Abstract - X-ray micro-computed tomography (μCT) has opened new possibilities for investigating the pore-scale behaviour of unsaturated soils. This webinar highlights recent applications of μCT in understanding both water retention and mechanical responses in granular soils, with a focus on experimental image analysis and micromechanics-based modelling. Hysteresis in water retention curves, caused by differences between drying and wetting paths, is a well-known phenomenon in unsaturated soil mechanics. While traditionally explained through conceptual models like the ink-bottle effect and contact angle hysteresis, μCT enables direct visualisation of these mechanisms. By analysing segmented images, local porosity, degree of saturation, and interface curvature can be quantified. This reveals that even under similar global saturation, the pore water morphology differs significantly depending on the hydraulic path. Pore water also contributes to shear strength through the formation of liquid bridges at particle contacts. The liquid bridge ratio (LBR)—the proportion of contacts connected by water—is introduced as a metric to represent this effect. μCT-based observations show that LBR is influenced by density and degree of saturation, but not by wetting–drying history. The orientation of liquid bridges follows the contact fabric and does not require separate anisotropic treatment. These findings are incorporated into a micromechanics model to simulate the suction-induced strengthening of unsaturated soils. By linking image-derived parameters to constitutive behaviour, the approach bridges the gap between pore-scale processes and macroscopic response.

Biography - Professor Yosuke Higo is a distinguished expert in geotechnical engineering and geomechanics, currently serving as a Professor at Kyoto University's Graduate School of Engineering. He also holds a concurrent position at the Graduate School of Management. His research focuses on understanding the complex behaviors of geomaterials—multi-phase mixtures of soil particles, water, and air—by linking microscopic interactions to macroscopic phenomena such as deformation, failure, and groundwater seepage. Utilizing advanced techniques like X-ray microtomography, Professor Higo develops multi-scale and multi-phase analytical methods to predict and evaluate geomaterial behaviors. His work has practical applications in addressing geotechnical challenges, including the design of robust earth structures like river levees and road embankments to withstand natural hazards such as earthquakes and heavy rainfall. Professor Higo's academic journey started at Kyoto University, where he earned his undergraduate, master's, and doctoral degrees in civil engineering. His professional career includes roles as Research Associate, Assistant Professor, and Associate Professor at Kyoto University's Graduate School of Engineering, leading to his current professorship. Beyond his research and teaching responsibilities, Professor Higo contributes to the academic community through editorial roles. He has served on the editorial boards of the Journal of the Japan Society of Civil Engineers, Series C (Geosphere Engineering), and Series A2 (Applied Mechanics), as well as on the editorial and executive boards of the journal Soils and Foundations. 

Abstract - Multiscale TRansport In porous Systems (MUTRIS) was established in 2015 and specializes in modeling multiphase flow and transport in multiscale systems, with a focus on the minerals and energy resources sectors. Our team explores a broad range of topics, from micro- CT imaging and modeling to applied deep learning, subsurface storage, and mineral recovery. In this talk, I provide a brief overview of the research areas covered by the MUTRIS group before highlighting a recent advancement. Specifically, I focus on the role of phase topology during fluid injection and withdrawal cycles within a porous medium. By linking pore-scale and continuum-scale governing equations through a novel morphological framework, we present a comprehensive approach for predicting the morphological evolution of a non-wetting fluid in porous media during these cycles. These advancements offer new insights into the dynamics of multiphase flow in porous media, deepening our understanding of hysteresis and providing valuable perspectives for future technologies, such as subsurface hydrogen storage and geological CO2 storage.

