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In recent years, landslides induced by underground mining have attracted much attention as they cause great harm and early warning signals are difficult to detect. The key work of the early warning of a mining landslide is to clarify its initiation mechanism and evolution process. Due to the complexity of the deformation and failure of the goaf overburden and the lack of monitoring of the slope evolution process, the deformation and failure law and evolution characteristics of mining landslides have always been difficult to analyze. In this paper, a typical mining landslide, the Madaling landslide, was selected as the study object. The soft-hard interlayer structure of the slope was generalized and explored by centrifuge model tests and a 3D discrete element model. The results showed that the evolution of the Madaling landslide are divided into four stages: (I) the bending and collapse of the goaf overburden, the slope settlement and the formation of tensile cracks at the trailing edge; (II) the upwards extension of the subsidence cracks of the rock mass; (III) the occurrence of shear cracks in the rock mass, with gradual slope deformation as a whole; and (IV) the connection of shear cracks, with the initiation of landslides. The long-term gravity creep of soft rock and the extension of trailing edge tensile cracks cause the internal rock mass of the slope to become the key block controlling slope stability. The slope surface displacement (S)-time (t) curve of mining landslides is divided into the settlement stage, rock mass crack development stage and landslide evolution stage. The formation time of shear cracks in the rock mass crack development stage is a sign of the transformation of subsidence into a landslide. The relationship between the horizontal displacement and the depth of the rock mass effectively reflects the development stage of shear cracks. The horizontal and vertical displacement of the deep rock mass can serve as the early warning criterion for mining landslides. [ABSTRACT FROM AUTHOR]

To investigate the temporal and spatial evolution process of overlying karst mountain instability caused by mining, the case of "8.28" mega landslide in Pusa, Nayong County, Guizhou Province, China, is taken as the example. Based on the results of the field investigation after the disaster, the complete process of rock strata fracture and slope instability under the descending and ascending mining conditions of gently inclined coal seam is reproduced by similitude model experiments. According to the key motion features of overburden deformation and fracture evolution law, the failure process of slope collapse controlled by deep and large karst fissures under mining action is summarized. And the change law of overburden pressure and displacement in the mining process is analyzed as well as the failure mode of slope collapse is proposed. The results show that the slope experiences four failure stages in the process of coal seam descending mining: coal seam roof caving, overburden cantilever tension fracture, overburden integral dumping subsidence and slope instability collapse, and the slope undergoes deformation toward the free surface and downward. During the ascending mining process, the slope experiences four failure stages: periodic caving of coal seam roof, upward transmission of separated fractures, overburden integral bending subsidence and slope instability collapse, and the slope undergoes deformation toward the inside of the slope and downward. The rock mass ahead of the advancing direction of working face has the phenomenon of tension–compression stress transformation. Along the mining direction, the overburden sequentially experiences the change process of pressure increase, decrease, or increase again, and stabilization. Deep and large karst fissures at the slope top are the structural basis for the occurrence of collapse. Coal mining activities have a certain promoting effect on mountain cracking and rock fragmentation. The failure mode of slope can be summarized as tension–shear–slip–toppling collapse failure. Improved understanding of the deformation movement characteristics and damage mode of slope can aid in early identification and timely warning of geo-hazards in karst area. Highlights: This paper focuses on the deformation movement features and failure modes of mountains controlled by deep and large karst fissures under mining action. The full process of rock strata fracture and slope instability under descending and ascending mining conditions is reproduced in a simulated model. Extensive karst fissures at the slope top are the main structural basis for the occurrence of collapse. Coal mining activities have a certain promoting effect on mountain cracking and rock fragmentation. The failure mode of slopes can be summarized as tension-shear-slip-toppling collapse failure. [ABSTRACT FROM AUTHOR]

