New geotextile manages water and soil stabilization issues
By Jan Brenny
The Industrial Fabrics Foundation (IFF) selected TenCate’s new water-wicking geotextile, Mirafi® H2Ri, as the recipient of this year’s Innovation Award. The product was officially launched with the announcement of the award at IFAI Expo Americas 2011.
The story of Mirafi H2Ri began with one question at a business meeting in Alaska between officials from that state’s Department of Transportation (DOT) and representatives from TenCate Geosynthetics North America, Pendergrass, Ga.
“We always ask, “What problem do you have today that can’t be solved with geosynthetics?’” said David Jones, TenCate’s director of product and application development.
Alaska officials cited the difficulties of building and maintaining roads in a harsh climate and over problematic geology. “When you build over the tundra, you’re on frost-susceptible soils, which take in water at different rates,” Jones explains. “When the water in the soil freezes, it expands and contracts at different rates, creating frost heaves or frost boils. We figured we can’t stop that, but then we figured if the entire road did the same thing at the same time, there wouldn’t be a problem.”
Moving the water
The TenCate team contemplated how to create an industrial fabric that would improve the situation. The initial planning phase, which involved qualifying and quantifying exactly what features the fabric should have and how it should perform, took about 18 months, Jones said. “Could we move water out of the road system? Yes, but how much would be enough?”
The textile would have stability applications, so it needed to allow sufficient water to pass through while holding back small soil particles. It would also need to be strong enough to withstand extreme stresses and pressure, but still be lightweight and cost-effective to use.
Once the plan was in place, the team began experimenting with composition and materials. In designing a fabric with the stated goals in mind, “We figured the only way to do it was to build the fabric vertically,” Jones said. “We needed to make it thicker.” With more than one layer, the fabric could channel enough water, but the holes could still be small enough to block particles from flowing through.
Developers knew the choice of yarn would play a significant role in how the fabric performed. They found a fiber with a geometric shape to maximize surface area, providing optimum wicking capabilities, but getting everything right took trial and error.
“Two-layer weaving was new to us,” Jones said. “We went through 23 trials on the loom, looking at the samples and trying to figure out how to balance soil retention and water flow-through.” The project was nearly complete.
A new fabric category
At about the same time the team in Georgia was working on the textile first conceived in Alaska, TenCate’s European division was finishing its own new product. After four years and more than 120 extrusion trials, the European division had developed a stiffer, high-modulus yarn that could bear increased loads at lower elongation points. The new fiber “basically doubled the modulus,” Jones said. “It was really an innovative breakthrough for us.”
That kind of strength—especially for applications such as road stabilization—coupled with the fabric’s water-wicking capabilities, would create a fabric in a category by itself. After another 12 loom trials adding the new yarn to the mix, Mirafi H2Ri was born. “Once we saw what we had, we said we need to revamp all of our products and put in this new-generation technology,” Jones said.
In August 2010, TenCate tested Mirafi H2Ri in Alaska on the Dalton Highway, a road running from north of Fairbanks to the Arctic Ocean and subject to frost-related damage due to uneven moisture levels in the soil.
To test Mirafi H2Ri’s water-wicking ability, TenCate engineers dug out several feet of the existing road at mile marker 110. They graded the surface and installed a section of Mirafi H2Ri at a depth of about 3 feet. Engineers covered that with a foot of dirt, compacted it, and installed a second piece of fabric at a depth of about 18 inches. Workers placed sensors between the layers of fabric, opened the road for use, and monitored the sensors for more than a year.
The results showed that the moisture moved out of the roadbed, preventing frost-related damage. Areas on either side of the fabric installation sustained the typical frost-related road damage.
“[The fabric] won’t drain a lake,” said Jones, “but it will move moisture around so you don’t have saturated and unsaturated areas. That’s the true benefit of the fabric.”
Not just the frozen North
The recently introduced (and patented) geosynthetic material is now installed in several roads vulnerable to frost-related damage in Alaska and northern Canada. As of this fall, more than 30 new or revamped products are on the innovation list, with half a dozen “on the same caliber” with the kind of innovation found in Mirafi H2Ri, Jones said. Most will be in development for another 18–24 months.
Jones says the product use potential is “anyplace where water and the need for stabilization come together”—for instance, the clay soils of Texas. “They’re expansive soils, so as long as they’re wet, they’re fine,” he said. “But they’re like Play-Doh. If they dry out, they develop huge cracks. If you’re building over those types of soils, foundations will crack, and that’s a problematic issue.”
Tests are continuing at The University of Texas at Austin.