Instrumented Becker Penetration Test. I: Equipment, Operation, and Performance
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 143, Issue 9
Abstract
The Becker penetration test (BPT) is a widely used tool for characterizing gravelly soils, especially for liquefaction assessment. Interpretation of BPT data is complicated by the variable energy transferred from the hammer to the drill and by the shaft resistance that develops along the drill string which generally increases with penetration depth. Existing BPT interpretation methods that use above-ground measurements have had limited success in accurately separating the shaft and tip resistance. Therefore, penetration resistance with depth cannot be reliably predicted. An instrumented Becker penetration test (iBPT) that measures acceleration and force directly behind the driving shoe in order to compute the energy delivered to the driving tip was developed and integrated into the standard closed-ended Becker drill system. The equipment and data acquisition system are described in this paper. The analysis procedure used to compute energy-normalized blow count values and produce continuous penetration resistance profiles is outlined. The energy-normalized blow count profiles generated are shown to be independent of penetration depth, predrilling depth, shaft resistance magnitude, and hammer operating conditions. In particular, the efficacy of a residual energy-based normalization scheme is demonstrated. Finally, a discussion regarding energy measurements, locked-in stress at the drill string tip, and the use of the pull-back and redrive procedure is presented.
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Acknowledgments
The authors appreciate the funding and support provided by the Division of Safety of Dams (DSOD) of the California Department of Water Resources (David Gutierrez) and Los Angeles Department of Water and Power (Jianping Wu). The support of Bill Sluis, Daret Kehlet, Jon Pearson, Chase Temple, Kevin Kuei, and Chris Krage of the Department of Civil and Environmental Engineering at the University of California, Davis, is also greatly appreciated. The technical contributions of John Lemke of Geodaq in developing the downhole data acquisition module are acknowledged. In addition, the collaboration with AMEC Foster Wheeler (Marty Hudson and Alek Harounian), AECOM (Wolfgang Roth and S. Nesarajah), GeoPentech (Jon Barneich, Andrew Dinsick, and Doug Wahl), and Great West Drilling (Jim Benson) is appreciated.
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Information & Authors
Information
Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 143 • Issue 9 • September 2017
Copyright
©2017 American Society of Civil Engineers.
History
Received: Sep 10, 2015
Accepted: Jan 26, 2017
Published online: Jun 15, 2017
Published in print: Sep 1, 2017
Discussion open until: Nov 15, 2017
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