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Geotechnical Drilling Explained

Geotechnical Drilling Explained

Large, complicated construction projects require careful planning. A big part of that process is making sure engineers have a clear understanding of the exact nature of the land that will be used for construction.

That’s what makes geotechnical drilling such an important technique. If you’re not familiar with the process or why it’s necessary, we will help you better determine whether it’s necessary for your next project.

What is Geotechnical Drilling?

Geotechnical drilling is a type of drilling that helps construction teams better understand the makeup of the soil that they’re going to build on. It involves investigating subsurface soil to collect data about the landscape.

The information that teams gather through geotechnical drilling can greatly impact their project.

It might tell them how deep they need to place piling and footings into the earth in order for them to remain stable. Or it could help them discover unique soil conditions that need to be accounted for in the construction planning and execution processes.

Types of Geotechnical Drilling

Geotechnical drilling companies can deploy several different versions of this technique to help their clients gather the information they need. Here’s an overview of the most commonly used types of geotechnical drilling.

Direct Push Technology (DPT)

DPT is a simple technique that involves pressing small drill rods into the ground and using weight or percussion to move them deeper. It’s one of the most cost-effective versions of geotechnical drilling and is perfect for shallow applications.

However, DPT is a method that can sometimes fall prey to depth refusal. So if you have to dig very deeply into the earth or through tough material like rocks, then another type of geotechnical drilling could better fit your goals.

Hollow Stem Auger

Hollow stem auger is a technique that leverages torque and force to send screw-like drillbits through tough formations. It’s another relatively inexpensive technique that works great on subsurfaces with sand, clay, and silts.

That being said, you probably don’t want to use the hollow stem auger technique if your site is full of rocky or dense materials because depth refusal is likelier to occur when using this strategy in those types of environments.


Sonic geotechnical drilling digs into the earth by resonating a series of connected steel drill pipes. This technique will create a continuous core sample of site materials with limited refusal. That makes it a good fit for teams that need to look very closely at a site’s underlying geography.

The one downside is that this is a more advanced drilling style, so it requires teams with special training. That means you’re probably going to pay more if your site needs this technique.


Rotary is a term often used to describe several different but closely-related types of geotechnical drilling. The common thread is that each technique involves digging into the ground with a rotating bit suspended by a drill pipe.

The main benefit of this technique is that it can be used to achieve greater depths of penetration and wider borehole widths. Since there are several different types of rotary drilling, this method is also a versatile one. That makes it easier to use rotary drilling on project sites with different geology.

Wireline and Diamond Coring

These two methods involve using a rotating core barrel bit to dig into tough formations. If you’re looking for a fast, efficient way to collect samples from your site, this could be your best option.

But the maximum size of the core sample that you can collect with each method is 3.27 inches. So if your samples need to be larger than that, you’ll likely need to use an alternative type of geotechnical drilling.

What Projects Require Geotechnical Drilling?

Geotechnical drilling services aren’t always necessary. Remember, this technique is specifically for obtaining samples of the land you will be building on top of when you start your project.

That means you only need to use geotechnical drilling in the instances where that’s necessary. For example, some of the most common projects that require geotechnical drilling are:

  • Roadways
  • Tunnels
  • Bridges
  • Dams
  • Large buildings
  • Levees

Even if your project isn’t on that list, you may still need geotechnical drilling. It’s best to check with an experienced environmental engineer before proceeding if you’re not sure. Otherwise, you could end up moving forward with a building plan that isn’t ideal for your plot of land.


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