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 Surface Armor for Erosion Protection
too steep for long-term geotechnical stability, although this is a flaw in design rather than an
inherent flaw of sacks themselves.
Synthetic bags, which are sometimes marketed as being suitable for filling with soil
or sand rather than a cementious mixture, may be vulnerable to environmental hazards such
as fire, ice, vandalism, livestock traffic, floating debris, and rupturing by the roots of
vegetation.
A fabric and/or granular underlayment ("filter") is usually required, whereas that may
not be the case with a riprap blanket. Successful performance of the underlayment is more
critical than with riprap.
A sack armor may not be as likely to support vegetative growth as readily as some
other armor materials, especially if a cementious filler is used, or if the sacks are placed on
a steep slope. However, in situations where vegetative growth is not desirable, this would
be an advantage.
7.2.2.4 Typical Applications
Sacks are especially suitable for use on transitions to steep slopes, or in areas where
they are aesthetically desirable. If low-cost labor is available, they may be the most cost-
effective method, especially on small projects.
7.2.2.5 Design Considerations
If commercial bags are used, then the manufacturer's guidance should be followed.
Otherwise, the following guidance should be used:
Sack material selection is not critical if the sacks are to be filled with a cementious
mixture, as long as they are strong enough to withstand the stress of handling, and will not
degrade before the cement sets up. The choice of sack material can then be based on
economics, considering the total operation of filling, closing and placing. Some commercial
bags have ingenious provisions to speed filling and closing, thus reducing labor costs.
Prefilled bags are available in some areas. An alternative to specifying a particular sack for
work to be contracted out is to allow bidders a choice of sacks, within broad guidelines.
Sack size should be small enough for laborers to handle. General purpose sacks such
as burlap bags or sandbags should have a capacity larger than the desired in-place volume, so
that the open end can be folded under the bag as it is placed.
The usual filler material is a sand/cement mixture. Since labor costs are high
regardless of fill material, use of a non-cementious filler should be considered only if
significant savings would result, and a long life is not required. One such case would be for
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