Goaf Areas Research Articles

The co-migration law of CO2 and As2O3 during the spontaneous combustion of goaf coal

ABSTRACT Coal plays a crucial role in the energy structure of China. However, coal oxidation in goaf areas can lead to spontaneous combustion and the release of harmful substances, such as CO2 and As2O3, which pose environmental hazards. The transport patterns of CO2 and As2O3 from the mining area to the surface were investigated, and the environmental impacts of their transport were preliminarily investigated. This study aimed to obtain data on the relationship between the release of CO2 and As2O3 during spontaneous coal combustion and coal temperature, serving as baseline information for numerical models of spontaneous coal combustion. From a macro perspective, we explored the correlation between the simultaneous transport of CO2 and As2O3. Additionally, we constructed a multi-physics coupled model of spontaneous coal combustion in goaf areas using COMSOL software to analyze the transport patterns of CO2 and As2O3 released during spontaneous coal combustion in the three-zone overburden and their collaborative transport. The results indicated consistent release patterns of CO2 and As2O3, with CO2 released in much larger quantities than As2O3, thus providing conditions for CO2 to act as a carrier for As2O3 transport. During independent transport in the three-zone overburden, CO2 was transported to the surface, whereas a significant portion of As2O3 was enriched in the fracture zone. However, when CO2 and As2O3 were transported collaboratively, As2O3 reached the surface and the transport patterns of both substances in the overburden remained consistent, indicating that CO2 facilitated the transport of As2O3. This study provides an important theoretical basis for the remediation of spontaneous coal combustion in goaf areas, contributing to the effective control of CO2 and As2O3 emissions and the protection of mining environments. The surface concentration of CO2 peaked at 1560 mol/m3 at 45 d, and the surface concentration of As2O3 also peaked at 0.016 mol/m3.

Investigating steeply inclined abandoned mines for unlocking the secrets of water level recovery

With the growing emphasis on environmental protection, many coal mines in northern China were closed. However, the cessation of pumping operations in those closed mines has caused a rise in groundwater levels, giving rise to various safety and environmental concerns. Understanding the patterns of water level recovery is vital for effectively managing abandoned mine sites and ensuring the uninterrupted production of adjacent coal mines. While the groundwater hazards in goaf areas have been extensively studied by scholars, there is a notable scarcity of research on water level recovery in closed coal mines. To address this knowledge gap, this study focuses on investigating the water level recovery patterns in abandoned mine sites, using the Zhaogezhuang Mine as a case study. Based on these research findings, we will conduct future studies of the impact of water level recovery on local communities, the ecological environment, and the geological environment.

Study on the Properties of Basalt Fiber-Calcined Gangue-Silty Clay Foam Concrete for Filling Undermined Goaf Areas of Highways.

The collapse of surface goaf beneath highways can result in instability and damage to roadbeds. However, filling the goaf areas with foam concrete can significantly enhance the stability of the roadbeds while considerably reducing the costs of filling materials. This study analyzes the effects on destructive characteristics, mechanical properties, stress-strain curve features, and relevant metrics, while also observing the microstructure of basalt fiber-calcined gangue-silty clay foam concrete (BF-CCG-SCFC). The results indicate that the water-binder ratio significantly influences the cubic compressive strength, split tensile strength, and fluidity of BF-CCG-SCFC. Silty clay reduces the cubic compressive strength, split tensile strength, and fluidity of BF-CCG-SCFC. Conversely, an appropriate amount of calcined gangue and basalt fiber significantly increases the cubic compressive strength and split tensile strength, while decreasing fluidity. To satisfy the strength and fluidity requirements of the filler material in hollow areas, the optimal water-binder ratio for BF-CCG-SCFC is 0.55, the ideal mixing ratio of calcined gangue to silty clay is 2:2, and the basalt fiber content should be 1%. The study examines the influence of varying water-binder ratios, the combined proportions of calcined gangue and silty clay, and different basalt fiber contents on the elastic modulus, peak stress, and peak strain of BF-CCG-SCFC. Additionally, the water-binder ratio influences the matrix strength through the non-hydration reactions of doped particles, while gangue and clay induce a "gradient hydration effect" during the hydration process. The incorporation of basalt fibers enhances the mechanical interlocking between the fibers and the matrix.

