Coal and gas outbursts are among the most severe hazards in deep underground mining, driven in part by the rapid desorption of gas from coal seams. This study investigates the multi-scale structural alterations induced by the rapid desorption of CH4 and CO2 in deep-buried coal samples from the Sydney Basin. A novel methodology integrating high-resolution 3D micro-computed tomography (μ-CT), scanning electron microscopy (SEM), low-pressure gas adsorption (LPGA-N2 and LPGA-CO2), and helium-based void volume measurements for full-scale quantification was employed. Results reveal that rapid gas desorption facilitates the expansion of existing fractures and the formation of new ones, with fracture volume increasing proportionally with equilibrium pressure. SEM reveals widening and propagation of surface microfractures consistent with μ-CT observations. CH4 desorption caused greater structural damage than CO2 under equivalent gas content, due to its higher equilibrium pressure and gas expansion energy. Microscale analysis revealed a slight reduction in micropore volume (−2.49%) and a significant increase in mesopores (9.67%), enhancing gas diffusion and potentially intensifying outburst severity. Structural damage was most significant in areas with pre-existing fractures. These findings establish a clear linkage between gas pressure, desorption dynamics, and coal structural alteration, providing a scientific basis for refining gas threshold limits and improving outburst-risk management in deep coal seams, thereby supporting safer and more sustainable mining practices.

This study systematically elucidates the mechanism by which HCl-modified SiO2 nanofluid efficiently suppresses dust through synergistic optimization of coal surface properties and pore structure. A series of experiments were conducted, including wettability characterization, pore structure analysis, dust generation evaluation, and surface morphology observation. Findings reveal that at low concentration of 0.01 wt%, this HCl-modified SiO2 significantly enhances coal hydrophilicity. Compared to deionized water, surface tension decreases by 16.83 % and contact angle reduces by 37.34 %. The HCl-modified SiO2 nanofluid induces a more complex pore structure in coal, expanding the hydrophilic surface area. This reduces surface roughness to form a stable, uniform wetting film, ultimately enhancing both wetting and water retention capabilities of the coal. Drop weight tests demonstrate that treated coal samples produce the largest dust particle size and the least respirable dust, achieving remarkable dust suppression. This study also elucidates the molecular-level mechanism of nanofluid's enhance wetting and optimize pore structure of coal. The findings provide experimental evidence for the practical application of HCl-modified SiO2 nanofluid in coal mine dust control.

Coal and gas outbursts are significant safety hazards in underground coal mining, particularly in deep Australian coal seams. While the traditional outburst risk management relies on threshold limit values of seam gas content, recent experiences have shown that this approach overlooks important factors such as coal toughness and strength. This study evaluates the effectiveness of the coal toughness test, also known as the Protodyakonov strength test, as a predictor of outburst risk. After upgrading the test rig and updating testing procedures, the toughness index f was compared with conventional strength parameters, revealing a strong positive correlation with uniaxial compressive strength (UCS) and drop hammer impact strength. An analysis of 98 coal samples taken from seven seams at three Australian mines revealed that lower moisture content and higher apparent relative density are associated with increased coal toughness. Specifically, the Pearson and Spearman correlation coefficients of −0.79 and −0.78 were observed, respectively, indicated a strong negative relationship between coal moisture content and toughness. Additionally, coal seams with lower volatile matter content exhibited higher toughness values. The study proposes adopting the coal toughness index as a robust alternative to the conventional indicators such as UCS, especially when obtaining intact coal samples is difficult. Incorporating the toughness index into the outburst risk assessment can improve safety by adopting a more comprehensive and reliable approach.

