Research Article
Jan 1979
Velocity Measurement of Free-Fall SPT Hammer
Publication: Journal of the Geotechnical Engineering Division
Volume 105, Issue 1
Abstract
Field measurements of the velocity just before impact of a Borros AB Standard Penetration Test (SPT) automatic trip hammer indicate that the average delivered energy is 99% of the theoretical available, free-fall energy. It is expected that other trip hammers used in Europe, Scandinavia, and Japan also give close to 100% of the theoretical energy during the performance of the SPT. In contrast, the delivered energy varies from 25% to 80% in U.S. practice where the cathead and rope system is used to 100% of that delivered when trip hammers are used. Since it has been shown theoretically and experimentally that the SPT blow count is inversely proportional to the delivered energy, it follows that for the same soil conditions, blow counts will vary where there are differences in delivered energy. Thus, engineers are cautioned in the interpretation of SPT data from countries where trip hammers are in use. Blow counts may differ by 200% or 300% from U.S. practice.
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Published In
Journal of the Geotechnical Engineering Division
Volume 105 • Issue 1 • January 1979
Pages: 1 - 10
Copyright
© 1979 American Society of Civil Engineers.
History
Published in print: Jan 1979
Published online: Feb 11, 2021
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Authors
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William D. Kovacs, M.ASCE
Assoc. Prof. of Civ. Engrg., Purdue Univ., West Lafayette, Ind
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