The Auger Bore Process

Auger boring is accomplished with an Auger Boring Machine by jacking a casing pipe through the earth while at the same time removing earth spoil from the casing by means of rotating auger inside the casing.

The typical Auger bore installation begins with the installation of bore pits at the beginning and the end of the proposed bore. Bore pit dimension vary depending on the size and length of the casing being used and the depth of the boring. Generally the length varies from 26 to 40 feet long and 8 to 12 feet wide. The bottom of the bore pit is usually over-excavated and backfilled with crushed stone in order to provide adequate support for the equipment.

Most Auger Boring equipment is track mounted. The boring machine slides along this track in order to advance the casing pipe. The master track (on which the boring machine is set) is placed in the pit and set to the required line and grade of the bore. This is a critical step in the auger boring process since there is little ability to correct line or grade deviations once an auger bore is started. Steerable auger boring equipment is now common and does allow for some minor adjustments or bore direction s it progresses; however, pro9pr setup is still critical.

The boring machine applies thrust in order to advance the carrier pipe. This thrust is applied against the back of the boring pit with hydraulic rams. In order to withstand this thrust, a backing plate must normally be installed against the back wall of the boring pit. The backing plate normally consists of steel piling, a steel plate, or wooden timbers. For long or large diameter bores, a concrete backstop may be used in addition to a steel plate.

After installation of the master track and backing plate, the auger boring machine is set on the master track. A cutting head, compatible with the soil conditions expected, is installed on the front of the first auger section; the first section casing pipe may have a steel band welder around the top ¾ of the outside diameter of the pipe. This process, called banding, slightly over-excavates the bore hole, thereby reducing skin friction on the following sections.

The bore is begun by carefully installing the first section of casing pipe to the correct line and grade. After the first section has been installed in the ground and checked for accuracy, the boring machine is disconnected from the casing pipe and auger and slid to the rear of the bore pit. The next section of casing pipe and auger are lowered into position. The second auger section is coupled to the first with an auger pin. The two casing sections are lined up and either welded together, or an interlocking casing pipe joining system may be utilized.

The bore is then again advanced by applying thrust and simultaneously rotating the flight augers inside the casing in order to remove spoil. This process is repeated until the required length of casing is installed. Once the bore is completed, the cutting head is removed at the receiving pit, and the augers are pulled out at the entrance pit.

If required, a carrier pipe can be installed. The carrier pipe is attached to wood skid or pre-manufactured casing chocks. The carrier pipe is pushed into the casing pipe using the auger boring machine, or by pulling it through with a winch.

Most auger bores are done without ability to steer the bore, that is, make line or grade adjustments once the bore has begun. However, equipment and techniques are available that do allow minor corrections or changes in alignment to be made.