Unsaturated sand in the stability of the cuesta of the Temple of Hera (Agrigento)

In the Valle dei Templi in Agrigento seven Doric temples stand lengthwise the crest of a rigid calcarenite cuesta over a layer of carbonate sand which lies along a thick stratum of clays. The environment is highly prone to landslides since topplings of calcarenite blocks often occur. The rock slopes are moving back and the slope edge draw near to the foundation of the Temple of Hera Lacinia contributing to increase their perilous condition. To assess the role of unsaturated sands in the instability processes, after the compositional and textural analysis of the material, direct shear tests and oedometer tests have been carried out on sand samples initially at the natural state, with low or very low values of natural water content, and finally at full saturation. The mechanical behaviour of sands seems one of the main causes of the instability influenced by the presence of an open metastable structure, which develops through bonding mechanisms generated via suctions and/or through cementing material such as clay or salts

Difficile equilibrio tra esigenze di sicurezza e di tutela ambientale nei problemi di stabilità di costoni rocciosi in ambiti di grande rilevanza ambientale: il caso di Capri

L'articolo tratta del problema della stabilità dei costoni rocciosi in zone di elevata valenza ambientale e affronta il delicato tema del confronto tra le esigenze di sicurezza e quelle della tutela ambiental

Terreni collassabili e processi di instabilità nella Valle dei Templi

Il complesso sacrale ellenistico della Valle dei Templi di Agrigento, Patrimonio UNESCO dell’Umanità, si snoda lungo la cresta di un banco di calcarenite, poggiante su un livello di sabbie. I costoni, in corrispondenza delle pareti calcarenitiche, risultano frequentemente in condizioni di equilibrio limite anche in prossimità delle principali strutture archeologiche, fra cui il Tempio di Giunone, il Tempio della Concordia, e il Tempio di Vulcano, le aree dei Donari e del Santuario Rupestre dedicato a Demetra, e la Necropoli Paleo–Cristiana. Tali strutture sono minacciate da fenomeni di instabilità e, in taluni casi, dall’arretramento del versante sino ad ora attribuito alla mesostruttura ed a fenomeni di erosione selettiva e scalzamento al piede. Recenti studi hanno individuato per le sabbie parzialmente sature, sovrastate dalle calcareniti, il tipico comportamento dei terreni collassabili caratterizzati da struttura aperta e metastabile, nei quali un incremento del contenuto d’acqua può innescare notevoli variazioni volumetriche. Sulla base di rilievi in sito, di prove di laboratorio e di analisi numeriche agli elementi finiti è stato possibile ipotizzare il ruolo attivo delle sabbie nei fenomeni di dissesto consentendo una nuova lettura e interpretazione dei fenomeni di instabilità

Evaluation of cliff recession in the Valle dei Templi in Agrigento (Sicily)

The sacral complex of the Valle dei Templi in Agrigento, added in the UNESCO Heritage Site List, stands over the crest of a rigid calcarenite cuesta, which overlies a layer of partially saturated (S = 6–12%) carbonate sand. In turn, the sand stratum lies on a thick stratumof clays. The environment is highly prone to landslides as highlighted by several previous studies that identify the undermining of slopes and the discontinuity pattern, occurred in the late Neotectonic phase, as causes of cliff failure. For wider and less exposed areas, where the undermining local instabilities can be present because of the specific morphology of the site, a recent research has proposed a new interpretation of the failure general mechanism. The new hypothesis here proposed would ascribe to the collapsible behaviour of the sand; both the failure mechanisms of the cliffs and the development of the discontinuities in the rock mass. A unitary framework is then proposed. A series of direct shear and oedometer tests was performed on the collapsible sand samples and values of collapse potentialwere estimated. As typical for collapsible soils when flooded, vertical strains occurred rapidly causing an increase of shear stresses in the upper calcarenite, characterised by low values of yielding and low values of tensile strength. As a consequence, additional discontinuities occur, volumes of rock fall and cliffs move back. Both by means of in situ surveys and the analyses of involved rock deformability and strength characteristics, a soilmodelwas considered and a modelling process developed. The model results were compared with measurements of displacements as well as dimensions of fallen blocks and consequently the comprehension of the effect of sand collapse was then possible. The identification of the new mechanism key factors allows the definition of the soil parameters that need to be monitored. In order to prevent the cliff recession for the archaeological site, the work proposes a plan of monitoring methods. These methods will be able to estimate the cliff recession, to localize “sensitive areas” and to quantify the parameters that could activate the instabilities

Meccanismi di collasso nelle Latomie di Siracusa

The aim of this work is to support, through geomechanical methods, the historical hypothesis proposed by the archaeologists according to which the latomiae of Syracuse, ancient Greek quarries, were originally mainly developed underground. In order to reach this objective, the finite elements numerical modelling was applied. The input data were inferred from the geologic history, from different archaeological reports and from the geomechanical characterization both of the intact rock and of the rock mass. The study highlighted the geotechnical events which modified the shape and the safety conditions of these amazing ancient quarries over the centuries.Il presente lavoro si propone di corroborare le ipotesi accreditate presso gli archeologi, secondo i quali l’attuale conformazione delle Latomie di Siracusa, cave greche risalenti al VII- V sec. a.C., ed in particolare della Latomia del Paradiso, sia imputabile a crolli che hanno interessato un imprecisato numero di ambienti ipogei oggi scomparsi. Attraverso una modellazione numerica, in cui i dati di input sono stati desunti dalla ricostruzione delle vicende geologiche dell’area di Siracusa, da ricerche bibliografiche e d’archivio relative alla storia delle latomie e dei manufatti presenti nel sito, dalla caratterizzazione geomeccanica della roccia e dell’ammasso, sono stati messi in luce gli eventi che possono avere determinato l’attuale configurazione delle cave storiche e l’insorgenza di fenomeni di instabilità

Durability of calcarenitic hypogea in the underground cultural heritage of Palermo (Sicily)

The paper deals with the stability conditions of hypogea, several hundred m 2 wide, dating from the Punic period to the XIX century, dug out of the calcarenitic table that makes up the bedrock of the Plain of Palermo in the Fossa della Garofala. This work concerns the influence that the shape of the hypogea and the characteristics of the lithotypes wields on the instability and decay phenomena taking place, by mean of laboratory tests on the calcarenite and parametric numerical models. The comparison between the numerical models and the actual instability phenomena validated the use of the empirical formula of Hoeck to the mechanical characterization of complex structured rock-mass in soft rock

The Latomiae of Syracuse: A Geotechnical Mapping Through Rock Reflectivity

The archeological site of the Latomia del Paradiso (Syracuse) is endangered by severe instability phenomena due to the shape of walls and underground excava-tion related with the poor mechanical characteristics of the weathered and wet rock. The failure of huge blocks from the ceiling of the underground areas and the detaching of rock "flakes" from the walls surface make the geotechnical zon-ing particularly complex. the zoning is based on the characteristics of the rock wall surface that, in first approximation, can be distinguished in regularized sur-faces because of mining , and in irregular surfaces characterized by fracture prop-agation. The elaboration of reflectivity values obtained from a laser scanner survey pro-vides a quick and reliable method, which can be very useful to assess the localization of alteration processes and their intensity. Alteration processes affect the mechanical characteristics and a decay of a rock mass shear strenght is associated to them. Therefore, it has been possible to obtain a differentiated assessment of the safety conditions of the rock mass walls in areas where a direct assessment was too expensive or difficult because of the wall extension, or impossible. The measurements of reflectivity have been correlated to the Hammer Schmidt rebound values r both in soft rocks, such as those under consideration, and in stone formations of different rock types