Getting Creative With Geosynthetics
Contractors find new erosion control applications.
Snow rarely fazes Denver residents. The winters here are traditionally long and hard, after all. But early spring 2003, a blizzard considered massive even by this Colorado city's standards wreaked havoc on Denver and its residents.
The skies above the Colorado city dumped more than 36 inches of snow in March of last year. The blizzard, the worst in 90 years here, left more than 20,000 residents without power and stranded hundreds of motorists on the city's snow-jammed roadways. Governor Bill Owens had to call in the National Guard to rescue stalled motorists.
Eventually, of course, the snow melted. But highway department officials found that the blizzard left them with plenty of problems. The biggest of these? The extreme amount of runoff from the melting snows was so intense that it washed out entire culverts that passed under E-470, a busy toll highway running along the eastern perimeter of the Denver metropolitan area. This caused massive sinkholes along the road, which had to be repaired—and quickly.
Officials with the E-470 Public Highway Authority knew where to turn. They called in the civil contractors with Littleton, CO–based American Civil Constructors and gave them a strict mandate: Fix the road, using whatever means and techniques the job required.
That meant tapping into the restorative powers of a host of geosynthetic materials, including blankets, turf reinforcement mats, and geogrid. In all, engineers with the firm worked on 7.5 miles of E-470 for about four months. After workers finished the initial phase of the job, toll authority officials had to call them back to repair only two tiny patches of roadway where their fixes didn't completely take.
"That was pretty good news. After a half-million dollars' worth of repair work, there were only two small areas to be concerned about," says Ron Dean of American Civil Constructors. "And once those repairs are made, that will be the end of it."
The E-470 project is one more example of the versatility of geosynthetic materials. These materials, of course, are not new. Engineers, developers, and landscapers have been using them for years to help eliminate erosion, stabilize the earth surrounding construction projects, and catch large chunks of sediment that might otherwise escape into streams, rivers, and other bodies of water.
Two main reasons account for the popularity of these products: First, they are stable and hardy, unlikely to suffer biodegradation or to experience chemical interaction with the soil surrounding them. Second, they are inexpensive when compared to many other erosion control methods.
But even with these benefits, many engineers and developers shy away from using these products. Some do so not because they dislike the way geosynthetic materials work, but because they have long used more-traditional erosion control measures—riprap or cement lining in a stormwater channel, for example—and are wary of trying different methods.
Lucinda Dustin, who provides erosion and sediment control consulting to Stevens, Ferrone & Bailey, an engineering firm based in Concord, CA, is familiar with this reluctance. She has spent most of her career in the erosion control field experimenting with different uses for geosynthetic materials and during the years has developed a special affinity for turf reinforcement mats. She recognizes, though, that not everyone in the field is as willing as she is to give geosynthetic materials a try, and she lays part of the blame for this on the manufacturers of these products themselves.
"The biggest problem I see out there is a lack of knowledge in how to install these materials," Dustin says. "It's not enough for the manufacturers to simply sell the product. The people who buy it need the technical knowledge to make it work. To me, that is the biggest gap we have. There is a lack of knowledge of the installation process."
To help illustrate the many benefits geosynthetic materials bring to the erosion control industry, several engineers and industry pros recently shared some real-life examples of projects in which turf reinforcement mats, geotextile tubes, geogrids, silt fences, and other geosynthetic erosion control devices played key roles.
Runoff Damage in Denver
To repair runoff-damaged E-470 in Denver, the staffers at American Civil Constructors turned to a host of geosynthetic solutions: turf reinforcement mats, rolled fabrics, bales, and Geo-Ridge, a permeable plastic sediment control berm manufactured by Denver–based Nilex.
|At Interchange E-470 and Highway 85 near Denver, vegetation returns after extensive repairs involving Geo-Ridge and other erosion control devices.|
Dean, from American Civil Constructors, says that he and his fellow civil contractors would never have been able to tackle the extensive repair work if it hadn't been for the availability of geosynthetics. That's because much of the work the firm did involved reshaping the roadway in a major effort to prevent similar damage should large amounts of runoff once again swamp the road.
