Geotechnical Drilling Techniques

Geotechnical drilling is a fundamental part of any construction site evaluation. Drilling deep into the ground helps reveal the conditions below, allowing engineers and architects insight into what kind of environmental hazards need to be accounted for. Some of the most commonly used geotechnical drilling techniques include mud rotary drilling, hollow stem auger drilling, and solid stem auger drilling, and depending on the site, you may need to use one or more techniques.

Mud Rotary Drilling

Mud rotary drilling is a frequently used geotechnical drilling technique that is favored for its speed and adaptability. This method lubricates the drill bit with pumped drilling fluid (typically water combined with various fluid enhancers such as bentonite), which allows the drill bit to stay cool while in operation.  It also pressurizes the bore hole to help keep the walls of the boring in place, minimizing caving.

Some of the advantages of mud rotary drilling include:

  • Efficiency: These drill rigs are very fast and can drill up to several hundred feet of soil per day if needed.
  • Flexibility: Mud rotary drilling lends itself to a vast array of soil conditions.
  • Range of soil sampling: This technique supports sediment sampling as well as thin wall and split barrel sampling.

Mud rotary drilling does have a few drawbacks though, particularly around the necessary drilling fluid. In order to pump in the fluid, support vehicles must accompany the rig, which can disturb the investigation area and compromise sampling findings. This technique is also not advised for conditions where environmental wells are needed.

Hollow Stem Auger Drilling

While hollow stem auger drilling is occasionally used for soil sampling, it’s most commonly used to set groundwater monitoring wells. Understanding water conditions and patterns around your construction site is incredibly important as they will affect the overall scope for your foundation planning.

Hollow stem auger drilling is known for:

  • Facilitating water sampling
  • Installing monitoring wells
  • Quick turnaround times
  • Operating without drilling fluids
  • More shallow applications

Complications with hollow stem auger drilling arise during use with unlithified sediments or when drilling is needed beyond 100 feet deep. This geotechnical drilling technique does not work well with shallow bedrock or other challenging subsurface materials.

Solid Stem Auger Drilling

Solid stem auger drilling excavates and transports samples and cuttings to the surface for future study. Using continuous flight augers in a range of diameters, this method produces reliable results with smaller-sized rigs than other techniques.

Teams choose solid stem auger drilling because it:

  • Excels at producing a good amount of samples
  • Doesn’t require drilling fluid
  • Can use smaller rigs which are more cost effective and easier to maneuver

Solid stem auger drilling is a more labor-intensive geotechnical drilling technique because the auger must be completely removed after drilling each hole. This method should only be used with solid soils that are not at risk of collapsing during the auger’s removal.

Central Geotech Provides Geotechnical Drilling

In order to complete your geotechnical report, you may need to implement geotechnical drilling around your project site. This vital service is provided by Central Geotechnical Services, your partners in project feasibility. For questions, contact us today.