Civil Engineering Reference
In-Depth Information
of ancillary plant. It is not just a matter of fitting the equipment into the site, since
manoeuvring space is needed, and double-handling materials as work proceeds in
order to make space is not economical. Inadequate working space constitutes a
safety hazard.
2 Is the headroom adequate to allow the intended equipment to function? Roofs,
overhead electrical cables and pipes, and overhangs on buildings all impose con-
straints. Occasionally cut-down equipment is made for special low headroom
circumstances, but this nearly always results in some other functional penalty
which is reflected in a lower rate of output than normal and a higher price.
3 Are the clearances from existing structures sufficient to allow pile construction?
There are many types of equipment, each with its own dimensional characteristics,
but as a generalization the centres of piles must lie no closer to adjacent walls than
about 0.75 m, although a fewmachines can work closer than this. It is particularly
difficult to work into the corners of a site, where buildings surround the corner
on each side, and minimum distance from each wall in such a case may have to
be 1.0 m to the pile centre or perhaps a little more. This kind of information is
readily available from specialist contractors.
4
Is the site surface sufficient to bear the weight of the piling equipment?Many piling
machines have self-weights in the range 35 to 100 tonnes or more, including the
self-weight of the base unit upon which equipment is mounted. With constant and
heavy usage, undrained and badly prepared site working platforms can quickly
become quagmires. This in turn delays pile installation and can endanger the
stability of the machines. Particular care should be exercised to ensure that old
excavations are properly backfilled for the same reason. To attempt to work on
poorly prepared, waterlogged or unsafe ground is false economy and is dangerous.
In general a carpet of hardcore is laid to enable piling to be carried out without
hindrance and more and more this is becoming a designed item rather than an
expression of opinion by a site supervisor. Machine loadings under all working
conditions, previous excavation history, sub-surface soils and carpet materials are
all required to be assessed and calculations presented before work is permitted
to start. The design of such granular platforms is covered in detail by the BRE
document 'Working platforms for tracked plant', (BRE 2004) prepared under a
contract let by the Federation of Piling Specialists (FPS) in the United Kingdom.
Sloping site surfaces are not generally satisfactory to work on except for the smallest
and lightest types of equipment. Traditional tripod percussive boring equipment is
light and adaptable and may be used in cases where no alternative may be possible.
Small diameter rotary drills of the kind used for rock drilling may also be appropriate,
working from designed platforms.
10.4.2 Contract size
In the case of cast-in-place piles, when a site is large enough and where the number
of piles to be installed justifies it, several machines may be used to speed the work.
The order of working has always to be thought about because it may be unwise to
construct immediately adjacent piles in sequence. The risk is that the installation of
a pile nearby may damage an already-cast pile, either by displacement in the case of
