FAILURE PROCESSES AND LOCALIZATION ANALYSIS OF PARTIALLY SATURATED MATERIALS BASED ON THERMODYNAMICALLY CONSISTENT GRADIENT POROPLASTIC THEORY

G.J. ETSE; J.L. MROGINSKI

Ibiza

Conferencia; V International Conference on Coupled Problems in Science and Engineering (COUPLED 2013); 2013

International Center for Numerical Methods in Engineering.

Failure processes of partially saturated porous material such as soils and concrete are evaluated by means of a thermodynamically consistent gradient poroplastic constitutive theory proposed by the authors. The general case of open porous media is followed which allows the consideration of heterogeneous fluid mass interacting with the surrounding media. A restricted form of gradient formulation is considered whereby the kinematic fields remain local while the state parameters are the only ones of non-local character. To predict the failure behavior of soil materials the cam-clay model is reformulated within the framework of the gradient poroplastic theory proposed by the authors. Thereby, the stress dissipations in hardening and softening regimes are derived from the free energy density in a consistent way with the thermodynamic foundation of the constitutive theory. A local and a non-local gradient poroplastic formulations are considered for the hardening and softening laws of the model, respectively. The gradient characteristic length in the post-peak regime is formulated in terms of both the governing stress and the hydraulic conditions to realistically capture the involved shear band width of porous materials during localized failure processes. After describing the main features of the constitutive model, the attention focuses on the localization analysis in the form of discontinuous bifurcation. The localization properties of the thermodynamically consistent gradient theory for porous material in this work are analytically and numerically evaluated. To this end, the conditions for discontinuous bifurcation of the fluid and solid phases of the particular non-local constitutive theory in this work are formulated. The localization analyses are performed for both, drained and undrained conditions. The results demonstrate the strong sensitivity of the localization properties of partially saturated porous materials to the governing hydraulic conditions and stress state.