EI 02C097
01 Jul 97
Chapter 6
of construction at locations specified by the design engineer or
Verification of Design
at suspicious locations to confirm the capability of the driven
piles to support the structure. PDA should also be performed
1. Foundation Quality
during the driving of indicator piles and some static load tests
performed to calibrate wave equation analyses. Table 6-1
Construction can cause defects in driven piles or drilled shafts.
illustrates an example procedure for verifying pile design.
Unfortunately, an installed deep foundation is mostly below the
Analyses by wave equation and pile driving are presented.
ground surface and cannot be seen. The quality of the
a. Wave equation analysis. The penetration resistance in
foundation should be verified to ensure adequate structural
integrity, to carry the required load without a bearing capacity
blows/feet (or blows/inch) measured when the pile tip has been
failure, to limit displacements of the structure to within
driven to the required depth can be used to calculate the ultimate
acceptable levels, and to avoid unnecessary overdesign of the
bearing capacity and verify design. Wave equation analyses can
foundation. This chapter describes methods commonly used to
relate penetration resistance to the static ultimate bearing
verify the capability of the foundation to support a structure.
capacity.
These methods are nondestructive and usually permit the tested
piles or drilled shafts to be used as part of the foundation.
(1) Computer program GRLWEAP. A wave equation
analysis is recommended, except for the simplest projects when
a. Indicators of problem with driven piles. Piles driven into
adequate experience and data already exist, for estimating the
soils with variable stratification that show driving records
behavior of pile driving and confirming pile performance. This
containing erratic data, which cannot be explained by the
analysis may be accomplished using program GRLWEAP
construction method, indicate possible pile damage. Failure to
(Goble et al. 1988), Wave Equation Analysis of Pile Driving,
reach the prescribed tip elevation or penetration rate also
licensed to WES. Program GRLWEAP and user's manual with
indicates pile damage. Other indicators include drifting of the
applications are available to offices of the Corps of Engineers.
pile off location, erratic driving unexplained by the soil
GRLWEAP models the pile driving and soil system by a series
stratification, and a sudden decrease in driving resistance or
of elements supported by linear elastic springs and dashpots with
interference with nearby piles as indicated by sound or
assumed parameters, Figure 6-1. Each dashpot and spring
vibration. A pile can also be damaged during extraction.
represent a pile or soil element. Information required to use this
program includes indentification of the hammer (or ram) and
b. Indicators of problems with drilled shafts. Most
hammer cushion used, description of the pile, and soil input
problems with drilled shafts are related to construction
parameters. Hammer selection is simplified by using the
deficiencies rather than design. Such problems result from
hammer data file that contains all the required information for
inadequate information of the subsurface soil and groundwater
numerous types of hammers. A simple guide for selection of
conditions provided to the contractor, inadequate clean-out
soil input parameters to model the soil resistance force is
including the presence of water in the excavation prior to
provided as follows:
concrete placement, inadequate reinforcement, and other
complications during concrete placement. Drilled shaft failures
(a) The soil resistance force consists of two components, one
may result from neglecting vertical dimensional changes in
depends on pile displacement, and theother depends on pile
shrinking and swelling soil as those described in TM 5-818-7.
velocity. Pile displacement dependent resistance models static
soil behavior, and it is assumed to increase linearly up to a
2. Driven Piles
limiting deformation, which is the quake. Deformation beyond
the quake requires no additional force. The pile velocity
Piles can be bent or sheared during installation and can cause a
component models depend on soil damping charactertistics
reduction in pile capacity. Piles can also undergo excessive
where the relationship between soil resistance and velocity is
tensile stresses during driving, specifically when soil layers have
linear and the slope of such relationship is the damping constant.
variable density or strength or when there is no significant end
Quake and damping constants are required for both skin friction
bearing resistance. Field test procedures such as standard
and end-bearing components. Table 6-2 gives recommended
penetration tests, pile driving analysis (PDA) with the wave
soil parameters, which should be altered depending on local
equation, restrikes, and pile load tests can determine the ability
experience. The distribution of soil resistance between skin
of the pile to carry design loads. Refer to paragraph 4, Chapter
friction and end bearing, which depend on the pile and soil
6, for guidance on load tests. Typically 2 to 5 percent of the
bearing strata, is also required. End-bearing piles may have
production piles should be driven as indicator piles, at the start
all of the soil resistance in end
6-1
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