Geosynthetics

To the average Joe, dirt is just dirt. It’s there to dig into or plant a few seeds in or maybe use for a nice, healthy mud bath, and that’s it. End of story.

But those who deal with soil erosion know there’s a lot more to it.

Keeping soil in place is key to maintaining a balanced environment, where erosion is kept to a minimum, water sources remain free of sediment and the earth beneath roadways and other man-made structures is kept stabilized. There’s a science behind soil that many fail to realize. It’s a science that has been studied for thousands and thousands of years, as far back as the construction of the Great Wall of China or the pyramids of Ancient Egypt.

The difference between now and then is that today, the means by which we stabilize soil has vastly improved. And what we have to thank for this improvement, more than anything else, is the advent of geosynthetics.

“Geosynthetics are used almost everywhere these days,” claims Ryan Collins, account manager for geotextiles at the De Witt Company, Sikeston, Missouri. “It’s hard to say where we’d be today without them, as far as what they’ve done for soil control and stabilization. They’ve become the standard of the industry.”

These durable, lightweight products came into usage in the middle of the twentieth century to serve as a replacement for the more traditional approach of using hard armor structures such as riprap or concrete blocks. A thin yet deceptively strong material made of polypropylene, geosynthetics can be used on a number of different types of jobs, from highway construction to the stabilization of steep slopes.

Unlike ancient times, when degradable materials such as wood and other plant-based fibers were used to stabilize the soil, geosynthetics don’t biodegrade. Because of this, they can last for a very long time. But perhaps what’s most important about geosynthetics is that they’re inexpensive and easy to install.

“If you’re not using geosynthetics to stabilize a site, then you’re probably using some type of stone aggregate,” says Paul O’Malley, national sales manager at Propex, Inc., Chattanooga, Tennessee. “When you’re installing hard armor structures, you’re dealing with a lot of stone and this is going to require a fair amount of manpower. Then there’s also the cost of the materials, which can really add up.”

O’Malley estimates that a typical geosynthetic application is anywhere from one-third to one-eighth the cost of an aggregate application. Installing geosynthetic products is also much easier, as it doesn’t require the use of any heavy machinery. When installing concrete blocks, heavy machinery such as fork lifts and skid steers is a must, making the process much messier as well as more time-consuming.

All geosynthetic products are resin-based, which makes them resistant to poor weather conditions and gives them a longer life span. “The design life for geosynthetics is typically 200 years,” says O’Malley, “and because they’re so durable, the maintenance of these systems is far less persistent than hard armor systems.”

But before you go applying just any kind of geosynthetic on just any kind of site, you’ll want to make sure you know what you’re doing. Geosynthetics are relatively simple to understand, but there are so many different types for many different uses that it can be a tad intimidating for those new in the business. For example, if you try to use a geomembrane to filter sediment in an area of high water flow, you’re going to block the flow and cause flooding. And using a geogrid to try to direct water runoff is just plain silly.

This is why it’s important to educate yourself. Misusing geosynthetics will not only discourage you from using them in the future, but they’ll make you look bad in front of your clients. So, for the sake of keeping business profitable, it pays to take a deeper look at the different types of geosynthetics and their uses.

Applications

There are several different ways in which geosynthetics can be used. Much of it depends on what type you’re using. We’ll get into the different types of geosynthetics later, but for now, let’s discuss the various applications in which geosynthetics play a part:

Separation

– A common function geosynthetics serve is separation, or the process by which geotextiles are placed between two dissimilar materials to prevent them from intermixing. Many roadways are constructed with geosynthetic products to prevent layers of asphalt from mixing with the base and causing portions of the road to sink and become destabilized. In the context of soil control, you’ll often see geosynthetics underneath riprap or gabions.

“When our clients are installing riprap, we’ll never have them do so without placing geosynthetics underneath,” claims J.W. Lemons, general manager of the Stormwater Environmental Compliance Alliance (SECA), a stormwater consulting firm based out of North Richland, Texas. “You want those geosynthetics to be permeable, so the water can go through them, but you also want structural integrity so the rocks won’t slip and slide away.”

Reinforcement

– It’s crucial that the soil be as stabilized as possible, especially on steep slopes.

Reinforcing the soil through the use of geosynthetics is one way to do that. They vastly increase the strength of large chunks of soil, adding tensile strength on steep slopes or reinforcing channels in areas where stormwater is prone to flow and break up the soil.

Filtration

– In spots where you have large structures erected to contain stray sediment, such as bulkheads, you will most likely find geosynthetics there as well. They will allow the water to flow through the soil while keeping sediment particles in place, and they don’t cost much to install.

“If you don’t put geosynthetic fabrics behind bulkheads, all that water will eventually go right through it and take all the sand with it,” says Bonn. “Geosynthetics will act as a filter to keep the water flowing and the sand in place.”

