Some Considerations on 3-D and 2-D Numerical Models for the Assessment of the Stability of Underground Caves

The application of numerical modeling to the analysis of the stability of both natural and manmade underground caves is rapidly increasing due to the availability of powerful numerical codes, that can account for either continuum or discontinuum behavior of the rock masses. Numerical methods allow to overcome traditional methods for cave stability analysis that assume too simplified geometrical, geological and geomechanical conditions. Further, they are also able to assess the potential failure mechanisms of underground systems. On the other hand, the application of numerical methods requires availability of a detailed geo-structural survey of the cave, as well as a proper geomechanical characterization of the rock and joint material properties for the pre-processing stage. The present contribution is aimed at describing some aspects related to implementation, and comparison of the outcomes, of two-dimensional or three-dimensional finite element analysis as regards artificial caves with complex geometries excavated within calcarenite rock masses. This type of man-made caves is very common in Southern Italy, and is at the origin of frequent sinkholes, often threatening the built-up areas. In particular, the results from 2-D and 3-D analyses of a case study represented by a cave with complex geometry are presented, showing that 3-D analysis leads to more stable conditions of the rock mass surrounding the cave. This is supposed to be the consequence of the different stress state as calculated by the two analyses, the 2-D one assuming plane strain conditions while the 3-D analysis assumes more general stress conditions