Biography - Ryan T. Armstrong is a Professor of Civil and Environmental Engineering at the University of New South Wales. His professional journey began with a period at Shell Global Solutions BV in the Netherlands, where he developed an expertise in petroleum engineering, subsurface flow processes, and digital rock physics. Prof Armstrong is recognised for his knowledge in energy resources engineering, which is highlighted by his roles as the Vice President of Technology for the International Society of Core Analysts and as a co-founder and Steering Committee member of the Australian Chapter of the International Society for Porous Media (INTERPORE). His involvement in the Reservoir Advisory Committee of the Society of Petroleum Engineers (SPE) and his co-authorship of the SPE Green Paper on ’Reservoir Technologies for the 21st Century’ have contributed to setting new standards for technological innovations. Currently, as an Australian Research Council (ARC) Future Fellow, his research benefits from productive collaborations with industry leaders and researchers, fostering advancements that bridge academic and industrial realms. Additionally, as an Editor for the Interpore Journal, he helps guide scholarly discussions in porous media research. Lastly, his receipt of the Interpore Award for Porous Media Research in 2024 acknowledges his ongoing contributions to the field.

Abstract - Establishing and validating models for granular flows is challenging because granular flows are inherently opaque.  They also exhibit complex and varied mechanics owing to the different conditions these flows maybe found in, from “gaseous” in one limit to “solid-like” motion in the other. Magnetic Resonance Imaging (MRI) is a promising tool for characterising granular flows as it permits visualisation of the flow structure in opaque three-dimensional (3D) systems. Flow MRI is now quite well established and can be used to study both steady and unsteady flows. However, a full description of the flow mechanics requires the knowledge of the solid volume fractions (3D density maps) as well.  The aim of this work is to establish methods for mapping solid volume fractions and flow fields of the same systems. 

The systems studied include silos and Couette cell devices. Measurements are shown to be quantitative by determining the mass flow rate and comparing these with macroscopic measurements of the mass flow rate [1]. The resulting data were then used to examine models of the flow in hoppers [2] and Couette cells [3], thus providing cross-validation to simulations and guidance for future research.

[1] M. Mehdizad, et al., J. Magn. Reson. 325 106935 (2021).
[2] M. Mehdizad, et al., Powder Technol. 392 69–80 (2021).
[3] D.A. Clarke et al., Phys. Fluids, 36 053317 (2024).

Biography - Professor Daniel Holland is the Head of Department of Chemical and Process Engineering at the University of Canterbury. He holds a PhD from the University of Cambridge in Chemical Engineering. His research focuses on developing experimental techniques to “see inside” complex multiphase flows, and hence improve our understanding of chemical processes. Much of his research has focused on granular flows, and gas-solid fluidised beds, however he also has interests in fluid mechanics and chemical reaction engineering.

Abstract - The modelling and simulation of granular materials at the Centre for Bulk Solids and Particulate Technologies (CBSPT) at the University of Newcastle, Australia goes back to the mid-90s. The period since has seen advancements from continuum mechanics-based analysis to application of Finite Element Method (FEA), Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) in assessment, design, technology development and commercialization. The areas of research and industry application vary widely in scale and outcomes depending on the ores and minerals, grains and powders handled. Applications include belt and pneumatic conveying, transfers, dust emissions, fluidization, biomass rheology, heat transfer, maritime cargo stability, moisture migration and dewatering, build-up and cohesion/adhesion, wear, particle degradation and vibrated screening.

In the recent past and at present, advancing technology and computational readiness has seen coupling between these different modelling approaches while calibration and validation methods have expanded in scope to include large physical scale models, carefully considered design of experiments and automation. This presentation will share some of the interesting applications in materials handling using different software, models and approaches that have been undertaken, including translation of expertise to engineering design and simulation standards adopted by industry. Presented are current activities and projects such as coarse particle separation in vibrated fluidized beds using CFD-DEM and moisture migration under oscillatory motions coupling DEM and smoothed particle hydrodynamics (SPH). 

