L'attività estrattiva a Canosa di Puglia. Le risorse lapidee dall'antichità ad oggi in area mediterranea.

The town of Canosa di Puglia is located at the northern end of the Murge (Southeastern Italy) and lies on Plio- Pleistocenic deposits, made up of calcarenites and clays. The old part of the town, built on a hypogeum maze of anthropic origin and underground quarries, is characterized by severe instability. The presence of calcarenites and clays helped to spread, since ancient times, the mining industry, becoming one of the most important economic and commercial income. Between the VIII and VI century BC the pottery export was well known in the whole Adriatic area. A large number of artificial caves dug in the calcarenitic mass are present under the inhabited sections of the town. These caves are often affected by crumbling and collapse phenomena, with damages to the fabric of the houses causing risk to public safety. In this paper the data obtained from laboratory analyses of rock samples taken from two underground cavities are discussed. The results have been related to the mineralogical and petrographical features of the calcarenites, well known as "Tufi". The blocks of "tufi" taken directly in quarry have good technical characteristics so that they are qualified to be used as building materials both for external and indoor panelling. On the other side, these rocks are defined "weak rocks" and have poor values of uniaxial compressive strengths due to the high porosity and water content. As a consequence, if these rocks are exposed to important in situ stress state, like those caused by underground excavations, sometimes rash, they may perform unexpected collapse phenomena at pillars and vaults of cavities. Moreover, also further factors are to take into account, such as viscous behaviours of tertiary kind, increased by the decay of the mechanical characteristics of these rocks due to different causes.