Sand-clay mixtures are often employed as typical reconstituted soils for geotechnical experiments in the laboratory. Sample preparation is an important factor that influences the mechanical behavior of reconstituted clayey soils. It is necessary to use an adapted sample preparation procedure to ensure an optimized sample homogeneity for sand-clay mixtures. There are various methods of soil sample preparation documented in the literature; however, the effect of sample preparation on soil-structure interface shear behavior and soil physical properties has not been well investigated so far. The objective of this paper is to characterize how sample preparation affects the shear behavior of the sand-clay mixture-structure interface and the related physical properties. Sand-clay mixture specimens with clay fractions of 13.75 %, 27.5 %, 41.25 %, and 55 % are prepared by the slurry method and the dry tamping method for the tests. Direct shear tests were carried out on the sand-clay mixture-concrete interface through a device in the laboratory. The physical parameters of the sand-clay mixture samples were measured after the sample preparation and shear tests. A comparison of these results provides an understanding of the role of sample preparation on the sand-clay mixture-concrete interface shear response and physical properties of the samples.

This study presents a plasticity-based macro-element (ME) for circular shallow foundations on rigid-inclusion (RI)-reinforced, layered soils subjected to seismic loading. The formulation includes: (i) an inclined interaction ellipse in the (h, m) plane with closed-form sizing and tilt (a, b, yr) linked to RI descriptors (alpha, HLTP, q'LTP); (ii) elastic terms extracted from dynamic impedance functions sampled at the soil-structure interaction frequency; and (iii) a vertical hardening variable y whose evolution included contributions from plastic horizontal displacement and rotation. A diagonal elastic matrix was adopted as a first-order approximation for shallow circular footings with small eccentricities. The model was validated against dynamic centrifuge tests on RI-reinforced ground: moment-rotation hysteresis and cyclic degradation were reproduced consistently, top-displacement histories were matched to a reasonable degree, and settlement trends were captured with a conservative response. The failure-envelope fit is limited to circular footings alpha is an element of [2.5,7.0]%, HLTP is an element of [0.5,1.0] m, and q'LTP is an element of [30 degrees, 42 degrees]. Within this domain, the ME offered an efficient tool for nonlinear soil-structure interaction analysis of RI-supported systems.

Air and water flows occurring in a porous material modify its mechanical properties. Evolution of the interface between saturated and partially saturated layers of a soil is of concern in this paper. In particular, the description of a drainage/imbibition front is developed gathering the two classical saturated and partially saturated poromechanical problems, with pressures of both fluids and solid displacement as unknowns. The presented model enables saturated and partially saturated layers to coexist without considering gaseous air dissolving into liquid water. Nucleation or collapse of the drainage/imbibition front moving from or reaching an air connected boundary is characterised considering the Signorini contact conditions on the liquid phase. The model abilities are confirmed numerically, via finite element simulations, showing among other that this new description of interface motion does not imply hysteresis phenomena. Parametric investigation developed with respect to drainage kinetics and thickness of the layer which regularises the interface between the saturated and the partially saturated domain are also provided.

In geotechnical engineering, the soil-structure interface is an important aspect to be taken into account in soil-structure interaction because it relates to the stability of supported structure. In particular, the shear behavior of the soil-structure interface plays a key role in the design of civil engineering structures and their analysis over time. The interface is a thin zone of soil in contact with the structure where major stresses and strains develop in. To our knowledge, previous works on the characterization of the mechanical behavior of the soil-structure interface mainly include typical soils (sand or clay) or natural soils, in contact with variable structural materials (concrete, steel, wood). However, natural soils are very complex, partly due to geological heterogeneities, and the mechanical response of typical soils does not always represent accurately intermediate soils between sand and clay. Previous studies on the mechanical behavior of those soils are significantly represented in the literature, especially in experimental research, however it is rather poorly documented on the interface between these soils and structural materials, whereas their response to mechanical loadings is different. The objective of this paper is to characterize the shear behavior of the soil-structure interface for intermediate soils between sand and clay, by experiments at the laboratory scale. Artificial mixtures of silica sand and kaolinite-rich clay are chosen to represent the intermediate soils in this study. For this propose, the research is organized in a main experimental campaign that aims to investigate the effect of the clay fraction, from 0% (sand) to 55% (kaolin clay) on the mechanical behavior of a soil-concrete interface by a direct shear device in the laboratory. The characterization of the shear behavior of the soil-concrete interface at various clay and sand fractions allows to enlighten the role of soil microstructure at the soil-structure interface on the stability of civil engineering structures.

The detection of an interface separating two zones of low contrast and evolving in a deformable medium is very challenging. The low-contrasted images describing a partially saturated granular medium are replaced by high contrasted images generated from the correlation error maps issued from a standard digital image correlation (DIC) calculation. A robust algorithm has been developed to capture automatically the sought interface evolving in 2D space through time. Capable of detecting all morphological reliefs, this approach is completed by a sequence of steps to remove aberrant contours and track the main advancing interface. Consequently, adequate algorithms have been developed to determine physical and morphological properties that will give insights on the factors that monitor the interface propagation.

