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To Combine Specifications
Planning & Design
Improve Soil Health
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Improve Soil Health & Provide Cover
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Steep Slope Techniques
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RECP Flap (Nonstandard)
What is This Treatment?
Slopes steeper than 2:1 (H:V) require a more aggressive approach to control erosion, particularly at the slope face. This technique builds up embankment (fill) slopes with layers of varying materials, and protects the slope face with Rolled Erosion Control Product (RECP). The layers of materials typically consist of:
- Geosynthetic reinforcement - typically placed 2' on center vertically.
- Backfill - typically structural material, local topsoil, imported topsoil, and/or compost.
- Rolled Erosion Control Product - coir/coconut blankets placed every other geosynthetic layer or 4' on center vertically. The blankets are placed to "flap over" and protect the slope face.
RECP Flap Training Video
When to Use This Treatment?
- Use for embankment (fill) slopes between 2:1 and 1.5:1 (H:V). Most commonly used to construct 1.5:1 (H:V) embankment slopes.
- For slopes steeper than 2:1 (H:V) a Geotechnical Design Report should be prepared by Caltrans Division of Engineering Services (DES) Office of Geotechnical Design. In addition, a preliminary evaluation may be required.
- Coordinate the use of this technique with Caltrans Division of Engineering Services (DES) Office of Geotechnical Design.
Consider Using With:
Even though the slope face is covered with RECP, vegetative cover is required to hold the soil in place after the RECP biodegrades. Healthy vegetative cover is promoted by also specifying:
- Local Topsoil
- Brush Layering
How is This Treatment Constructed?
- Structural backfill is placed in 8-inch lifts, and "keyed-in" to the adjacent existing slope at least 6.5 feet horizontally. Lifts of backfill are brought to 90% compaction by tractors (track-mounted crawlers).
- A geosynthetic reinforcement layer is placed horizontally between structural backfill lifts, typically every 2' on-center vertically.
- Following placement of the first geosynthetic reinforcement layer (and at every other primary geosynthetic reinforcement layer thereafter) RECP is placed and fastened longitudinally with fabric anchors.
- Placement of structural backfill and geosynthetic reinforcement continues in layers, like a cake. At every other geosynthetic reinforcement layer, typically every 4' on-center, the RECP is flapped over the slope face as shown in the detail below.
Note: This typical section is schematic only and can not be used in a contract document. The scale, key dimensions, and critical details have purposely been omitted.
- Slopes greater than 2:1 (H:V) are too steep to be compacted by trackwalking. In lieu of surface compaction, the RECP Flap protects the slope face from surface erosion.
- This technique does not require wrapping the backfill so it is less labor intensive to construct than the RECP Wrap.
- The slope face is stabilized and protected as the embankment (fill) is constructed. Completed lifts are protected from storm events and construction can resume quickly following rainfall.
- Promotes vegetation establishment and natural succession.
- May be cost prohibitive on large earthwork projects.
- Must be implemented during construction of embankment (fill) slopes. Cannot be retrofitted.
- Unsuitable for embankment (fill) slopes steeper than 1.5:1 (H:V) or slopes with limited access. Consider using Welded Wire Confinement on these slopes.
- Vegetation establishment may be limited when specifying a RECP with limited open area - such as 900 grams/square meter coir netting.
- Not suitable for slopes with subsurface water unless subsurface drainage is provided.
Technical Design Tips:
- Always protect the face of embankment (fill) slopes steeper than 2:1 (H:V) to prevent the slumping of soil from between horizontal geotextile layers.
- Strongly consider covering (flapping) the face of 2:1 (H:V) embankment (fill) slope faces, based upon evaluation of constraints to compaction, angle of repose, backfill material, and rainfall intensities.
- Backfill lifts typically range from 2 - 4 feet thick. Consider specifying Local Topsoil in the outer face of structural backfill lifts.
- Fill slopes steeper than 2:1 (H:V) will typically require reinforcement by a geosynthetic fabric such as a geogrid. Geosynthetic reinforcement strength needs to be sufficient to meet slope engineering requirements and should be specified by a geotechnical engineer.
- Consider the benefits and liabilities of natural geosynthetic products versus longer lasting inorganic (plastic) products.
- Specifications and details are under development.
- RECP Flap prices vary, but could run $50,000/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