Retaining Walls . . . What’s New?

Contrary to the popular Carole King song, feeling the earth move under your feet is not necessarily a pleasurable experience, especially when it comes to soil erosion. When the earth moves in such a way as to impede upon the quality of life, then that movement needs to be controlled. Mother Nature created water and wind, Man invented retaining walls.

The term retaining wall has traditionally been used to describe any type of free-standing wall whose main function is to hold in place soil which would otherwise collapse into a more natural shape.

For thousands of years, retaining walls in one form or another have been used to hold back the flow of soil from eroding onto villages and roads.

When we cut into a natural slope to build a highway or other structure, we disrupt what was once a relatively stable system. Without support, the disturbed earth will seek its stable angle by sliding, slipping, washing out and otherwise eroding. Successful retaining walls hold earth in an unnaturally vertical position, and this is no easy task.

In today’s times, retaining walls are commonly used not only for control of erosion, but also to protect shorelines and keep rainwater from seeping into unwanted areas. They also provide soil stability in areas where there is a risk of significant changes of ground elevation due to earthquakes and floods. Although retaining walls are used in the landscape, especially where new developments appear, we will not address that segment of the market in this article.

Creating an artificial structure that can withstand the forces of nature requires engineering skills to ensure the wall does its job. Along the way, manufacturers looked for ways to get a leg up on their competitors, so they began to explore different ways to construct blocks that would be both aesthetically pleasing and environmentally friendly. This desire to “build a better mousetrap” has created innovations in well-established companies and has also given birth to entirely new concepts in vegetative “living” wall designs.

For the most part, the basic material used in the construction of retaining walls is concrete, which is meant to serve the functions of strength and durability. Because of their weight, and the resultant expensive shipping costs, contractors

will order the blocks from a local manufacturer and have them shipped directly to the project site.

The Keystone Company in Minneapolis, Minnesota, has been manufacturing concrete retaining walls for more than 20 years. Their units performed the task of controlling soil erosion just fine, but they are always improving their products. To meet the ever-increasing demands in aesthetics, they have developed a process that utilizes a stamp-face system called Sculpterra Technology. This produces specially designed natural textures in a wide variety of colors.

The process combines the strength of the retaining wall structure with the aesthetic look of natural stone. This new technology applies a natural texture to any retaining wall block, which enhances the landscape project and complements the architectural elements of any commercial site, while also working as a functional retaining wall.

Keystone isn’t alone in its desire to improve upon the traditional concrete block. Ben Manthei, managing partner, Redi-Rock International, Charlevoix, Michigan, found traditional small blocks that were set by hand and require geogrid tiebacks to be too labor intensive and costly. He wanted bigger, heavier concrete blocks, but couldn’t find anything like that on the current market. So he and his brothers developed their own big block retaining wall system built entirely from wet cast concrete. Instead of needing a geogrid, concrete blocks are pre-cast with knob and groove connections. Manthei saw a need for bigger, and when he couldn’t find what he was looking for, he created it.

Other manufacturers prefer to fill a need in the concrete block market by simply improving on the basic design. One such person is Fred Agee, president of GeoStone, Birmingham, Alabama. A longtime construction company owner, Agee experienced first-hand the limitations and restrictions to wall construction imposed by modules that were currently available. Because he couldn’t find exactly what he was looking for, Agee created a totally new design of concrete block.

“It’s just a block with an open core,” says David Agee, Fred’s son and vice president of the company. “Because of the open core, the blocks are easy to grip and install. Then, the core is filled with crushed stone. We call it the Rock Interloc System.”

The modules interlock with each other because of the friction created by hundreds of rocks within the core rubbing together. The weight of the block and the rock together creates the strength in the wall to hold back soil.

But for some, it’s not enough to simply re-design the concrete block component of a retaining wall. For those individuals seeking to solve a particularly challenging problem, the need arises to create a new design of the wall itself.

