Saturday, November 17, 2012

Types of Deep Foundations.

Deep foundations are classified with respect to displacements as  large displacement, small displacement, and nondisplacement, depending on the degree to which installation disturbs the soil supporting the foundation  (Table 1-2).  Large displacement and small displacement piles are fabricated prior to installation and driven into the ground, while nondisplacement piles are constructed in situ and often are called drilled shafts.  Augered cast concrete shafts are also identified as drilled shafts in this publication.

Table 1-2 Types of Deep Foundations

a.  Large displacement piles. the materials from which the pile is constructed, i.e., timber,
concrete, or filled or unfilled steel pipe.
(4)   Steel piles.  
(5)  Compaction piles. These are sometimes driven with
the objective of increasing the density of loose, cohesionless
soils and reducing settlement.  Piles with a heavy taper are
often most effective in deriving their support from friction.

b.  Nondisplacement piles.  This pile consists of a drilled shaft with a concrete cylinder cast into a borehole.  Normally, the  drilled shaft does not cause major displacement of the adjacent ground surface.  The hole is usually bored with a short flight  or bucket auger.  Loss of ground could occur if the diameter  of the hole is decreased because of inward displacement of soft soil or if there is caving of soil from the hole perimeter.  Such unstable boreholes require stabilization by the use of slurry or slurry and casing.  Drilled shafts are not subject to handling or driving stresses and therefore may be designed  only for stresses under the applied service loads.

Nondisplacement may be categorized as follows:

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