Surrounding rock deformation control of gob-side coal-rock roadway in inclined coal seams (GCRICS) is a major problem in gob-side entry technology application practice. This paper describes a case study of the surrounding rock deformation characteristics and control technology of a typical GCRICS in Guizhou, China. As according to data obtained during a field investigation, the reasons for the deformation and failure of 151509 tailentry and the shortcomings of the original support scheme were analyzed. In combination with existing theory and field experience, the "anchor cable + U-shaped steel + shotcreting + grouting" (CUSG) support method was proposed. The plastic zone distribution, displacement, and stress evolution law of the roadway-surrounding rock under the four support modes were analyzed and compared by numerical simulation. The results show that the supporting effects of several support methods varied from good to poor; CUSG was the best, followed by anchor cable support, U-shaped steel support, and then no support. Based on the previous seepage grouting theory, a slurry diffusion model of hollow grouted anchor cable (HGC) was established and the calculation formulas of slurry diffusion radius and grouting time were deduced, which provided guidance for field construction. Finally, the CUSG surrounding rock control technology was applied to 151509 tailentry subsequent roadway support. Through drill holes, analysis of the surrounding rock of the non-grouting area and the grouting area was conducted. It was found that the surrounding rock of the grouting area was high in integrity and strong in bearing capacity. Throughout the excavation period to the end of roadway mining, the roadway did not have to be repaired. This case study has high practicability, high popularization value, and provides a useful reference for the engineering support design of the GCRICS. [ABSTRACT FROM AUTHOR]

In order to study the influence of roof stress and fracture distribution characteristics on the stability of stope surrounding rock under repeated mining in close-distance coal seams, the research background of this paper is the close-distance coal seam mining of a mine in Guizhou province, China. The dynamic evolution characteristics of stope roof caving and the stress environment change law under repeated mining are studied by using the method of similar simulation experiment, numerical simulation, and field verification. The results show that the roof stage under repeated mining can be divided into four stages: normal mining, roof deterioration, end face roof leaks, and support crushing. The tip-to-face distance, support height, and support working condition are the main influencing factors in end face roof control. The main reason for the support crushing is that the roof above the support is broken, the main roof cannot form the self-stable structure, and the support force is insufficient. The roof dynamic load is high, and the subsidence of the end face roof is large, which is prone to roof caving during the stope roof weighting. Moreover, the roof weighting is frequent under repeated mining, which leads to the broken roof and the support cannot be supported, resulting in the occurrence of the support crushing accident. The control strategies for stope roof under repeated mining are provided based on the thorough study findings. The working face 17101 roof is successfully controlled by the aforesaid procedures, which provides the foundation for the management of stope surrounding rock under repeated loading. [ABSTRACT FROM AUTHOR]

The hydrogeological conditions of the Qianbei coalfield are complex, and karst water in the roof rock frequently disrupts mining operations, leading to frequent water inrush incidents. Taking the representative Longfeng Coal Mine as a case study, research was conducted on the development pattern of the water-conducting fracture zone and the water inrush mechanisms beneath karst aquifers. On the basis of key stratum theory and calculations of the stratum stretching rate, the karst aquifer in the Changxing Formation was identified as the primary key stratum. It was deduced that the water-conducting fracture zone would develop into the karst aquifer, indicating a risk of roof water inrush at the working face. Numerical simulations were used to study the stress field, displacement field, and plastic zone distribution patterns in the overlying roof strata. Combined with similar simulation tests and digital speckle experiments, the spatiotemporal evolution characteristics of the water-conducting fracture zone were investigated. During the coal mining process, the water-conducting fracture zone will exhibit a "step-type" development characteristic, with the fracture morphology evolving from vertical to horizontal. Near the goaf boundary, the strain gradually decreases, and the instability of the primary key stratum significantly impacts the mining space below, leading to the closure of interlayer voids or the redistribution of water-conducting fissure patterns. Field measurements of the water-conducting fracture zone reveal that postmining roof fractures can be classified into tensile-shear, throughgoing, and discrete types, with decreasing water-conducting capacity in that order, the measured development height of the water-conducting fracture zone (51 m) aligns closely with the theoretical height (51.37 m) and the numerical simulation height (49.17 m). Finally, from the perspective of key stratum instability, the disaster mechanisms of dynamic water inrush and hydrostatic pressure water inrush beneath the karst aquifers in the northern Guizhou coalfield were revealed. The findings provide valuable insights for water prevention and control efforts in the Qianbei coalfield mining area. [ABSTRACT FROM AUTHOR]