About 15 years ago, retired engineer and physicist Ed Veazey of King George, Virginia, woke up to discover that his house on the Potomac River was three feet closer to the bank than it had been the night before. Veazey was accustomed to meeting difficult challenges with water pressure, having designed submarines for the U.S. Navy in WWII. He figured it couldn’t be that hard to design a retaining wall to keep the ocean from his front door. “I like things that last, will do a good job and not break down,” he adds.

Veazey designed the ‘L-wall’ with that very thought in mind. Each wall unit section is attached to the next with steel channel bars and tongue-and-groove joints in the concrete, which are placed along the horizontal and vertical edges. The 8,000 pound unit is then set in place, bolted together, backed with filter cloth and back-filled with sand, gravel and soil to act as a run-off filter for surface water pollutants. The splash plate that extends out near the base gives the appearance of the letter ‘L’.

Green walls win favor

An entire wall made completely of concrete would definitely be functional, but with the increasing popularity of “going green”, there is a growing demand for retaining walls that incorporate vegetation. Vegetated walls are becoming a very attractive option for retaining wall projects. Green walls can contribute points for building projects seeking LEED certification. Among other things, they typically qualify as green space, they reduce the heat island effect, and they filter surface water runoff.

With environmental awareness on the rise, companies are not only adding new products to their line, but they are creating entirely new divisions of their business. That’s exactly what the St. Louis Retaining Wall Company did. In 1992, they were searching for a plantable retaining wall system that would work with their concrete wall modules and, once they found the perfect combination, they formed The

Hercules Modular Block Retaining Wall System.

The complete wall system is composed of concrete blocks that are installed into the landscape then dusted with topsoil and spray-seeded with a variety of vegetation.

Over time, the plants grow over the concrete and create an ecological environment, while continuing to function as a retaining wall.

“There are no clips or joints on the blocks. The coarse bottoms on the blocks hold them in place and you don’t need as much geogrid enforcing,” says Michael Hellwig, sales manager, Hercules Manufacturing. “Maintenance is very easy.

You just fertilize, water and plant.”

Going one step further by eliminating concrete altogether, Madison, Wisconsin-based Agrecol has created Envirolok. This system of vegetated walls is constructed by weaving rows of stacked, soil-filled geotextile bags together and locking them in place with spikes.

Then, the face of the wall is planted with native plant plugs placed between the stacked rows of bags, along with a mixture of native plant seeds. Within weeks, plants and grasses grow through the bags and develop extensive root systems that lock into the native soil and form an ecologically-sound vegetated erosion control system with permanent structural strength.

Vegetation is also an integral part of the Deltalok system. Geotextile bags are filled with soil and sand and are connected to each other with interlocking polypropylene plates. “The strength of the wall increases as roots develop and further anchors the soil bags to each other and to the earth,” says Randy Nulle, CEO of Deltalok USA. “The bags mold together and create a root-reinforced soil block that keeps hills from eroding away.”

Even the best designed retaining wall will succumb to the effects of hydro-pressure without some type of drainage system installed within the concrete. Traditionally, round drainage pipes were the design which was most widely used. Although they performed their job well, having a black hole protruding from a wall of decorative concrete was not the most pleasing to the eye.

Then along came Haynes Sloan, Jr., a landscape contractor from Gallatin, Tennessee, who was frustrated by having to use products that were limited to a few areas of drainage applications. Sloan began to make a “wish list” of what he envisioned as the “perfect” emitter. He then began experimenting with a variety of designs until he came up with a product that was

After installation After planting fills in aesthetically pleasing as well as being functional. He named it StealthSpout. The product is being marketed by a new company, Invisaflow.

All of these retaining walls serve their basic function which is to help prevent soil erosion or protect shoreline erosion, saving millions of dollars in property and sometimes lives. They also create a more aesthetically pleasing and ecologically helpful world.

Whether the retaining wall industry is “going green” for the environment, going bigger for added strength or being redesigned to meet new challenges, advances in design and ingenuity will always be part of the evergrowing retaining wall future.

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