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This paper presents a general three-invariant model to evaluate the theoretical prediction of strain localization against laboratory measurements performed during mechanical loading experiments, for a high-porosity Vosges sandstone (North-Eastern France). The model is based on a mean stress and Lode angle-dependent yield surface, calibrated using extensive experimental data from mechanical tests in triaxial, biaxial and true triaxial loading conditions. The general expression of a three-invariant and non-associated constitutive relation is then developed for 10 true triaxial loading paths, performed at constant mean stresses and prescribed Lode angles. The Rice's criterion by bifurcation analysis enables the theoretical prediction of deformation bands (onset, orientation and volumetric strain). The qualitative evolution of predicted band kinematics, as well as quantitative values obtained for the 10 loading paths, proves to be in good agreement with experimental observations from full-field characterization of localized zones. The relevance and predictiveness of the presented three-invariant model are further evidence by comparisons with simplified, associated and two-invariant models using the same initial dataset. [ABSTRACT FROM AUTHOR]

There are three main electrochemical factors affecting the electroosmotic flow in clay soil: the voltage loss at the clay/electrode interface, the type of current carriers in the soil, and the ion composition change in the clay due to voltage application. Appropriate evaluation of these factors is important to cost effectively implement electroosmosis for in situ soil consolidation projects. In this study, three different experimental systems were developed and used to investigate electrochemical reactions occurring in reconstituted and natural marine clay during electroosmotic consolidation. The results of polarization tests show that the voltage loss at the clay/electrode interface is different depending on the combination of the clay material and electrode material. The results of electroosmotic element test also show that electroosmotic dehydration does not increase if large current–voltage value is applied and that an optimal current–voltage value for causing electroosmosis depends on the cohesive soil composition. If the clay contains a lot of oxidizable ions, such as sodium, these ions affect electrophoresis and chemical reactions that occur in the soil. Therefore, the optimal configuration to apply electric current also differs depending on the clay. The results of laboratory-scale electroosmotic dehydration tests, arranged in a realistic in situ layout, are performed to study the relationship between soil dehydration, consolidation, and surface crack generation. [ABSTRACT FROM AUTHOR]

Sequestration of CO2 relies on the storage capabilities of the deep geologic setting throughout the lifetime of the storage activity. Preferred storage horizons are largely composed of sandstone, which is considered to be chemically inert to the injected CO2. Carbonate rocks and carbonate zones existing as seams or lenses in sandstone formations are, however, prone to chemical alteration during reactive flows of CO2-acidized water that can be created by the mixing of the injected CO2 with either fresh or saline water present in a storage horizon. Reactive flows can erode the fabric of carbonate rocks leading to the creation of high permeability pathways that are referred to as wormholes. The paper first examines the generation of wormholes in cylindrical samples of calcium carbonate-rich Indiana Limestone that are subjected to geostatic stress states representative of deep sequestration sites. The leakage potential of the wormhole is examined by appeal to computational fluid dynamics simulations of Stokes' flow in wormhole features and an elementary approach involving Stokes' flowbased hydraulic diameter concept in cylindrical pathways with deviating segments, representing the passages for flow in a wormhole. [ABSTRACT FROM AUTHOR]

This study systematically investigates the effect of deviatoric loading paths on diffuse and localized deformation developing during the mechanical loading of a high porosity (20%) Vosges sandstone (Eastern France). Laboratory scale experiments are performed using a high pressure true triaxial apparatus, designed to provide access to full-field surface kinematics at high spatial and temporal resolutions during the loading phase. The true triaxial experiments, with independent control of the three principal stress, are conducted at two constant mean stresses, in the brittle-ductile transition regime, and at five prescribed Lode angles, from axisymmetric compression (ASC) to axisymmetric extension (ASE). First, the transition from diffuse towards localized deformation is analyzed in different loading increments and shows an intermediate step of early strain localization, characterized by a large number of early deformation bands developing well before the stress peak and with a predominantly dilatant behavior. Secondly, the evolution of the mechanical behavior and localization patterns, such as deformation band angles and localized dilatancy, indicate a transition from the brittle regime to the ductile regime that is not only dependent on an increase in the mean stress, but also on a decrease in the Lode angle. The analysis of full-field measurements also provides insights into the emergence and evolution of local strains, as deformation structures coalesce or relocate and different failure modes develop depending on the prescribed stress paths. [ABSTRACT FROM AUTHOR]