Article provided by Stephen West, Ramboll

On 15^th September the AGS hosted a webinar on the evolution and use of the Standard Penetration Test which was generously sponsored by Socotec.

Stuart Wagstaff and Peter Reading built on their respective articles published earlier this year in the AGS magazine providing their insights on the history and development of the SPT and the issues that all geotechnical practitioners must consider when specifying, executing, and using the SPT.  This was a very popular subject with nearly 400 live views of the webinar.  After their presentations Stuart and Peter were joined by Julian Lovell and Stephen West to discuss this topic further and reflect on the many questions and feedback provided by the viewers on this topic.  The webinar also included a number of polls which provided information on how the SPT is used.  Many correspondents supported the use of the SPT as part of an effective ground investigation however there were also calls for development of the test to better measure energy expended in the test to provide more information on the state of the ground during the test and to automate the recording of key pieces of data collected during the test.  Observations were also made on improving safety precautions for drill crews during the test.

It’s clear that there is enthusiasm in the industry to evolve the execution and use of the SPT.  The need for research and investment by the Geotechnical Industry was discussed and the AGS is well placed to help encourage this evolution.  If you missed this webinar there is a recording on the AGS website which can be viewed HERE or on the AGS’ Vimeo channel.  Look out for further technical webinars from the AGS over the coming months.

Polls results

Do you use SPT N60 values to correlate to geotechnical properties / analytical input factors?

• Yes: 77%
• No: 22%
• Other: 1%

Do you routinely use ‘improved’ sampling techniques to obtain Class 1 samples?

• Yes: 46%
• No: 53%
• Other: 1%

Do you think techniques such as rotary coring or pressuremeter testing and the results obtained are value for money?

• Yes: 69%
• No: 30%
• Other: 1%

Would you like to see a better ‘standardisation’ for the SPT test and more reliable correlation factors?

• Yes: 94%
• No: 5%
• Other: 1%

What is your preferred method to characterise ground strength?

• Standard Penetration Test: 28%
• Laboratory shear strength testing: 45%
• Direct observation of undisturbed soil samples: 3%
• Other in situ test: 12%
• Other: 12%

What method do you typically use to derive soil stiffness parameters?

• Published correlation with Standard Penetration Test N values: 47%
• Laboratory stiffness measurements such as oedometer tests: 26%
• In-situ measurements using CPT: 8%
• In-situ measurements using pressuremeter: 5%
• Other: 14%