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Coal mining under the Quaternary thick loose layer affects key strata breakage, Bed-separations development, ground subsidence, and other studies. This paper presents a method for solving the deflection of a large-deflection inclined thin plate under a thick loose-layer cover with additional lateral loads and midplane forces. The methods presented are based on the principle of large-deflection of thin-plate, energy method, and fracture mechanics theory. The 7225 work face in Anhui Province, China, was studied. Combined with the large-deflection inclined thin plate model, the initial breakage distance within the main roof plate was calculated to be 33 m with the initial breakage angle of 61.2°, and the period breakage distance was calculated to be 21 m with the period breakage angle of 55.4°. The distribution range of "Vertical Three Zones" from 7225 working face to the ground, including the height of the caved zone is 38.07 m, the height of the fractured zone is 41.13 m, and the height of the curved zone with the thick loose layer removed is 187.56 m. During the dynamic development of the principal key strata (PKS), the deflection value develops from 0 mm to 2714 mm with 7225 working face mining, and the maximum value of the spatial volume is 56,485 m3, which is verified by Three-dimensional Discrete Element Code (3DEC) numerical simulation. The dynamic development of Bed-separation within the overlying strata, with a maximum development height of 545.2 mm and a maximum volume of 11,228.1 m3 of the Bed-separation cavity. The dynamic development of the Bed-separation height and the cavity under different mining length and width conditions of the working face are also discussed. The large-deflection inclined thin plate model proposed in this paper effectively explores the dynamic deflection and fragmentation law of the overlying strata induced by the inclined working face of Longwall mining and provides a theoretical basis and computational model for quantitatively evaluating the dynamic development of the Bed-separation cavity. [ABSTRACT FROM AUTHOR]

The TRIZ theory was used to accurately discover the problems to be solved in the design of roadway surrounding rock control technology. This paper tried to solve the complex issue of surrounding rock control in deep roadways from a new perspective. Based on the functional component analysis and causal axis analysis of the problem's primary reason, simultaneously, the surrounding rock control technology was optimized through technical contradiction analysis, physical contradiction analysis, and substance and field model analysis. As a result, a fully enclosed wire-shell support technology was proposed. Finally, taking the typical soft rock roadway engineering of Pansan Coal Mine in Huainan Mining Area, Anhui Province, China, as the engineering background, the engineering application and effect evaluation were completed. This paper provides a reference for controlling the instability of deep soft rock roadways in coal mines. A new idea of optimizing roadway support engineering based on TRIZ theory was proposed. [ABSTRACT FROM AUTHOR]

To fully comprehend the patterns of land and ecological damage caused by coal mining subsidence, and to scientifically carry out ecological mine restoration and management, it is urgent to accurately grasp the information of coal mining, particularly in complex coaling areas, such as North Anhui, China. In this paper, a space–air–ground collaborative monitoring system was constructed for coal mining areas based on multi-source remote sensing data and subsidence characteristics of coaling areas were investigated in North Anhui. It was found that from 2019 to 2022, 16 new coal mining subsidence areas were found in northern Anhui, with the total area increasing by 8.1%. In terms of land use, water areas were increased by 101.9 km2 from 2012 to 2022, cultivated land was decreased by 99.3 km2, and residence land was decreased by 11.8 km2. The depth of land subsidence in the subsidence areas is divided into 307.9 km2 of light subsidence areas with a subsidence depth of less than 500 mm; 161.8 km2 of medium subsidence areas with a subsidence depth between 500 mm and 1500 mm; and 281.2 km2 of heavy subsidence areas with a subsidence depth greater than 1500 mm. The total subsidence governance area is 191.2 km2, accounting for 26.5% of the total subsidence area. From the perspective of prefecture-level cities, the governance rate reaches 51.3% in Huaibei, 10.1% in Huainan, and 13.6% in Fuyang. The total reclamation area is 68.8 km2, accounting for 34.5% of the subsidence governance area. At present, 276.1 km2 within the subsidence area has reached stable subsidence conditions, mainly distributed in the Huaibei mining area, which accounts for about 60% of the total stable subsidence area. [ABSTRACT FROM AUTHOR]

Interferometric Synthetic Aperture Radar (InSAR) has become the primary remote sensing detection method for monitoring significant surface subsidence and deformation caused by underground coal mining. Time Series InSAR has been intensively researched in mining-caused deformation monitoring for its ability to provide surface deformation time series, with Small Baseline Subset InSAR (SBAS-InSAR) and Permanent Scatter InSAR (PS-InSAR) being two classical methods. To obtain the incline and curvature in mining areas and assess the building damage, this paper exploits the SBAS-InSAR and PS-InSAR techniques to estimate surface incline and curvature, following the principle of directional derivatives. The surface beneath the villages and the industrial square near the 7221 Grout-filled working face in the Huaibei mining area of Anhui Province, China, was analyzed. The estimated surface incline and curvature with SBAS-InSAR were within the threshold values specified for Class I damage, while PS-InSAR showed <1% of measurements that exceeded this threshold. This paper provides a method for monitoring the surface deformation beneath the buildings in the mine area. Meanwhile, the dynamic analysis of the damaged buildings provides a basis for determining the influence range with grout-filled working faces. [ABSTRACT FROM AUTHOR]

