Auger

An auger is primarily used for general exploration, advancing and cleaning the borehole, and drilling accessible borings. Augers also are used for various construction operations, such as drilling drainage wells and excavating for piers and caissons. Disturbed or undisturbed samples can be obtained from boreholes advanced by augering methods. However, disturbed samples may not be representative of the in situ deposit because materials may have segregated during the augering process or may have been contaminated with soils from different depths. The quality of undisturbed samples also may be questionable as a result of stress relief, especially if drilling mud is not used to stabilize the borehole. Augers cannot be used for soils in which the gravel particles or rock fragments are greater than approximately one-tenth of the diameter of the hole.

Disk augers and solid- and hollow-stem flight augers are helical augers. Spoon augers are similar to closed-spiral augers. The diameter of power augers ranges from approximately 2 inches to 96 inches. The depth of samples obtained with power equipment can exceed 100 feet or more, depending upon the ground water conditions and the type of equipment that is used.

In general, power augers can be used wherever the borehole is stable and will remain open. The principal disadvantage of sampling by auger methods is that samples are highly disturbed and soils from different strata can be mixed. Because of the potential for mixing soils from different strata, stratigraphic logging using cuttings from auger borings is extremely difficult. An exception does exist, however. When a hollow-stem auger is used, the center plug can be removed at any time and either disturbed or undisturbed samples can be obtained with conventional sampling equipment. Large bucket augers also can be used for drilling large-diameter boreholes that will permit a person to enter and obtain hand-carved samples. The limiting depth for power-augering usually is controlled by the power that is required to rotate the auger or the depth to the ground water table. For continuous-flight augers and bucket augers, the limiting depth is about 100 feet. For short-flight augers, the depth is limited to the length of the kelly on the drill rig, which is about 10 feet to 20 feet, depending on the particular device.