Collapsibility of metastable sand by non-conventional oedometer tests

The stability of foundations soils could represent a clear and present threat for the conservation of even well preserved buildings, particularly for Architectural heritage conservation and land art heritage. A dramatic case is the presence of collapsible metastable sands as foundation soils, as it occurs in the sacral complex Valle dei Templi in Agrigento. This site listed by UNESCO, stands on a crest of a calcarenite cuesta, overlaying a layer of these sands. When the collapsible sand is dry, the structure is strong enough to bond the sand particles together. When the sand becomes wet, a de-structuration mechanism occurs and the soil’s strength is compromised. This paper has a twofold aim: (1) to gain a better understanding of the kind of bonding forces between the textural components of the collapsible metastable sand and (2) to identify a proper consolidant, that could combine the compatibility of inorganic systems and the performance of polymeric materials, paying attention to the environmental issues related to this site. Soaking tests have been performed by submerging sand samples in different solvents in order to verify the role of water menisci in mechanical stability of the sand highlighting a perfect stability using a non polar solvent. Sand samples have been consolidated by using poly ethylene glycol and nanosilica. Oedometer tests on consolidated and untreated samples have been used to verify the reduction of collapse potential induced by the treatment with the proposed mixtures.