Aide au dimensionnement de l'exploitation de marbre en carrières souterraines par modélisation numérique

National audienceCe travail s'inscrit dans le cadre d'un programme européen dont l'objectif était de développer un savoir-faire pour le dimensionnement des exploitations de marbre en carrière souterraine. Nous avons étudié l'impact de la fracturation sur la rentabilité et la sécurité des chantiers. Le logiciel RESOBLOK, développé par PINERIS au sein du LAEGO, a été utilisé pour simuler la fracturation du milieu de façon déterministe ou statistique à partir d'une mesure adéquate de ces caractéristiques in situ, puis pour améliorer la rentabilité des exploitations en déterminant la géométrie des travaux (orientation des galeries, choix des extensions) qui maximise la taille des blocs récupérés et minimise le coût du renforcement nécessaire par garantir la sécurité des chantiers

Nonlinear mechanical and poromechanical analyses : comparison with analytical solutions

International audienceThe validation of computational schemes for modelling multiphysic phenomena in porous geomaterials is a key importance in geoenvironmental applications. This paper focuses on the vadiation of nonlinear and coupled hydromechanical schemes by comparing the results of numerical predictions performed with COMSOL and the mathematical solutions. Firstly, we simulate the nonlinear mechanical behaviour of rock mass around a deep cylindrical hole. The second example treats on the simulation of the well-known one-dimensional consolidation of a column of saturated porous rock. Finally a validation of poroelastic calculations based on the drainage of a cylindrical hole in porous media is achieved by comparison to an existing analytical solution

Effets prévisibles en surface et traitement de galeries minières creusées à faible profondeur dans les grès vosgiens

17 pages et 7 figuresNational audienceThe conditions of the stability of the drifts excavated in the Vosges sandstones, that might be modified by overburden weakening and/or flooding of drifts, have been analysed. The effects of potential instabilities on the surface level have also been quantified. In the worst case, the performed analysis predicts formation of a sinkhole at soil surface only if the drifts are very close to the surface and in case the mechanical properties of the sandstones and those of natural discontinuities are very poor. Beyond eight meters of depth, evolution of collapse arch is stopped prior to reaching soil surface, as a matter of dilatancy of collapsed strata. The “Houillères du Bassin de Lorraine” uses these results for safety assessment of the drift belonging to mining infrastructure such as old drift FALCK driven in 19th century for water seepage

3D simulations of an injection test done into an unsaturated porous and fractured limestone

We have developed a numerical model to represent the effect of injection test in unsaturated porous and fractured rock mass. The test was conducted at the LSBB (Laboratoire Souterrain à Bas Bruit) site close to Rustrel, Vaucluse, France in the field of the French ANR project called 'HPPP-CO2'. The results underline the impact of fractures on the hydro-mechanical response of the rock mass. Indeed fractures allow a faster dissipation of the water pressures and stress variations induced by the water injection. Back analysis lead us to also estimate the rock mass intrinsic permeability and compressibility of the injected laye

Interprétation d'essais dilatométriques réalisés dans un pilier abandonné par modélisation numérique

International audienceDilatometer tests were carried out in an abandoned pillar of a Lorraine iron basin to characterize the in situ iron ore. Modules of deformability and their variability were determined using the traditional approach. A more comprehensive interpretation, based on numerical modeling and inverse methods, made it possible to estimate the strength properties of the in situ iron ore.Des essais dilatométriques ont été réalisés dans un pilier abandonné du bassin ferrifère lorrain dans le but de caractériser le minerai de fer in situ. Les modules de déformabilité et leur variabilité ont été déterminés par l'approche classique. Une interprétation plus complète, basée sur la modélisation numérique et la méthode inverse, a permis d'estimer les caractéristiques de résistance du minerai de fer in situ

Elaboration et utilisation d'un modèle représentatif pour optimiser le soutènement des galeries minières profondes

The use of a same roadway to serve two workings allows to reduce the mining costs. However, at great depth, the roadways behavior become bad and their treatment have to be adapted. In-situ measurements and numerical modelling have allowed to understand the main deformation mechanisms. On this base, treatment modifications have been tested using UDEC code.L'utilisation d'une même galerie pour desservir deux chantiers d'exploitation présente des avantages économiques évidents. A forte profondeur cependant, le comportement des voies se dégrade et le soutènement habituellement mis en oeuvre n'est pas toujours bien adapté. La combinaison des mesures in situ et de la modélisation numérique a permis de déterminer les mécanismes principaux de déformation de ces voies. Sur cette base, deux modifications de leur soutènement ont été testées numériquement à l'aide du logiciel UDEC

Les apports de la modélisation numérique des massifs rocheux discontinus pour l'étude du renforcement par boulonnage des ouvrages miniers

