The ideal soil for construction projects is easily compactible and free draining. Unfortunately, a free draining soil is often difficult to compact. Non-compacted or weak soils can be displaced by stress forces and are subject to erosion. Cellular confinement (EnviroGrid™) is a solution. By confining the soil particles, cellular confinement allows the use of free draining and poorly compacting soils.
Aggregate is another free draining material that may not compact well. It can also be expensive to produce and haul. When used with a nonwoven geotextile separator, cellular confinement can significantly reduce both the amount and the quality of aggregate required to stabilize a poor load bearing soil.
How Envirogrid™ Works
EnviroGrid™ confines material and prevents lateral movement away from the applied load. The connected and filled cells create a panel that acts like a large mat, spreading the load over an extended area. As such, cellular confinement works in a myriad of applications: driveways and parking lots; wetland crossings; nature and bike trails; sports fields; beach access and emergency vehicle access areas.
A Bit of Cellular Confinement History
It is interesting to note that the first cellular confinement was not necessarily black in color or made of polyethylene. Early attempts included wax-coated craft paper, drainage pipe stapled together, thin and hexagon shaped aluminum glued together, various medium-density recycled materials, polyethylene without UV stabilizers and square cells constructed in a pattern similar to egg cartons.
In the late 1970's The US Army Corps of Engineers (USACE) began research and development of a stronger confinement system for sand applications that would maintain strength under heavy vehicle loads. They welded strips of plastic into a rectangular, expandable honeycomb structure that when filled with sand supported the heavy loads applied by military vehicles and resisted erosion by wave action.
In 1984, the military demonstrated the effectiveness of cellular confinement in an exercise at Fort Story, Virginia involving thousands of passes by military vehicles over roads constructed of sand and cellular confinement.
In 1990, 6,400,000 sf of cellular confinement were successfully utilized during Operation Desert Storm, including the rapid construction of fortified walls.
Vertical Walls With Envirogrid™
The price of prime land often prohibits the least expensive approach to stabilizing a slope: reducing the slope angle. This method produces a stable, vegetated structure, but wastes land space by creating a large footprint at the toe of the embankment. A cast-in-place concrete retaining wall creates a similar problem because the size of the footing of a cantilevered wall gets wider as the wall gets taller.
A mechanically stabilized wall with a facing of precast panels would minimize the structures' footprint, but is by far the most expensive option. Utilizing segmental block for the face can be cost effective, but labor intensive due to the weight of the blocks (80#-125#). Neither of these structures offers the environmentally pleasing option of a vegetated face. With any vertical wall, hydrostatic pressures developing behind the face are a concern.
An EnviroGrid™ wall can be an esthetically pleasing, labor efficient and cost effective solution. These structures have the flexibility to conform to the curves and contours of the landscape and accommodate potential settlement. The use of perforated EnviroGrid™ efficiently relieves hydrostatic pressure by providing drainage throughout the entire structure. The outer cells can be vegetated, creating a green structure that will blend into the surrounding, natural area. The first flexible cellular confinement wall was constructed in 1988 in Richmond Hill, Ontario.
EnviroGrid™ as Erosion Control
EnviroGrid™ is an excellent choice for use in steepened slopes and channels where erosion is a concern. Three fill options (granular, vegetated, concrete) create a durable system with the flexibility to address hydraulic concerns and control individual particle movement, piping, undercutting, gutting and rills.
Envirogrid™ in Green Roofs
For green roof slopes exceeding a few degrees, a reinforcement material may be required to prevent downward sliding. Cellular confinement such as US Fabric's Envirogrid® offers flexibility in achieving this goal. Next time you are at the new Washington Nationals Park, check out the batter's eye in center field. Envirogrid® is reinforcing the vegetation in this unique architectural feature!
Envirogrid™ Features & Benefits
EnviroGrid™ reduces the size of retention/detention pond areas and decreases maintenance and repair costs up to 50% over asphalt. The cell opening is 68% smaller than any other confinement product available and the large panel expansion increases installation rates. Made from flexible HDPE, EnviroGrid™ is resistant to damage during shipping and installation, the panels are easily cut in the field with a utility knife and ship collapsed for easy storage. A 7' x 3.5' x 3' pallet holds up to 5,800 sf of material.