AbstractsEngineering

A coupled constitutive model is developed for describing the flow and deformation behaviours of fractured porous media subject to elasto-plastic damage. Adopting a systematic macroscopic approach, the governing differential equations are derived based on the effective stress concept, equations of static equilibrium, and the conservation of momentum and mass. The constitutive equations are formulated for both intact and damaged materials and take into account the elastic and plastic deformations, continuum damage, permeability evolution and fluid flow. This research focuses on the rigour and consistency in the formulation of the constitutive model and emphasises the identification of all model coefficients in terms of measurable entities. An elasto-plastic damage model is developed for fractured porous media. The elastic-plastic response of stress-strain is captured by a bounding surface plasticity within the critical state framework, while the damage evolution due to hydro-mechanics effects is addressed using a continuum damage model that is distinguished from the existing models by accounting for the plastic hardening parameter, stress ratio, confining pressure and strain rate. The coupling effect of the elastic-plastic response and damage is established by accounting for the effects of plastic volumetric strain and the damage parameter on the hardening of the bounding surface, with the coupling between the fluid flow and deformation addressed using the effective stress concept. The solution for the governing differential equations is obtained numerically by applying the finite element method. The Galerkin method is used for spatial discretisation and the finite difference approach for temporal discretisation. Modified Euler’s integration schemes with an auto error-controlling substepping method are used to integrate the non-linear algebraic equations. Yield surface correction approaches are applied to improve the accuracy of the obtained solutions. To demonstrate the capability of the coupled model, comparisons are made between the model simulations and experimental/numerical results from the literature for different rock materials subject to isotropic and deviatoric loading in drained and undrained conditions. A good agreement between the numerical results and experimental data demonstrates that the proposed model can predict essential characteristics of flow deformation of fractured porous media.