pinecone/core-2020-05-10-deduplication huggingface dataset:
Numerical modeling of three-phase dissolution of underground cavities using a diffuse interface model

Natural evaporite dissolution in the subsurface can lead to cavities having critical dimensions in the sense of mechanical stability. Geomechanical effects may be signiﬁcant for people and infrastructures because the underground dissolution may lead to subsidence or collapse (sinkholes). The knowledge of the cavity evolution in space and time is thus crucial in many cases. In this paper, we describe the use of a local nonequilibrium diffuse interface model for solving dissolution problems involving multimoving interfaces within three phases, that is, solid–liquid–gas as found in superﬁcial aquifers and karsts. This paper generalizes developments achieved in the ﬂuid–solid case, that is, the saturated case [1]. On one hand, a local nonequilibrium dissolution porous medium theory allows to describe the solid–liquid interface as a diffuse layer characterized by the evolution of a phase indicator (e.g., porosity). On the other hand, the liquid–gas interface evolution is computed using a classical porous medium two-phase ﬂow model involving a phase saturation, that is, generalized Darcy’s laws. Such a diffuse interface model formulation is suitable for the implementation of a ﬁnite element or ﬁnite volume numerical model on a ﬁxed grid without an explicit treatment of the interface movement. A numerical model has been implemented using a ﬁnite volume formulation with adaptive meshing (e.g., adaptive mesh reﬁnement), which improves signiﬁcantly the computational efﬁciency and accuracy because ﬁne gridding may be attached to the dissolution front. Finally, some examples of three-phase dissolution problems including density effects are also provided to illustrate the interest of the proposed theoretical and numerical framework
FFT-based bounds on the permeability of complex microstructures

International audienceA numerical scheme for the computation of the permeability of complex microstructures is presented. As a darcean counterpart of the FFT-based scheme in elasticity, the method is designed to be directly coupled with 3D imaging techniques of porous samples, without meshing or definition of an equivalent pore network. The method relies on the variational principle of Hashin and Shtrikman which ensures a rigorous upper bound status to the estimated permeabilities and provides an energetically consistent rule for heterogeneous voxels comprising both the solid and fluid phases
On the calculation of cumulative strain around full-flow penetrometers in steady-state conditions.

An approximate solution for the effects of high strain rates, and gradual strength degradation, on the penetration resistance of penetrometers can be obtained by combining the strain-path method with the classical upper bound theorem. The stream path calculations require the integration of the material constitutive equation along the streamlines. Unless the geometry is simple so that the integration can be evaluated analytically, numerical procedures are required to backtrack streamlines. The strain at any location is calculated by finding the streamline that passes through the given point and integrating the strain rate along that streamline from its inlet boundary. Thus, the calculations can be complicated, and errors can be accumulated during the calculation procedure.\ud
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This paper presents an efficient approach for evaluating cumulative strains around penetrometers without the need to backtrack individual streamlines. In this approach, the strain components are treated as field variables. The global solution is obtained using the streamline upwind Petrov–Galerkin method. The new method together with an Eulerian-based finite element formulation was used to study the cone penetration test and evaluate the effect of strain softening on the cone resistanc
Numerical computations of rock dissolution and geomechanical effects for CO 2 geological storage

International audienceThe paper is motivated by the long term safety analysis of the CO 2 geological storage. We present a methodology for the assessment of the ge-omechanical impact of progressive rock dissolution. The method is based on the use of X-ray tomography and the numerical dissolution technique. The influence of evolution of the microstructure on the macroscopic properties of the rock is analysed by using periodic homogenization method. The numerical computations show progressive degradation of all components of the stiffness (orthotropic) tensor. Moreover, the evolution of associated mass transfer properties (as tortuosity and conductivity tensors), by using the periodic homogenization method, is also calculated. The correlation between the mechanical parameters and the transfer properties during the dissolution pro-cess is presented. The results show that the highest increase of the hydraulic conductivity (in direction Y) is not associated with the highest decrease of Young modulus in this direction. Moreover, the highest decrease of Young modulus (in the direction X) is not associated with percolation in this direction. Finally, an incremental law to calculate settlement, in case of a rock with evolving microstructure, is proposed. The solution of the macroscopic settlement problem under constant stress and drained conditions showed that the geomechanical effects of the rock dissolution are rather limited
Poroelastic two-phase material modeling: theoretical formulation and embedded finite element method implementation