Ordovician limestone in North China coalfield has the characteristics of karst fissure development and strong water yield. Coal mines in North China have been threatened by Ordovician limestone water for a long time. Taking the mining of 32 coal seam in the first eastern mining area of Qianyingzi coal mine in Anhui Province in China as the engineering geological prototype, this paper uses the self-developed fluid solid coupling similarity model test device to carry out the similarity model test of overburden stress and pore water pressure response of coal mining under Ordovician limestone nappe aquifer. Based on the variation law of pore water pressure and overburden stress in a stope, it can be seen that the variation law of pore water pressure in confined aquifer is jointly affected by two factors: the vertical distance between the monitoring point and coal seam and the horizontal distance between the monitoring point and DF200 fault. According to the analysis of experimental results, the maximum height of a water flowing fracture zone in the stope is fifteen times the mining thickness. Compared with the theoretical calculation results of empirical formula, the coupling effect of seepage field and stress field and the geological structure characteristics of the stope promote the development of a water flowing fracture zone. The research results of this paper have important theoretical and practical significance not only for the safe mining of Qianyingzi coal mine but also for the safe mining of the coal mine facing the double threat of roof Ordovician limestone confined aquifer and reverse fault. [ABSTRACT FROM AUTHOR]

Ultra-high-pressure hydraulic slotting technology is an effective method to realize pressure relief and permeability enhancement of a single coal seam. In this paper, through a hydraulic slotting borehole-based total gas extraction amount calculation model, it was concluded that ultra-high-pressure hydraulic slotting technology could increase the gas extraction surface area, improve the gas flow mechanism, and transform single-layer radial flow into interlayer, radial composite flow, thus greatly enhancing the gas extraction efficiency. Based on theoretical results, a field test was conducted in the Renlou coal mine, Anhui Province, China. According to the actual characteristics of the 72 coal seam in the Renlou coal mine, the key slotting parameters of this coal seam were determined. The gas extraction sources of each coal seam could be determined accurately through multi-gas source identification and tracer technology, and the effect of hydraulic slotting pressure relief and permeability enhancement was investigated. The test results indicated that the 100-day gas extraction concentration in boreholes using ultra-high-pressure hydraulic slotting technology was 2.68–7.59 times that in conventional boreholes. The average daily pure extraction volume of slotting boreholes was 3.94 times that of conventional boreholes. Based on the calculation of the gas extraction radius of boreholes in the slotted area, it was found that, under the condition of meeting the same control range of outburst elimination, drilling work could be reduced by more than two-thirds. These achievements could provide critical references for the application of ultra-high-pressure hydraulic slotting technology. [ABSTRACT FROM AUTHOR]

Copyright of Mine Water & the Environment is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Strata control of ultrasoft coal seam has been a critical problem for mining and geotechnical engineers in years. In this paper, the No. 66207 longwall panel at Xinzhuangzi coal mine, Anhui, China, was used as an example for study. A systematic approach using laboratory testing, numerical simulation, and field validation was implemented to investigate the influences of roadway layout and presplit blasting on mechanical properties of surrounding rock. Based on the results, an inward-stagger roadway layout with presplit blasting on roof was proposed for the regional strata control. The investigation on the relationship between angle of repose of ultrasoft coal and water content showed that the angle of repose first increased then decreased with increasing water content. The peak value was observed at 17.659% water content, suggesting water injection into ultrasoft coal seam can improve the coal mechanical properties and rib stability. The "high resistance, integral beam, two-stage rib+roof support system" was design to replace the traditional equipment, which can support the ultrasoft coal seam. The combination of this system and proposed "difference stepping" mining technique was capable of preventing roof and rib from failure, as well as mitigating the rockfall during moving hydraulic support. Based on the field validation, it was found that the stress concentration coefficient was relatively low during mining process. This was able to effectively manage the mining-induced stress while improving the productivity three times than without the technique. There was also no failure event observed during mining, such that the safety of mine workers was improved significantly. [ABSTRACT FROM AUTHOR]

The strong disturbance of upward mining of the short-distance multiseam results in frequent fractures in the coal seam to be mined, jeopardizing the operation safety due to the instability of the surrounding rock of the overlying stope and risks of coal and gas outburst. A lucrative alternative is the downward mining of multiseam, which wide implementation is limited by the lack of reliable data on stress evolution characteristics. In this paper, the evolution, nonlinear interaction, and superposition characteristics of mining-induced stress after multiple pressure relief in the short-distance multi-seam were investigated by the numerical simulation and physical simulation, taking the endowment and mining technology characteristics of group B short-distance multiseam in Pan'er Coal Mine in Anhui Province of China as an example. The numerical and physical models of multiple (2—5 times) mining activities in pressure relief multiseam (with five main coal layers) under downward mining are constructed and implemented with the FLAC3D software and 1 : 100 scaling, respectively. The results showed that a pressure relief arch, which bears and transfers stresses, is formed on the coal seam's roof and floor. In downward mining, the local arch expands to the long arch, which bearing capacity within the influence range of multiple mining disturbances is weak, and the arch structure is prone to instability. If a coal pillar is left in the upper coal seam after its mining, the lower coal seam mining will switch from the large-scale low-stress area under the goaf to the small-scale high-stress area of nonlinear interaction of the multiple mining stresses with the stress under the coal pillar. [ABSTRACT FROM AUTHOR]