Moisture content of rock/coal can change its mechanical properties and absorption capacities, which can directly affect gas diffusivity, change the stress distribution and hence cause significant impacts on the overall gas or coal extraction process. Observation of the water penetration process and water distribution in the coal matrix will be beneficial for the understanding of the fluid-solid coupling mechanism in hydraulic fracturing, aquifer cracking and coal seam infusion. However, the observation of water penetration process and the determination of water distribution mode were hard to be non-destructively achieved as coal is a non-uniform, inhomogeneous and un-transparent material. µ-CT imaging, which is based on variation of X-ray attenuation related to the density and atomic composition of the scanned objects, enables a four-dimensional (spatial-temporal) visualise of the heterogeneous and anisotropic coal samples. The primary aim of this paper is extending the application of µ-CT imaging to explore the moisture penetration and distribution within coal samples during water infusion process, which has been reported by very little literature. The working principle and procedures of CT imaging was firstly introduced. Then, the determination equation of moisture distribution based on density profile was established. The CT determined moisture content has been compared with weighting method for verification. The paper has demonstrated that µ-CT can be used for non-destructively imaging the moisture distribution within coal samples.

Methane (CH4) and carbon dioxide (CO2) are primary components of coal seam gas (CSG). Understanding their adsorption-desorption hysteresis characteristics, along with the fundamental mechanism, is crucial for CSG exploitation and related hazards mitigation. This research focused on the representative Bulli coal seam in the Sydney Basin, Australia. Through the purpose-built indirect gravimetric high-pressure isothermal adsorption-desorption hysteresis experiment, a novel Langmuir-based desorption model, incorporating hysteresis effect and residual gas, was proposed. Quantitative characterization of the adsorption-desorption hysteresis degrees of CO2 and CH4 in coal particles of various sizes and in Phi 50 mm x 100 mm intact coal samples were achieved using the improved hysteresis index (IHI). The experimental findings validated that the proposed desorption model accurately describes the desorption behavior of CO2 and CH4 in coal (R-2>0.99). Based on the adsorption-desorption properties of inkbottle-shaped micropores and pore deformation caused by gas adsorption-induced coal expansion, the occurrence mechanism of adsorption-desorption hysteresis and the fundamental reasons for the presence of residual gas were elucidated. Furthermore, the study explored the impact of CO2 and CH4 adsorption-desorption hysteresis effects on coal and gas outbursts, suggesting that coal seams rich in CO2 do not have a higher propensity for outbursts than those rich in CH4. (c) 2024 Published by Elsevier B.V. on behalf of China University of Mining & Technology. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Underground miners in Australia are facing continued threats from dust-related diseases. To address these issues, improved knowledge of airflow migration patterns and respirable dust dispersion characteristics within a continuous-miner-driven heading under an exhausting ventilation system is required. Based on site-specific conditions of a development heading in New South Wales, a three-dimensional computational fluid dynamics (CFD) model was constructed and validated with onsite dust monitoring data, where a good agreement was achieved. Three scenarios of coal cutting at the middle, floor and roof positions were considered and simulated, with dust generated at four different sources. The simulation results indicated that the operators on the left-hand-side (LHS) with the extraction duct should be equipped with fit-for-purpose personal protective equipment and stay behind the ventilation duct inlet during coal cutting process, while miners standing at the right-hand-side (RHS) of the continuous miner for roof and rib bolting and machine operating should stay immediately behind the roof and rib bolting rig where dust concentration is relatively low. In addition, an increase in airflow rate through the exhausting ventilation duct or a reduction in the distance from the duct inlet to the heading face assisted in reducing dust levels within the heading, particularly at the LHS of the continuous miners. Finally, compared to the scenario of the current ventilation scheme, an on-board exhausting ventilation system could improve dust removal performance, with dust concentration at the breathing level reducing by approximately 43.6%. This modelling study can advance the understanding of multi-source dust diffusion characteristics in the heading face and provide guidance on dust mitigation, thus improving the health and safety of miners and creating a cleaner underground working environment.

Rock fragmentation is a common physical and mechanical phenomenon that exists in a variety of ranges from the mining and processing. Communication is an important operation in coal processing whereby the coal block coming from coalmines is crushed into fragmentations with reduced size, which accounts for 80% of the electricity consumption of mineral processing circuits. Fragmentation energy, which is related to the coal particle size distribution, is an essential parameter for improving the efficiency of shearer, road-header, and crusher. Coal particles are generally simplified into fine or near spherical shapes for analytical and numerical simulation purposes. This research aims to establish the fragmentation energy calculation model for coal fragmentations with coarse and wide size distribution based on the analysis of size distribution and energy-size relationships of coal particles. It has been demonstrated by the results that the fragmentation energy of impact load crushed coal can be determined based on Rittinger's theory with fractal or RR model particle size distribution.