Study on the influence of gas transmission characteristics of positive pressure beam tube system under graded pressurization

The positive pressure beam tube system addresses issues related to gas composition distortion, concentration variations, and long transmission delays observed in traditional negative pressure systems. It has increasingly become the primary system for early monitoring and warning of coal spontaneous combustion in goaf areas. Nevertheless, there remains a deficiency in comprehensive research concerning critical aspects like gas transmission characteristics and transmission lag time in the positive pressure beam tube system. This study aims to construct an experimental platform for the positive pressure beam tube monitoring system and systematically investigate how the choice of pressurization device, pipe length, pipe diameter, and driving pressure in the transmission pipeline affect gas transmission characteristics. The findings indicate that the most effective pressurization occurs under conditions of two-stage high positive pressure transport, with a driving gas pressure of 0.65 MPa. The optimal diameter for positive pressure gas transmission is 7 mm. Long-distance negative pressure pipelines result in decreased transmission efficiency, necessitating increased output pressure with the lengthening of positive pressure pipelines to maintain efficiency.

Vulnerability Evolution Mechanism of High-Speed Railway Construction System in the Goaf Site of Qinshui Coalfield

The main reason for serious consequences caused by disasters is “insufficient emergency preparedness and obvious system vulnerability”. To ensure the safe operation and maintenance of the high-speed railway in goaf sites and achieve effective hierarchical management, the vulnerability theory was introduced, based on the system approach, to explore the characteristics of hierarchical evolution. Firstly, based on the analysis of the internal and external disturbances of the high-speed railway construction system with underlying goaf areas, the vulnerability characteristic elements were defined, and a conceptual vulnerability model was proposed. Secondly, based on the literature research, accident cases, and standards and specifications, 25 factors affecting vulnerability were identified and a two-dimensional cross matrix was used to establish a vulnerability evaluation index system. Then, ISM was used to build hierarchical relationships among indicators, analyze the vulnerability characteristics of direct factors, indirect factors and essential factors, and a vulnerability evolution analysis framework was proposed. Finally, the Taiyuan–Jiaozuo high-speed railway project was selected for hierarchical and progressive vulnerability management. The study analyzed the coupling effect and evolution mechanism of various elements of the safety management system under external disturbances, identified the weak links of the high-speed railway system in the goaf site, and provided a decision-making basis for continuous dynamic optimization and emergency response technology, which complied with the strategic policy of sustainable development.

Study on the influence of advancing speed on the dynamic distribution laws of spontaneous combustion hazard zones and high-temperature points in goaf areas

Spontaneous combustion of coal occurs when arising from a combination of factors, including oxidation and heating of residual coal in goaf and favorable heat retention conditions, and the spontaneous combustion hazard zones and high-temperature points formed exhibit dynamic, concealed, and three-dimensional characteristics, further complicating the on-site prevention and control of coal spontaneous combustion. Therefore, it is particularly important to study the dynamic evolution of coal spontaneous combustion (CSC) hazard areas in the goaf during the working face advancement process. With 010803 working face of Wang Wa Coal Mine for reference, the paper develops a three-dimensional Multiphysics coupling model of the goaf through field tests, laboratory experiments, and numerical simulations. For the first time, three-dimensional dynamic mesh technology is employed to investigate the spatial dynamic variation laws of spontaneous combustion hazard zones in goaf areas under advancing speeds ranging from 2 to 8 m/day. The results indicate that the relative error between simulated leakage airflow and field measurements is 1.4 %. As the advancing speed of the working face increases, the oxidation zone in the goaf shifts deeper, and its area increases linearly, though the rate of increase gradually decreases. With higher advancing speeds, the temperature of the high-temperature points in the goaf decreases, and the distances of these points from the lower corner of the working face grow exponentially in both strike and dip directions. However, the high-temperature points remain within the oxidation zone, with their strike migration ranging from 86.3 to 149 m and dip migration from 44 to 51 m. Based on this analysis, a spatial distribution function for high-temperature points in goaf areas is proposed. This study provides theoretical support for preventing and controlling coal spontaneous combustion in goaf areas.

Research on the Analysis and Evaluation of Risk Factors for Gas and Coal Spontaneous Combustion in Large-Scale Goaf Areas

In response to the potential hazards of spontaneous combustion and gas in large-scale goaf areas, the risk factors such as coal spontaneous combustion status, gas status, and ventilation status in goaf are analyzed. And simulation software is used to simulate the internal flow field of large-scale goaf, and the distribution law of its internal flow field is obtained. Then, the index evaluation method is used to conduct special evaluations of spontaneous combustion risk and gas risk in large-scale goaf areas. Finally, based on the determination of the warning indicators, levels, rules, and warning signals for large-scale goaf hazards, the results of the special evaluation of goaf hazards are transformed into corresponding warning signals for release, forming a set of large-scale goaf hazard analysis and evaluation technology system.

Optimizing Methane Control in Composite Goaf Areas: Insights from Multisource Emission Analysis and Numerical Modeling in the Tongxin Coal Mine.

Coal mine methane poses a threat to both coal production and the well-being of workers. This study investigates the complex challenge of managing methane emissions from multiple sources in coal mines prone to gas. Coal mining creates multiple air leakage channels in the mine goaf, increasing the risk of gas explosions. Tracer SF6 measurements were employed to identify multiple air leakage channels. A comprehensive numerical model, incorporating multiple air leakage channels, was developed to simulate methane distribution in the goaf and upper corner. By adjusting the combination of gas drainage rate (U) and working face ventilation flux (Q), the concentration of methane at the upper corner is expected to be decrease, ensuring safe production at the Tongxin mine. A total of 48 simulation cases were conducted, determining that U = 1080 m3/min and Q = 2250 m3/min are recommended for the 8201 working face in the Tongxin coal mine. This combination provides not only an effective solution but also a cost-efficient one for methane control. The findings offer a new insight into effective methane control providing a foundation for improving mine safety.

Preparation and Effectiveness of a Nano-Modified Composite Gel Foam in Preventing the Spontaneous Combustion of Coal

ABSTRACT In China, coal is considered the cornerstone in the energy mix for ensuring the security of national energy production. With the increasing intensity and depth of coal seam mining in China, spontaneous coal combustion in goaf areas has become a major issue affecting mine safety. The development of a nano-modified composite gel foam to prevent the spontaneous combustion of residual coal was therefore investigated in the current study. Chemical modification through intercalation and grafting was found to significantly enhance the water retention performance of the antioxidant component. In addition, the optimal component ratios were determined using single-factor experiments and response surface methodology. The modified gel foam, consisting of 2.995 wt% gelling agent, 0.25 wt% foaming agent, 0.296 wt% crosslinker, 0.491 wt% foam stabilizer, 3.772 wt% nanoparticles, and 2.964 wt% modified antioxidant, demonstrated environmental friendliness. Thermogravimetric experiments showed that the critical temperature for achieving a significant increase in the dehydration rate rose from 80 to 120°C after modification. Compared with typical inhibitors, the nano-modified gel foam exhibited a superior performance in terms of preventing coal oxidation and spontaneous combustion, particularly at low temperatures. Oxidation during the oxygen absorption and weight gain stages was also effectively inhibited, and the high temperature combustion processes were suppressed.

The Effect of CO on the Exothermic Characteristics of Low-Temperature Oxidation in Coal

ABSTRACT In recent years, abnormally high concentrations of CO gas have often been detected in goaf areas of coal mines in China, which have posed a serious threat to safe production in coal mines and the life and safety of underground personnel. The effect of CO on the exothermic characteristics of low-temperature oxidation in coal was studied by analyzing the exothermic characteristics, heat release, oxidation stages, and activation energy of coal at different CO concentrations using a C600 microcalorimeter. The experimental results indicated that CO promoted the coal oxidation at low temperature, but inhibited it after reaching 144°C. When the CO concentration is 30%, the exothermic characteristics of coal in low-temperature oxidation adsorption stage were significantly affected, with the heat flow value decreased by 27.0% and the initial exothermic temperature point moved forward by 3.9 K. In the later stage of the oxidation reaction, the heat release of coal was linearly negatively correlated with CO concentration. The higher the concentration, the lower the heat release. These findings contribute to understanding the combustion mechanism of coal in high-concentration CO atmosphere and provide valuable insights for designing and optimizing coal utilization technologies.

Pore Morphology and Oxidation Behaviour of Deep-Loaded Granular Coal at High Initial Temperatures

ABSTRACT As coal mining proceeds deeper, fragmented coal is subjected to high geostress and elevated thermal environments, causing changes in its micro-physical properties and spontaneous combustion (SC) risks. Deep mining operations entail significant risks of coal fires. In order to investigate the effects of high stress and high thermal environments on the microstructural and physicochemical damage of fragmented coal, and to elucidate the mechanisms influencing oxidation behavior, we conducted experiments including low-temperature nitrogen adsorption, synchronous thermal analysis, and in-situ diffuse reflectance spectroscopy. These experiments aimed to explore the pore morphology and oxidation characteristics of high initial temperature unloading granular coal (HITU-GC) unloading conditions. The results indicate that with increasing initial temperature, characteristic point temperatures initially rise and then decrease, while both the mass loss and heat release during the low-temperature oxidation stage decrease. After pressure-unloading composite treatment, the oxidation process accelerates with more intense reactions, resulting in an overall increase in heat release. The pore shapes of HITU-GC show no significant difference compared to the original coal, mainly comprising non-rigid aggregates of micropores, platy or layered matrix particles, including numerous slit-shaped pores. The coal surface also exhibits ink bottle-shaped pores and cone-shaped pores. Higher pre-oxidation temperatures correlate with higher specific surface areas. Higher stress levels from pressurized unloading correlate with lower specific surface areas. The specific surface area of sample O60-P16 is reduced by 0.879 m2/g compared to sample O60-P0. Pressurized unloading treatment disrupts mesoporous pores. Following thermal environment and pressure-unloading, the coal’s aromatic hydrocarbon content decreases, while the contents of hydroxyl, aliphatic hydrocarbons, and oxygen-containing functional groups (FG) all increase. Sample O60-P4 shows the highest content of active FG. While thermal environments enhance coal oxidation activity, pressure-unloading treatment increases the extent of coal surface fragmentation. The synergistic effect of both significantly increases the SC risk of coal. This study provides a theoretical basis for controlling thermal hazards associated with high-initial-temperature unloading fragmented coal in deep goaf areas.

Research on CO Migration Patterns in Shallowly Buried Coal Seam Composite Goafs.

To address the issue of CO exceedance in the close-range composite goaf, this paper focuses on the composite goaf of the Shaping Mine as the research subject and investigated the migration dynamics of CO within shallowly buried composite goaf areas. Sulfur hexafluoride gas (SF6) tracer experiments were conducted at the 13103 working face in Shaping Mine to assess surface fissures and air leakage, yielding insights into the distribution patterns of air leakage channels and facilitating the identification of critical areas for channel sealing. Programmed heating and oxidation experiments were conducted on coal seams 8# and 13# to determine the CO generation patterns during coal oxidation. The results show that higher concentrations of O2 corresponded to elevated CO production at equivalent temperatures. Subsequent data analysis unveiled exponential relationships between the O2 consumption rate and CO production rate within the goaf area, offering a theoretical framework for understanding CO migration patterns. Through numerical simulations, the study analyzed the CO migration patterns in the composite goaf area, observing downward diffusion of CO emanating from coal oxidation in the overlying goaf areas followed by dispersion toward the working face and roadways. Driven by airflow dynamics, CO accrued in the return air corner of the working face. Building upon these insights, comprehensive CO management strategies were implemented, resulting in sustained reductions of temperatures and CO concentrations to safe levels within the original high-temperature, high-concentration CO zones. Notably, CO concentrations at the return air corner of the working face continued to decline over the management period, reaching below 24 ppm within 10 to 15 days, highlighting the effectiveness of the management measures in ensuring safe underground production.

