Driven cast-in-situ concrete piles are constructed by driving closed-ended hollow steel or concrete casing into the ground and then filling it with concrete.
The casing may be left in position to form part of the pile, or withdrawn for reuse as the concrete is placed. The details of driven cast-in-situ piles are shown in the figure below.
The concrete is then rammed into position by a hammer as the casing is withdrawn ensuring firm contact with the soil and the compaction of concrete. Care must be taken to see that the concrete is not over-rammed or the casing is withdrawn too quickly.
There is a danger that as the liner tube is withdrawn it will lift the upper portion of the in-situ concrete, thus leaving a void or necking in the upper portion of the pile. This can be avoided by good quality control of the concrete and slow withdrawal of the casing.
Driven cast-in-situ concrete piles can prove to be economic for sand, loose gravel, soft silts and clays, particularly when large numbers of piles are required. For small numbers of piles, the on-site costs can prove expensive.