main reason for this concern over
proper operation Of equipment when driving
l o a d - b e a r i n g piles is that driving
i s usually terminated when the resistance
exceeds a certain number of blows
per inch. I n order for driving resistance
t o be meaningful, it is necessary
that the equipment be operated consistently.
4 . What method of measuring penetration for calculating bearing during
d r i v i n g is being used by CQCI? D o e s method exclude introduction of deliberate
e r r o r by the operator? C o n t r a c t o r s have found it to their advantage to
u n d e r d r i v e load-bearing piles. One means of deception used by a pile driver
o p e r a t o r to underdrive load-bearing piles is manipulation of hammer
c o n t r o l s . Carefully watch for proper hammer operation.
A second method of subterfuge is manipulation of cushion block materials.
According to the pile formulas, a small penetration corresponds to a high
b e a r i n g capacity. Thus, an inadequate pile can, by manipulation of cushion
block materials, be made to appear acceptable to the unwary CQCI or QAP.
R e s e a r c h the specifications carefully. I f the applicable specification
s e c t i o n does not address control over cushions, establish control over hammer
cushions.
Only cushions of known characteristics should be used.
(Aluminum and micarta discs are recommended as hammer cushions since the
d i s c s both work well and usually last throughout the entire job.) Either
s p e c i f y the cushion block size and material or require the cushion block size
and material for hammer cushions be submitted to the Contracting Officer for
a p p r o v a l using authority of General Provision 9, the " Material and
Workmanship" clause. Require that the approved cushion block be held constant
t h r o u g h o u t all pile driving.
A third method of deception, u s e d to deliberately underdrlve piles, is
m e c h a n i c a l modification. This is very difficult to detect. The QAP would
have to check all hammer parts against the manufacturer's machine drawings,
w h i c h is generally infeasible unless QAP is extremely familiar with structure
a n d moving parts of a pile driver.
Is
the
CQCI
checking
template
for
sturdiness?
5.
6 . A s s u r e that CQCI checks that penetration of pile is sufficient to
d e t e r m i n e Its course before template is moved.
7 . A s s u r e that CQCI checks inside of pipe pile or casing of cast-in-place
pile for loose soil and water with mirror or drop light. Do not let concrete
b e dumped in pipe piles or casings through water; loose soil must be cleaned
out and the water must be drawn down to an acceptable depth before placing
c o n c r e t e . H a v e you satisfied yourself that the CQCI is automatically rejecting
p i l e s containing water, s o i l or debris? If the specs do not state an
a c c e p t a b l e depth of water, It is recommended that 2-6 inches be the maximum
d e p t h of water allowed in the bottom of the pile.
8 . Is CQCI insuring that concrete is being placed in bucket and tremie
to
a v o i d segregation? I s the concrete at the top of the pile consolidated by
m e c h a n i c a l vibrator?
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