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Design of the compression tests on transversely isotropic rocks with different bedding angles and confining pressures.
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It is of great significance to develop a failure criterion that can describe the orientation-dependent behavior of transversely isotropic rocks. This paper presents a simplified parabolic model that is successful in predicting the strengths of rocks under different confining pressures and bedding angles. The model is a modified version of the norma...
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Citations
... Mechanical properties of the rocks that make up the geological section were taken in accordance with the laboratory test results [27,28]. Determination of the stress-strain state of rocks was based on the model of an ideal elastic-plastic medium, which, in the area of compressive stresses, was implemented in the variant of the parabolic Coulomb -Mohr criterion [29]: In physical terms, plastic deformation zones in the areas of compression and tension are associated with fracturing due to the development of shear and rupture fractures. ...
In favourable mining conditions, in particular at the Starobinskoye potash deposit (Belarus), longwall mining systems are used. They cause a high human-induced load on the subsoil, including intense deformation of the ground surface. The presented investigations are aimed at studying the dynamics of the ground surface displacement during the longwall face advance. Mathematical modelling was carried out in an elastic-plastic formulation with numerical implementation by the finite element method. The condition for the roof rocks collapse was opening of the contact between the seams when its boundaries were reached by shear fractures or formation of the tensile stresses area at the outcrop. With the working front advance, an increase in subsidence is observed, followed by its stabilization to a value determined by the process parameters of mining operations and the physical and mechanical properties of collapsed rocks. In this case, each point of the ground surface experiences sign-alternating horizontal deformations: when the front approaches, it causes tension, and when it moves away, compression. The obtained results of mathematical modelling are in good agreement with the data of instrumental measurements of the ground surface displacements, which indicates the adequate description of the rock mass deformation during the slice excavation of sylvinite seams by longwall faces.
... Due to structural heterogeneity of salt rocks two indicators are usually used: uniaxial compressive ( c ) and tensile ( t ) strength. S In this regard, the strength of salts is mainly described by the linear Mohr-Coulomb criterion [13] or its parabolic analogue [14]. These criteria generally provide an acceptable assessment of the ultimate stress-strain state of salt rocks. ...
... Their use is complicated by large number of parameters. One of the frequently applied parabolic criteria in rock strength certificates (including salts) is the parabolic envelope of Mohr circles [14]. It assumes that the Mohr circles under uniaxial compression and tension are tangent to the envelope. ...
The study of salt rocks deformation and fracture processes is an essential part of mining parameters justification for mineral salt deposits. The results of uniaxial compression tests on large salt rock specimens are presented as a loading curve and diagrams of the transverse-longitudinal displacements at various distances from the side faces. Based on an isotropic elastoplastic model, a multivariant numerical simulation was performed. Its purpose was to select of fracture criteria that accurately describe the loading diagram of specimen and its transverse-longitudinal deformations. The following fracture criteria are considered: Tresca with the associated plastic flow rule, the associated and non-associated Mohr-Coulomb, the parabolic analogue of Mohr-Coulomb criterion and the volumetric fracture criterion. Numerical simulation was carried out by the displacement-based finite element method. Three-dimensional hexahedral eight-node isoparametric elements were used for discretization of the solution domain. It has been established that within the elastoplastic model of media the process of uniaxial compression of a large cubic salt rock specimen is adequately described by the linear Mohr-Coulomb fracture criterion with the non-associated plastic flow, as well as by the associated volumetric parabolic yield criterion with the linear isotropic hardening.
... We then plot the obtained flow stresses with respect to the confining pressures (see Fig. 9), where the best fit function is a parabola. This recovers the parabolic failure criterion, recently suggested and experimentally verified (see Yuan et al. (2020), Wang et al. (2019), Singh and Rao (2005)). This also captures the transition from a linear behavior at low confining pressures to a pressure-insensitive behavior for high confinement (Yuan et al. (2020)). ...
The influence of the microstructural geometry on the behavior of porous media is widely recognized, particularly in geomaterials, but also in biomaterials and engineered materials. Recent advances in imaging techniques, such as X-ray microcomputed tomography, and in modeling make it possible to capture the exact morphometry of the microstruc-ture with high precision. However, most existing continuum theories only partially account for the morphometry. We propose here a unifying approach to link the strength of porous materials with the necessary and sufficient microstruc-tural information, using Minkowski functionals, as per Hadwiger's theorem. A morphometric strength law is inferred from synthetic microstructures with a wide range of porosities and heterogeneities, through qualitative 2D phase-field simulations. Namely, the damage is modeled at the microstructural level by tracking the solid-pore interfaces under mechanical loading. The strength is found to be best described by an exponential function of the morphometers, thus generalizing early works on metals and ceramics. We then show that the predictiveness of this relationship extends to real porous media, including rocks and bones.
... The linear M-C criterion uses only a linear failure envelope, which makes it more consistent with the typical failure line at low confining pressures. However, as shown in Figure 1, the gradient of typical failure envelope tends to decline under higher confining pressures, which means that with the increase of confining pressures, the increase rate of rock strength gradually declines [31,32]. In this case, the linear M-C criterion is inaccurate to characterize rock failure under higher confining pressures. ...
