2002-06-26 CC Packet - Laserfiche WebLink

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"" . j I. Sedi ment_CtQntrol -Sill f1'ences Construction General Notes and Cautions lnstallation of each type of silt fence should meet the requirements ofMnDOT Specifications 3886. Silt fence that is inadequatelY' embedded in the ground will blowout, releasing water and sediment under the fence. Failure to properly install, inspect and maintain are the primary causes of this failure. . Another common failure is when silt fences are overtopped in concentrated flow areas. The silt fence is not meant to be placed in concentrated flow areas-the slope length calculations in this document do not apply to concentrated flows. Silt fences are not terraces; they cannot be put in sequence to extend the slope lengtb allowable. Otber methods must be used if the allowable distance is exceeded. Improperly designed and installed silt fences are often eroded around the ends. Tbe fence must be tied into the slope so that the base of the fence is above the design storage depth. Construct the silt fence from a continuous roll of geotextile if possible. Cut to the length of the barrier to avoid joints. When joints are necessary, securely fasten tbe geotextile fabric. It is preferred that the material be overlapped to the next post or the adjoining fabrics wrapped together around posts. . Never attach silt fence to trees. Heavy Duty Silt Fence Posts should be spaced maximum of 8 feet apart The geotextile should be attacbed to the upstream side of the post and any backing. The bottom edge of the geotextile sbould be buried at least 6 inches deep in a vertical slot or trench, with tbe soil pressed firmly against the embedded geotextile. When wire mesh is used, wire fasteners (hog rings) shall fasten the geotextile of the top of the mesh along tbe upper edge at a maximum spacing of I foot. A minimum of3 metal U-shaped clips or wire shall fasten the wire mesh and two layers of geotextile to the metal posts. When plastic mesh is used, the mesh backing should be joined to the gcotextile at the top with two rows of stitching. Geotextile should protrude below the bottom edge ofthe plastic mesh to allow embedment. A mini- mum of 3 metal U-shaped clips or wire shall fasten the plastic mesh and geotextiles to the metal posts. Machine-Sliced Silt Fence . Posts should be set a maximum of 6 feet apart. A geotextile fabric should be inserted in a slit in the soil (6 to 12 inches deep). The slit should be created such that a horizontal chisel point, at the base of a soil-slicing blade, slightly disrupts soil upward as the blade slices through the soil. This upward disruption minimizes horizontal compaction and creates an optimal soil condition for mechanical compaction against the geotextile. The geotextile should be mechaniCally inserted directly behind the soil-slicing blade in a simultaneous operation, achieving consistent placement and depth. No turning over (plowing) of soil is allowed for the slicing method. Metropolitan Council I Barr Engineering Co. 3-109 L__~____ _