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Experimental and Theoretical Investigation of Rheological Behavior of Dry and Saturated Granular Flows

Kamali Zarch, Mohsen | 2025

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 57854 (09)
  4. University: Sharif University of Technology and Hong Kong University of Science and Technology
  5. Department: Civil Engineering
  6. Advisor(s): Haeri, Mohsen; Zhang, Limin
  7. Abstract:
  8. Flow-type landslides, including debris flows, mudflows, and other mass flows, are among the natural hazards triggered by factors such as rainfall or earthquakes. The dynamics of these flows are heavily influenced by the rheological behavior of their constituent mixtures, which encompass a wide range of particle concentrations and sizes. This variability in particle concentration and size significantly alters the rheological behavior of the mixtures. Previous studies have primarily focused on the behavior of equivalent fluids in fine-grained mixtures, often overlooking the role of various interactions and multiphase behavior in coarse-grained mixtures. In this dissertation, the rheological behavior of dry and saturated granular flows was experimentally measured using rotational rheometry, with a focus on the contributions of different interactions, such as particle-fluid, colloidal, collisional, and frictional interactions. Initially, a preliminary classification of mixtures with low, moderate, and high concentrations was proposed based on the dominant contribution of each interaction. For dilute and moderately-concentrated soil-water mixtures, the contributions of particle-fluid, collisional, and colloidal interactions were investigated using a small-scale viscometer. For highly-concentrated mixtures, the contributions of frictional and collisional interactions in the dry state were first evaluated using a large-scale vane rheometer, followed by an examination of the two-phase behavior in the saturated state. The results indicated that for dilute mixtures, the Bingham model is appropriate, where the mixture viscosity reflects the contribution of particle-fluid interactions, and the yield stress reflects the contribution of colloidal interactions. For moderately-concentrated mixtures, shear-thinning behavior was observed for mudflows, while shear-thickening behavior was observed for debris flows, as the contributions of colloidal and collisional interactions becomes gradually dominant, respectively. A new classification of mixtures based on soil type, mass number, and dominant interaction was proposed. For dry, highly-concentrated mixtures, a descending-ascending pattern in the effective friction parameter was observed. This pattern indicated a transition from shear-weakening solid-like behavior in the quasi-static regime to shear-strengthening fluid-like behavior in the intermediate regime. Additionally, dynamic dilation was identified in these flows, and new rheological laws, including a non-uniform friction law and a dynamic dilatancy law for dry granular flows, were proposed. For saturated, highly-concentrated mixtures, in addition to the solid-fluid transitional behavior, two-phase behavior due to the relative motion of the fluid phase was observed. A new dimensionless number, termed the fluidization number, was proposed to control the transitional and two-phase behavior of these mixtures. This number accounts for interphase forces such as buoyancy and drag. Finally, a new non-uniform friction law was proposed, relating the effective friction parameter to the fluidization number, which describes the two-phase behavior of saturated, high-concentrated mixtures
  9. Keywords:
  10. Landslide ; Debris Flow ; Rheological Behavior ; Constitutive Laws ; Granular Flow ; Mudflow ; Flow-Type Landslide

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