Care should be taken to prevent damage to the creosote protection by avoiding the use of
slings or hooks which gouge the pile deeply. The damage caused by minor incisions is no
more than the scratching caused by stones encountered while driving the piles.
3.4.2 Driving precast (including prestressed) concrete piles
The methods of handling the piles after casting and transporting them to the stacking area
are described in Section 2.2.2. They must be lifted from the stacking positions only at the
prescribed points. If designed to be lifted at the quarter or third points, they must not at any
stage be allowed to rest on the ground on their end or head. Particular care should be taken
to avoid over-stressing by impact if the piles are transported by road vehicles. Additional
support points should be introduced if necessary.
A helmet of the type shown in Figure 3.20 and its packing are carefully centred on the
pile, and the hammer position should be checked to ensure that it delivers a concentric blow.
The hammer should preferably weigh not less than the pile. BS8004 requires that the weight
or power of the hammer should be sufficient to ensure a final penetration of about 5 mm per
blow unless rock has been reached. Damage to the pile can be avoided by using the heavi-
est possible hammer and limiting the stroke. BS8004 states that the stroke of a single-acting
or drop hammer should be limited to 1.2 m and preferably to not more than 1 m. The
Swedish piling code requires a drop hammer to weigh at least 3 tonne, except that 2-tonne
hammers can be used for piles with a maximum length of 10 m and a maximum load of
450 kN, but a 4-tonne hammer should be used for long piles in compact materials. This code
recommends that the drop of the hammer should be limited to 300 to 400 mm in soft or loose
soils to avoid damage by tensile stresses. The drop should be limited to 300 mm when
driving through compact granular soils.
The driving of the piles should be carefully watched, and binding by toggle bolts due to
the pile rotating or moving off line should be eased. The drop of the hammer should be
reduced if cracking occurs, and if necessary the hammer should be changed for a heavier
one. After the completion of driving the pile heads should be prepared for bonding into the
pile caps as described in Section 7.7. Hollow piles with a solid end may burst under the
impact of the hammer if they become full of water, and holes should therefore be provided
to drain off accumulated water. Where a soil plug is formed at the toe of an open-ended pile,
water accumulation or arching of the soil within the pile may also result in bursting during
driving. Further guidance is given in CIRIA Report PG8(3.19).
3.4.3 Driving steel piles
Because of their robustness steel piles can stand up to the high impact forces from a diesel
hammer without damage other than the local distortion of the pile head and toe under hard
driving. Open-ended tubular or box piles or H-piles can be driven to a limited penetration by
a vibrator. By using rolled steel corner sections, plugged tube-bearing piles can be formed
by driving a number of interlocking U-section sheet piles sequentially. As the resistance to
driving is less than for welded box piles, vibrators or press-in pilers can be used to install
high capacity piles to greater depths at sensitive sites where impact driving cannot be tolerated.
To achieve the required depth of penetration it is sometimes necessary to reduce the base
resistance by removing the soil plug which forms at the bottom of an open-ended tubular or
box pile. A sandy-soil plug can be removed by simple water jetting. A plug of clay or weak
Piling equipment and methods 125