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RECP Wrap (Nonstandard)

Coir Confinement System

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 wraps slope backfill material in Rolled Erosion Control Products (RECP) to resist soil and hydrostatic pressures that may erode a 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 wrap the vertical face of the slope.

When to Use This Treatment?

  • Use to construct fill or reconstructed cut slopes that are between 2:1 and 1.5:1 (H:V). Most commonly used to construct 1.5:1 (H:V) fill slopes.
  • Use in lieu of RECP Flap where there are subsurface water flows.
  • 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.
  • 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 wrapped in RECP, vegetative cover is required to mitigate the visual impact of sagging RECP and hold the soil in place after the RECP biodegrades. Healthy vegetative cover is typically promoted by:

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 (typically geogrid) 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 wrapped around the slope face as shown below.

Coir Confinement Detail

 

Coir Confinement Detail 2

Benefits:

  • Slopes greater than 2:1 (H:V) are too steep to be compacted by trackwalking. RECP Wrap provides the resistive force necessary to hold the soil at the slope face firmly in place in lieu of trackwalking.
  • 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 for slopes that have 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.
  • Subsurface drainage may be required for slopes that contain subsurface water.

Technical Design Tips:

  • Always wrap the face of embankment (fill) slopes steeper than 2:1 (H:V) to prevent the slumping of soil between geotextile layers.
  • Strongly consider wrapping the face of 2:1 (H:V) embankment (fill) slopes, based upon evaluation of compaction constraints, angle of repose, backfill materials, and rainfall intensities.
  • Encapsulated 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:

Guidance:

External Links: