Reduction Factor for the Unloading Point Method at Clay Soil Sites
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 136, Issue 4
Abstract
Full-scale testing can be an integral component of quality control/quality assurance for projects involving construction of deep foundations. Rapid load tests are being used in the deep foundation industry as a method for assessing the axial static behavior of deep foundations. Since rapid load tests involve dynamics, inertial and damping forces must be considered in analyzing measured pile response to estimate the static pile response. The unloading point method (UPM) is typically used for this purpose. Generally considered a consequence of load rate effects in clays, results from the UPM must be further modified by a reduction factor to obtain a reasonable estimate of the static pile response. A reduction factor of 0.65 applied to the UPM for clay soil sites has been recommended by others. However, a review and analysis of readily available literature reporting static and rapid pile load test results at sites predominantly consisting of clay soils indicate that an average reduction factor of 0.47 is more appropriate. Rapid load testing should be used judiciously. When using the UPM to estimate static pile capacity from rapid load tests in clay, static load tests should be performed to validate the reduction factor used to interpret rapid load tests.
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References
Bermingham, P., and Janes, M. (1989). “An innovative approach to load testing of high capacity piles.” Proc., Int. Conf. on Piling and Deep Foundations, Balkema, Rotterdam, The Netherlands, 408–413.
Briaud, J-L., Ballouz, M., and Nasr, G. (2000). “Static capacity prediction by dynamic methods for three bored piles.” J. Geotech. Geoenviron. Eng., 126(7), 640–648.
Brown, M. J., and Hyde, A. F. L. (2008). “Rate effects from pile shaft resistance measurements.” Can. Geotech. J., 45(3), 425–431.
Brown, M. J., Hyde, A. F. L., and Anderson, W. F. (2006). “Analysis of a rapid load test on an instrumented bored pile in clay.” Geotechnique, 56(9), 627–638.
Butcher, A. P., Powell, J. J. M., Kightley, M., and Troughton, V., and (2009). “Comparison of behavior of CFA piles in London clay as determined by static, dynamic, and rapid testing methods.” Proc., 5th Int. Symp. on Deep Foundations on Bored and Auger Piles (BAP V), W. F. Van Impe and P. Van Impe, eds., Taylor and Francis, London, 205–212.
Davisson, M. T. (1972). “High capacity piles.” Proc., Lecture Series Innovations in Foundation Construction, ASCE, Illinois Section, Chicago.
Ealy, C., Iskander, M., Justason, M., Winters, D., and Mullins, G. (2002). “Comparison between statnamic and static load testing of drilled shafts in varved clay.” Proc., 9th Int. Conf. on Piling and Deep Foundations, DFI, Hawthorne, N.J., 645–650.
Holeyman, A., Couvreur, J. M., and Charue, N., and (2001). “Results of dynamic and kinetic pile load tests and outcome of an international prediction event.” Proc., Symp. on Screw Piles: Installation and Design in Stiff Clay, A. Holeyman, ed., Balkema, Rotterdam, The Netherlands, 247–273.
Justason, M. D., and Fellenius, B. H. (2001). “Static capacity prediction by dynamic methods for three bored piles.” J. Geotech. Geoenviron. Eng., 127(12), 1081–1084.
McVay, M., Kuo, C., and Guisinger, A. (2003). Calibrating resistance factors for load and resistance factor design for statnamic load testing, Univ. of Florida, Dept. of Civil and Coastal Eng., Gainesville, Fla.
Menge, P. (2001). “Soil investigation at Sint-Katelijne-Waver (Belgium).” Proc., Symp. on Screw Piles: Installation and Design in Stiff Clay, A. Holeyman, ed., Balkema, Rotterdam, The Netherlands, 16–62.
Middendorp, P., Beck, C., and Lambo, A. (2008). “Verification of statnamic load testing with static load testing in a cohesive soil type in Germany.” Proc., 8th Stress-Wave Conf., IOS, Fairfax, Va., 531–536.
Middendorp, P., Bermingham, P., and Kuiper, B. (1992). “Statnamic load testing of foundation pile.” Proc., 4th Int. Conf. on Application of Stress-Wave Theory to Piles, Balkema, The Netherlands, 581–588.
O’Neil, M. W., and Reese, L. C. (1999). “Drilled shafts: Construction procedures and design methods.” Rep. No. FHWA-IF-99-025, Federal Highway Administration, Washington, D.C.
Paikowsky, S. G. (2006). “Innovative load testing systems.” NCHRP Research Rep. No. 21-08, Geosciences Testing and Research Inc., Transportation Research Board, Washington, D.C.
Schellingerhout, A. J. G., and Revoort, E. (1996). “Pseudo static pile load tester.” Proc., 5th Int. Conf. Application of Stress-Wave Theory to Piles, Univ. of Florida, Gainesville, Fla.
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© 2010 ASCE.
History
Received: Oct 28, 2008
Accepted: Oct 5, 2009
Published online: Oct 6, 2009
Published in print: Apr 2010
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