Comparative size of drilled shaft reinforcement shaft foundations, with the ancillary benefit of providing the data needed to continue improving LRFD design. References Cited AASHTO (2014), AASHTO LRFD Bridge Design Specifications, Customary U.S. Units, 7th Ed. Allen, T. M., (2005). "Development of Geo- technical Resistance Factors and Downdrag Load Factors for LRFD Foundation Strength Limit State Design," Publication No. FHWA- NHI-05-052, Federal Highway Admin- istration, Washington, DC, 41 p. Allen, T.M., Nowak, A.S., and Bathurst, R.J. (2005). “Calibration to Determine Load and Resistance Factors for Geotechnical and Structural Design,” Transportation Research Circular E-C079, Transportation Research Board, Washington, DC, 83 p. LRFD for Drilled Shafts in Context In any discussion of drilled shaft design it is important to consider the big picture. The design methodology is one of many ingredients that goes into the recipe for baking a good drilled shaft cake. Construction plays a significant, and sometimes overriding, role that is at least as important as the LRFD resistance factors that one might select for design. Poor construction practices such as failure to place concrete promptly following excavation, inadequate removal of cuttings from the base, concrete with inadequate workability and others are not accounted for in LRFD or any other design method. Adequate subsurface investigation, appropriate geomaterial classification and testing, competent engineering, field inspection and post-construction integrity testing are all important to project success. In summary, LRFD for drilled shafts provides a framework for major improvement over past design practice. While not all of the potential benefits are apparent, and some are yet to be realized, the geotechnical community has embarked on the journey to its eventual adoption. Much work is needed to establish 62 • DEEP FOUNDATIONS • MAY/JUNE 2015 resistance factors that are reliability-based and not simply fit to factors of safety from past practice. LRFD is now widely adopted in the transportation sector, with varying levels of adoption in other sectors of the drilled shaft market. Incentive to perform load testing and to utilize the most effective and technologically advanced construction methods is improving the quality of drilled Brown, D., Turner, J., and Castelli, R. “Drilled Shafts: Construction Procedures and LRFD Design Methods,” Geotechnical Engineering Circular No. 10 and FHWA/NHI Publication 10-016, Federal Highway Administration, Washington, D.C., May 2010, 972 p. Withiam, J.L., Voytko, E.P., Barker, R.M., Duncan, J.M., Kelly, B.C., Musser, S.C., and Elias, V. (1998). “Load and Resistance Factor Design (LRFD) for Highway Bridge Substructures,” Publication No. FHWA HI- 98-032, Federal Highway Administration, Washington, DC. Polymer slurry for drilled shaft construction
