Page 55 - Trenchless Technology Piping Installation and Inspection

28 Cha pte r O n e

product pipe. For this procedure, a pneumatic pipe rammer is
attached to the exposed end of the partially installed product pipe in
an orientation that tends to pull the pipe from the ground. This can be
accomplished through a fabricated sleeve. A winch or other type of
pulling device is used to assist the rammer during the pipe removal
operation. The percussive power of the pipe rammer is often suffi-
cient to free the stuck pipe and allow it to be readily removed from
the ground.

Drill Stem Recovery: There are two possible configurations for apply-
ing a pneumatic pipe rammer to assist in drill stem recovery. Depend-
ing on the situation, contractors can directly pull the drill stem from
the ground using the power of a ramming tool or, if the stem is still
attached to the drill rig, they can use the ramming tool power to push
on the opposite end of the stem to assist with the drill rig pullback
action.

Pullback Assist: The pullback-assist technique helps install the product
pipe in problematic situations. For example, when drilling underwa-
ter or in loose flowing soil conditions, or when there is loss of drilling
fluid circulation, a condition known as hydrolock can occur.
Hydrolock results when the pressure at the leading end of the prod-
uct pipe restricts its forward movement. Alternatively, soil pressure
along the side of the pipe due to partial collapse of the borehole may
cause additional frictional drag, thus inhibiting the pipe movement.
In such cases, the required pull forces may exceed the drill rig’s pull-
back capability or the product pipe’s tensile strength. The percussive
pushing action of a pipe rammer applied at the tail end of the product
pipe may be used to help free the immobilized pipe.
The pullback assist technique has been successfully used on steel
pipe as well as high-density polyethylene. The technique can be used
initially as a precaution in anticipation of possible problems, such as
those described above, or after the pipe has become immobilized.
Response time, however, is a key factor. The rate of success greatly
improves as the response time decreases. Therefore, many drilling
contractors bring ramming equipment to directional drilling sites
enabling them to respond quickly to problems that may develop.

Conductor Barrel: The success of a drilling operation can often be
determined before initiating the drilling operation. If the soil condi-
tions at the planned entry point are problematic, the success of the
entire project may be jeopardized. In such cases, the conductor barrel
process may be appropriately used. The conductor barrel technique
differs slightly from the preceding methods because it is incorporated
into the initial boring plan, rather than being deployed only in the
event of a problem that may arise at some stage. In this method, a