Numerical Analysis of Chemo-Mechanical Couplings in Geomaterials at the Microscale

Abstract

To reduce the impact of human activities on climate change, engineering applications envision the injection of fluid into an underground reservoir, resulting in a modification of the chemistry. This destabilization instigates an evolution of the microstructure of the host material through local dissolution/precipitation reactions, impacting the mechanical parameters at the sample scale. The development and application of numerical models, which explicitly describe the microstructure, have emerged as a promising method for enhancing our comprehension of the interactions between mechanics and chemistry along the different scales involved. Indeed, the local addition/removal of mass (chemistry) occurs at the scale of the grains. Subsequently, the mechanical properties at the sample scale evolve while the morphology of the grains and the microstructure are modified.This study focuses on three phenomena involving chemo-mechanical couplings: the debonding, the hydration of a cement-based material, and the pressure-solution phenomenon. In these investigations, the chemistry is captured with a Phase-Field description, while the mechanics are modeled with a Discrete Element Model. Furthermore, these formulations have been coupled to develop the Phase-Field Discrete Element Model, a formulation available to capture (i) granular reorganization, (ii) irregular grain shape, (iii) force transmitted at the contacts, (iv) heterogeneous dissolution/precipitation, (v) diffusion of the solute in the pore space and (vi) rate-limiting processes. This study depicts the pivotal impact of chemistry on the mechanical characteristics of a geomaterial. Notably, the state of stress of a cemented granular material appears impacted by the dissolution of bonds. In a similar vein, the mechanical properties of a cement-based material can be deduced from the evolution of the microstructure modeled explicitly during the hydration process. Finally, the novel Phase-Field Discrete Element Method has been calibrated and validated with experimental data available in the literature for the pressure-solution phenomenon. Furthermore, the impact of the precipitation and granular reorganization, which have been frequently neglected in the literature, on creep behavior due to pressure-solution has been emphasized.