This research presents a simple, noninvasive, and cost effective approach where geoelectric measurements are employed to characterize gap-graded granular soils. Variations in electrical conductivity are measured using a four-point impedance analyzer and a custom-designed sample holder, which enabled geoelectric parameters to be linked to the fines content and particle shape characteristics of gap-graded soils. Experiments were conducted on sand-gravel and glass bead mixtures, representing irregular and spherical particle shapes, respectively. For each mixture, fines content was varied from 0% to 100% in 20% increments. X-ray mu CT imaging was employed to quantify the shape parameters of the constituent materials. The combination of X-ray mu CT imaging with geoelectric measurements is a particularly novel element of the experimental methodology. From the measured electrical conductivity data, three key geoelectric parameters were defined: formation factor, surface conductivity, and cementation exponent. These parameters are essential for understanding the electrical properties of the soil mixtures and were correlated to the porosity, specific surface area, and particle shape characteristics of the gap-graded mixtures. The surface conductivity was directly linked to the specific surface area of the mixture, and was able to distinguish between fines-dominated behavior and coarse-dominated behavior of gap-graded soils. The formation factor showed the expected inverse relationship with porosity, as per Archie's model, and exhibited the same trend as the relationship between porosity and fines content for gap-graded soils. Most significantly, the formation factor was able to identify the threshold fines content for both the sand-gravel and glass bead mixtures. Additionally, the cementation exponent clearly distinguished between the irregular and spherical shape characteristics of both mixtures. These results highlight the potential of geoelectric measurements to characterize gap-graded soils and the proposed preliminary classification serves as a foundation to further develop these capabilities for a wider array of soils.

In this paper, we present a detailed case study of in-situ carbon dioxide (CO2) mineralization in the Greenhills dunite deposit in New Zealand, highlighting a comprehensive approach to well design, hydraulic fracturing, and injection modeling using carbonated water. Leveraging experimentally derived geomechanical and reaction kinetics data, an integrated hydraulic fracturing and reservoir simulator was used to evaluate various well trajectories and injection parameters under strike-slip stress conditions. Results show that optimized multistage horizontal wells, particularly those aligned in the S-hmin direction, can generate fracture networks with surface areas sufficient to store up to 90 kt of CO2 per well, with annual injection rates exceeding 50 kt/yr. While mineralization kinetics were studied in a previous publication, this case study provides a technically grounded framework for deploying ultramafic formations as long-term carbon sinks. The study also outlines strategies for well completion and monitoring and emphasizes the importance of future economic assessments and regulatory readiness to advance field deployment of in-situ mineralization technologies.

Clay-rich soils and sediments are key components of near-surface systems, influencing water retention, ion exchange, and structural stability. Their complex dielectric behavior under moist conditions arises from electrostatic interactions between charged mineral surfaces and exchangeable cations, forming diffuse double layers that govern transport and retention processes. This study investigates the broadband dielectric relaxation of four water-saturated clay minerals (kaolin, illite, and two sodium-activated bentonites) in the 1 MHz to 5 GHz frequency range using coaxial probe measurements. The dielectric spectra were parameterized using two phenomenological models - the Generalized Dielectric Relaxation Model (GDR) and the Combined Permittivity and Conductivity Model (CPCM) - alongside two theoretical mixture models: the Augmented Broadband Complex Dielectric Mixture Model (ABC-M) and the Complex Refractive Index Model (CRIM). These approaches were evaluated for their ability to link dielectric relaxation behavior to petrophysical parameters such as cation exchange capacity (CEC), volumetric water content (VWC), and porosity. The results show distinct spectral signatures correlating with clay mineralogy, particularly in the low-frequency range. Relaxation parameters, including relaxation strength and apparent DC conductivity, exhibit strong relationships with CEC, emphasizing the influence of clay-specific surface properties. Expansive clays like bentonites showed enhanced relaxation due to ion exchange dynamics, while deviations in a soda-activated bentonite highlighted the impact of chemical treatments on dielectric behavior. This study provides a framework for linking clay mineral physics with electromagnetic methods, with implications for soil characterization, hydrological modeling, geotechnical assessment, and environmental monitoring.

