Experimental review of fluid pressure effects on sheared granular materials

Natural faults are typically viewed as rock surfaces filled with fluids and wear detritus, called fault gouge. In the laboratory, there is an apparent discrepancy in frictional behavior between observations of sliding on bare rock surfaces and shearing granular gouge materials. Experiments on bare rock surfaces and rock surfaces separated by a thin layer of gouge indicate that slip between two rock surfaces is much more stable at high than at low fluid pressure. In contrast, the majority of experiments on granular gouge materials indicate that slip is less stable at high than at low fluid pressure. While some studies speculate on the role of dilatancy in the frictional behavior of fluid-filled gouge materials, the exact explanation behind this discrepancy is unclear.

The goal of this project is to identify the factors that control the stability of fluid-filled gouge materials, and to evaluate possible physical mechanisms underlying the observed discrepancy. The student is expected to: (1) review gouge experiments in detail, (2) learn the conditions under which gouge experiments were performed, (3) use the analysis by Segall and Rice (1995) on dilatancy, compaction and slip stability of a fluid-infiltrated fault as a starting point for theory, and (4) explore ways to extend it to include the effects of gouge breakage on stability.