Retaining Walls: Safety can be beautiful
|By Larry Bernstein|
Thanks to today’s materials, a retaining wall can be as attractive as it is functional.
As any parent of a teenager knows, one of the hazards of the job is repetitive stress disorder in one’s index finger. It comes from wagging it so much, reminding them to “be practical” about whatever it is they’re choosing, from a new coat to a college major. How something looks, or its “coolness factor” among his peers is often more important than whether it keeps him warm or results in a job after graduation. It takes life experience to choose practicality over appearances. Occasionally though, both desires can be served by the same object.
This is true of a retaining wall. Although it’s the very epitome of practicality as a hardscape element, its function made clear by its very name, a retaining wall needn’t be boring or humdrum. It can be both beautiful and practical all at the same time and even enhance a landscape design.
But first, safety
The purpose of a retaining wall is to hold soil back (in the case of a hillside, a massive amount of soil) so it doesn’t bury someone’s business or home under tons of mud. That sounds simple, yet it’s complicated. A retaining wall that does not keep an area safe from the soil it’s supposed to be holding back is useless and even dangerous. Hence, the multiple codes and restrictions that states and municipalities have created regarding the installation of retaining walls. In Massachusetts, for instance, any retaining wall over 4 feet tall must be designed by an engineer.
And people want safety, or at least, the feeling of it. Aaron Wiltshire, owner of Oklahoma Landscape in Tulsa, estimates that he and his team put up 50 retaining walls every year. “People are very cognizant of safety factors when it comes to retaining walls,” he says. “That’s why people want lighting installed and railings put on top as well as wanting to adhere to codes.”
Drainage is one safety factor that most people who aren’t involved in construction work don’t know about but is crucial when it comes to building retaining walls. When a retaining wall fails, it’s almost always because of water. Hydrostatic pressure — a fancy way of saying “a buildup of water” — behind a retaining wall will eventually knock it down. That’s why proper drainage is essential.
Installing retaining walls is a complex task. For one thing, no two job sites are exactly the same. A number of factors need to be considered, including “rise over run” (a mathematical formula for determining the steepness ratio of a slope), the pitch and the grade.
Many, many materials
A well-engineered, well-built retaining wall can be costly to install, and it’s important to explain that to the customer. A retaining wall is not something one should cut corners (or costs) on.
Retaining walls can be built out of many different natural and manufactured materials. There’s segmented concrete block, split-faced block, wood, boulders, natural stone, gabions, brick, even a type of engineered foam.
While natural boulder and natural rock walls tend to cost more and can be more challenging to work with, some customers are willing to pay the extra price. If the aesthetics of the home or business are conducive to natural rock, it’s a viable option. Another way to go is build a wall out of another, less costly material, such as concrete block, and face it with stone veneer.
“Natural stone is sometimes requested by those clients who want a specific look or those who think it blends well with their house,” says Robert Welch, a manager and foreman at Mt. Baker Landscaping, a family-owned business that operates primarily in the Bellingham, Washington, area. Building retaining walls is one of its specialties. “They’re willing to spend extra money to get that kind of retaining wall.”
The large number of materials that can be used for a retaining wall is a boon to those who need or want one and makes for a wide spectrum of price points. This allows just about every customer to find something that fits into his or her budget, and those materials at the higher end of the cost spectrum aren’t necessarily any more durable than those at the lower end.
Back in the 1970s and ’80s, many retaining walls were built out of discarded railroad ties. As the century came to a close and we moved into the 2000s, interest in railroad ties as a material for retaining walls had passed; part of the reason for that is the toxic chemicals they contain. “The railroad ties were rotting, and people wanted something that doesn’t have to be replaced,” says Wiltshire. “If built right, a retaining wall shouldn’t ever have to be replaced.”
Minnesota-based Genadek Landscaping and Excavating Inc., specializes in building large structural retaining walls. The owner, Stan Genadek, who also trains contractors through his Dirt Monkey University, says big concrete blocks with the appearance of natural stone are gaining popularity for residential properties, not necessarily due to their appearance but more because homeowners have seen them holding up on larger-scale projects. And by big, he’s talking massive. One product has a face dimension of 16 inches by 48 inches and weighs between 1,400 and 4,100 pounds.
“They became popular because of big, state-run projects,” he says. “Residents see them and think if they’re great for those massive jobs, then they must be strong enough to keep my home safe, too.”
Material preference is often influenced by location. Wiltshire says natural boulders are popular in Tulsa, and Welch says Allan Block, another segmental retaining wall product, is big in the Pacific Northwest.
Safety, durability and practicality; check, check, check. But simply slapping up any old retaining wall to hold back the soil won’t cut it for most property owners these days. For many, the decision comes down to aesthetics; they’re trying to create a look for their home or business and consider a retaining wall an accessory, albeit a practical one. “Customers don’t know much about retaining walls,” says Genadek. “They just want something that looks good.”
