Coupling a fluid phase with a discretised solid phase: Benchmarking a Computational Fluid Dynamics-Discrete Element Methods (CFD-DEM) model with analogue experiments

Surface deformation measured from satellites has provided useful information about the magma plumbing system at active volcanoes. Observed deformation results from complex interactions and coupling between the magma and the host rock. Fracturing of the crust during its deformation can make the pattern of surface displacement even more complex. Models taking into account both the fluid and solid phases of natural systems and linking them are a crucial next step for a better understanding of natural systems and observed deformation. We use the software MFiX (Multiphase Flow with Interphase eXchanges) which considers two phases: a fluid phase computed with a Computational Fluid Dynamics (CFD) method, and a solid phase discretized as spherical particles computed using Discrete Element Methods (DEM) method. Spherical particles are bonded together. Bonds can break at any time step, such that actual fractures can develop through the simulations. We present here the modified drag force between fluid and particles that allows us to model a bonded packing of particles impermeable to a fluid phase. Reproducing a set of analogue experiments, we simulate the injection of fluid in a spherical cavity. Rock tests implemented in MFiX allow us the precise calibration of the packing to the gelatine mechanical properties. The injected volume, the cavity dilatation, the fluid pressure evolution and the surface deformation are measured in the numerical modelling and compared to analogue experiment for benchmarking. We show that this new model has the potential to model the magmatic phase and coupling it to the elastic and brittle deformation of the surrounding rock.