Geoscience Reference
In-Depth Information
Geotextile mattresses
Geotextile mattresses comprise two interconnected layers of geotextile where the
space between is filled with sand and, in special cases, concrete. Cells or tubes form
compartments within the mattress, which facilitates an even distribution of the fill
material in the geotextile mattress and maintains its shape and combats movement of
the fill material during use.
Geotextile mattresses are manufactured from woven geotextile materials or from
combinations of woven and nonwoven geotextile materials. The choice of geotextile
depends on the hydraulic, mechanical and environmental requirements of the method
of construction.
4.1 APPLICATION AREAS AND GENERAL
EXPERIMENTAL DATA
Geotextile mattresses are used as bank or bed protection along rivers and canals,
often in countries where there is no natural bank protection materials (blocks or
rock) available and/or where there is a lack of technical personnel to construct proper
granular filters or similar layers. Figure 4.1 shows a typical geotextile mattress used
for a bank revetment.
To determine the appropriate dimensions of geotextile mattresses, use is often made
of the design approach for sloping revetments using set stone. For geotextile mattresses,
the drainage length of the structure may also be expected to have some influence. The
drainage length is determined by the relationship between the hydraulic conductivity
of the mattress layer and that of the subsoil. With a relatively impermeable subsoil,
the mattress is prone to become unstable more quickly; with a relatively permeable
subsoil, instability occurs less quickly, but the load on the subsoil is greater.
When geotextile mattresses are used, they are normally placed directly on the
subsoil. In some instances they may be supplemented by a sand layer as an extra fill
layer.
The appearance of a mattress can be of flat-tubular form or can be waffle-like.
Sometimes the tubes or 'sausages' of the waffle-like geotextile mattress are placed
horizontally on the slope, but more often the tubes are placed down the direction of
the slope (average 1V:2H to 1V:4H) - see section 4.3. Placing the mattresses down the
direction of the slope also enables easy filling (by gravity) on site. In this direction, the
seams between the tubes in the mattress follow the inclination of the slope. Because
