Factors of safety and pile load tests

The factor of safety used in designing pile foundations for vertical load should depend on three things, prior information on load capacity summarized by empirical correlations with load capacity models, site specific information derived from load tests, and an objective function reflecting economic and safety considerations. A statistical approach to factor of safety selection was developed in order to suggest improvements of current standards for driven pile design. This approach recognizes a distinction between the variability of pile load capacity within individual sites, and the global variability upon which model correlations are based. Charts have been prepared for determining the FS required to achieve specified reliability indices, as a function of the number of load tests at a particular site and their outcomes.