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RECP Flap With Brush Layering (Nonstandard)

Brush Layering on a Fil lSlope

What is This Treatment?

This treatment involves the use of coir netting, local cuttings, geosynthetic reinforcement and structural backfill material to construct embankment (fill) slopes.

More specifically, this treatment consists of placing layers of:

  • Geosynthetic reinforcement - typically placed 2' on center (measured vertically).
  • Backfill - typically structural material.
  • Coir (coconut fiber) netting, typically placed every other geogrid layer or 4' on center (measured vertically) which is used to cover and protect the slope face.
  • Local topsoil or compost to provide a rooting media for cuttings.
  • Green locally harvested cuttings of alder, cottonwood, or willows.

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:

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).
  • 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) coir netting is placed and fastened longitudinally with fabric anchors.
  • A layer of local topsoil and compost is placed on top of the coir netting.
  • A layer of locally harvested cuttings is placed on top of the local topsoil and compost growth media.
  • 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 coir netting is draped or flapped over the slope face, and a layer of harvested cuttings, topsoil, and compost is put in place.

Cori Flap

Graphic showing coir flap construction without brush layers.

 

Cori Flap 1 Coir Flap 2

Coir Flap 3 Coir Flap 4

Photographs of installation sequence for coir flap with brush layering.

Benefits:

  • Provides immediate slope reinforcement from unrooted brush cuttings and horizontal geotextiles. As roots develop, improves slope stability and shear resistance by creating a rooting matrix with geogrids throughout structural lifts.
  • Cuttings create slope breaks that shorten slope length and reduce runoff velocities.
  • Cuttings extract subsurface water from backfill material.
  • Provides for vegetation establishment, cover, and natural recruitment.
  • Since this treatment does not require wrapping the backfill, it is less labor intensive to construct than the Coir Confinement.
  • Slopes greater than 2:1 (H:V) are too steep to be compacted by trackwalking. Coir confinement provides the resistive force necessary to hold the soil 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.

Limitations:

  • Unsuitable for embankment (fill) slopes steeper than 1.5:1 (H:V), or slopes with limited access.
  • Subsurface drainage may be required for slopes with subsurface water.
  • Requires accessible, local stand of alders, cottonwoods or willows from which to harvest cuttings.
  • Unsuitable for slopes with limited equipment access.
  • May require supplemental irrigation during establishment period, particularly during first dry season and on south-facing slopes.

Technical Design Tips:

  • Always cover (flap) the face of embankment (fill) slopes steeper than 2:1 (H:V) to prevent the slumping of soil between 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.
  • Geotechnical and hydrologic conditions must be evaluated.
  • Typical encapsulated lifts range from 1 to 3 feet thick Topsoiling may be used between 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.
  • Reinforcement strength needs to match application conditions. Use of natural, biodegradeable products vs. long-lasting geotextiles should be weighed.

Specifications:

  • Specifications and details under development.

Estimate Information:

  • RECP Flap with Brush Layering prices not currently available..

Guidance:

External Links: