Efficacy of Several Design Methods for Predicting the Axial Compressive Capacity of Piles

A variety of design methods for determining piles’ axial compressive load capacity are routinely employed in current practice. These range from methods specified in building codes to proprietary methods developed and employed by an assortment of engineering firms. In this study, the performance of eight commonly used design methods was evaluated using a database of 505 load tests and associated geotechnical design parameters compiled from Professor Olson’s database and that of the Iowa State Department of Transportation. The methods investigated included standard penetration test (SPT)-based methods, such as those recommended by the Federal Highway Administration (FHWA), U.S. Army Corps of Engineers, American Petroleum Institute, and Revised Lambda; and cone penetration test (CPT)-based methods such as those recommended by the Norwegian Geotechnical Institute, Imperial College, Fugro, and University of Western Australia. Pile capacities were calculated using APILE software and were compared with the measured capacities interpreted using the standard Davisson criterion and stored in the databases. The performance of all design methods was evaluated in relation to accuracy, precision, effect of soil type, diameter, and length. Both SPT and CPT methods exhibited similar accuracies, however, CPT-based design methods exhibited significantly better precision compared with SPT-based methods. All methods had shortcomings and appeared to work best under certain conditions, which are documented in this paper. The authors believe that this evaluation will permit practicing engineers and regulating bodies to better understand the efficacy of various design approaches in common use.