Long-term exposure to respirable coal and silica dust during underground tunnelling operations has gained increasing attention in recent years. The solution to effective mitigation of dust exposure depends not only on higher-order engineering controls, but also on administrative controls for frontline workers. However, there is a disconnect between knowledge gathered in the field of dust exposure monitoring and the frontline worker, resulting in important learnings being overlooked in underground tunnelling operations. To remedy this discrepancy, an immersive educational tool was developed to visualise computational fluid dynamics (CFD) modelling datasets of ventilation and respirable dust flow characteristics in the tunnel face in a virtual reality (VR) environment. An algorithm was developed for processing the large and complex CFD datasets into a form that can be processed and visualised using standalone VR headsets with limited processing power. The VR-CFD system was assessed by an industry expert and via many industry showcases, where regular feedback was received for making significant improvements in this education tool. This tool has been developed as a training platform to allow frontline workers to better understand the results of decisions made during tunnelling operations and the best practices for dust controls. A number of key technological achievements were made that can be used in the future to quickly translate real-world particulate readings collected from underground space into a VR visualiser. This VR-CFD digital technology can readily be extended to mining, construction and other tunnelling operations in the underground space, thus improving health and safety.

The gas content is crucial for evaluating coal and gas outburst potential in underground coal mining. This study focuses on investigating the in-situ coal seam gas content and gas sorption capacity in a representative coal seam with multiple sections (A1, A2, and A3) in the Sydney basin, where the CO 2 composition exceeds 90%. The fast direct desorption method and associated devices were described in detail and employed to measure the in-situ gas components ( Q 1 , Q 2 , and Q 3 ) of the coal seam. The results show that in-situ total gas content ( Q T ) ranges from 9.48 m 3 /t for the A2 section to 14.80 m 3 /t for the A3 section, surpassing the Level 2 outburst threshold limit value, thereby necessitating gas drainage measures. Among the gas components, Q 2 demonstrates the highest contribution to Q T , ranging between 55% and 70%. Furthermore, high-pressure isothermal gas sorption experiments were conducted on coal samples from each seam section to explore their gas sorption capacity. The Langmuir model accurately characterizes CO 2 sorption behavior, with fit coefficients ( R 2 ) greater than 0.99. Strong positive correlations are observed between in-situ gas content and Langmuir volume, as well as between residual gas content ( Q 3 ) and sorption hysteresis. Notably, the A3 seam section is proved to have a higher outburst propensity due to its higher Q 1 and Q 2 gas contents, lower sorption hysteresis, and reduced coal toughness f value. The insights derived from the study can contribute to the development of effective gas management strategies and enhance the safety and efficiency of coal mining operations.

Microscopic pores significantly impact the coalbed methane (CBM) storage, hence gas energy recovery and gas-related problems mitigation. However, the quantitative relationship between microscopic pore properties and CBM storage dictated by gas adsorption capacity remains unclear. In this study, high-pressure isothermal gas adsorption experiments were conducted using differently ranked coal samples to investigate gas adsorption characteristics. High-pressure mercury injection (HPMI), low-pressure nitrogen adsorption (LPGA-N2), low-pressure carbon dioxide adsorption (LPGA-CO2) and scanning electron microscopy (SEM) tests were employed for full-scale microscopic pore structure characterization. Considering potential energy induced by CH4 mole-cules and microscopic pore wall interaction, an improved method was proposed to quantitatively characterize gas adsorption capacity and obtain CH4 occurrence characteristics for different-scale pores. The results show that microscopic properties of differently ranked coal samples vary remarkably with evident heterogeneity. The micropore specific surface area (SSA) is 79.396-232.253 m2/g, accounting for 90.03%-99.45% of the total specific surface area (TSSA). The adsorption capacities of differently ranked coal samples present significant differences and range between 13.38 and 20.08 cc/g, and shows an asymmetric U-shaped trend as coal meta-morphism deepens. Based on microscopic pore properties, the Langmuir volume theoretically calculated using the new method ranges between 12.29 and 20.85 cc/g. The calculated results agree well with experimental results with a relative error of less than 10%, proving that this theoretical model can predict gas adsorption capacity with sufficient confidence.