This paper studies the evolution rule of inclination fracture field in close distance and inclined coal seams. It can fully understand the evolution rule and distribution characteristics of overlying strata in the coal cutting process. Taking the 21003 mining face of a mine in Guizhou as the engineering background, numerical simulation is used to simulate the evolution process of the overlying strata fracture field and deformation characteristics caused by the mining effect of the mining roadway during coal cutting. Finally, it is concluded that "triangular closed" structure at the bottom of mining face greater than upside during mining face, resulting in a large deformation of the roadway at the bottom of mining face; the composite support technology can effectively control the large deformation of surrounding rock roadway caused by the "triangular closed" structure. [ABSTRACT FROM AUTHOR]

This paper reports the mineralogical compositions of super-low-sulfur (Yueliangtian 6-upper (YLT6U)) and high-sulfur (Yueliangtian 6-lower (YLT6L)) coals of the Late Permian No. 6 coal seam from the Yueliangtian coal mine, Guizhou, southwestern China. The mineral assemblages and morphology were detected and observed by X-ray diffractogram (XRD), optical microscopy and field-emission scanning electron microscope (FE-SEM) in conjunction with an energy-dispersive X-ray spectrometer. Major minerals in the coal samples, partings and host rocks (roof and floor strata) include calcite, quartz, kaolinite, mixed-layer illite/smectite, chlorite and pyrite and, to a lesser extent, chamosite, anatase and apatite. The Emeishan basalt and silicic rocks in the Kangdian Upland are the sediment source for the Yueliangtian coals. It was found that there are several modes of chamosite occurrence, and precursor minerals, such as anatase, had been corroded by Ti-rich hydrothermal solutions. The modes of occurrence of minerals present in the coal were controlled by the injection of different types of hydrothermal fluids during different deposition stages. The presence of abundant pyrite and extremely high total sulfur contents in the YLT6L coal are in sharp contrast to those in the YLT6U coal, suggesting that seawater invaded the peat swamp of the YLT6L coal and terminated at the YLT6U-9p sampling interval. High-temperature quartz, vermicular kaolinite and chloritized biotite were observed in the partings and roof strata. The three partings and floor strata of the No. 6 coal seam from the Yueliangtian coal mine appear to have been derived from felsic volcanic ash. Four factors, including sediment-source region, multi-stage injections of hydrothermal fluids, seawater influence and volcanic ash input, were responsible for the mineralogical characteristics of the Yueliangtian coals. [ABSTRACT FROM AUTHOR]

The pore structure of coal has a great influence on the exploitation of coalbed methane. The primary coal and tectonic coal of the Faer Coal Mine and Wenjiaba Coal Mine in Guizhou, China, were selected for low-temperature liquid nitrogen and high-pressure mercury injection experiments. Based on the Frenkel–Halsey–Hill fractal model and multifractal model, combined with nano-CT system, the difference between primary structural coal and tectonic coal and their relationships with fractal dimension were analyzed. According to the results, coal can increase its pore volume and surface area by tectonic action. From the perspective of pore volume and surface area, micropores occupy the main part. According to the pore volume and pore surface area of micropores, that of primary structural coal was lower than that of tectonic coal. For the studied coal samples, their pores have fractal characteristics and complex structure. It can be seen from the fractional dimension that that of tectonic coal was higher than that of primary structure coal, indicating that the microscopic pore structure of coal tends to be complex after tectonic action. According to the results of multifractal and nano-CT analysis, the Hausdorff dimension of tectonic coal was slightly smaller than that of primary structure coal, but the multifractal parameter value was higher than that of primary structure coal. After tectonic action, the connected pores of coal increased by 142.86% compared with the connected pores of primary coal, and the adsorption capacity was further improved. It is further proved that the structure can affect the adsorption and desorption capacity by changing the distribution of pore structure. [ABSTRACT FROM AUTHOR]

This paper investigates the distribution of coal gangue dumps and their reuse status in four counties of Liupanshui prefecture: Zhongshan, Shuicheng, Panxian and Liuzhi. Coal gangue reuse programme was developed for the prefecture after testing the physical and chemical properties of the waste material. [ABSTRACT FROM AUTHOR]

Taking the geological conditions of a coal mine in Liupanshui City, Guizhou Province, as the background. The fracture law of the roof in the coal face and the height of the "Two zones" were obtained through theoretical analysis and empirical formula calculation, and the results were verified using similar simulation experiments. Through numerical simulation were researched the stress distribution characteristics of the overlying strata on the working face under the influence of multiple faults. The results showed that in the early stage of mining, F1 undergoes activation under the influence of the main roof weighting, leading to an increase in the degree of plastic damage to the coal seam and strata behind the working face, causing a redistribution of the behind abutment pressure. Finally, under the influence of the F1 barrier effect, the vast majority of the behind abutment pressure is transferred to the lower strata of F1, leading to a continuous increase in stress concentration there. But as the working face continues to advance, the blocking effect of the roof plastic zone above the goaf on the transmission of the behind abutment pressure of the working face begins to appear and continues to increase, leading to a decrease in the peak stress at the lower strata of F1. The stress change process on the F2 side is similar to that on the F1 side, the front abutment pressure is initially distributed in the strata in front of the working face, but as the activation degree of F2 continues to intensify, it gradually shifts to the lower strata of F2, and ultimately the majority of the front abutment pressure is borne by the lower strata of F2. [ABSTRACT FROM AUTHOR]

The extraction of underground minerals in hilly regions is highly susceptible to landslides, which requires the application of InSAR techniques to monitor the surface displacement. However, repeated mining for multiple coal seams can cause a large displacement beyond the detectable gradient of the traditional InSAR technique, making it difficult to explore the relationship between landslides and subsurface excavations in both temporal and spatial domains. In this study, the Tengqing landslide in Shuicheng, Guizhou, China, was chosen as the study area. Firstly, the large-gradient surface displacement in the line of sight was obtained by the fusion of SAR offset tracking and interferometric phase. Subsequently, a multi-segment logistic model was proposed to simulate the temporal effect induced by repeated mining activities. Next, a simplified probability integral method (SPIM) was utilized to invert the geometry of the mining tunnel and separate the displacement of the mining subsidence and landslide. Finally, the subsurface mining parameters and in situ investigation were carried out to assess the impact of mining and precipitation on the kinematic process of Tengqing landslides. Results showed that the repeated mining activities in Tengqing can not only cause land subsidence and rock avalanches at the top of the mountain, but also accelerate the landslide displacement. The technical approach presented in this study can provide new insights for monitoring and modeling the effects of repeated mining-induced landslides in mountainous areas. [ABSTRACT FROM AUTHOR]

Coal mining and coalbed methane (CBM) development in Western Guizhou are hampered by the tectonically deformed coal (TDC). In this article, the support vector machine algorithm was used to train and establish coal body structure detection models based on logging and seismic data, and the coal body structure distribution in the Dahebian block was predicted. The fivefold cross-validation prediction accuracy for identifying coal body structure using logging data is 96.46%. The coefficient of determination of fivefold cross-validation for predicting coal body structure thickness using seismic data is generally greater than 0.99. The coal body structure distributions in the No.1, 4, and 7 coal seams are similar, containing about 2–3 layers, and are dominated by cataclastic coal. The primary undeformed coal is usually found in the inter-fault area, whereas the cataclastic and granulated coals are mostly developed along the fault. The No.11 coal seam generally has more than 5 layers of coal body structures, mainly granulated coal. The primary undeformed coal is primarily distributed along the fault, and the granulated coal is widespread and not restricted to the fault area. The No.11 coal seam contains the most CBM resources, with more than half stored in TDC. The CBM resources in the No.1, 4, and 7 coal seams are mostly stored in cataclastic and granulated coal. The cumulative gas production is adversely associated with the proportion of TDC, and the increase in the gas production rate of wells with a high proportion of TDC is relatively slow. When releasing stress through protective layer mining, the No.11 coal seam is suitable as the protected layer. The utilization of horizontal well cavity completion for stress relief is an appropriate approach for CBM development in the No.11 coal seam dominated by thick granulated coal. This study has significant theoretical guidance and engineering reference significance for coal mining and CBM development in the study area and areas with similar demands. [ABSTRACT FROM AUTHOR]