Solid waste backfill mining can effectively deal with gangue and other mining wastes, as well as control the movement and damage of rock strata. In this paper, the RFPA2D rock failure process analysis software is used to study the fracture evolution and seepage response mechanism of the key aquiclude strata (KAS) under the conditions of different structural characteristics, interlayer rock thickness, and backfilling ratios in backfill mining. The simulation results show that, in backfill mining, soft rock plays a crucial role in the fracture repair of KAS with different structural characteristics. An increase in the KAS thickness from 15 to 35 m is shown to results in a continuously improved repair of KAS fractures. At the advancing distance of the working face of 50~100 m and the KAS thickness of 35 m, the minimum vertical seepage velocity of 0.06 ‐ 0.78 × 10 − 2 m / s is reached. An increase in the backfilling ratio from 45 to 80% improves the control effect on the overlying strata. A case study of backfill mining in the Wugou Coal Mine located in the Anhui Province of China was conducted. At the goaf backfilling ratio of 80%, the composite KAS's good control effect was achieved, which minimized seepage and avoided the water in rush phenomena. The above engineering application ensured the safe backfill mining of coal resources. [ABSTRACT FROM AUTHOR]

In this paper, the 36 topsoil (0–10 cm) samples were collected and the contents of Cr, Mn, Co, Ni, Cu, Zn, As, Cd and Pb were analyzed. The results indicated that the contents of Cu and As in all samples exceeded the soil background values of Anhui province, while the Co and Pb contents were lower than the background values. Geo-statistics and positive matrix factorization were applied to identify the sources of soil heavy metals, which were nature factor (15.7%), industrial activities (21.2%), coal mine (50.9%) and traffic emission (12.2%), respectively. The calculation results of health risk model based on positive matrix factorization model showed that coal mine activities accounted for the largest proportion of total source contribution, followed by industrial activities. In addition, compared with adults, the trend of health risk of children from four sources in three lands were same as adults, but their health risk was higher than adults. [ABSTRACT FROM AUTHOR]

A large number of subsided wetlands have formed in eastern China in areas with high-intensity mining. However, data are not currently available to indicate their spatial distribution and expansion in the past thirty years. This paper uses a modified normalized difference water index (mNDWI) and a maximum between-cluster variance (OTSU) image segmentation algorithm to extract the subsided wetlands in mining areas with high ground-water levels of eastern China from 1988 to 2018 based on Google Earth Engine. The results show that the overall accuracy of the extraction of subsided wetlands is 98%; the Kappa coefficient reached 0.81. The total area of subsided wetland in 2018 was 26,034.88 ha, of which 14,290.97 ha was in Anhui Province, accounting for 54.89% of all such wetlands. The spatial extent of subsided wetlands has grown rapidly in the past three decades with the area of subsided wetlands expanding by 11.86 times from 1988 to 2018. The total area of subsided wetlands in the winter of 2018 was 25,296.25 ha, which was smaller than in summer. This indicates that seasonal precipitation affects the spatial extent of subsided wetlands. Although some restoration activities have been successful, most of the subsided wetlands still need active development and management. In conclusion, mNDWI and OTSU image segmentation algorithms could quickly and accurately allow the extraction of the spatial extent of subsided wetlands. Subsided wetlands have strong potential for development in future ecological restoration. The ecosystem services of wetlands and availability of dynamic monitoring technology should be considered important in the future. [ABSTRACT FROM AUTHOR]

Along with the increase of population, land resources are becoming more and more precious. Therefore, the evaluation of the reclaimed soil fertility is very important. The level of soil fertility is comprehensive reflection of many basic properties of soil, and is closely related to soil quality. In this paper, integrated digitization evaluation of soil fertility is used to evaluate soil of three typical reclamation areas in Huainan city, Anhui province, China. The results show that in three reclamation areas, the order of soil fertility level is XinZhuangZi reclamation area > DaTong ecological wetland > PanYi reclamation area. [ABSTRACT FROM AUTHOR]

With the increasing number of closed mines, the geological environment problems around closed mines have become increasingly prominent, especially in terms of soil pollution. In this paper, a total of 32 topsoil samples were collected from Qianling closed coal mine and the contents of Cu, Zn, Co, Cr, Mn, As, Cd and Pb were analyzed. The results indicated that the contents Zn and As exceeded the surface soil background values of Anhui Province. Compared with the soil of production mines, the contents of Pb and Zn were higher. The assessment results of pollution and ecological risk of soil based on Nemerow index, Geological accumulation index and potential ecological risk assessment method showed that the closed coal mine was in the mild to moderate pollution and mild hazard ecological risk. The Pearson correlation and positive matrix decomposition model were applied to identify the sources of soil heavy metals, which included atmospheric dustfall (22.47%), natural factors (22.51%), agricultural activities (4.40%), transportation (8.90%) and industrial emissions (42.08%), respectively. [ABSTRACT FROM AUTHOR]

