Driven piles
are structural elements for the transfer of loads through weak
soil layers to a suitable bearing layer of soil or rock. They
are suitable foundations for all types of land-based and
marine-based structures. Their choice over other deep
foundation methods is a matter of economic and site-specific
factors.
Types of
Driven Piles and Their Capacities
Piles
develop their capacity through a combination of side (skin)
friction and end bearing. Piles driven to a very hard layer
such as rock will develop their capacity primarily by end
bearing, while piles driven soil will develop their capacity
from both side friction and end bearing. Piles have been
driven to capacities over 1,000 tons (US) in the offshore oil
industry. However, most projects only require piles with less
than 100-ton design loads
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Steel (over 25 tons)
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Concrete (up to 100 tons)
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Wood (up to 25 tons)
Sheet Piles
are a special type of pile used to form in situ walls for
earth retention and excavation support. Steel sheet piles are
commonly used today, while wood and concrete sheet piles can
only be used in very limited conditions.
Driven Pile
Applications
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Deep foundations (most common)
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Excavation support (Sheet and soldier piles)
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Docks and wharfs
Important
Driven Pile Parameters
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Skin friction and end bearing values
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Allowable stress for the pile material
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Drivability of the pile hammer, cushion,
capblock, and pile system
Driven Pile
Design Steps
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Geotechnical site investigation
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Determine load to be supported
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Design pile-to-structure connection
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Design pile-to-soil or rock load transfer
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Develop a pile testing program
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Determine the driving resistance by the Wave
Equation Analysis
Driven Pile
Installation Methods
Piles are
typically driven into the ground using impact hammers. These
hammers are powered by:
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Compressed air (or steam)
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Diesel
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Hydraulic fluid
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Gravity (drop hammers)
drive head
containing cushion material is used between the hammer and
pile to prevent damage to the hammer and pile. The drive head
also keeps the pile centered under the hammer. The hammer and
pile are guided by set of leads that are supported by a crane.
Typically, 50 to 150-ton capacity crawler cranes are used to
drive piles. Vibratory hammers can also be used to drive
piles, particularly low displacement piles such as sheet
piles, but these do not penetrate hard soils or give an
accurate indication of pile.
Vibration
and Noise Considerations
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Vibrations generally will not harm structures
in good condition when using small to medium sized impact
hammers.
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Vibrations pose more risk to deteriorated
structures, and can interfere with nearby sensitive
electronic instruments.
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Steady-state vibration produced by vibratory
hammers is much more likely to cause damage to structures
and cause settlement of loose soil. Predrilling greatly
reduces the magnitude of the vibrations transmitted through
the ground to nearby structures.
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Noise from pile driving can be cause for
concern on sensitive job sites such as hospitals. Timber and
concrete piles driven with air or hydraulic hammers are much
quieter than steel piles driven with diesel hammers.
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Noise levels near the pile and hammer are
high enough to require hearing protection for those on and
near the job site.
Driven Pile
Quality Assurance/Quality Control
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Consider the use Wave Equation Analysis
software to model the pile – hammer – soil interaction. This
program estimates ultimate load. Typically, a factor of
safety of 2 is used with this analysis. This program can be
used to check the driving stress in the pile, and guide
hammer selection. This relationship, once established for a
pile project, offers a very reliable quality control tool.
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Test selected piles to local code
requirements (usually two times the static design load) ASTM
standards D 1143, D 3689, and D 3966, provide standard
static testing methods for compression, tension and lateral
test, respectively. Also, the pile can be tested using ASTM
D 4945 High-Strain Dynamic Testing of Piles. This test can
be done in lieu of the static test, and is very economical
for testing a large number of piles.
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Determine, from the Wave Equation Analysis
and load test results, the required driving resistance for
the production piles.
Benefits of
Driven Piles
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High-performance
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Appropriate for a wide range of ground
conditions
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Design loads up to 1,000 tons
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Suitable for land-based and marine-based
structures
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Usually the fastest deep foundation
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