International audienceThis paper presents the formulation of finite element methods for the numerical modeling of a poro-elastic two-phase (aggregates/mixture phase) solid. The displacement and pressure fields are decomposed, following the EAS method, into a regular part and an enhanced part. This leads to discontinuous strain and pressure gradient fields allowing to capture the jump in mechanical and hydrical properties passing through the interface between the aggregates and the mixture phase. All these enhanced fields are treated in the context of the Embedded Finite Element Method through a local enhancement of the finite element interpolations as these jumps appear. The local character of these interpolations lead after a static condensation of the enhanced fields to a problem exhibiting the same structure as common poro-elastic finite element models, but incorporating now the mechanical and hydrical properties of a two-phase solid
Hydro-mechanical response of collapsible soils under different infiltration events

The behavior of a partially saturated soil during surface-water infiltration is analyzed by means of an elasto-plastic constitutive model formulated in terms of effective stress and extended to unsaturated conditions. The model is calibrated considering laboratory-scale experimental results under suction-controlled conditions. The wetting process in two collapsing soils, initially loaded at in situ stresses, is simulated by imposing two different boundary conditions: surface ponding and water flow. The stress paths resulting from the imbibition process are analyzed at different points inside the laye
Reservoir characterization in an underground gas storage field using joint inversion of flow and geodetic data

Characterization of reservoir properties like porosity and permeability in reservoir models typically relies on history matching of production data, well pressure data, and possibly other fluid-dynamical data. Calibrated (history-matched) reservoir models are then used for forecasting production and designing effective strategies for improved oil and gas recovery. Here, we perform assimilation of both flow and deformation data for joint inversion of reservoir properties. Given the coupled nature of subsurface flow and deformation processes, joint inversion requires efficient simulation tools of coupled reservoir flow and mechanical deformation. We apply our coupled simulation tool to a real underground gas storage field in Italy. We simulate the initial gas production period and several decades of seasonal natural gas storage and production. We perform a probabilistic estimation of rock properties by joint inversion of ground deformation data from geodetic measurements and fluid flow data from wells. Using an efficient implementation of the ensemble smoother as the estimator and our coupled multiphase flow and geomechanics simulator as the forward model, we show that incorporating deformation data leads to a significant reduction of uncertainty in the prior distributions of rock properties such as porosity, permeability, and pore compressibility.Eni S.p.A. (Firm
Numerical modelling of landslide-generated waves with the particle finite element method (PFEM) and a non-Newtonian flow model

Landslide-generated impulse waves may have catastrophic consequences. The physical phenomenon is difficult to model because of the uncertainties in the kinematics of the mobilised material and to the intrinsic complexity of the fluid–soil interaction. The particle finite element method (PFEM) is a numerical scheme that has successfully been applied to fluid–structure interaction problems. It uses a Lagrangian description to model the motion of nodes (particles) in both the fluid and the solid domains (the latter including soil/rock and structures). A mesh connecting the particles (nodes) is re-generated at every time step, where the governing equations are solved. Various constitutive laws are used for the sliding mass, including rigid solid and the Newtonian and non-Newtonian fluids. Several examples of application are presented, corresponding both to experimental tests and to actual full-scale case studies. The results show that the PFEM can be a useful tool for analysing the risks associated with landslide phenomena, providing a good estimate to the potential hazards even for full-scale events.Peer ReviewedPostprint (author's final draft
On the risk of hydraulic fracturing in CO2 geological storage

We present a contribution on the risk of hydraulic fracturing in CO2 geological storage using an analytical model of hydraulic fracturing in weak formations. The work is based on a Mohr???Coulomb dislocation model that is extended to account for material with fracture toughness. The complete slip process that is distributed around the crack tip is replaced by superdislocations that are placed in the effective centers. The analytical model enables the identification of a dominant parameter, which defines the regimes of brittle to ductile propagation and the limit at which a mode-1 fracture cannot advance. We examine also how the corrosive effect of CO2 on rock strength may affect hydraulic fracture propagation. We found that a hydraulically induced vertical fracture from CO2 injection is more likely to propagate horizontally than vertically, remaining contained in the storage zone. The horizontal fracture propagation will have a positive effect on the injectivity and storage capacity of the formation. The containment in the vertical direction will mitigate the risk of fracturing and migration of CO2 to upper layers and back to the atmosphere. Although the corrosive effect of CO2 is expected to decrease the rock toughness and the resistance to fracturing, the overall decrease of rock strength promotes ductile behavior with the energy dissipated in plastic deformation and hence mitigates the mode-1 fracture propagation
A numerical investigation of the incremental behavior of crushable granular soils

