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.
Highlights
Tunneling has an important role in urban construction to address the rapidly increasing demands and utilization of underground space, especially for transportation systems in congested urban areas (Mair, 2008; Kolymbas, 2008)
To further develop the available tunnel-soil-pile interaction analyses based on cavity expansion methods, this paper presents an analytical method based on cavity expansion theory in association with critical state soil mechanics (Schofield and Wroth, 1968)
The analysis indicates that the tunnel converges at a tunnel volume loss of approximately 1.75%, at which the predicted normalized pile settlement is less than the required value of 0.1 to apply the pile settlement criterion
Summary
When the pile is located beyond the plastic region of soil caused by tunneling, pile settlements are due solely to the tunneling induced ground movement, s1,Vl. The above comparison with centrifuge data of dense sand tests provides a reasonable validation of the proposed cavity expansion-contraction based method for tunnel-soil-pile interaction. These results indicate the empirical pile capacity criterion (i.e. RQf = 0.85) gives the best fit to the experimental results for the loose sand tests, this is not an ideal outcome since RQf does not take into account the initial pile safety factor, which clearly has an effect.
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