Identifying coal texture has an important influence on the exploration and development of coalbed methane (CBM), but the prediction at the block scale is still insufficient. This paper combines the core idea of machine learning algorithm, coal body deformation mechanism, and critical layer theory to establish a prediction method for coal texture of CBM reservoir at block scale. The factor analysis method was used to eliminate the information redundancy of logging data, and the key logging parameters for identifying the coal texture were optimized. These include density (DEN), natural gamma ray (GR), X well diameter (CALX), and deep lateral resistivity (LLD). The K-means clustering algorithm was used to extract the numerical characteristics of crucial parameters. The K-nearest neighbor (KNN) classification algorithm established the identification equation of coal texture. The following classification was obtained: primary structural coal (T ≥ 0.70), broken-mylonite coal (T ≤ −0.50), and cataclastic coal (−0.50 < T < 0.70); these were used to accurately and finely divide the coal texture of multiple coal seams. Subsequently, from the fact that the structure of the coal body of a coal seam is necessarily influenced by the critical layers of the coal-bearing rock system in which it is located, the value of S for the strength of the coal-bearing rock system is proposed. According to the deformation characteristics of the coal body and the critical layer theory of the coal reservoir in the mining area, the length of the coal-bearing rock system section is determined as 30 m for the top plate and 20 m for the bottom plate of the coal seam and combined with the strength adjustment coefficient. The S value calculation is derived. The S value was calibrated using the calculation results of the coal texture logging identification model: primary structural coal (S ≥ 4.50), cataclastic coal (3.50 < S < 4.50), and broken-mylonite coal (S ≤ 3.5). Finally, the above methods are used to identify the block scale coal texture of the main coal seam of Kele syncline in western Guizhou. The identification prediction results are the same as those of underground sampling. • The strength value (S) of coal-bearing rock series and its calculation method are proposed.According to the deformation mechanism of coal and the theory of key strata, the strength S value of coal-bearing rock series is established and used to identify and predict the coal texturestructure. • The strength value (S) of coal-bearing rock series can be used to identify the coal texture. • The coal texture prediction method of the block scale CBM reservoir is constructed. [ABSTRACT FROM AUTHOR]

The evolution of fissures and permeability associated with mining of the upper protective layer of the coal seam is crucial for pressure relief gas drainage of the underlying seam. To understand the influence of mining the upper protective layer on gas drainage within the underlying coal seam, this study utilized the M16 and M18 seams in the Qinglong Coal Mine in Guizhou. Theoretical analysis, discrete element numerical simulation, and field tests were used to characterize the evolution of fractures associated with mining of the upper protective layer and the effects of pressure relief gas drainage within the protected coal seam. The results show that mining-related stress changes controlled the development of fractures, altering the permeability values of coals. An analysis of the crack development in the coal mass caused by mining of the upper protective layer shows that during the initial stage of mining, the produced cracks exhibited a butterfly shape network. Yet, with further development of the mining, these cracks and the stress changes gradually produced an inverted butterfly shape network. According to simulations, the areas of maximum deformation via expansion in the protected coal seam were located near the open cut and the mining end line of the working face. The maximum deformation values were 29.06 and 26.68 mm, respectively, and the corresponding deformation rates were 9.37‰ and 8.61‰, which are greater than the required 3‰. The findings of this study provide a new reference for gas control in pressure relief coal seams under similar working conditions. [ABSTRACT FROM AUTHOR]

