This proposal focuses on the development and modification of numerical techniques for simulating the discrete mechanics of granular shear zones using the distinct element method (DEM). The goal of the research is to study frictional processes within these shear zones using simple, physical experiments to calibrate the numerical methods. Recent experiments conducted by Dr. J. Gollub at Haverford College reveal many characteristics of geologic shear zones: stick-slip sliding behavior that stabilizes with increasing sliding velocity, precorsory deformation events within the assemblage, and a hysteretic time-dependence of friction on velocity attributed to dilation effects in the assemblage. The P.I. proposes to try to reproduce the results of Gollub's experiments using DEM simulations, and in so doing calibrate numerical implementations of specific contact laws such as force damping and interparticle friction. In particular, she will explore the use of rate-state friction laws for implementing sliding friction at particle surfaces, which may explain some of the complexity associated with gouge-filled shear zones. In turn DEM simulations will be used to highlight some of the deformational features that Gollub has observed, shedding further light on the slip and localization phenomena that develop in granular materials.
