Reliability-Based Design of Augered Cast-in-Place Piles in Granular Soils

Although a variety of methods exist to estimate axial capacity for augered cast-in-place piles, they are generally limited to allowable stress design (ASD) procedures, with little consideration of design reliability. This paper describes the addition of static loading test results to a global augered cast-in-place pile data set to assess the accuracy of new and existing design methods and to address the current lack of reliability-based design methods for augered cast-in-place piles. The new static loading tests in western Washington were carried out on piles installed in granular materials, with pile diameters and lengths ranging from 0.41 to 0.51 m and 9.5 to 29 m, respectively. The preparation of beta coefficients and unit toe bearing resistance values is discussed within the framework of strain-dependent composite tangent moduli and observed residual loads. New relationships for the beta coefficient and toe bearing resistance values are proposed, and the accuracy of new and existing design procedures is statistically characterized using the updated global data set. Resistance factors for axial compression and uplift are calibrated at the strength limit for use in load and resistance factor design (LRFD).