New ring shear deformation apparatus for three-dimensional multiphase experiments: First results

Multiphase deformation, where a solid and fluid phase deform simultaneously, play a crucial role in a variety of geological hazards, such as landslides, glacial slip, and the transition from earthquakes to slow slip. In all these examples a continuous, viscous or fluid-like phase is mixed with a granular or brittle phase where both phases deform simultaneously when stressed. Understanding the interaction between the phases and how they will impact deformation dynamics is essential to improve hazard assessments for a wide variety of geo-hazards. Here, we present the design and first experimental results from a ring shear deformation apparatus capable of deforming multiple phases simultaneously. The experimental design allows for three dimensional observations during deformation in addition to unlimited shear strain, controllable normal force, and a variety of boundary conditions. To impose shear deformation, either the experimental chamber or lid rotate around its central axis while the other remains stationary. Normal and pulling force data are collected with force gauges located on the lid of the apparatus and between the pulling motor and the experimental chamber. Experimental materials are chosen to match the light refraction index of the experimental chamber, such that 3D observations can be made throughout the experiment with the help of a laser light sheet. We present experimental results where we deform hydropolymer orbs and cubes (brittle phase) and Carbopol&reg; hydropolymer gel (fluid phase). Preliminary results show variability in force measurements and deformation styles between solid and fluid end member experiments. The ratio of solids to fluids and their relative competencies in multiphase experiments control deformation dynamics, which range from stick-slip to creep. The presented experimental strategy has the potential to shed light on multi-phase processes associated with multiple geo-hazards.</p

New ring shear deformation apparatus for three-dimensional multiphase experiments: first results

Multiphase deformation, where a solid and fluid phase deform simultaneously, plays a crucial role in a variety of geological hazards, such as landslides, glacial slip, and the transition from earthquakes to slow slip. In all these examples, a continuous, viscous, or fluid-like phase is mixed with a granular or brittle phase, where both phases deform simultaneously when stressed. Understanding the interaction between the phases and how they will impact deformation dynamics is crucial to improve the hazard assessments for a wide variety of geohazards. Here, we present the design and first experimental results from a ring shear deformation apparatus capable of deforming multiple phases simultaneously. The experimental design allows for 3D observations during deformation in addition to unlimited shear strain, controllable normal force, and a variety of boundary conditions. To impose shear deformation, either the experimental chamber or lid rotate around its central axis while the other remains stationary. Normal and pulling force data are collected with force gauges located on the lid of the apparatus and between the pulling motor and the experimental chamber. Experimental materials are chosen to match the light refraction index of the experimental chamber, such that 3D observations can be made throughout the experiment with the help of a laser light sheet. We present experimental results where we deform hydropolymer orbs (brittle phase) and Carbopol® hydropolymer gel (fluid phase). Preliminary results show variability in force measurements and deformation styles between solid and fluid end-member experiments. The ratio of solids to fluids and their relative competencies in multiphase experiments control deformation dynamics, which range from stick–slip to creep. The presented experimental strategy has the potential to shed light on multiphase processes associated with multiple geohazards.This article is published as McLafferty, S., Bix, H., Bogatz, K., and Reber, J. E.: New ring shear deformation apparatus for three-dimensional multiphase experiments: first results, Geosci. Instrum. Method. Data Syst., 12, 141–154, https://doi.org/10.5194/gi-12-141-2023, 2023

Deformation and Frictional Failure of Granular Media in 3D Analog and Numerical Experiments

Frictional sliding along grain boundaries in brittle shear zones can result in the fragmentation of individual grains, which ultimately can impact slip dynamics. During deformation at small scales, stick–slip motion can occur between grains when existing force chains break due to grain rearrangement or failure, resulting in frictional sliding of granular material. The rearrangement of the grains leads to dilation of the granular package, reducing the shear stress and subsequently leading to slip. Here, we conduct physical experiments employing HydroOrbs, an elasto-plastic material, to investigate grain comminution in granular media under simple shear conditions. Our findings demonstrate that the degree of grain comminution is dependent on both the normal force and the size of the grains. Using the experimental setup, we benchmark Discrete Element Method (DEM) numerical models, which are capable of simulating the movement, rotation, and fracturing of elasto-plastic grains subjected to simple shear. The DEM models successfully replicate both grain comminution patterns and horizontal force fluctuations observed in our physical experiments. They show that increasing normal forces correlate with higher horizontal forces and more fractured grains. The ability of our DEM models to accurately reproduce experimental results opens up new avenues for investigating various parameter spaces that may not be accessible through traditional laboratory experiments, for example, in assessing how internal friction or cohesion affect deformation in granular systems.This article is published as Ioannidi, P.I., McLafferty, S., Reber, J.E. et al. Deformation and Frictional Failure of Granular Media in 3D Analog and Numerical Experiments. Pure Appl. Geophys. (2024). https://doi.org/10.1007/s00024-024-03464-6. This open-access article is licensed under a Creative Commons Attribution 4.0 International License. A dataset associated with this study is available at https://doi.org/10.25380/iastate.24061518P.I. Ioannidi, S. McLafferty, J.E. Reber, and G. Morra have been supported through National Science Foundation CAREER award #1843676