Engineers working on the project laid an extensive amount of geosynthetic erosion control blankets in ditch lines, under drain spouts, and around bridge abutments, basically attacking anywhere where the road might one day get hit again by high flows of water. Such measures, Dean says, will control any future erosion or rutting, even if another blizzard should descend upon the city.
"I am confident that the fabrics we used will do the job," Dean says. "The fabrics will do a superior job to hay or straw mulches when you're talking about having lots of heavy flow running over them. In a ditch line, for instance, water will eventually erode through hay or straw mulch. The erosion control fabrics stand up far better to concentrated flows of water."
The company is now in the maintenance phase of the E-470 project. So far, Dean's predictions concerning the geosynthetic products are holding true.
Will success stories like the one on E-470 encourage more local construction firms to turn to geosynthetic materials? Dean doesn't know the answer, but he does say that the products already have earned a solid reputation in his region.
"A lot of folks, it seems, in the Rocky Mountains area are fairly up on these kinds of products," he says. "We've experienced a drought during the last couple of years, and homeowners haven't been allowed to do sodding or tree planting. So during this time, a lot of that area has been inundated with advertisements and self-help programs on using erosion control blankets to help maintain lawns, that kind of thing. So people in this area have a good notion already of what these products are all about. I'd say it was already in the forefront of people's minds around here."
The owners of E-470 had also long ago accepted the benefits of geosynthetics, Dean adds. "The owners of the road had gotten away from using riprap in the bottom of ditches as an erosion control measure. They had already turned to using more turf reinforcement mats and reinforcing them with newly planted grass," he says. "Visually, the rock is not as nice as grass and wildflowers."
Anna Coplen, whose firm, Nilex, provided much of the geosynthetic material used by American Civil Constructors in the project, says that demand for many of the company's products, including Geo-Ridge, has grown steadily during the years. Successful projects like the one in Denver, she says, can only help boost demand even more.
Coplen also shared another recent success story. High stormwater volume resulting from a runoff from a nearby overpass had caused heavy erosion along a 250-foot section of drainage ditches on Interstate 94 near Lawrence, MI. Compounding the erosion problem was the site's sparse vegetation and sandy soils.
Contractors hired by the Michigan Department of Transportation installed Geo-Ridge. The berm reduced water velocity, slowing the amount of erosion and allowing vegetation to establish itself. Contractors also installed turf reinforcement mats and erosion control blankets to provide additional protection from erosion.
"The more people get aware of new products and what they can do, the more people want to buy them," Coplen says. "We are a very dynamic industry. There are a lot of new products in it."
An Experimental Nature
Lucinda Dustin isn't afraid to experiment. For years she has experimented with using geosynthetic materials in unusual ways. She's earned such a reputation for this, in fact, that her colleagues now call on her to tackle the most challenging erosion control problems they encounter. That's how she arrived last May at a canyon in Calistoga, CA, in the middle of the Napa Valley.
Construction crews are now busy building a high-end resort in this canyon, one that when finished will attract wealthy vacationers from across the country. Flowing through the middle of the canyon, and the construction zone, is a lazy creek. Unfortunately for the creek, the construction project's storm drainage system discharges directly into it, meaning that loads of clay sediment have been pouring into its water. It was up to Dustin to devise some way to stop this from happening. The health of the creek, after all, depended on it.
The first solution Dustin came up with was a relatively simple one: She attached sandbag holding basins with three-inch PVC pipe to the temporary outfalls that lined the storm drainage system. The hope was that the clay sediment would sink to the bottom of the basins while the now-clean water rushed through the pipe.
But that solution didn't work. The clay sediment remained suspended, and again ended up in the creek.
Dustin then decided to get creative. She attached a smaller gravel bag to the ends of her PVC pipes. This worked somewhat better, catching larger pieces of sediment. But the smaller clay pieces still managed to slip through.
Dustin then called on Chris Marr, general manager of the erosion division at California's Sacramento Bag Manufacturing Company. Marr is also known as someone who isn't afraid to experiment with geosynthetic materials, and Dustin was hoping that he would be able to develop a new type of gravel bag to help solve her problem. "Chris is pretty amazing. You ask him to come up with something, and he will," Dustin says.
