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
should not be applied to the whole section of H-piles because it would
be unable to derive the designed frictional reaction from soils.
(iv) Design the piles as end-bearing so that they can take up more load.
22. How do fixed and pinned connections between piles and pile caps
affect the load carrying capacity of piles?
The type of connection between piles and pile caps affects the load
carrying capacity of pile groups. The fixity of pile head into pile cap, instead
of pinning into pile cap, enhances higher lateral stiffness of the pile groups.
For instance, for the same deflections, a cap with fixed connected piles can
sustain far more loads than that of pinned connected piles. To satisfy the
criterion of fixed connection, the minimum embedded length of piles into
pile caps should be at least two times the diameter of piles.
Moreover, the fixed connection of piles at pile caps allows significant
bending moment to be transmitted through the connections when
compared with pinned connections.
23. Is critical depth of piles a fallacy? (FD6)
The critical depth of piles are normally assumed as 10-20 pile diameter
deep and is the depth beyond which the resistance is constant and is equal
to respective value at critical depth.
The critical depth is a fallacy which comes from the failure to interpret the
results of full and model-scale pile tests. In full-scale test, the neglect of
presence of residual loads renders a measured load distribution to be
linear below the so called “critical depth”. Residual loads refer to loads that
are induced in piles during and after installation of piles.
24. Which of the following stages is noisier, at the ending of pile
driving operation or at the end of pile driving operation?
When the piles are progressively driven into the ground, the pile section
above the ground declines. As a result, the degree of damping on the piles
increases. Moreover, the area of exposure of piling surface reduces,
thereby reducing the area generating noise form piles. Hence towards the
end of pile driving operation, the noise level shall be reduced accordingly.
Noise screen shall be installed to tackle the noise problem. Noise screen
made of plywood might not be sufficient because it tends to reflect the
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