Erosion Control Toolbox: Rolled Erosion Control Product Flap
Slopes steeper than 2:1 (H:V) require a more aggressive approach to control erosion, particularly at the slope face. This technique builds up embankment (fill) slopes with layers of materials, and protects the slope face with Rolled Erosion Control Product (RECP). The layers typically consist of:
- Geosynthetic reinforcement - typically placed 2' on center vertically
- Backfill - typically structural material, local topsoil, imported topsoil, and/or compost
- 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
Rolled Erosion Control Product Flap Training Video
When to Use This Treatment
- Use to construct embankment (fill) 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
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) 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 in the detail below.
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.
- RECP Flap protects the slope face from surface erosion
- This technique does not require wrapping the backfill and is less labor intensive to construct than RECP Wrap
- The slope face is stabilized and protected from storm events as the embankment (fill) is constructed, therefore construction may resume immediately after rainfall
- Promotes vegetation establishment and natural succession
- Vegetative cover is required to hold soil in place after RECP degrades
- May be cost prohibitive on large earthwork projects
- Must be implemented during construction of embankment (fill) slopes and cannot be retrofitted
- Unsuitable for embankment (fill) slopes steeper than 1.5:1 (H:V) or slopes with limited access
- Vegetation establishment may be limited when specifying a RECP with limited open area - such as 900 grams/square meter coir netting
- Not suitable for slopes with subsurface water unless subsurface drainage is provided
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) slopes 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 on the outer face of structural backfill lifts.
- Fill slopes steeper than 2:1 (H:V) typically require reinforcement with 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: January 30, 2019