Biography - Dr Dusan Ilic is a fellow, chartered engineer and research academic at the University of Newcastle, located at the Newcastle Institute for Energy and Resources with 20 years’ experience of consultancy and applied research. Since starting in his current role in 2017, he has used a foundation of bulk solids handling and particle science to establish and grow multi-disciplinary research programmes in engineering and beyond. His project portfolio includes ARC Discovery biomass pneumatic conveying, Industrial Transformation Hub advancing Australian iron ore technologies, Centre of Excellence for enabling eco-efficient beneficiation of minerals, MRFF's EPCDR initiative on bushfire smoke and direct engagement with industry and government.

Abstract - The concept of random close packed or maximally random jammed configurations in particles is well established: Granular particles, particularly frictionless spheres, do not manage to attain the crystalline close packed configurations but ‘get stuck’ in this amorphous state. This effect is due to a geometric frustration that the locally densest configuration cannot expand into the globally densest crystalline configuration. 

In this talk, we will look at a broader range of packing or tessellation models and discuss amorphous states similar to what the random close packed is for the packing problem. We will look at tessellations and packing problems defined by optimization with respect to certain properties, such as interface area in the Kelvin problem, packing density in the Kepler problem, or cell centrality as in the Quantizer problem. 

In all known cases, the optimal solutions are crystalline configurations with long range order. Amorphous disordered structures are generally considered to be intermittent metastable states that prevent the system from attaining the optimal ordered structures. To date, no optimization problem has been identified where the groundstate  is a disordered configuration. While we do not find a disordered groundstate, we here show that the use Lloyd’s algorithm as a fast quench generates a very stable universal disordered state in the three-dimensional Quantizer problem, despite the existence of lower-energy crystalline configurations.

We will discuss these states in terms of the degree of density uniformity of the packings and ask the question whether these pertinent disordered states can be used as a signature of the model that defines the tessellation. 

Biography - Prof Gerd Schröder-Turk hold a PhD degree from the Australian National University, for his thesis “Skeletons in the Labyrinth”. 

He has held academic appointments in theoretical physics and applied maths departments at the Australian National University, the Friedrich-Alexander University Erlangen-Nuremberg and Murdoch University. 

He is a Fellow of the American Physical Society and the recipient of the 2014 Emmy-Noether-Prize, the 2019 Camurus Lipid Research Foundation Fellowship award and the 2023 Allan Schoen Award. He is currently a Professor at Murdoch University and an Honorary Associate Professor at the Australian National University. Aside from his teaching and research roles, he takes a keen interest in higher education policy and university governance, and has held roles as Senate member of Murdoch University and in the National Executive of the Australian Institute of Physics. 

Abstract: Suspensions of fine and cohesive particles demonstrate pressure dependent rate and extent during solid-liquid separation. This is usually termed ‘compressible’ behaviour. Such suspensions are common across minerals processing, water treatment, and food processing, to name but a few. Unfortunately, traditional theories of sedimentation and filtration assume incompressible behaviour. In contrast, compressional rheology, developed in 1987, is a theoretical framework for compressible suspensions that explicitly incorporates pressure dependent effects. Since 1987, researchers at The University of Melbourne have developed a suite of sedimentation, centrifugation and filtration techniques for extracting locally varying compressibility and permeability. These properties are used in process models of thickeners, filters, and centrifuges, for example, to predict performance and provide insights into process optimisation.

Biography: A/Prof Anthony Stickland is an academic in Chemical Engineering at The University of Melbourne, where he lectures ‘Fluid Mechanics’, ‘Particle Technology’, and ‘Sustainable Minerals and Recycling’.  He is a Chief Investigator in the ARC Centre of Excellence for Enabling Eco-Efficient Mineral Beneficiation and leads the Sludge Group, which undertakes research in particulate suspension rheology and solid-liquid separation. This research covers (1) material characterisation techniques and analysis tools to be able to adequately describe particle and suspension behaviour, (2) models of processes to be able to predict performance for design and optimisation, and (3) development and commercialisation of novel technologies for suspension dewatering and handling. The Sludge Group works closely with industries such as water treatment and minerals processing.

Recording of the seminar here.