SPT Hammer Energy Ratio versus Drop Height
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VIEW THE REPLYPublication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 134, Issue 3
Abstract
Automatic trip hammers have advantages for standard penetration test (SPT) of consistent drop height and low friction loss during hammer fall. These advantages, however, generate high energy transfer ratios (ER), typically about 90%. This efficiency causes lower sensitivity and higher energy correction coefficients, . To reduce ER and and to increase the sensitivity of SPT conducted at the Wildlife Liquefaction Array (WLA) and the Garner Valley Downhole Array, instrumented Network for Earthquake Engineering Simulation sites, a long sleeve was placed in the hammer mechanism to reduce the drop height from to . To calibrate the energy for these drop heights, measurements were made for a series of SPT tests in Borehole X2 at WLA on November 21, 2003. For these SPT, sleeves were inserted with lengths of , , and no sleeve. Resulting drop heights were , , , and . Results indicate that: (1) ER increases with rod length as expected; (2) corrections for rod length, , increased with rod length in accordance with published in 2001 by Youd et al.; and (3) for lengths greater than , ER increased approximately linearly with drop height. Average [ER based on a drop height] were 43% for a drop, 60% for a drop, 84% for drop, and 89% for a drop.
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Acknowledgments
Funding for the project reported herein was provided through NSF Award No. NSF0217421. Mr. Tim Boyd, Pitcher Drilling Co., supervised the drilling and testing and Mr. Camilo Alvarez, GRL Engineers, Inc. performed energy measurements and calculations. This support is gratefully acknowledged.
References
Daniel, C. R., Howie, J. A., Jackson, R. S., and Walker, B. (2005). “Review of standard penetration test short rod corrections.” J. Geotech. Geoenviron. Eng., 131(4), 489–497.
Youd, T. L., et al. (2001). “Liquefaction resistance of soils: Summary report from the 1996 and 1998 NCEER Workshops on Evaluation of Liquefaction Resistance of Soils.” J. Geotech. Geoenviron. Eng., 127(10), 817–833.
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© 2008 ASCE.
History
Received: Sep 12, 2006
Accepted: Jun 20, 2007
Published online: Mar 1, 2008
Published in print: Mar 2008
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