May 21, 2012 04:20

Geo Innovate

It's almost like a kid's riddle.
Question: What erosion control technology has been around since time immemorial, but is brand new every day?
Answer: Geotextiles.

Using geotextiles for soil erosion and soil stabilization had its origins 35 centuries ago in ancient Egypt, where Pharoah’s slaves were made to lay woven mats of reeds to help stabilize roads and byways. With projects l ike the pyramids, that required the dragging of thousands of stone blocks weighing two and a half tons or more, roadway stability was as important then as it is now.

Geotextile technology has come a long way in 3,500 years. Nowadays, these souped-up fabrics are more durable, more flexible, more affordable, and more useful than ever.

Traditionally, geotextiles are used in a variety of ways. They are used on slopes, riverbanks and streams to control erosion—even underwater erosion.

Getting water to an arid area, where it can turn a desert into an oasis, was the goal when the Coachella Canal was being built. The canal is a nine-foot deep, 122 mile-long construct that carries water from the Colorado River in Southern California, to the Coachella Valley of Riverside County, California.

Begun as a WPA project in the 1930s, and completed in the 1940s, water flows through the canal entirely by gravity flow, so there is no pumping involved. The canal, when it was originally constructed, was earthen. As water moved along, quite a bit of it leached through the earth and back into subsoil before it reached its intended destination.

Engineering surveys determined that the canal was leaking 115,000 acre-feet of water a year—enough fresh water to service 150,000 households. When water was more abundant, see page from the Coachella Canal was tolerable. In recent years though , loss due to see page became too significant to ignore. Counter - measures had to be taken.

In some sections of the canal, the banks and base were converted to straight - ahead concrete. In another section, however, engineers decided to experiment by adding a non-permeable geotextile to the mix.

Environmental Protection, Inc., based in South Mancelona, Michigan, designed a PVC geotextile— more properly, a geomembrane— that would be used under a layer of concrete in the canal. Moreover, the installation would need to be done even as water flowed in the canal.

The company constructed both a dredge and a paver that graded the canal, unrolled the geomembrane in place, and then covered that geomembrane with the final layer of concrete. The project was a success, and marked the first time that geomembranes had been installed underwater in an operating canal. The canal currently can deliver almost a million acre feet of water annually.

In a recreational context, the same company’s products were used to attack a leaky lake at the Hidden River Golf and Casting Club. Hidden River is a combination golf/fishing club hard on the shores of the Maple River in northern Michigan. The club had constructed an irrigation lake near the seventh hole of the course, but poor quality clay soil made it impossible to store water in the lake as the club had envisioned.

To remedy the problem, 249,000 square feet of 30-mil PVC geomembrane were installed by Carter Enterprises, a landscape consulting and contracting firm based in Pelston, Michigan. The installation of custom-sized geomembrane panels took just three days; the geomembrane panels were joined using chemical fusion welding.

In addition to the main irrigation lake, Carter Enterprises also lined a two-acre pond near the eighteenth hole. For that installation, a wooden golf cart bridge that crossed a section of the pond had to be taken into account, so that water would not erode and rot the base of the wood pilings that support the bridge. Again, it was geomembrane to the rescue. The company field-fabricated PVC geomembrane “boots” to wrap around the base of the piling and seal it properly.

Projects involving water, though, don’t all call for geomembranes. Sometimes, geotextile mats and blankets can be the preferred method to forestall soil erosion.

For example, an irrigation canal runs just north of the United States Border Patrol fence between the U.S. and Mexico, near the west Texas town of El Paso. That canal is dry much of the year, but can be prone to flooding during the rainy season.

In fact, flooding of the canal can be predicted days in advance, since the canal is so long that rain falling well upstream will cause downstream flooding. The Border Patrol has even rescued would-be illegal immigrants attempting to ford the canal at treacherous flood stages. One such rescue finished a mile downstream from where the effort began. That’s how strong the floodwaters were.

Engineers determined that this recurrent flooding was both eroding the banks of the canal and posing a structural danger to the border fence itself. The solution was a geotextile. Signature Contracting Services of Grand Prairie, Texas, was charged with the installation of geotextile blankets that would protect the channel from degradation, and thus protect the fence as well.

Signature president Corey Tompkins oversaw the installation of a Pyramat geotextile turf reinforcement mat from Contech Engineered Solutions, whose American headquarters are in West Chester, Ohio. The Pyramat, constructed of three-dimensional interwoven polypyrene yarn, is designed to both shield and stabilize the earth below it, while at the same time locking in seed and soil that can vegetate and grow. It’s also very stable under the sun’s punishing rays. After 10,000 hours of exposure to direct sunlight, it retains 85 percent of its original strength.

