While the precautions listed above are essential for successful construction of a stable
mattress, other considerations can further improve the chances that the revetment will provide
long-term bank protection.
Holes can be cut, drilled, or burned in the tire sidewalls to prevent flotation.
Presorting the tires by size may help to fit them together.
Earth screw anchors (or some other type of anchor) fastened to the mattress can be
placed in the bank at various points on the face of the revetment.
The tires can be packed with stone or rubble.
Willows can be planted inside the tires preferably at the beginning of the growing season.
Once established the root system will further strengthen the bank and obscure the
unsightly mattress. If willows are not readily available, other species should be planted.
Possible species for use are discussed later in this text.
If the mattress effectively controls the streambank erosion and remains intact, sediment may
gradually cover the revetment. If willows have not been planted, volunteer vegetation will may
become established in areas with a temperate climate.
Prior to constructing a stacked-tire revetment, the bank face should be shaped so that the tires
can be laid in horizontal rows on a geosynthetic filter material. The revetment should be
started at the toe of the bank and stepped back 150 to 300 mm (6 to 12 in.) per row. Each tire
should overlap the two tires under it. The stacked tires should be packed tightly with stone or
rubble. Any space behind the tires should be filled with free-draining soil so that the soil mass
will not become saturated and cause the revetment to fail. In addition, the upstream and
downstream ends of the revetment should be tied into the bank so that there is no flow behind
the revetment.
6.6.8 Soil Cement
In areas where riprap is scarce, use of in-place soil can sometimes be combined with cement
to provide a practical alternative. HEC-23 (Lagasse et al. 2001) provides design guidelines
and specifications for soil cement revetments. Figure 6.24 shows a detail of a typical
soil-cement construction for bank protection. For use in soil-cement, soils should be easily
pulverized and contain at least five percent, but not more than 35 percent, silt and clay
(material passing the No. 200 sieve). Finer textured soils usually are difficult to pulverize and
require more cement as do 100 percent granular soils which have no material passing the No.
200 sieve. Soil cement can be placed and compacted on slopes as steep as one horizontal to
one vertical.
A stairstep construction is recommended on channel embankments with relatively steep
slopes. Placement of small quantities of soil-cement for each layer 150 mm (6-inch) layers can
progress more rapidly than a large quantity of fill material. Special care should be exercised to
prevent raw soil seams between successive layers of soil-cement. If uncompleted
embankments are left at the end of the day, a sheepsfoot roller should be used on the last
layer to provide an interlock for the next layer. The completed soil-cement installation must be
protected from drying out for a seven day hydration period. After completion, the material has
sufficient strength to serve as a roadway along the embankment. Procedures for constructing
soil-cement slope protection by the stairstep method can be found in "Suggested
Specifications for Soil-Cement Slope Protection for Embankments (Central-Plant Mixing
Method)," Portland Cement Association Publication IS052W and numerous other PCA
publications.
6.42
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