Underground pneumatic piercing tools are often referred to as hogs,
air hogs, or pneuma-gophers. The tool is used to bore a hole underground
between two points without disturbing the surface ground. This open air
chamber is referred to as the bore hole and is used to either run
ducting for product or the raw product itself between the two points.
Uses
The tool is used in the installation of all public utilities
electricity, gas, phone, and cable television these are referred to as
product. It is also used to install home sprinkle systems and auxiliary
home power lines. The tool is utilized in instances when it is difficult
or cost prohibitive to plow or trench the product into the ground, some
of these instances are under driveways, roads, sidewalks, and
landscaping. Pneumatic piercing tools are a lower cost alternative to directional boring.
How it works
The tool uses air to pound its way through the ground underneath the
obstruction. The tools is cylindrical in shape and ranges from two to
five inches in diameter and between three and six feet long. It is made
from metal. Different manufacturers have different front styles and
control mechanisms. Some have bullet shaped front and others have a
stepped front similar to a unibit. Compressed air is used to power the
tool, this air is run through a durable hose. The tool works in a way
very similar to a jack hammer, inside the cylinder is a piston. A valve
opens and the air blows into the chamber forcing the piston forward
which in turn propels the tool forward. The valve then shuts and the
piston is pushed at a slower speed back in the tool, the valve reopens
the piston pounds again and the tools moves forward. This process is
continually repeated until the bore has run the intended distance. Both
the lighter reverse hit of the piston and the friction of the ground
surrounding the tool keep it moving forward instead of stopping. The
speed of the tool can be controlled by a valve that connects the tools
hose to the air supply this valve is outside the tool and remains
accessible to the operator. As the tool pounds through the ground it
compresses the soil this compaction maintains the same diameter as the
tool and leaves the bore hole though which the product is passed.
Performing a bore
The purpose of the bore is to get from point A to point B under the
obstruction. First the operator surveys the area and the obstacle(road,
sidewalk, driveway). Utility locates must be present for any underground
work, the path most clear of utilities is chosen to send the tool
through. The first hole is now dug on one side of the obstacle. This
hole must be large enough to fit the tool and the operator in it so they
can aim the tool. The hole also must be deep enough that as the tool
compacts the ground the surface remains undisturbed. The depth of the
starting bore pit depends on the type on soil that is being worked in
and how well it compacts. The operator aims the tool to the desired exit
point and allows it to perform its function creating a bore hole under
the ground without disturbing the surface. The tool is tracked by the
operator who feels the tool pounding and can approximate the tools
location under the ground. The operator also monitors the surface to
make sure that it is undisturbed. As the tool nears the exit point it is
slowed down and an exit pit is dug to locate both the tool and the
bore. As the tool enters the exit pit the operator chooses to either dig
up the tool to retrieve it or reverses the tool back into the first
bore pit to retrieve it. Now between the two pits is a completed bore
under the obstacle which can be used to run the product.
Drawbacks
Pneumatic bore tools do have drawbacks which can cause difficulties
completing the bore. First the distance of the bore the tool can create
is limited by the length of the hose that supplies the tool with air.
Also the tool is not steerable once it has exited the bore pit the
operator no longer has control over it. The tool can be deflected by
rocks and soil density to a path the operator had not intended. If this
deflection is in the direction of the surface the tool can cause damage
to the obstacle being bored under if it is downward the tool can dive to
unrecoverable depth. If it is deflected side to side the tool could
also run into other utilities. These hazards make it important for the
operator to maintain close observation of the tool. The type of ground
the tool is working in can also lead to problems if the soil is to loose
the tool cannot compact the soil stalling it out or leaving no bore
hole. If the soil is rocky the tool may be deflected or fail to pound
forward due to its inability to break the rock. These drawbacks can be overcome by directional boring.
(Wikipedia 2010) |