Hangingand swinging leadersare suspended from the top of the crane jib with a head
block which allows free movement to fit over a stabbed pile where guides are provided.
Alternatively, there is a stabbing point at the bottom of the leader to fix the location for pile
driving, either hanging vertically or swung to the required rake. The Liebherr LRH 600,
50 m long hanging leader has a maximum capacity of 65 tonne when used with the Liebherr
HS 895 HD carriage, but account has to be taken of bending moments induced by the weight
of the piling hammer when driving raked piles (Figure 3.4). Delmag ‘European style’box
leads constructed from tubular sections, lattice-braced, are light and stable and can be
attached to any make of crane for driving piles at rakes up to 1:1 subject to bending moment
considerations.
Backward and forward rakes in excess of 1:3 (Figure 3.5) are possible depending on the
stability of the crawler crane. There is a practical limit to the length of pile which can be
driven by a given type of rig and this can sometimes cause problems when operating the rig
in the conventional manner without the assistance of a separate crane to lift and pitch the
pile. The conventional method consists of first dragging the pile in a horizontal position
close to the piling rig. The hammer is already attached to the leader and drawn up to the
cat-head. The pile is then lifted into the leaders using a line from the cat-head and secured
by toggle bolts. The helmet, dolly and packing are then placed on the pile head (Figure 3.20)
and the assembly is drawn up to the underside of the hammer. The carriage of the piling rig
is then slewed round to bring the pile over to the intended position and the stay and angle of
the crane jib are adjusted to correct for verticality or to bring the pile to the intended rake.
In determining the size of leader whether rig-mounted, fixed or hanging it is always
necessary to check the available height beneath the hammer when it is initially drawn up to
the cat-head. Taking the example of leaders with a usable height of 20.5 m in conjunction
with a hammer with an overall length of 6.4 m, after allowing a clearance of 1 m between
the lifting lug on the hammer to the cathead and about 0.4 m for the pile helmet, the maximum
length of pile which can be lifted into the leaders is about 12.7 m.76 Piling equipment and methods
Figure 3.3ICE 225 spotter with optional front lead rotation (courtesy International Construction
Equipment).