A coupled poroplastic damage model accounting for cracking effects on both hydraulic and mechanical properties of unsaturated media

Abstract

SUMMARYDamage induced by microcracking affects not only the mechanical behaviour of geomaterials but also their hydraulic properties. Evaluating these impacts is important for many engineering applications, such as the safety assessment of radioactive waste disposal facilities. This paper presents a new constitutive model accounting simultaneously for the impact of damage on hydraulic and mechanical properties of unsaturated poroplastic geomaterials. The hydro-mechanical coupling is formulated by means of the thermodynamic framework for partially saturated media, extended by taking into account isotropic damage and plasticity. State and complementary laws are governed by the so-called plastic effective stress and equivalent pore pressure. Assuming a bimodal pore size distribution for cracked porous media, the hydraulic part (water retention curve and hydraulic conductivity) is modelled using phenomenological functions of damage variable. The participation of damage on both mechanical and hydraulic part enables this model to describe bilateral couplings between them. This coupled model is then validated against a number of experimental data obtained from Callovo-Oxfordian argillite, which is the possible host rock for a radioactive waste disposal in France. Parametric studies are also carried out to check the consistency and to better demonstrate the bilateral couplings in the model.

Modelling the poroplastic damageable behaviour of earthen materials

“…One possible explanations is that some form of localization may appear, which cannot be simulated by a purely continuous modelling approach. Note that this kind of deviation is also faced with in previous modelling work [27,29]. Figure 6a, b shows the results of triaxial compression tests and model simulations of Lim at 600 kPa confining pressure.…”

“…Zhang et al [28] developed a unified elastic-viscoplastic damage model to describe long-term hydromechanical behavior of argillites under unsaturated condition. Bui et al presented a new constitutive model accounting simultaneously for the impact of damage on hydraulic and mechanical properties of unsaturated poroplastic geomaterials, by means of the thermodynamic framework for partially saturated media [29]. The present work follows a similar path of this last reference.…”

“…C e is the elastic compliance matrix which is usually expressed in terms of the bulk and shear moduli K and G. To account for the effects of damage on the stressdependent elastic properties, the following expressions are adopted based on the previous results of [23,27,29]:…”

“…The damage force Y D is assumed to depend on the tensile parts of principal strains defined above and a simple damage criterion is proposed in the following form based on [26,28,29]:…”

An enhanced sequential fully implicit scheme for reservoir geomechanics

“…A linear dependency of φ p on pv is written as: (22) where the parameter α p shares the same restrictions of α, i.e. φ • ≤ α p ≤ 1 [49,57]. This parameter is identified as the plastic effective stress coefficient [58,57] or nonlinear Biot parameter [59].…”