When a longwall face approaches the finish-off line, 1 month is normally required to relocate the longwall equipment and seal the longwall panel, during which time the goaf gas atmosphere changes and the risk of spontaneous combustion and gas explosion considerably increases. To minimise the occurrence of these hazards, an improved insight into gas flow dynamics within the longwall panel is essential during the panel sealing-off process. Based on mining conditions of an Australian underground coal mine, three-dimensional computational models were developed and calibrated with onsite gas monitoring data, allowing for evaluating ventilation arrangements and understanding methane dispersion in the longwall workings during the six-stage panel sealing-off process with confidence. The simulation results indicate that nitrogen should be injected on the travel road side at a distance of 120 m behind the longwall face at a rate of 0.75 m 3 /s and the rear of the travel road should be tightly sealed at the final sealing-off stage, resulting in oxygen levels lowering than 5% in the longwall workings and producing desired panel sealing-off performance. In addition, gas sensors should be employed and positioned at the appropriate locations to reliably monitor goaf atmosphere change. This study sheds improved insights into evaluating ventilation arrangements and understanding gas flow dynamics during the panel sealing-off process and provides critical knowledge of effective proactive goaf inertisation strategies, thus minimising the risk of spontaneous heating and gas explosion and reducing environmental pollution induced by these hazards.

Well-developed pores and cracks in coal reservoirs are the main venues for gas storage and migration. To investigate the multi-scale pore fractal characteristics, six coal samples of different rankings were studied using high-pressure mercury injection (HPMI), low-pressure nitrogen adsorption (LPGA-N2), and scanning electron microscopy (SEM) test methods. Based on the Frankel, Halsey and Hill (FHH) fractal theory, the Menger sponge model, Pores and Cracks Analysis System (PCAS), pore volume complexity (Dv), coal surface irregularity (Ds) and pore distribution heterogeneity (Dp) were studied and evaluated, respectively. The effect of three fractal dimensions on the gas adsorption ability was also analyzed with high-pressure isothermal gas adsorption experiments. Results show that pore structures within these coal samples have obvious fractal characteristics. A noticeable segmentation effect appears in the Dv1 and Dv2 fitting process, with the boundary size ranging from 36.00 to 182.95 nm, which helps differentiate diffusion pores and seepage fractures. The D values show an asymmetric U-shaped trend as the coal metamorphism increases, demonstrating that coalification greatly affects the pore fractal dimensions. The three fractal dimensions can characterize the difference in coal microstructure and reflect their influence on gas adsorption ability. Langmuir volume (VL) has an evident and positive correlation with Ds values, whereas Langmuir pressure (PL) is mainly affected by the combined action of Dv and Dp. This study will provide valuable knowledge for the appraisal of coal seam gas reservoirs of differently ranked coals.

Spontaneous combustion of coal occurs in the longwall (LW) goaf during mining cycles due to coal oxidation at low temperatures and air ingress. Coal seam orientations, dictated by the elevations of maingate (MG) and tailgate (TG) and the height of working face and starting-up line, significantly impact the gas distribution in the goaf. Despite this, there has been limited study on the effects of coal seam orientations on spontaneous heating management. To fill this knowledge gap, extensive computational fluid dynamics (CFD) modeling was conducted based on the actual conditions of an Australian underground coal mine and verified with onsite gas monitoring data, after which extensive parametric studies of how coal seam orientations influenced gas distribution were conducted. Simulation results indicate that coal seam orientations significantly impact spatial gas distribution in the LW goaf and the development of proactive goaf inertisation strategies. Regardless of coal seam orientations, nitrogen performs better than carbon dioxide in reducing the oxidation zone area. In addition, at least 1.5 m3/s of nitrogen is required to effectively prevent spontaneous heating, and the area ratio of oxidation zone to active goaf is approximately 10%, reducing by about 15% compared to scenarios without inertisation. The modeling results shed insight into the goaf gas distribution characteristics under various coal seam orientations and provide guidance on developing corresponding proactive inertisation strategies for managing spontaneous heating in the goaf, thus improving mining safety.