The mechanical behavior of granular materials is characterized by strong nonlinearity and irreversibility. These properties have been differently described by a variety of constitutive models. To test any constitutive model, experimental data relative to the nature of the incremental stress–strain response of the material is desirable. However, this type of laboratory data is scarce because of being expensive and difficult to obtain. The discrete element method has been used several times as an alternative to obtain incremental responses of granular materials. Crushable grains add one extra source of irreversibility to granular materials. Crushability has been variously incorporated into different constitutive models. Again, it will be helpful to obtain incremental responses of crushable granular materials to test these models, but the experimental difficulties are increased. Making use of a recently introduced crushing model for discrete element simulation, this paper presents a new procedure to obtain incremental responses in discrete analogs of granular crushable materials. The parallel probe approach, previously used for uncrushable discrete analogs, is here extended to account for the presence of crushable grains. The contribution of grain crushing to the incremental irreversible strain is identified and separately measured. Robustness of the proposed method is examined in detail, paying particular attention to aspects such as dynamic instability or crushing localization. The proposed procedure is later applied to map incremental responses of a discrete analog of Fontainebleau sand on the triaxial plane. The effect of stress ratio and granular state on plastic flow characteristics is highlighted.Peer ReviewedPostprint (author's final draft
Continuously unique anisotropic critical state hyperplasticity.

This paper presents the theoretical development and methodological motivation of a single surface anisotropic hyperplasticity model. The model extends the isotropic family of models developed by Coombs and Crouch by: (i) introducing anisotropic shearing into the yield surface, (ii) relating two of the material constants to a single physical quantity and (iii) using a more physically realistic pressure sensitive elastic free energy function. This model overcomes the difficulty of determining the constants of the isotropic two-parameter surface by analytically relating them to a single experimentally measurable physical quantity, namely the normalised hydrostatic position of the Critical State. This provides a model with a Critical State surface that is constant throughout the loading process, invariant of the level of anisotropy inherent in the yield envelope. The model is compared with experimental data from triaxial tests on Lower Cromer Till, contrasted against the SANIclay model and the recent model of Yang et al. (2015) as well as being compared with rarely considered experimental data from hollow cylinder tests on London Clay
A multiscale framework for the simulation of the anisotropic mechanical
  behavior of shale

Shale, like many other sedimentary rocks, is typically heterogeneous,
anisotropic, and is characterized by partial alignment of anisotropic clay
minerals and naturally formed bedding planes. In this study, a micromechanical
framework based on the Lattice Discrete Particle Model (LDPM) is formulated to
capture these features. Material anisotropy is introduced through an
approximated geometric description of shale internal structure, which includes
representation of material property variation with orientation and explicit
modeling of parallel lamination. The model is calibrated by carrying out
numerical simulations to match various experimental data, including the ones
relevant to elastic properties, Brazilian tensile strength, and unconfined
compressive strength. Furthermore, parametric study is performed to investigate
the relationship between the mesoscale parameters and the macroscopic
properties. It is shown that the dependence of the elastic stiffness, strength,
and failure mode on loading orientation can be captured successfully. Finally,
a homogenization approach based on the asymptotic expansion of field variables
is applied to upscale the proposed micromechanical model, and the properties of
the homogenized model are analyzed.Comment: submitted to International Journal for Numerical and Analytical
  Methods in Geomechanic
Comprehensive study of the drying behavior of Boom clay:Experimental investigation and numerical modeling

This paper presents a thermo-hydro-mechanical framework to model the dryingbehavior of Boom clay. First, the experimental campaign conducted Noémie Primeis briefly presented because it is used to validate the model. The data acquisitionand processing is emphasized because of the use of X-ray microtomography to beable to more accurately compare experimental and numerical strain fields. The dif-ferent submodels are introduced. Numerical simulations are performed to illustratethe capability of the proposed model to reproduce the observed behavior. Finally,a comprehensive sensitivity study on several key model parameters associated withthe water retention curve, and the permeability of the medium, is performed to get abetter understanding of the physics behind the coupled model.Peer reviewe
A new damage model based on non-local displacements

A new non-local damage model is presented. Non-locality (of integral or gradient type) is incorporated into the model by means of non-local displacements. This contrasts with existing damage models, where a non-local strain or strain-related state variable is used. The new model is very attractive from a computational viewpoint, especially regarding the computation of the consistent tangent matrix needed to achieve quadratic convergence in Newton iterations. At the same time, its physical response is very similar to that of the standard models, including its regularization capabilities. All these aspects are discussed in detail and illustrated by means of numerical examples.Peer ReviewedPostprint (author’s final draft
Adaptation of existing behaviour models to unsaturated states: Application to CJS model