The aesthetics associated with retaining walls are not just about the types of materials used to construct them. Simply wanting one in the first place can be an aesthetic choice. Some people want a wall to cut a hill away and create a flat spot. Others want to create elevation changes to break up flat ground. Others want them as backups to a built-in seating area in an outdoor living space.
“There’s not always a purpose that I can see for them,” says Welch, whose primary customer base is residential. He only recommends a retaining wall when there’s a distinct need because they are not cheap to build.
The turn toward appearance considerations is relatively new. Wiltshire says, “Newer homeowners spend more money and want things that are not only functional, but that are aesthetically pleasing and creative. And while they’re willing to spend more, their expectations are higher, too.”
This trend offers an opportunity for contractors and manufacturers alike. Versa-Lok, Oakdale, Minnesota, pioneered the solid, pinned segmental concrete retaining wall system and licenses the product to manufacturers around the country. Though its main markets are commercial properties even they are paying more attention to the aesthetics of its products. Versa-Lok is striving to meet that demand.
“Our Mosaic product is made from solid units, which comes in different widths and heights, and was designed with a premium look,” says Karen Nelson, engineering services manager at Versa-Lok, says. Blended colors are also becoming quite a popular option.
It’s a good business
Genadek says, “Once you understand how to build retaining walls, you have more options as a contractor. It’s a way to separate yourself from the pack.”
That’s been true for Wiltshire, who says, “We’ve distinguished ourselves through our designing and building of retaining walls. It’s our sweet spot.”
Genadek sees them as potential upsell items for a landscaper. To make the sale, “you need to educate customers about their options and explain why they should choose one thing over another.”
Thanks to technology, there is a way to do this very effectively. A vast number of companies use simulators to show how a product will look in one’s home or how an article of clothing will fit on one’s body. They’ve incorporated these simulators because many people are visual learners.
Wiltshire uses software that can do this with a retaining wall. Before designing one, his team photographs the site and has a predesign meeting with the client, who is shown exactly how the finished wall will look on his or her property via 3-D and AutoCAD mockups.
Those already in the business of building retaining walls are reaping the rewards. Welch says the owners of the company he works for have benefited from the turn toward visually pleasing materials.
“As the market gets better, people are spending more money, and they are more concerned about aesthetics,” Welch says, adding that choosing the right sizes, colors and caps will make any wall aesthetically satisfying. He helps his customers review the available options and suggests they consider “what materials will blend in well and harmonize with the contours of their property.”
A retaining wall is definitely a practical item; the parent with the wagging finger would approve. Thanks to the wide variety of materials available nowadays, retaining walls can be so much more than just something that holds back soil.
The increased demand for them offers the landscape contractors who build them a moneymaking opportunity. To paraphrase “Field of Dreams,” if you build them pretty, and build them well, the customers will come.TYPES OF RETAINING WALLS
A gravity wall depends on its mass to resist pressure from behind. They are often built leaning back toward the retained slope to improve stability. Shorter gravity walls are often made from stone, boulders or segmental concrete units. Other types of gravity walls include crib walls, consisting of cells built up log-cabin style from precast concrete or timber and filled with granular material, and soil-nailed walls, where soil is “nailed” in place with steel or concrete rods. Taller gravity walls are increasingly built using polymer cellular confinement systems.
These retaining walls begin with a core typically made of steel-reinforced, cast-in-place concrete or mortared masonry in the shape of an inverted “T.” They’re called “cantilevered” because the load is transferred to the footing.
This type of retaining wall can be built as a gravity or cantilevered type with the addition of metal cables anchored into the rock or soil behind it.
Typically made of steel, reinforced concrete, vinyl or wood planks with interlocking edges driven into the ground, this type is often used in soft soil and tight spaces. Taller sheet pile walls need to be tied to an anchor or “dead-man” placed in the soil a distance behind the wall.
A method that involves drilling a circular hole into the ground, installing steel reinforcement and filling the hole with concrete to form a piling. A wall is built by assembling a sequence of bored piles anchored to the earth behind it.WHAT WALLS ARE MADE OF
• Poured concrete block
• Split-faced block (also called rock-faced block), a concrete unit that appears hand-chiseled but is made by pouring concrete into a textured form
• Natural stone, limestone or stone veneer over concrete or timbers
• Wood timbers
• Gabions (wire baskets filled with rock or concrete rubble)
• Clay brick
• Geocells (3-D polymer cells that can be vegetated or infilled with concrete or soil)
• Articulated concrete block (interconnected blocks that can adapt to changes in subgrade, used in large erosion control projects)
• Engineered geofoam (bricks of polymer foam for special applications where weight it critical)