Use of Integrated Regional Data and Local Low Impact Investigations for the Geo-Mechanical Characterisation of Rupestrian Cultural Heritage in Apulia (Southern Italy)

Over time, human activities have modified natural systems generating hybrid systems. The natural/anthropic interaction makes hybrid systems more vulnerable, and less resilient than natural ones. As a consequence, the equilibrium of hybrid systems can evolve through various critical paths culminating in disastrous events, such as local or total collapses, which may lead to the loss of cultural heritages but also of human lives. In such contexts, the assessment of signals, which emerge due to the resilience decrease, could be useful to manage connected hazards. Puglia (Southern Italy) includes widespread rupestrian settlements located on the flanks of typical ephemeral fluvial valleys where calcarenite rock masses outcrop. These settlements of historical and artistic importance well represent hybrid systems, which are characterized by the integration of natural and man-made caves, and urban fabrics. From a geo-mechanical standpoint, calcarenite rocks are characterized by fragility, i.e., under critical stress fields, by sudden failure without significant strains or displacements. This makes it difficult to appreciate signals useful for an early warning and then, for safe management of rupestrian cultural heritages. In the technical testing of cultural heritages, to gain an accurate knowledge of the site stress and deformation the use of non-Destructive Tests (NDTs) is recommended as an alternative to Destructive Tests (DTs). This research analyses emerging signals in three hybrid cave systems (Villa Giustiniani and Santa Candida in Bari and one private property in Ginosa) with in-situ NDTs (temperature, humidity index, ultrasound velocity, rebound number). The NDT results are consistent with the literature and archive DT data concerning calcarenite rocks of Puglia and the neighbouring Basilicata region. The application of a combined NDT method, as an alternative to DTs, has proved expeditious, easy to perform, and cheap; results can be useful in supporting the assessment and management of deterioration of cultural heritage.