EI 02G001
CEMP-E
01 July 1997
(d) An indicator pile should be driven where the soil is dense sand, silt, or where the soil is a
stiff, fissured clay, friable shale, or a clay stone. Pore water pressures in these soils may decrease while
driving and cause the penetration resistance to increase substantially. The penetration resistance may get
so great as to exceed the capacity of the selected pile driving system and to exceed the capacity of the
selected pile to take the driving stresses. This is soil relaxation.
(2) Pile Driving Analyzer. PDA is recommended while driving the indicator piles to increase the
reliability of wave equation analysis. PDA equipment measures signals from two strain transducers and two
accelerometers bolted to the pile near its top. These two different sets of measurements are interpreted to
provide force versus time and velocity versus time plots of the pile driving. Soil input data such as skin and
toe resistances and the distribution of skin resistance can be modified to cause the force and velocity versus
time plots to match. This calibrates the wave equation analysis.
(a) Driving stresses calculated by wave equation from PDA results can be checked to be within
allowable stresses.
(b) The PDA results when output on an oscilloscope can be interpreted by the PDA technician
to indicate the quality of the pile that had been driven and signs of any damage as a result of driving the pile.
(c) The PDA results can indicate the effectiveness of different pile driving systems and assist
selection of the best system for pile installation.
(d) Further information on the PDA is indicated in paragraph 4-2 and chapter 6 of TM 5-809-7.
(3) Restrikes. Some indicator piles should be restruck at a later time; e.g., 1 day, 2 days, and
5 days after original driving of the pile. Restriking the pile will indicate any significant change in the
penetration resistance that could occur from soil freeze or relaxation. The soil freeze that is observed may
provide adequate pile capacity and avoid the need for any redesign and/or remedial treatment of the
foundation. If soil relaxation is significant, a pile that may cause negligible soil displacement such as an
H-section may be preferred over a pile that could displace the soil significantly such as a precast concrete or
steel pipe pile.
c. Wave Equation Analysis. The wave equation analysis is most useful for determining the ultimate pile
capacity from the penetration resistance of the pile measured while driving to its embedment depth. This
analysis will be performed by the Government as part of the design process.
(1) Computer Program GRLWEAP. The wave equation analysis is accomplished with program
GRLWEAP (Goble, et al. 1988) licensed to the U.S. Army Engineer Waterways Experiment Station
(USAEWES). Program GRLWEAP and User' Manual with applications are available from the Engineering
s
Computer Programs Library, Information Technology Laboratory of the USAEWES, to offices of the Corps of
Engineers.
(a) The data recorded on the pile driving record of the indicator piles plus an estimate of the
quake and damping values, skin friction distribution, and a range of ultimate capacities are input into
program GRLWEAP. The results of the analysis provide a calculation of the driving stresses and a bearing
graph of the penetration resistance versus the ultimate pile capacity.
(b) The quake is the limiting deformation at which the maximum resistance is observed.
Quakes are required for both skin and toe (end bearing) resistance and often set at 0.1 inch.
(c) Damping is velocity dependent component of soil resistance, and it is the slope of the
velocity of the pile versus the soil resistance. The choice of skin and toe damping can have a substantial
influence on the results of the wave equation analysis. Selection of these values depends on whether driving
is hard or easy. The GRLWEAP User' Manual provides some guidance for these values. The standard
s
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