California Department of Transportation
 

RECP Flap With Brush Layering (Nonstandard)

Brush Layering on a Fil lSlope

What is This Treatment?

This treatment involves using locally obtained green cuttings, coir netting, a Rolled Erosion Control Product such as coir netting, structural backfill material, and local topsoil to construct embankment (fill) slopes. More specifically, this treatment consists of placing layers of:

  • Geosynthetic reinforcement - typically placed 2' on center vertically.
  • Backfill - typically structural material.
  • 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.
  • Local topsoil or compost to provide a rooting media for cuttings.
  • Green locally harvested cuttings of cottonwood or willow.

When to Use This Treatment?

Consider Using With:

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) 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.

Brush Layer With RECP Flap

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.

Photos of Installation

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.
  • Promotes 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.
  • Promotes vegetation establishment and natural succession.

Limitations:

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

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:

  • Specifications and details under development.

Estimate Information:

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

Guidance:

External Links: