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Cellular Confinement

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What types of fill can I use with cellular confinement?

Depending on the application, fill options for cellular confinement includes: sand or granular fill; top soil with vegetation; aggregate; and concrete.

Do I need a geotextile separator under cellular confinement?

The use of a geotextile separator under cellular confinement depends on the application, the type of fill used in relation to the existing subgrade, as well as other factors. For park-on, drive-on applications, often a geotextile is required to provide the critical function of separation. For slopes, a geotextile may create a slip plane for the cell. Please consult a geotechnical engineer for guidance.

What is a J-Hook?

A J- Hook is basically #3 rebar bent like a candy cane.

How long do J-Hooks need to be?

The length of the J-Hook should be 3 times the Envirogrid® cell depth.

Which product and cell depth are appropriate for a channels?

It depends on the infill material. For most channels utilizing rock, the EGA30 product is used due to its larger cell aperture. The cell depth depends on how much rock is required. The rock should be an angular rock with a size no larger than 1/3 the depth of the cell.

Which product and cell depth are appropriate for park-on drive on applications?

This depends on the vehicle tire footprint. For passenger vehicles, the EG20 is typically appropriate. For larger vehicles, the EG30 is typically appropriate. If you are not sure of vehicle size, default to the EGA20. This information is offered with the understanding that it does not constitute a specific engineering design.

What would be the steepest slope you would recommend for the embankment sides while using your product?

The maximum steepness of the slope depends on the infill material. The infill materials’ specific angle of repose will determine at what steepness the infill will fall out of the cell. The project engineer will need to make this determination.

What product would you suggest for light duty road construction?

For light duty road construction we would suggest the 4" EGA20 material. Always verify product suitability with an engineer that is familiar with the project conditions.

What product would you suggest for heavy duty road construction?

For heavy duty roads (those experiencing maximum load weighted 18 wheelers) we would suggest the 6" or 8" EGA30 material. If the infill material is different than the subgrade, we would suggest adding a 6 oz. nonwoven geotextile (US 160NW) under the cell. This information is not offered as an engineered design.

Can Envirogrid™ be used under track with railroad ballast?

Railroad ballast is an excellent application for Envirogrid™. The function of ballast in a railroad application is the same as the function of crushed rock in an unpaved road: to spread the loads imposed upon it by traffic from above to the layer below. If an Envirogrid™ panel with a small cell area is used with well-compacted ballast, the Envirogrid™/ballast system would distribute loads effectively as long as that compaction is maintained.

Internal friction is the mechanism that allows the ballast to spread the load and reduce the pressure on the subgrade. As the ballast is fouled with soil fines over the life of the track, the ballast layer must be cleaned or replaced. Fouling diminishes the internal friction, or the piece-to-piece (individual rock to individual rock) friction. However, the Envirogrid™ will confine the full depth of the ballast, maintaining a large percentage of its load distribution property even after some fouling takes place.

If the ballast layer is exposed directly to the subgrade soil, the Envirogrid will not prevent soil particles from being forced up into the ballast section. So a key question for the engineer is whether or not to use a separation fabric to prevent migration of fines and pumping. The separation geotextile should be a heavy weight non-woven. However, introduction of a nonwoven fabric on a steep grade, even if it has a relatively high coefficient of friction with respect to the subgrade, would increase the sliding potential of the fabric/Envirogrid™/ballast system. Therefore, you would need to anchor the track to the subgrade.

This information is offered with the understanding that it does not constitute an engineering opinion for a specific project.

Can an Envirogrid™ gravity wall be placed in front of an existing wall?

Envirogrid gravity walls can be built in front of existing walls. If the cellular confinement wall comes into intimate contact with the existing wall, it creates a composite wall system with greater sliding and overturning resistance and is better suited to resist loading. This information is offered as a guideline and does not constitute a project specific design.

Is exposure to the environment an issue for Envirogrid™?

Envirogrid is made of HDPE, the same material from which landfill liners are made, so exposure to the elements is typically not of great concern.

What is the coefficient of friction for Envirogrid™?

The polyethylene strips are textured and perforated such that the peak friction angle between the surface of the textured/perforated plastic and a #40 silica sand at 100% relative density is no less than 85% of the peak friction angle of the silica sand in isolation when tested by the direct shear method per ASTM D 5321.

Do you have any cellular confinement installation videos?

Yes. Click on this link to watch a YouTube video showing Envirogrid™ installed on a slope. This video shows stapling of panels; drilling holes for tendons; and tendon installation: Envirogrid™ Installation

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Cellular Confinement

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.