Feasibility experimental study on plugging leakage in goaf based on two-phase foam

Air leakage in goaf often leads to coal spontaneous combustion (CSC), which not only directly affects the safety production of mines but also causes significant environmental damage. Therefore, effectively sealing the airflow in goaf is crucial for preventing CSC. Feasibility experiments on using two-phase foam to seal air leakage in goaf were conducted, leveraging the advantages of large flow rate, wide diffusion range, and good accumulation characteristics of two-phase foam. The research results indicate that continuous injection of foam into loose media with maintained ventilation can completely seal the air leakage, with the foam capable of withstanding wind pressures of nearly 600 Pa. When the foam is used for one-time sealing with a length of 2 m, it remains effective for 60 min, and the sealing effectiveness improves with longer distances sealed against air leakage. Numerical simulation analysis and field measurements of airflow leakage in mine working faces reveal that effectively sealing the airflow passage in the goaf behind the corner of the return airway is crucial for preventing CSC. Two methods are proposed for sealing external airflow during coal mining: foam injection using a point drilling method near the heading and an incremental buried pipe injection method. Finally, the feasibility of two-phase foam sealing technology for goaf airflow leakage is analyzed from multiple perspectives including sealing effectiveness, practicality, economy, foaming process, and engineering implementation. The research findings provide new insights into goaf sealing technology, aiding in addressing safety and environmental issues caused by spontaneous combustion in goaf areas.

Study on the Influence of Grouting Treatment on the Movement and Deformation of Surface in Longwall Coal Mining Goaf Areas

Study on the Influence of Grouting Treatment on the Movement and Deformation of Surface in Longwall Coal Mining Goaf Areas

Study on the preparation and characteristics of thickened slurry to prevent coal spontaneous combustion

In response to the problems of small diffusion area, short solidification time, and poor flowability of existing fire extinguishing materials in preventing coal spontaneous combustion in goaf areas of western mining areas, this paper studies a thickened slurry with good flowability and fast diffusion ability. The optimal ratio of thickened slurry was determined through orthogonal experiments, and the rheological properties, impregnation characteristics, and wall hanging characteristics of the material were studied. The results showed that when the water to soil ratio was 8:1, and the concentrations of sodium alginate (SA) and apigenin were 0.6 % and 0.5 %, the flowability and suspension performance of the thickened slurry were the best. When the soaking time is 14 days, the best soaking degree of the material can be achieved, with a soaking depth of 0.93 mm. Through wall hanging tests, it was found that the thickened slurry can naturally air dry on the surface of vertically placed coal pillars with a small sliding distance, which has good adhesion and retention characteristics. Further on-site experiments have shown that by injecting thickened slurry, the CO concentration at the return air corner is significantly reduced, indicating that thickened slurry can cover a large area of residual coal in the goaf, prevent contact between coal and O2, and effectively prevent the composite reaction between coal and oxygen.

