CETN-III-3
2/80
P U R P O S E : To call attention to the use of geotechnical fabrics as an alter-
native to sand and gravel filters for coastal structures.
BACKGROUND: Normally, filters to protect soils from surface erosion of pip-
ing losses are made-up of layers of graded sand, gravel, and stone materials
in various combinations and thicknesses. Often these materials are expensive
and, in some locations , proper materials are not economically available.
Even
if the required materials are readily available, proper placement in the field,
particularly at inwater sites can be tedious and demands close inspection.
GEOTECHNICAL FABRICS: The term "Geotechnical Fabric" applies to a variety of
synthetic fiber textile products used in the construction of engineering works
including coastal engineering projects. These fabrics, both woven and non-
woven, have been used in projects involving quarrystone revetments, groins,
seawalls , jetties, and breakwaters. In these coastal structures the fabric
can replace one or more layers of a graded sand-and-gravel filter and is also
effective for erosion-control where the fabric can prevent piping and erosion
of cohesionless materials while allowing drainage and dissipation of excess
hydrostatic pore pressures. The seawall shown in the Figure was constructed
at the north end of Carolina Beach, North Carolina, in 1970, by the Corps of
Engineers, and utilizes a geotechnical fabric. Structures of a generally sim-
ilar cross section using these fabrics have been built along the Atlantic sea-
board since 1958. Stone weights, slopes, and elevations varied with local con-
d i t i o n s . More recently fabrics have been used behind steel, concrete, and timber`
sheet-pile bulkheads in connection with french drains, weepholes, and joints.
A
3000-6000 Lbs.
B
500-2500 Lbs.
c stone:
2"-I2"Bed stone
Beach
Fill
Geotechnical
Fabric
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Figure - Use of Geotechnical Fabric in Seawall at Carolina
Beach, NC (Corps of Engineers project).
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