Comparison of the Bidirectional Load Test with the Top-Down Load Test (05-1593)**
Oh Sung Kwon, Daelim Industrial Company, Ltd., South Korea
Yongkyu Choi, Kyungsung University, South Korea
Ohkyun Kwon, Keimyung University, South Korea
Myoung Mo Kim, Seoul National University, South Korea

For the last decade, the Osterberg testing method has been advantageous over the conventional pile load testing method in many aspects. However, because the O-cell test uses a loading mechanism entirely different from that of the conventional pile loading testing method, many investigators and practicing engineers have been concerned that the O-cell test would give inaccurate results, especially about the pile head settlement behavior. Therefore, a bi-directional load test using the Osterberg method and the conventional top-down load test were executed on 1.5 m diameter cast-in-situ concrete piles at the same time and site. Strain gauges were placed on the piles. The two tests gave similar load transfer curves at various depth of piles. However, the top-down equivalent curve constructed from the bi-directional load test results predicted the pile head settlement under the pile design load to be about one half of that predicted by the conventional top-down load test. To improve the prediction accuracy of the top-down equivalent curve, a simple method that accounts for the pile compression is proposed. It was also shown that the strain gauge measurement data from the bi-directional load test could reproduce almost the same top-down curve.