Gradient-based poroplastic theory

In this work, a thermodynamically consistent gradient-based formulation for partially saturated cohesive-frictional porous media is proposed. The constitutive model includes a local hardening law and a softening formulation with state parameters of non-local character based on gradient theory. Internal characteristic length in softening regime accounts for the strong shear band width sensitivity of partially saturated porous media regarding both governing stress state and hydraulic conditions. In this way the variation of the transition point of brittle-ductile failure mode can be realistically described depending on current confinement condition and saturation level.

The strain localization problem is studied by the spectral analysis of discontinuous bifurcation condition in gradient-based poroplastic media. To evaluate the dependence of the transition point between ductile and brittle failure in terms of the hydraulic and stress conditions, the localization acoustic tensor for discontinuous bifurcation is formulated for both drained and undrained conditions, based on wave propagation criterion.

In this work, two materials models are used in order to describe the inelastic mechanical behavior of both clay and young concrete, within the framework of the theory of porous media, the Modified Cam Clay, which is widely used for saturated and partially saturated soils, and the gradient-dependent Parabolic Drucker-Prager material model for concreter.

To solve the boundary value problems a new finite element formulation for non-local gradient poroplastic materials is proposed. This finite element includes interpolation functions of first order (C1) for the internal variables, while classical C0 interpolation functions for the kinematic and pore pressure fields. The numerical results demonstrate the capabilities of this FE formulation to capture diffuse and localized failure modes of boundary value problems of porous media, depending on the acting confining pressure and on the material saturation degree. leer todo...