Influence of the Soil-atmosphere Interaction on the Collapse of Sand in the Valle dei Templi in Agrigento

Abstract

The sacral complex of the Valle dei Templi in Agrigento, belonging to the UNESCO Heritage Site List, stands over the crest of a stiff calcarenite bench, which overlies a layer of partially saturated carbonate sand. The retrogression of slopes and toppling phenomena that have occurred in the past, caused by the undermining combined with the discontinuity pattern, threaten some of the more relevant archaeological structures. Recent studies identified an open and metastable structure, typical of collapsible soils, for the sand layer under the calcarenite bench. In the sandy collapsible layer, significant vertical strains occur rapidly when the water content changes locally, decreasing suction and causing differential settlement and an increment of tensile stresses in the above calcarenites, where discontinuities might arise or increase their opening, resulting in possible progressive failure. By using meteorological and rainfall events data, the research presented here is focused on the study of the evapo-transpiration of a one-dimensional model of sand which was carried out in order to predict the water content change in the sandy layer. Successively, by calibrating the results through oedometer tests, the increments of water content were correlated to the amount of collapse. A first assessment of the influence of the soil-atmosphere interaction on the mechanism of collapse is then proposed.