International audienceThis paper proposes a general formulation of an elastoplastic model adapted to unsaturated soils. This formulation enters within the framework of two independent state variables descriptions. The choice of a particular effective stress combined with suction is made. The definition of this effective stress is based on the formulation of an equivalent pore pressure which is an essential point of this type of models. It will be discussed in this paper. This general formulation can be seen as a methodology allowing to adapt in a straightforward way most of elastoplastic behaviour models classically used in saturated soils mechanics to unsaturated states. It is shown that this synthesis can include most of recent models developed within the same framework. The last part of this paper is devoted to the adaptation of an existing complex elastoplastic model (CJS model) to unsaturated states using the methodology previously exposed. The model thus obtained is validated on various loading paths including oedometric, isotropic or triaxial compressions and also wetting tests simulating collapse phenomenon. This model extension shows the easiness introduced by the proposed methodology to adapt a given elastoplastic model to unsaturated states. Its validation illustrates by the way the abilities of the extended model to reproduce complex volumetric responses of an unsaturated soil
Effective Stress Concept in Unsaturated Soils: Clarification and Validation of an Unified Framework

The effective stress principle, conventionally applied in  saturated soils, is reviewed for constitutive modelling purposes. The assumptions for the applicability of  Terzaghi’s single effective stress are recalled and its advantages are inventoried. The possible stress  frameworks applicable to unsaturated soil modelling are reassessed in a comparative manner, specifically the  Bishop’s single effective stress, the independent stress variables approach and the generalized stress framework.  The latter considerations lead to the definition of a unified stress context, suitable for modelling soils  under different saturation states. In order to qualify the implications brought by the proposed stress framework,  several experimental data sets are re-examined in the light of the generalized effective stress. The  critical state lines (CSLs) at different saturation states  tend to converge remarkably towards a unique saturated line in  the deviatoric stress versus mean effective stress plane. The effective stress interpretation is also applied  to isotropic paths and compared with conventional net stress conception. The accent is finally laid on a  second key feature for constitutive frameworks based on a unified stress, namely the sufficiency of a unique  mechanical yield surface besides the unique CSL
Nonlinear response of laterally loaded piles and pile groups

In spite of extensive studies on laterally loaded piles carried out over years, none of them offers an expedite approach as to gaining nonlinear response and its associated depth of mobilisation of limiting force along each pile in a group. To serve such a need, elastic-plastic solutions for free-head, laterally loaded piles were developed recently by the author. They allow the response to be readily computed from elastic state right up to failure, by assigning a series of slip depths, and a limiting force profile (LFP). In this paper, equivalent solutions for fixed-head single piles were developed. They are subsequently extended to cater for response of pile groups by incorporating p-multipliers.   The newly established solutions were substantiated by existing numerical solutions for piles and pile groups. They offer satisfactory prediction of nonlinear response of all the 6 single piles and 24 pile groups investigated so far after properly considering the impact of semi-fixed head restraints. They also offer the extent to ultimate state of pile groups via the evaluated slip depths. The study allows ad hoc guidelines to be established for determining input parameters for the solutions. The solutions are tailored for routine prediction of nonlinear interaction of laterally loaded fixed-head piles and capped pile groups.Griffith Sciences, Griffith School of EngineeringFull Tex
On the capillary stress tensor in wet granular materials

This paper presents a micromechanical study of unsaturated granular media in
the pendular regime, based upon numerical experiments using the discrete
element method, compared to a microstructural elastoplastic model. Water
effects are taken into account by adding capillary menisci at contacts and
their consequences in terms of force and water volume are studied. Simulations
of triaxial compression tests are used to investigate both macro and
micro-effects of a partial saturation. The results provided by the two methods
appear to be in good agreement, reproducing the major trends of a partially
saturated granular assembly, such as the increase in the shear strength and the
hardening with suction. Moreover, a capillary stress tensor is exhibited from
capillary forces by using homogenisation techniques. Both macroscopic and
microscopic considerations emphasize an induced anisotropy of the capillary
stress tensor in relation with the pore fluid distribution inside the material.
In so far as the tensorial nature of this fluid fabric implies shear effects on
the solid phase associated with suction, a comparison has been made with the
standard equivalent pore pressure assumption. It is shown that water effects
induce microstrural phenomena that cannot be considered at the macro level,
particularly when dealing with material history. Thus, the study points out
that unsaturated soil stress definitions should include, besides the
macroscopic stresses such as the total stress, the microscopic interparticle
stresses such as the ones resulting from capillary forces, in order to
interpret more precisely the implications of the pore fluid on the mechanical
behaviour of granular materials.Comment: 39 page