Uncased Shafts: Drilled Shaft Details.

Figure 1-4 illustrates a typical uncased drilled shaft with an enlarged base.  The base is not perfectly flat because the shaft is drilled first, then the belling tool rotates in the shaft.  Uncased shafts may be constructed in firm,  stiff soils where loss of ground is not significant.

Examples of uncased shaft are given in the American Concrete Institute (ACI) Manual of Concrete Practice (1986).  Other terms used to describe the drilled shaft are “pier” or “caisson.” Large shafts greater then 36 inches in diameter are often called caissons.  The term “pile” is commonly associated with driven deep foundations of relatively small diameter or cross section.

Figure 1-4.  Drilled shaft details (1 in. = 25.4 mm)