01 July 1997
can be powered either by their own hydraulic power system or from the crane' own hydraulic system. An
example of such a spotter is shown in figure 3-26.
(d) Vertical Travel Leaders. Vertical travel leaders are fixed leaders with hydraulic spotters which
can also move the leaders up and down relative to the spotter and boom point. They are most advantageous
when positioning of the leaders is exceptionally difficult, such as with railroad construction. Figure 3-27 shows
an example of vertical travel leaders.
(2) Swinging Leaders. Swinging leaders are leaders that are suspended from the crane using a wire
rope. These are by far the most common leaders in use. Advantages and disadvantages of swinging leaders
are shown in table 3-5. A typical swinging leader is shown in figure 3-28. Swinging leaders are generally used
with plumb pile; however, under certain conditions, and with the proper equipment and crane operator, they
can be used on batter piles, as shown in figure 3-29. It is important when swinging leaders are used to avoid
supporting weight of hanging leaders on the pile lest the pile buckle.
(3) Underhung Leaders. Underhung leaders are similar to fixed leaders, except that the boom point
connection is made at the top of the leaders, and generally the leader can move only fore and aft from the
crane. These leaders can be used with or without a spotter. Table 3-6 lists the strengths and weaknesses of
these leaders, and typical underhung leader setups are shown in figure 3-30.
(4) Hammers without Leaders. Most impact hammers require leaders to operate; however, some
hammers can be fitted with pants. Such an arrangement is shown in figure 3-31. Not all hammers can be
fitted with pants; these should only be installed in accordance with the manufacturer' recommendations.
(5) Leader Accessories. Leaders are used with a wide variety of accessories. Some of these are
(a) Cradle or Extension. A cradle or extension is used when the hammer is either too small for
the leaders used or must be driven outside of the leaders. A typical extension is shown in figure 3-32.
(b) Pile Gate. This is used to help guide the pile into the leaders and to keep it in alignment
during driving. Pile gates can be either manually or hydraulically operated. They open to admit the pile and
close before driving.
(c) Stabbing Point. A stabbing point is used with swinging leaders to fix the lower end of the
leaders. These are very important to assist in the stabilization of the leaders. Figure 3-33 shows stabbing
3-4. SPECIALIZED OPERATIONS AND EQUIPMENT. Because of the diverse situations under which pile
foundations are driven, sometimes specialized operations are necessary to supplement the regular equipment
a. Jetting. Jetting is the use of pressurized fluid to temporarily loosen the bond between pile and soil,
thus reducing the resistance of the pile to sinking into the ground. Piles may be sunk into place by jetting which
may or may not be accompanied by impacts on the pile or by alternatively raising and dropping the pile.
Jetting is also used to relieve driving stresses, to save time, to obtain increased penetration of piles, and to
decrease vibration incident to driving piles. Piles should always be driven to their final penetration depth after
jetting has ceased.
(1) Types of Jets. Various configurations of jets are shown in figure 3-34. There are basically two
types of jets, fixed and movable jets.