Erosion Control: Tests & Capabilities
EROSION AND SEDIMENT CONTROL AND STORMWATER MANAGEMENT SYSTEMS
TRI is unequaled in implementing test methods to assist clients with product characterization.
TRI provides laboratory conformance/verification testing as well as performance related studies for erosion control products. In addition to routine index testing in accordance with ASTM, ISO, BS, DIN and GRI test methods, TRI also provides bench scale indicator tests, and large scale performance tests. TRI’s state-of-the-art large-scale facilities at Denver Downs Research Facility (DDRF) make it the only independent commercial laboratory offering such a wide array of performance testing capabilities.
Most materials use in erosion and sediment control and stormwater management systems can be tested, including:
- Rolled Erosion Control Products (RECP)
- Turf Reinforcement Mats (TRM)
- Hydraulically Applied Erosion Control Product (HECP)
- Sediment Retention Fiber Rolls (SRFR)
- Erosion Control Mulches
- Compost Logs
- Membrane barriers
- Geotextiles and Geogrids
- Plastic Pipe and Stormwater Chambers
- Green Roof Systems
EROSION CONTROL TESTS PERFORMED
Variations in the mass per unit area, raw materials, manufacturing processes, and other product and production components make frequent testing imperative for accurate characterization and quality control of erosion control products (ECPs) and sediment retention devices (SRDs).
Standards For Index Testing And Evaluation Of RECPS
MASS PER UNIT AREA
The mass per unit area, also known as the weight per square yard of a sample, is an important quality control property. ASTM D 5261 was developed for testing this property of geosynthetics and was, until recently, commonly used for RECPs as well. But since sampling and cutting RECPs can be quite challenging, two new standards have been developed by ASTM:
ASTM D 6566, Standard Test Method for Measuring Mass per Unit Area of Turf Reinforcement Mats (TRMs), which uses ten 8 x 8 specimens at ambient laboratory conditions, and ASTM D 6475, Standard Test Method for Measuring Mass per Unit Area of Erosion Control Blankets (ECBs), which uses five larger (typically 12 x 14) specimens that have been dried at 50º overnight.
Thickness is another important quality control property. ASTM D 5199 was developed as a geosynthetic test method, but it is commonly applied to RECPs using a modified procedure in order to accommodate the uniquely compressive, three-dimensional nature of RECPs. The modifications typically included replacing the standard 2.22-inch diameter plate with a 6-inch diameter presser foot and testing under a 0.029 psi pressure, rather than the 0.29 standard. ASTM has recently approved a new standard specifically for TRMs that adopts these modifications titled ASTM D 6525, Standard Test Method for Measuring Nominal Thickness of Permanent Rolled Erosion Control Products (RECPs).
Tensile strength is the other primary quality control property measured on RECPs. Arguably, tensile strength may also be important if an RECP is subjected to emergency and recreational vehicular traffic and maintenance such as mowing. Originally, ASTM methods D 5035 and D 1682, textile test methods, were used to measure RECP tensile strength. More recently, a new ASTM tensile test method, that uses at least 5 inch-wide grips, has been approved and is titled ASTM D 6818, Standard Test Method for Ultimate Tensile Properties of Turf Reinforcement Mats (TRMs).
The stiffness of an RECP is a measure of how much it will deflect under its own weight. Products with lower test results are more flexible and can more easily conform to the subgrade. Establishing and maintaining intimate contact with the subgrade is paramount to a successful installation. While ASTM D 1388 has historically been used to measure stiffness, appropriate procedures have been incorporated into a new test method that is explicitly applicable to TRMs of any fiber content and any number of components: ASTM D 6575, Standard Test Method for Determining Stiffness of Geosynthetics Used as Turf Reinforcement Mats (TRMs).
A light box has commonly been used to quantify the openness of textile materials. It illumines a light source inside a box on one side of the specimen. On the other side, a calibrated meter measures the amount of light that is able to pass through the specimen. The Lumite Light Projection test method has been used for years to determine the percent of open area of woven geotextiles. This test method has also been used to measure the amount of light from a 60 watt bulb that penetrates through an RECP. This amount – stated as a percentage of the amount associated with no specimen in place – is the light penetration. The inverse of light penetration is the ground cover. A balance of ground cover and light penetration is important for rapid seedling emergence. The values stated as a percentage are to be regarded as nominal values. A light box procedure that increases the bulb wattage to 150 watts has been standardized by ASTM specifically for TRMs and is titled ASTM D 6567, Standard Test Method for Measuring the Light Penetration of a Turf Reinforcement Mat (TRM).
Compression is reduction in thickness experienced by the RECP under a standard loading. Five 4.7 x 4.7 specimens are tested at a compressive rate of 10% of thickness per minute. It gives an indication of the RECP’s resistance to flattening. The standard test procedure for TRMs is ASTM D 6454. The same procedures are generally used for geosynthetics.
