Measuring Rock Strength While Drilling Shafts Socketed into Florida Limestone
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 144, Issue 3
Abstract
The focus of this research was the real time assessment of rock strength during drilled shaft installations in Florida. Measures of unconfined compressive strength, a function of rock strength used commonly in shaft design, are provided through five monitored drilling parameters: torque, crowd, rotational speed, penetration rate, and bit diameter. This study is part of a larger project in which laboratory and field investigations were performed. This paper covers the laboratory portion of the investigation in which synthetic limestone blocks were cast at four design strengths representative of Florida limestone and drilled in a controlled environment. The laboratory drillings revealed that torque provides a better correlation with unconfined compressive strength than crowd force, which was found to be the case independent of drilling parameter groupings, and when groupings based on variations in bit diameter and the penetration rate to rotational speed ratio were enforced. During the analysis, multiple drilling equations were investigated, and a unique relationship was developed with Teale’s specific energy equation for nonpercussive rotary drilling using a rock auger.
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Acknowledgments
The authors would like to express their sincere appreciation of the assistance of the FDOT’s State Materials Office, as well as the district and central geotechnical engineers. A special thanks is extended to all the FDOT participants who assisted in the development and production of Gatorock: Richard Delorenzo, Patrick Carlton, Patrick Gallagher, Thomas Frank, Dale Deford, Dan Pitocchi, and John Shoucair. The authors also would like to thank the University of Florida research team: Phillip Rodgers, Jerry Paris, Jordan Nelson, Shelby Brothers, Katie Maslak, Mike Stephenson, Tim Copeland, Matt Andrews, Aaron Hendricks, Michael Ferguson, Richard Booze, Ryan Mackey, and Vik Adams. Without your tremendous efforts, this research would not have been possible. This work was supported by the Florida Department of Transportation through Research Contract No. BDV 31 977 20.
Disclaimer
The opinions, findings, and conclusions expressed in this publication are those of the author(s) and not necessarily those of the Florida Department of Transportation or the U.S. Department of Transportation.
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©2017 American Society of Civil Engineers.
History
Received: Mar 17, 2017
Accepted: Sep 6, 2017
Published online: Dec 23, 2017
Published in print: Mar 1, 2018
Discussion open until: May 23, 2018
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