CRAFS®
- 1. CRAFS® (Corrugated Retention and Filtration System) The Sediment Retention Device (SRD) for Critical Spots with Trouble Conditions where Silt Fences Fail
- 2. Critical Spots with Trouble Conditions … Where Silt Fences Fail Problem = Build Up of Retained Runoff
- 3. Silt Fence Problems - very slow to no seepage - overflow, knock down, and scour beneath /////////////////////////////////////////////////////////////////////////////// Conventional Solutions … Limit Buildup Silt Fence J-Hooks Silt Fences in Series ///////////////// OR ///////////////// “Crushed Stone Control Outlets” (i.e., Reduced Flow Rate … Select Locations) But NO “Sediment Retention and Filtration”
- 4. The CRAFS® Alternative at Critical Spots with Trouble Conditions for Retention and Filtration
- 5. CRAFS® Eliminates Blunt Impact UPSTREAM support post(s) “SPLITS” runoff entering system . … diagonal flow of runoff toward DOWNSTREAM support posts
- 6. CRAFS® DIVIDES & DISTRIBUTES retained runoff into multiple retention wedges … low stress on retention system, … broad sediment “deposition” upstream , and … more filter fabric surface area against retained runoff
- 7. Heavy loads of retained runoff = Instability and Overflow CRAFSTM 3-D Structure = “Lateral Load Support” CRAFS® Lateral Load Support … with interaction between upstream and downstream support posts
- 8. … stability for corrugated structure … support to adjacent silt fences CRAFS® Lateral Load Support means …
- 9. CRAFS® Filter Cake Cleansing Runoff Washes “Filter Cake … Rejuvenates Faster Filtered Seepage ! … see top lines of “unwashed filter cake” on fabric from prior runoff events … filter cake below “top lines” has been washed away by subsequent runoff
- 10. CRAFS® Faster Filtered Seepage More Filter Fabric Surface Area = Faster Filtered Seepage that means less chance of overflow, knock down, and scour beneath sediment retention device
- 11. ^ Immediately following sediment slurry into systems ^ ^ One hour after slurry retention ^ (>4 hr) (1 ¼ hr) ^ Total time for dewatering ^ SLURRY RETENTION AND FILTRATION TEST Linear System Corrugated System
- 12. CRAFS® ... the Problem Solver Eliminates Blunt Impact Divides and Distributes Lateral Load Support Filter Cake Cleansing Faster Filtered Seepage
- 13. The CRAFS® Alternative for sediment retention and filtration in Critical Spots with Trouble Conditions … more structural stability and faster filtered seepage at outlets, inlets, and other localized problem areas.
- 14. CRAFS® INSTALLATION 1. Clip banding at top & bottom of packaging, slide CRAFS® from fabric sleeve, and unroll CRAFS® system with nonwoven fabric apron against the ground and woven monofilament filter fabric atop apron. 2. Pull all four corners of system’s apron taught with bottom of apron against ground surface. Upstream edge of apron should extend 12” upstream of the “stake sleeves” for the system’s “vertical filter fabric component”, and be parallel with alignment of toe-in trench. 3. Dig toe-in trench for CRAFS® in straight line perpendicular to the direction of flow for sediment runoff. If CRAFS® is adjacent to and connected with a silt fence alignment, toe-in for both systems will follow the same trench alignment perpendicular to direction of sediment runoff. 4. Because CRAFS® is intended for critical spots with trouble conditions, proper apron “toe-in” is critical. Assure apron “toe-in fabric” is placed against the downstream vertical wall of 6” deep “toe-in trench” (adjacent to system’s upstream vertexes), and laid across the bottom of the “toe-in trench” full 6” width. (See Step 8 below regarding compaction of toe-in backfill.) 5. Slide fence posts through sleeves at the upstream vertexes of system, and drive vertically through the apron fabric in bottom corner of trench, until post stands stable. 6. Pull down stream edges of apron taught and assure apron lays flat against the ground surface. Slide fence posts through sleeves in downstream vertexes, and pull taught in perpendicular direction against upstream post alignment. Drive downstream posts vertically into the ground while maintaining through fabrics between all posts in system (upstream and downstream), i.e., to eliminate wrinkles in the “vertical corrugated filter fabric system” as well as the apron lying on the ground. 7. While assuring vertical posture of all posts and “no slack” in system’s fabrics, firmly drive all upstream and downstream support posts “firmly” into the ground. 8. Provide “firm” compaction of all backfill in “toe-in trench”, and assure elevation of densely compacted backfill is same or slightly higher than adjacent native soil level. Add and compact more backfill if necessary. 9. Confirm vertical posture of support posts, and be sure that all other steps of post and toe-in installation are completed per ASTM D6462 Section 8.2 “Construction”. Make corrections if necessary to assure system stability and long term performance after installation. 10. For routine inspection and maintenance of CRAFS® units installed, follow the general guidelines provided in ASTM D6462 Section 8.3 “Maintenance”.
