Hollow stem augers are used extensively for soil sampling and groundwater monitoring in industrial and commercial installations. The auger flighting acts as a screw conveyor to move the dirt from the bottom of the hole while the cutterhead and pilot bit break up and drill the material. The auger pitch determines the efficiency and lifting speed of the auger. The cutterhead is slightly larger than the auger flighting diameter to increase the life of the flighting edges and improve soil removal. The advantages of hollow stem augers are many. Unlike the solid stem method, drill rods can pass through the center of the auger section and an undisturbed sample of the soil can be taken for analysis or ground water monitoring pipe can be installed. Mills Machine Augers Mills Machine Company has been a leader in the development of Hollow Stem Augers and their related components. Several of our designs have established a standard in the industry. Mills Machine hollow stem augers are fully reversible through the use of drive keys that transfer the torque directly from auger to auger. The auger lock bolts are used when lifting the auger string. We furnish double key or triple key systems depending on the application along with standard and heavy-duty tool joints. Drilling Operation For normal hole advancement, a pilot bit is inserted through the cutterhead to drill the center of the hole. The drill rod is bolted to the inside of the drive cap with a rod to cap adapter so that the pilot bit can turn in tandem with the augers. Drill rods must be added each time an auger is added. In soft formations (dirt and sand), a tapered plug may be inserted into the end of the cutterhead to prevent material from going up inside the augers and to eliminate the use of drill rod. When the hole is completed the plug may be knocked out the bottom of the auger string. The next step is to insert the monitoring screen and casing which is then grouted into place to prevent contamination from the top of the hole. The center section may also be used for intermittent or continuous sampling.
Mills Machine Company, Inc. manufactures a broad line of soil sampling tools. In some applications, hollow stem augers are used as temporary casings to prevent caving and sloughing of the borehole wall. In other applications, the auger walls may be slotted to allow water to pass through the center of the auger for sampling of the ground water as it passes through the auger.