Developing mechanically-based charts to address the assessment of underground cave stability

Natural or anthropogenic sinkholes threaten diffuse areas of the italian territory. A specific research project aimed at defining an overall methodology for susceptibility analysis and risk mitigation of underground cave sinkholes, from cave identification to modelling failure mechanisms and defining mitigation interventions, has been recently developed. Based on two levels at different scale of analysis, i.e. urban area and single cavity scale, the methodology at the first level is aimed at defining quantitative procedures to assess in a preliminary way the stability of underground caves at the urban area scale. As a matter of fact, when dealing with a large number of cavities, single-cavity scale investigations can be time- and cost-consuming, resulting in huge economical investments. Therefore, a preliminary approach to detect those caves that are characterized by relatively high failure susceptibility level is necessary to make choices for investing more sophisticated analyses. In particular, the project has furtherly developed a methodology already proposed by Perrotti et al. (2018, 2019) aimed at assessing the stability conditions of underground caves by using charts based on the results of parametric finite element analyses. The use of such stability charts is straightforward since they are based only on simple information regarding the cave geometry and the geo-mechanical parameters. An advanced version of the charts has been proposed in the aforementioned project, which includes also the quantitative assessment of a safety factor range. The enhanced version of the stability charts has been also validated against field data.The methodology is not intended to replace proper site-specific stability analyses and models implementing the actual cave geometry and the rock mass stress-strain state and should be considered only for speditive preliminary stability assessment.