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RECP Flap (Nonstandard)

Coir Flap

What is This Treatment?

Slopes steeper than 2:1 (H:V) require a more aggressive approach to erosion control due to an increased loss of soil at the slope face. This treatment covers slope backfill material with a flap of a Rolled Erosion Control Product (RECP) to reduce erosion at the slope face.

In general, this treatment consists of placing alternate layers of:

  • Geosynthetic reinforcement - typically placed 2' on center (measured vertically).
  • Backfill material - structural material, local topsoil and/or compost.
  • RECP, typically placed every other geogrid layer or 4' on center (measured vertically) which is used to cover and protect the slope face.

When to Use This Treatment?

  • Use for fill or reconstructed cut slopes between 2:1 and 1.5:1 (H:V). Most commonly used to construct 1.5:1 (H:V) fill slopes.
  • For 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.
  • Coordinate the use of this technique with the Division of Engineering Services (DES) Geotechnical Design Unit.

Consider Using With:

  • Even though the slope face is covered in RECP, vegetative cover is still required to mitigate the visual impact of decomposing RECP and hold the soil in place after the RECP biodegrades. Healthy vegetative cover is typically promoted by:

  • Local Topsoil
  • Duff
  • Compost Blanket
  • Hydroseed

How is This Treatment Constructed?

  • Structural backfill material 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.
  • 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 below.

Cori Flap

Benefits:

  • Since this treatment does not require wrapping the backfill, it is less labor intensive to construct than the RECP Wrap.
  • Slopes greater than 2:1 (H:V) are too steep to be compacted by trackwalking. RECP Flap reduces erosion at the slope face..
  • The slope face is stabilized and protected as the embankment is constructed. In the event of a sudden storm event exposed soil surfaces are protected. Construction can resume rapidly following a storm event.

  • Yields a stable and visually aesthetically pleasing slope compatible with its natural surroundings.

  • Easy to build.

Limitations:

  • 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 is difficult when RECP products with limited open area (such as 900 grams/square meter coir netting) is used as the flap material.
  • Not suitable for slopes with subsurface water unless subsurface drainage is provided.

Technical Design Tips:

  • Always cover (flap) 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 the use of 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 long-lasting inorganic products.

Specifications:

  • Specifications and details are under development.

Estimate Information:

  • RECP Flap prices vary, but could run $50,000/acre.

Guidance:

External Links: