Modelling complex fault systems with the Particle Finite Element Method (P-FEM)

Developing numerical models of faulting in the upper crust remains a challenge due to limitations in numerical algorithms and problems in choosing realistic constitutive models. This results in strong limitations when trying to model the strain and stress fields, and elastic and plastic energy release (i.e. stress times strain), under realistic parametrization obtained from lab experiments, particularly regarding mechanical and chemical weakening that leads to localization as observed in nature.

Here we explore applications of the Geotechnical Particle Finite Element Method (P-FEM), a large-deformation numerical tool developed to capture detailed progressive failure and fracturing using a non-local formulation.

P-FEM allows modelling localized shear bands that naturally emerge independent of mesh discretization, both in thickness and orientation. Moreover, continuous remeshing in a Lagrangian framework enables modeling of large deformations, and techniques used to minimize numerical diffusion help produce realistic localized shear/fault zone patterns.

The elastoplastic constitutive models can be calibrated using multi-method lab tests (e.g. monoaxial, triaxial, Brazilian, oedometer, etc.) to include complex non-linear effects, such as strain weakening and softening, poroelasticity, strength envelopes with a cap (i.e. porosity collapse in compression), and mechano-chemical degradation. This allows for realistic simulations of geo-materials with contrasting properties, including non- or weakly-cohesive fault gouges, weak porous rocks, and stronger brittle frictional-plastic materials.

After an overview of the method, we will show how P-FEM is particularly suited for investigating deformation in the upper crust including (i) fault nucleation and growth in mechanically layered materials, (ii) the interplay between faulting and folding in thrust belts, and (iii) the development of fault damage and/or process zones in materials with heterogeneous mechanical properties.