CEMP-E
TI 809-02
1 September 1999
(1) Augured Uncased Piers. Augured uncased pier foundations are constructed by
depositing concrete into an uncased augured hole. The drill hole diameter can range from 250
mm (10-inches) to 1825 mm (72-inches), and up to 60 meters (200-feet) deep. In advancing
through granular materials, drilling mud is often required to keep the hole open. The drilled
shaft is filled with concrete in the dry, or by means of a tremie pipe through the drilling mud.
When the concrete is to be reinforced, care and planning is required to assure the
reinforcement can be placed in the desired location and to the depth required. For drilled
piers installed with a hollow stem auger, where longitudinal steel reinforcement is placed
without lateral ties, the reinforcement will be placed through ducts in the auger prior to the
placement of concrete. When transverse reinforcement is required, the reinforcement is
fabricated in cages which are securely tied so they will not rack or otherwise distort when
handled and placed in the augured hole. Transverse confinement reinforcing similar to that
indicated for prestressed piling is required for uncased concrete piers constructed in high
seismic areas.
(2) Drilled Shaft Piers. Drilled shaft piers can be generalized as large diameter cast-
in-place concrete filled pipes. Pier diameter range from 300mm (12-inches) to 900 mm (36-
inches), and the casing may, or may not remain part of the load-carrying element. Casings
where used are usually thick-walled. Drilled shaft piers can be designed to carry extremely
heavy loads to extreme depths. Once installed to the desired depth, the pipe is cleaned,
reinforcement placed, and filled with concrete if dry, or filled by the tremie method if water is
present. The pipe can then either be pulled for reuse, or left in place to increase load carrying
capacity. Transverse confinement reinforcing similar to that indicated for prestressed piling is
required for caisson piers constructed in high seismic areas in those cases where the pipe is to
be pulled. When the pipe is left in place, the pipe can be used to provide the necessary
concrete confinement.
3-7. FOUNDATIONS FOR MACHINERY. Commonly used machines such as centrifugal
pumps, fans, centrifuges, blowers, generator engines and compressors have vibrational
characteristics that can be damaging to foundations. The design of foundations supporting
these types of equipment requires special consideration to assure the equipment and
foundations supporting the equipment are not damaged due to resonant vibration. Information
and references pertaining to the design of foundations for vibratory loads can be found in the
ACI Committee 350 Report, "Environmental Engineering Concrete Structures". Additional
information can be found in ACI Committee 351 Report, " Foundations for Static Equipment,"
and in Military Handbook (MIL-HDBK) 1007/3, "Soil Dynamics and Special Design Aspects."
a. Minimum Requirements for Spread Footings Supporting Machinery. Machinery and
generator foundations will be reinforced as required by design loads but in no case with less
than 0.15 percent reinforcing each way distributed at top and bottom. Minimum bar size will be
No. 4, and maximum spacing of bars will be 300 mm (12 inches). These foundations will be
completely isolated from floor slab on grade with isolation joints. The allowable bearing
pressure will be one-half that assumed for static load conditions. When the depth of
foundation (D) is 900mm (36 inches) or more and its length-to-width (L /W) ratio is 3 or more,
the following reinforcing steel requirements will be met.
(1) Longitudinal reinforcing will be distributed at top, bottom, and faces of foundation
within 150 mm (6 inches) of the surface.
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