Practical Analytical Approach for Estimating Long-Term and Set-Up Shaft Resistance of Prebored Piles

Abstract

This paper presents a practical analytical approach to evaluating the long-term and set-up shaft resistance of prebored piles. The key contributions of this study lie in the fact that not only all aspects involved, from pile installation to pile loading, but also the residual stress propagated from the vertically shearing effect during pile installation are properly considered in the proposed analytical approach. The installation effects of a prebored pile are simulated as undrained expansion of a cylindrical cavity followed by vertically shearing the soils along the boundary of the pile shaft. To develop the possible analytical approximation technique, simplified solutions for the stress and excess pore pressure changes in critical sate soils due to cavity expansion are adopted in the formulations, while a modified Terzaghi’s consolidation theory that incorporates a variable coefficient of consolidation with respect to the void ratio and mean effective stress of the soil is employed to model the consolidation process after the pile installation. The proposed analytical approach has been well validated through comparisons with a finite-element numerical model that involves the entire process from pile installation to loading. The approximate analytical model developed in this work, owing to its relative formulation simplicity, computational efficiency, and prediction reliability, is expected to be able to serve as a feasible analysis method and guidance for the design and construction of piles involving the preboring procedure.