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Ground Stability, Foundations and Substructures 109
Photograph 3.4 Driven segmental steel piles (http://www.roger-bullivant.co.uk).
A driven cast-in-place pile without permanent casing is illustrated in Figure 3.45. The
base of a steel lining tube, supported on a piling rig, is filled with ballast. A drop hammer
rams the ballast and the tube into the ground. At the required depth, the tube is restrained
and the ballast is hammered in to form an enlarged toe as shown in Figure 3.45. Concrete
is placed by hammering it inside a lining tube; the tube is gradually withdrawn. The effect
of driving the tube and the ballast into the ground is to compact the soil around the pile,
and the subsequent hammering of the concrete consolidates it into pockets (voids) and
weak strata. The enlarged toe provides additional bearing area at the base of the pile. This
type of pile acts mainly as a friction pile.