Geotechnical characterization of ash collected during recent eruptions of Mount Etna: from dangerous waste material to environmental friendly resource

An exponential increase in the activity of Mount Etna (Catania, Italy) has been observed between the massive eruptions that lasted from 1991 to 1993 and the very significant ones, which occurred between 2012 and 2018. Large amounts of ash repeatedly covered the city of Catania, causing environmental problems for road and air traffic, agriculture and human health. Recent thinking has been to consider volcanic ash as a resource rather than a waste material, thus avoiding damage to both the environment and human health. This goal could be achieved using this material in several fields of geotechnical engineering but first static and dynamic laboratory geotechnical tests must be performed. This paper deals with a static and dynamic geotechnical characterization of volcanic ash collected during recent eruptive activity on Mount Etna. Grading and index properties tests, oedometer tests, direct shear tests and dynamic resonant column tests were performed in the Geotechnical Laboratory at the University of Catania. Particle crushing was also analysed following oedometer tests and direct shear tests. The tested materials are essentially of a gravelly-sandy nature and showed very different strains due to the different grain size distribution curves as well as to the aptitude to crushing of these materials. Cohesion is negligible both at peak state and at the critical state, in line with granular soil behaviour. A light curvature of the failure curves can be observed for some peak envelopes. The results of dynamic tests are in quite good agreement with those of well-known sands. Thus, taking into account crushing, it is possible to appropriately reuse these materials in geotechnical engineering avoiding inhalation and ingestion