NEW METHODS FOR INTERPRET THE ULTIMATE AXIAL LOAD CAPACITY OF DRIVEN SQUARE CONCRETE PILES

Abstract

Piles are usually designed using analytical methods, empirical models, or dynamic formulas. Because of the uncertainties involved in the analysis and design of pile foundations, it has become customary, and in many cases mandatory, to perform full-scale pile loading tests. Often, the pile load test will not reach the ultimate load because of cost and time limitations. Therefore, the ultimate capacity must be calculated by a technique based on the load-settlement records. Numerous techniques were published to interpret pile load test curves. The capacity predicted by the interpretation techniques often varies depending on the techniques used. Using high-quality data based on pile load tests are required to resolve some uncertainties for interpreting the ultimate pile capacity. However, there is also a need to improve a method to estimate the ultimate capacity more accurately. In the study, three methods, Nimer, Cubic, and Cubic Limited, to interpret the ultimate pile capacity are proposed. The Nimer method can define the ultimate load more accurately and reliably as compared with existing methods without the need for loading the pile to a large settlement or extrapolate the load-settlement curve. In contrast, the "Cubic" technique can extrapolate the load-settlement curve beyond the maximum test load. It often gives the ultimate pile capacity higher than the actual test failure load because the maximum load can only be achieved at large displacements. Therefore, the procedure was modified and named “Cubic Limited.” The modified procedure defines the pile capacity as the point where the Cubic fit curve intersects with a settlement of the pile equal to nine percent of the pile diameter. The proposed Cubic Limited extrapolation method can be used to improve the accuracy of the predicted ultimate pile capacity based on failure or proof load tests and overcome common problems faced with current extrapolation methods.