Three-dimensional Finite-element Analysis of the Influence of Tunneling on Pile Foundations

Advancing tunnel boring machine (TBM) during tunnel construction induces a surface settlement, affecting adjacent buildings and facilities. A three-dimensional finite-element model (Plaxis 3D) was used to simulate and analyze this process. A comparison between the numerical model and field measurements of the Greater Cairo Metro (Line 3) was made to validate the obtained results. A sensitivity analysis was conducted to determine how changes in some parameters, such as constitutive models, pile position relative to the tunnel axis and pile spacing, affect the results of the finite-element model. Three constitutive models: hardening soil small (HSS), hardening soil (HS) and the Mohr-Coulomb (MC) models, were used to evaluate the effect of the constitutive models on the results. From the numerical analysis, it is clear that the numerical results are in good agreement with field measurements. The results of the HSS model are more realistic and closer to field measurements than those of the HS and MC models. Furthermore, the effect of the tunnel construction on the settlement of adjacent piles is virtually null at a distance of 2 D (where D is the tunnel diameter). Finally, increasing the pile spacing decreases the effect of tunnel excavation on adjacent pile foundations.