Remote-sensing techniques are changing the way of investigating the Earth and its surface processing. Among these, rock fall from vertical cliffs are very frequent and difficult to be investigated because they frequently occur from inaccessible places. At this regard, terrestrial remote-sensing techniques represent a great opportunity for investigating inaccessible cliffs from a remote position. In this paper, a new approach for the investigation of rock cliff and the prioritization of rock fall hazard based on data collected by remote-sensing techniques has been developed and applied to a real coastal cliff located in the southern part of Italy. By the herein presented approach, data derived from a survey performed by the combination of terrestrial laser scanner, ground-based SAR interferometry and infrared thermography are used in order to identify both predisposing factors (mapping of discontinuities) and state of activity indicators of rock instabilities. Hence, a prioritizations map of the cliff in terms of stability interventions is achieved that can be easily used by local authorities in charge of land management.
The study proposes geological evolution models for the cliff slopes of the two Italian towns of Orvieto (Umbria) and Radicofani (Tuscany). The models were validated by the use of a stress-strain numerical modelling, implemented by the finitedifference code FLAC 5.0. The numerical modelling was approached in a sequential way, by assuming specific stiffness values related to the evolutionary stages. For this purpose, unconventional laboratory tests were performed aiming at reproducing the stress path related to the geological evolution model, using standard equipment for CID triaxial testing. The geological evolution models infer that deformation in both cases is driven by stress reduction. At the Orvieto plateau, stress reduction is induced by stress relief involving a tuff plate; in the case of Radicofani, stress reduction is due to stress release in consequence of lateral erosion of clay. Numerical simulations refine the lithotechnical zoning of the two investigated slopes, introducing a stress-strain criterion in addition to the conventional geological and geomechanical ones.
The morphological features of submarine canyons significantly modify the amplitude, duration and frequency content of free-field seismic ground motions. This paper examines the influence of these morphological features through a series of seismic centrifuge tests on kaolin clay models with canyon sloping angles of 15, 30 and 45°. These tests were performed using the IFSTTAR (the French Institute of Science and Technology for Transport, Development and Networks) geotechnical centrifuge at an acceleration of 40g by applying a set of dynamic excitations, varying in amplitude and frequency content. The response of the clay canyon models was monitored by means of accelerometers and pore-pressure transducers. In-flight characterisation was performed on each clay model with bender element and T-bar tests prior to the application of seismic excitations. The study shows that the topographic shape of the canyon can substantially affect peak values and the frequency content of the free-field motions along the slope surface. Low-intensity seismic excitations and frequency contents along with the dominant frequency of the soil deposit were found to cause substantial amplification. In addition, the reduction of the shear modulus and the corresponding increase in damping tend to increase the fundamental site period.
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