Chemo-Hydro-Mechanical variational phase-field fracture model

We present a fully coupled chemo-hydro-mechanical variational phase field model for simulating fracture initiation and propagation, including chemical reactions in cementitious systems. Using a staggered approach, we coupled three subprocesses: (i) fluid flow in porous media, (ii) reactive transport, and (iii) mechanical deformation of fractured porous media using a variational phase field. The geochemical package PHREEQC was coupled in an operator-splitting approach with a finite element transport solver to calculate chemical reactions in thermodynamic equilibrium (dissolution or precipitation), considering changes in porosity. Mechanical deformation and fluid flow were coupled using the fixed-stress splitting approach. For chemical damage, we introduced a variable to a constitutive relation representing a degree of chemical damage ranging from zero (intact) to one (damaged material). This chemical damage variable represents changes in porosity caused by chemical reactions independently from the phase field variable that represents the mechanical damage.

Additionally, as effective diffusion and hydraulic conductivity increase in the presence of fracture and changes in porosity, the phase field variable and chemical damage should impact the hydraulic conductivity and the diffusion coefficient. We conducted different benchmarks to demonstrate the model's capabilities and properties in capturing fracture initiation and propagation due to chemical reactions. The proposed model was implemented in the open-source finite element framework OpenGeoSys.