TM 5-818-1 / AFM 88-3, Chap. 7
grained soils can produce high-strength, durable
(2) Clam and oyster shells as a structural
materials. Lime treatment levels of 3 to 8 percent by
fill material over soft marsh deposits represent a new
weight of dry soil are typical.
development. The large deposits of clam and oyster or
c. Portland cement. With treatment levels of 3
reef shells that are available in the Gulf States coastal
areas can be mined and tasportd short distances
to 10 percent by dry weight, portland cement is
economically. Clam shells are 1/4, to 1/2 inch in
particularly well suited for low-plasticity soils and sand
diameter; whereas, oyster shells, which are coarser and
d. Stabilization using fills.
more elongated, are 2 to 4 inches in size. When
dumped over soft ground, the shells interlock; if there are
(1) At sites underlain by soft, compressible
finmes and water present, some cementation develops
soils and where filling is required or possible to establish
owing to the high calcium carbonate (>90 percent)
the final ground elevation, load-bearing structural fills can
content. In the loose state, the shell unit weight is about
be used to distribute the stresses from light structures.
63 pounds per square foot; after construction, it is about
Compacted sands and gravels are well suited for this
95 pounds per square foot. Shell embenkments "float"
application as are also fly ash, bottom ash, slag, and
over very soft ground; whereas, conventional fills would
various lightweight aggregates, such as expended shale,
sink out of sight. About a 5-foot-thick layer is required to
clam and oyster shell, and incinerator ash. Admixture
be placed in a single lift. The only compaction used is
stabilizers may be incorporated in these materials to
from the top of the lift, so the upper several inches are
increase their strength and stiffness.
more tightly knit and denser than the rest of the layer.