Surface Armor for Erosion Protection
7.2.1.4 Typical Applications
In addition to typical application as bank armor, blocks can be used effectively for
special features such as ditch and spillway linings, culvert outlets, walkways. They are
suitable for areas to be vegetated which are subject to erosive forces which vegetation alone
could not withstand.
Manufactured blocks are sometimes the least-cost alternative for self-adjusting armor.
This is usually in regions where riprap must be transported long distances at great expense,
or at sites of high erosive forces where a thick armor of riprap can be replaced by a thinner
armor of concrete blocks.
They are well-suited for projects where labor-intensive hand placement is acceptable.
Efficient mechanized placement is an option when the blocks are fabricated into mattresses.
7.2.1.5 Design Considerations
Manufacturers' recommendations and/or guidance from laboratory tests and field
experience, should be followed in determining block thickness and other details.
7.2.2 SACKS
7.2.2.1 Description
Sacks as an armor material can be considered to be artificial "rocks" of uniform size
and shape. The sacks may be made of paper, burlap, or a synthetic material. The fill material
may be soil or aggregate of various types, with or without cement.
7.2.2.2 Advantages
Sacks can be placed on a steeper slope than stone.
Materials are often available locally. The hydraulic roughness is low, and they form
a walkable surface. The "cobblestone" effect may be more aesthetic than some other
materials.
7.2.2.3 Disadvantages
A sack armor may tend to act monolithically on steeper slopes, therefore small failures
can lead to large ones. The characteristic of being "stackable" may lead to their use on slopes
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