What Does Auger Boring Mean?
Auger boring is defined as a trenchless application in which a casing pipe is jacked into the earth’s surface while simultaneously rotating helical augers remove the excavated spoil.
Auger boring works using Archimedes Screw Principle. In Archimedes’ application, a helical surface surrounding a hollow cylindrical shaft (screw) is rotated either manually or by motors. As rotation continues, the bottom of the shaft collects water. The water slides up the tube through the helical rotation. This water is poured from the top of the machine.
In auger boring, excavated soil is removed from the top of the casing tube instead of water. Auger boring employs a cutting edge attached to the auger within the casing pipe and hydraulic jacks, to rotate and penetrate the soil. So that there is unimpeded rotation within the casing, the auger diameter tends to be slightly less than that of the casing pipe.
Rotation of the helical auger chain causes the cutting edge to bore through the ground, moving spoil behind the casing pipe, allowing for removal. Excavated material can be removed by mechanical means such as conveyors or excavators, by hand or through the use of muck buckets.
Auger boring is referred to as jack and bore or dry boring.
Trenchlesspedia Explains Auger Boring
Auger boring is suitable for scopes of work that involve trenchless operations, including the installation of water and sewer pipes, ducts, and gas mains. It is the preferred method for pipeline installations that span highways since the required horizontal boring is done quickly and with minimal disruptions to traffic and other services.
In determining whether auger boring is the best suited trenchless method, there is evaluation of parameters such as ground conditions, type of installation required in terms of pipe type and grade, right of way restrictions, and expected length. For example, fiber optic and electric lines which require tiny diameter bores may not be suitable for auger boring. Since ground conditions are a significant component of auger boring, it is essential that a geotechnical report form part of all auger boring projects.
Auger boring machines are generally designed for casing pipes that range from 102 mm to 1830 mm in diameter and span distances of approximately 200 m. Pipes that are greater in diameter typically require more considerable bore lengths, although bore lengths of less than 100 m are generally more common.
The Auger Boring Process
One of the initial steps in the pipe installation process requires that a launch pit be adequately designed and constructed. The launch pit is dimensioned to allow the safe operation of the auger boring machine and accommodate a usable length of pipe. Some factors taken into consideration in the launch pit design include slope stability, flooding potential, and the presence of other underground utilities.
Using controls on the auger boring machine, an operator sets the device at the required elevation on a set of tracks or rack arrangement. The length of the tracks dictates the limit in the movement of the auger machine. Once the boring machine reaches the end of the tracks, the casing pipe is released, and the machine returns to its starting position.
If additional pipe lengths are necessary, the new length of the casing is positioned, with its own auger flight. To ensure the cutter heads are adequately driven, the auger flights are connected, and the pipe ends welded for continuity. The arrival of the cutter head at the reception pit, the subsequent auger equipment withdrawal, and clean out of casing conclude the process, ensuring that the required underground pipe is ready for installation.
Figure 1: Typical Set Up for Auger Boring Process (source)