This study investigates the impact of CO2 injection on mineral transformations and fracture transmissivity within fractured ultramafic rocks, essential for evaluating in-situ carbon mineralization potential. Experiments were conducted using continuous injections of dry CO2 and carbonated water under controlled temperature (25 degrees C to 55 degrees C) and pressure (2.07 MPa to 4.83 MPa) conditions in a high-pressure triaxial cell. Changes in mineral volume, fracture transmissivity, and surface morphology were quantitatively monitored using Xray micro-computed tomography (mu CT) and interferometry. Results indicated significant volume alterations of serpentine and olivine, driven primarily by hydration and serpentinization reactions. In contrast, dry CO2 injections showed negligible influence on transmissivity. Carbonated water injections initially decreased transmissivity, which stabilized over time, highlighting the complex interplay between fluid chemistry, mineralogical evolution, and fracture dynamics. These findings provide critical insights for upscaling CO2 mineralization strategies in fractured ultramafic reservoirs and emphasize the need for future studies over broader ranges of temperature, pressure, and reaction duration.

In this study, we present a new integrated experimental approach to investigate simultaneously the electrical spectral induced polarization (SIP), mechanical, hydraulic and chemical properties of synthetic clayey soil mixed with different types and quantities of organic matter. It addresses knowledge gaps that aim to advance SIP as a non-destructive analysis tool for soils. We used an inorganic clay as a proxy for clayey soil with a moderate cation exchange capacity to achieve more realistic test conditions since most studies use sand. Three organic matter (OM) types with contrasting properties, biosolids, peat and sugar cane residue, broaden the range of organic carbon materials that have been tested. Our study demonstrates a strong relationship between the imaginary part of the complex conductivity and the total organic carbon content of the soil-OM mixtures. It indicates that the relationships depend on the degree of aromaticity, with the slope angle increasing as the degree of aromaticity of the OM increases. Hence, the quantity of OM, as well as its chemical structure, plays a key role in SIP response. Interestingly, these relationships are independent of soil water saturation and bulk density. These findings are of paramount importance for enabling field-scale applications and confirm the potential of SIP as a non-invasive tool for monitoring and characterizing soil in situ.

In this paper, we present a novel approach to study the electrical properties of intact rock by combining impedance and vector network analyzer measurements in the frequency range from 5 Hz to 3 GHz. For the first time, this study enables electrical characterization of the exact same rock sample over nine orders of magnitude in frequency range, utilizing a coaxial cell apparatus with specifically prepared rock samples. Three types of rocks (basalt, sandstone and granite) with low to intermediate porosity (12.24%, 16.9% and 7.49%, respectively) were characterized at varying saturation levels. The relaxation behavior of the samples was quantified using an advanced phenomenological model incorporating both the dielectric constant and electrical conductivity in the form of Debye and Cole-Cole representations. Across the frequency range, three distinct relaxation processes were identified: a high-frequency water process and two interfacial processes related to interactions between the aqueous pore solution and mineral particles (membrane relaxation and Maxwell-Wagner effects). Additionally, an apparent direct current conductivity was observed. This comprehensive broadband analysis represents a further step toward the in situ characterization of rocks using electromagnetic field measurement methods and demonstrates advancements in both methodology and understanding of rock properties compared to existing studies.

Soil stabilization, which may be achieved through mechanical, chemical, or biological means, is a key exercise undertaken to improve the engineering behavior of soils. To that end, this study systematically investigated the effect of xanthan gum (XG), a biodegradable and ecofriendly biopolymer, on several hydromechanical and electromagnetic (EM) properties of kaolin, a reference fine-grained geomaterial. The properties investigated included particle size distribution (PSD), consolidation behavior, soil-water retention behavior, evaporation, shrinkage, and high frequency EM (HF-EM) properties. It was observed that XG treatment leads to flocculation in kaolin, increasing the particle size and decreasing the coefficient of consolidation. Evaporation and shrinkage behavior of the samples were found to be sensitive to environmental conditions such as ambient temperature and relative humidity, emphasizing the need to consider climatic factors in practical applications. XG acted as a natural binding agent, forming a gel-like matrix within the soil that enhanced interparticle cohesion and altered the studied soil properties. A comparison was also made among the load deformation behavior of the XG-treated kaolin samples under mechanical (consolidation) and hydraulic (evaporation) loading conditions. The HF-EM properties of the XG-treated samples correlated well with the respective instantaneous moisture content and suction in the samples, thus demonstrating a potential to be used as a proxy for measurement of effectiveness of XG treatment on hydromechanical properties of kaolin. Its application is envisaged to be beneficial in various infrastructure projects, erosion control measures, and environmental remediation efforts, offering a greener alternative to conventional chemical stabilizers.