Relationship between channel flow initiation and crustal viscosity in convergent settings: an analog modeling approach

Channel flow has been proposed as one mechanism to explain the normal sense ductile shear along the Himalayan orogen. The key requirements for channel flow are i) extruding middle crust of low viscosity, and ii) excess gravitational potential due to topography. We present scaled two-layer physical models where the effect of the gravitational potential with respect to the plate convergence rate is investigated. Viscous middle crust starts moving towards the surface where the strain rate imposed by the convergence is 30% of that arising from the lateral pressure gradient. The degree of extrusion is directly linked to the imposed pressure gradient. A simple correlation between the extruding rock’s viscosity, the convergence rate, and the topography imposing the pressure gradient is established. The upward motion of viscous material is expected already for a mid-crustal viscosity of 1021 Pa.s. This is significantly higher than previously expected, suggesting that one of the fundamental requirements for channel flow might not be necessary.This is a manuscript of an article published as Reber, J.E., Vidal, C.S., McLafferty, S. et al. Relationship between channel flow initiation and crustal viscosity in convergent settings: an analog modeling approach. Int J Earth Sci (Geol Rundsch) (2021). doi:10.1007/s00531-021-02057-1.</p

New ring shear deformation apparatus for three-dimensional multiphase experiments: First results

Multiphase deformation, where a solid and fluid phase deform simultaneously, play a crucial role in a variety of geological hazards, such as landslides, glacial slip, and the transition from earthquakes to slow slip. In all these examples a continuous, viscous or fluid-like phase is mixed with a granular or brittle phase where both phases deform simultaneously when stressed. Understanding the interaction between the phases and how they will impact deformation dynamics is essential to improve hazard assessments for a wide variety of geo-hazards. Here, we present the design and first experimental results from a ring shear deformation apparatus capable of deforming multiple phases simultaneously. The experimental design allows for three dimensional observations during deformation in addition to unlimited shear strain, controllable normal force, and a variety of boundary conditions. To impose shear deformation, either the experimental chamber or lid rotate around its central axis while the other remains stationary. Normal and pulling force data are collected with force gauges located on the lid of the apparatus and between the pulling motor and the experimental chamber. Experimental materials are chosen to match the light refraction index of the experimental chamber, such that 3D observations can be made throughout the experiment with the help of a laser light sheet. We present experimental results where we deform hydropolymer orbs and cubes (brittle phase) and Carbopol® hydropolymer gel (fluid phase). Preliminary results show variability in force measurements and deformation styles between solid and fluid end member experiments. The ratio of solids to fluids and their relative competencies in multiphase experiments control deformation dynamics, which range from stick-slip to creep. The presented experimental strategy has the potential to shed light on multi-phase processes associated with multiple geo-hazards.This preprint is from McLafferty, S., Bix, H., Bogatz, K., and Reber, J. E.: New ring shear deformation apparatus for three-dimensional multiphase experiments: First results, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2022-1004, 2022.This work is distributed under the Creative Commons Attribution 4.0 License

3D analog and numerical experiments on grain comminution

This dataset contains data from analog and numerical experiments, both subsets investigate the comminution of grains under simple shear conditions. The analog subset contains photographs (.jpg) of 6 analog experiments performed in the ring shear apparatus designed at the Structure Lab of Iowa State University—taken before, halfway, and after the experiments. In addition, “CF_LG” contains a video (.mov) in real time (30 minute 30 seconds); “CF_D” contains a 52-second video (.mp4) that corresponds to 30 minute 30 seconds in real time. The numerical subset contains input files (.csv), scripts (.py, .prm), and videos (.avi) from 8 numerical experiments performed using the open-source Discrete Element code ESyS-Particle version 2.3.5. The numerical experiments are benchmarked by the analogy experiments, and each 25-second video corresponds to 15 minute 50 seconds in real time.</p