Industry specifications guide application of rolled erosion control products
BY THE EROSION CONTROL TECHNOLOGY COUNCIL
The use of rolled erosion control products (RECPs) has grown at a swift pace during the last decade. These advanced systems shelter seed and soil from potential loss, as well as control water to promote faster vegetation growth. Permanent turf reinforcement mattings (TRMs), a type of RECP, even provide anchoring for root and stem systems of plants at the soil surface.
RECPs have proven to be a consistently efficient way to stop erosion on moderate to extreme slopes, low- to high-flow channels, and numerous other applications. Furthermore, they typically cost as much as 75 percent less than hard armor solutions. RECPs also provide the environmental and aesthetic benefits lacking in some erosion control alternatives, such as rock riprap and concrete paving.
The RECP industry consists of several manufacturers that create a variety of erosion control blankets, TRMs, and other products that work in a wide range of situations (see "Types of rolled erosion control products," page 35). All of these options, however, sometimes can make choosing the right RECP for an application seem like a difficult process.
In 1992, the Erosion Control Technology Council (ECTC) was created to encourage manufacturers, universities, consultants, agencies, and research laboratories to work together to formulate and establish performance standards for RECPs. Most of the members of the ECTC have a mix of engineering and agronomic expertise. As a unified group, the ECTC has the technical capability to establish industry- wide standards that help define the appropriate use of RECPs.
Once it is determined that an RECP can be used appropriately for an application, the next challenge is selecting the appropriate properties and specifying the correct values for the application.
The ECTC recommends using both performance properties and index testing when specifying products.
Simple tests that measure a specific property of a material for the purpose of comparing products or monitoring production are called index tests. Some index tests are performed during manufacturing to evaluate product integrity, quality, and continuity, as well as to assess the impact of changes in production methodology on product properties. Typical RECP quality control tests include mass per unit area, thickness, and tensile strength.
Performance tests evaluate properties under bench- or large-scale conditions that indicate how a product might perform in the end-use application. Typical RECP performance properties include maximum shear resistance, C-factor, and ultraviolet resistance.
The ECTC developed standard specifications using index values and performance capabilities for both temporary and permanent RECPs. (The specifications, which are available at www.ectc.org/spec.html, were improved recently; the June 2004 version is the most up-to- date.) The ECTC guidelines for specifying products closely correlate to the Federal Highway Administration’s FP-03 document.
For temporary applications, where natural vegetation alone will provide permanent erosion protection, design recommendations are indicated for maximum gradient and C-factor values for slope applications. Also, maximum shear stress values for channel applications are listed.
Additionally, the minimum tensile strength necessary for each product type for specific durations (3-, 12-, 24- and 36-month functional longevity) is provided.
For permanent applications, where vegetation alone will not sustain expected flow conditions or provide sufficient long-term erosion protection, the ECTC offers recommendations for maximum gradient values for slope applications and maximum shear stress values for channel applications. Additionally, minimum thickness, ultraviolet stability, and tensile strength values for permanent TRMs are indicated.
The proper installation of RECPs is just as crucial to a project’s success as the selection of the appropriate product. Therefore, the ECTC has compiled construction requirements for erosion control blankets, open-weave textiles, and TRMs for both slope and channel installations. (These requirements also are provided at www.ectc.org/spec.html.)
Additional efforts by the ECTC
The ECTC currently is coordinating its activities with other industry product standardization efforts executed by organizations such as the Federal Highway Administration, the American Association of State Highway and Transportation Officials, and the Geosynthetics Institute. Members of the ECTC are involved in these organizations, assisting in their activities, and ensuring that overlapping responsibilities are avoided.
Some of the industry’s ongoing standardization activities include the International Erosion Control Association’s recently established Standards Committee, which is responsible for developing standards for erosion control mats and blankets. Also, ASTM has Task Groups in Committee D-35 on Geosynthetics and in Subcommittee D-18.25 on Erosion and Sediment Control Technology, which are working on performance index test standards for erosion control products.