Analysis of stage parameters of low-temperature oxidation of water-soaked coal based on kinetic principles

Mine fires caused by spontaneous coal combustion are major disasters in coal mines. The staged oxidation kinetic parameters of various coal samples at oxygen concentrations of 21 %, 15 %, 10 %, 5 %, and 3 % were analyzed using a programmed temperature testing system. Herein, the temperature increase rate of coal, the temperature difference between the furnace and coal, and the oxygen consumption characteristics were obtained. Based on the amount of CO produced and the temperature sensitivity coefficient, three characteristic temperatures and four stages of low-temperature oxidation (LTO) were identified. The results showed that at a critical temperature (TC), the amount of CO gas released from the coal samples increased with increasing oxygen concentration, and the difference in the oxygen consumption rate increased. After the limit temperature (Tu), the amount of CO gas increased steadily, and the increase in the oxygen consumption rate stagnated. CO production, the maximum heating rate, and the maximum heat release rate were positively correlated with the oxygen concentration. As the oxygen concentration increased, the activation energy during the oxygen absorption stage gradually decreased. The average reaction enthalpy (ΔH) of pre-oxidized water-immersed coal was 19.37 kJ/kg greater than that of raw coal. The equation for the conservation of energy of the coal oxidation warming process was normalized. The theoretical values of the awakening stage and the stable stage were τν and τν (1-B), respectively. When B was >1, pre-oxidized water-immersed coal at a low oxygen concentration was prone to crossover points during the oxygen absorption stage, which increased the risk of coal spontaneous combustion (CSC). The research results could provide a theoretical basis for the staged control of the spontaneous combustion of water-immersed coal in goaf areas.

Constructing artificial cover layers for supercritical carbon dioxide sequestration: A novel approach to old goaf remediation and carbon emission reduction

Over the past centuries, global coal mining activities have resulted in the formation of 242.36 billion cubic meters of underground goaf areas, resulting in the waste of billions of square meters of land resources. Furthermore, this phenomenon has introduced significant safety hazards and environmental risks. In addressing the challenge of the inability to directly sequester supercritical carbon dioxide in coal mine goaf areas due to extensive fracturing of the surrounding rock mass caused by underground mining, an innovative approach is proposed. This involves the construction of artificial cover layers within the overlying rock strata of abandoned coal mine goaf areas, offering a novel strategy for the sequestration of supercritical CO2 in such geological contexts. Considering the development characteristics of fractures in the overlying strata of coal mine goaf areas, a functional relationship model is established to delineate the sealing capacity of artificial cover layers in relation to the burial depth, length, width, and thickness of the cover layers. A design methodology for constructing artificial cover layers tailored for sequestering supercritical CO2 in abandoned coal mine goaf areas is proposed, providing technical support for its widespread application. Building upon this foundation, an assessment model for the sequestration capacity of abandoned coal mine goaf areas for supercritical CO2 is developed. The calculations indicate a global sequestration potential of approximately 72.71–218.12 billion tons of supercritical CO2, with anticipated economic benefits ranging from 657.36 to 1991.47 billion USD. The research outcomes present a promising avenue to assist carbon-neutral initiatives in coal-dependent urban areas globally.

Experimental Investigation on Hydrophobic Alteration of Mining Solid Waste Backfill Material

To address the issues of corrosion weakening of solid-waste-based backfill material caused by mine water, a novel hydrophobic solid waste backfill (HSBF) material was developed using polydimethylsiloxane (PDMS) and a silane coupling agent (SCA) as hydrophobic modification additives, and NaOH (SH) and sodium silicate (SS) as alkali activators. Fly ash and slag were chosen as the primary raw solid waste materials. The rheological properties of the hydrophobic-treated backfill slurries were measured, and the resulting physicochemical properties were compared with the unmodified reference group. This study reveals that the fresh HSBF slurry follows a Modified Bingham (M-B) model with shear-thinning characteristics. The addition of PDMS causes an increase in the water contact angle of the hardened HSBF material with F8S2 to up to 134.9°, indicating high hydrophobicity. Morphological observations indicated that PDMS mainly attaches to the inorganic particles’ surface through the bridging action of SCA for the hydrophobic modification of the backfill material. The overall strength of the HSBF materials was further ensured via fly ash–slag ratio optimization, and was found to be enhanced up to 98% by increasing slag content from 20% to 50%. This is mainly attributed to the hydration of slag, forming C-S(A)-H gel, which contributes to the increased strength. The novel HSBF material enables the elimination of cement in mine backfilling applications, demonstrating good economic benefits. Its excellent mechanical and hydrophobic properties can not only prevent overburden displacement in goaf areas, but can also mitigate water resource loss from overlying strata and simultaneously reduce the safety risks associated with long-term mine water deterioration.

