Model uncertainty representation in geotechnical reliability analyses

An adequate representation of model uncertainties is important for reliability analyses based on geotechnical analysis models of unknown credibility. A procedure is outlined for calibration of the probability distribution function for the model uncertainty associated with such a geotechnical model. The calibration is based on available field test measurements of quantities, which can be predicted by means of the actual model. The procedure is generally applicable, provided a sufficient amount of field test measurements is available. The procedure is outlined with specific reference to a prediction model for axial pile capacity and a set of pile capacity measurements from field tests on full-scale piles. An example is presented to demonstrate the applicability of the procedure, based on the American Petroleum Institutes's method for prediction of shear capacities of piles. A first-order reliability analysis of an example pile is carried out and demonstrates the significant importance of a best-possible representation of model uncertainty in geotechnical reliability analyses.