01 July 1997
(a) The analysis can show the effect of reduced throttle settings or steam pressure.
(b) The analysis can calculate the maximum energy actually transmitted to the pile. This
energy should be compared with the rated hammer energy to determine the efficiency of the hammer
assembly. Low efficiencies indicate problems in the driving system and that maintenance is required.
(c) The analysis can assist in determining where the energy losses are occurring in the
c. Restrikes. Restrikes are useful for determining effects of soil freeze or relaxation and to evaluate
long-term pile capacity. Restrikes of previously driven piles should be accomplished using a swinging
leader to minimize time required for positioning the rig and pile driving system.
(1) Restrikes are recommended during installation of the production piles if restrikes performed
prior to or at the start of pile installation indicated more than 25-percent change in the penetration
resistance after a delay exceeding 16 hours.
(2) Restrikes are required when pile driving records indicate significant changes in penetration
resistance, i.e., > 25 percent compared to those piles driven earlier.
(3) Restrikes are required when pile driving records indicate penetration resistances that are not
compatible with adequate pile capacity.
4-3. PREVENTION OF PILE DAMAGE DURING DRIVING. Damage can be prevented by eliminating
overstressing (overdriving) of the pile. Overstressing occurs when driving stresses exceed the allowable
a. Pile Damage. Overstressing is frequently attributed to using a hammer too large for the pile being
driven, misalignment of the pile and hammer, material failure within the drive cap such as loss or insufficient
cushion, or malfunction of the equipment.
(1) General Indicators of Damage. The pile is probably damaged if any of the indicators given in
table 4-2a are observed.
(a) Hollow piles that can be inspected after driving may show overdriving from crushing or
distortion of the pile material.
(b) Any piles suspected of being damaged will be promptly evaluated to determine its effect
on the overall foundation design.
(c) Repetitive damage to piles may require modification of the installation equipment or
(2) Specific Indicators of Damage. Table 4-2b illustrates types of damages observed in timber,
concrete, and steel pile.