## 3 The Studied Case of the Murisengo Underground Quarry in Italy  
The underground gypsum quarry, which is studied in this work, is located in the northwest of Italy, specifically in the Piedmont Region (Figure 1). The gypsum extracted from this quarry is mostly used in the construction industry. The adopted exploitation method is the room-and-pillar method, with the use of explosives. The gypsum formation was formed in the Messinian, approximately 5-7 million years ago, with the evaporation of the water of the Mediterranean Sea, which subsequently confined the gypsum within the lakes, following the lifting of the Earth's crust in this area. The deposit, which is homogeneous and flattened in shape with a thickness of around 30-40 m and a plant development of a few hundred meters, is covered by incoherent soil and a layer of marl and calcareous sandstone that is of a thickness of approximately 20-30 m.  
Figure 1: Geographical location of the Murisengo Underground Quarry in the Piedmont Region of the northwest of Italy. With respect to the aforementioned information, there are six exploiting levels, as outlined in the following:  
* Level \"A\", which has the oldest and most geomechanically unstable portion, which is now depleted;
* Level \"B\", which connects the two parts of the mine (Prato Nuovo and San Pietro), and is now depleted;
* Level \"C\", which has outstanding mineralogical characteristics, and is now depleted;
* Level \"D\", which has an excellent quality gypsum, and is now depleted, but with the possibility of a future expansion;
* Levels \"E\" and \"F\", which have an excellent quality gypsum, and are currently active. Due to the reduced geomechanical characteristics of the gypsum, it is necessary to abandon pillars of considerable size (with a section of 8 m \(\times\) 8 m) in the deposit. The rooms also have dimensions that are comparable to those of the pillars (Figure 2). The height of the pillars and rooms is around 8 m. A slab of approximately 4 m is left between one level and another. The adopted exploitation method involves using machines for drilling blast holes and transporting the broken rock. This method is flexible, allowing a simultaneous attack on multiple faces and a specific adaptation of the dimensions of rooms and pillars to the actual characteristics of the deposit in the various zones of the mine. Ventilation in the mine involves the entry of an air flow rate of around 18 m\({}^{3}\)/s from a lateral ramp called S. Pietro. The ventilation reaches different levels, and the exit of the contaminated air is via a central ramp named Prato Nuovo. Levels B to E connect the two areas of the mine and the two ramps. Level F has only one access point from Level E, with a specific ramp called the E-F ramp. The deeper levels (E and F) are also connected by a small well made in the separation slab, where the main fan is located. This fan sucks in the air from Level F where it arrives through the E-F ramp and sends it to Level E, near the Prato Nuovo ramp, thanks to which the air reaches the outside. The analysis of the ventilation circuit has highlighted a certain degree of air recirculation in the deepest area of the mine. In addition, the transit of the significant air flows in the more superficial levels (B, C, and D) that are now abandoned. The more superficial levels, therefore, constitute a short circuit in the ventilation, thereby limiting the flow of fresh air that reaches the deepest and most active levels. Due to these aspects, the exhaust gases of diesel vehicles operating underground are removed with a certain difficulty, and their concentration can rise to reach values that are considered inadmissible. For this reason, the following improvements have been made to the ventilation circuit:  
Figure 2: A view of the inside of the Murisengo Underground Quarry with abandoned rock pillars and rooms. An air pipe at the fan's outlet in order to direct exhausted air toward the Prato Nuovo ramp (i.e., the outlet duct) that crosses Level E;
2.