Silt fence

Filtration installations include wrapping the trench of a pavement-edge drain system to prevent contamination of the underdrain placement behind retaining walls and bridge abutments to prevent contamination of the sand blanket placed against the stmcture to allow dissipation of pore pressures in order to avoid failure of the stmcture as silt fences to allow surface mnoff from a site while retaining the soil suspended in the mnoff and on earth slopes beneath larger stone or other overlay materials to prevent erosion of the slope as water escapes from the interior of the slope. 

Installation and maintenance of corrosion control measures Onduding. swales, silt fencing, and seeding). 

Use of geotextiles in silt fences, which consist of geotextiles placed vertically on posts to prevent eroded material from being transported away from the construction site by runoff water. 

Artificial seaweed tufted into a multifilament woven fabric was developed in 1965 by Sun Oil Co. and used to encourage sand buildup in the seabed and prevent further erosion. Both Nicolon and ICl followed with similar applications in the late 1960s (Brashears and DartneU, 1967). Silt fences, both on sloping gravel surfaces and underwater, were developed by Erosion Control Co., Burlington Industries, and the Mirafi Co. in the late 1960s (Koemer and Welsh, 1980). 

Depending on the application of the filter, often a second property of the geotextUe is asked for. Some uses need tensile strength, such as silt fences or geosynthetic enclosed sand columns some require high general robustness, eg, filters under hard armour or fabric for geosynthetic containers. 

The line fraction filtration test (Sansone and Koemer, 1992) can also provide valuable information about the long-term behaviour of filter fabric. In this test, the geotextile specimen is subjected to the flow of a mixture of water and soil. It may be particularly interesting for evaluating geotextile performance in silt fences in erosion control works. Palmeira and Farias (2000), eg, reported on test series in which slurries were used with soils from erosion in Brazil. The results showed that often the flow rate tended to stabilize even though conventional design would not recommend that use. 

Erosion control Geotextiles reduce soil erosion caused by rainfall impact and surface water runoff. For example, temporary geosynthetic blankets and permanent lightweight geosynthetic mats are placed over the otherwise exposed soil surface on slopes. Geotextile silt fences are used to remove suspended particles from sediment-laden runoff water. Some erosion control mats are manufactured using biodegradable wood fibers and related biomass. 

In light of these regulations, the earliest use of geotextiles in commercial projects was for the sediment control and stabilization of construction entrances. Sht-fihn wovens used in silt fences with specific opening sizes were required by soil... 

Figure 22.1 Silt fence functioning at a private development site.

In general, the benefits of geosynthetic sediment control systems over traditional stmctures such as rock checks and sediment traps include the minimal labor required to install them, the low cost, their high efficiency in removing sediment, their durability, and sometimes their reusabUity. The performance of sediment control systems typically depends on the proper selection and deployment of SRDs. SRDs such as silt fences typically cause the following to happen ... 

Table 24.3 Silt fence test results (Sprague and Lacina, 2010)... 

Silt fence Soil type ASTM D5141 ASTM D7351 ... 

GSWCC test method 11340 Because silt fences and wattles are also often used as perimeter devices around construction sites to intercept modest sheet flows, characterization testing associated with this application has been established in test method 11340. The test protocol closely follows the ASTM D6459 procedure described earlier. The accumulated data are used to determine an appropriate P-factor for use in the Revised Universal Soil Loss Equation. The GSWCC used test method 11340 to test a range of SRDs. Fig. 24.23 summarizes the results of the testing. It relates... 

Test method Test property Separation stabilization Filtration Reinforcement Sediment control (silt fence)... 

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