Reliability Analysis of Shaft Resistance of Axially Loaded Bored Piles

As part of Load and Resistance Factor Design (LRFD) implementation effort in Korea, reliability levels for side resistance of bored piles socketed in weak rock were evaluated by using bi-directional pile load test results. Bi-directional pile load tests are widely used to predict the load–settlement behavior of large-diameter bored piles. A database of 24 bidirectional load test data sets and soil property tests was compiled from case studies collected from Korea. The resistance bias factors for the three static design equations [O'Neill and Reese (1999), Horvath and Kenney (1979), and Williams et al. (1980)] were calculated by comparing the representative measured bearing capacities defined by Davisson's criterion with the predicted values. Reliability analysis was conducted following the First-Order Reliability Method (FORM) using the statistics of bias factors. The reliability levels of the three shaft resistance equations evaluated from FORM method for safety factors in the range of 2.0-5.0 were in the ranges of 1.15-2.79 for O'Neill & Reese equation, 0.97-2.62 for Horvath and Kenney equation, and 1.73-3.38 for Williams et al. equation, respectively