ROLE OF PROGRESSIVE ROCK FATIGUE AND FAILURE IN FLUID FLOW SELF-FOCUSING AND ASSOCIATED WEATHERING IN THE CRITICAL ZONE (Invited Presentation)

The Critical Zone is dominated by chemomechanical interactions between water, life, soil and rock. The biosphere cycles at rapid rates (days to decades). Water in the critical zone changes chemically and physically at time scales of days to millenia – but chemomechanical feedbacks in the geosphere range in timescale from minutes (landslides and elastic response) to years to 100,000s years, depending on stress state, availability of water, and available water-rock interactions. On short time scales, chemomechanical rock processes may disrupt and reset hydro-biological processes. At long time-scales, chemomechanical rock processes control material properties such as strength, permeability, porosity, and specific surface area by producing sediment, fractures, and weathering alterations. The material properties controlled by chemomechanical processes are assumed to be constant in time when in hydro-biological studies. However, there are positive feedbacks between the long-term chemomechanical evolution of the rocks and sediments, and the hydro-biological cycling, where the creation of new fractures or sediment creates preferential flow-paths and biological hotspots, which in turn may lead to faster chemomechanical coupling. The system may self-focus flow, fracture and biological cycling into localized zones. To explore these direct feedbacks, we examine the formation of fractures under hillslopes, as proposed in St. Claire et al. (2015) through a combination of approaches. One approach is to model groundwater-level change and surface-loading (snow or biota) driven high-cycle count fatigue fracture using a phase field model of fatigue fracture coupled with porous media and fracture flow in a multiphysics finite element model. The other approach is to examine changes in chemomechanically assisted fatigue fracture vs. dissolution/mineralization rates in the subsurface based on scaling arguments.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.