3D failure envelope of a rigid pile embedded in a cohesive soil using finite element limit analysis

In this paper, numerical limit analysis is applied to evaluate the bearing capacity of a single rigid pile embedded in a ponderable homogeneous cohesive-frictionless soil subjected to vertical, horizontal, and moment (VHM) loading combinations. All loads act in the same plane. Accurate lower and upper bounds are calculated using finite element limit analysis code OPTUMG3. As the gap between the bounds hardly exceeds 5%, the average limit load provides a good estimate of the exact ultimate load and can be used with confidence for design purposes. By adopting typical values for the dimensionless pile length-to-diameter ratio, most cases of practical interest are treated. The numerical results are compared against failure surfaces predicted by theories from the literature. Comparison shows that previously developed methods can be conservative or slightly overestimates the limit loads. New design charts are provided. The safe loads domain is constructed in the VHM space using the average limit load. Closed-form expressions are proposed to describe the native and the normalized VMH failure envelope as a function of the pile length-to-diameter ratio. In the VH plane, the failure surface is described by an eccentric superellipse, whereas in the MH plane, the limit curve is an inclined ellipse.

Automated summary

This paper applies numerical limit analysis to evaluate the bearing capacity of a single rigid pile in a homogeneous cohesive-frictionless soil under different loading combinations, providing new design charts for estimating safe loads in engineering design.