Abstract
Abstract. The stability of man-made underground cavities in soft rocks interacting with overlying structures and infrastructures represents a challenging problem to be faced. Based upon the results of a large number of parametric two-dimensional (2-D) finite-element analyses of ideal cases of underground cavities, accounting for the variability both cave geometrical features and rock mechanical properties, specific charts have been recently proposed in the literature to assess at a preliminary stage the stability of the cavities. The purpose of the present paper is to validate the efficacy of the stability charts through the application to several case studies of underground cavities, considering both quarries collapsed in the past and quarries still stable. The stability graphs proposed by Perrotti et al. (2018) can be useful to evaluate, in a preliminary way, a safety margin for cavities that have not reached failure and to detect indications of predisposition to local or general instability phenomena. Alternatively, for sinkholes that already occurred, the graphs may be useful in identifying the conditions that led to the collapse, highlighting the importance of some structural elements (as pillars and internal walls) on the overall stability of the quarry system.
Highlights
The presence of underground cavities as a result of past mining operations of soft rocks, to be used as building material, nowadays induces high-risk conditions for those regions characterized by a large number of underground quarries and mines
The problem of assessing the stability of underground cavities in soft rocks is generally faced with approaches characterized by different levels of accuracy and reliability
Based upon the results of a large number of parametric two-dimensional (2-D) finite-element analyses of ideal cases of underground cavities that considered variability of geometrical features and mechanical properties found for a large number of underground cavities excavated in soft carbonate rocks, Perrotti et al (2018) have proposed specific charts to assess at a preliminary stage the cave stability and to evaluate a safety margin with respect to the occurrence of failure
Summary
The presence of underground cavities as a result of past mining operations of soft rocks, to be used as building material, nowadays induces high-risk conditions for those regions characterized by a large number of underground quarries and mines. Wide regions throughout the world (e.g., southern part of Italy) are characterized by a huge number of cavities affecting the underground environment, so representative three-dimensional numerical analyses cannot be developed efficiently for all the case studies For this reason, physically or mechanically based stability charts can be useful to provide a preliminary assessment on the stability of the underground system, as a function of the geometrical and mechanical parameters (Evangelista et al, 2003; Federico and Screpanti, 2003; Suchowerska et al, 2012). Based upon the results of a large number of parametric two-dimensional (2-D) finite-element analyses of ideal cases of underground cavities that considered variability of geometrical features and mechanical properties found for a large number of underground cavities excavated in soft carbonate rocks, Perrotti et al (2018) have proposed specific charts to assess at a preliminary stage the cave stability and to evaluate a safety margin with respect to the occurrence of failure. The purpose of this paper is to validate the efficacy of the aforementioned stability charts proposed by Perrotti and coauthors by means of the application to several case studies of underground cavities, either subjected to collapse in the past or still stable, based upon the geometrical features and the geomechanical parameters known for the case studies; stability charts were applied either to (i) cases of sinkholes or to (ii) cavities that have not reached the collapse; in the first case (i) they show the importance of specific structural elements as pillars and partitions on the stability of the entire system of quarries, while in the second case (ii) it is possible to assess the degree of susceptibility and predisposition to instability phenomena
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