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Changes in the chemistry of the pore fluid are known to have an impact on the hydro-mechanical behaviour of clays. Experimental evidence collected in recent decades has led to the formulation of constitutive chemo-mechanical models for expansive soils used in engineering practice for the containment of pollution, such as bentonite. Less attention has been paid to modelling the chemo-mechanical behaviour of non-expansive clays, which are less frequently used for geoenvironmental applications, but equally exposed to chemical changes. Key differences between the impact of salinity on the fabric of expansive and non-expansive clays are pointed out. At the macroscopic scale, an increase in salinity causes a translation of the normal compression line of non-expansive clays to higher void ratios, which in some cases is also accompanied by an increase in compressibility. The opposite occurs for expansive clays. Such experimental evidence provides the basis for a chemo-mechanical model formulated in the frame of elasto-plasticity with generalised hardening, whose yield surface expands with pore fluid concentration. The model is validated against experimental results, both original and from the literature. Simulation results compare very well with those of tests performed on reconstituted, compacted and intact samples.

Funding Information: The first author acknowledges the financial support provided by the Erasmus+ programme for her stay at Aalto University. Publisher Copyright: © 2021 The Authors The chemical composition of pore fluid and matric suction rule the mechanical behaviour of soils. In case of clays, their fabric changes in line with those variables. Since both the increase in matric suction and salinity cause a transition from an open to a close microstructure of low and medium activity clayey materials, a unique framework could tackle problems where salinity and saturation changes are expected. This paper presents a simple elasto-plastic model capable of reproducing the behaviour of unsaturated clayey soils in saline environments. Changes in the pore fluid composition are addressed through the use of osmotic suction as a variable. The proposed model extends the Barcelona Basic Model for partially saturated soils to consider the effect of osmotic suction. The model, implemented in the Thebes code, is calibrated for Boom Clay. The reproduced tests include mechanical loading at different matric and osmotic suctions in oedometric conditions, as well as more complex chemo-mechanical stress paths. Despite the simplicity of the formulation, the agreement between the experimental results and the simulations is encouraging. It seems that the modelling approach addresses the most important features of partially saturated soils with saline pore fluid which are slightly or moderately expansive.

Knowledge of the in situ stress state of rock mass is fundamental for engineering, geological and geophysical applications. In situ stress state determination requires in principle the evaluation of the three principal stresses and the related principal directions, but it is widely recognized in the literature that the maximum horizontal stress is the most difficult component to accurately estimate. In the context of borehole methods, this paper proposes a step-by-step analytical procedure to estimate some bounds to the maximum horizontal stress, starting from a geomechanical description of the rock and relying on information generally available in the engineering practice. The procedure is divided in substeps, each one requiring additional information about the mechanical properties of the rock and on the geometrical properties of the failed portion of rock: more information available implies a lower uncertainty on in situ stress estimate. Furthermore, since the proposed procedure is analytical, it allows a complete and very easy implementation in a spreadsheet. The aim of the work is thus to provide a rigourous but simple analytical tool that can be used in engineering practicte to estimate some bounds to the maximum horizontal in situ stress state. The approach is finally validated by means of both numerical simulations, performed with a sophisticated numerical tool, and experimental field data coming from the literature.