The Mediterranean region is affected by considerable daily and seasonal temperature variations due to intense solar radiation. In mid-seasons, thermal excursions can exceed tens of degrees thus influencing the long-term behaviour of jointed rock masses acting as a preparatory factor for rock slope instabilities. In order to evaluate the thermal response of a densely jointed rock-block, monitoring has been in operation since 2016 by direct and remote sensing techniques in an abandoned quarry in Acuto (central Italy). Monthly InfraRed Thermographic (IRT) surveys were carried out on its exposed faces and along sections of interest across monitored main joints. The results highlight the daily and seasonal cyclical behaviour, constraining amplitudes and rates of heating and cooling phases. The temperature time-series revealed the effect of sun radiation and exposure on thermal response of the rock-block, which mainly depends on the seasonal conditions. The influence of opened joints in the heat propagation is revealed by the differential heating experienced across it, which was verified under 1D and 2D analysis. IRT has proved to be a valid monitoring technique in supporting traditional approaches, for the definition of the surficial temperature distribution on rock masses or stone building materials.

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The use of Mt. Epomeo Green Tuff (MEGT) as a building stone is widespread on Ischia Island (Italy). We assess here the fire resistance of MEGT by thermally stressing samples to temperatures up to 1000°C. Porosity and uniaxial compressive strength increase and decrease from 44% and 4.5 MPa at ambient temperature to 48% and 1.5 MPa following exposure to 1000°C, respectively. Complementary thermogravimetric and X-ray powder diffraction analyses, experiments that monitor acoustic emissions during heating/cooling, and microstructural observations highlight that these changes are the result of thermal microcracks, formed due to the breakdown of zeolites and clays (MEGT contains 35 wt.% analcime, 15 wt.% smectite, and 3 wt.% illite) at high temperature. Although the stability of structures built from MEGT will be jeopardised at high temperature, a very low thermal diffusivity requires that fires must burn for many hours to compromise the strength of a typical dimension stone: tuffs are tough in the event of fire. Résumé Le tuf vert de Mt. Epomeo (MEGT) est très utilisé comme matériau de construction dans l'ile d'Ischia (Italie). Nous avons analysé la résistance au feu du MEGT en soumettant cette roche à des traitements thermiques à des températures allant jusqu'à 1000°C. Si la porosité du MEGT augmente de 44% à température ambiante, à 48% à 1000°C, sa résistance en compression uniaxiale décroit de 4,5 à 1,5 MPa sur le même intervalle de température. Des analyses thermogravimétriques et par diffractométrie de rayons X, l'enregistrement des émissions acoustiques durant le chauffage et le refroidissement, ainsi que des observations de la microstructure montrent que les changements observés sur le MEGT après traitement thermique sont liés au développement de microfissures. Ces microfissures se forment à cause de la rupture des zéolites et des argiles à haute température. Le MEGT contient 35% d'analcime, 15% de smectite et 3% d'illite. Bien que la stabilité de structures construites avec le MEGT puisse être compromise à haute température, la très faible diffusivité thermique de cette roche nécessite un incendie très long (plusieurs heures) pour vraiment réduire la résistance des blocs de roche typiquement utilisés dans les édifices de l'ile d'Ischia. Le tuf peut de ce fait être considéré comme une roche résistante en cas d'incendie.

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The study of strain effects in thermally-forced rock masses has gathered growing interest from engineering geology researchers in the last decade. In this framework, digital photogrammetry and infrared thermography have become two of the most exploited remote surveying techniques in engineering geology applications because they can provide useful information concerning geomechanical and thermal conditions of these complex natural systems where the mechanical role of joints cannot be neglected. In this paper, a methodology is proposed for generating point clouds of rock masses prone to failure, combining the high geometric accuracy of RGB optical images and the thermal information derived by infrared thermography surveys. Multiple 3D thermal point clouds and a high-resolution RGB point cloud were separately generated and co-registered by acquiring thermograms at different times of the day and in different seasons using commercial software for Structure from Motion and point cloud analysis. Temperature attributes of thermal point clouds were merged with the reference high-resolution optical point cloud to obtain a composite 3D model storing accurate geometric information and multitemporal surface temperature distributions. The quality of merged point clouds was evaluated by comparing temperature distributions derived by 2D thermograms and 3D thermal models, with a view to estimating their accuracy in describing surface thermal fields. Moreover, a preliminary attempt was made to test the feasibility of this approach in investigating the thermal behavior of complex natural systems such as jointed rock masses by analyzing the spatial distribution and temporal evolution of surface temperature ranges under different climatic conditions. The obtained results show that despite the low resolution of the IR sensor, the geometric accuracy and the correspondence between 2D and 3D temperature measurements are high enough to consider 3D thermal point clouds suitable to describe surface temperature distributions and adequate for monitoring purposes of jointed rock mass.