- 15. CRAFS® SRD SPECIFICATIONS (CORRUGATED RETENTION & FILTRATION SYSTEM) COMPONENTS Components within each unit include 1) vertical filter fabric, 2) horizontal fabric +apron, and 3) vertical post sleeves. Each of the system’s components are described below. STANDARD CRAFS® UNITS - DIMENSIONS & FABRICS COMPONENTS Widths of a standard CRAFS® unit are 8’ (i.e., distance between outside post sleeves on each end of unit). Standard height of corrugated filter fabric is 36” from Apron to top edge of filter fabric. These “standard” dimensions have been selected based on typical project needs and performance requirements. Unit dimensions can be modified if site or performance conditions merit deviations. Alternate fabrics can be substituted for the standard “monofilament filter fabric” as well as the standard 8 osy nonwoven apron if deemed necessary for special performance conditions by the specifying engineer. VERTICAL FILTER FABRIC The vertical corrugated structure of CRAFS® is a woven monofilament “filter fabric” that provides the primary retention and filtration functions of the system. The fabric’s pore size, porosity, and permeability must be balanced to provide adequate retention, while it resisting total clogging of its pore structure to allow continued seepage through the system. Strength, abrasion resistance, and U.V. Stability are critical to assure the integrity of the fabric structure during system installation and throughout its service life. The minimum certifiable properties of this filter fabric are listed in Table 1. HORIZONTAL APRON The CRAFS® Apron is a horizontal blanket of heavy weight nonwoven fabric across the entire base of the system that is mechanically joined to the vertical corrugated filter fabric of the system. The APRON 1) provides dimensional stability to the vertical filter fabric system, 2) allows linear “toe-in” of the CRAFS® structure, and 3) prevents passage of runoff beneath the “corrugated retention and filtration system”. The mechanical connection between the filter fabric and the apron prevents the unfiltered passage of retained sediment runoff through the system. The APRON extends upstream from the vertical support sleeves of the system’s filter fabric to provide sufficient apron “toe-in” (per ASTM D6462 requirements, i.e., 6” vertical depth from ground surface to base of toe-in trench plus 6” horizontal at base of toe-in trench). See Table 1 for physical property requirements of the nonwoven fabric of the CRAFS® Apron. The lateral spacing between upstream vertexes is typically uniform like the spacing between downstream vertexes, as well as the diagonal spacing between the upstream and the downstream vertexes. UPSTREAM - DOWNSTREAM VERTEXES CRAFS® corrugated structure has vertexes located at regular intervals along the upstream and the downstream edges of the system. The lateral spacing between upstream vertexes is typically uniform like the spacing between downstream vertexes, as well as the diagonal spacing between the upstream and the downstream vertexes. VERTICAL SUPPORT POST SLEEVES Vertical “support sleeves” are fabricated into the vertical filter fabric component at each of the CRAFS® vertexes. These sleeves allow insertion of vertical support posts. Posts are driven into the ground until vertically stable giving the entire structure in-place stability to resist the loads for sediment runoff and debry. Support posts should be metal “T” posts driven into the ground per installation guidelines of ASTM D6482. Pressure treated 2” X 2” wood posts may be substituted for the metal “T” posts when approved by the specifier based on field conditions and performance requirements.
