Swelling and swelling pressure of a clayey soil: Experimental data, model simulations and effects on slope stability

• Published in: Engineering geology 2022-02, Vol.297, p.106512, Article 106512
• Main Authors: Ghalamzan, Farzaneh, De Rosa, Jacopo, Gajo, Alessandro, Di Maio, Caterina
• Format: Article
• Language: English
• Subjects: Chemo-mechanical coupling; Clay; Finite element modeling; Landslide; Model simulation; Swelling; Swelling pressure
• ISSN: 0013-7952; 1872-6917
• DOI: 10.1016/j.enggeo.2021.106512

•The paper deals with experimentation and modelling of pore fluid composition influence on swelling and swelling pressure of a low activity clay.•Swelling and swelling pressure were induced by unloading or by exposure to distilled water of a soil reconstituted with NaCl solutions.•The observed processes were modelled with the FEM method by using a user-defined UEL subroutine implemented in the commercial code ABAQUS.•An extended elasticity law constitutive model is proposed and coupled chemo-mechanical interactions are considered.•A simplified slope stability analysis shows that the role of swelling/swelling pressure onset on the stability of a slope in low activity clay. The behaviour of soils and rocks containing clay minerals is the effect of complex chemo-mechanical processes of interparticle interaction. This paper presents experimental results and model simulations of the influence of mineral composition and pore fluid composition on swelling and swelling pressure of clayey soils frequently affected by instability problems. The soil from a landslide in tectonized clay shales, characterized by wide ranges of plasticity and activity, was analysed. Soil fractions at different liquid limit wL were reconstituted with distilled water or salt solutions at different concentrations and they were compressed in oedometric conditions. The tendency to swell was induced by unloading or by exposure to a fluid different from the pore fluid. Swelling was permitted in a set of specimens and it was prevented in another set by applying increasing pressures. The temporal evolution of swelling and swelling pressure was monitored, and ion concentration in the pore fluid was evaluated by monitoring the cell fluid composition. The chemically induced swelling was very large in the most plastic soil and negligible in the least plastic. Swelling pressure too attained different values, however, it was also very large in the least plastic soil. The observed coupled chemo-mechanical processes were successfully modelled with the FEM method by using a user-defined UEL subroutine that was implemented in the commercial code ABAQUS. The subroutine takes account of the chemo-mechanical interactions in the solid skeleton, through a suitable constitutive model, and of the coupled fluxes in the porous space, in addition to water desorption/adsorption at clay platelets. In the proposed constitutive model, chemical interactions are assumed to affect both the plastic and the elastic response,