Geology Reference
In-Depth Information
Figure 6.5
Diesel
hammer (centre of
photo) being used
to drive pre-stressed
concrete piles, Drax
Power Station,
UK. Elsewhere,
piles are being
pitched into holes
formed by auger. In
the background,
the kentledge can
be seen for a proof
test on a working
pile.
and the piles were pre-stressed to improve their resistance to tensile
stresses and to allow the piles to be lifted from their forms quickly. For
most sites, piles will be manufactured off site, sometimes as different
lengths that are joined together on site to suit requirements. One of the
advantages of using driven piles is that an estimate can be made of the
driving resistance, given the known energy being used to drive the pile
and the penetration into the ground per blow of the hammer. Piles are
therefore driven to a set, which is a prede
ned advance rate (such as 25
mm for 10 blows by the hammer). However, resistance during driving
may not always give a very good indication of how the pile will behave
under working conditions, because of false sets, generally due to water
pressure effects, as described for the Drax operation in
Chapter 7.
Figure 6.6
Piles
being cast in
formers, Drax
Power Station,
UK. Note lifting
eyes cast into the
concrete piles, steel
(trapezoidal) and
pre-stressing cables,
which are to be cut
before lifting piles
from the casting
beds.
