Static load test interpretation using the t-z model and LRFD resistance factors for auger cast-in-place (AC IP) and drilled displacement (DD) piles

Abstract

Static load test data for augered cast-in-place (ACIP) and drilled displacement (DD) piles were interpreted using the <i>t-z</i> model method. Eighteen load tests consisting of load-settlement and load transfer data were obtained from two different construction sites. A series of back-calculations were performed using the <i>t-z</i> model method to enhance the static load test data, which were then analyzed to obtain resistance bias factors for the currently used ACIP and DD pile design methods. The <i>t-z</i> model method enhanced load test data provides the ability to interpret field data for loading conditions beyond those measured during test. The resistance bias for the various design methods were then used to obtain the resistance factors based upon the traditional calibration approach. Furthermore, resistance factors were also obtained using probabilistic analysis based upon the <i>t-z</i> model method. The comparison of these two sets of resistance factor indicates that those obtained from the traditional calibration approach contain a wide range of magnitudes, while the resistance factors from the <i>t-z</i> model method design result in a consistent level of reliability.