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Erosion Control Toolbox
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Improve Soil Health
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Wire Blanket (Nonstandard)
When to Use This Treatment?
- Use for cut slopes 1.5:1 (H:V).
- To use this product on slopes steeper than 2:1 (H:V) a Geotechnical Design Report should be prepared by the Division of Engineering Services (DES) Geotechnical Design Unit. In addition, a preliminary evaluation may be required by DES Geotechnical Design.
- Use of this product should be coordinated with the Division of Engineering Services (DES) Geotechnical Design Unit.
What is This Treatment?
Wire blanket is composed of biodegradable coir netting sandwiched together with a welded wire mesh, that is anchored in place with slope anchors. A vegetative cover is provided by a final hydroseeded application of fiber, seed, and fertilizer.
Wire Blanket is also known as Erosion Control (Type B).
This treatment includes the following products:
Netting consists of a braided coir strand weave with 3/4 inch openings that yield a 63-70% open area, an opening sufficient to accept and germinate hydroseeded material. This coir netting has an estimated life span of 4-6 years.
Using Rolled Erosion Control Product (Netting) instead of Rolled Erosion Control Product (Blanket) allows erosion control materials to be applied as the last treatment. When using blankets, the erosion control hydroseed treatment must be applied first on the ground surface prior to the placement of the blanket material. Often, due to steep slope conditions, much of the erosion control materials is displaced, migrates and is covered during placement and anchoring of the blanket material. This results in spotty vegetative growth. The use of coir netting allows the mechanical erosion control treatment to be installed first and the hydroseeding to occur when scheduling permits. This is a distinct advantage when stabilizing disturbed slopes at the earliest opportunity given that a general contractor can install the mechanical erosion control materials and then call in the hydroseed contractor at a later date.
Welded wire mesh with a nominal opening of 2" x 4" is placed atop the coir netting to help prevent slope slumping. Coir netting alone has proven ineffective at holding back saturated material in steep slope conditions. The wire mesh provides mechanical support while the coir netting controls surface erosion. Adjoining sections of wire mesh are fastened together with 10-gage wire.
The wire mesh and coir netting are fastened in place with slope anchors. Composed of either ductile iron or aluminum, the slope anchor is designed to provide holding capacity as well as pull out resistance once locked in place. A 1/2 inch diameter threaded anchor rod, 30 inches in length, secures the anchor to a surface mounted plate. Anchor plates, as seen in the photo above, are composed of either metal treated with corrosion-resistant coating, or hardened polyethylene.
The final element of this technique is a Erosion Control (Hydroseed) application of fiber, seed, fertilizer, and tackifier that is applied over the netting face. The hydroseed materials are applied at a close range so that the materials are well integrated into the netting face and in contact with the soil surface below.
A typical hydroseed seed mix consists of native grass species mixed with a sterile cereal grain such as Briggs barley, Re-green (triticum) or California red oats. Cereal grains provide a quick vegetative cover and grow in shallow soils with low nutrient value. Even though sterile cereal grains provide fast cover, they are not invasive or persistent, a particularly desirable habit in undisturbed native plant communities where re vegetation will occur naturally and there are concerns about introducing non-native plant material.
- Provides immediate slope reinforcement.
- Increases infiltration rates on dry sites.
- Provides for vegetation establishment, cover, and natural recruitment.
- Unsuitable for rocky slopes as it is difficult for slope anchors to fasten the materials in place.
- Specifications and details under development.
Consider Using This Specification With:
To effectively treat sites with compacted, sterile or poorly draining soils, consider combining this treatment with:
- Cost varies, but could run $120,000 per acre.
- David W. Yam, " Slope Face Stabilization For Critical Slope Surfaces", State of California, Department of Transportation, District 04, 2008.
- Bowers H.D. "Erosion Control on California State Highways", State of California Division of Highways, 1949.
- Gray D.H. and Leiser A.T. "Biotechnical Slope Protection and Erosion Control", Van Nostrand and Reinhold Company Inc., New York 1982, pg. 26.
- Hoek E. and Bray J.W. "Rock Slope Engineering", The Institution of Mining and metallurgy, London 1981 pg. 27