As it turns out, Marr did have another trick up his sleeve. He supplied Dustin with what amounts to a double gravel bag, one that acts as a sandbag and filtration bag at the same time. Basically, Dustin inserted a fine filament into a larger snake bag. The snake bag itself prevents larger particles from sneaking through. The filament insert, which Dustin changes after every major rainstorm, blocks the finer clay particles.
So far, the system has been foolproof. Dustin calls the resort project now the "cleanest project in the country." The creek is protected.
Of course, the sediment-collection bags aren't the only geosynthetic materials Dustin has called on to prevent erosion on the project. She is also using blankets, silt fences, and turf reinforcement mats. She's needed them all because of the unusual nature of the project.
The biggest challenge? The area's watershed stretches over 157 acres of land that dumps into a 19-acre construction zone at the bottom of the canyon. Dustin describes it as a big funnel. It resulted in frequent bouts of heavy flooding—basically, whenever a big rainstorm roared through the area.
"The project had already been under construction for 18 months before I was brought onboard. The year before they had terrible problems with flooding and erosion," Dustin says. "That kind of environment was new for the construction team and the general contractor. They were trying to control something they weren't sure they could control. That's when the civil engineering firm recommended that we come in and take a look. Generally, I work on projects that are already heavily impacted. I think a lot outside the box."
When Dustin first started working on the project last May, she spent four days a week on-site, developing solutions to the flooding problems. Now that she's come up with several working solutions, including the double-bag sediment-collection system, she's spending just two days a week on-site. That is proof, she says, that her geosynthetic solutions are working.
"Are more people in this field aware now of how well these products can work? That's an interesting question. For the most part, those of us who are obsessed with using new ways to solve problems—and I have to be honest, anyone will tell you I am very obsessed with what I do—will always seek out new solutions, including using geosynthetic materials in new ways," Dustin says. "To me it is a constant learning situation. I study products a lot. I am always looking for something better, more cost-effective to use on projects."
This doesn't mean, though, that Dustin will ignore old standbys if they are appropriate. "What I do sometimes see in this industry is that sometimes people latch on to something they really like, and they then become overly focused on it, and they look toward it as the solution for almost anything," she notes. "I try not to do that. I would much prefer turf reinforcement mats to riprap. But I also recognize that there are situations where the mats are not feasible. We have to work with what is there."
Marr is hoping that adventurous souls such as Dustin will help spread the word about the benefits of geosynthetic materials. He, too, is hoping to do his part. He is now developing a new geotextile tube that can be used to create underwater berms that can provide a latching-on place for, say, endangered kelp beds.
Developing a new product like this takes an active mind and a dedication to erosion control. Getting it onto the market, though, takes something else entirely: patience with politics and red tape. Currently, Marr is trying, so far unsuccessfully, to land approval for a test study of his new product in the ocean waters immediately off the coast of Santa Barbara, CA. He hopes to one day dredge up a piece of the bottom of the ocean floor, fill a geotextile tube with the dredging materials, and sink the tube to the ocean floor. The goal is that endangered kelp beds can reattach themselves to this tube, which will be made of a special material that will not react to the presence of sea water.
So far, Marr hasn't gotten approval, but he will keep trying. He's persistent for a reason: The more innovative uses people discover for geosynthetics, the more apt engineers and contractors will be to use them in erosion control projects.
"Personally, I don't think the manufacturers of geosynthetic materials have done a good enough job marketing the erosion control uses of their products," Marr says. "They haven't been very good at getting the word out to the engineers. The bulk of these geosynthetic materials have been geared toward road projects and housing production, not for actual erosion control."
Keeping Homes Dry
The stream running through St. Louis County in Missouri slowly crept toward a nearby home. This, understandably, made the homeowner nervous. It also inspired officials with the Metropolitan St. Louis Sewer District to call in Jeff Collins, an erosion control specialist with Middletown, OH–based CONTECH Construction Products.
Collins—who finished work on the project in March—immediately saw that the stream had eroded its banks at its toe. To solve the problem, Collins and his crew dug a trench, laid a geotextile erosion control blanket on the trench bottom, and covered that with a rock base. They then covered this with a product called A-Jacks, 70-pound interlocking concrete pieces each measuring two feet in length.
