New proposal to assess the seismic stability of shallow underground cavities in soft intact rocks

The seismic stability assessment of anthropogenic cavities is a challenging issue for land and urban planning, particularly in areas of possible interaction with surface structures and infrastructures. The paper proposes a novel methodology for the preliminary assessment at urban scale of the safety level against roof collapse of underground cavities under seismic actions through seismic stability charts, SSCs. The SSCs are the result of extensive parametric two-dimensional FEM analyses focused on cavities excavated in soft rock, as it is frequent in many inhabited areas all over the world. The study is mainly oriented to the instability of shallow cavities, includingthe effects at the ground surface. The SSCs allow evaluation of stability conditions of a generic cavity through a factor of safety, calculated as the minimum ratio between the resistant and loading bending moment of the critical sections of the cavity roof during the whole earthquake duration. The method is applied to the case study of Sant'Agata de' Goti, a historical center in Southern Italy, rising on top of a volcanic tuff ridge.