EI 02C097
01 Jul 97
Table 6-1
Procedure for Verifying Design and Structural Integrity of Driven Piles
Step
Procedure
1
Complete an initial wave equation analysis selecting soil damping constants Jc , quakes u , distribution of soil
resistance between skin friction and end bearing and the ultimate bearing capacity Qu . Use the proposed pile and
driving system. Adjust driving criteria as needed to reduce pile stresses and to optimize pile driving.
2
Drive indicator piles, typically 2 to 5 percent of the production piles, at locations specified by the design engineer using
driving criteria determined by the wave equation analysis. Complete additional wave equation analysis using actual
hammer performance and adjust for changes in soil strength such as from freeze or relaxation. Drive to various
depths and determine penetration resistances with the PDA using the Case method to determine the static ultimate
bearing capacity Qu .
3
Restrike the piles after a minimum waiting period, usually 1 day, using the PDA and Case methods to determine actual
bearing capacity that includes soil freeze and relaxation.
4
Perform CAPWAPC analysis to calibrate the wave equation analysis and to verify field test results. Determine Qu ,
hammer efficiency, pile driving stresses and structural integrity, and an estimate of the load-displacement behavior.
5
Perform static load tests to confirm the dynamic test results, particularly on large projects where savings can be made
in foundation costs by use of lower factors of safety. Dynamic tests may also be inconclusive if the soil resistance
cannot be fully mobilized by restriking or by large strain blows such as in high capacity soil, intact shale, or rock. Static
load tests can be significantly reduced for sites where dynamic test results are reliable.
6
Additional piles should be dynamically tested during driving or restruck throughout pile installation as required by
changes in soil conditions, load requirements, piles, or changes in pile driving.
7
Each site is unique and often has unforeseen problems. Changes may be required in the testing program, type and
length of pile, and driving equipment. Waivers to driving indicator piles and load testing requirements or approval for
deviations from these procedures must be obtained from HQUSACE/CEMP-ET.
bearing, while friction piles may have all of the soil resistance in skin
Government personnel using clearly defined data provided by the
friction.
contractor.
(b) A bearing-capacity graph is commonly determined to relate
(2) Analysis prior to pile installation. A wave equation analysis
the ultimate bearing capacity with the penetration resistance in
should be performed prior to pile driving as a guide to select
blow/feet (or blows/inch). The penetration resistance measured at
properly sized driving equipment and piles to ensure that the piles
the pile tip is compared with the bearing-capacity graph to
can be driven to final grade without exceeding the allowable pile
determine how close it is to the ultimate bearing capacity. The
driving stresses.
contractor can then determine when the pile has been driven
sufficiently to develop the required capacity.
(3) Analysis during pile installation. Soil, pile, and driving
equipment parameters used for design should be checked to closely
(c) Wave equation analysis also determines the stresses that
correspond with actual values observed in the field during
develop in the pile. These stresses may be plotted versus the
installation. Sound judgment and experience are required to
penetration resistance or the ultimate pile capacity to assist the
estimate the proper input parameters for wave equation analysis.
contractor to optimize pile driving. The driving force can be
adjusted by the contractor to maintain pile tensile and compressive
(a) Hammer efficiencies provided by the manufacturer may
stresses within allowable limits.
overestimate energy actually absorbed by the pile in the field and
(d) GRLWEAP is a user friendly program and can provide
results within a short time if the engineer is familiar with details of
the pile driving operation. The analysis should be performed by
6-2
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