Doctoral Dissertations
Date of Award
12-2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Civil Engineering
Major Professor
Khalid A. Alshibli
Committee Members
Angel Palomino, Anna Herring, Nick Dygert
Abstract
Predicting granular materials' behavior has been challenging due to their complex nature. Many models predict soil constitutive behavior using laboratory test results, such as axisymmetric triaxial compression (ATC), to represent soils’ in-situ conditions. 3D synchrotron microcomputed tomography (SMT) allows for the acquisition of 3D particle-scale information without disturbing the material. Coupling ATC with fast 3D-SMT enables continuous investigation of the response of granular materials as shearing progresses at multiple scales, from global responses based on boundary measurements, such as volume change, to local responses, such as changes in water-air menisci. This dissertation utilizes 3D SMT imaging of saturated sand specimens to examine the growth of air phase within specimens as loading progresses, the evolution of sandwater-air interaction characteristics with shear, and the onset of shear band (SB). Various testing conditions were conducted to investigate the effects of drainage, back pressure (BP), and gradation on sand response at different scales. Drained and undrained ATC tests were performed at different BP using rounded and angular sands, with the angular sand comprising two different gradations. The global-scale analysis revealed the failure of conventional ATC measurements to detect volume change due to air growth, and the invalidity of the assumption of no volume change for undrained conditions. The observed reduction in the degree of saturation was significant enough that the saturated framework was no longer valid in some cases. Relative particle translation gradient analysis revealed a delayed formation of SB for undrained conditions, which is consistent with peak strength for undrained specimens occurring at higher axial strain. A new particle-tracking algorithm is proposed to achieve more accurate and efficient identification of angular particles of varying sizes. Localized analysis focused on solid-water-air interaction and explored how the specimen characteristics and flow characteristics varied within regions of interest depending on the utilized testing parameters, using tortuosity analysis and simulating changes in capillary pressure of isolated air voids with loading and variation depending on proximity to the SB. Flow analysis within the SB revealed highly connected flow path for narrow gradation specimen while wider gradation specimen exhibited the presence of dominant flow paths with some voids being isolated.
Recommended Citation
Elnur, Mohammed, "Assessment of the Behavior of Saturated Sheared Sand at Multiple Scales Using Axisymmetric Triaxial Testing and 3D X-Ray Computed Tomography. " PhD diss., University of Tennessee, 2025.
https://trace.tennessee.edu/utk_graddiss/13594