Dealing with asbestos presence in tunnel excavation: the Castagnola case study and the importance of the geological model

The presence of Naturally Occurring Asbestos (NOA) is one of the greatest danger during excavations and tunneling.  The most important instrument for the NOA content prediction is the geological model.

As part of the consultancy provided in the works of the "Terzo valico dei Giovi" which includes the excavation of numerous tunnels in areas potentially affected by rocks containing asbestos, the case study of the tunnel called "Castagnola" is illustrated. The opera is the new high velocity railway connection between Genova and Milano and the case study is located in the Piedmont southern area near Fraconalto (AL).

The “Castagnola” tunnel area is characterized by greenish - reddish rocks metabasalt covered by recent grey shales in the upper part of the area; it refers to the ophiolitic Figogna Unit, elongated in a north-south direction, which belongs to Sestri-Voltaggio Zone.

Starting from geological sections and thanks to surface investigation and core drilling, an effective geological model was built.

This study highlights how, during the progress of the works, situations other than the forecast geological model are encountered. It also highlights the importance of the environmental monitoring of the airborne fibers dispersion inside the tunnel, which has proved extremely effective even in the presence of low asbestos content in the excavated rock.

Moreover, this study describes the trends in asbestos content in the material excavated during the route of the tunnel in comparison with the concentration of airborne fibers. Furthermore, the management of the asbestos problem, from the abatement of dust to the excavation and storage methods and the installation of efficient technologies such as an aspirating ventilation system already successfully tested in a previous excavation phase, are presented.