Numerical Modeling and Back-Analysis Approach on a Monitored Underground Cavern for the Extraction of Marble for Ornamental Uses

Abstract

The Cava Madre of Candoglia represents an important underground rock cavern in the northwest of Italy, both for historical reasons and for the material that is extracted there: the marble for the continuous reconstruction and renovation works of the Milan Cathedral. Over time, the cavern reached considerable dimensions, and the existing state of stress (considerable horizontal stresses) required the creation of impressive structures to contrast and support the side walls. A complex and effective monitoring system guarantees the continuous control of the cavern. To improve the reliability of the geomechanical characterization and, therefore, of the numerical model that allows the analysis of the stress and strain behavior of the cavern, a back-analysis was developed. This allowed us to “calibrate” the two geomechanical parameters on which there was the greatest uncertainty: the elastic modulus of the marble at the scale of the problem and the lateral thrust coefficient at rest (k0). Finally, the numerical model made the results of the back-analysis more effective, allowing us to verify the support and contrast structures of the walls and to proceed with a careful definition of the project relating to future mining works for the continuation of the exploitation of the existing marble bench.