Applying the livelihood resilience theory to the relocation of coal mining villages, the present study explored the levels and the factors hindering livelihood resilience among farmers under different relocation models. This has important implications for enhancing the livelihood resilience of farmers during coal mining relocation and promoting rural revitalization in coal mining areas. Based on the livelihood resilience framework and the actual conditions of mining areas, we formulated an evaluation index system, employed the stratified mean square deviation method to determine weights, used the comprehensive index method to assess the livelihood resilience level, and investigated the obstacles to livelihood resilience among farmers under different relocation models using the random forest model. The results indicate the following: first, the overall livelihood resilience level in the coal mining relocation area of Huaibei City is low and is not significantly different among the four types, with the ranking being as follows: central village agglomeration type > township-centered village construction type > mining-village combination type > suburban community type. Significant differences exist in the indicators and dispersion levels of the resilience dimensions of buffering capacity, self-organization ability, and learning ability among farmers under different relocation models. Second, factors such as household deposits, labor force quantity, social networks, and participation in village collective meetings significantly affect the livelihood resilience level of farmers. However, the degree of influence varies under different relocation models. Third, improvements such as increasing employment opportunities, investing in education resources, and building social networks are necessary to improve farmers' livelihoods under the four types of relocation models. [ABSTRACT FROM AUTHOR]

Green Mining Construction (GMC) is the Chinese national strategy of the environmental regulation of the mining industry to motivate mining enterprises to improve their resource utilization efficiency, protect the environment and harmonize the relationship between enterprises and communities. This paper uses system dynamics (SD) and the Malmquist-Luenberger (ML) Index to model the sustainable effect of the policy instruments of Green Mining Construction, namely, environmental taxes and subsidies. A case study of typical coal mining enterprises in Anhui, China, is provided to demonstrate the application of the proposed model in which the corporate performances of three optional strategies in response to the Green Mining Construction policies are examined. The responsive strategies are categorized as scale expansion, technical innovation and environmental protection. The simulation results show the following: (i) The environmental taxes and subsidies with disparate rates can help enterprises that focus on technical innovation and environmental protection perform better, albeit with a certain degree of lag. (ii) The synergy impact of subsidies and taxes is not significantly more than the separate ones. (iii) Environmental regulations reduce the productivity of mining enterprises, but to varying extents. This negative effect of environmental regulation should be compensated by other measures. This study offers insights to help enterprises select optimal strategies in response to the Green Mining Construction policies and to inform the government of possible sustainable policy designs to promote the Green Mining Construction. The limitations of the model are discussed for further improvements in simulating the effect of environmental regulation. • The hybrid model is used to test the effect of mining environmental policy in China. • Environmental taxes and subsidies are effective, but there are delays. • The effect of policy combination is not better than that of the single policy. • The model negates the Porter hypothesis, but there are differences among enterprises. [ABSTRACT FROM AUTHOR]

Air leakage in mine gas drainage drilling is a critical factor that affects gas extraction efficiency. It leads to a rapid decline in gas concentration, resulting in lower extraction efficiency and potential secondary disasters. To address this issue, a fully coupled gas–air mixed flow model is established in this study. The model examines the effects of extraction time, different negative pressures, and gas leakage on gas concentration. Additionally, it reveals the mechanism of air leakage around gas drainage boreholes. The simulation data are then compared with field gas drainage monitoring data to verify the reliability of the model. This verification serves as a basis for extraction regulation and control. The results demonstrate that during the later stages of extraction, the negative pressure decreases, causing a decline in gas concentration. Moreover, higher negative pressure leads to increased air inflow into the borehole, thereby reducing gas concentration. Consequently, selecting an appropriate negative pressure is crucial to improve pumping efficiency. The research findings hold significant guidance in achieving efficient gas mining. [ABSTRACT FROM AUTHOR]

Anthropogenic and geological factors play an essential role in the variability of groundwater quality, resulting in a weak spatial dependence of groundwater trace elements. Thus, it is an essential study to investigate the factors affecting groundwater quality and its spatial abundance of trace elements (including As, B, and other metalloids). In this study, samples are obtained from a Permian sandstone fracture aquifer in a coal mining area. A multivariate statistical analysis, hydrogeochemistry modeling, and spatial autocorrelation analysis were used to analyze the data. The results showed that Moran index was positive for all trace elements, which had good spatial autocorrelation. The Local indicators of spatial association (LISA) indicated that trace elements were clustered. The hydrogeochemical modeling results indicated that the precipitation and stability of iron-phase minerals, such as rhodochrosite and arsenic (As) absorption on the surface of iron-phase minerals in the aquifer, may limit concentrations in the southern region. The spatial autocorrelations of both As and Boron (B) were positive (high-high) in the western areas, indicating that As contamination occurred from both natural geological causes and human coal mining activities. In contrast, B contamination was mainly linked to the influence of human agricultural or industrial activities. Over 96% of the groundwater concentrations of As (10 μg/L) and B (300 μg/L) in the study area exceeded World Health Organization (WHO) limits. Overall, the results of this work could help decision-makers involved in regional water quality management visualize disperse zones where specific anthropogenic and geological processes may threaten groundwater quality. [ABSTRACT FROM AUTHOR]

