Search Results (82)

Underground storage of green hydrogen is a strategic enabler of large-scale renewable deployment, but its feasibility rests on a hard problem: keeping a small, highly mobile molecule confined underground for decades without safety or environmental risk. This critical review examines the containment mechanisms of hydrogen across underground storage types, focusing on geological barriers, well integrity and sealing materials. We evaluate the containment capabilities of salt cavities, deep aquifers and depleted reservoirs, with particular attention to the viscoplastic, self-healing properties of salt that promote confinement, and to the vulnerabilities of well infrastructure and salt–cement interfaces. Emerging alternatives, including lined rock caverns and repurposed abandoned mines, are assessed alongside their distinct operating configurations and use cases. Leakage mechanisms including diffusion, advection, microcracking, cement degradation and hydrogen–material interactions are analysed alongside geomechanical modelling, microbial activity, monitoring strategies, regulatory frameworks, and techno-economic and environmental considerations, including the integration of carbon capture, utilisation and storage (CCUS) with underground hydrogen storage. Well integrity emerges as the dominant risk factor across storage types. The review concludes with design criteria, monitoring priorities and research needs to guide the safe, sustainable deployment of underground hydrogen storage, providing a scientific foundation for future numerical and experimental work on storage tightness. Full article

This study presents an integrated multidisciplinary framework for evaluating the reuse of abandoned underground mining infrastructure in Bosnia and Herzegovina as sustainable underground energy storage systems that support the energy transition and decarbonization. The research focuses on the Central Bosnia and Tuzla coal basins, using case studies from the Zenica and Tuzla mining regions to assess Underground Pumped Hydroelectric Energy Storage (UPHES), Compressed Air Energy Storage (CAES), and gravity-based energy storage technologies. The methodology integrates geological and geotechnical characterization, thermo-hydro-mechanical (THM) analysis, thermodynamic calculations, and Multi-Criteria Decision Analysis (MCDA) to evaluate technical, operational, and safety performance. Methane mitigation, smart ventilation, thermal stability, and geomechanical behavior under cyclic loading were also considered. The results indicate that sedimentary coal basins are well suited for UPHES and gravity-based storage systems, with UPHES capacities reaching 1.75 GWh per cycle under optimized conditions, while the separately evaluated solid-mass gravity storage system provides a capacity of 6.15 MWh. Evaporite formations in the Tuzla Basin offer favorable conditions for CAES because of the low permeability and plasticity of halite, enabling storage capacities exceeding several GWh. THM analysis confirmed acceptable geomechanical stability during cyclic operation, while the economic assessment based on the Levelized Cost of Storage (LCOS) demonstrated the long-term competitiveness of Abandoned Mine Energy Storage (AMES) compared with battery technologies. Overall, the findings highlight abandoned mines as strategic low-carbon assets for renewable energy integration and regional post-mining transition. Full article

In mining methods such as the “three-underground” shortwall strip mining and other methods involving coal pillar retention, research on the instability mechanism of overburden–coal pillar groups considering the rheological properties of coal and rock is of great significance for ensuring the long-term safety and stability of the coal pillar system, the safe and efficient production of mines, and the safety of surface structures. Based on the interaction between the coal pillar and the surrounding rock, a plane strain model of residual coal pillars in inclined coal seams is established, and analytical expressions for the stress and displacement fields of the coal pillar are derived using the Ritz method. Combined with the actual conditions of strip mining in a certain village, a three-dimensional numerical calculation model for coal pillar group stability is established, which incorporates the rheological characteristics of coal-rock media. The influence of time effect on the long-term stability of coal pillar group is investigated. The impact of coal pillar width, mining depth, and coal seam dip angle on the plastic zone, stress distribution, and deformation characteristics of coal pillar groups is further studied. Research findings indicate that under the long-term action of the gravity of the overlying strata, the two sides of each coal pillar entered the plastic yielding state after 1 day of creep, and present a shear failure form. With the width of coal pillars increasing, both the extent of plastic zones and stress and deformation within each pillar decrease to varying degrees. When the pillar width reaches 40 m, the disparity in plastic zone coverage between pillars diminishes from a maximum of 21.14% to 10.16%. As mining depth increases, the rate of growth in plastic zones, stress, and deformation across coal pillars gradually accelerates, with the range of plastic zones expanding from 3.55% to 11.36%. An increase in coal seam dip angle similarly accelerates the development of the plastic zone within the coal pillar group. However, the vertical stress and vertical displacement of individual coal pillars exhibit varying degrees of reduction, while the maximum shear stress and horizontal deformation of the coal pillar group increase more rapidly. Full article