It is sometimes useful to measure the impact of cyclic loading on the thickness of TRMs. The associated test method establishes the procedures for evaluation of the permanent deformation of a TRM under short-term, repeated compressive loading. It may be relevant to a TRM’s ability to protect newly developing seed from damage during loading. Three 100-psi loads are applied, and the resulting thickness is expressed as a percentage of the original. ASTM D 1777 was originally used to measure thickness before and after loading. The newer thickness measuring procedures of ASTM D 6525 have been incorporated into the TRM-specific ASTM standard titled ASTM D 6524, Standard Test Method for Measuring the Short-Term Compression Behavior of Turf Reinforcement Mats (TRMs).
RECPs may need to retain relevant properties when exposed to sunlight. Typically the ultraviolet (UV) portion of the light spectrum is used in accelerated exposure tests. The most common standard accelerated lab test is ASTM D 4355, which uses a Xenon Arc light source. Specimens are exposed to continuous 120-minute cycles of 90 minutes of light only, followed by 30 minutes of water spray and light. Specimens are typically removed after 150, 300, and 500 hours of exposure and tested for residual tensile strength in accordance with ASTM D 6818. The retained strength is reported as the measure of a material’s UV light stability. (Note: Since accelerated tests have not shown a consistent correlation to outdoor exposures, ASTM’s D 5970, is available to assess an unaccelerated site-specific UV stability via outdoor exposure.)
Other Non-Standard Index Tests For RECPS
The standardization process takes time to build the necessary consensus for a standard to be accepted industry-wide. While already commonly in use, the following test methods are not ASTM standards:
Porosity is the measure of air voids in the material. Porosity is calculated from thickness, mass per unit area, and specific gravity.
OPEN VOLUME PER UNIT AREA
Open volume per unit area is the measure of void volume within a material. The value disregards the size of the voids. It is calculated using thickness and porosity.
Water absorption is a measure of a material’s capacity to absorb water and is generally applicable to organic RECPs. The standard test procedure is ASTM D 1117 and ECTC-TASC 00197.
Related to water absorption is the swell of an organic RECP resulting from water absorption. The test procedure has been proposed by the ECTC in the ECTC-TASC 00197 using ASTM D 5199 to measure before and after thicknesses. ASTM D 1777 has also been used for measuring swell.
Specific gravity (SG) is a measure of the unit weight of a material as compared to that of water. The standard test procedure is ASTM D 792, Method A.
Smolder resistance is a measure of an organic material’s resistance to ignition by a smoldering cigarette. The test procedure has been proposed by the ECTC in the ECTC-TASC 00197.
The ash content of an RECP is that portion of the material that doesn’t burn when exposed to very high temperatures. It is basically a measure of the amount of inert matter in the product and is determined using test procedure ASTM D 586.
The organic matter in an RECP is that portion which is likely to biodegrade over time. It can be quantified by measuring the amount of the material that burns when exposed to very high temperatures. The standard test procedure is ASTM D 2974.
Bench Scale Index Testing
|ASTM D 7101
|Slope Erosion & Runoff Reduction
|ASTM D 7207
|Permissible Shear and Channel Erosion
|ASTM D 7322
|Not yet standardized
|ASTM D 5141
|Filtration Efficiency and Flow Rate
Bench-scale tests have been developed for slope erosion, channel erosion, vegetation enhancement, and biodegradability for ECPs, and filtration efficiency and flow rate for SRDs.
TRI Performs The Following Bench-Scale Performance Tests:
ASTM D 7101
Slope Erosion & Runoff Reduction
Establishes procedures for evaluating the ability of RECPs to protect soils from rain splash and immediate runoff-induced erosion.
- The RECP absorbs the impact force of raindrops, reducing soil particle loosening through “splash” mechanisms.
- both bare and RECP-protected soil exposed to simulated rainfall and immediate runoff for 30 minutes
- sloped table enclosed by a “shower” curtain.
- Rainfall simulated – laboratory drip-type simulator
- uniform drops with a median diameter of 3.0 to 3.5 mm from a drop height of 2.0±0.1 m
- rainfall intensities as high as 150 mm/hr.
- The amount of soil that splashes or is washed out of the containers is collected and weighed. From this data, an appropriate soil loss ratio or associated C-factor can be calculated by comparing the RECP-protected soil loss to the control for a given soil type and a project-specific slope and rainfall intensity.
ASTM D 7207
Permissible Shear and Channel Erosion
Establishes procedures for evaluating the ability of RECPs to protect soils from flow-induced erosion.
- RECP-protected soil is subjected to shear stresses caused by the rotation of a three-blade impeller for 30 minutes
- The amount of soil that erodes is found by weighing the containers under water.
