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Micro Piles |
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Our
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We
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are experienced in these applications:
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Our specialties are
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Driven Piles
JULY
1997
7-45
Spudding is another method used to assist penetration. This is where an “H” pile or similar
section is driven to break or cut through hard material. Contract piles should not be used
for spudding unless the pile has been specifically designed for this type of action.
The term “hard driving” is subject to much individual interpretation and there are no set
guidelines in the specifications, save certain requirements for timber piles. When the blow
count for timber piles reaches specified limits, the Contractor is required to take prescribed
measures of assistance. This could include predrilling, jetting or a change to a larger low
velocity hammer.
In the case of steel or concrete piles, no measures are specified to mitigate hard driving at
predetermined blow count levels. However, the Contractor is required to employ the mea-
sures described above to obtain the required penetration and is also required to use equip-
ment which will not result in damage to the pile.
Physical damage to the pile, even when it is below ground, is fairly easy to determine.
Impending damage and/or high driving stresses are not as easy to pinpoint. In situations of
high driving resistance, the Engineer is well advised to investigate pile stresses. In the book
Pile Foundations, Chellis covers this subject fairly well and it is recommended as reference
material.
The subject of pile refusal has to be included in discussions about hard driving. Unfortu-
nately, there are nearly as many definitions for the term “refusal” as there are those who
attempt to define it. Some popular interpretations range from: (1) twice the required blow
count, (2) 10 or more blows per inch, or (3) no penetration of the pile under maximum
driving energy. Some contractors would like us to think of refusal as something in the
double the required blow count range. These contractors also feel that Caltrans labors
under the concept of refusal as that point just prior to self destruction of the hammer.
Is any specific definition valid. Not really. Refusal should be viewed as very little or no
penetration of the pile with a reasonable amount of delivered hammer energy. In determin-
ing a reasonable amount of hammer energy one should be satisfied that the hammer is
(1) operating efficiently, (2) operating at maximum energy, and (3) sized properly.
One should keep in mind that proper hammer sizing is not accomplished simply by
meeting the minimum energy requirement given in the Standard Specifications. It is
important to be aware of the relative weights of the hammer and the pile. Certain “light”
hammers will meet our minimum penetration or energy requirements and, at the same