Influence of Torque on Lateral Capacity of Drilled Shafts in Sands
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 132, Issue 4
Abstract
As a result of recent changes in the requirements involving hurricane extreme events (e.g., wind velocities), the Florida Department of Transportation has moved away from cable-stayed signs, signals, and lights systems to mast arm/pole structures. Unfortunately, the newer systems develop significant lateral and torque loading on their foundations (e.g., drilled shafts). Current design practice for a mast arm/pole foundation is to treat lateral loading and torsion separately (i.e., uncoupled); however, recent field-testing suggests otherwise. This paper reports on the results of 91 centrifuge tests. 54 of the tests were conducted in dry sand and 37, in saturated sands. The tests varied the lateral load to torque ratios, shaft embedment depths, and soil strengths. The experiments revealed that even though the torsional resistances of the shafts were not influenced by lateral load, the shafts’ lateral resistance was significantly impacted by torsion. Reductions in lateral resistance of 50% were recorded for shafts under high torque to lateral load ratios. Using the free earth support assumption and the ultimate soil pressure the soil pressure distribution along the shaft was developed. Using force and moment equilibrium, as well as the applied torque, maximum shear, and moments were computed. The predicted values were found to be within 25% (10% on average, except for the tests in saturated dense sand with polymer slurry) of the experimental results.
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Acknowledgments
Support from the Florida Department of Transportation, Contract No. 4910450472312, BC-354 is greatly appreciated, as well as the suggested revisions by ASCE reviewers.
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© 2006 ASCE.
History
Received: Dec 2, 2004
Accepted: Aug 10, 2005
Published online: Apr 1, 2006
Published in print: Apr 2006
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