. Cast-in-place concrete piles may be used
when conditions are favorable. They are made by
pouring concrete into a tapered hole or cylindrical
form previously driven into the ground or into a hole
in the ground from which a driven mandrel has been
withdrawn.
The left-in-place form may be a steel
shell heavy enough to be driven without a mandrel, or
it may be a steel form designed for driving with a
mandrel that is removed on completion of driving (fig.
12-77).
20. Composite piles. Composite piles are formed of
one material in the lower section and another material
in the upper section (fig. 12-78). A composite pile that
is constructed of wood and concrete is used to support
loads of 20 to 30 tons.
A composite pile that is
constructed of steel and concrete is used to support loads
up to 50 tons. As shown in figure 12-78, the first section
of wood or steel is driven first, then a mandrel and steel
casing are driven on top of the first section. The mandrel
is removed and the casing is filled with concrete.
21. Sheet piles.
Sheet piles are special shapes of
interlocking piles that are made of steel, wood, or formed
concrete which are used to forma continuous wall to resist
horizontal pressures, resulting from earth or water loads.
Figure 12-77.—Cast-in-place concrete piles.
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