Amid growing global instability and the escalating impacts of climate change, there is an increasing need to develop resilient human habitats, particularly underground environments. At the same time, resource-extraction activities have left behind extensive underground voids in abandoned mines, presenting a valuable opportunity to expand multifunctional spaces that can serve daily needs as well as emergency shelter functions (dual-use), while also supporting urban–rural transformation and sustainable development goals. Due to their geological conditions and mining methods, underground goafs offer inherent advantages for dual-use development. In light of this, this study proposes a theoretical approach to address the three fundamental challenges associated with the dual-use of underground goafs in gypsum mines from the perspective of architectural space creation. This study does not present a completed empirical validation; instead, it develops a conceptual and interdisciplinary methodological framework intended to guide future empirical research and engineering implementation. Specifically, the framework is as follows: (1) defining escape safety capacity under disaster impacts by constructing a dynamic assessment model integrating disaster physics, behavior simulation, and VR-calibrated experiments; (2) elucidating the correlation mechanism between spatial topological features and human response patterns using space syntax and multi-modal psychological experiments to reveal how spatial morphology influences orientation, emotion, and behavior; and (3) moving beyond the traditional notion that space should be adapted to functional requirements, proposing an innovative strategy involving adapting predefined functions to the space. Full article

Acidic mine water generated during underground CO₂ sequestration and sulfide oxidation can alter the pore-fracture structure of coal, and threaten the stability of abandoned mine spaces. However, the mechanism through which acidic environments influence the deterioration of coal remains insufficiently understood. In this study, uniaxial compression experiments were conducted on coal samples treated with solutions with different pH values, and acoustic emission (AE) monitoring technology was used to characterize fracture activity and damage evolution during loading. A quantitative model linking acidity to the mechanical behavior of coal was established by integrating fractal theory with damage mechanics. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were further employed to reveal the microstructural and mineralogical mechanisms of coal deterioration. The results show that acidic environments significantly degrade the mechanical properties of coal samples. With decreasing pH, peak stress and elastic modulus of the selected representative sample progressively decrease, and the failure mode becomes increasingly fragmented and dispersed. At pH = 1, the degradation of peak stress and elastic modulus reaches 73.01% and 49.38%, respectively. Increasing acidity also enhances AE activity during loading and increases the correlation dimension, indicating greater crack complexity and instability. On this basis, the proposed quantitative model accurately describes the transformation process of coal samples from microscopic damage to macroscopic mechanical degradation induced by acidity. SEM and XRD results further show that stronger acidity promotes pore enlargement, crack interconnection, mineral dissolution, secondary mineral formation, and weakening of cementation, revealing the physical essence of the multi-scale damage and degradation of coal samples. The findings can provide a theoretical basis for assessing coal stability in acidic environments and ensuring the safe storage of CO₂ in abandoned mines. Full article

In recent years, unmanned aerial vehicles (UAVs) have increasingly become carrying platforms for Earth observation systems equipped with optical, microwave, and other types of sensors, primarily enabling high-resolution observations of above-ground targets. With the development of geophysical methods, bulky instruments originally designed for deep subsurface detection have been progressively miniaturized and made more lightweight, allowing their integration with civilian UAVs and opening new technological avenues for subsurface investigation. We have developed a semi-airborne transient electromagnetic system based on a UAV that is capable of simultaneously obtaining underground resistivity and polarization rate parameters. A survey was conducted over the M’sesa mining area in the Democratic Republic of the Congo. This is a mine pit that has been abandoned for over 50 years and has been flooded to form a lake, making it difficult to detect its deep mineralization potential using traditional ground-based methods. The results clearly delineate the spatial distribution of the Shangoluwe–M’sesa compressional fault and reveal a deep low-resistivity and high-chargeability zone, which provides clues for the exploration of deep deposits. This study will be of significant importance for accelerating the promotion and application of UAV-based semi-airborne electromagnetic exploration technologies. Full article