Recently, many types of coalbed methane (CBM) engineering practices have been applied in western Guizhou. However, most of these CBM practices (e.g., vertical well, horizontal well, cluster well.) have failed due to the complex geological conditions. To improve the success rate of CBM development projects, this paper proposes a CBM engineering mode selection method based on the geological conditions of the CBM resources found in western Guizhou. By analyzing the geology and considering the Upper Permian coal seams in western Guizhou as a case study, the geological conditions associated with CBM development were examined using measured data. In addition, the selective matching of existing CBM engineering methods to the geological conditions was examined and preliminarily demonstrated. The results indicated that the evolution of the geological conditions was primarily controlled by the vertical distribution of the coal strata, the hydrogeological conditions, and the tectonic stresses. The classification of the geological conditions into different types of CBM development geology was conducted according to the regional configuration of the geological parameters. A basic relationship exists between the type of geology and the engineering method for CBM development. To optimize the development engineering method and obtain high CBM production, the engineering methods of thin-layer staged fracturing of multiple coal seams, supplementary fracturing of sandstone reservoirs in coal deposits, and reservoir stimulation via protected coal seams during mining were preliminarily established. These methods represent a new direction for the CBM development of thin to moderate coal seams in western Guizhou. The technical feasibilities of the selected CBM development methods were verified by engineering practices, and certain CBM wells reported good production. This study describes the engineering effectiveness and adaptability of CBM engineering practices from the perspective of the development methods in the study area. In addition, this study emphasizes that the relationships between the geological conditions and the engineering methods might be broadly applicable when choosing the best CBM development engineering method for zones with multiple coalbeds in China. [ABSTRACT FROM AUTHOR]

This paper reports the mineralogical characteristics of a complete coal seam in the Late Permian Longtan Formation from the Yueliangtian mine, western Guizhou, southwestern China. The minerals in the coal were identified using optical microscopy, scanning electron microscopy with an energy dispersive X-ray spectrometer (SEM–EDS), and low temperature ashing plus X-ray diffraction (LTA + XRD). The results show that quartz and kaolinite are the major components of the coal mineral matter; followed by pyrite, marcasite, anatase, and calcite; and in some cases, mixed-layer illite/smectite, chamosite, illite, ankerite, apatite, and anorthite. The highly-elevated concentration of quartz in the coal is mostly derived from siliceous solutions produced by weathering of the Emeishan basalt. However, quartz discrete particles with large size (>100 μm) and rounded shape probably resulted from the input of felsic rock materials. The distribution and modes of occurrence of kaolinite, mixed-layer illite/smectite, illite, and anatase reflect a terrigenous origin. In comparison with the coals from eastern Yunnan, the Yueliangtian coals have lower proportion of authigenic chamosite, the formation of which was probably related to the injection of seawater. Pyrite occurring as individual particles or clustered framboids was most likely influenced by seawater during the stages of peat accumulation or early diagenesis, while fracture-filling pyrite probably had an epigenetic origin. Additionally, an intra-seam volcanic ash-derived tonstein layer, which contains sharp-edged quartz, vermicular kaolinite, and well-developed zircon crystals, has been identified in the coal of the present study. [ABSTRACT FROM AUTHOR]

Most of the coal mines in Southwest China are located in mountainous areas with high vegetation coverage, and most activities are carried out under the mountains. The deformation monitoring and mechanical behavior analysis of the mining area helps reveal the typical mountain deformation and failure mechanism caused by underground mining activities and reduce the risk of mountain collapse in the mining area. In this manuscript, a research method for mountain stability in mining areas is proposed, which combines InSAR deformation monitoring with numerical analysis. Based on the high-precision deformation information obtained by DS-InSAR and the landslide range, a three-dimensional explicit finite difference numerical analysis method was used to reconstruct the landslide model. According to the layout of the coal mining working face, the variation mechanism of overlying stratum stress and the mountain slip in the coal mining process is inverted, and the mechanism of mountain failure and instability in the mining area is analysed. Based on the sentinel data, the experiment performed time series monitoring and inversion analysis of the mountain collapse in Nayong, Guizhou, China. The results show that mining activities a certain distance from the mountain will affect mountain stability, and there are specific mechanisms. From 2015 to 2017, the stress redistribution of overlying strata above the goaf area resulted in dense longitudinal cracks in the landslide body due to coal mining. The mountain is in a continuous damage state, and the supporting force to prevent collapse continues to decrease, resulting in a gradual decrease in landslide stability. Both the time series DS-InSAR monitoring results and numerical simulation results verify the actual occurrence and development of the on-site subsidence. [ABSTRACT FROM AUTHOR]

