Very few weather events can test the strength of geosynthetics as a hurricane.
That’s exactly what happened last August 19 when Hurricane Dean—which had grown to be a Category 4 hurricane—pounded the southern coast of Jamaica with wind speeds of up to 155 miles per hour, killing three people and causing about $5 billion in damage.
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Photo: GeoProducts |
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Photo: GeoProducts |
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Photo: GeoProducts |
Nonwoven geotextile and Envirogrid lined earthen pond structures at a wastewater treatment plant in Jamaica.
The structure withstood a Category 4 hurricane in 2007. |
Employees of In-Line Plastics, a manufacturer and installer of polyethylene geomembranes for GeoProducts, had attained 95% completion of a geosynthetic project at the Soapberry Wastewater Treatment Plant near Kingston, Jamaica, when the hurricane hit.
In-Line Plastics produces low-density and high-density polyethylene (HDPE) in measurements of 12, 20, 30, and 40 mils. Crews travel worldwide for installation, or panels are prefabricated and shipped to end users.
In Jamaica, the installation suffered no damage as a result of the hurricane, although the entire installation crew could not be demobilized to fly back to the United States, with two remaining behind to ride out the hurricane.
In the four months leading up to the storm, the crews had been working at the Soapberry plant, Kingston’s first wastewater treatment plant.
“In the past, all of the sewer disposal was going directly into the ocean,” says the company’s Al Florez. “There is a set of ponds for the wastewater treatment plant. The requirement the engineer had was that they have enough clay materials for the bottom of these ponds, but they did not have enough for berms that they were creating that would separate one pond from the one adjacent to it.
“There were two sets of dikes for ponds that were next to each other. We lined the dikes for the slopes with a 40-mil high-density polyethylene and then used a 6-ounce nonwoven geotextile and then 3-inch Envirogrid [a three-dimensional HDPE system] that was filled with concrete.
“The reason for the liner was to impede the water from filtrating through the soil and deteriorating those berms for the dikes,” says Florez. “The Envirogrid filled with concrete was to protect against any type of impact from hurricanes.”
The original design had called for earthen dikes and slopes and then for the Envirogrid filled with concrete or 60-mil liner on top of that, notes Florez. “We reversed the order by allowing the concrete structure to be on top,” he says. “Being able to use material that was not so thick—dropping it from a 60-mil to a 40-mil—saved the project owner 50% of the cost of the liner alone.”
The initial concern about water penetrating the berms was of high priority, and the liner being in place limited the ways that concrete could be poured on top of that liner, because the typical situation was to create wooden forms, says Florez. “The forms have to be anchored to the ground below, and when you anchor it, you would then perforate the liner,” he says. “With the Envirogrid material, you expand the cells on top of the geotextile, which is on top of the liner, without any need of penetrating the geomembrane whatsoever.”
This type of application is becoming more common with engineers and those owning ponds who want to protect pond perimeters, says Florez. “Sometimes it’s to protect it from puncturing, and at other times it’s so it is aesthetically pleasing,” he says.
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Photo: GeoProducts |
| Workers place the three-dimensional grid at the Soapberry plant. |
Ponds can look “ugly,” Florez notes, “because when the water goes down, you see the black liner. But by laying the Envirogrid on top of it and filling it with soil, you can vegetate it so the pond looks natural.
“In Jamaica, [the Envirogrid] was used to protect the geomembrane, and the best way to protect it was with concrete, but the standard way of pouring concrete would have not done the job. It would have damaged the liner, so the use of Envirogrid allowed them to pour the concrete directly on top of the geomembrane on the geotextile without any use of stakes.”
Expansion in Edmonton
The city of Edmonton in Alberta, Canada, has been expanding rapidly to the south and west. Two years ago, the only freeway to transport traffic through the area was the Whitemud Freeway.
But the freeway was constantly congested during rush hour, and it was evident that a new roadway had to be constructed to reduce the inevitable gridlock that would occur with Edmonton’s continued population boom.
The result was the construction of the Anthony Henday Drive, also known as Highway 216, which traverses the southern and western boundaries of Edmonton.
Its construction, however, crossed the North Saskatchewan River and several creeks. That, coupled with steep slopes, called for an erosion control approach that would protect the adjacent waters.
The original design featured an arch structure with wing walls and a tiered concrete-faced wall system. The plans were changed to incorporate a geogrid-reinforced soil slope (RSS) system.