Study on Spontaneous Combustion Risk Areas in Narrow Coal Pillar-Utilized Deep Mining and Double-Pipe Liquid CO2 Injection Technology

ABSTRACT Coal spontaneous combustion (CSC) in goafs, one of the most serious disasters in coal mines, not only wastes resources and destroys the ecological environment, but also causes casualties. As global underground mining gradually shifts to the deep, this problem becomes increasingly prominent. Deep mining is operated in a complex mechanical environment characterized with high stress, high permeability, high temperature, and strong mining disturbance. To avoid stress concentration areas, narrow coal pillars are often utilized in roadway excavation along the goaf. However, narrow coal pillars are likely to fracture and lose stability during the mining process. Consequently, goaf areas of two adjacent working faces might connect, which promotes the CSC risk in the goaf. Most of the current researches are focused on CSC risk areas under shallow mining conditions and the CSC-gas coupling disasters, yet research on CSC risk areas in the goaf triggered by narrow coal pillars under deep mining conditions is rarely reported. Moreover, there is a lack of relevant means to prevent and extinguish fires. This study takes the narrow coal pillar-utilized 130,205 working face in Yangchangwan Coal Mine as the research object. First, the development of coal pillar fractures was simulated by adopting the discrete element method of PFC. Besides, on-site monitoring and FLUENT numerical simulation were conducted to identify CSC risk areas in the goaf of the narrow coal pillar-utilized working face. Finally, a double-pipe liquid CO2 injection technology was proposed for fire prevention and extinguishing. The following beneficial results were obtained. Affected by high stress in deep mining, the coal pillar collapses, which expands the range of the oxidation zone on the return side. Meanwhile, the adjacent goaf is also exposed to CSC risk. Double-pipe liquid CO2 injection can effectively reduce air leakage near the working face and suppress spontaneous combustion of residual coal by inerting the goaf. This study can provide guidance and reference for fire prevention and extinguishing in goafs under the condition of narrow coal pillar-utilized deep mining.

Research on Collapse Detection in Old Coal Mine Goafs Based on Space–Sky–Earth Remote Sensing Survey

A considerable number of coal mines employed room and pillar mining in the last century in northern China, where the goaf remained stable for a period of time; however, with the increased exposure of coal pillars, their collapse may gradually increase. The stability assessment of these old rooms and pillar goafs is challenging due to their concealment, irregular mining patterns, and the long passage of time. The methodology developed in this study, based on “space-sky-earth” remote sensing such as InSAR to trace historical deformation, the UAV observation of current surface damage, and comparison of mining spaces, can rapidly detect on a large scale the collapse of old goafs and the trend of damage. This study is conducted with an example of a coal mine in Yulin, Northern China, where obtained quantitative surface deformation values were integrated with qualitative surface damage interpretation results, followed by a yearly analysis of the overlying rock movement in accordance with the underground coal mining process. The results show that from 2007 to 2021, corresponding surface deformation and damage occurred following mining progress. However, the room and pillar goaf areas had not undergone any surface deformation, nor had there been incidents of landslides or ground fissures; therefore, it was speculated that no roof collapse had occurred in this region. The surface deformation and damage associated with underground coal mining are complex and influenced by the coal seam occurrence, mining methods, strata lithology, terrain slope, temporal evolution, and anthropogenic modifications. These phenomena are representative of the coal mining area, and this methodology can provide a reference for similar endeavors.