Drainage

– One of the biggest challenges of erosion control is channeling the water. If you have stormwater, there’s a good chance you’ll have erosion as well, so you’ll want to find a way to channel that stormwater so it doesn’t become a problem. Many contractors will install French drains to redirect the water away from certain structures or areas that are prone to erosion. They can be used to reduce pressure on retaining walls, or even to provide roof gardens with a means of directing the water from the roof and into a cistern.

Containment

– Wherever you find large spoil piles of soil dredged up and set aside to use as backfill, you’ll find a need for geosynthetics. Containment usually involves draping an impermeable geosynthetic fabric over the piles to protect them from rainfall. Landfill covers and pond or canal liners are the most common ways in which you’ll find geosynthetics being used for containment.

Finding the right fit

There are numerous types of geosynthetics for numerous applications. Because there is no magic “cure-all” geosynthetic that will work every single time for each type of application, it’s important that you know what those different types are as well as the uses you can get out of them.

Geotextiles

– Within the last 30 years, geotextiles have grown immensely in popularity, gaining a solid foothold in the industry as the number-one type of geosynthetic there is. As stated earlier, there is no cure-all geosynthetic, but geotextiles come pretty darn close.

They can be used for separation, filtration, reinforcement and drainage. These flexible, permeable sheets can be either woven or nonwoven. Geotextiles are made of entirely polymer-based fibers, so they’re great if you want to install a long-lasting product. However, some clients prefer their products to degrade over time. To give the area a more natural, aesthetic look, you might want to opt for other types of geosynthetics that integrate biodegradable, natural-based fibers such as wood, straw or coir.

Geogrids

– These grid-like sheets are used exclusively to reinforce the soil. Geogrids have a rather unique structure. They contain openings which will interlock with the soil to firmly hold them in place and form a strong composite mass. Picture the way Lego blocks lock together with other Lego blocks. This is essentially what geogrids are doing to the soil.

They can either be stretched in one direction or two directions, depending on what use you want to get out of them. Bi-directional geogrids are better suited for when you want to distribute the tension over a wider area, such as under interstates, while one-directional products are used mostly on steep slopes.

Geomembranes

– Unlike other geosynthetics, geomembranes are impermeable, so no water can pass through them. It makes sense then that geomembranes would be a popular product to use in containment applications, when you need to ensure that no water leaches through them whatsoever.

“A lot of soil has to be stockpiled while the grading is being done, so we’ll end up leaving stockpiles there temporarily,” says Lemons. “In accordance with state laws, those piles have to be protected, so we’ll use massive amounts of geomembranes to keep them from washing away.”

Turf Reinforcement Mats (TRMs)

– TRMs have gained widespread recognition in recent years as popular alternatives to riprap.

These geosynthetic nets will cover the soil to help lock it in place while still allowing for vegetation to sprout out and become well established. Once the plants have grown, the vegetation will almost completely cover up the netting, rendering it practically invisible. TRMs are also capable of capturing loose seed and soil and sheltering it from wind and rain.

There are other types of geosynthetics, such as geonets (which are basically lightweight forms of geogrids), geocells, geosynthetic clay liners, geofoams and many, many more, but to go into any sort of detail on them would be enough to fill a textbook.

“There are probably about 500 different types of geosynthetics that are being used in the construction industry,” says Lemons.

“The key is discovering which ones you’ll need and which work best for you.”

The great learning curve

As practical a solution as geosynthetics are, some of those in the business are still struggling to come around to the technology. The reason for this, as O’Malley theorizes, is an inability to break from tradition.

“There are some who might give up on geosynthetics because they don’t understand all the nuances and details and maybe had a bad experience with an incorrect installation,” O’Malley explains.

“Instead of giving up completely, they just need to take a little bit of time to figure out what they did wrong.”

Simply Googling the term “geosynthetics” is sure to yield a tremendous wealth of useful information that you can take to work with you. But if you’re looking for more of a traditional classroom approach to learning, try contacting organizations such as SECA, which offer a variety of training classes to get contractors educated when it comes to geosynthetics.

“At SECA, we work to protect our clients from suffering the wrath of local erosion control laws,” says Lemons. “I’ve been in this business for more than three decades now, and I still find that there are tons of design engineers who don’t know a thing about geosynthetics.

If the contractors and the design engineers don’t know, then they probably won’t put up the proper erosion controls. As a result, they won’t be in compliance with state requirements, and this opens up a Pandora’s Box of trouble. I mean, you can face millions of dollars in fines if you don’t work to stabilize the area.”

Perhaps what should be stressed more than anything else is cost. Without geosynthetics, you could be stuck for days busting your back while building stone structures to keep the soil stabilized. This wastes countless dollars on labor and equipment. And it is becoming more and more expensive to install hard armor structures. Converting to geosynthetics has never been so practical an option.

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