UNCERTAINTY IN API PARAMETERS FOR PREDICTION OF AXIAL CAPACITY OF DRIVEN PILES IN SAND

A questionnaire sent to experienced pile designers to obtain their opinions on geotechnical practice took the API (American Petroleum Institute) recommended practice as reference and concentrated on medium to very dense sands. Each expert was asked to estimate a probability distribution function for five parameters used in predicting the axial capacity of driven piles in sand. The parameters investigated were: limiting unit end bearing, limiting unit skin friction, bearing capacity factor, pile-soil friction angle and the coefficient of lateral earth pressure. Replies from 31 experts were combined by a linear opinion pooling method and compared with API recommended values. The expert opinion average suggests that, except for the pile-soil friction angle and the lateral earth pressure coefficient, API values may be conservative by 20% to 40%.