Figure 8-26.Jetting with two jet pipes.
than fairly coarse, dense sands, jetting is not necessary
or advisable. Jetting equipment consists of a water
pump, a length of flexible hose, and a metal JET PIPE;
jet pipes run from 2 1/2 to 3 inches in diameter.
A single jet pipe is used as follows. The pile is set
in position with the hammer resting on it for extra
weight, and the jet pipe is manipulated to loosen and
wash away the soil from under the tip, as shown in figure
8-31. As the soil is washed away, the pile sinks under
its own weight and that of the hammer. A few hammer
blows are struck occasionally to keep the pile moving
downward. When it is 3 feet above the final tip
elevation, the jet pipe is withdrawn and the pile is driven
the rest of the way with the hammer.
The action of a single jet pipe on one side of a pile
tends to send the pile out of plumb. Whenever possible,
two pipes are used and lashed to the pile on opposite
sides, as shown in figure 8-26.
A pile that has met an obstruction or that has split
or broken in driving or that is to be salvaged (steel sheet
piles are frequently salvaged for reuse) is usually
PULLED (extracted). Pull the pile as soon as possible
after driving it; the longer the pile stays in the soil, the
more compact the soil becomes, and the greater will be
the resistance to pulling. Methods of pulling piles are
In the DIRECT LIFT method, a crane is used to pull
the pile. The crane whip is slung to the pile, and a
gradually increased pull is applied up to just a little less
than the amount that is expected to start it. Lateral