Cavity Expansion–Contraction-Based Method for Tunnel–Soil–Pile Interaction in a Unified Clay and Sand Model: Drained Analysis

Abstract

This paper proposes an analytical method based on drained solutions of cavity expansion and contraction in a unified clay and sand model to investigate tunnel–soil–pile interactions. Cavity expansion analyses are used to evaluate the effects of pile installation on ground stresses and to determine pile end-bearing capacity and the distribution of shaft friction. Cavity contraction methods were adopted to replicate the tunnel convergence–confinement response using the singularity and image method for ground loss and ovalization of a shallow tunnel in a semi-infinite medium. A 2D model was developed that evaluates changes in mean stress and specific volume during pile installation and tunnel excavation. Outcomes from the developed analytical approach are compared against data from centrifuge tests in silica sand; results demonstrate that trends in pile load capacity degradation, mobilized safety factor, and tunneling-induced pile settlement can be satisfactorily predicted for the case of a tunnel excavated beneath a pile with a constant service load. Criteria based on pile capacity, safety factor, and settlement are proposed that can be used to determine a critical tunnel volume loss or evaluate pile safety level. The paper contributes to the understanding of tunnel–soil–structure interaction mechanisms and provides an efficient means of conducting a preliminary risk assessment of tunnel–pile interaction.