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
spacing to the reinforcement cage. After concreting barrettes/bored piles, a
small volume of water is injected under high pressure into these pipes to
crack the concrete. The cracking process should be carried out within 24
hours after concreting. The purpose of cracking is to create a path for grout
to go through. About a week after concreting of barrette, grouting is then
carried out in these pipes to improve the friction between the foundation
and the surrounding soils.
10. Why is sleeving applied in piles constructed on slopes?
For high-rise buildings constructed on steep cut slopes, these buildings are
usually supported by large diameter piles. Though the piles are founded at
some depth below the slopes, lateral load arising from wind on buildings
may induce loads on the slop and causes slope failures. For shallow
depths of slope which is marginally stable, it is more vulnerable to slope
failure.
Hence, an annulus of compressible material called sleeving is introduced
in piles so as to reduce the transfer of lateral loads from buildings to
slopes.
11. Should compaction be carried out to freshly-placed concrete piles?
(PC1)
In normal practice, reliance is placed on the self-compaction of specially
designed concrete mixes to achieve adequate compaction. The use of
vibrating devices like poker vibrators is seldom adopted for the compaction
of concrete piles. In fact, other than the consideration of the impracticality
in using vibrating device in long piles, there is serious concern about the
possible occurrence of aggregate interlock which poses difficulty during
casing extraction [64]. In the worst scenarios, the temporary casings
together with reinforcement cages are extracted during the lifting up of pile
casings. This is another reason which accounts for not using vibrating
machines for piles with casing extraction.
12. Is the quality of concrete impaired by free-falling concrete
placement method in bored piles? (PC2)
Based on the research by STS Consultants Ltd. [57], it was found that
concrete placed by free falling below 120 feet would not suffer from the
problem of segregation and the strength of concrete would not be
detrimentally impaired provided that the piles’ bore and base are dry and
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