Surface Armor for Erosion Protection
7.2.5.5 Design Considerations
Principles of design are the same as for stone riprap. Slag from oxygen or electric
furnaces is denser than that from blast furnaces, and may even be denser than stone.
Therefore, the riprap design criteria in Appendix A would be applicable. The designer may
have a choice of different gradations if slag is commonly used locally for construction. The
size gradation is sometimes enhanced by the addition of scrap refractory brick.
Slag has been used both with and without an underlayment. On the Ohio River, an
18 inch blanket without underlayment was as successful as a 12 inch blanket on top of
engineering fabric.
7.2.6 AUTOMOBILE BODIES
Automobile bodies are included is this listing only because they have been used
occasionally for erosion protection. No redeeming features beyond low cost can be claimed.
Environmental considerations make their use as streambank protection objectionable.
7.3 RIGID ARMOR
The following paragraphs outline the general description, advantages, disadvantages,
typical applications, and design considerations for most rigid armor used as a bank
stabilization method:
Rigid armor is an erosion-resistant material which has little or no flexibility to
conform to bank irregularities occurring after construction. Typically, the
armor is placed directly on the bank slope in a fluid or chemically reactive
state, then hardens.
The most common rigid armors are:
Asphalt;
Concrete;
Grouted riprap (or other grouted armor material); and
Soil-cement.
Materials which have a more restricted use, but which can be classified as
rigid armors, are chemical soil stabilizers, and clay.
Advantages, disadvantages, typical applications, and design considerations for
rigid armor are discussed collectively, followed by a discussion of distinctive
characteristics of each type and sources for additional information on each
type.
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