The present paper explores the combination of unmanned aerial vehicle (UAV) photogrammetry and three-dimensional geomechanical modeling in the investigation of instability processes of long sectors of coastal rocky cliffs. The need of a reliable and detailed reconstruction of the geometry of the cliff surfaces, beside the geomechanical characterization of the rock materials, could represent a very challenging requirement for sub-vertical coastal cliffs overlooking the sea. Very often, no information could be acquired by alternative surveying methodologies, due to the absence of vantage points, and the fieldwork could pose a risk for personnel. The case study is represented by a 600 m long sea cliff located at Sant’Andrea (Melendugno, Apulia, Italy). The cliff is characterized by a very complex geometrical setting, with a suggestive alternation of 10 to 20 m high vertical walls, with frequent caves, arches and rock-stacks. Initially, the rocky cliff surface was reconstructed at very fine spatial resolution from the combination of nadir and oblique images acquired by unmanned aerial vehicles. Successively, a limited area has been selected for further investigation. In particular, data refinement/decimation procedure has been assessed to find a convenient three-dimensional model to be used in the finite element geomechanical modeling without loss of information on the surface complexity. Finally, to test integrated procedure, the potential modes of failure of such sector of the investigated cliff were achieved. Results indicate that the most likely failure mechanism along the sea cliff examined is represented by the possible propagation of shear fractures or tensile failures along concave cliff portions or over-hanging due to previous collapses or erosion of the underlying rock volumes. The proposed approach to the investigation of coastal cliff stability has proven to be a possible and flexible tool in the rapid and highly-automated investigation of hazards to slope failure in coastal areas.

The stability of shallow, artificial underground cavities in soft rocks interacting with overlying structures and infrastructures represents a challenging problem to be faced. This paper discusses a methodology that can be useful for a preliminary stability assessment of underground cavities in soft calcarenites based upon the results of parametric two-dimensional (2D) and three-dimensional (3D) finite-element analyses of ideal underground cavities. The study aimed at exploring those relationships between the geometrical parameters of the cave system and the strength properties of the rock material to define charts that can be useful to evaluate the stability of the rock mass. Moreover, the influence of three-dimensionality was also accounted for based on 3D parametric analyses with variable cavity length and the comparison with the results of the corresponding 2D analyses.

In December 2013, a portion of a large and deep ancient landslide on the southern slope of the Montescaglioso town (Basilicata, Southern Italy) was abruptly reactivated, as a consequence of exceptional rainfall events, causing relevant damages to structures and infrastructures. The sliding surface is supposed to be located within a thick deposit of Pleistocene stiff clays overlain by dislocated blocks of calcarenites and cemented conglomerates. This paper discusses the research carried out to investigate the failure mechanism that occurred during the landslide event and the factors that controlled the reactivation. To this purpose, geological and geomorphological analyses were first proposed, followed by a back-analysis of the landslide process, performed via limit equilibrium calculations implementing time-dependent pore water pressure distributions derived from transient seepage finite element analyses. Furthermore, the overall landslide mechanism was investigated through a three-dimensional finite element analysis, built using the monitoring campaign carried out in the post-failure stage and calibrated according to the in situ failure mechanism evidence. Both the limit equilibrium and finite element analyses provide results in good agreement with the geomorphological evidence, further allowing us to recognize the effects of rainfall infiltration in the increase of pore water pressure along the sliding surface and the variation of the stress–strain state leading to failure occurrence.

Multi-temporal UAV and digital photo surveys have been acquired between 2017 and 2020 on a coastal cliff in soft rocks in South-Eastern Italy for hazard assessment and the corresponding point clouds have been processed and compared. The multi-temporal survey results provide indications of a progressive deepening process of erosion and detachment of blocks from the mid-height portion of the cliff, with the upper stiffer rock stratum working provisionally as a shelf against the risk of general collapse. Based on the DEM model obtained, a three-dimensional geomechanical finite element model has been created and analyzed in order to investigate the general stability of the cliff and to detect the rock portions which are more susceptible to failure. Concerning the evolving erosion process, active in the cliff, the photogrammetric analyses and the modeling simulations result in agreement and a proneness to both local and general instabilities has been achieved.

A large amount of underground cavities nowadays exists throughout the Apulian region (south-eastern Italy) as a result of mining processes of soft calcarenite, which frequently followed the “room and pillar” technique. In these cave systems, pillars and septa are critical structures, whose failure can lead to a significant increment of the sinkhole hazard. The behaviour of these rocky structures in the dynamic field is poorly studied in literature, and the present study aims to investigate their dynamic stability, according to regional seismicity data. For this purpose, ideal pillar geometries were considered, for which the evolution of the stress–strain field under dynamic inputs was observed in both 2D and 3- configurations by means of parametrical finite element analysis. For shallow cavities, slender septa were found to be the most affected by the influence of seismic loading. For deep cavities, dynamic instability is observed only for rather squat septa, with the cavity width also influencing the dynamic behaviour. To quantitatively assess the septum stability, a stability index was also proposed in 2D models. Moreover, three-dimensional analyses showed a stabilizing effect in the pillar exerted by the stress component perpendicular to the earthquake.