The Many Uses of Gabion Baskets

The banks of Texas Mountain Creek, which winds through Grand Prairie, TX, had eroded so severely that officials with the Texas River Authority were concerned that a catastrophic slope failure could occur. And in this particular location, that would be bad news.

First, there was the creek’s location. The waterway wound past busy Interstate 30 and a golf course. Its waters had already eaten away at one of the course’s manicured fairways, and course officials worried that the creek would only destroy more grounds as the years passed.

But the more serious problem was the 78-inch reinforced concrete sewer interceptor that ran beside and parallel to the creek. Years of erosion had exposed the interceptor’s pipeline in several areas, including in some places where the line’s center, once buried, now stood 15 to 20 feet above the creek bed. River Authority officials were concerned that a slope failure would one day cause the pipeline to separate and fall into the creek’s waters, spilling pollution into it.

Ark Contracting Services, based in Fort Worth, TX, along with Dallas-based GWC Engineering LP, tackled this challenge last summer. Geotechnical engineering for the project was provided by CMJ Engineering, based in Fort Worth. During the four-month project, experienced builders at Ark and structural engineers at GWC turned to a host of erosion control measures to stabilize the stream’s banks, including concrete soil anchors, backfill, blankets, and, most importantly, gabions.

There is little surprise that gabions were included in these plans. Gabions-wire baskets or cages filled with rock-are often used to stabilize channels, streambanks, and steep slopes. They are sturdy enough to provide structural integrity to a variety of engineering applications and are relatively inexpensive. They can be aesthetically pleasing, too: Once they’re in place, construction crews can quickly cover them with soil and vegetation. Over time, gabions naturally vegetate.

These benefits made gabions the logical choice for the Texas Mountain Creek project, says Steve Bowman, president and partner with Ark Contracting Services. “Gabions are one of our primary tools. Properly installed and engineered, they give you tremendous structural strength, which is something most people don’t realize. They are an excellent building tool. And gabion stone is readily available in the Dallas-Fort Worth area. The gabions are a very attractive alternative.”

Bowman is far from the only contractor, engineer, or developer who has turned to gabions for his most challenging erosion control projects. Gabions, because of their versatility, strength, and affordable cost, have long been a popular choice. Manufacturers of the products, and the erosion experts who use them, say this isn’t about to change.

A Versatile Solution
Colin Glass of Fort Smith, AR–based Terra Aqua Gabions says that these days, he doesn’t have to sell the products quite as hard: A growing number of construction pros have already learned that gabions, when used in the right situations and on the right projects, are an effective, easy-to-use solution for streambank and slope stabilization projects.

Gabions are considered hard-armor products, unlike products such as erosion control blankets. Such hard products may be out of favor with many permitting bodies-municipal officials often prefer “soft” erosion products, such as blankets and mats, that are, in their eyes, more aesthetically pleasing and environmentally friendly-but there are certain projects, notably riverbank stabilization jobs with high water flows, that require hard-armor solutions. And gabions, Glass notes, are the most attractive hard-armor option available.

“Overall, contractors are more aware now than they ever have been about how important it is to control soil erosion. That’s due to a lot of market forces, but the bottom line is that people are looking for solutions,” Glass says. “When agencies are looking for hard-armor solutions, gabions stand out. There are very few products out there that do what gabions can do.”

Glass points to an example: Say a contractor most stop erosion on a channel with a bank that is roughly 9 feet tall and 1,500 linear feet long. If the bank is failing because of erosion at the toe of the slope, there are few products besides gabions that can stabilize it. Contractors can go with riprap, concrete, or a confined gabion system.

Gabions, Glass says, are the best option of those choices. They are affordable and easy to install and have a long lifespan. This is why gabions have become popular choices for gravity retaining walls, mechanically stabilized earth walls, slope stability applications, channel-lining jobs, and streambank protection.

Gabions, though, may not always prove to be the first choice of contractors. Some, looking to complete a project while spending the least amount of time and money possible, may prefer to simply dump a load of rock into a stream. Terra Aqua fights this by constantly educating builders, developers, and municipal officials on the benefits of gabions.

Terra Aqua must also convince builders and contractors that gabions are easy to use. Gabions, after all, require full excavation. They differ from erosion control blankets, which contractors can simply roll out and stamp down. Contractors must rely on a good labor force to manipulate the wire baskets.

“The key is convincing people that gabions are going to be cost-effective,” Glass says. “If you can’t reach their comfort level on the cost or on the methods of construction, you’re not going to have a lot of luck convincing them that they should go with gabions.”

The good news is that more contractors are getting this message. Take Bowman. He’s long been a proponent of gabions.

“I find the gabion structures to be very attractive,” he says. “They are also very durable to floodwaters. They are free-draining. Any hydrostatic pressures that can possibly build up behind the structures are mitigated with gabions. They can be installed in very difficult environments. If you wanted to instead pour concrete footers, you’d have to be working in a location that was very dry for a long period of time. There is typically a very long lag time between excavation and installation with cast-in-place structures. That’s not the case at all with gabions. You can go right in and install them.”

