AFTER FEBRUARY 1, 2010 ITEM 709 TRIANGULAR FILTER FABRIC FENCE 709.1 Description. This work shall consist of furnishing, installing, and removing temporary erosion protection and sediment control triangular filter fabric fence, utilized during construction operations and prior to final stabilization, in accordance with these specifications and construction drawings, and as directed by the Engineer. The triangular filter fabric fence consists of a geotextile fabric supported by a wire mesh fence which filters sediment laden water. 709.2 Materials. Geotextile fabric (filter fabric) shall consist of long-chain synthetic polymers composed of at least 95 percent by weight of polyolefins in a woven fabric. The geotextile fabric shall meet the following specifications: Geotextile Fabric Properties: The geotextile fabric used shall equal or exceed the stated property values listed in Table 1 below: Table 1 Silt Fence Geotextile Fabric Properties Supported Silt Fence Requirements Unsupported Silt Fence Geotextile Elongation 50% Geotextile Elongation <50% Units Grab Strength Machine Direction lbs. 90 123 123 X-Machine Direction lbs. 90 100 100 Permittivity sec -1 0.05 0.05 0.05 Apparent Opening Size (maximum average roll value) Ultraviolet Stability (Retained Tensile Strength) mm/sieve 0.6/30 0.6/30 0.6/30 % 70 after 500 hrs exposure 70 after 500 hrs exposure 70 after 500 hrs exposure NOTES: 1. Table 1 adapted from AASHTO M 288 Geotextile Specification for Highway Applications Table 6. Temporary Silt Fence Property Requirements. 2. All numeric values in Table 1 except Apparent Opening Size (AOS) represent minimum average roll values (MARV). Values for AOS represent maximum average roll values.
Page -2- AFTER FEBRUARY 1, 2010 Geotextile fabric shall contain stabilizers and/or inhibitors to make the fabric resistant to deterioration resulting from exposure to sunlight or heat. Geotextile fabric shall be resistant to commonly encountered soil chemicals, mildew, rot, and insects. Geotextile fabric shall be free of defects or flaws that affect its physical and/or filtering properties. Geotextile fabric shall provide an expected useable life comparable to the anticipated construction period. Standard hog wire fence shall be 14-1/2 gage minimum with maximum 6-inch x 6-inch openings and bent as shown on the attached drawing. Wire ties shall be 14 gage minimum. 709.3 Construction Methods. No clearing and grubbing or rough cutting, other than as specifically directed by the Engineer to allow for soil testing, surveying and installation of erosion protection and sediment control measures, shall be permitted until sediment control and erosion protection systems are in-place. Provide triangular filter fabric fence at the locations shown on the construction drawings, in accordance with the drawing attached to this specification, and as directed by the Engineer. Filter fabric fences shall be installed in such a manner that surface runoff will percolate through the system in sheet flow fashion and allow sediment to be retained and accumulated. Triangular filter fabric fences shall be constructed in accordance with an approved schedule that clearly describes the timing during the construction process that the various erosion control measures will be implemented. The filter cloth is to be secured to the woven wire fence with minimum 14 gage wire ties or shoat rings spaced every 24-inches, top and midsection. The triangular filter fabric fence may be secured in place using one of the following methods: A. The skirt may be toed in 6-inches with mechanically compacted material; B. The skirt may be weighed down with a continuous layer of 3-inch to 5-inch graded rock;
Page -3- AFTER FEBRUARY 1, 2010 C. The entire structure may be trenched in 4-inches. The triangular filter fabric fence structure should be anchored securely in place using 6-inch wire staples on 2-foot centers on both edges. As an alternative, it may be held in-place with 3/8-inch x 18-inch rebar, as stakes. The filter fabric material should be lapped over 6-inches to cover the segment joints. The joints should be fastened with wire ties or shoat rings. The Contractor shall inspect the triangular filter fabric fences at least once every week or as directed by the Engineer. The Contractor shall remove projections or other irregularities which will impede normal flow. Erosion protection and sediment control systems shall be maintained by the Contractor until final stabilization. Damage caused to erosion protection and sediment control systems shall be repaired immediately. Upon removal of the triangular filter fabric fence, the area shall be returned to the grades specified on the construction drawings and the area stabilized with vegetation, or other. The Contractor is responsible for removal and disposal of sediment and debris from the triangular filter fabric fence and as directed by the Engineer. Sediment deposits shall be removed when or before they reach one-third of the height of the fence. Sediment shall not be allowed to flush into the storm sewer system, waterways, jurisdictional wetlands, or onto adjacent properties. Uncontaminated sediment can be placed at the project spoil site or, if properly handled, spread out to supplement fill requirements. The Engineer will designate how the sediment deposits are to be handled. Uncontaminated sediment shall not be placed in waterways or jurisdictional wetlands, unless as approved by the Engineer. If sediment has been contaminated, then it shall be disposed of in accordance with the applicable federal, state and local regulations. Off-site disposal shall be the responsibility of the Contractor. After final stabilization and at the direction of the Engineer, the Contractor, when required, shall be responsible for removing all erosion
Page -4- AFTER FEBRUARY 1, 2010 protection and sediment control systems, that are not permanent, from the project. 709.4 Quality Assurance. The Contractor is responsible for the control of the quality of materials incorporated into the construction and quality of completed construction. The County will engage materials engineering services to provide quality assurance testing and inspection to assist the County Engineer in determining the acceptability of materials and completed construction. Quality assurance services provided by the County do not relieve the Contractor of his responsibility for quality control. The Materials Engineer shall not have control of the means, methods, techniques, sequences or procedures of construction selected by the Contractor. 709.5 Measurement and Payment. When paid for separately as a pay item, measurement and payment for the triangular filter fabric fence shall be by the linear foot of completed and in-place fence between the limits of the beginning and end of the fence structure. Payment for triangular filter fabric fence shall include and be full compensation for all labor, equipment, materials, supervision and for all incidental expenses for the construction of this item, complete in-place, where 60% of the total unit cost shall be for furnishing and placing filter fabric, hog wire fence and placing other required material. Thus, 40% of the total unit cost shall be for the removal of erosion protection and sediment control systems: triangular filter fabric fence, after final stabilization, at the end of the project. There are line code(s), description(s), and unit(s) for this item. Note: This specification requires a drawing. END OF ITEM 709
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Page -6- AFTER FEBRUARY 1, 2010 SUMMARY SHEET ITEM 709 - TRIANGULAR FILTER FABRIC FENCE Other Specifications Required: Item 725 - General Source Controls Item 708 Filter Fabric Fence Item 713 Reinforced Filter Fabric Barrier Item 751 SWPPP Inspection and Maintenance Reference Standards: AASHTO M 288 ASTM D 4355 ASTM D 4491 ASTM D 4632 ASTM D 4751 Geotextile Specification for Highway Applications. Deterioration of Geotextiles from Exposure to Ultraviolet Light and Water (Xenon-Arc Type Apparatus). Water Permeability of Geotextiles by Permittivity. Grab Breaking Load and Elongation of Geotextiles. Determining Apparent Opening Size of a Geotextile. Description: Describes method for constructing erosion protection and sediment control triangular filter fabric fence. Payment: If paid for separately, paid for by the linear foot of triangular filter fabric fence measurement being made along the length of the structure. DO NOT INCLUDE THIS SHEET IN CONTRACT SPECIFICATIONS.