Geological survey and numerical modeling of the potential failure mechanisms of underground caves

Natural or man-made underground caves potentially represent a serious hazard to the built-up areas. Urban development and construction of infrastructures is generally carried out without taking into account the possibility of interacting with subsurface cavities, and the corresponding hazard these might pose. In addition, loss of memory of man-made cavities under the historic part of many towns adds further problems. This is especially true for countries with a long history, such as Italy, where during the centuries a large number of artificial cavities have been excavated underground for different purposes. Assessment of the stability of rock masses in these settings is not an easy matter, since it requires, in addition to the geological and engineering background, speleological skills and techniques in order to explore and survey the cavities, identify the type of failures occurring therein, and collect the data necessary for the implementation of specific numerical analyses, these being aimed at defining the stress–strain state of the mass. In this article we present an approach involving cavers, geologists, and engineers to assess the rock mass stability in natural and man-made caves, aimed at determining the control of rock failures in the formation of sinkholes. The methodology is described through the application to a natural karst cave and an anthropogenic cavity in Apulia, SE Italy. In both cases, following a detailed speleological survey which was specifically addressed to define the complete cave geometry, the geomechanical characterization of the carbonate rock mass was carried out and the data so obtained used to evaluate the rock mass stability by means of numerical modeling