Characterization of method Uncertainty for Axial Pile Design

Abstract

The paper describes two approaches for deriving the mean, standard deviation and probability density function of the method uncertainty for an axial pile capacity calculation method. The focus of this paper is on estimating the statistical description of the method uncertainty parameters for a pile design method on the basis of performance of the method in predicting the capacities of high-quality pile load tests. The method uncertainty can have a strong influence on the safety level associated with the foundation design. Establishing the statistics of the "error" in a calculated capacity prediction (Qc) from the measured values of capacity (Qm) in pile load tests requires careful consideration of several factors. In particular, case studies demonstrated that only the pile load tests where the pile capacity method overpredicts the actual (measured) capacity are of interest. Therefore, with method uncertainty defined as Qm/Qc, the part of the cumulative distribution function where Qm/Qc < 1 should be fitted as well as possible. The possible dependence of the standard deviation of method uncertainty on pile penetration depth was also investigated in the derivation of method uncertainty statistics.