01 July 1997
pile is driven to the design embedment depth. The pile should be restruck after 1 or 2 days, even if the pile
had been driven to the embedment depth, to determine if the soil will relax and the soil strength will be
reduced following equalization of pore pressures. If the penetration resistance had decreased following the
delay, driving can continue until the pile is driven to the design embedment depth or until the driving
stresses again exceed the capacity of the pile or the driving system.
(c) Soil strength gain as a result of relaxation can exceed the capacity of the driving system to
install the pile. Delays of 1 or more days may be required to drive the pile to the design embedment depth
if the capacity of the driving system and/or pile are not increased. The driving energy should be increased
until driving stresses reach the allowable limit to optimize driving efficiency. The capacity of the pile may
also be increased to avoid excessive overstresses by increasing wall thickness of H-piles or steel open-end
(d) Assisted installation by specialized operations described in paragraph 3-4 is an option that
can be used to install piles where relaxation effects are significant.
(e) Several production piles should be restruck after a long term delay such as 1, 2, 5, and
10 days to be certain that long term equalization of pore pressures will not reduce the penetration
resistance and pile capacity to excessively low levels. The decrease in penetration resistance recorded
during the restrikes should be plotted with time to determine the rate that relaxation occurs. If the decrease
in penetration resistance is negligible after 5 or 10 days, then no later restrikes should be necessary.
(3) Obstructions. Obstructions such as cobbles, boulders, and large bodies in landfills will cause
significant increases in the penetration resistance leading to refusal of the pile to be driven further and/or
the pile can be deflected by the obstruction. The pile will be damaged if driving stresses exceed the
(a) Obstructions near the ground surface are evident by drift of the pile or by abrupt increases
in the penetration resistance. Deep obstructions are indicated by an abrupt increase in the penetration
resistance or by a significant difference between tip elevations of adjacent piles when the pile had been
driven to refusal.
(b) Deep obstructions can deflect the pile without any apparent effect to the exposed portion of
the pile above the ground surface. If the deflection breaks the pile, then the penetration resistance may be
decreased abruptly. If the deflection caused by the obstruction bends the pile, then the pile capacity may
not be adequate. Steel piles can bend through large angles approaching 180 degrees so that the tip is
driven toward the ground surface and may even break the surface.
(c) Obstructions may be removed by assisted installation or may be pierced with a spud. A
spud is a mandrel, heavy steel pipe or H-pile section driven to provide a pilot hole. The spud is withdrawn
and the pile inserted into the hole and driven to the embedment depth.
(d) A production pile may also be pulled when difficult driving is encountered and redriven.
However, skin friction may be reduced causing these piles to be unacceptable friction piles.
c. Problems with Ground Movement. Displacement piles such as timber, precast concrete, and
closed-end pipe piles displace the ground as they are driven to the embedment depth. Driving these piles
in dense sands or saturated cohesive soils will probably cause heave of the ground surface around the
(1) Heaved Piles. Piles that heave should be redriven to their original embedment elevation, but