Limitations of the Driving Formulas for Predicting the Bearing Capacities of Piles in Sand

Abstract

It has often been shown by previous investigators that the existing pile driving formulas yield bearing capacities which usually do not stand in good correlation to the actual bearing capacities of piles in sand. These poor correlations have always been attributed to the formulation of the equations.Based on the observations made on a very large foundation built in an homogeneous sand deposit it is shown in the present paper, that the poor quality of the usual pile driving formulas originates essentially in the estimate of the driving energy; while it is assumed that each blow delivers a constant energy equal to W × H for drop hammers, it appears actually that the energy delivered by a given equipment varies systematically from blow to blow. This conclusion, drawn from a statistical analysis of 478 driving records, is confirmed by the driving tests made on four instrumented piles.The results of 45 load tests also confirm this conclusion in showing no correlation between the actual bearing capacities and the estimated driving energy or the bearing capacities computed from five different formulas. The observations also show a possible time effect on the bearing capacities of concrete piles in sand.