Spontaneous heating of coal continues to present a health and safety hazard in underground coal mines. The influence of seam gas composition on gas flow dynamics and distribution characteristics in the active longwall goaf has not been studied in-depth, and corresponding effective proactive goaf inertization strategies for preventing potential spontaneous heating from occurring have limited investigation. To advance this knowledge, an 80-m-height goaf model was constructed and developed based on specific conditions of an Australian underground coal mine, and onsite gas monitoring data was collated to verify base model results, which allowed for various scenarios of seam gas composition to be simulated and investigated with confidence. This study involved modeling five different gas composition scenarios for the goaf atmosphere, namely, 100% CO 2 (case 1), 80% CO 2 and 20% CH 4 (case 2), 50% CO 2 and 50% CH 4 (case 3), 20% CO 2 and 80% CH 4 (case 4), and 100% CH 4 (case 5). Simulation results show that O 2 is primarily distributed at the middle and upper part of the CO 2 -dominant goaf model, while it is mainly layered at the floor level of the CH 4 -dominant goaf model. N 2 is superior to CO 2 in the goaf inertization for the CO 2 -dominant goaf model, whereas CO 2 performs better than N 2 for the CH 4 -dominant goaf model. The optimal inert gas flowrates for case 1 to case 5 are 1.5, 1.75, 0.75, 0.5, and 1.0 m 3 /s, and the oxidation zone area is reduced by 55.76%, 67.21%, 58.04%, 78.17%, and 81.82%, respectively. The simulation results allow for increased insight and understanding of the gas distribution patterns in the active goaf with different seam gas composition and the development of corresponding proactive goaf inertization practices, thus minimizing potential spontaneous-heating-related hazards and improving mining safety.

Computational fluid dynamics (CFD) is an effective methodology that has been widely used for decades to solve engineering problems involving spontaneous combustion and abnormal gas emissions. However, most of the previous CFD modelling focused on qualitative rather than quantitative analysis, and the factors influencing spontaneous combustion control and gas management are numerically under-researched. The onset of spontaneous heating in the goaf area is dictated by many operational and environmental parameters, including mining method, ventilation and geology. Based on field data from a real mine site, extensive CFD modelling was conducted and analyzed qualitatively and quantitatively to investigate the impact of ventilation design and operational measures on the management and control of spontaneous combustion and gas exceedance. Real-time gas monitoring data was utilized for model validation, and a good agreement between simulation results and monitoring data was reached. The tightness of goaf seals described by permeability was quantitatively investigated, revealing that the permeability should be smaller than 10(-9) m(2) to prevent air leakage effectively. Goaf inertisation parameter optimization is crucial to minimize the risk of spontaneous combustion. The systematic study revealed that the oxidation zone area (OZA) was the largest for nitrogen injection (29706 m2), followed by boiler gas (28396 m(2)), while it was the smallest for carbon dioxide (11902 m2), which produced the best goaf inertisation performance. Injection flow rate is another significant factor influencing the effectiveness of heating prevention. The simulation results indicated that a critical injection rate of 1750 m(3)/h was determined, and the ratio of the OZA to the goaf area (GA) fluctuated around 7% once the injection rate was beyond this critical value. The installation location of curtains and brattices both on the longwall face and tailgate end was also simulated and optimized. Noticeable methane reduction at the tailgate end was observed with optimal configurations of brattices and curtains. Results from the modelling will shed light on improving current practices to effectively contain goaf heating in the longwall goaf areas and mitigate methane exceedance on the longwall face.

