Contributions of Numerical Modelling to the Stability Analysis of Old Masonry Tunnels

This paper presents the stability verification of an old masonry tunnel that belongs to the archaeological site of ancient Nemea, Greece. The calculations are carried out using a 2D nonlinear finite element analysis with a damage model. The study presents the results of a structural evaluation in the case that the overburden load above the tunnel increases. This tunnel was initially studied by Alexakis and Makris (2013, 2014) and solutions were provided using Limit Analysis. In this study, a comparison is given regarding the calculated bearing capacity of the tunnel between Limit Analysis and the proposed FE model. Then, several aspects of the numerical modelling of masonry tunnels are discussed. Firstly, the influence of the constitutive law of masonry and the differences between the damage model and two plastic models. Secondly, the stiffness of the surrounding ground, which has an impact on the bearing capacity of the tunnel because the earth pressure is a function of the deformation on the tunnel. And finally, the mesh size, which impacts the depth of the cracked zone and produces a variation of about 15% in the bearing capacity results. From the damage model it was found that horizontal convergences are about 3 cm before failure. This output is a major advantage of the FEM analysis with respect to limit analysis, for it allows to suggest some displacement thresholds. Lastly, a brief discussion is presented regarding the rotational capacity of the hinges as a stability verification criterion.