Copyright of Mine Water & the Environment is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• A dynamic two-stage SBM model with non-discretionary variables is proposed. • China's CPLR efficiency under four scenarios of extreme temperatures is measured. • The influences of extreme temperatures on the CPLR efficiency are highlighted. • A comparative analysis of CPLR efficiency under four scenarios is provided. With the influence of climate changes resulting in more extremely days, we might expect to face a rise in associated coal productivity losses and land destruction. Numerous studies have focused on measuring the efficiency of coal production system. Yet scant studies have considered their internal structure, reconstructed lands, and especially the impact of extreme temperatures. Then, this paper divided such a system into stages of coal production (CP) and land reconstruction (LR), named the CPLR system. This study proposes a modified two-stage dynamic slacks-based measure model with non-discretionary variables for measuring the CPLR efficiency under four scenarios of extreme temperatures. The results are as follows. (1) The CPLR system for 24 provinces under four scenarios spanning 2012 to 2017 had relatively low efficiency except for Fujian, Inner Mongolia and Sichuan, which is mainly caused by the bad performance of the LR system. (2) Extreme temperatures must be considered in measuring CPLR efficiency and its stage efficiency, or otherwise the underestimation of CPLR efficiency and CP efficiency will become in 18 provinces. The negative impacts of extreme temperatures on the efficiency of reconstructed lands and raw coal production should be noticed, especially for Anhui. [ABSTRACT FROM AUTHOR]

This paper presents an investigation on the effect of grouting into multi-bed-separation to control mining-induced surface subsidence. In the overburden without obvious thick-and-hard strata for generating large-scale bed separation, overburden grouting is carried out by increasing the number of boreholes and grouting strata. The scale model test, numerical simulation, and field measurements are used to study distribution and process of bed separation and to compare the overburden failure with surface subsidence due to pre- and post-overburden grouting, with a case study of the Qi'nan Coal Mine, Anhui Province, China. The scale model test and numerical simulation results of the overburden grouting process are in close agreement with those obtained from the field measurements. Filling masses with different diffusion radii are commonly formed in the different bed separation, which are overlaid to control the surface subsidence. It is proven that overburden grouting can successfully mitigate overburden failure and subsidence without obvious hard strata and bed separations. This provides an effective and cost-efficient approach for addressing the surface subsidence and overburden deformation problems due to mining. [ABSTRACT FROM AUTHOR]

This study investigated the environmental geochemical characteristics of rare-earth elements (REEs) in surface waters in the Huainan mining area, Anhui Province, China. The REEs concentrations were determined by ICP-MS, and the inorganic species of dissolved REEs in the river and coal mining subsidence area water samples were calculated by using the Visual MINTEQ (version 3.1) code. On this basis, the distribution and geochemical characteristics of REEs in the surface waters were systematically analyzed, and the main inorganic species of REEs were investigated. The results showed the following: (1) The REEs concentrations in the surface waters were relatively low, ranging from 0.1361 to 0.3536 μg/L, and the average ∑REEs concentration was 0.2062 μg/L. Compared with light rare-earth elements (LREEs), heavy rare-earth elements (HREEs) were significantly enriched, with an average enrichment factor of 1.4642. Due to the interaction of high pH values and high cation concentrations, the ∑REEs content in the subsidence area water was significantly lower than that in the river water. (2) The distribution pattern of REEs in the surface waters normalized against the North American Shale Composite (NASC) showed that the REEs in the study area had different degrees of cerium (Ce) and europium (Eu) anomalies. The negative Ce anomalies were probably closely related to the pH conditions, whereas the positive Eu anomalies were mainly attributed to preferential chemical weathering and the dissolution of feldspar minerals. (3) The simulation results obtained by using Visual MINTEQ code showed that the dominant and typically inorganic complex form of REEs in the surface waters was carbonate complexes, and this form was one of the reasons for the enrichment of HREEs in the surface water. [ABSTRACT FROM AUTHOR]

Goaf-side roadway driving with narrow coal pillars could obviously improve coal resource recovery rates compared with traditional large, wide pillars, and this is pivotal to the sustainable development of underground mines. However, it is very difficult to control the stability of goaf-side roadway driving, especially in deep, thick coal seams with large and high working faces. In order to control the stability of goaf-side entry driving in working face 210106 of the deep and thick coal seam in Xinji No. 2 Coal Mine in Anhui Province of China, we carried out field investigations, theoretical calculations, numerical simulations, and an engineering practice to identify the main factors influencing the deformation of the surrounding rock in order to optimize the width of the narrow coal pillar and to propose countermeasures for goaf-side entry driving. Our results show that the main factors influencing deformation of the rock surrounding the roadways at working face 210106 in Xinji No. 2 Coal Mine include high ground stress, large mining height, thick sandstone in the roof, and the residual abutment pressure of the adjacent goaf. The results obtained from theoretical calculations, the numerical simulations, and the engineering practice indicate that a 5 m-wide coal pillar is relatively appropriate and feasible. The countermeasures of pressure relief by blasting roof cutting and bolt grouting reinforcement were carried out to control the stability for goaf-side entry driving. Field measurements indicated that deformations of goaf-side entry driving in deep, thick coal seams could be efficiently controlled. The maximum deformations of sidewall-to-sidewall and roof-to-floor were 100 mm and 350 mm, respectively. [ABSTRACT FROM AUTHOR]