Ark Contracting hired GWC Engineering to design the erosion control measures. The final plan included a combination of concrete drilled shafts inserted next to the exposed pipeline, a concrete beam running linearly along the pipeline area, and, for support, grouted soil anchors that carried loads of 60,000 to 140,000 pounds per anchor. This soil-anchor system worked in concert with a vertical gabion structure that ran the entire length of the eroded areas. Bowman says the gabion walls, built out of 3-foot by 3-foot gabions and running 12 to 18 feet in height, not only added erosion protection but also improved the entire project’s structural integrity.

The gabion walls faced the streambank, allowing Ark crews to backfill the eroded areas and encase the exposed pipeline in earth. Crews also laid an erosion control mattress along the bottom of the gabions sloping down to the edge of the creek to add further erosion protection.

The job proved a complex and sensitive one. Crews had to install temporary steel H-beams to shore up the exposed pipeline during construction. If crews had simply begun the project by building the permanent erosion control and stabilization structures, the pipe could have broken or fallen into the creek.

Rather than gabions, crews could have used sheet piling to stabilize the streambank. But the vibrations from installing the pilings could have caused the pipeline to crumble. By using gabions, crews could work in smaller areas at a time. Ark crews were able to dig, install the gabions, fill in the exposed area with dirt, and then move on to the next section of the project. Such an approach provides far greater stabilization during construction than other methods. By installing steel pilings, crews would have exposed much larger sections of the pipeline for longer periods of time.

Ark Contracting installed about 2,500 cubic yards of gabions, manufactured by Terra Aqua, on the project, Bowman says. So far, the gabions are working exactly as Bowman and the engineers with GWC predicted.

“We are finding that the sheer mass of a gabion structure compared with other structures is making a big difference on our projects,” Bowman notes. “Gravity is free, as they say. You put in these massive structures and you’ve created quite a buttress against sliding and overturning. Gabions are not a cure for all situations, but we’ve found that they are a good solution quite often.”

Saving Backyards
The homeowners of the Augustine Heights housing subdivision in Eureka, MO, enjoy the creek that flows around their subdivision. It is scenic, after all. But they don’t enjoy the erosion that’s steadily hit the creek’s bank. What homeowner would? The eroding banks mean that the creek is slowly eating away at their backyards.

That’s what homeowners here faced before the City of Eureka paid last September to repair the 5- to 10-foot vertical cuts that had been eroded in the creek’s banks. Don Thieman of Fenton, MO-based A.S.P. Enterprises, a distributor of erosion control products, provided the gabions, built by Terra Aqua, for the project, which was scheduled for completion by the end of 2005.

“Residents were continually losing parts of their backyards,” Thieman says. “There were liability issues, too. There were 10-foot drops off the backs of some properties. Ultimately, it was a clean water issue, too. As that erosion takes place, you are polluting the stream with sediment.”

Crews installed about 500 cubic yards of gabions at the base of the creek. Above that, they added a Geoweb cellular confinement system. In all, crews worked on about a mile and a half of creek bank.

The combination of gabions and blankets worked well, Thieman says. The gabions provided a hard-armor structure at the toe of the creek. Meanwhile, the cellular confinement system, which crews vegetated, provided additional stability and added an aesthetic quality to the project.

“Using a combination of products is not unusual at all,” Thieman notes. “Ultimately, you have to have to be able to work with multiple products. No matter how good a product is, there is not one out there that can fix all erosion problems by itself.”

In this case, crews went with Geoweb atop the gabion layer because the blanket has pockets of soil that allow them to plant vegetation quickly and easily. Vegetation is important, with more municipalities requiring in their job specifications that contractors put in “green” products.

“Permitting agencies don’t want to see rock structures along the water,” Thieman says. “It heats up the water. That’s actually a form of temperature pollution. By putting vegetation in the baskets, through a live staking process, we can get vegetation on the face of gabions. That provides shading for water. It keeps the water cooler while providing a habitat for aquatic life and structure to a bank. Of course, a gabion will ultimately vegetate itself over time. To speed that along, though, you put live stakes through the gabion that go deep enough to get into the vegetative soil.”

A.S.P. also provided the gabions for a project in the city of Ladue, MO, last September. This time, a creek running alongside a golf course had been eroding steadily and was now close to tearing up portions of the links. The big problem area was a 90-degree turn the creek took as it flowed out of a culvert pipe.

“There was a lot of water shooting through the culvert,” Thieman says. “Hard armor could withstand that. Once the water got to a certain height, the hydraulic impact was reduced some. At that point, we just needed turf reinforcement mat. The mat provides good erosion control, too, and has aesthetic value. We can vegetate that very easily.”