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Photo: GeoProducts |
| Aerial view of the Soapberry plant |
That system was provided by the Layfield Group. Using LP 120T PVC-coated polyester geogrid, the company worked with the prime contractor and geotechnical engineer to complete a final design. The slope was completed in early 2005.
“The main issue was to provide slope reinforcement, erosion protection, and long-term stability to a steep slope,” says Robin Tweedie, a principal with Thurber Engineering, the geotechnical engineering firm.
“The contractor had looked at several alternate proposals—including a reinforced earth–type scenario—and eventually he decided this one met his requirements best, so we were involved in the geotechnical design of it.”
The slope started at about 1.2:1 and, moving away from the arch, eventually became a general slope of 3:1. The steep area that required slope stabilization was close to the arch and adjacent to Whitemud Creek.
Dallas Lindskoog, the project manager on behalf of Kiewit Management, the prime contractor, notes that there was not a large area in which to work.
Obviously a 1:1 slope doesn’t stand up on its own, so we had to find some way of reinforcing it. That’s why we went to the geogrid,” he says.
Other materials provided by the Layfield Group include the LP 30T polyester geogrid, 4-inch geocell, and PP5-10 turf reinforcement mat (TRM). “The only other options were retaining wall structures, which were not feasible at the time,” says Lindskoog.
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Photo: Layfield Group |
Turf reinforcement mats and geogrid were used on the
Highway 216 expansion in Edmonton. |
The erosion matting used was a combination of a Geoweb system with a criss-cross pattern about 4 inches deep to hold topsoil. It was nailed into the slope. The Geoweb was filled with topsoil and seeded, and then the PP5-10 TRM was placed on top to provide the erosion protection.
The erosion control approach was necessary to protect the creeks adjacent to the freeway. “With the steep slopes around the creek, you certainly don’t want any runoff eroding the clay soils we have around here and ending up in the creeks,” says Tweedie. “The turf reinforcement matting on the slope was used specifically to anchor the material and prevent erosion until the natural vegetation got a chance to take hold.”
The only challenge was that the project was delayed due to wet weather. “Because of that, it took a long time to put the geogrids in and raise the slope up, but from a geotechnical point of view there were no significant delays after we had completed a reasonably good design,” says Tweedie.
“The workability of the geogrid was fantastic,” notes Lindskoog. “The rolls didn’t have a memory. You lay them on the ground, and they stay where you put them. They didn’t kick back on us. You could cut it with a pair of scissors, so it was safer than using a retractable blade of any kind. It was lightweight and easy to work with.”
Lindskoog drives on the road every day, “and there are no signs of any kind of lateral movement whatsoever,” he notes.
Two years after the project, the product has been performing well, Tweedie notes. His company has been involved with a similar project for Edmonton, addressing a slope failure with geogrid reinforcement, clay, and a cover of coconut (coir) matting, which also is performing well, he notes.
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Photo: GeoProducts |
| Ponds at the Jamaica treatment plant |
Increasing Buildable Space
As plans were under way to build Castleberry Community—a residential development in Cumming, GA—one major erosion control challenge manifested itself: the sheer size of the wall.
“The stream buffers were quite a challenge, as well as the height of the structures, the close proximity of the building units behind the structures, and the overall size of the project,” says Thomas Rainey, a senior geotechnical engineer with Soil Reinforcement Design in Woodstock, GA.
The main purpose of the slope was to provide more build space for condominiums and residential homes. The slope started at the base of the project and peaked at 30 feet high in several areas. A vegetated slope was determined to be the most cost-effective approach.
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Photo: TenCate |
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Photo: TenCate |
| Geosynthetic fabric and welded wire baskets provided reinforcement for this 30-foot wall. |
The wall was designed to allow loading at the top of the slope. There were more than 71,000 feet of face.
The base was a well-compacted subgrade, and TenCate Mirafi HS Geosynthetics were installed as a primary reinforcement. Mirafi HS400PP and HS800PP are blended polypropylene/polyester high-strength geosynthetics that were used to provide primary reinforcement to the slope. Some 53,500 yards of the HS400PP were used in addition to 58,000 yards of the HS800PP. The HS400PP embedment lengths varied from 15 to 20 feet.
About 42,500 square yards of Mirafi MMESH, a biaxial geogrid, was installed as the face wrap material with 3-foot welded wire baskets to provide secondary reinforcement as well as a stable platform for hydroseeding.
