A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
Moreover, it should be capable of transmitting the hammer energy
effectively to the piles.
Drive cap is inserted at hammer tip to enhance uniform distribution of
hammer energy to the pile. Pile cushion is positioned between the drive
cap and the pile top. It intends to protect the pile from driving stress
induced during hammer blows. Moreover, it also serves to provide a
uniform driving load on top of the pile.
4. Should light or heavy hammers be used in pile driving? (DP3)
In pile driving operation, proper selection of piling hammers is essential to
prevent the damage of piles. For instance, a light hammer with higher drop
causes a higher impact stress than a heavy hammer with lower drop
provided that they generate the same energy per blow.
During driving, the piles are continuously subjected to considerable
reflected tensile stresses and compressive stresses. In case the pile
sections are incorrectly aligned, the lack of straightness may induce
significant bending stresses being locked in piles during pile driving.
Moreover, if obstructions are encountered during pile driving, bending
stresses would be induced in piles.
5. In driven piles, the allowable set is limited between 25mm and
50mm per 10 blows. Why? (DP4)
In final set table it is commonly to limit pile set between 25mm/10 blows
and 50mm/10 blows. The reason of the provision for lower limit of set value
of 25mm/10 blows is to avoid possible damage at pile toe owing to
compressive stress reflected at the bottom of pile. The upper limit of
50mm/10 blows is established principally to avoid very heavy hammer
impacting at pile head so that the pile head may be damaged owing to
excessive compressive stress. These limitations are believed to be applied
originally to precast concrete piles.
6. What is the widespread usage of 45 o load spread rule? (Dp5)
Under the 45 o load spread rule, when the horizontal distance between the
toe level of adjacent piles is smaller than the vertical difference between
the piles, additional load is deemed to be added by the pile at lower
founding level. Hence, when the pile at lower founding level is within the
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