- The shear stress test apparatus includes a tank, test well, motor, plastic lid, and impeller.
- The three-blade impeller is mounted in the cylindrical tank so that the lower edge of the blades is slightly above the floor of the tank.
- The sample test well is a recession in the floor of the tank that holds the pots of soil prepared for testing.
- When pots are placed in the well, the test surface is flush with the floor of the tank.
- Pots holding soil and test specimens are normally 200 mm diameter plastic pipe sections with height of 100 mm.
- The results of the testing include the amount of soil lost at various shear stresses.
- From this data, an appropriate permissible shear (tp) can be calculated by assuming a critical amount of soil loss (typically 13 mm).
- Permissible Shear and Channel Erosion
ASTM D 7322
Establishes procedures for evaluating the ability of RECPs to encourage seed germination.
The results of the test can be used to compare RECPs and other erosion control methods to determine which are the most effective at encouraging the growth of vegetation in different climates.
- Testing is done within a growth chamber.
- Containers of soil are sown with seeds and then covered with an RECP.
- Additional containers are left uncovered as controls.
- The light, water, and temperature are regulated and documented.
- The rate of germination is measured periodically throughout the test, and the weight of vegetation is calculated at the conclusion of the test.
- Test sets are designed to evaluate an RECP’s ability to enhance the rate and quantity of germination.
- The testing results include the rate and total weight of germination after 21 days.
- From this data, a percent enhancement can be calculated by comparing results from the RECP covered soil to the control.
Not yet standardized
Establishes the procedures for evaluating the ability of RECPs to resist biodegradation.
- A single test is used to determine an RECP’s rate of biodegradation.
- Measures CO2 generation for 60 days and compares the carbon lost to gas formation to the theoretical total carbon.
- Flasks containing RECP and inoculum are monitored periodically for CO2 generation and compared to the theoretical total carbon content.
- A “standard” cellulose material is simultaneously exposed to confirm inoculum’s strength.
- From this data, a half-life or “functional longevity” can be projected. A linear trend on a semi-log plot has produced reasonable projections based on reported field evidence.
ASTM D 5141
Filtration Efficiency and Flow Rate
This bench-scale test has been used for years to characterize silt fence efficiency.
Recently modified method facilitates sediment retention characterization testing of other types of sediment retention devices (SRD).
- Test apparatus can have an open end enclosed by a vertical SRD (i.e. silt fence) or incorporate a horizontal “box” extension to the end of the bench-scale flume to simulation a stormwater drain inlet.
- A sediment-laden runoff is created by combining water and soil in the mixing tank and agitating prior to the test. The amount of water (50 L / 13.3 gal) and sediment (0.15 kg / 0.33 lb) and the maximum particle size (2mm / #10 sieve) are prescribed in the standard.
- The sediment-laden flow passing through the SRD is collected and filtered, and the time to the end of flow is recorded.
- Filtered sediments are dried and weighed.
The weight of collected sediment is compared to the initial amount put into suspension to determine the filtering efficiency of the SRD, and the time for passage of the flow is used to calculate the associated flow rate.
Large-Scale Performance Testing
|ASTM D 6459
|Determination of Rolled Erosion Control Product (RECP) Performance in Protecting Hillslopes from Rainfall-Induced Erosion
|ASTM D 6460
|Determination of Rolled Erosion Control Product (RECP) Performance in Protecting Earthen Channels from Stormwater-Induced Erosion
|ASTM D 7208
|Determination Of Temporary Ditch Check Performance In Protecting Earthen Channels
|ASTM D 7351
|Determination Of Sediment Retention Device Effectiveness In Sheet Flow Applications
ASTM D 6459
Determination of Rolled Erosion Control Product (RECP) Performance in Protecting Hillslopes from Rainfall-Induced Erosion.
This is full-scale simulated rainfall on 3:1 slopes with bare and RECP-protected soil, including:
- Rainfall Intensities = 50, 100, 150 mm/hr @ 20 minutes each
- 1 control + 3 replicate slopes
- Inclined (3:1) slopes, 40-ft long and 8-ft wide
- 12-inch compacted soil veneer
- Simulated rain system with 14-ft drop height & up to 6+ inches/hr capacity
ASTM D 6460
Determination of Rolled Erosion Control Product (RECP) Performance in Protecting Earthen Channels from Stormwater-Induced Erosion.
This is full-scale channel flow with RECP-protected soil, including:
- Increasing Shear Levels psf @ 30 minutes each
- 3 replicate test sections
- Rectangular (flume) or Trapezoidal cross-section with 5% slope
- Rectangular cross-section has 2-ft width and 2-ft high side walls
- Trapezoidal cross-section has 2-ft bottom and 2H:1V side-slopes
- 12-inch compacted soil veneer
- 40-ft total length
- Flow capacity up to 50cfs for 30 minutes.
