Publications

Discrete microbubbles flow in transparent porous media

The coal seam gas and underground coal gasification industry has caused concerns with the risk of potential groundwater contamination. Gases leaked from coal seams are thought to be a source of groundwater pollution. However, the basic principles and controlling parameters for gases seepage from deep ground formations to the surface are not fully understood. Microbubble transport, as a possible mechanism for gases transport in the subsurface, is investigated here through a laboratory-scale experiment. Microbubbles were generated from a bubble diffuser and released into a 2D artificial transparent porous medium. The point source of bubble injection was used to simulate the release of gases from geological faults/fractures. The medium's transparency enabled a clear visualization of the bubble pathways. Images captured by cameras were used to facilitate analyses on the bubble transport behavior affected by advection and dispersion.

A Quasi-2D Exploration of Mixed-Mode Fracture Propagation in Concrete Semi-Circular Chevron-Notched Disks

Most semi-circular bend (SCB) tests on concrete have been conducted with a pre-crack with a straight-through tip, thereby undermining the determination of the tensile fracture toughness (KIc). Therefore, the present study involved mixed-mode (tensile–shearing) fracture propagation in concrete semi-circular chevron-notched disks (i.e., with a sharp notch tip) using SCB tests and the FRANC2D numerical simulation software. The inclined notch angle (β) was varied from 0° to 70° while the other settings remained fixed, and the crack mouth opening displacement (CMOD) of the notch was measured constantly. The stress distribution was analyzed using finite-element simulations, and the experimental results showed that this testing method was robust. The maximum failure load and the fracture propagation angle increased with β, and wing fracture was observed. With FRANC2D simulating these SCB tests successfully, it was found that the tensile stress concentration around the notch tip moved toward the upper face of the notch, and the compressive stress concentration formed on the notch tip. The tensile mode was generated as the CMOD kept increasing for β = 0–30°, whereas the mixed mode became more evident as the CMOD kept decreasing for β = 45–70°. The fracture process zone was found for β = 0–30° but not for β = 45–70°. This mixed-mode fracture is predicted better by the criterion of extended maximum tangential strain than by other criteria, and there is a linear relationship between CMOD and KIc, as examined previously for pavement and concrete materials.

A lattice Boltzmann exploration of two-phase displacement in 2D porous media under various pressure boundary conditions

Broadband Dielectric Characterization With Flow Through Coaxial Cell

No abstract is provided for this article.

Quantification of Soil State Variables Using Electromagnetic Methods

The possibility to quantitatively measure changes in state variables both in laboratory and in situ is the key for the comprehensive assessment and understanding of many problems in geotechnical engineering. The analysis of the processes in unsaturated soils, for...

Primary imbibition curve measurement using large soil column test

For analyzing unsaturated conditions of hydraulic and mechanic tests, the Soil Water Retention Curve (SWRC) is the most important information which should be experimentally measured. Therefore, the measurement of SWRC becomes the vital puzzle in the entire map for predicting unsaturated soil behavior regarding seepage, failure, and deformation. Standard SWRC test employs the standard Axis Translation Technique (ATT). However, beyond the primary draining path, it is extremely time-consuming to measure the primary imbibition curves with this device. In order to provide an alternative way for measuring the primary imbibition curve, two 2 m long sandy soil columns were set up with an advanced measuring technique for measuring water content profile. The results of this method are compared with measurements using the hanging column method providing observations in the lower suction range (0~20 kPa). The performance of this experimental setup is demonstrated with a discussion of advantages and disadvantages.

A machine learning-driven model for predicting macro- and micro-mechanical responses of rockfill materials considering particle breakage

Conventional constitutive models encounter challenges in comprehensively capturing the nonlinear behavior and particle breakage effects of rockfill materials subjected to large deformation and multiaxial loading conditions. To address this issue, this study proposes a constitutive model based on machine learning (ML) that considers particle breakage in rockfill materials. By learning the underlying patterns from a large dataset of experimental data, this model can effectively reconstruct the nonlinear and high-dimensional characteristics of the material while also accounting for its loading history and stress path dependence. The model shows outstanding predictive performance on the test set, with relative prediction errors confined to within ± 5 %. Utilizing this model, the macro- and micro-mechanical responses of rockfill materials are systematically investigated, revealing the mechanisms and quantitative relationships between particle gradation, intermediate principal stress coefficient, and ellipsoidal axis ratio on particle breakage behavior. Additionally, the ML model exhibits robust interpolation within its training range (mean absolute percentage error, MAPE < 3.5 %), yet its extrapolation performance varies outside this scope, maintaining high accuracy for unbreakable particles and cyclic loading (MAPE < 2.7 %) but declining for extreme shapes (e.g., MAPE > 10.0 % for breakage rate), highlighting data dependency as a key limitation. This study brings fresh insights and establishes a novel theoretical framework for understanding the mechanical behavior of rockfill materials while also highlighting potential avenues for future model optimization.

