, Tecco’s unobtrusive mesh, which is available in colors to match the surrounding soil/rock, is comparable with solid building constructions such as retaining walls. For rock slopes, Tecco can be nailed in or used as a “curtain” that will guide falling rocks straight down rather than allow them to crash onto adjoining pavement.
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Photo: Lock+Load |
| Walls often surround high-end homes. |
Hi-Tech Rockfall Construction of Forest Grove, OR, performed the first US installation of the Tecco system. “We’ve been in the rockfall business since 1996. We’re licensed in 23 states,” says President Chris Ingram. “Torrential rains in 2001 caused massive mudslides across State Highway 9 near Boulder Creek, California, outside of Santa Cruz. Massive trees slid off the hill, closing the whole road. Caltrans [the California Department of Transportation] gave out emergency contracts. Someone else did the initial cleanup, and then we reshaped the slope and put in the nation’s very first Tecco anchored mire mesh system. The slope was 60 degrees when we got to it, and we reshaped to 45 degrees.
“Caltrans engineers determined what needed to be done—the length of the soil nails and how deep they needed to be to get to solid material,” Ingram continues. “Caltrans also determined the pattern and the spacing closeness of mesh. We did the mesh on an on-center, 6-foot pattern and put the soil nails 15 to 20 feet deep—not into bedrock but into competent material. Soil nails must withstand a pull-out strength of 12 tons. One has to test them, by pulling on them with a hydraulic jack system, to make sure the nails make that rating.”
What was done to such hillsides before such systems were introduced? “They just didn’t secure the soil hillsides, or they just put up a retaining wall or hoped it didn’t fall again,” Ingram says.
The Boulder Creek project required about 30,000 square feet of mesh and 2,275 linear feet of soil nails. “We used a special drill spider excavator—like a backhoe with three hydraulic legs, plus a cab with an arm on it, which grabs onto the hillside—to drill all the holes needed.”
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Photo: WestBlock Systems |
| Residents go the scenic route. |
Ingram explains the installation: “We dug an 18-inch-square depression into the hill and then put a 10- to 15-foot-deep hole in the middle of that depression. We sank the nails into the hill, laid down erosion control fabric, and stapled it into the hill. We then installed the Tecco mesh, a super-high-strength carbon steel netting, over the erosion control fabric. In the depression, we installed a spike plate, put it over the bolt, put a nut on it, and then tightened the nuts down, sinking the plates, stretching the wire to hold it all in place. That’s the gist of the system—between the bolts you hydrospray and seed it. The Tecco system has a 70-year lifespan in a salt environment.”
The system is still relatively new in the US. “I’d say it’s only used in 15 to 20 jobs per year, and I do maybe three to five of those. I can install this from coast to coast. I run into competition in New York, Colorado, and California, but we still perform jobs in 23 states.”
Rocky hillsides are stabilized with a similar system. “We do about 50 projects like that per year. We used Tecco mesh for some of those type jobs. We anchor it at the top and blanket the hillside. You can get the mesh colored so it blends in, for aesthetic reasons. For desert jobs we often use ‘Arizona Sand’ colored mesh. Colorado jobs get a dark brown mesh. As for other colors—I could probably do a US flag on a hillside. I haven’t done that yet but would like to.”