The study aims to investigate how the mechanics of swelling of a polymer gel is affected by the presence of free-chains due to a partial cross-linking process. The analysis is focused on the equilibrium solution of the mechano-diffusion problem under different as-prepared states, corresponding to different polymer network fractions before diffusion starts. The limit situations of perfectly cross-linked polymer gel and solution of polymeric chains are recovered by the model.

Biphasic flow propagating through a granular medium can be established as an unstable infiltration and can be precursors of nonnegligible deformations. Capturing such infiltration through the lens of a high-resolution camera, full-field strain maps are determined via digital image correlation (DIC). However, this image analysis technique is based on the fundamental assumption of grey level conservation between the reference and deformed images. In this paper, DIC algorithm is recalled, and suitable controlling parameters are introduced to improve the accuracy of the output displacement fields and to remove the grey level variations induced by an air-water flow percolating through a Fontainebleau sand. In addition, an in-depth investigation on the full-field volumetric strain maps is conducted in order to extract the hidden relationship between the front propagation and the strains evolution.

This paper investigates the effects on the behavior of a saturated porous material of an evolving microstructure induced by the mass exchange between the solid and the fluid phases saturating the porous network, using two-scale asymptotic expansions. A thermodynamically consistent model of the fluid physics flowing through the porous network is proposed first, describing microstructure variations to be captured implicitly via the level set method. The two-scale asymptotic expansions method is then applied to obtain an upscaled model capable to account for mass transfer. This last is proven to depend not only on the gradient of the macroscopic forces, such as the fluid pressure and the chemical potential, but also on the average velocity of the solid–fluid interface. Numerical simulations are carried out using the finite element method in order to evaluate the relative weight of the new terms introduced.

The paper focuses on the identification of the 3D failure envelope of a shallow foundation on soft soil reinforced by rigid inclusions. A nonlinear 3D finite element model is first validated against literature results and novel centrifuge experimental data. The failure envelope, defined in the vertical force (V), bending moment (M) and horizontal force (H) space, is then constructed using numerical swipe tests. Analytical formulas are introduced to describe the 3D failure envelope shape and inclination, considering the influence of the coverage area, the thickness, and the friction angle of the load transfer platform. Finally, the efficiency of a rigid inclusion foundation is highlighted by comparing its failure envelope to that of the same foundation without rigid inclusions. The proposed analytical failure envelope can be used by engineers to quantify the bearing capacity of rigid inclusion foundations and by researchers to develop novel macroelements submitted to complex coupled loads.

A generalized finite element beam with an embedded rotation discontinuity coupled with a 3D macroelement is proposed to assess, till complete failure (no stress transfer), the vulnerability of symmetrically reinforced concrete frame structures subjected to static (monotonic, cyclic) or dynamic loading. The beam follows the Timoshenko beam theory and its sectional behavior is described in terms of generalized forces and generalized strains. The beam response up to the peak is described by a macroelement, based on plasticity theory, that adopts a 3D failure criterion expressed in terms of axial force, shear force and bending moment. The Embedded Finite Element Method is then adopted to reproduce bending dominated failure, with a global cohesive model that links the cohesive moment to a rotational jump. The formulation allows for remedy of localization phenomena and significant reduction of the necessary computational time. The performance of the proposed simplified strategy is illustrated by comparison with experimental results.

The technique of ground reinforcement using Rigid Inclusions (RIs) is known to reduce settlements and enhance bearing capacity in soft soils.This approach leads to significant nonlinear interactions among the load transfer platform, piles, and the surrounding soil.The main objective of this paper is to identify the failure envelope of a shallow foundation on soft soil reinforced by RIs.This is a critical step in the safety assessment of this combined foundation system under static and dynamic (seismic) loading.The failure envelope, defined in the vertical force (V), bending moment (M) and horizontal force (H) space, is constructed using swipe tests from numerical simulations.A simple analytical formula is proposed to describe the failure envelope in V-M-H space.The failure envelope described by the proposed equation is the key ingredient for the macro-element modeling for the analysis of Soil-Structure Interaction of RIs foundation systems.

SummaryFingered infiltration of a wetting fluid through a porous network is a widely studied subject in the field of fluid mechanics. However, the effect of this heterogeneous percolation on the response of granular materials, in particular fine‐grained soils, is a poorly investigated and badly understood topic which deserves deep analysis, considering, among others, possible applications in soil remediation and underground energy storage. This paper presents a first application of a new formulation of unsaturated poromechanics based on a phase field approach that allows to characterize on the one hand the occurrence of fingering hydraulic instabilities and on the other one to capture their effects on the irreversible, and possible unstable, deformation of the solid skeleton. The envisaged application concerns the behavior of fine‐grained soils whose dilatant/contractant behavior is more and more attracting the interest of the scientific community both in the fields of experimental research and numerical modeling.

In this study, the effect of fluid fingering on the solid remodeling of a granular material during the drainage phenomenon is investigated. A new biaxial apparatus, endowed with two transparent windows and adapted to unsaturated soils, is used to capture the effects of hydraulic instabilities on the mechanical response, by means of high-resolution cameras. A specimen of (40 × 50 × 11) mm3, of Fontainebleau sand NE 34 initially saturated by water, is connected to a pressure-controlled gas source to inject the gas into the sample. During the injection phase, fluid instabilities are detected and filmed. Using imaging techniques, the grain remodeling and strain localization due to the two-phase fluid flow are measured.