The wall was sealed immediately after completion to allow grass to grow as quickly as possible. Project installation lasted about 10 months. After its completion, the grass successfully took to the wall.
“We’ve used this approach on a number of other projects. The owner/developer wanted a green solution; they wanted something vegetative,” says Rainey. “They didn’t want the stark concrete look, so the vegetative reinforced slope was a good fit.
“Our firm worked hand-in-hand with the contractor and the owner/developer to work out field adjustments when changes needed to be made on plans,” says Rainey. “In the field, the topography might have been off a little bit, so having an engineer onsite during construction really helped. It allowed us to address questions and changes quickly.”
The overall project began in March 2005 and was finished in September 2006. “We’ve had no complaints, and there have been no adverse impacts to the residential structures. It’s performing admirably,” says Rainey.
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Photo: GeoProducts |
| Liner is placed on earthen berms at the Soapberry plant. |
Protecting Dams
Over the years, Colorado Lining International has engaged in a number of projects involving dam protection or rehabilitation.
At the Tesla Hydroelectric Facility in Colorado Springs, CO, the Tesla Regulating Reservoir was completed in late 1996 and involved the fabrication and installation of approximately 2 million square feet of geotextile, geocomposite, and geomembrane. Colorado Lining International deployed an installation crew of 25 to address the long, steep slopes and handle the large fabricated panels.
The geosynthetic design featured an 8-ounce nonwoven geotextile underlayment under the entire lining system, with a single-sided composite drainage net along the face of the dam and approximately halfway out into the reservoir. Some 800,000 square feet of 36-mil reinforced Hypalon geomembrane was laid on top.
Boulder’s Goose Lake Dam is located at 10,500 feet and is fed by snowmelt from the continental divide. Colorado Lining was called upon to assist in the rehabilitation of an existing rock and crib dam, built by Boulder in the early 1900s for water storage. The highest section of the dam is 36 feet and varies from being vertical to a 1:1 slope.
The geosynthetic design called for a 16-ounce nonwoven geotextile protective layer against the face of the dam with a 45-mil reinforced polypropylene geomembrane mechanically attached to the top and bottom of the dam, enabling the panels to be fabricated to size, limiting the number of vertical field welds. The membrane was installed with four field seams. The total underlayment involved 18,900 square feet.
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Photo: Layfield Group |
| A geogrid-reinforced system helped stabilize slopes around this arch structure on the North Saskatchewan River. |
In Cabo San Lucas, Mexico, is a water reservoir designed to service the water needs of a Tom Fazio 18-hole golf course and 250-home community, the Querencia Golf Club. In the first of two phases of a geosynthetic installation, Colorado Lining installed a cofferdam in the upper section of the main reservoir to facilitate immediate water storage for irrigation of newly planted sod.
The lining system consisted of a 12-ounce nonwoven geotextile underlayment with a 45-mil reinforced polypropylene geomembrane. A total of 77,454 square feet of material was used. The panels were custom-fabricated to enable a rapid and efficient installation.
Following the completion of the cofferdam section, Colorado Lining continued the lining, installing 565,000 square feet of materials for each layer, including a double-lined dam facing.
In Gardnerville, NV, Colorado Lining was involved in a project at Mud Lake Dam, which is located at the base of the Sierra mountain range and built more than 100 years ago. As such, it had no longer met Nevada Dam Safety standards.
A geomembrane with geotextile protective layers and a concrete-filled tendon-supported Presto Geoweb armor cover was proposed by Colorado Lining as a cost-effective alternative to a traditional reinforced concrete faced dam.
For the first layer, 16-ounce nonwoven geotextile was installed over the entire dam face to provide protection for the membrane and drainage. The second layer consisted of custom-fabricated 45-mil reinforced polypropylene panels (RPPs).
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Photo: GeoProducts |
| Work at the Soapberry Wastewater Treatment Plant |
The third layer entailed nonwoven geotextile providing an additional protective and supporting layer between the RPP- and tendon-supported Geoweb cellular confinement system.
The fourth layer was tendon-supported Geoweb, with tendons secured to 80 deadmen along crest anchor trench, which was filled with 500 cubic yards of concrete.
The geomembrane provides a barrier to prevent water infiltration through the dam face. The tendon-supported Geoweb filled with 3 inches of concrete was expected to provide long-term membrane protection.
The construction allows for quick retrofits of dam facing structures, while simultaneously cutting costs. The project has endured mild earthquakes without damage to the facing elements.