Squeezed Interstitial Water and Soil Properties in Pleistocene Blue Clays under Different Natural Environments

Studies dating almost a century relate clay properties with the structure of the DDL, where 17 the charged surfaces of clay crystal behave like an electric capacitor, whose dielectric is the 18 interstitial fluid. The intensity of the inner electric field relates to the concentration and type of ions 19 in the DDL. Other important implications of the model are less stressed: this part of the clay soil 20 system, energetically speaking, is conservative. External contribution of energy, work of overburden 21 or sun driven capillarity and long exposure to border low salinity waters can modify the 22 concentration of pore-waters, thus affecting the DDL geometry, with electric field and energy 23 storage variations. The study of clay soils coming from various natural geomorphological and 24 hydrogeological contexts, determining a different salinity of interacting groundwater, shows how 25 the clay interaction with freely circulating waters at the boundaries produces alterations in the 26 native pore water salinity, and, at the nano-scale, variations of electric field and stored energy from 27 external work. The swelling and the shrinkage of clay soil with their volumetric and geotechnical 28 implications should be regarded as variations of the electrostatic and mechanical energy of the 29 system. The study is based on tests on natural clay soil samples coming from a formation of stiff 30 blue clays, widespread in southern Italy. Geotechnical identification and oedometer tests have been 31 performed, and pore waters squeezed out from the specimens have been analysed. Tested samples 32 have similar grain size, clay fraction and plasticity; sorted according to the classified 33 geomorphological/hydrogeological contexts, they highlight good correlations among dry density, 34 mechanical work performed in selected stages of the oedometric test, swelling and non-swelling 35 behaviour, and electrical conductivity of the squeezed pore waters. The work performed for 36 swelling and non-swelling samples shows well-defined differences; this endorse the relevance of 37 pore-water salinity in determining the volumetric state of clay soils under overburden and specific 38 hydrogeological border conditions, which together define a specific energetic state.