White hydrogen (H2), naturally occurring within the Earth's crust, represents a promising yet underexplored opportunity in the transition to clean energy. The aim of this review is to synthesize the current state of knowledge on white H2, particularly its formation mechanisms, geological occurrence, and generation rates. It provides a detailed evaluation of past studies identifying white H2 in a variety of geological environments, including ultramafic rocks, sedimentary basins, and fault zones. Additionally, this review aims to position white H2 within the broader H2 economy by comparing it with other forms of H2 production (green, blue, and grey). This review integrates findings from geological, geochemical, and energy production studies that have identified and measured the presence and generation rates of white H2. Key methodologies explored include geological surveys, H2 flux measurements, and isotopic analysis to determine the natural generation processes of white H2. Extraction techniques are also reviewed, with a focus on scalability, technological feasibility, and cost-effectiveness in relation to current H2 production technologies. Data from real-world studies and models are critically assessed to understand the potential economic and environmental impacts. The review finds that white H2 can be found in significant quantities in various geological formations, particularly in regions with ultramafic rocks and active tectonic faulting. The results suggest that with advancements in detection and extraction technology, white H2 has the potential to become a competitive and scalable source of clean energy. Comparisons with other H2 sources highlight its potential lower environmental impact, especially in terms of greenhouse gas emissions. However, challenges remain in refining extraction processes and integrating white H2 into existing energy markets and infrastructure. White H2 represents a largely untapped resource, with unique geological conditions offering a pathway to produce H2 naturally, without the need for water electrolysis or fossil fuels. This review contributes to the existing body of knowledge by emphasizing white H2's potential role in complementing other H2 sources. It highlights the need for further research into its natural production rates, detection technologies, and commercial viability. The findings underscore white H2's potential as a significant contributor to global decarbonization efforts, particularly in regions rich in geological formations conducive to its generation.

This study investigates the practical effectiveness of in-situ CO2 mineralization in ultramafic rocks under realistic conditions, focusing on early-stage reactions. Samples from a pilot well intersecting an ultramafic body in New Zealand, along with other ultramafic samples from New Zealand and Australia, were used. The tests involved serpentinite and dunite samples subjected to low bottom-hole static temperatures (25-70 degrees C) in a batch reactor designed to replicate in-situ conditions. Results indicated early mineralization yields of up to 4% within 5 h. The highest reaction rate of 1.95x10(-5) mol g(-1)s(-1) was observed for a Greenhills dunite milled core sample from New Zealand at low-temperature conditions (<70 degrees C). Additionally, hydrogen was collected during the reaction of another dunite sample from the Greenhills cored well, suggesting significant potential for geological hydrogen production. A generation rate of 0.5 mmolkg(olivine)(-1)center dot h(-1) was estimated under these low-temperature conditions over the 5-h test period. These findings highlight the dual benefits of CO2 sequestration and hydrogen generation, with the Greenhills Complex theoretically capable of sequestering a minimum of 5 billion tons of CO2 due to its area of 14 km(2) and dunite thickness exceeding 600 m. The region's proximity to major emission sources enhances the feasibility of large-scale sequestration and highlights the valuable insights this work offers for sustainable carbon management.

The growing global demand of rare earth materials and efficient metal recovery techniques from natural resources highlight the significance of advanced methods for identifying and characterising metallic mineral in complex porous matrix. The study aims to characterise metal particles captured in a porous sand matrix using Spectral Induced Polarisation (SIP) method, mainly focusing on the sensitivity of SIP to variations in metal content. An experimental setup was designed to perform SIP measurements on pyrite-sand mixtures, specifically aimed at capturing the complex conductivity of the samples. This setup incorporated a custom-designed cup equipped with four embedded electrodes, facilitating four-point impedance measurements essential for analysing complex conductivity responses. Experiments were performed on sand, mixed with 3 distinct pyrite concentrations. All the measurements were performed three times to comment on the measurement variability. The SIP responses were found to vary with the concentration of pyrite particles. The results suggest that SIP is a promising method for identifying and measuring metal inclusions in porous geological materials.

