(57) Various aspects provide for a drill bit assembly, which may include at least two
drill bits (210, 220, 230). An inner drill bit (210) may be removably coupled to an
outer drill bit (220), which may be coupled to a casing ring (230). Various apparatus
and methods may be used to drill a hole (100) having two or more different diameters.
The inner and outer drill bits (210, 220, 230) may be connected to a drive tube (214)
to drill a hole (100) having a diameter of the outer drill bit (220) and thereafter
a set able fluid (730, e.g. concrete) may be supplied to form a joint composite pillar,
leaving the drill bits (210, 220, 230) and drive tube (214) to form reinforcement,
preferably also a casing (234). The inner drill bit (210) may be decoupled from the
outer drill bit (220) to drill a hole (120) (e.g., an extension of the first hole)
having a diameter of the inner bit (e.g., smaller than that of the outer drill bit),
prior to supplying the set able fluid (730).
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