Development of New Pile-Driving Formula and Its Calibration for Load and Resistance Factor Design

Abstract

Before 1997, the Washington State Department of Transportation (WSDOT) used the Engineering News (EN) formula for driving piling to design capacity. WSDOT-sponsored research published in 1988 had shown that the EN formula was quite inaccurate and that adopting the Gates formula would be a substantial improvement. In 1996, an in-house study was initiated to identify or develop a new driving formula to be used for routine pile-driving acceptance in the WSDOT standard specifications. Recently, compiled databases of pile load test results were used as the basis for developing improvements to the Gates formula to improve the prediction accuracy of pile-bearing resistance. From this empirical analysis, the WSDOT driving formula was derived. Once the WSDOT driving formula had been developed, the empirical data used for its development were also used to establish statistics that could be used in reliability analyses to determine resistance factors for load and resistance factor design. The Monte Carlo method was used to perform the reliability analyses. Other methods of pile resistance prediction were analyzed, and resistance factors were developed for those methods. Of the driving formulas evaluated, calibration of the WSDOT formula produced the most efficient result, and a resistance factor of 0.55 was recommended. Dynamic measurement during pile driving using the pile-driving analyzer, combined with signal matching analysis (e.g., Case Analysis Pile Wave Analysis Program), produced the most efficient result of all the pile resistance prediction methods.