Spontaneous heating in the active goaf area during normal mining processes poses increased threats to mine productivity and safety, as evidenced in events induced by spontaneous combustion of coal. To control and mitigate this engineering problem, there is a need to gain critical knowledge of spontaneous combustion in the longwall goaf area, which can be achieved through a combination of field tests and numerical modeling. This paper introduces the spontaneous combustion management system widely used in Australia and presents Computational Fluid Dynamics (CFD) models for the simulation of gas flow dynamics in the goaf area, based on the site conditions of an underground coal mine where coal seam gas is predominantly comprised of carbon dioxide. The models were validated with gas monitoring data and used to conduct parametric studies for proactive goaf inertisation optimization. Qualitative and quantitative analysis of simulation results indicated that better goaf inertisation could be achieved when nitrogen was injected via cut-through at 250 m on the maingate (MG) side and surface boreholes at 100 m and 700 m on the tailgate (TG) side, with a total injection rate greater than 1750 l/s. The oxygen concentration on the MG and TG side dropped below 5% at distances of 120 m and 75 m behind the longwall face, with an oxidation zone area of 35375 m2, which was approximately one-third of the oxidation zone area of the scenario without inert gas injection. Simulation results help shed light on improving current goaf inertisation practices to effectively reduce the risk of heating in goaf areas and improve mining process safety based on Australian conditions and practices.(c) 2022 Institution of Chemical Engineers. Published by Elsevier Ltd. All rights reserved.

In this study, complex variable theory was employed to study the stress distribution for rock mass containing a hole with complex shapes. The method of mapping function calculation using optimization technique was investigated and improved. The shape-related mapping function was defined for parameter analysis. A new objective function for mapping function determination was developed to calculate related parameters without the consideration of restrictive conditions between boundary points in z-plane and zeta-plane, which significantly simplified the calculation process. In addition, the mapping function for planes containing a rotated hole was deducted to simplify analytical stress solution process for holes under complex stress conditions. Finally, for six kinds of holes with typical shapes in practical rock engineering, the mapping functions were determined, and the external analytical stress distribution were further presented. The analytical solutions combined with numerical and experimental results show that holes with arched boundaries suffer less stress concentration compared with those with corners. Hole shape mainly affects the stability of rock containing a hole via its influence on stress concentration extent around the hole.

Lean-oxygen environment caused by methane in high gassy coal mine goaf has a significant influence on the prediction index gases of residual coal spontaneous combustion. The coal sample from Xishan coalfield in China was used to conduct the low-temperature oxidation experiments under different lean-oxygen environments. The experimental results show that different lean-oxygen environments had a significant delay effect on the formation of CO, CO2, H-2 and C2H6, and the lower the O-2 concentration, the more obvious the delay effect, and the delay effect of methane was greater than that of N-2. A lean-oxygen environment caused by methane also had a significant influence on the values of CO/Delta O-2 ratio and CO2/Delta O-2 ratio. However, when the temperature was < 170 degrees C, the change of O-2 concentration had no significant influence on the value of CO/CO2 ratio, and the relationship between the value of CO/CO2 ratio and temperature T can be accurately expressed by exponential function. The absolute amount of CO, CO2 and C2H6 generated by 1kg residual coal (C-CO, C-CO2 and C-C2H6), which can reduce the influence of air leakage and residual coal mass on prediction index gases, were introduced to predict the spontaneous combustion in high gassy coal mine goaf. Then, the distribution diagrams of C-CO, C-CO2 and C-C2H6 with temperature and O-2 concentration were obtained, so as to accurately predict the degree of spontaneous combustion in high gassy coal mine goaf. The research results are of great significance to the prevention of spontaneous combustion in goaf of high gassy mine.

In this study, the accuracy and generality of stress calculation for a plate containing double holes via Schwarz alternating method was investigated. The original Schwarz alternating method with inverse mapping function shows a good performance in terms of the stress solution for a plate containing two arched holes. However, for a plate containing two holes with corners, evitable error may be produced during the calculation because of the unsatisfying accuracy of inverse mapping function. This error is particularly obvious in the stress calculation for a plate containing two triangular holes. To address the problem, an improved Schwarz alternating method without the consideration of inverse mapping function was proposed in this study. The coordinate transformation of points around hole boundaries is realized by an optimization method instead of the inverse mapping function, which leads to little error during the calculation and thus improves the stress solution accuracy especially for plates containing holes with corners. With the employment of the improved method, the influences of connecting angle and lateral pressure coefficient on stress solutions for plates containing double U-shaped holes were discussed. In addition, DEM simulations were further conducted to study the influence of stress characteristics on the failure patterns of rock mass. The result shows that the hoop stress linearly relates to lateral pressure coefficient in the elastic plate and fractures always initiate around hole boundaries where high stress concentrates.