Le renforcement des massifs rocheux fracturés au moyen des techniques de boulonnage est le plus souvent étudié et déterminé par référence aux "règles de l'Art" c'est-à-dire par des approches de nature empirique. Au cours de ces dernières années, profitant des nouveaux développements de l'informatique, une volonté de systématisation assez poussée, en quelque sorte de "domestication" de l'empirisme, a vu le jour (Piguet, 1995). Elle a en particulier conduit à la réalisation de systèmes-experts, ou de systèmes d'aide à la décision, avec de nombreuses applications dans le domaine minier

Hydromechanical interactions in a fractured carbonate reservoir inferred from hydraulic and mechanical measurements

10 pagesInternational audienceHydromechanical coupled processes in a shallow fractured carbonate reservoir rock were investigated through field experiments coupled with analytical and numerical analyses. The experiments consist of hydraulic loading/unloading of a water reservoir in which fluid flow occurs mainly inside a heterogeneous fracture network made up of vertical faults and bedding planes. Hydromechanical response of the reservoir was measured using six pressure–normal displacement sensors located on discontinuities and two surface tiltmeters. A dual hydraulic behavior was characterized for low-permeability bedding planes well connected to highpermeability faults. Displacement responses show high-variability, nonlinear changes, sometimes with high-frequency oscillations, and a large scattering of magnitudes. Initial normal stiffnesses and effective normal stresses along fault planes were estimated in the field by interpreting pressure–normal displacement relations with a nonlinear function between effective normal stress and normal displacement. Two-dimensional discontinuum modeling with transient fluid flow was performed to fit measurements during hydraulic loading tests. Results show that the hydromechanical behavior of the reservoir is restored if a high stiffness contrast is allocated between low- and high-permeability discontinuities. Thus, a dual-permeability network of discontinuities will likely also be a contrasting stiffness network, in which the deformation of major flow-conducting discontinuities is significantly influenced by the stiffness of the surrounding less-permeable discontinuities

Hydromechanical modeling of pulse tests that measure both fluid pressure and fracture-normal displacement of the Coaraze Laboratory site, France

21International audienceIn situ fracture mechanical deformation and fluid flow interactions are investigated through a series of hydraulic pulse injection tests, using specialized borehole equipment that can simultaneously measure fluid pressure and fracture displacements. The tests were conducted in two horizontal boreholes spaced one meter apart vertically and intersecting a near-vertical highly permeable fault located within a shallow fractured carbonate rock. The field data were evaluated by conducting a series of coupled hydromechanical numerical analyses, using both distinct-element and finite-element modeling techniques and both two- and three-dimensional model representations that can incorporate various complexities in fracture network geometry. One unique feature of these pulse injection experiments is that the entire test cycle, both the initial pressure increase and subsequent pressure fall-off, is carefully monitored and used for the evaluation of the in situ hydromechanical behavior. Field test data are evaluated by plotting fracture normal displacement as a function of fluid pressure, measured at the same borehole. The resulting normal displacement-versus-pressure curves show a characteristic loop, in which the paths for loading (pressure increase) and unloading (pressure decrease) are different. By matching this characteristic loop behavior, the fracture normal stiffness and an equivalent stiffness (Young's modulus) of the surrounding rock mass can be back-calculated. Evaluation of the field tests by coupled numerical hydromechanical modeling shows that initial fracture hydraulic aperture and normal stiffness vary by a factor of 2 to 3 for the two monitoring points within the same fracture plane. Moreover, the analyses show that hydraulic aperture and the normal stiffness of the pulse-tested fracture, the stiffness of surrounding rock matrix, and the properties and geometry of the surrounding fracture network significantly affect coupled hydromechanical responses during the pulse injection test. More specifically, the pressure-increase path of the normal displacement-versus-pressure curve is highly dependent on the hydromechanical parameters of the tested fracture and the stiffness of the matrix near the injection point, whereas the pressure-decrease path is highly influenced by mechanical processes within a larger portion of the surrounding fractured rock

Simulation of CO2 storage in coal seams: Coupling of TOUGH2 with the solver for mechanics CODE_ASTER®

A symposium on applications and enhancements to the TOUGH codes for multiphase fluid, heat, and chemical transport at the Lawrence Berkeley National Laboratory (LBNL)International audienceAmongst the various geological storage options currently under consideration, CO2 storage in coal formations presents the most economic potential for middle-term spreading but also the most uncertainties and technical difficulties. This study (part of the CARBOLAB project) investigates coupled flow and mechanical processes that will take place around the injection point at the bottom of the Montsacro mine in Asturias, Spain. In order to quantify the strain and stress fields due to changes in the fluid pressure field and to account for stress/sorption dependent porosity/permeability effects, an efficient coupling between TOUGH2/EOS7C, a special module with an Extended Langmuir Sorption model, and the solver for mechanics CODE_ASTER® has been developed by BRGM