2. TYPES OF PROTECTION AVAILABLE. The usual protection against erosion by
wind and rainfall is a layer of rock, cobbles, or sod. Protection from wave
action may be provided by rock riprap (either dry dumped or hand placed),
concrete pavement, precast concrete blocks, soil-cement, fabric, and wood.
See Table 8, Chapter 6 for additional guidance.
a. Stone Cover. A rock or cobbles cover of 12" thickness is sufficient
to protect against wind and rain.
b. Sod. Grasses suitable for a given locality should be selected with
provision for fertilizing and uniform watering.
c. Dumped Rock Riprap. This provides the best protection against wave
action. It consists of rock fragments dumped on a properly graded filter.
Rock used should be hard, dense, and durable against weathering and also
heavy enough to resist displacement by wave action. See Table 5 for design
guidelines. For additional design criteria see Figure 14, Chapter 6.
d. Hand-placed Riprap. Riprap is carefully laid with minimum amount of
voids and a relatively smooth top surface. Thickness should be one-half of
the dumped rock riprap but not less than 12". A filter blanket must be
provided and enough openings should be left in the riprap facing to permit
easy flow of water into or out of the riprap.
e. Concrete Paving. As a successful protection against wave action
concrete paving should be monolithic and of high durability. Underlying
materials should be pervious to prevent development of uplift water
pressure. Use a minimum thickness of 6".
When monolithic construction is not possible, keep the joints to a
minimum and sealed. Reinforce the slab at mid depth in both directions with
continuous reinforcement through the construction joints. Use steel area in
each direction equal to 0.5% of the concrete area.
f. Gabions. Slopes can be protected by gabions.
Use of these is
discussed in DM-7.02, Chapter 3.
Change 1, September 1986
7.1-346
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