Direct Solution of the Brinch-Hansen 90% Pile Ultimate Failure Load-Article

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The technical note develops a direct method for estimating pile ultimate failure load and deflection using Brinch Hansen’s 90% failure criterion. This criterion is especially relevant because it is included in the International Building Code, whereas the better-known 80% criterion is not.<br /><br />The method builds on Kondner’s hyperbolic model of soil stress–strain behavior. For pile load-test data, pile-head deflection is plotted against the square root of deflection divided by load. A best-fit straight line is then calculated, focusing on the higher-load data because lower-load points can distort the fit. Its slope and intercept are used to determine failure load and corresponding deflection.<br /><br />The article explains how the existing direct solution for the 80% criterion can be derived, then derives expressions for the 90% criterion. The resulting 90% solution is approximate but, in the example discussed, differs from a more precise calculation by only 0.004 tons. Hansen’s two criteria generally produce similar failure loads.<br /><br />Applied to a previously published pile-load test, the method estimates a 90% failure load of 209 tons (190 tonnes), close to the reported value of 205 tons (186 tonnes). The author recommends checking results from either direct-solution method against the observed load–movement curve.

Keywords

pile ultimate failure load

deflection estimation

Brinch Hansen 90% criterion

International Building Code

Kondner hyperbolic model

soil stress-strain behavior

pile load test

failure load calculation

load-movement curve

direct solution method