Application of Image Analysis on Two-Dimensional Experiment of Ground Displacement Under Strip Footing

The two-dimensional experiment of sandboxes for simulating ground failure has become a popular teaching tool in the current geomechanics laboratory. Most of them need cameras with high resolution and well-textured soil for digital image correlation (DIC). Those...

Mesoscopic model framework for liquid slip in a confined parallel-plate flow channel

We investigated the liquid slip in a planar confined flow channel by proposing an exponentially decaying interaction force between fluid particles and two flat walls in the mesoscopic lattice Boltzmann model framework. In this way, we can explicitly link density profile, velocity profile, and apparent slip length with the mesoscale interaction parameters (force strength and decay length), and formulate the permeability-enhancement ratio as a function of two dimensionless numbers that indicate the role of interaction strength and interaction distance (relative to gap size of flow channel) in the slip-flow system.

Application of Spatial Time Domain Reflectometry for investigating moisture content dynamics in unsaturated sand

The strength of unsaturated soil is defined by the soil water retention behavior and such suction acting inside the soil matrix. In order to obtain suction and moisture profile in the vadose zone specific measuring techniques are needed. Time Domain Reflectometry (TDR) conventionally measures moisture at individual points only. Therefore, Spatial Time Domain Reflectometry (Spatial TDR) was developed for characterizing the moisture content profile along the unsaturated soil strata. This paper introduces an experimental set-up used for measuring dynamic moisture profile in high spatial and temporal resolution. Preliminary measuring results are presented and discussed.

Pore-Scale Simulations of Simultaneous Steady-State Two-Phase Flow Dynamics Using a Lattice Boltzmann Model: Interfacial Area, Capillary Pressure and Relative Permeability

The dynamics of simultaneous flow of immiscible two-phase fluids at the steady state in the capillary force-dominated regime were investigated. It was desc

Application of Spatial Time Domain Reflectometry for Investigating Moisture Content Dynamics in Unsaturated Loamy Sand for Gravitational Drainage

The strength of unsaturated soil is defined by the soil water retention behavior and soil suction acting inside the soil matrix. In order to obtain the suction and moisture profile in the vadose zone, specific measuring techniques are needed. Time domain reflectometry (TDR) conventionally measures moisture at individual points only. Therefore, spatial time domain reflectometry (spatial TDR) was developed for characterizing the moisture content profile along the unsaturated soil strata. This paper introduces an experimental set-up used for measuring dynamic moisture profiles with high spatial and temporal resolution. The moisture measurement method is based on inverse modeling the telegraph equation with a capacitance model of soil/sensor environment using an optimization technique. With the addition of point-wise soil suction measurement using tensiometers, the soil water retention curve (SWRC) can be derived in the transient flow condition instead of the static or steady-state condition usually applied for conventional testing methodologies. The experiment was successfully set up and conducted with thorough validations to demonstrate the functionalities in terms of detecting dynamic moisture profiles, dynamic soil suction, and outflow seepage flux under transient flow condition. Furthermore, some TDR measurements are presented with a discussion referring to the inverse analysis of TDR traces for extracting the dielectric properties of soil. The detected static SWRC is finally compared to the static SWRC measured by the conventional method. The preliminary outcomes underpin the success of applying the spatial TDR technique and also demonstrate several advantages of this platform for investigating the unsaturated soil seepage issue under transient flow conditions.