This approach is not only a sound one—one that will stem the erosion of the streambank—but also an efficient one. The physical work took Collins and his crew a total of just four days. "We were in and out," Collins says.
And the result of his work? "This will stabilize the toe and keep that homeowner sleeping at night," Collins says.
Tim Anderson, manager of erosion control systems for CONTECH, says that Collins's project is just one of many across the country where his firm's engineers are turning to geosynthetic products to solve erosion problems. "There is still a considerable amount of growth that needs to take place in the geosynthetic industry," Anderson notes. "But they are becoming more popular options for people."
He points to three reasons for the steady growth in the popularity of geosynthetics. First, and probably most important, is the fact that geosynthetic products have been proven to be strong weapons in the fight against erosion. Contractors, developers, highway departments, and others are seeing this and are becoming better educated about how to use the products.
Secondly, the new National Pollutant Discharge Elimination System stormwater regulations are also having an impact, encouraging developers to more efficiently reduce the amount of erosion their construction projects cause, Anderson says. This, though, is not happening as fast as many in the industry might have hoped, he adds.
And finally, he says, a growing number of property owners are seeking "green" solutions as replacements for riprap or concrete channel lining. Anderson admits, though, that this reason is a far-distant third.
"That is a small segment of the industry," he says. "But those people are out there, and they are having at least a small impact."
When most people think of geosynthetic products and erosion control, they think of materials such as blankets, turf reinforcement mats, and silt fence. But there are other geosynthetic products that prevent erosion before it even happens.
Varicore Technologies Inc., for instance, produces the Multi-Flow Drainage System. This drainage system, made of plastic and PVC, makes use of nonwoven geotextile fabric to help prevent heavy rainfalls from soaking soil. The soil then remains stable, preventing erosion from becoming a future problem.
"Basically, this is about getting to the problem before it begins to develop," says Arnold Plowman of Varicore. "People know that if we leave the soil in its original condition, problems will develop down the road that will lead to erosion."
Contractors have installed the system under a practice field used by the football players at San Diego State University. Workers have also used the system for airport runway drainage projects in Montana. To Plowman, this diversity is further evidence that professionals in the erosion control field are more than willing to try geosynthetic materials.
"People are much more likely to look at the broad spectrum of available products to solve problems today than they were 10 or 15 years ago," he says. "I think education is the key. A lot of the manufacturers have spent a lot of time and resources educating the engineering community about the use of geosynthetic products.
"There is a natural maturation process in this industry," he continues. "When you come out with a good idea, that idea has a maturation cycle. People need to watch the product and see how it performs. Once they see that it performs, they'll begin using it. The products often have to become household names. That has happened now with geosynthetics, in my opinion."
No one has to tell this to Ed Lange of Tri-State Stone in Bethesda, MD. He has been using geosynthetic materials for years and has been a big fan ever since he and his firm participated in a major erosion control effort along the banks of the Chesapeake Bay's Maryland shoreline.
Lange served as consulting engineer on the 1988 project overseen by the US Army Corps of Engineers and the Maryland Department of Natural Resources. As of 1988, before the project began, erosion had claimed 45,000 acres of Chesapeake Bay shoreline.
To solve this problem, Lange used Typar 3601, a nonwoven polypropylene geotextile manufactured by BBA Fiberweb. Lange used 13,500 square feet of the product, along with 1,400 tons of stone, to shore up the eroding shoreline.
"Let me tell you, geotextile products work," says Lange. "You can go back and dig it up 20 or 30 years after you put it down and it'll still be there, 80 to 90% intact."
Lange should know. He's solved countless erosion problems with the help of geosynthetic materials, including projects he's completed for Andrews Air Force Base and the National Park Service.
He watched his project get put to the test recently when a hurricane tore through the Chesapeake Bay area. The strong winds ripped up a road. The geotextile fabric that had been installed under the road, though, was still there, separating aggregate product from the road's base material.
"It was still doing its job," Lange says. "The material is ideal for erosion control."
Author's Bio: Dan Rafter is a technical writer and frequent contributor.