Surface Armor for Erosion Protection
7.2.3.2 Advantages
Besides the general characteristics of adjustability to bank irregularities and self-
healing properties, soil-cement blocks allow the utilization of locally available materials.
7.2.3.3 Disadvantages
Soil-cement blocks have a lower specific weight than riprap, and obtaining acceptable
gradation and durability are highly dependent on closely controlled construction operations.
Construction operations are adversely affected by wet or cold weather.
7.2.3.4 Typical Application
Soil-cement blocks are most often used when stone is prohibitively expensive, suitable
soil for aggregate is available at or near the job site, and personnel experienced in making the
blocks are available. Cost savings over alternative methods are more likely on larger projects
which amortize the cost of operations set-up.
7.2.3.5 Design Considerations
Since soil-cement blocks are simply man-made rocks, the general principles of
effective riprap design apply. However, the lower specific weight of soil-cement requires
larger block sizes for equivalent protection, and size criteria as precise as those for riprap do
not exist.
For other aspects of design, extensive research and field experience has resulted in
detailed recommendations by the Portland Cement Concrete Association and others. The
following points are especially important:
Specifying a suitable soil as aggregate is critical. Although soil-cement can be
made from almost any soil, soil with at least 55 percent sand and no more than
35 percent fines is recommended. A "graded" soil of mostly sand, but with
some non-clayey fines and gravel provides the optimum combination of
workability, strength, durability, and minimum cement requirements.
Blocks with a low cement content may be vulnerable to damage from waves,
impingement by high velocity streamflow, and abrasion from transported
sediment.
A controlled gradation of finished blocks is best obtained by spreading mixed
soil-cement in slabs of varying thicknesses, then scarifying the upper portion
of each slab early in the curing process. Following curing, the slabs can be
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