Flows involving immiscible displacement of one fluid by another in a porous media are known to destabilize and form fluid fingering. When the non-wetting fluid is a highly mobile gas (air) and the wetting fluid is an in-compressible liquid (water) the classical macroscopic theory is unable to describe the fingered flow. In Part I of this study we have introduced a model that interprets the mixture of wetting and non-wetting fluids within the pore space as a single saturating non-uniform pore fluid characterized by a phase field parameter, which is considered to be the saturation degree of the wetting fluid. In the current study we present a linear stability analysis of its solutions which describe both imbibition and drainage. The analysis sheds light on the sensitivity of the flow stability on injection flux, imposed pressure gradient and initial saturation degree. Two-dimensional numerical simulation results are as well presented which verify the stability analysis and reveal the rich structure of the fluid fingering realized by this model. While these results are found to be in qualitative agreement with experimental observations, they also warrant further experimentation to explore the additional features predicted by the model.

The article focuses on non-uniqueness, bifurcation and stability conditions in elasto-viscoplastic boundary value problems when inertia terms are neglected. Analytical and numerical studies are presented to investigate the capability of an elasto-viscoplastic model to regularize the behavior in the occurrence of strain localization with respect to number of strain bands formed and mesh dependency. It is found that elasto-viscoplasticity in a Cauchy medium neither restores the uniqueness of the solution nor provides mesh independent results. A high value of the viscosity parameter can sometimes provide results that are mesh independent, up to a certain limit strain, as it actually modifies the response of the constitutive law by an ad-hoc increase of its hardening branch. On the contrary, coupling elasto-viscoplasticity with a second gradient model that introduces an internal length parameter reproduces realistically the rate dependent behavior and regularizes the results.

study of coupled hydromechanical instabilities, where the notion of mechanical instabilities is enriched 13 by the complementary (and not necessarily independent) notion of hydraulic instabilities, with a key role 14 played by interfaces and coupled hydromechanical phenomena.Geomaterials are intrinsically multi-phase, the porous network being typically saturated by a mixture of Hydromechanical Instabilities in Geomaterials et al. (2009, 2013), to explain the formation of desiccation cracks in soils, an alternate capillarity-driven 73 mechanism is proposed at the continuum scale.We hope that readers will enjoy reading the carefully selected papers on the growing and exciting research 75 area of coupled hydromechanical instabilities in geomaterials.

3D interactions diagrams for symmetrically Reinforced Concrete (RC) square sections with various reinforcement ratios are constructed using 3D non-linear finite element simulations. The interaction diagrams are expressed in terms of generalized forces (axial force, bending moment and shear force) and allow to identify two characteristic states: the first characteristic state corresponds to the elastic limit of the reinforcement bars (while concrete exhibits a non-linear behavior) and the second characteristic state to the peak values of the generalized forces generalized displacements curves. Firstly, 3D non-linear finite element simulations of RC cantilever-type columns are presented and validated with experimental results. Numerical interaction envelopes are then derived and analytical convex expressions are provided. Finally, a comparison with existing interaction diagrams from the literature is proposed.

Within the context of immiscible biphasic flow in porous media, when the nonwetting fluid invades the pore spaces which are a priori saturated with the wetting fluid, capillary forces dominate if the pore network is formed by fine-grained soils. Owing to the cohesion-less frictional behavior of such soils, a capillary force–driven fracturing phenomenon has been put forward by some researchers. Unlike the purely mechanistic tensile force–driven mode-I fracturing that typically has been attributed to the formation of desiccation cracks in soils, attempts to model this alternate capillarity-driven mechanism have not yet been realized at a continuum scale. However, the macro-scale counterpart of the capillary energy associated with the various pore-scale menisci is well-established as the interfacial energy characterized by the soil-water retention curve. An investigation of the possible contribution of this interfacial energy in supplying the dissipation related to fracture initiation is the essence of this work, inspired by the vast literature on gradient damage modeling.

Natural soils are usually heterogeneous and characterized with complex microstructures. Sand–clay mixtures are often used as simplified soils to investigate the mechanical properties of soils with various compositions (from clayey to sandy soils) in the laboratory. Performing laboratory tests on a sand–clay mixture with definite clay fraction can provide information to understand the simplified soils’ mechanical behavior and better predict natural soils’ behavior at the engineering scale. This paper reviews previous investigations on sand–clay mixture and soil–structure interface direct shear test. It finds that even though there are many investigations on sand–clay mixtures and soil–structure interfaces that consider pure sand or pure clay, limited data on the mechanical behavior of the interface between sand–clay mixture and structure materials are available. Knowledge is missing on how the clay content influences the mechanical behavior of interface and how the soil particles’ arrangement changes as the clay content increases. Further study should be performed to investigate the interface in terms of a reconstituted sand–clay mixture and structure by interface direct shear test, to highlight the influence of clay fraction on the interface response, under various loading conditions.