The failure criterion of rocks is a critical factor involved in reliability design and stability analysis of geotechnical engineering. In order to accurately evaluate the triaxial compressive strength of rocks under different confining pressures, a nonlinear empirical strength criterion based on Mohr-Coulomb criterion was proposed in this paper. Through the analysis of triaxial test strength of 11 types of rock materials, the feasibility and validity of proposed criterion was discussed. For a further verification, six typical strength criteria were selected, and the prediction results of each criterion and test results were statistically analyzed. The comparative comparison results show that the prediction results obtained by applying this new criterion to 97 conventional triaxial compression tests of 11 different rock materials are highly consistent with the experimental data. Statistical analysis was executed to assess the application of the new criterion and other classical criteria in predicting the failure behavior of rock. This proposed empirical criterion provides a new reference and method for the determination of triaxial compressive strength of rock materials.
Using the example of the Tyubegatan potash deposit (Uzbekistan), a complex of geophysical and geomechanical safety assurance for mining operations in conditions of the complex tectonic structure of the undermined rock mass is considered. Geophysical research included ground-based seismic surveys using a profile system in combination with «light» standard electro- and gravimetric techniques. Based on the results of these works, a physical and geological model of the deposit areas was built with the weakened zones and faults localization. As part of the meaningful interpretation, the physical and geological model was transformed into a geomechanical calculation scheme, which reflected the main mining-geological and mining-technical condition of development and was based on a model of elastoplastic deformation of salt rocks. The geomechanical model was calibrated from radar interferometric surveys. The time factor was taken into account in accordance with the developed modification of the well-known method of variable deformation modules. The formation of plasticity zones in physical terms was identified with the formation of fracturing areas in the water protection layer, which determine the danger of violating its continuity. Numerical implementation of the geomechanical model using the finite element method made it possible to substantiate the optimal parameters of the chamber development system, ensuring the safety of the water protection layer, including fault zones.
A failure criterion fully considering the anisotropy and hydration of shale is essential for shale formation stability evaluation. Thus, a novel failure criterion for hydration shale is developed by using Jaeger’s shear failure criterion to describe the anisotropy and using the shear strength reduction caused by clay minerals hydration to evaluate the hydration. This failure criterion is defined with four parameters in Jaeger’s shear failure criterion (S1, S2, α and φ), three hydration parameters (k, ωsh and σs) and two material size parameters (d and l0). The physical meanings and determining procedures of these parameters are described. The accuracy and applicability of this failure criterion are examined using the published experimental data, showing a cohesive agreement between the predicted values and the testing results, R2 = 0.916 and AAREP (average absolute relative error percentage) of 9.260%. The error (|Dp|) is then discussed considering the effects of β (angle between bedding plane versus axial loading), moisture content and confining pressure, presenting that |Dp| increases when β is closer to 30°, and |Dp| decreases with decreasing moisture content and with increasing confining pressure. Moreover, |Dp| is demonstrated as being sensitive to S1 and being steady with decrease in the data set when β is 0°, 30°, 45° and 90°.
The influence of the microstructural geometry on the behavior of porous media is widely recognized, particularly in geomaterials, but also in biomaterials and engineered materials. Recent advances in imaging techniques, such as X-ray microcom-puted tomography, and in modeling make it possible to capture the exact morphom-etry of the microstructure with high precision. However, most existing continuum theories only partially account for the morphometry. We propose here a unifying approach to link the strength of porous materials with the necessary and sufficient microstructural information, using Minkowski functionals, as per Hadwiger's theorem. A morphometric strength law is inferred from synthetic microstructures with a wide range of porosities and heterogeneities, through qualitative 2D phase-field simulations. Namely, damage is modeled at the microstructural level by tracking the solid-pore interfaces under mechanical loading. The strength is found to be best described by an exponential function of the morphometers, thus generalizing early works on metals and ceramics. We then show that the predictiveness of this relationship may extend to real porous media, including rocks, bones, and ceramics.
Les formations argileuses profondes telles que celles du Callovo-Oxfordien (COx) sont une des options actuellement envisagées pour le stockage des déchets radioactifs en France par l’Agence nationale pour la gestion des déchets radioactifs. Les observations (déformation, pression interstitielle, …) menées à l’échelle des ouvrages in situ du laboratoire de recherche souterrain de Meuse/Haute-Marne ont, cependant, révélé un comportement hydromécanique complexe avec une fracturation induite fortement anisotrope que les modèles constitutifs classiques ont du mal à appréhender. Le travail de cette thèse s’est focalisé sur la formation des zones de fractures connectées et discrètes induites par l’excavation et leurs conséquences sur les propriétés de transports. Sur la base des résultats expérimentaux et des modèles rhéologiques récents pour cette roche, il a été proposé un modèle macroscopique anisotrope, élastoplastique et endommageable qui décrit les mécanismes clés du comportement à court terme (pré et post-pic) de l’argilite du COx. Ce modèle a été implémenté dans Comsol Multiphysics®. L’application du modèle proposé a été menée sur la galerie GCS du LS M/HM par de simulations hydromécaniques en conditions saturées. Les résultats numériques ont été confrontés avec succès aux observations et mesures in situ en termes, notamment, de distribution de pression de pore et d’extension de ZFC/ZFD (approchée par les zones plastiques en post-pic et pré-pic, respectivement) et de convergences horizontale et verticale. Enfin, le caractère opérationnel du modèle pour des applications de modélisation thermo-hydro-mécanique d’alvéoles HA (projet Cigéo) a été étudié sur une géométrie réduite à un micro-tunnel d’alvéoles.