The collective drive towards achieving net-zero greenhouse gas emissions by 2050 has spurred interest in engineering solutions for carbon capture and storage worldwide. One such approach involves the permanent storage of CO 2 in earth-abundant Ca-, Fe-, and Mg-bearing silicate rocks and minerals as carbonates via the process of CO 2 mineralisation. This necessitates a thorough understanding of carbonate conversion under geologically relevant conditions. Nevertheless, research on CO 2 injection for mineralisation via naturally fractured host rocks or induced fractures, with a research emphasis on rock mechanics and stimulated reservoir volumes (SRV) within geoengineering CO 2 storage, is continuously expanding. This research addresses critical challenges related to identifying favourable geographic locations for CO 2 mineralisation. It specifically focuses on the abundant availability of Mg, Ca, and Fe cations for exothermic CO 2 reactions and their impact on fracture conductivity during in -situ mineralisation. A comprehensive analysis of 26 dunite and serpentinite samples from diverse locations in Australia and New Zealand, including 10 from a cored drilled hole, was conducted. Quantification of divalent cation (Mg, Ca, Fe) content and cation release capacity using XRF and XRD revealed higher cation percentages in dunite samples (approximately 30 %) compared to serpentinite samples (approximately 26 %). Additionally, the study estimated the stimulated rock mass-toCO 2 sequestered ratio, R CO 2 , with dunite samples averaging approximately 2.20 R CO 2 values and serpentinite samples averaging approximately 2.53. Geomechanical testing enabled the prediction of fracture propagation pressures during aqueous CO 2 injection for in -situ mineralisation and the estimation of fracture geometries, emphasizing the role of rock stiffness in determining fracture width (averaging 6.0 mm). Furthermore, the research estimated the rock volume exposed to CO 2 -laden fluid during injection, particularly focusing on the GHQ -3 sample, which theoretically amounted to approximately 600 kg of rock capable of sequestering around 300 kg of CO 2 for a 10 m3 fluid volume with a CO 2 concentration of 1 mol kg - 1 . The study established a relationship between injected volume and CO 2 uptake, suggesting the potential for significant CO 2 sequestration scalability by employing horizontal wells and frac- turing additional zones, thereby creating and intersecting multiple transverse fractures along a single target zone.

The drive towards achieving net-zero greenhouse gas emissions by 2050 has spurred interest in solutions for carbon capture and storage. One such approach involves the storage of CO2 in earth-abundant Ca-, Fe-, and Mg-bearing silicate rocks and minerals as carbonates via the process of CO2 mineralisation. However, CO2 injection for the purpose of mineralisation through naturally fractured host rocks, or via the creation of fractures, remains a relatively unexplored area in geoengineering CO2 storage. This research addresses identifying optimal geographic locations for CO2 mineralization, with a specific focus on the availability of Mg, Ca, and Fe cations for exothermic CO2 reactions and their impact on fracture conductivity during in-situ mineralization. A comprehensive analysis of 26 dunite and serpentinite samples from diverse locations in Australia and New Zealand, including 10 from a cored drilled hole, was conducted. Quantification of divalent cation (Mg, Ca, Fe) content and cation release capacity using XRF and XRD revealed higher cation percentages in dunite samples (approximately 30%) compared to serpentinite samples (approximately 26%). Additionally, the study estimated the rock-to-CO2 sequestered ratio (RCO2), with dunite samples averaging approximately 2.20 RCO2 values and serpentinite samples averaging approximately 2.53. Geomechanical testing enabled predicting fracture propagation pressures and fracture geometries during aqueous CO2 injection for in-situ mineralization, emphasizing the role of rock stiffness in determining fracture width. Furthermore, this research estimated the rock volume exposed to CO2-laden fluid during injection, which theoretically amounted to ~ 750 kg of rock mass capable of sequestering ~ 400 kg of CO2 for a 10 m3 fluid volume with 1 mol kg–1 of CO2. The study established a relationship between injected volume and CO2 uptake, suggesting the potential for significant CO2 sequestration scalability by employing horizontal wells and fracturing additional zones, thereby creating, and intersecting multiple transverse fractures along a single target zone.

The geometric properties of the pore space govern the electrical and hydraulic properties of soils. Recognizing this commonality, this paper proposes a new approach to determine permeability from high-frequency electromagnetic (HF-EM) measurements on geomaterials undergoing evaporative dewatering. Two materials have been used; (1) kaolin, a reference geomaterial; and (2) a dredged sediment sample from the Port of Brisbane (PoB) reclamation site (Queensland, Australia). Based on a dielectric mixture equation that integrates Archie's parameters, the evolution of formation factors as a functions of porosity have been derived. Several models that are available in the literature have been used to estimate proxies for geometric length scales for pore radii. With knowledge of the formation factors and proxies for pore radii as functions of porosity, permeabilities of the materials under saturated conditions have been estimated. The results have been compared with experimentally obtained permeabilities. Using the formation factors from HF-EM measurements and two of the proxies for pore radii (hydraulic and characteristic pore radii, as defined in this paper), a good degree of agreement with the experimental data has been obtained within a variation in one-order of magnitude for kaolin. For the PoB material, the use of hydraulic pore radius yielded the best estimation of permeability.

