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
transferred to piles in ground. When the hammer force and displacement is
plotted, the energy absorbed by piles is the area under the curve. Since the
curve of elastic component is linear with a positive slope, the area i.e.
energy should be the area of triangle (0.5xRxc) where R is reaction force
and c is elastic compression due to helmet, piles and soil system. For
settlement, it is of horizontal line in force-displacement diagram and hence
the energy transferred to pile-soil system is (Rxs).
Fig. Settlement displacement curve for pile driving
12. What is the function of followers in driven H-piles? (DP6)
A follower is an extension between the pile head and the hammer that
transfers the blow to the pile in which the pile head cannot be reached by
the hammer or is under water .For construction of driven piles, the piling
frame and hammer are normally erected on existing ground level but not at
the base of pile caps. However, H-piles are designed to be terminated near
the base of pile caps. If piles are driven at ground level, a certain length of
H-piles is wasted and cut when constructing pile caps. In this connection,
pile followers are used so as to save the wasted section of H-piles because
followers can be removed during subsequent construction of pile caps.
13. What is the difference between hammer efficiency and coefficient
of restitution? (DP7)
Hammer efficiency refers to the ratio of kinetic energy of the hammer to the
rated energy (or potential energy). In essence, it is undoubtedly that certain
energy losses are induced by the hammer itself prior to the actual impact
on the driven piles. For instance, these losses may include the
misalignment of the hammer, energy losses due to guiding friction,
inaccurate dropping height etc…
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