Colmation phenomena play a critical role in long-term gas flow through porous media, significantly influencing methane migration, mine ventilation efficiency, and emission control in both active and abandoned coal mines. In colmation modeling, three fundamental kinetic types are commonly distinguished, with the third kinetic providing a generalized nonlinear formulation capable of describing state-dependent and spatially variable permeability degradation. However, the strong nonlinearity of the coupled transport–colmation equations prevents the derivation of closed-form solutions, which necessitates the application of linearization techniques. In this study, gas flow with colmation governed by third-kinetics is analyzed with particular emphasis on methane migration in underground mining environments. Linearization of nonlinear kinetic terms is applied at the level of the coupled mass balance and colmation equations, resulting in an approximate form of Darcy’s law and an explicit analytical solution describing the evolution of the porous medium state. The primary objective of the study is to quantify the error introduced by the adopted linearization and to analyze its spatial and temporal propagation with respect to the nonlinear reference solution. A rigorous error estimation based on Taylor series truncation is developed, yielding an explicit criterion that defines the validity range of the linearized solution. The results demonstrate that the approximation remains reliable within the regime of weak colmation, while the associated error is locally generated and propagates through transport mechanisms without exhibiting uncontrolled growth. Full article

Abandoned mining areas provide valuable opportunities to investigate ore-forming processes, supergene mineral transformations, and the geochemical behaviour of metals. In this sense, the old Preguiça mine (Beja, Portugal), exploited for Fe–Zn–Pb, was studied providing new mineralogical and geochemical data aimed at improving the understanding of the secondary mineral assemblages of this deposit. A total of 70 samples collected from three accessible underground levels (first, second and third) and mine waste, complemented by 16 samples from a deeper level (fourth) previously collected, were analysed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and a portable X-ray fluorescence (pXRF) equipment. Mineralogical phases are dominated by a wide range of secondary oxides, carbonates, arsenates, vanadates, silicates, phosphates and sulphates, but remnants of primary sulphides were also found. The following minerals can be emphasised: goethite, hematite, calcite, dolomite, descloizite, willemite, mimetite, cerussite, smithsonite and fraipontite. The presence of massicot in the Preguiça mine, is described for the first time. Bulk geochemical analyses show high concentrations of Fe, Ca, Zn and Pb, consistent with the observed mineralogy. The presence of vanadium- and arsenic-bearing minerals highlights the occurrence of critical raw materials, supporting the importance of reassessing other abandoned mining areas in the context of sustainable resource management and strategic raw-material planning. Full article

Methane emissions from abandoned coal mining operations represent a persistent environmental and safety challenge in post-mining regions undergoing urban redevelopment. As urban infrastructure expands over former underground workings, the uncontrolled migration of mine gas can compromise public safety, exacerbate greenhouse gas emissions, and undermine sustainable development goals. This study investigates the origin of methane emissions detected in an urban area of the municipality of Lupeni, Romania, following the commissioning of a new natural gas distribution pipeline installed within a historically mined perimeter. The emissions had not been previously reported and were unexpectedly discovered during technical inspections conducted after the gas network installation, highlighting the absence of historical data on gas presence in this area. This is the first documented case of an accidental discovery of methane emissions in an urban perimeter overlying historical coal mine workings in Romania, granting this study a pioneering status, both scientifically and in terms of urban risk management. The findings emphasize that administrative mine closure does not equate to risk closure, as latent methane emissions may reactivate during urban transformations (e.g., excavations, utility upgrades, drainage changes). To ensure a scientifically sound and sustainable risk assessment, an integrated diagnostic framework was applied, combining chronological field monitoring with chromatographic gas composition analysis. This methodology enabled precise attribution of the methane source to abandoned underground mine workings, excluding the public gas network as a contributor. Based on this diagnosis, a controlled drainage and methane recovery system was implemented, resulting in the elimination of detectable concentrations at all monitoring points by February 2025. The captured methane was redirected for local energy use, transforming an environmental liability into a usable resource. This intervention supports circular economy principles and aligns with EU climate and energy transition goals. The proposed methodological framework provides a replicable model for identifying and managing residual mine gas in post-industrial urban environments. Although emission fluxes were not quantified, concentration-based screening enabled risk diagnosis, prioritization, and targeted intervention. These findings are relevant to EU Regulation (2024/1785) on methane emission reduction, emphasizing the need to include post-mining methane (AMM) in urban planning and environmental monitoring strategies. Limitations of the study include the absence of baseline data and the inability to calculate total methane flux. However, the results support immediate and practical risk mitigation and highlight the need for future work focused on long-term monitoring and emission quantification. This case provides critical insights for other post-mining cities in Central and Eastern Europe facing similar challenges at the intersection of legacy coal infrastructure and modern urban development. This study is designed as a concentration-based diagnostic and risk-oriented case study and does not aim to quantify methane emission fluxes. Full article

