Application of rate-and-state friction laws to creep compaction of unconsolidated sand under hydrostatic loading conditions

Abstract

Rate-and-state variable friction laws describe the time-dependent fault-normal compaction that occurs during holds in slide-hold-slide friction tests on unconsolidated materials. This time-dependent deformation is qualitatively similar to that observed during volumetric creep strain tests on unconsolidated sands and shales under hydrostatic loading conditions. To test whether rate-and-state friction laws can be used to model volumetric creep processes in unconsolidated sands, the rate-and-state formulation is expanded to include deformation under hydrostatic stress boundary conditions. Results show that the hydrostatic stress form of the rate-and-state friction law successfully describes the creep strain of unconsolidated sand. More importantly, values obtained for rate-and-state friction parameters by fitting these data are in the same range as those obtained from more traditional tests by fitting the fault-normal compaction of simulated gouge during a hold in a laboratory friction experiment. Copyright 2007 by the American Geophysical Union.