Erosion Control Toolbox: Rolled Erosion Control Product Flap With Brush Layering

Introduction

 

This treatment uses locally obtained green cuttings, 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, which "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

• Use to construct embarkment (fill) or reconstructed cut slopes between 2:1 and 1.5:1 (H:V).
• Coordinate the use of this technique with Caltrans Division of Engineering Services (DES) Office of Geotechnical Services, which may prepare a Geotechnical Design Report for slopes greater than 2:1 (H:V).

Consider Using With

• Local Topsoil
• Duff
• Compost Blanket

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 compacted to 90% by 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 green 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, coir netting is draped or flapped over the slope face, and a layer of harvested cuttings, topsoil, and compost is placed.

 

Note: This typical section is schematic only and is not to be used in a contract document. The scale, key dimensions, and critical details have been intentionally omitted.

Benefits

• Provides immediate slope reinforcement with unrooted brush cuttings and horizontal geotextiles. As roots develop, slope stability and shear resistance are improved by creating a rooting matrix with geogrids throughout structural lifts.
• Cuttings create slope breaks that shorten slope length and reduce stormwater runoff velocities.
• Promotes vegetation establishment, cover, and natural recruitment.
• This treatment does not require wrapping the backfill, and is less labor intensive to construct than RECP Wrap.
• Provides the resistive force necessary to hold the soil firmly in place in lieu of compaction by trackwalking.
• The slope face is stabilized and protected from storm events as the embankment is constructed, therefore construction may resume immediately after rainfall.
• Yields a stable and 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 the 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 slumping of soil from between horizontal geotextile layers.
• 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) 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.

Updated: February 1, 2019