Mechanical sensitivity to hydro-chemical processes of Monastero Bormida clay

The paper presents the results of an experimental study on the mechanical behavior of a marly clay, motivated by the recurrent episodes of slope failure induced by intense rainfall events over the area of Langhe (NW Italy). The sensitivity of the material to environmental actions has been systematically explored by reproducing on laboratory samples hydrological and chemical processes similar to those expected to arise on site. Chemomechanical effects due to pore fluid dilution and decalcification have been investigated by testing both reconstituted and intact samples with different degrees of weathering. Pore water salinity was found to have minor consequences on the mechanical behavior of the material at its intact state and at the original calcite content. Decalcification enhanced the chemical sensitivity of the clay minerals constituting the soil matrix, not only by affecting the residual shear strength and the stiffness, but also by magnifying the tendency to swell under chemical loads, inducing a chemical sensitivity over swelling on saturation and enhancing water retention properties. Field observations also support the hypothesis that decalcification followed by interstitial pore water dilution are key factors to take into account to understand the degradation of the mechanical properties and that these phenomena can enhance the instability onset.