Assessing the Critical Depth Concept for Piles Driven in Cohesionless Soils

Abstract

The goal of this study is to assess the existing design methods for piles driven in cohesionless soils with an explicit focus on the concept of critical depth. The critical depth is defined as the depth below which the shaft resistance of driven piles does not change; above this depth, the shaft resistance increases with depth reaching to its maximum value at the critical depth. In this study, the critical depth in common design methods for driven piles installed in cohesionless soils is first estimated as a function of the pile width. We then compare the different critical depths from the various design methods to determine the wide variability in such depth among the considered design methods. Thereafter, we assess the validity of the critical depth concept in light of recent arguments that have challenged such a concept. In the end, we present a driven pile design example to compare the ultimate static capacity of the pile estimated using methods that consider the critical depth and those that do not. The significance of the critical depth is then assessed based on the results of this design example.