Development of Silt Fence Tieback Design Methodology for Highway Construction Installations

This research effort focuses on improving sediment control practices used at highway construction projects by employing properly designed and correctly installed silt fence applications. Previous research indicated that tying silt fence installations back into the contour and creating a J-shaped hook (or a tieback) is an effective way to improve the efficiency of silt fence installations. Silt fences with tiebacks form a temporary detention basin, which helps facilitate sediment removal by sedimentation. The purpose of this research was to develop a rational numerical method for designing such silt fence tiebacks at highway construction sites. The proposed method employs a hydrological model to estimate the volume of runoff water generated by the watershed and balances the water with the storage capacity of the silt fence installed with a tieback. First, the Soil Conservation Service's method is used to estimate the amount of storm water generated during a design storm event. Then, with the cross-sectional data from a highway construction project, a graph is generated to estimate the storage volume available behind a silt fence for various ditch and highway slopes. Using these data, the designer can determine the proper placement frequencies of silt fence tiebacks along a linear highway construction project. This paper provides the mathematical details of this novel design procedure. An example problem is also provided to illustrate its practical applicability.