2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 11
Presentation Time: 10:55 AM

Discrete Element Modeling of Coupled Processes


MALTHE-SØRENSSEN, Anders, Physics of Geological Processes, University of Oslo, PO BOX 1048, Oslo, 0316, Norway, anders.malthe-sorenssen@fys.uio.no

Discrete element models (DEM) have been widely used to model deformation and fracturing processes in geological materials. A particular strength of the modeling approach is that internal and external surfaces are treated identically, and that the model can handle material behavior ranging from a completely dissociate particle assembly to an elastic body. We have used discrete element models to study the behavior of coupled deformation, fluid-flow and reaction processes ranging from hydro-fracturing, fluidization and fragmentation in fluid-filled solids, to diffusion-reaction processes such as dessication cracking, material decomposition during devolatilization, and hierarchical fracturing and fragmentation in weathering processes. A particular interesting class of processes is coupled diffusion-reaction-fracturing processes where the reaction leads to a change in local volume in the solid. As a fluid diffuses into the solid and reacts it generates stresses which eventually may lead to fracturing of the solid. As a result the boundary conditions for the diffusion-reaction process are changed, hence the need for a coupled model.

We have developed methods to couple a DEM-based description of a deforming solid to a continuum description of a diffusion-reaction process. We have applied this model to study self-propagating fracture fronts observed in drying and cooling fronts, and we demonstrate that the front propagates at a constant velocity with a constant width, contrary to diffusion-dominated processes. Recently, we have also used this model to study weathering and serpentinization processes in which the reaction leads to a local expansion. In this case, we observe both spalling (spheroidal weathering) and hierarchical fragmentation, resulting in a significant acceleration in the propagation of the reaction front, and we argue that this process may provide a first order control on weathering and serpentinization rates.