The bucket auger is used primarily on unconsolidated material, for constructing large-diameter boreholes ranging from 24 inches to 48 inches. These large-diameter boreholes are ideally suited for areas producing low-yielding wells in aquitards.
The drilling system consists of a truck-mounted drill with a separate deck-mounted engine, which must be capable of generating enough torque to overcome the friction associated with drilling such a large-diameter hole.
The support equipment required includes a service truck to carry the casing and grouting materials. Two drilling technicians are required to operate the bucket auger drilling system.
The cutting action is rotary cut. The bucket is rotated and advanced until it is full of cuttings, at which time it is tripped out of the hole, swung to one side, and a trip is released, emptying the cuttings onto the adjacent ground. Note that no flushing media is used, since the bucket auger removes the cuttings as hole penetration occurs. This produces cuttings which are clean, unmasked, and representative of the geology.
This drill utilizes a large-diameter table drive to rotate the telescoping kelly, which in turn advances the bucket auger. Penetration rates are generally quite rapid in favorable conditions. During the drilling process, the hole may require the installation of temporary or working casing to stabilize the hole until permanent casing is installed. Drilling continues through the working casing, using a smaller bucket until such time as an adequate aquifer is located. The four telescoping sections of the kelly bar enable the bucket auger to drill up to 100 feet in depth, without the use of additional kelly bar sections.
The next step in this process is the installation of the permanent casing, which can be manufactured from concrete, galvanized steel, or fiberglass. Shown here is the installation of concrete casing using a tile center. The annular space between the casing and the borehole wall at the aquifer area is filled with permeable material, such as gravel or washed stone. The well is grouted and developed to a sand-free state, as per Regulation 903.