Unsaturated soil water retention curve of road material using evaporation method

It is imperative to the understanding of water movements and moisture conditions in unbound pavement layers and subgrades for different types of road constructions in various climatic conditions for improving the performance of roads. Especially, soil suction fluctuates significantly in unsaturated zone during drainage and imbibition process due to seasonal variation. Moreover, changing in volumetric moisture content and soil suction might be accelerated for the varying density of materials because of cyclic traffic loading. To address these issues, soil water retention curves (SWRC) of road base materials compacted at moulding moisture content and placement density similar to that expected in real life scenario are reported in this study. Simultaneous and continuous soil moisture and suction measurements are performed with a setup comprising of tensiometers and programmed bench scales. Tensiometer is inserted in the compacted soil mass, and the top surface boundary condition is set to evaporation. Soil suction is measured from tensiometer reading, while moisture content and outflow are obtained by weighing the soil column. In this study, we discuss following four aspects pertaining to the road base material: (i) variation of soil suctions with time; (ii) the SWRC of road base material in drying process; (iii) the estimation of unknown parameters of the existing models; (iv) the suitability of SWRC with existing prediction models. This research is expected to contribute to a better understanding and prediction of moisture migration and solute transport in road structures.

A flow through coaxial cell to investigate high frequency broadband complex permittivity: Design, calibration and validation

This paper presents a new apparatus: a large flow through coaxial cell designed for broadband dielectric characterization of material under controlled hydraulic and chemical boundaries. The cell is calibrated with a single measurement made on a perfectly known dielectric liquid (deionized water) together with an optimization procedure. Then, two methods are proposed to compute the dielectric characteristics: an iterative solver and an optimization method. These two methods are systematically investigated for two reference liquids: a low loss dielectric material (ethylene glycol) and high loss dielectric liquid (saline solutions with different concentration). Tabulated data were used to perform a quantitative error analysis in terms of estimated complex permittivity. The results have shown high performance in terms of real part and good performance in terms of real part. The measurements on saline solution also highlight the impact of electrode polarization with dramatic effect in the lower part of the frequency range.

The Technical Challenges for Applying Unsaturated Soil Sensors to Conduct Laboratory-Scale Seepage Experiments

Although many unsaturated soil experiments have successfully delivered positive outcomes, most studies just concisely illustrated sensor techniques, because their main objectives focused on bridging research gaps. Inexperienced research fellows might rarely follow up those techniques, so they could encounter very trivial and skill-demanding difficulties, undermining the quality of experimental outcomes. With a motivation to avoid those, this work introduces technical challenges in applying three sensor techniques: high precision tensiometer, spatial time-domain reflectometry (spatial TDR) and digital bench scales, which were utilized to measure three fundamental variables: soil suction, moisture content and accumulative outflow. The technical challenges are comprehensively elaborated from five aspects: the functional mechanism, assembling/manufacturing approaches, installation procedure, simultaneous data-logging configurations and post data/signal processing. The conclusions drawn in this work provide sufficient technical details of three sensors in terms of the aforementioned five aspects. This work aims to facilitate any new research fellows who carry out laboratory-scale soil column tests using the three sensors mentioned above. It is also expected that this work will salvage any experimenters having troubleshooting issues with those sensors and help researchers bypass those issues to focus more on their primary research interests.

Granular Flow through Porous Media: Implications for Geological Fluid Dynamics

Granular Flow through Porous Media: Implications for GeologicalFluid Dynamics

Size distribution measurement for densely binding bubbles via image analysis

For densely binding bubble clusters, conventional image analysis methods are unable to provide an accurate measurement of the bubble size distribution beca

Measurement of In-Situ Flow Rate in Borehole by Heat Pulse Flowmeter: Field-Case Study and Reflection

Large-scale groundwater flow modelling demands comprehensive geological investigation (GI) to accurately predict groundwater dynamics during open-cut and underground mining. Due to the existence of large-scale heterogeneity (e.g., fault and fracture) in natural geological strata (e.g., overburden soil, rock mass and coal seam), the in-situ flow measurement in boreholes, compared to laboratory seepage tests, can bring more reliable information to estimating the in-situ seepage properties (e.g., hydraulic conductivity, intrinsic permeability, transmissivity and specific yield). In this paper, a flow-measuring technique-heat pulse flowmeter (HPFM) is methodologically introduced and then practically applied for GI in the mining extension zone of Hunter Valley Operations (HVO), New South Wales, Australia. The measuring experiences, including both positive and negative outcomes, are reported and discussed with a series of datasets of in-situ flow rates measured in the selected boreholes. The pros and cons of the HPFM application in HVO are also discussed and summarised based on the user experience collected through this field trip. Finally, through a thorough reflection, some practical recommendations are provided to help other HPFM practitioners bypass all difficulties experienced on this trip. It is anticipated that valuable user information can contribute to better GI in other sites when performing this measuring technique.