Surface Armor for Erosion Protection
7.4.4 GRID CONFINEMENT
7.4.4.1 Description
This approach uses a grid several inches thick, resembling a "honeycomb," to confine
soil or other material on the bank slope. It provides a level of protection which is less
resistant to erosion than conventional armoring, but more resistant than unsupported soil,
granular fill, or vegetation.
7.4.4.2 Advantages
By using locally available materials, grid confinement may offer a cost savings where
erosive forces are moderate. When filled with soil, it is highly compatible with vegetative
treatment.
Grid confinement also enhances the resistance of the slope to shallow failure. The grid
can also serve as a form for bituminous or similar armor material on steep slopes, in which
case some beneficial increase in flexibility of the armor can be expected, since the grid
material acts as joints in the armor.
7.4.4.3 Disadvantages
When filled with a non-cohesive material, grid confinement will not withstand as high
velocities as some other flexible mattresses. When filled with asphalt or concrete, it assumes
to some extent the unfavorable characteristics of rigid armor discussed in 7.3.
7.4.4.4 Design Considerations
Some manufacturers have developed guidance for allowable velocities and other
hydraulic factors, and can furnish specific recommendations for particular applications based
on laboratory tests and field experience.
The manufacturer may recommend a geotextile underlayment, and, if the grid is filled
with a non-porous material, filter points to allow drainage should be incorporated into the
design.
The grid should be anchored to the bank slope according to the manufacturer's
recommendation.
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