The effect of SiO2 on coal graphitization was investigated by adding SiO2 as an additive to vitrinite in coal from the Gemudi mining area in Guizhou province (SW China) via a high-temperature heating treatment. The graphitization products of the samples were analyzed by X-ray diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM), and the influence of the SiO2 additive on the process of coal graphitization was investigated. The results showed that, with the temperature increases, the graphitization degree of all samples was promoted, and the orderliness of the microcrystalline structure in the vitrinite increased. Compared with the samples without additives, the graphitization degree, graphite lamellae ductility, and stacking degree of the samples with SiO2 additives were higher, and the carbon layer spacing reached 0.3379 nm at 3000 °C, entering the graphite stage. The Raman spectra showed that the peak intensities of the defect structures (D1 and D2) in the samples with SiO2 were lower than those of the samples without additives, exhibiting fewer in-plane and interlayer defects in the samples with SiO2. The microstructures of the experimental samples were observed by HRTEM; at the same temperature, the carbon layer stacking degree of the samples with the SiO2 additives was higher than that of the samples without SiO2, and large graphite lamellae with smoother and clearer edges were observed. [ABSTRACT FROM AUTHOR]

The karst landscape is widespread in the southern region of China. As a result of underground mining activities, the original stress equilibrium is disrupted, causing the redistribution of stress in the overlying rock layer, inducing the longitudinal fracture of mining to expand and penetrate upwards, resulting in the rupture and destabilization of the karst cave roof, thus triggering a series of engineering problems such as karst cave collapse, landslide, the discontinuous deformation of the ground surface, and soil erosion. In order to study the evolutionary characteristics of buried rock fissures in shallow coal seam mining under the karst landform, taking the shallow coal seam with the typical karst cave development landform in Guizhou as the engineering background, based on the similarity simulation experiment and fractal theory, the evolution law of buried rock fissures and network fractal characteristics under the disturbance of the karst landform mining are analyzed. The research shows that the mining-induced fracture reaches the maximum development height of 61 m on the left side of the cave, and the two sides of the cave produce uncoordinated deformation. The separation fracture below the cave is relatively developed, and the overall distribution pattern of the cave rock fracture network presents a "ladder" shape. The correlation coefficient of the fractal dimension of the rock fractures under different advancing distances is more than 0.90, and the rock fracture network under the karst landform has high self-similarity. The variation of fractal dimension with the advancing degree of the working face can be divided into four stages. The first and second stages show an exponential growth trend, and the third and fourth stages show linear changes with slopes of 0.0007 and 0.0014, respectively. The fluctuation of the fractal dimension is small. The periodic weighting of the upper roof in the cave-affected zone is frequent, the fragmentation of the fractured rock mass becomes larger, and the fractures of the upper rock mass are relatively developed. The research results can provide a reference for the study on the evolution law of mining-induced rock fissures under similar karst landforms. [ABSTRACT FROM AUTHOR]

• The influence of stope roof structure movement on direct roof is expounded. • The mechanism of roof fall under repeated mining was studied. • Different instability conditions of cantilever beam structure are obtained. • Reasonable support working resistance is an important reason to maintain the stability of cantilever beam structure. In view of the problem that the broken stope roof under repeated mining is prone to end face roof leaks, this paper's research background is the close distance coal seams mining of a mine in Guizhou province, China. The impact of stope roof structure movement on the immediate roof was elucidated from the analysis of stope roof structure movement under repeated mining employing a combination method of field measurement, physical simulation, theoretical analysis, and numerical simulation. As a result, the mechanism of end face roof leaks under repeated mining is investigated, and the corresponding control measures are proposed. The results show that the cantilever beam structure instability of the stope roof under repeated mining is an important reason for the end face roof leaks and support crushing accident. The fracture forms of cantilever beam structure are divided into direct fracture and hinged structure fracture. The direct fracture is affected by the support working resistance. The cantilever beam hinged structure is divided into sliding and rotational instability. The periodic weighting interval is small and the fracture degree is large under repeated mining, which leads to the sliding instability. It is concluded that reasonable support working resistance is the important reason to keep the cantilever beam structure stability. Therefore, the stope roof leakage control countermeasures under repeated mining are proposed. The UDEC numerical simulation is used to verify the above analysis again, so as to provide the basis for the end face roof leaks prevention and control under repeated mining. [ABSTRACT FROM AUTHOR]

