A Unified Base Bearing Capacity Formula for Piles

Abstract

Various base bearing capacity formulae for piles have been proposed based on the rigid-plastic theory and/or the elasto-plastic cavity expansion theory. None of them, however, can explain the multiphase phenomena of failure patterns: i. e., (1) general, (2) local, and (3) punching shear failure modes. Firstly, three base bearing capacity formulae corresponding to the abovementioned failure modes in cohesionless soils were discussed. It was then interpreted that the ultimate base resistance of a pile may be estimated from the minimum in the values calculated by those formulae, i. e. Min. ((1), (2). (3)). Large model pile tests in sands, whose data have been published, were analyzed using the unified formula proposed. The results can explain the phenomena having been pointed out from experiment; e. g., a pile whose embedded depth is larger than a certain depth never fails in general shear failure mode and the certain depth depends on the sand density. The formula proposed indicates that the dilatancy property has great influence on the mechanism and magnitude of the base resistance. As the application of the formula proposed, the scale effect in the transposition of the results of in-situ penetration tests on the ultimate base bearing capacity of piles was discussed and 4 pile-diameters above the pile base and 6 pile-diameters below the pile base have been suggested as the influence zone.