Committee D-35.05 is responsible for developing index test standards for TRMs, and Subcommittee D-18.25 is responsible for developing index tests for degradable products, as well as performance tests for degradable RECPs and TRMs.
In addition to working to establish uniform specifications for RECPs, the ECTC also provides educational seminars for transportation departments.
"DOTs are the leading users of RECPs in the world," said Laurie Honnigford, the ECTC’s executive director. "Now more than ever, it’s crucial that they have reliable, costeffective erosion control tools. Through these seminars, the ECTC is working to fulfill its goal of providing pertinent information in a timely manner to all DOT professionals." An introductory course is available free of charge to DOTs, which frequently invite consulting engineers and contractors that they work with to attend. Topics included in the two-hour session are an introduction to RECPs, how to design using RECPs, and how to install RECPs. A full-day course taught by industry expert Jerald S. Fifield, Ph.D., P.E., CPESC, also is offered by the ECTC for a fee. This expanded workshop is worth five professional development hours and covers regulations; structural and nonstructural measures; and selection, design, installation, and inspection of RECPs. These courses are taught at the request of DOTs at times and in locations convenient to their employees and contractors.
The Erosion Control Technology Council’s mission is to be recognized as the industry authority in the development of performance guidelines and installation techniques for RECPs. To reach the ECTC, call 651-554-1895 or e-mail email@example.com.
Types of rolled erosion control products
The two basic types of RECPs are temporary degradable and long-term nondegradable.Temporary RECPs include erosion control blankets,mulch control nettings, and open weave textiles. These products are used to protect newly seeded areas from soil loss caused by environmental and erosive forces,such as wind and rain.Additionally,they are applied to regulate areas exposed to intense sunlight,with the ultimate goal of enhancing vegetative growth.Once established, the vegetation must be able to resist erosive forces since temporary products will degrade.
Long-term nondegradable RECPs,also known as TRMs,are constructed of an ultraviolet-stabilized, synthetic, 3-D matrix at least 0.25 inches (6.7 mm) thick. In addition to protecting seed, they inhibit erosion before germination. TRMs provide permanent vegetation reinforcement that is capable of withstanding much higher velocities and shear stresses than vegetation alone.
The following list summarizes the four main types of RECPs:
Mulch control netting—A planar woven natural fiber or extruded geosynthetic mesh used as a temporary degradable RECP to anchor loose fiber mulches.
Open weave textile—A temporary, degradable RECP composed of processed natural or polymer yarns woven into a matrix.
Erosion control blanket—A temporary, degradable RECP composed of processed natural or polymer fibers mechanically, structurally, or chemically bound together to form a continuous matrix.
TRMs, which may be supplemented with degradable components, are designed to impart immediate erosion protection,enhance vegetation establishment, and provide long-term functionality by permanently reinforcing vegetation during and after maturation.TRMs typically are used in hydraulic applications, such as high-flow ditches and channels, steep slopes, stream banks, and shorelines,where erosive forces may exceed the limits of natural,unreinforced vegetation,or in areas where limited vegetation establishment is anticipated.
DOT benefits from standardized specs and training
The Alabama Department of Transportation’s (ALDOT) product evaluation board recently adopted the ECTC specifications as the official specifications for the state of Alabama.The specs also were used as guidelines for the state’s erosion control manual.
"More designers are beginning to recognize the benefits of RECPs and consider them as an option," said Billy Bullard, CPESC, product evaluation engineer for ALDOT. "They really need to be educated on the uses of these products so they use them in the right situations." Although every highway project in Alabama has required the use of RECPs since the early 1990s, Bullard said that the product selection criteria covered in the seminars conducted by the ECTC for ALDOT last year were especially helpful. "Before the seminars, our designers really weren’t sure what products to use for each application. The ECTC classes and the new specifications have made that part of the process easier."