The International Society for Trenchless Technology

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Pilot Tube
The pilot tube process, as its name suggests, involves the controlled installation of hollow tubes on a precise line and grade through displaceable ground. The guidance system consists of a digital theodolite, camera, monitor screen, and an illuminated LED target. The LED target located in the head of the pilot tube displays the head position and steering orientation, which is viewed by the operator on a monitor screen. A camera mounted on a digital theodolite provides a real-time image of the LED target through the optical path in the hollow tubes. The operator controls the direction of the pilot tube by rotating the orientation of the slant-faced head of the pilot tube. The pilot tube is advanced by applying a jacking force on the tubes.

The pilot tube method was initially used to install small diameter pipes such as service laterals. The pilot tube is launched from a manhole or pit. Once the pilot tube string has reached the recovery pit, a service lateral is pulled in as the pilot rods are extracted.

The pilot tube method subsequently has been modified to allow larger pipes to be installed on a precise line and grade. The most common method of installing larger pipes requires three steps: (1) the installation of the pilot tube, (2) the enlargement of the pilot tube bore, and (3) the installation of the product pipe.
 

Pilot Tube



The initial step for installing the product pipe involves the controlled installation of the pilot tube between the jacking and reception shafts using the method described above. Once the pilot tube has been installed, a reaming head coupled with auger casings are jacked along the path created by the pilot tube. The turning action of the auger transports the soils back to the jacking shaft where it is removed. The pilot tubes are advanced by the auger casings into the reception shaft and removed. The product pipe, which is slightly smaller than the auger casing pipe, is jacked into the enlarged bore hole advancing the auger-casings into the reception shaft where they are removed. The product pipe installation is complete when it reaches the reception shaft replacing the previously installed auger casings.


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by pavoneggi