Effective means of Silt Fence Installation
J. Kent Evatt, Kody Featherston, Candice Johnson, Monica Johnston
Silt fence is a temporary sediment barrier consisting of filter fabric entrenched in the soil and attached to supporting posts(Salix, 2000). A silt fence is solely intended to control sediment. Current designs consist of a vertical geotextile fabric with a toe section compacted into the soil and vertical stakes holding it in place. The geotextile is designed to retain sediment-laden water, allowing the soil particles to fall out of suspension and separate from the runoff. This restriction traps the eroded soils, preventing offsite pollution of surface waters surrounding construction sites
Current methods of installation are the primary causes of fence failure (Salix, 2000). Proper design of the fence requires that it be installed along the contour of the slope, preventing runoff from traveling along the length of the fence. If the fence is installed along the slope, it can create concentrated flow that may increase erosion (fig. 2). An edge or toe of the fabric is installed in a shallow trench that is rarely compacted adequately, thereby allowing undercutting to occur. Placement of the fabric is also critical when determining the volume of water that can be retained behind the fence and the area of runoff being captured by each section of fence. If the area of runoff is too great, the fence will stretch and eventually be overtopped allowing soil particulates to leave the site (fig. 3). In addition, supporting posts are typically undersized and unable to support the forces imposed during times of high runoff flow.
Scope of Work
Dr. Billy Barfield of the Biosystems and Agricultural Engineering (BAE) department at Oklahoma State University and a research team are developing improved methods of controlling sediment and storm water (Barfield et al., 2000). They have been working for three years with sponsorship from the Environmental Protection Agency to design a replacement for the current silt fence. The research team will implement the proposed standards developed by the new filter fence project, “Failure Avoidance and Effective Silt Fence Technology” (FAESF). Standards for the project are: 1. Control undercutting and overtopping due to cross-contour installations, 2. Control lateral flow along the silt fence, 3. Improve the trapping of fine silts and clays through the use of polyacrilamides incorporated into the fabric, 4. Provide posts and fence with adequate strength to prevent excessive stretching and overturning, and 5. Provide post footings with adequate bearing capacity. Charles Machine Works of Perry, Oklahoma has joined this team’s effort by providing resources to develop machinery and equipment to install the new filter fence. The use of a machine will mechanize the process and improve the consistency of installation. Charles Machine Works is the parent company of Ditch Witch™, a world-wide manufacturer of digging and trenching equipment.