01 July 1997
Smith damping is the recommended option.
(d) The driving stresses calculated by the wave equation analysis are checked with the
allowable stresses for the pile to be sure that the structural integrity of the pile will be maintained.
(e) If recorded blow counts are low, but tension stresses calculated by wave equation analysis
are too high, the cushion thickness should be increased, the hammer stroke should be decreased, or a
heavier ram should be used. A reanalysis with GRLWEAP should then be completed to optimize driving of
the production piles.
(f) If the recorded blow count is satisfactory, but compressive stresses in the pile calculated by
GRLWEAP are too high, the cushion thickness should be increased or the stroke decreased. A reanalysis
with GRLWEAP should then be completed to optimize pile installation.
(g) If the recorded blow count is too high and compressive stresses are also too high, the size
of the pile or pile wall thickness should be increased and a reanalysis with GRLWEAP should be completed.
(2) The Bearing Graph. Estimates of the quakes, damping values, and skin resistances of soils are
encountered during installation of the piles, and pile and driving equipment parameters should be input into
program GRLWEAP to evaluate the penetration resistance versus pile capacity relationship which is the
(a) Hammer efficiencies provided by the manufacturer may be an overestimate of the actual
energy absorbed by the pile in the field and could lead to an overestimate of the pile capacity. Significant
overestimates of hammer efficiency are also possible for batter piles. A bracket analysis is recommended to
provide a probable range of the pile capacity. Results of the PDA and load tests discussed below can be
used to improve the results of the wave equation analysis.
(b) Results of wave equation analysis may not be applicable if soil freeze or relaxation effects
occur. Restrike of the pile after 1, 2, or 5 days should be performed to provide a better estimate of the
actual pile capacity.
(c) Driving stresses calculated by GRLWEAP should not exceed allowable limits. Refer to
paragraph 1-6a and TM 5-809-7 for further information on allowable driving stresses.
(d) Results of the wave equation analysis can be contested by the contractor and resolved at
the contractor' expense through resubmittals performed and sealed by a registered engineer, by field
verification using driving, and load tests approved by the design engineer.
(3) Selection of Pile Driving Equipment. The bearing graph and driving stresses calculated by the
wave equation analysis is useful to check the suitability of the selected hammer.
(a) If blow counts are low (5 blows/foot) and tensile or compressive stresses exceed allowable
limits, then hammer energy may be excessive and a smaller hammer may be appropriate.
(b) If blow counts are high (240 blows/foot), then a larger capacity hammer may be appropriate.
d. Load Tests. Field load tests determine the axial and lateral load capacity, displacements for applied
loads, and prove that the tested pile can support the design loads within tolerable settlement. Load tests
verify capacity calculations and structural integrity of the pile. These tests should reflect the range of
potential site conditions (e.g., on-shore and off-shore) after a minimum waiting period, usually 1 day. Refer
to TM 5-809-7 for further information on load tests.