About the research
Flows in the Earth's interior are often heterogeneous, with different solid constituents surrounded by fluid or gas.
We classify these flows according to the fraction of space occupied by one constituent (the inclusion) in another:
Isolated inclusions: Even simple geological systems with a low inclusion fraction can exhibit rich flow behavior. To first order, one can study complex pattern formation around an isolated deforming inclusion of variable shape embedded in a matrix of different material properties, where effects related to anisotropy and viscoelasticity may play a significant role. Relevant geological phenomena of such fluid-solid interfaces include: rotation of particles in shear zones (e.g. associated with glacier/rock interfaces or fluid rich debris flows), folding around cracks and stretching of magmatic vesicles.
Suspensions: With larger solid volume fractions, (solid-solid) interactions between inclusions become significant while solid-fluid interfaces still play a strong role. This regime is usually not amenable to analytical treatment, so numerical and/or experimental modeling is required. However, effective media theory can be used to predict the overall effective viscosity. Shear-induced mixing and homogenization processes are particularly interesting for poly-disperse systems and in complex background flow. Direct numerical simulations of such processes are quite challenging due to a large number of particles and unprecedentedly long time series required for reliable statistical analysis of particle dynamics
Granular Material: At still larger solid volume-fractions, the “percolation threshold” can be exceeded, leading to the formation of an extensive network of contacting particles and many clusters. Granular materials are an example, such as the broken debris generated along earthquake faults or in rockslides and the deformation of reservoir rocks. System spanning chains are ubiquitous and the densely packed skeleton is continuously reconfigured during flow. The effective mechanical behavior is dominated by solid-solid interface interactions such as fracturing of grains and frictional interactions at grain contacts leading to strongly non-linear rheological behavior, largely independent of the interstitial fluid.
Intermediate Systems: Many natural systems have intermediate fraction values and exhibit a spectrum of rheological behavior, including concomitant ductile and brittle mechanisms. It is largely unknown how these mechanisms combine, whether shear localization could occur in such systems, and how widely the transition depends on microstructural characteristics such as grain size distribution, aspect ratio or roughness.