The border canal was a big project: 1.48 million-square-feet of Pyramat were laid in ten days in February 2009, despite severe sandstorms that blew through the area. It was a good thing that the project didn’t run overtime, since Tompkins had signed a contract guaranteeing a ten-day installation.

“We covered seven and a half miles and used somewhere between 150 and 175 people on the project,” Tompkins relates. “Some of the slope covered was 30 or 40 feet deep, and we knew that water could rise as high as 10 feet from the top. What was challenging about the project was that we knew the water was coming. There’d been a release from a reservoir upstream, so time was truly of the essence.”

The canal bank being protected was so sandy that the crew ended up driving holding pins into the mat as much as 18 inches into the soil. Tompkins reports that he has been out to the site fairly recently, and that there has been no degradation at all, neither in the canal bank nor in the geotextile mat. “That’s a durable product,” he says. Currently, his company is at work on a similar project on the San Antonio Riverwalk in Texas.

One of the main uses for geotextiles is in roadway construction.

Chatfield College, in St. Martin, Ohio, wanted to put in a half-mile long alternate entrance for construction and service vehicles to use during a renovation project. The project called for a geotextile liner under a top layer of gravel. Though the original engineering specifications called for a woven fabric that cost more than a dollar a square yard, careful study indicated that a fabric that cost half as much would be sufficient to prevent soil erosion and support the roadway for its intended use, according to Dan Bonn, president of U.S. Fabrics in Cincinnati, Ohio.

“It took two days and a crew of four to lay down 2,800 feet of fabric and cover it with a sufficient thickness of gravel,” Bonn reports.

“Without the geotextile liner, that road was projected to last for eighteen months. I was recently out there to take a look, and now, five years later, it’s still going strong.”

Often, when we think of geotextiles in road applications, we think of major league highway projects. Yet geotextiles are just as useful in smaller road projects, and never more useful than in snow country, where spring melting and runoff turns many a dirt or gravel access road into a quagmire.

Conway, New Hampshire, roadand-driveway contractor Russ Lanoie knows mud. He specializes in rural living projects, and often has to deal with springtime dirt road quagmires. He says the normal solution to “firming up a muddy road is to add gravel,” but points to the adage that “adding a bucket of gravel to a bucket of mud just gets you a bigger bucket of mud.”

Instead of the usual gravel dump, Lanoie recommends geotextiles on his popular website about rural living. “Once frost has left the road base and the road has become workable, I use geotextile stabilization fabric with outstanding results. Geotextile fabrics can effectively eliminate muddy conditions by keeping gravel surface materials from mixing into the road base.”

The last several years have brought significant innovation to the arena of geotextiles, according to Dr. Robert Koerner, president emeritus of the Geotextile Institute in Philadelphia, Pennsylvania, whose 1980 Geotechnical Engineer- ing Using Synthetic Fabrics was the very first book on the subject— it’s now in its sixth printing—and established Koerner as a go-to guy for geotextile consulting. Choices include the ubiquitous sheets and rolls like those used in the canal, lake lining, and road construction projects. There are geogrids, like those installed along the border fence canal, which lock soil in place but contain intention- al openings where whatever is underneath can pop through, such as grass or vegetation.

Geogrids also have close cousins, called geotextile reinforcement mats. Like geogrids, these lock soil in place and allow plant material to sprout and thrive, but have a wide enough weave that vegetation will eventually hide them from the casual observer. Add to these products such eso teric and specialized recent addi- tions as geofoam blocks, a lightweight synthetic fill material that’s 100 times lighter than soil and 30 to 40 times lighter than other light- weight fills. There are also new expanded geocells made of high-density polyethylene that expand to form a synthetic honeycomb that can be filled with gravel or soil, and then compacted. Also on the market are geosynthetic clay liners specifically designed for landfills. Koerner talks through some of his favorite design innovations . “Over the last several years, we’ve seen the advent of geosynthetic fibers that are hydropic as opposed to hydrophobic. That is, they draw water out of whatever is underneath them, as opposed to being water repellent. I’m also excited about ‘concrete cloth,’ which comes in a rolled form. You unroll it, moisture hydrates it, and it hardens to form a permanent erosion control barrier.”

With all these new developments in their manufacture, and successful projects around the country, maybe the riddle posed at the top of this article needs to be revised. “What erosion control technology has been around since time immemorial, but is brand new and indispensible every day?” The answer, though, needs no revision: geotextiles.

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