An Up-and-Down Industry
Despite their versatility, gabions have not always been the product of choice for contractors. Thieman, for instance, says that his company has provided fewer yards’ worth of gabions the last five years as contractors turn more often to “soft” erosion control products such as turf reinforcement mats and blankets.

Jason Hoeft of King-Hughes Fasteners Corp., an Imlay City, MI-based manufacturer of fasteners used in conjunction with gabions, agrees that the gabion business is a cyclical one. “The past four or five years, demand for gabions has been a little slower,” he notes. “This year, though, demand has blown up again. We’ve had a couple fairly large projects in the United States that have helped. It seems we do a lot of gabion work for a period, it slows down, and then it comes back again a few years later.”

This year, King-Hughes products have been in demand in places like California, where contractors are tackling more soil-stabilization projects in the wake of serious landslides and fires. Texas has also proven to be a strong market for the company’s fasteners: Hoeft cites the tremendous surge of new construction in the Dallas-Fort Worth area as one reason.

“They have to make sure that everything is as stable as can be before they build those multimillion-dollar homes,” Hoeft notes. “They don’t want them to end up falling in the river.”

Why the ups and downs in the business? Hoeft has no idea. “I wish I had the magic ball that told me why it’s the way it is,” he says. He and his company face some of the same challenges that gabion manufacturers see: Contractors often seek to spend the least amount of money possible on their projects. They are then less likely to buy extra tools, including King-Hughes’ fasteners and rings.

Hoeft combats this in much the same way gabion makers do: He tries to educate builders, developers, and municipal officials, teaching them that his company’s fasteners actually make working with gabions easier, saving them both time and money over the long haul.

“Labor is not exactly cheap in the United States,” Hoeft says. “Anything you can do to speed up a job and decrease the labor costs is a big benefit. Usually when they use our rings, compared to hand-lacing, the savings in labor costs are three-fold the extra cost of the products. Our challenge is getting them to try it, to consider it.”

Another key to giving the gabion industry an extra boost lies with municipalities and regulatory bodies themselves, Hoeft says. If government officials require products such as retaining walls on their stabilization jobs, more contractors would be forced to look at gabions.

“We’ll often see contractors simply dump a truck full of rocks down the riverbank,” Hoeft says. “The rocks then tend to shift and move themselves down the river. Over time, that method is ineffective. Using a gabion basket whenever you hit a corner or a major elevation change is a much more effective method. The baskets are anchored. They are very heavy. They are locked together in one big mass. You are not going to see a lot of shifting in your protection wall. And it lasts longer.”

Officials with the International Erosion Control Association, the industry trade association based in Steamboat Springs, CO, don’t recommend any one erosion control product over another. But they do point out that gabion baskets are ideal solutions for many erosion control projects.

“Our stance is that there are a lot of erosion control products out there. If they are used properly and in the right situation, they are all very good,” says Kim Kline, technical resource director for the association. The key, Kline says, lies in having engineers analyze each project and run through the pros and cons of different erosion control products before choosing the right one or mix of tools.

“We have had many field days and have gone on many site tours. Any product can fail if it’s not used properly,” Kline says. “If the products are used properly, they can be truly beneficial. It takes the planning. It’s the full circle, from the planner to the installer to the maintenance, that makes a product work well.”

Brent Smith of International Erosion Control Systems, a manufacturer of gabions in West Lorne, ON, says he’s rarely surprised when clients ask for gabions. “You get such a nicer appearance by using that gabion wall,” he says. “People are getting educated that simply putting broken-up concrete and riprap on the side is not necessarily the answer. There is more design consideration that goes into these jobs now. We are seeing more emphasis being put on aesthetics. With gabion walls, you can build something with a pattern. You can plant grass on top of it to give it a natural appearance. It’s not the short-term fix. It’s not the cheap fix.”

Replacing a Road
Officials with Henry Heyink Construction in Chatham, ON, turned to gabions last May when they embarked on the total reconstruction of a kilometer and a half of Clachan Road in Chatham-Kent. The project, which included the replacement of a culvert, ran into the middle of August.

The road crossed the Thames River at an angle, and it was here that the greatest erosion controls surfaced. Municipal officials wanted guarantees that the road reconstruction wouldn’t send soil and dirt into the river.

Henry Heyink turned to gabion blocks manufactured by International Erosion Control Systems to tackle the challenge. Crews installed about 175 blocks to build a wall on both sides of Clachan Road, effectively protecting the river that it crossed over.

The project had some unusual challenges. The terrain the road travels is hilly and susceptible to erosion. To deal with the potential of soil moving into the Thames during construction, Henry Heyink crew members used an asphalt sprayer on the road’s shoulders to keep materials in place.

Now that the project is done, though, those challenges seem far away. “It looks like a million bucks,” says Rob Hoekstra, project manager with Henry Heyink. “The problem with gabion baskets is that they have a more rugged look. The wall looks much better. This has more of an appealing look.”