Geosynthetics April/May 2021 - 40

GSI NEWS

By George R. Koerner

A new specification for geotextile
grout filled mattresses
GEOSYNTHETIC
INSTITUTE
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and transfer knowledge,
assess and critique
geosynthetics, and provide
services to the member
organizations.

www.geosynthetic
- institute.org

George R. Koerner is the
director of the Geosynthetic
Institute in Folsom, Pa.

eotextile grout filled mattresses (GGFM), also referred to (in ASTM D18.25/
D35.05) as fabric-formed concrete (FFC) or fabric-formed concrete revetments
(FFCR), are erosion-resistant concrete linings made from durable, permeable fabric
forms that are filled with high-strength grout. GGFMs are generally sloping structures
placed on shorelines to absorb the energy of incoming water. Grouted in place, they
adapt to uneven contours, curves and subgrades as they are filled. GGFMs provide an
economic and durable solution for erosion control, scour protection, shoreline protection
and soil stabilization. They are highly effective in environmental and marine construction applications.
Advantages of GGFMs are as follows:
* Cost-effective alternative to traditional concrete slope paving, gabions and riprap
* Reduce hydraulic uplift by slowing flow velocities and reducing wave run-up
* Conform to soil contours to reduce the potential for scour
* Resist stresses associated with high-velocity flows
* Have no steel reinforcement or concrete finishing
* Do not require dewatering
* Low cost of transportation and mobilization
* Limited environmental impact
GGFMs can be used both above and underwater, by laying the fabric forms over the
area to be protected and pumping fine-aggregate concrete into the forms. Fine-aggregate
concrete is used in place of regular concrete because of its pumpability, strength, density and
absorption resistance. They can even be colored to blend in with the natural environment.
The GGFM is a double-layered fabric that acts as a formwork to allow the injection
of a high-strength grout between the layers. The geotextile is not intended to be permanent. The GGFM acts as a barrier to prevent erosion that can occur on engineering
structures, including:
* Wharf and harbor embankments
* Embankment and lake linings
* Culverts, spillways and boat ramps
* Seawalls and river linings
* Bridge abutments and road shoulder protection
* Boat ramps and hovercraft pads
* Sludge lagoons and aeration ponds
The two layers of textile of a GGFM are connected via a vast array of internal restraining
ties. As well as providing internal fiber reinforcement for the grout that is pumped between
the layers, the length of these ties can be modified to determine the final thickness of the
inflated mattress. The product provides a smooth, watertight finish with a high coefficient
of friction, which can be trafficable with a low-ground-pressure vehicle.

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Geosynthetics April/May 2021

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