Assessment of Several Interpreted Pile Capacity Criteria for Large-Diameter Open-Ended Piles

The interpretation of field load tests on piles has many important practical considerations especially with respect to identifying the capacity of a pile. A number of interpretation criteria have been used in the past. With the increase in the use of large-diameter open-ended piles (LDOEPs) for support of infrastructure projects, it is important to ascertain that the interpretation criteria are suitable for LDOEPs. Fourteen of the most commonly used interpretation criteria were chosen for investigation in an effort to determine the best criterion to be used for LDOEPs. These methods were evaluated using a database of 68 load tests conducted on LDOEPs. The applicability of these criteria and their correlation with each other was examined. The effects of the pile diameter, pile length, and the soil type on the performance of each criterion were investigated, as well as the capacities corresponding to several serviceability limit states. It was concluded that none of these methods was superior to the others, and their performance was somewhat correlated. The original Davisson offset method and the New York City Building Code (NYCBC) criteria performed best in comparison to the average of all methods exhibiting the highest accuracy and the lowest of the standard deviations for the load tests considered. A variation of the NYCBC criterion is proposed for LDOEPs, where the capacity is taken at the smallest of (1) a settlement corresponding to the elastic compression plus 0.75 in. (20 mm); (2) the capacity at plunging or strain-softening; or (3) settlement corresponding to 5 % of the pile diameter, unless the settlement threshold is modified by the structural engineer of record. The proposed criterion is not influenced by diameter, length, or soil type. Additionally, the proposed criterion is well correlated with several well-known published criteria and introduces safeguards against capacities corresponding to excessive settlement in slender piles.