- 16. MECHANICAL CONNECTIONS The vertical filter fabric and horizontal apron must be mechanically joined to assure system continuity and total retention and filtration to all sediment runoff flowing into and seeping through the CRAFS® fabric structure. Vertical support sleeves are also fabricated with mechanical connections. All mechanical connections must have at least 80% of the fabric’s tensile strength as determined according to ASTM D4884 Standard Test Method for Strength of Sewn or Bonded Seams of Geotextiles. INSTALLATION APRON TOE-IN The apron extends upstream from the vertical support sleeves of the system’s filter fabric an adequate distance to provide sufficient “apron toe-in” per ASTM D6462 requirements (i.e., 6” vertical depth from ground surface to base of toe-in trench plus 6” horizontal at base of toe-in trench). Note that CRAFS® Toe-In is a linear alignment along the upstream vertexes of the system, similar to the linear alignment for a traditional silt fence installation . This linear alignment allows a simple connection between a silt fence on both sides of the CRAFS® units that will prevent escape of unfiltered sediment runoff between the two systems. SYSTEM ALIGNMENT Align the upstream vertexes of the CRAFS® units perpendicular to the flow direction of sediment runoff. Be sure the APRON’s “toe-in fabric” is pointed in the upstream direction during its installation. Slide the support posts through the sleeves in the filter fabric. Pull taught between the upstream vertexes to remove all slack in the apron at its upstream alignment. Pull the APRON’s “toe-in” down vertically into trench and then horizontally across the bottom of toe-in trench. Hold upstream support posts vertical at back of toe-in trench, and drive the posts through the apron’s toe-in lying in the trench. Drive stakes firmly into the ground in a vertical posture adjacent to the “downstream side of the toe-in trench”. Center the downstream support posts between the two upstream vertexes and pull the diagonal walls of the retention chambers taught in the downstream direction while driving the support posts into place. Care must be taken to provide adequate tension between the downstream posts as done with the upstream posts. And tension must be applied to the downstream posts pulling against the resistance from the adjacent upstream posts, to eliminate the slack in the vertical filter fabric structure. TOE-IN BACKFILL Backfill excavated soil into the toe-in trench. Assure complete burial of the apron at the upstream edge of the CRAFS® system. Firmly compact “toe-in” backfill to optimum density . Be sure compacted backfill is at or above natural ground level. Add and compact extra soil backfill if necessary to reach native ground level or slightly higher in toe-in trench of CRAFS® installation. CRAFS® is manufactured and marketed by: ACF Environmental, Inc. 2831 Cardwell Road Richmond, VA 23234 Ph: 800-448-3636 FAX: 804-743-7779 acfenvironmental.com
- 17. /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// Table 1: CRAFS® Fabric Property Requirements* PROPERTY TEST METHOD UNITS VALUE1 VALUE1 “Woven Monofil. “Needle-punched Filter Fabric” 2 Nonwov Fabric Apron” 2 /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// AOS ASTM D4751 U.S. Std Sieve #30 (max) #80 (nominal) Flow Rate ASTM D4491 gpm/sf 75 (min) 90 (min) Grab Tensile ASTM D4632 Strength lbs 260 X 180 (min) 200 X 200 (min) Elongation % 15 (nominal) 50 (nominal) Mullen Burst ASTM D3786 psi 175 (min) -- Trapezoid Tear ASTM D4533 lbs --- 80 (min) UV Resistance ASTM D4355 % 80% (4) 70% (4) /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// FOOTNOTES: * Fabric Properties noted in Table 1 are the components of a Standard CRAFS® unit. CRAFS® units are available with alternative filter fabric and apron components if special conditions or performance requirements are deemed necessary by the project specifier. 1- Certifiable Min or Max 2- Woven Monofilament “Filter Fabric” - Vertical System Component 3- Needle-punched Nonwoven Apron Fabric - Horizontal System Component 4- Strength retained after 500 hr UV exposure ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
- 18. Natl Transportation Product Eval Prog – AASHTO NTPEP-SRD Pilot Project Testing w/ CRAFS® … 6-8-16 Three rainfall intensities … mild to severe (2“, 4“, and 6" in/hr) Results Monitored … Runoff Volume & Turbidity, Cummul Soil Loss, Cummul R Factor, and Avg P Factor. CRAFS® Avg Retention Efficiency = 95 %
- 19. NTPEP-SRD Pilot Test (TRI Demo 10/2016 – full test abbreviated by “Very Brief” Rainfall Event) Note: Water levels upstream of SRD tested … CRAFS® provides much faster “filtered seepage for dewatering” retained runoff than “Specialty Silt Fence fabric”. ^ CRAFS® ^ ^ Specialty Silt Fence Fabric ^
- 20. … for runoff outlets and other problem areas. ... a new wrinkle for the old problems of sediment control = less overflow, knock down, and scour beneath CRAFS® … the Problem Solver