In coal mining areas, ground subsidence persistently happens, which produces serious environmental issues and affects the development of cities. To monitor the ground deformation due to coal mining, a modified time-series InSAR technique combining persistent scatterers (PSs) and distributed scatterers (DSs) is presented in this paper. In particular, DSs are efficiently identified using classified information and statistical characteristics. Furthermore, a two-scale network is introduced into traditional PSI to deal with PSs and DSs in a multi-layer framework by taking the advantage of the robust of PSs and the widely distribution of DSs. The proposed method is performed to investigate the subsidence of Huainan City, Anhui province (China), during 2012–2013 using 14 scenes of Radarsat-2 images. Experimental results show that the proposed method can ease the estimation complexity and significantly increase the spatial density of measurement points, which can provide more detailed deformation information. Result shows that there are obvious subsidence areas detected in the test site with subsidence velocity larger than 5 cm/year. The proposed method brings practical applications for non-urban area deformation monitoring. [ABSTRACT FROM AUTHOR]

• Deep-buried TBM-excavated coal mine roadways were supported by rockbolts. • Support schemes of installing inclined and perpendicular rockbolts were compared. • Stress concentration and damage of surrounding rocks were quantitatively analyzed. • Loads applied on rockbolts were monitored by self-developed instrumented rockbolts. There is an increasing number of TBMs applied in coal mine roadway excavation projects due to the higher safety, faster tunnelling speed and fewer labor works. Nevertheless, the experiences gained from TBM tunnelling projects of transportation or water conveyance tunnels are not well applicable in underground coal mines because of their special engineering and geological conditions. This paper proposed a case study of the excavation disturbance behaviors and support design of TBM-excavated roadway in Zhangji coal mine in Anhui Province, China. Mechanical properties of roadway surrounding rocks were obtained based on parameters of intact rocks and Rock Quality Designation (RQD) values of rock masses. The Universal Discrete Element Code (UDEC) software was used to establish numerical model of the roadway and micro-parameters are also calibrated. The excavation disturbance behaviors of unsupported roadway were firstly simulated. Moreover, the excavation disturbance behaviors and rockbolts loading characters under two different support schemes were studied and compared based on simulation and monitoring results. In this case, simulation results are in good agreement with monitoring results. Research results and experiences obtained from the working site suggest that installing rockbolts perpendicularly to rock surface can better satisfy the requirements of TBM tunnelling in weak grounds of coal mine roadways. [ABSTRACT FROM AUTHOR]

Investigations were undertaken at the Xutuan and Renlou coal mines in Huaibei coalfield, Anhui Province, China to determine the effects of mining on the geochemical evolution of groundwater in the area. A total of 77 samples were collected between 1999 and 2017 from Neogene, Permian, and Carboniferous aquifers in two coal mines for hydrogeochemical analysis. The variation of hydrochemical types and the difference of Cl− and TDS suggest that the groundwater in the Neogene aquifer flow from the Xutuan coal mine to the Renlou coal mine. The high concentrations of chloride in groundwater in the Permian aquifer may be associated with recharge from the Neogene aquifer under the effects of mining. Principal component analysis and the results of chemical analysis of water samples were used to explore the water–rock processes in the three aquifers. The results suggest that the main controlling process of the Xutuan coal mine is ion exchange between Na+ and Ca2+, while the principal chemical processes in the Renlou coal mine are likely to be ion exchange and reverse ion exchange between Na+ and Ca2+. Mining will lead to the decline of the Neogene aquifer potentiometric heads and the compaction of aquifer sediments. This, in turn, could lead to the development of fissures caused by mining which could increase the hydraulic connection between the Neogene and the Permian aquifer, and increase the ion-exchange intensity of the Permian aquifer. The inverse geochemical modeling results of groundwater flow-paths in the Neogene and Carboniferous aquifers suggest that reverse ion-exchange process is taking place in these aquifers, which provides additional evidence for geochemical evolution. This combined method of using various lines of evidences from hydrogeology, multivariate statistical analysis, hydrogeochemical research, and geochemical models can explain the hydrogeochemical evolution processes of groundwater at a deeper level. [ABSTRACT FROM AUTHOR]