The growing global demand for critical raw materials has highlighted the need for autonomous systems in abandoned underground mines. We propose a multi-robot coordination architecture using Hierarchical Finite State Machines (HFSMs) for sequential task execution in GPS-denied, infrastructure-less environments. Unlike existing centralized approaches, our system enables each robot to execute its own HFSM behavior triggered through inter-robot communication, eliminating dependency on persistent connectivity. We implemented and validated this architecture using a Deployer robot and a Stinger robot within the EU Horizon PERSEPHONE project. Experimental validation demonstrated successful coordination both with persistent connectivity and during network interruptions, proving the system’s fault tolerance capabilities. The system successfully executed sequential deployment and anchoring tasks, demonstrating that this coordination approach enables multi-robot coordination without requiring persistent connectivity, thereby addressing critical limitations for autonomous operations in underground environments. Full article

Methane emissions from underground coal mines are a significant source of greenhouse gases (GHGs) and a major safety concern. In highly methane-prone operations, a large proportion of emissions comes from low-content abandoned mine methane (LCAMM) accumulated in post-mining goafs, where concentrations usually stay below 30% CH₄. Building on the Research Fund for Coal and Steel (RFCS) REM project, this paper presents a cost–benefit analysis of a comprehensive scheme for capturing, transporting, and utilising LCAMM from post-mining goafs for electricity generation. The concept involves long-reach directional boreholes drilled behind isolation dams, a dedicated methane-reduced drainage system connected to a surface methane drainage station, and four 2 MWe gas engines designed to run on a 20–40% CH₄ mixture. Greenhouse gas performance is evaluated by comparing a “business-as-usual” scenario in which post-mining methane is combusted in gas engines to produce electricity without further GHG cost–benefit consideration. The results indicate that the project can achieve a positive net present value, highlighting the role of LCAMM utilisation for methane-intensive coal mines. The paper also explores the monetisation of non-emitted methane using the European Union Emissions Trading System (EU ETS), as well as social cost benchmarks and penalty levels consistent with the emerging EU Methane Emissions Regulation (EU MER). Full article

Underground gas storage (UGS), encompassing hydrogen, natural gas, and compressed air, is a cornerstone of large-scale energy transition strategies, offering seasonal balancing, security of supply, and integration with renewable energy systems. However, the complexity of geological conditions, multiphysics coupling, and operational uncertainties pose significant challenges for UGS design, monitoring, and optimization. Artificial intelligence (AI)—particularly machine learning and deep learning—has emerged as a powerful tool to overcome these challenges. This review systematically examines AI applications in underground storage types such as salt caverns, depleted hydrocarbon reservoirs, abandoned mines, and lined rock caverns using bibliometric and knowledge-graph analysis of 176 publications retrieved from the Web of Science Core Collection. The study revealed a rapid surge in AI-related research on UGS since 2017, with underground hydrogen storage emerging as the most dynamic and rapidly expanding research frontier. The results reveal six dominant research frontiers: (i) AI-assisted geological characterization and property prediction; (ii) physics-informed proxy modeling and multi-physics simulation; (iii) gas–rock–fluid interaction, wettability, and interfacial behavior prediction; (iv) injection-production process optimization; (v) intelligent design and construction of underground storage, especially salt caverns; and (vi) intelligent monitoring, optimization, and risk management. Despite these advances, challenges persist in data scarcity, physical consistency, and generalization. Future efforts should focus on hybrid physics-informed AI, digital twin-enabled operation, and multi-gas comparative frameworks to achieve safe, efficient, and intelligent underground storage systems aligned with global carbon neutrality. Full article

