Reliability Based Design of Pile Foundations Considering both Parameter and Model Uncertainties

Abstract

There are two types of uncertainties in the design of large diameter bored piles, i.e., parameter uncertainty and model uncertainty. This paper illustrates how model uncertainty associated with a pile capacity prediction model can be characterized, and describes a procedure to develop resistance factors for the design of large-diameter bored piles with explicit consideration of both types of uncertainties. The deterministic pile capacity model is first described. Then, the parameter uncertainty associated with the model is characterized. It is shown that the parameter uncertainty alone cannot explain the disparity between predicted and measured pile capacities. Thereafter, the model uncertainty associated with the prediction model is characterized using pile load test data. The effect of pile load tests not conducted to failure on model uncertainty characterization is discussed. Finally, based on the characterized parameter and model uncertainties, resistances factors are developed for practical reliability based design using the design point method. To comply with load factors specified for structural design, the resistance factors determined directly based on the design point method are scaled such that the safety of the pile foundation is not lower than the target reliability level.