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118 Barry’s Advanced Construction of Buildings
Large diameter bored pile
Figure 3.50a and Photograph 3.7a illustrate the formation and casting of a large diameter
bored pile formed in cohesive soils. Figure 3.50b shows the same operation performed in
non-cohesive soils with a coring barrel. A tracked crane supports hydraulic rams and a
diesel engine which operates a kelly bar and rotary bucket drill. The diesel engine rotates
the kelly bar and bucket. In the bottom of the bucket are angled blades that rotate, excavating
the strata and filling the bucket with soil. The hydraulic rams force the bucket into the
ground. The filled bucket is raised and emptied and drilling proceeds. In non-cohesive soils,
the excavation is lined with steel lining tubes. To provide increased end bearing, the
drill can be belled out to twice the diameter of the pile (Figure 3.50c). The augers and
core barrels for cutting through rock, cohesive and non-cohesive soils are shown in Photograph
3.7a–e.
Kelly bar rotates and the auger
bites into the ground
Tracked excavator
The auger is removed from the
bore hole and the cohesive soil
stays trapped within the thread of
the auger
The auger with the soil is moved
to the side of the excavation and
by jerking the rotating movement
the soil is deposited on the ground
(a)
Figure 3.50 (a) Bored pile with augur: cohesive soils. (b) Bored pile with core barrel:
non-cohesive soils. (c) Forming a large toe with belling tool.