Using Sonic for SPT Sampling
Posted on Dec 17, 2018 by Cascade
When choosing drilling technologies for different projects, many of us fall back on what we know is tried and true—but are we missing out? In a recent webinar, I discussed the use of a less traditional drilling technology for tieback anchor installation: sonic. That selection saved one of our clients weeks of installation time, as well as associated costs.
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In this blog post, I’ll highlight another geotechnical application for which you should be considering sonic: standard penetration test (SPT) sampling.
Generally speaking, sonic technology has several key benefits:
- Fast drill time
- Minimizes drill waste
- Less “refusals” due to subsurface conditions
- Often offers a smaller footprint than other drill technologies
However, sonic is not the standard drill method used for SPT sampling because most geotechnical consultants have questions and concerns about its use in this type of application. Let’s discuss three of the most common:
- Does sonic drilling affect soil conditions beyond the drill head?
- If so, is the SPT data collected accurate?
- Have there been any side-by-side comparisons using conventional and sonic drilling methods?
Does sonic drilling affect soil conditions beyond the drill head?
Yes—but not as much as you’d think.
If you speak with engineers and manufacturers who developed and built the sonic heads used throughout the drilling industry, they will tell you the energy created by the sonic head is transmitted through the sonic casing, which keeps the formation being drilled in a “fluid” state. This fluid state has been referenced as “liquefaction,” which occurs when vibrations or water pressure within a mass of soil cause the soil particles to lose contact with one another. Those same experts will also tell you the impact to the borehole while drilling is only 1/8 of an inch.
Is the SPT data collected accurate?
Yes. Based on the expertise of sonic head engineers and manufacturers, SPTs collected using sonic methods to drill are accurate and can be trusted.
Have there been any side-by-side comparisons using conventional and sonic drilling methods?
Yes. For example, Aquifer Drilling and Testing, A Cascade Company completed a project where mud rotary and sonic drilling methods were both used to collect SPT samples. The rigs were on different parts of the site, and the SPT data was extremely close—close enough to accept the sonic data and use it in the design of the structure being built.
Sonic’s SPT sampling accuracy, combined with its other benefits, has increasingly made it an attractive option for our clients with site characterization projects, especially those on tight deadlines. Not only is sonic a faster drill technology, but it can be used for both environmental and geotechnical investigations—and using the same borehole to collect both sets of data can result in tremendous time savings, cost savings and waste reduction.
If you haven’t considered sonic for your SPT sampling projects in the past, it might be worth taking another look.
About THe Author
Bill Poupis is the Vice President of Operations at Aquifer Drilling & Testing, Inc. (ADT), a subsidiary of Cascade Environmental. Bill holds a BS degree in Geology and has over 38 years of drilling experience and related services for oil and gas, environmental, geotechnical and geothermal applications. ADT provides a full range of environmental and geotechnical drilling services with an extensive fleet of sonic and conventional drilling rigs and specialty equipment.