Dynamic Behaviour of Abandoned Underground Mines: Insights from Numerical Simulations

The Apulian region (south-east of Italy) is characterized by the presence of old underground cavities used for the extraction of soft calcarenite rocks and then abandoned over time. The assessment of stability of these caves represents a challenging problem, especially for the areas of possible interaction of the caves with overlying structures and infrastructures. The role of environmental factors in triggering disruption processes in the cave has been extensively studied in the literature, but the instability effect related to dynamic loads is often underestimated. Consequently, the purpose of the present work is to propose some advancements in this field by evaluating the effects of dynamic loads, consistent with the regional seismicity, on the stability of calcarenite underground cavities. A large number of two-dimensional parametric finite element analyses has been carried out on ideal cases of single rectangular cavities. The study allowed to detect appreciable instability effects caused by the dynamic input, depending on the cavity width, the thickness of the roof, and the energy content of the dynamic input. The interaction between twin cavities under dynamic conditions has been also studied from a numerical point of view. The results show that plastic failure in the septum is reached earlier under dynamic conditions than static and it is again dependent on the cavity width and the roof thickness. Lastly, a numerical procedure to calculate factor of safety against either shear failure or tensile failure mechanisms has been proposed, which allows to quantify the change of the stability conditions from static to dynamic conditions.