ASTM D 7208:
Determination Of Temporary Ditch Check Performance In Protecting Earthen Channels
This is full-scale channel flow (up to 3 cfs) in a trapezoidal channel with check structure(s) installed. The test method evaluates the ability of temporary ditch checks to protect earthen channels from storm water-induced erosion. Critical elements of this protection are the ability of the temporary ditch check to:
- Slow and/or pond runoff to encourage sedimentation, thereby reducing soil particle transport downstream
- Trap soil particles upstream of structure; and
- Decrease soil erosion.
This test method utilizes full-scale testing procedures and is patterned after conditions typically found on construction sites at the conclusion of earthwork operations, but prior to the start of revegetation work. Therefore this test method considers only unvegetated conditions and provides a comparative evaluation of a temporary ditch check to baseline bare soil conditions under controlled and documented conditions.
ASTM D 7351
Determination Of Sediment Retention Device Effectiveness In Sheet Flow Applications
This is a full-scale installation of an SRD in which sediment-laden water is allowed to “sheet flow” up to and seep through, over, and/or under an installed sediment retention device (SRD). The measurement of sediment that passes through, over, and/or under the SRD compared to the amount in the upstream flow is used to quantify the effectiveness of the SRD in retaining sediments.
An important variable in any testing procedure is the establishment of test “conditions”. For a sediment control performance test this means selecting an appropriate design storm event and associated runoff along with an expected amount of sediment to be transported by the runoff. The default for D 7351 is a standard 10-year, 6-hour storm event (mid-Atlantic region of US). This return frequency is commonly used for sizing sediment control ponds and, thus, was deemed appropriate for the testing of other SRDs. Using this criterion, a 100 mm (4 in) rainfall was selected. It was also assumed that approximately 25% of the storm would occur during the peak 30 minutes, and that 50% of the rainfall would infiltrate into the ground. A theoretical contributory area of 30 m (100 ft) slope length by 6 m (20 ft) wide was selected to limit runoff to sheet flow conditionsRunoff and associated sediment were calculated using the Modified Universal Soil Loss Equation (MUSLE) which allows for calculating a storm-specific quantity of sediment.
Additional Non-Standard Large-Scale tests:
The following non-standard large-scale tests are also available to assist clients with product development and characterization:
- Vegetated RECP shear testing in 20% channels in accordance with ASTM D 6460
- SRD effectiveness in inlet flow applications (D7351-modified)
- Storm water inlet protection provided by sediment retention devices in curb and gutter applications
- SRD effectiveness in construction perimeter control applications (TM11340)
- Pond skimmer evaluations and flow capacities
- Shoreline protection under wind-induced wave action
- Buried pipe and stormwater chamber strength/durability evaluations
- Large-scale germination and functional longevity testing of erosion control products.
All Tests with Standards
|American Standards for Testing Materials (ASTM Std.)
|Apparent Opening Size, AOS
|Geosynthetic Accreditation Institute (GAI)
|Biodegradation of RECPs (ECTC Std)
|Density / Specific Gravity
|Light Penetration / Percent Shading
|Lignin Content (TAPPI TM T222 om-98)
|Mass per Unit Area – Geotextiles
|Mass per Unit Area – ECB
|Mass per Unit Area – TRM
|Percent Open Area
|Smolder Resistance (ECTC-TASC 001)
|Swell Index (ECTC-TASC 001)
|Tensile Properties – Strip Tensile
|Tensile Properties – Wide Width Tensile
|Thickness – Geotextiles
|Thickness – TRMs
|Water Absorption (ASTM D 1117 / ECTC)
|UV Resistance / Degradation Rate
|SRD: Filtration Efficiency & Flow
|SRD: Horizontal Permeability
|RECP & HECP: RainSplash & Runoff Erosion
|RECP: Hydraulic Shear
|RECP & HECP: Germination Enhancement
|RECP & HECP – Slope Performance
|RECP – Channel Performance
|SRD: Toe-of-Slope Performance
|D 7351 modified
|SRD: Inlet Protection Performance
|SRD: Channel Check Structure Performance
|SRD: Perimeter Device Performance
In 1994, the Erosion Control Technology Council (ECTC), an organization of rolled erosion control product (RECP), hydraulically applied erosion control product (HECP), and sediment retention fiber roll (SRFR) manufacturers commissioned TRI/Environmental to initiate a program to identify and establish a common terminology and to develop standardized index tests for the characterization of RECPs. In January 1997, a manual of common terminology and recommended index testing standards (ECTC Technical Guidance Manual: TASC 00197) was issued to the industry.
Subsequent to these development efforts, TRI has played a leadership role in coordinated efforts to work through the ASTM International development process to achieve consensus standardization of index, bench-scale, and large-scale test procedures for characterizing a wide range of erosion control products and sediment retention devices.