An investigation of 43 soil samples and their corresponding wheat samples collected from Qinan (QN) and Luling (LL) coal mining areas in Suzhou, China, was conducted to study the accumulation of heavy metals (Cu, Pb, Zn, Cd, Cr and Ni) in the soil-wheat system, and to evaluate the potential human health risk posed by heavy metals from long-term ingestion of local wheat. Results showed that Cu, Zn, Cd and Ni were accumulated in the soils from the two mining areas, higher proportions of all the investigated metals in residual fraction were recorded, while large amounts of Cd, Cu, Zn, Pb were also observed in the bioavailable or potential bioavailable fractions. Metal contents in the different parts of wheat mainly followed the order of Root>Stem>Grain. The trends of Bioaccumulation factor (BF) and Translocation factor (TF) values were Zn>Cd>Cu>Ni>Pb>Cr and Cu>Cd>Zn>Cr>Pb>Ni, respectively. Correlation analysis suggested that the accumulated metals in the grain were mainly supplied from exchangeable and carbonate bound fractions in soil. Since the health risk posed by heavy metals ingestion was very close to the maximum allowable limit, the safety of wheat consumption in the coal mining areas should be continually concerned. [ABSTRACT FROM AUTHOR]

Correct identification of water inrush sources is particularly important to prevent and control mine water disasters. Hydrochemical analysis, Fisher discriminant analysis, and geothermal verification analysis were used to identify and verify the water sources of the multi‐aquifer groundwater system in Gubei coal mine, Anhui Province, North China. Results show that hydrochemical water types of the Cenozoic top aquifer included HCO3–Na+K–Ca, HCO3–Na+K–Mg and HCO3–Na+K, and this aquifer was easily distinguishable from other aquifers because of its low concentration of Na++K+ and Cl–. The Cenozoic middle and bottom aquifers, the Permian fissure aquifer, and the Taiyuan and Ordovician limestone aquifers were mainly characterized by the Cl–Na+K and SO4–Cl‐Na+K or HCO3–Cl–Na+K water types, and their hydrogeochemistries were similar. Therefore, water sources could not be identified via hydrochemical analysis. Fisher model was established based on the hydrogeochemical characteristics, and its discrimination rate was 89.19%. Fisher discrimination results were improved by combining them with the geothermal analysis results, and this combination increased the identification rate to 97.3 % and reasonably explained the reasons behind two water samples misjudgments. The methods described herein are also applicable to other mines with similar geological and hydrogeological conditions in North China. [ABSTRACT FROM AUTHOR]

In coalbed methane (CBM) exploitation, liquid nitrogen (LN2) fracturing has attracted much attention as a promising and effective means to enhance coal seam permeability. Considering the bituminous coal in the Xutuan coal mine of Anhui Province, China, the permeability characteristics of coal samples under different pressure and stress conditions, and a single LN2 treatment and cyclic fracturing conditions were studied. Additionally, an evaluation of the macroscopic cracking behavior of coal was carried out. LN2 treatment can be very effective in promoting the generation of macroscopic fissures in the coal, and the degree of damage increases with the number of fracturing cycles. The results of a single LN2 treatment showed that under a constant confining pressure, the permeability increased exponentially with the increase in gas pressure. The cyclic LN2 treatment showed that permeability first decreased and then increased with increasing gas pressure, which is consistent with the quadratic function distribution. The permeability of the coal sample increases exponentially with the number of cycles, but the growth rate gradually slows down. For the same absolute fracturing time, cyclic fracturing had a better fracturing effect than a single cycle, and the ratio of the permeability increment is 126.3%‐213.8%. The research results provide some guidance for the development of the LN2 freeze fracturing technology. [ABSTRACT FROM AUTHOR]

In this study, the provenance of anthropogenic lead, a major pollutant of surface sediments, was determined in Huainan Panji coal mining area. The lead concentrations and the pollution degree were investigated by the enrichment factor. Tessier five-step morphology extraction method was used to discuss its potential hazard. By comparing the lead isotope ratios of surface sediments and surrounding potential polluted end-members, the lead isotope ternary mixture model was appropriated to explore the sources and relative contribution fractions. The results showed that: (1) The lead concentrations ranged from 31.44 to 64.07 mg/kg which was mild-moderate pollution. (2) The chemical forms of lead were residue state > iron-manganese oxidation state > exchangeable state > organic state > carbonate state. (3) The anthropogenic lead in surface sediments originated from soil, vehicle exhaust, coal gangue. And the relative contribution fractions were 51.70%, 30.90%, and 17.40%. [ABSTRACT FROM AUTHOR]

Total concentrations of heavy metals in soils may not be enough to understand their mobility and bioavailability. It is important to evaluate the degree of association of heavy metals with different chemical forms of soil. The sequential extraction method was applied to evaluate the mobile behavior of Cd, Cr, Cu, Ni, Pb, and Zn in 42 representative soil samples from the Linhuan subsidence of Huaibei Coalfield, Anhui Province, China. The results showed that mean concentrations of heavy metals were higher than background values of Huaibei City surface soil by a factor of 1.16 to 3.21 (Cd, 3.21; Cr, 1.19; Cu, 1.16; Ni, 1.23; Zn, 1.85) except Pb (0.89). Most of the total Cr, Cu, Ni, Pb, and Zn were present in the residual forms (above 70 %), while Cd was dominated by the exchangeable forms (42 %). The correlations analysis showed that the mobility of Cd, Cu, Pb, and Zn in soil was affected by both physicochemical properties and total metal concentrations. In contrast, the moblity of Cr and Ni of soil was mainly affected by their total metal concentrations. According to assessments by the potential ecological risk index ( RI) and the risk assessment code (RAC), Cr, Cu, Ni, Pb, and Zn posed no or low risk. However, Cd presents high to very high risk, due to its higher exchangeable and carbonate-bound fractions. [ABSTRACT FROM AUTHOR]

