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- Title
Testing Apparatus Stiffness Variations With Application to Rock and Sediment Deformation.
- Authors
Ikari, Matt J.; Haberkorn, Philipp
- Abstract
Frictional slip instability, resulting in intermittent "stick‐slip" rather than continuous sliding, is a phenomenon that depends on the frictional properties of the sliding area and the stiffness of the surrounding material. For geomechanical rock and sediment testing, the stiffness of the testing apparatus partially controls the occurrence of stick‐slip sliding behavior. Under a wide range of conditions, we directly measured the shear loading stiffness of five direct‐shear apparatuses in the Marine Geotechnics laboratory at MARUM, University of Bremen. Under constant normal stress, the shear loading and unloading curves are non‐linear and exhibit significant hysteresis. Shear stiffness values generally increase with increasing normal and shear stresses. Absolute values of stiffness as well as their dependency on shear and normal stress vary amongst the apparatuses despite the same basic apparatus design. For the application of stiffness concepts to stick‐slip sliding in the Earth, for example, earthquakes, the most appropriate stiffness value is obtained at a shear stress value comparable to the sample strength, and measured during stress unloading. Well‐characterized apparatus stiffness under a wide range of testing conditions is recommended to optimize analyses of laboratory friction data. Plain Language Summary: When sliding occurs, it may occur smoothly or in a "jerky" motion called stick‐slip. Whether or not stick‐slip sliding occurs depends on the friction of the sliding surfaces and also the stiffness or "springiness" of the material around the sliding surface. In laboratory experiments that replicate sliding in rocks, stick‐slip represents earthquakes, the sliding surface represents a fault and the testing machine represents the rock mass around the fault. Under a wide range of conditions, we directly measured the stiffness of five direct‐shear apparatuses used in the Marine Geotechnics laboratory at MARUM, University of Bremen. The shear stress versus apparatus distortion curves are non‐linear and exhibit differences between loading and unloading. Machine stiffness is generally larger when the machine experiences larger pressures. Stiffness varies amongst the apparatuses despite the same basic apparatus design. For laboratory experiments designed to study fault motion and earthquakes, our data show that it is important to carefully identify the machine stiffness under the exact conditions of the experiment in order to best translate the results to the Earth. Key Points: We systematically measured the stiffness of five direct‐shear apparatuses in the Marine Geotechnics laboratory at the University of BremenApparatus stiffness depends on shear stress and normal stress and exhibits loading path hysteresis, but does not depend on loading rateLaboratory studies of frictional stick‐slip behavior should consider apparatus stiffness variations as a function of testing conditions
- Subjects
UNIVERSITAT Bremen; ROCK deformation; TESTING equipment; MARINE geotechnics; SURFACE fault ruptures; SHEARING force; LOADING &; unloading
- Publication
Geochemistry, Geophysics, Geosystems: G3, 2023, Vol 24, Issue 10, p1
- ISSN
1525-2027
- Publication type
Article
- DOI
10.1029/2023GC011104