On the strength of transversely isotropic rocks

Abstract

Summary Accurate prediction of strength in rocks with distinct bedding planes requires knowledge of the bedding plane orientation relative to the load direction. Thermal softening adds complexity to the problem since it is known to have significant influence on the strength and strain localization properties of rocks. In this paper, we use a recently proposed thermoplastic constitutive model appropriate for rocks exhibiting transverse isotropy in both the elastic and plastic responses to predict their strength and strain localization properties. Recognizing that laboratory‐derived strengths can be influenced by material and geometric inhomogeneities of the rock samples, we consider both stress‐point and boundary‐value problem simulations of rock strength behavior. Both plane strain and 3D loading conditions are considered. Results of the simulations of the strength of a natural Tournemire shale and a synthetic transversely isotropic rock suggest that the mechanical model can reproduce the general U‐shaped variation of rock strength with bedding plane orientation quite well. We show that this variation could depend on many factors, including the stress loading condition (plane strain versus 3D), degree of anisotropy, temperature, shear‐induced dilation versus shear‐induced compaction, specimen imperfections, and boundary restraints.

A bounding surface model for anisotropically overconsolidated clay incorporating thermodynamics admissible rotational hardening rule

“…A scrutiny of the data from triaxial compression and extension at the start of shearing indicates distinctly diffident dilatancy responses, which reflect the interplay of the initial fabric and loading direction. Although the proposed model can reasonably consider the effect of the initial fabric due to the application of different stress ratios of consolidation, employing an explicit measure of the fabric in constitutive modeling is necessary to simulate a more accurate anisotropic behavior of clays under general loading conditions, like the anisotropy due to the orientation of the bedding plane . While future work is encouraged, the present model framework represents a “smeared” approach to describe the anisotropic behavior of clay in a simple yet efficient way.…”

“…Although the proposed model can reasonably consider the effect of the initial F I G U R E 1 2 Comparison between experimental data and model simulations for constant k consolidated Kaolin clay with various overconsolidation ratio (OCR) values (k = 0.57) A, effective stress paths; B, stress-strain curves fabric due to the application of different stress ratios of consolidation, employing an explicit measure of the fabric in constitutive modeling is necessary to simulate a more accurate anisotropic behavior of clays under general loading conditions, like the anisotropy due to the orientation of the bedding plane. [9][10][11][12] While future work is encouraged, the present model framework represents a "smeared" approach to describe the anisotropic behavior of clay in a simple yet efficient way. Furthermore, the requirement of zero-inclination of the yield surface at the critical state can limit the accumulation of free energy.…”

“…[1][2][3][4][5][6][7] There are two types of fabric anisotropy that can be distinguished: one is the inherent anisotropy that is associated with the deposition history, eg, sedimentation process of soil particles under gravity, and the other is the stress-induced anisotropy due to stress variations with reference to initial state. 8 The natural soil on the ground ubiquitously possesses an inherent Yanni Chen is currently a PhD student at the Northwestern University, USA anisotropy forming in the long geological history, [9][10][11] but the soil fabric could be altered when experiencing the subsequent loading or deformation history, which generates the new fabric anisotropy, referred to as induced anisotropy.…”

Coupled poromechanics‐damage mechanics modeling of fracturing during injection in brittle rocks

“…We extend the fixed-stress method, proposed earlier for isotropic deformation, [36][37][38][39] to model the anisotropic deformation and flow behaviors observed due to microcracking at the reservoir scale 40,41 and the core scale. 42 Role of anisotropy in altering flow patterns 43 and mechanical strength of naturally fractured rocks 44,45 has been emphasized recently. We use the Irwin-Griffith theory 46,47 combined with the continuum damage mechanics (CDM) approach [48][49][50][51][52] to model fracture propagation and associated changes in mechanical and hydraulic properties of the medium.…”

Numerical modelling of damage evolution and fracture propagation in brittle materials

“…Anisotropic damage models for transverse isotropic and orthotropic materials have been proposed by Olsen-Kettle [57][58][59]. A thermoplastic constitutive model [160] for transverse isotropic rocks assumed that the rocks remained transverse isotropic in both their elastic and plastic responses to predict strength and strain localization properties. An anisotropic thermoelastoplastic framework for modelling coupled thermomechanical behaviour in transversely isotropic materials and for predicting the onset of strain localization in the form of a deformation band was studied by Semnani et al [161].…”