Subsidence due to underground coal mining caused considerable damage to the houses of Paifang village. In this work, damage levels (A-D according to Chinese National Guidelines) were determined by measuring the magnitude of cracks with a steel tape. Buildings were subdivided by structure, quality and location; differentiated structures included one-storey, one-storey with footing beams, and two-storey with footing beams. Results indicate that the damage levels of houses are closely related to the structures and the location in respect to the extracted area. Poor quality houses were more easily damaged than well-built ones; two-storey houses were more unstable than one-storey; and the houses near the boundary of the extracted area suffered larger distensional strain, and were more heavily damaged. The findings will be useful to house maintenance and to reinforcing newly built houses. [ABSTRACT FROM AUTHOR]

Understanding the hydro-chemical variation of groundwater is important for water usage in the coal mines. In this study, twenty-one and eleven samples have been collected from the coal bearing and limestone aquifer systems, respectively in a coal mine in northern Anhui Province, China. And their major ion concentrations have been analysed by statistical methods including correlation, factor and cluster analysis. The results indicate that the hydro-chemical characteristics of the groundwater samples from these two aquifer systems are different, the groundwater samples from the coal bearing and limestone aquifer systems are dominated by Na-HCO3 and Ca-HCO3 types, respectively. Correlation and factor analysis, as well as traditional hydro-chemical methods indicate that dissolution of evaporates and carbonates, as well as weathering of silicates are contributors for the chemical variations of the groundwater samples. In combination with traditional methods, the study demonstrated that statistical analyses are useful tools for understanding the hydro-chemical variation of groundwater. [ABSTRACT FROM AUTHOR]

Coal mining area is highly subject to lead (Pb) pollution from coal mining activities. Several decades of coal mining and processing practices in dozens of coal mines in the Huainan Coal Mining Area (HCMA) have led to the accumulation of massive amounts of coal gangue, which piled in dumps. In order to investigate the impacts of coal gangue dumps on Pb level in the supergene media of the HCMA, a systematic sampling campaign comprising coal gangue, soil, wheat, and earthworm samples was conducted. The average Pb content in the coal mining area soil is 24 mg/kg, which is slightly higher than the associated coal gangues (23 mg/kg) and markedly higher than reference region soil (12.6 mg/kg). Soil in the HCMA present a slight to moderate Pb contamination, which might be related to the weathering and leaching of coal gangue dumps. Lateral distribution of Pb in HCMA soil differed among individual coal mines. The soil profile distribution of Pb depends on both natural and anthropogenic contributions. Average Pb content is higher in roots than in stems, leaves, and wheat husks, while the Pb level in seeds exceeded the maximum Pb allowance for foods (Maximum Levels of Contaminants in Foods of China, GB 2762-2012). Earthworms in the selected area are significantly enriched in Pb, suggesting higher bio-available Pb level in soil in the HCMA. [ABSTRACT FROM AUTHOR]

The extraction of underground ore body inevitably causes a large amount of land subsidence. Current reclamation technologies in China mainly focus on stable subsided land, which means most of the affected lands are submerged into water because of the high groundwater table in some areas, leading to the loss of soils and inefficient reclamation. Therefore, a new technology for reclaiming unstable subsiding land is being studied for restoring farmland as much as possible, based on a case study in northern Anhui, China. In consideration of the mining plan, subsidence processes in various stages were analyzed and some related factors such as vertical subsidence, post-mining slope, water area, and land use condition were also simulated. Due to mining activities, useful farmland has gradually decreased to merely 14.4 % of the pre-mining area. In this study, the following stages were modeled from pre-mining to post-mining: (1) percentage of farmland was 100 % in stage (a) (pre-mining), (2) 72.5 % in stage (b), (3) 67.3 % in stage (c), and (4) 14.4 % in stage (d) (post-mining). The results show that 86.6 % of cultivated land was submerged into water and lost its capacity for cultivation after coal mining. Reclamation plans for stages (b), (c), and (d) were made by a traditional reclamation method called 'Digging Deep to Fill Shallow'. Based on scenario simulation of reclamation, the farmland reclamation percentages were improved to 78.3, 73.3, and 40.70 %, respectively. Taking the percentage of reclaimed farmland as the preferred standard, concurrent mining and reclamation for stage (b) and (c) could increase farmland reclamation percentages to 37.6 and 32.6 %, respectively, compared with the farmland reclamation percentage of post-mining [reclaiming the land in stage (d)]. The results reveal that optimum reclamation time should be at stage (b). Therefore, under current technical conditions, concurrent mining and reclamation could enhance the quantity of cultivated land and provide better land protection and food security in the mined areas with high groundwater table. [ABSTRACT FROM AUTHOR]