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Destructuration of typical Sicilian calcarenites
No full textThe paper discusses some interesting features of Sicilian fine grain calcarenites. Uniaxial, triaxial, oedometer and isotropic compression tests were undertaken on intact specimens of two types of calcarenite in order to investigate their mechanical characteristics It was found that the strength and deformability is significantly influenced by the structure (fabric and bonding) and by the destructuration processes. A better understanding of fracture development behaviour is gained through a combination of acoustic emission and photographic monitoring on non-homogeneous samples with natural pre-existing heterogeneities due to cementation or to density. The results show that the destructuration and fracture propagation, as well as the structural strength, are highly dependent on the position and distribution of heterogeneities in the sample. With the Marsala calcarenite, the critical state was not reached, even with large strains, while with the Palermo calcarenite the critical state was reached for lower strain values and the material demonstrated the yielding behaviour typical of brittle rocks
Cavità sotterranee e regimentazione idraulica dell’Agro Nolano nel XIX secolo (Provincia di Napoli)
No full textL’estrazione dell’Ignimbrite Campana (I.C., 39 Ka) iniziò nella vasta plaga a nord-est del Somma-Vesuvio per rifornire di materiali da costruzione la capitale del Regno dopo il terremoto del 26 luglio 1805 a fronte della carenza di Piperno Flegreo. Questa attività minatoria, per le peculiarità della risorsa geologica, si afferma in piccoli centri abitati a nord della Città di Nola, in aree di fragilità idrografica che diventano teatro di disastrose alluvioni. L’analisi di documenti inediti e il rilievo cartografico dei siti di coltivazione hanno permesso di ricostruire i dissesti avvenuti, di descrivere i rimedi intrapresi per combattere la violenza delle acque montane nella piana, di definire le soluzioni tecniche a salvaguardia degli abitati e dell’attività di sfruttamento lapideo. Allo stato attuale, una parte del territorio convive con una rete di cavità tufacee che, nel particolare stato di abbandono, costituisce la causa di diversi dissesti (voragini da sprofondamento, subsidenza di superficie) La creazione di uno strumento di pianificazione ha inteso prescrivere regole di sorveglianza e prevenzione di una parte del territorio esposto e, nel contempo, garantire una più attenta gestione del carico urbano
Laser scanner terrestre per la caratterizzazione geotecnica degli ammassi a struttura orientata
No full textSoftening and instability of shallow sloping covers in overconsolidated clay
No full textMechanical weakening of shallow sloping covers is a typical phenomenon occurring in overconsolidated clay, that in the long term leads to slope instability. Several factors contribute to weakening and subsequent instability. Weathering, swelling associated to stress release, strain softening, creep, destructuration caused by cycles of wetting-drying or of freezing-thawing, are all physical and mechanical phenomena that are often invoked to justify soil weakening. In contrast, the effects of changes of the soil structure due to osmotic phenomena have been investigated to a lesser extent. The paper deals with shallow landslides occurring in highly plastic overconsolidated clay of marine origin. The key idea is that weakening can be caused by infiltration of fresh water and consequent osmotic phenomena leading to a transformation of the clay structure and decrease of cohesion, dilation angle and friction angle. Some available data suggest that these phenomena are very active in highly plastic clays. The instability phenomena occurring in the Bisaccia Clay are described and discussed within this framework. Either steep slopes caused by fast erosion or gentle slopes are present in the same deposits. Slides mostly occur along steep slopes as a consequence of suction decrease, but the material accumulated at the foot of them quickly softens giving rise to mudslides. Gentle slopes are mainly subjected to mudslides that develop as a consequence of pore pressure fluctuations. In both cases, soil weakening appears to be an additional cause of instability. In fact, a number of laboratory tests show that swelling induced by stress release and facilitated by opening of fissures is dramatically enhanced if distilled water is provided to specimens: hence, osmotic phenomena are likely to occur. A number of CPTU and of tests carried out with an environmental cone in the same sections, shows a strong variation of the shear strength with depth,associated with a similar variation of pH. This confirms that softening could be associated with a change of the features of the internal structure of clay as a consequence of adsorption of fresh water from the ground surface
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