This paper investigates the relevance of an inductive sensor for non-contact blood glucose continuous monitoring purposes. The considered sensor is based on a flexible passive radiofrequency single-turn transmission-line resonator (STLR), which allows wearable, low cost, non-invasive and wireless sensing implementations to be considered. The STLR sensor is coupled to an inductive reading probe and used as a wireless transmit-and-receive high sensitivity sensor. The relevance of the used STLR sensor is evaluated using a high-Q 60 MHz STLR fabricated on a flexible Kapton substrate, implemented to monitor reference liquid samples mimicking the dielectric properties of blood, and featuring various D-glucose concentration in the 0.24 g/L to 5 g/L range, consistent with human blood glucose concentration levels. Thanks to an equivalent electrical circuit modelling the coupling between the STLR and the liquid sample, three sensor output parameters are defined and assessed at 60 MHz to monitor the dielectric changes induced by the modifications of the samples with D-glucose concentration. The obtained results are compared to those provided by a conventional open ended coaxial probe immersed in the liquid and operated at the same frequency, and to data published with similar coaxial sensors. The obtained results show full consistency between the proposed STLR non-contact sensor and contact dielectric sensors, and open the way to a new generation of non-contact and wearable sensors dedicated to low cost and easy to use continuous blood glucose measurement applications.

This paper builds on exploring the applications of biomediated pathways to solve geotechnical challenges. First, the state of the art of biological remediation strategies including microbial remediation and phytoremediation have been introduced and critically reviewed in the context of decontaminating the soils. Next, biopolymerisation, biomineralisation and bioneutralisation processes have been depicted with a special emphasis on the applications including but not limited to soil stabilisation, soil erosion prevention, anti-desertification and pH neutralisation. Each of these methods have their own limitations and bottlenecks while scaling up, and these challenges have been summarised and some possible paths to overcome the challenges have also been discussed. The state of the art of electromagnetic (EM) monitoring methods to capture the effects of biomediation on spatio-temporal soil properties are then highlighted as a non-invasive and rapid pathway to track the progress of biomediated soil processes. Finally, each of the technologies discussed have been evaluated for their maturity level using the principles of technology readiness level (TRL). A majority of the technologies amounting to around 77% are still in the TRL 4–7, i.e. in the valley of death. It is thus evident that development of these technologies needs to be supported with appropriate funding for improving their maturity to a level of industrial deployment.

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.

Suffusion experiments were utilised to quantify the evolving degree of heterogeneity in gap-graded soils. Upward flow was imposed on test specimens comprising a mixture layer with varying finer fraction contents overlaid by a coarse layer. A coaxial permeameter cell enabled the local permeability to be obtained using spatial time domain reflectometry. Three methods (coefficient of variation, Dykstra-Parsons coefficient, and Lorenz coefficient) were employed to quantify heterogeneity based on spatial variability in local permeability. For the two-layered specimen in this study, all three methods demonstrated that suffusion had a homogenising effect with particle migration from the mixture layer to the coarse layer. Detailed insights were obtained from a multi-layered approach, where the Dykstra-Parsons coefficient was found to be more sensitive to spatial variations, while the Lorenz coefficient was less dependent on the amount of data. The key observation was that an increase in heterogeneity led to a reduction in particle migration. This is an important finding as prior studies focused on homogeneous specimens, while this study demonstrates that small amounts of heterogeneity can significantly impact particle migration characteristics. This reinforces the need to quantify the evolving degree of heterogeneity.

The dynamic effects in soil water retention curves (SWRCs) have been the focus of much research. However, most studies implemented short column tests in a few centimeters, under which a semi-permeable porous media inevitably minimizes or magnifies the dynamic effects. In this study, full-scale sand column tests were conducted to eliminate this flaw by preparing a saturated zone under the unsaturated one. The soil suction and moisture profiles were monitored using high-precision tensiometers and spatial time-domain reflectometry, thereby providing a rational overshooting range of the dynamic SWRC. The results confirm that the dynamic primary drainage curve overshoots the static one. The dynamic effects were estimated quantitatively from the soil moisture re-equilibrium time (τS) and dynamic coefficient (τp), falling within reasonable ranges from previous studies. The τp increases log-linearly with decreasing moisture content and can be estimated well from the corresponding τS and the first derivative of SWRC. Also, the τp increases as the soil becomes finer and better graded, which agrees with more-prominent dynamic effects for lower-permeability reservoirs from petroleum studies but disagrees with more-significant dynamic effects for higher-permeability sand from soil-hydrology studies. The analysis shows that the dynamic effects are not dominated solely by the τp or permeability but also by the groundwater dynamics, which can be seen as a pressure boundary from the saturated zone. This finding explains the significant dynamic effects for both high- and ultra-low-permeability geomaterial. Therefore, the present full-scale soil column setup with a prepared saturated zone is recommended for academic investigations of dynamic SWRCs.