Three-Dimensional Nonlinear Analyses of a Metro Tunnel in São Paulo Porous Clay, Brazil

Tropical residual clays with a highly porous structure react to the stress changes induced by tunneling in such a way that surface settlements can be larger than crown-level settlements along a tunnel axis. This behavior, which is not readily simulated by most numerical analyses, was also observed in the Paraiso tunnel, built for the São Paulo Metro, Brazil. This is a shallow tunnel driven through porous clayey soils by the sequential method. Detailed results of field monitoring are presented and discussed. 3D finite-element analyses that allowed a detailed simulation of the construction sequence have been carried out, considering two distinct constitutive models for the soil: a simple elastic-perfectly-plastic Mohr-Coulomb model, and the elastoplastic model developed by Lade. The results of these analyses are compared with the observed behavior as well as with the results from a plane strain finite-element analysis. It is shown that only the 3D finite-element analysis coupled with the more sophisticated soil constitutive model provides a full reproduction of field performance, with particular relevance for the deformations in the soil mass over the tunnel.