Power-Auger Borings

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Operation of a Power Auger (Image Source: Forest & Kim Starr)

"Auger borings often provide the simplest method of soil investigation and sampling. They may be used for any purpose where disturbed samples are satisfactory and are valuable in advancing holes to depths at which undisturbed or in-place testing is required. Mechanical hollow-stem auger drilling and sampling are the most preferred methods for drilling in existing dam embankments to avoid hydraulic fracturing. Hollow-stem augers are frequently used for drilling potentially contaminated ground because fluids are not used. Sometimes, depths of auger investigations are limited by the ground-water table, by rock, and by the amount and maximum size of gravel, cobbles, and boulders as compared with the size of equipment being used."

"A soil auger can be used both for boring the hole and for bringing up disturbed samples of soil. It operates best in somewhat loose, moderately cohesive, moist soils. Usually, holes are bored without addition of water; but in hard, dry soils or in cohesionless sands, introduction of a small amount of water into the hole will aid with drilling and sample extraction. It is difficult to avoid some contamination or mixing of soil samples obtained by small augers. Rock fragments larger than about one-tenth the diameter of the hole cannot be successfully removed by normal augering methods. Large-size holes permit examination of soils in place; therefore, they are preferred for foundation investigation."

"Auger drills are mechanical, engine-powered drills that are designed to produce high rotational torque at low revolutions per minute as required to drill into and collect subsurface soil samples. Drill cutting and soil samples are removed by the auger's rotation without using fluid circulation media; thus, the requirement for high torque capability of the drill. Multipurpose drills are available which are capable of auger, rotary, or core operations."

"Truck or trailer-mounted power augers are used for dry boring in unconsolidated materials. They range in size from Giddings rigs, which turn small diameter, solid stem flight augers to large rigs capable of turning 12-inch inside diameter, hollow stem augers. Test holes are advanced by rotating a cutting bit into the materials. A wide variety of materials may be bored with power augers. They are not suitable for use in materials containing cobbles or gravel, hard cemented soils, or saturated cohesionless soils. Unstable materials require casing, particularly below the water table."

"Two different techniques of power-auger boring may be used to sample earth materials:

1. "Screw the auger into the soil like a corkscrew, without mixing. The auger is then pulled from the hole and the materials are sampled and logged off the flights of the auger.
2. "Screw the auger into the soil like a corkscrew and then spin until the materials at the leading edge of the auger is brought to the surface. This is done when the power auger lacks the power to pull the auger from the soil after it is screwed in. The soil materials are logged and sampled as they are transported to the surface. Mixing of the materials is a problem, but with experience, good samples and interpretive information can be obtained."
   
   

Best Practices Resources

National Engineering Handbook: Chapter 5 - Engineering Geology Logging, Sampling, and Testing, NRCS

Citations:

Revision ID: 7432
Revision Date: 07/21/2023