Rate- and State-dependent Deformation: Beyond Two-dimensional Frictional Sliding
Abstract
The laboratory-based rate- and state-dependent (R-S) constitutive relations have been a cornerstone for research into rock friction for over a quarter of a century and have been applied to various studies related to friction analysis and fault mechanics. The most widely used forms of the R-S relations employ descriptions of friction that are limited to deformation in two dimensions. As such, these forms are incapable of properly capturing the interplay between hydraulic and mechanical properties that necessarily involve three-dimensional volumes. I present an alternative form of the R-S constitutive relations that accounts for poromechanical deformation in three-dimensional volumes. The new 3D expression is based on pre-existing forms of the R-S relations but differs in that it contains parameters that relate to stress invariants and volumetric strains. By incorporating descriptions of porosity evolution that depend on the state variable, the R-S relations can be coupled to poromechanics via two widely used geotechnical parameters (i.e. Biot-Willis and Skempton coefficients). I report on experiments designed to explore the common features of sheared granular layers and deformed cylindrical aggregates of quartz sand. Frictional stress- relaxation tests were performed in direct shear geometry on layers of Ottawa sand at room temperature and humidity. Loading perturbations were initiated near the critical stress required to sustain steady-state shear. The observed time- and slip-dependent frictional behavior is consistent with previous results and is well described by 2D R-S relations. Similar relaxation-creep experiments were performed on 3D cylindrical aggregates of water-saturated, granular St Peter quartz sand in a triaxial deformation apparatus. Triaxial creep tests show behavior consistent with results from friction studies. Strength data, porosity evolution, and geotechnical parameters for the triaxially deformed sands are well described by models that employ a 3D form of the R-S relations. Such a description will be a valuable component for models of granular media (e.g. clastic strata, faults) subjected to varying stress conditions such as occurs during tectonic loading, dynamic deformation associated with fault shear, or rapid changes in reservoir effective pressures.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.S41D..07K
- Keywords:
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- 3902 Creep and deformation;
- 5104 Fracture and flow;
- 5114 Permeability and porosity;
- 8163 Rheology and friction of fault zones (8034)