The uncased piles are used only where it is certain that neither soil nor water will fall in to the hole after withdrawing a driven mandrel or shell and also where adjacent pile will not damage the green concrete.

The uncased piles have the advantage that i) They need no storage place ii) they do not require cutting off excess length iii) do not require special equipment and iv) the concrete is not liable to damage from driving.

The bearing capacity of vibro-expanded piles is increased by enlarging its diameter at the bottom.

The following are the common types of uncased cast-in-situ concrete piles:

Franki pile is more useful where a bearing stratum of limited thickness can be reached at a reasonable depth, so they are best suited for the granular type of soil.

In simplex pile if the soil is firm enough to stand, the cast iron shoe at the base is provided with alligator jaw point.

The Franki pile has an enlarged base of mush-room shape, which gives the effect of a spread footing.

Vibro-piles are used where the ground is shaft, thus offering little frictional resistance to the flow of concrete.

The bottom of a vibro-pile is provided with a conical shoe so that it can be easily driven up to the desired depth.

In a simplex tamped pile, tamping of green concrete is done after the casing is withdrawn, at regular intervals.