J.F. Shao

Modeling of elastoplastic damage behavior of a claystone

This paper is devoted to the constitutive modeling of coupled elastoplastic damage in a hard claystone. A summary of experimental data, obtained from triaxial compression tests including unloading cycles, is first presented. These results show an important plastic deformation, which is coupled with an induced anisotropic damage. The damage is due to initiation and growth of oriented microcracks and manifested as directional deterioration of elastic properties. Influences of mineral compositions and water content on the mechanical behaviour are also investigated. A constitutive model is then proposed for the description of plastic deformation and induced damage. The plastic behaviour is described by a typical cohesive-frictional model. The material damage is represented by a second rank symmetric tensor. The damage evolution rate is related to both elastic and plastic strains. The damage effect on plastic flow is also considered. A simple procedure for the determination of model parameters from standards tests is proposed. The validity of the model is tested for different loading paths by comparing numerical simulations and experimental data.

Modeling of creep in rock materials in terms of material degradation

In this paper, we present a constitutive model for creep deformation in rock materials. Starting from an elastoplastic model for the description of short term behavior, the time-dependent deformation is described in terms of evolution of microstructure, leading to progressive degradation of elastic modulus and failure strength of material. The proposed model is applied to predict material responses in creep and relaxation tests. There is a good agreement between numerical simulations and experimental data. The proposed model is able to describe the main features observed in most cohesive frictional geomaterials (rocks and concrete), such as plastic deformation, damage, volumetric dilation, pressure sensitivity, rate dependency and creep.

Assessment of some failure criteria for strongly anisotropic geomaterials

This paper is devoted to the assessment of some representative failure criteria in the framework of modelling the failure behaviour of strongly anisotropic geomaterials. Experimental data concerning the failure behaviour of a typical strongly anisotropic rock; the schist of Angers are first presented. Nine widely used failure criteria are then selected and classified into three groups, the mathematical continuous models, the empirical continuous models and the discontinuous weakness planes based models. This classification is made up according to the main assumptions and techniques used in each criterion to describe the strength anisotropy. The calibration of each one is carried out with respect to the laboratory data of Angers schist. Qualitative and quantitative comparisons between the selected criteria and with the experimental data are provided.

A continuum damage constitutive law for brittle rocks

Abstract The non-linear mechanical behaviour of two different granites was investigated. Short term triaxial tests have been performed in order to study the short term behaviour (instantaneous growth of cracks) of the rock. A continuous damage model is then proposed. The internal damage variable is directly related to the second order crack density tensor used by Kachanov in the study of effective elastic properties of cracked solids. An instantaneous crack growth criterion has been used to describe the time-independent evolution of the damage tensor. The verification of the model has been performed for various loading paths. The results of a numerical modelling show that it is possible to reproduce most of the observable characteristics of damaged zone around an underground opening excavated into brittle rocks.

Modelling of induced anisotropic damage in granites

This paper deals with numerical modelling of induced damage in three granites. A continuous anisotropic damage model is proposed in the framework of thermodynamics and fracture mechanics. A second rank tensor is used to describe damage state which is directly related to orientation and density of microcracks. Both time independent and time dependent (or sub-critical) growth of microcracks are taken into account. A simple procedure for the determination of model parameters from standard laboratory tests is proposed. Comparisons between model simulation and experimental data are presented for some basic loading paths. Finally the application of the model to stability analysis of the Mine-by test tunnel of the URL in Manitoba (Canada) is presented. A comparison between numerical predictions and in situ observations makes it possible to evaluate the performance of the proposed model.

Study of poroelasticity material coefficients as response of microstructure

Using an asymptotic homogenization method, the effect of the porous medium microstructure on the values of poroelastic coefficients is studied in this paper. First, the Biot’s poroelasticity theory and general relations linking the macroscopic poroelastic coefficients with the averaged micromechanical solutions are recalled. Considering a variational formulation of appropriate boundary values problems stated for the representative volume element, microstructural parameters affecting the values of poroelastic coefficients are identified. In order to clarify specific roles of some relevant microstructure parameters, numerical investigations for some simplified pores geometries are presented. The numerical results obtained clearly show a strong dependence of the poroelastic coefficients on the internal geometry of pores as well as on the global porosity of the medium. In the last part, based on the micromechanics analysis, the definition of initial plastic yield condition for saturated porous media is introduced and a new interpretation of the effective stress concept in inelastic domain is proposed. Copyright

Experimental and numerical investigations on transient creep of porous chalk

Abstract A set of hydrostatic and triaxial creep tests has been performed on a white porous chalk. The results obtained show important creep deformations in this rock. In the present paper we study the transient creep only, since in the time intervals considered it was the only one exhibited by the rock. A constitutive equation is developed using the general theory proposed by Cristescu (1994, Int. J. Plasticity 10(2), 103–132). The yield function and viscoplastic potential are determined from the data obtained in creep tests. The proceduce for the determination of the model parameters is directly related to the way in which the model is step by step build up. Comparisons between the model predictions and the experimental data will be shown.

Prediction of rock burst classification using the technique of cloud models with attribution weight

Rock burst is one of the common failures in hard rock mining and civil construction. This study focuses on the prediction of rock burst classification with case instances using cloud models and attribution weight. First, cloud models are introduced briefly related to the rock burst classification problem. Then, the attribution weight method is presented to quantify the contribution of each rock burst indicator for classification. The approach is implemented to predict the classes of rock burst intensity for the 164 rock burst instances collected. The clustering figures are generated by cloud models for each rock burst class. The computed weight values of the indicators show that the stress ratio

An Experimental Investigation and an Elastoplastic Constitutive Model for a Porous Rock

Ts = \sigma_{\theta } /\sigma_{c}