Tunnelling-induced deformation and damage on historical masonry structures

The analysis of deformation and damage mechanisms induced by shallow tunnelling on masonry structures is carried out using an integrated, geotechnical and structural, numerical approach based on two-dimensional finite-element analyses. The masonry construction, schematised as a block structure with periodic texture, is regarded at a macroscopic scale as a homogenised anisotropic medium. The overall mechanical properties display anisotropy and singularities in the yield surface, arising from the discrete nature of the block structure and the geometrical arrangement of the blocks. The soil is modelled by means of a linear elastic-perfectly plastic model. The numerical analyses are performed assuming plane strain and plane stress conditions for the soil and the masonry structure, respectively. A displacement-controlled technique is adopted to simulate the tunnel construction, which produces settlement troughs in agreement with the empirical Gaussian predictions at different volume losses under free-field conditions. In order to test the numerical approach, a preliminary set of parametric analyses is carried out considering a simple masonry wall, characterised by different geometrical and mechanical properties, founded on a clayey deposit. Then, the case study of the Felice aqueduct in Rome (Italy), undercrossed by two tunnels of a new metro line, is considered. Significant differences are observed between the uncoupled analysis, where displacements predicted under free-field conditions are simply applied at the foundation level of the structure, and the interaction-based one, the latter being characterised by a reduced amount of tensile plastic strain. Numerical results in terms of vertical displacements at the ground level and on the structure are found to be in good agreement with monitoring data, thus validating the numerical model for this class of soil-structure interaction problems.