The recovery of timber residues from abandoned underground coal mines presents a unique opportunity to expand the raw material base for wood-based composites, aligning with the principles of cascade utilization. Large amounts of structural wood, embedded for decades under anaerobic and humid mining conditions, remain remarkably well-preserved and can be valorized as a secondary feedstock. The aim of this work was to investigate and evaluate the feasibility of incorporating recovered mining timber into the production of medium-density fiberboards (MDFs). Six types of laboratory panels were produced, containing different ratios of recovered and virgin pine fibers (0–100%), bonded with melamine–urea–formaldehyde resin and hot-pressed at 180 °C. Comprehensive testing of physical and mechanical properties demonstrated that panels with up to 40% recovered fibers fully complied with European standards for general-purpose boards, while up to 60% substitution was acceptable with respect to internal bond strength. At higher substitution levels, however, dimensional stability and strength were significantly reduced. These findings highlight the potential of mine timber recovery as a viable raw material pathway for MDF manufacturing, extending the service life of wood resources and reducing pressure on primary forests. The study emphasizes the role of recovered biomass in advancing circular bioeconomy objectives and resource efficiency in the wood-based panel sector. Full article

Ecological restoration of mine wastelands is central to biodiversity conservation and ecosystem recovery worldwide. However, the long-term ecological consequences of active restoration versus natural regeneration remain debated, particularly in mountainous karst landscapes. Using a space-for-time substitution, we established a five-stage chronosequence—recently abandoned, 10 years, 20 years, 30 years, and a late-successional forest (>35 years)—in a typical underground coal-mine wasteland in eastern Yunnan, southwest China. Each age class contained paired active restoration and natural regeneration sites; the late-successional forest served as a reference. We surveyed nested vegetation plots (20 × 20 m with shrub and herb subplots) in summer and autumn, recorded vertebrate species with camera traps, and quantified α-diversity (species richness, Shannon–Wiener diversity, Simpson’s diversity, Pielou’s evenness) and β-diversity (Bray–Curtis dissimilarity, non-metric multidimensional scaling). Overall plant α-diversity was highest in natural regeneration and lowest in active restoration, whereas tree-layer diversity was highest in active restoration and shrub and herb layers were richer under natural regeneration. Preliminary data from our camera traps suggested that animal species richness ranked late-successional forest > natural regeneration > active restoration, but evenness peaked in active restoration, suggesting early-stage homogenization. Plant β-diversity indicated stronger compositional divergence among active restoration sites and greater similarity between natural regeneration and the reference forest; both modes converged toward the reference forest over time but followed distinct patterns. These findings suggest that active restoration accelerates structural development yet increases between-site heterogeneity, whereas natural regeneration maintains higher overall diversity and compositional similarity to reference communities. Our results provide preliminary empirical guidance for selecting restoration strategies in similar karst coal-mine landscapes. Full article

This paper aims to develop a robust empirical–analytical model using the statistics of mine water level rebound in abandoned mines and the basic physical principles of underground hydraulics. The data collected and treated included the time series of the mine water level for 35 closed and flooded mines from four European countries. Within the developed model, mine water level evolution is governed by an ordinary differential equation with one fitting parameter that depends on the floodable cavity volume in a mine and water inflow before flooding begins. The model assumes that rock properties and residual void distribution are homogeneous, and the mines being flooded are almost isolated hydraulically from the neighboring ones. The exponential formula, as the governing equation solution, was found to be the most suitable for fitting the measurements. The calculated exponential curves allow for excellent or very good fitting of the measured water levels for 17 of 35 mines, and acceptable fitting for 11 mines in terms of minimizing mean-square-root deviation. The proposed approach can be applied to preliminary assessments of mine water level rebound in developing and calibrating sophisticated numerical flow models. Full article