The coal-bearing Longtan Formation is widely distributed in South China. However, its gas concentration often exceeds the standard limit in tunnels, which compromises the safety of tunnel construction and operation. In this study, statistical analysis of gas-bearing tunnels in the Longtan Formation (GTLF) and coal bed methane (CBM) experiment of Longtan Formation as related to engineering information, gas content, and pressure are discussed with the regional distribution features and influencing factors of GTLF revealed. The hazards of Longtan Formation in each province to tunnels are evaluated by fuzzy synthetic evaluation approach. The findings strongly suggest that the distribution of GTLF is characterized by east–west zonation and controlled by coal-rich zones and sedimentary facies. The western region is more harmful than the eastern region because of weak tectonic movement and more developed karstification. The influencing factors mainly include coal seam conditions, sedimentary environments, tectonic evolution history, hydrogeology, geological structure, and CBM weathering zone. Longtan Formation in Guizhou and Chongqing is the most harmful to tunnels. [ABSTRACT FROM AUTHOR]

Coal resources are widely distributed in Guizhou province, China and environmental pollution caused by coal mining is becoming increasingly serious, especially mine drainage. A total of 120 mine water samples collected from different coalfields were analyzed to investigate the hydrogeochemical characteristics and assess the water quality for drinking, domestic, and irrigative purposes. Water samples had a pH of 1.90–9.12 and most of them were acidic or weakly acidic. Total dissolved solids (TDS) ranged from 254 to 13,944 mg/L and correlated closely with the electrical conductivity (EC). The coal mine drainage of Guizhou was characterized typically by low pH value, high Fe and SO42− concentration, which were mainly attributed to oxidative weathering of pyrite. The most dominant type for abandoned coal-mine drainage was Ca-Mg-SO4, while that of the underground drainage for active mine were mainly Na-SO4 and Na-HCO3 because of high concentration of Na+ from the dissolution of evaporites and clastic rocks. High concentration of the TDS, SO42−, Fe, Mn, et al. made it unsuitable for drinking and domestic use, but part of the coal mine drainage could be used for irrigation at some sites. [ABSTRACT FROM AUTHOR]

The seasonal and spatial changes in the chemical composition of the water in abandoned mine drainages and rivers in Yudong River area in the years of 2017–2018 were analyzed. The effects of mine water drainage on the seasonality and physicochemical properties of the river water after mine closure were evaluated, and the feasibility of irrigation using river water and the degree of pollution to farmland were assessed using the Water Quality Standard for Farmland Irrigation. The results show that the mine water has low pH value (< 3.5–4) and high levels of total hardness, SO42−, Fe, Al, and Zn. In addition, the pH of the mine water is negatively correlated with the presence of other metal ions. The correlation coefficient between the chemical oxygen demand (COD) and Fe reached 0.989. While the pollution levels of Pinglu and Baishui rivers were low, the confluence region of the two rivers was seriously polluted. However, only the levels of Fe and Cd slightly exceeded the Surface Water Environmental Quality Standard after the confluence of Yudong and Chongan rivers. Overall, the heavy pollution type of the confluent river is consistent with mine water pollution. The water quality is slightly better in the dry season compared than in the high-water period. Sulfate and Fe content decreased by 39 and 16 mg/L, respectively, and Cd content decreased two-fold. Despite these findings, this study shows that from 2017 to 2018, the pH and Cd content of the rivers at the confluence exceeded the irrigation limit and the water quality continued to deteriorate, which may pose a soil contamination risk. Long-term use of the river for irrigation water may cause toxic elements such as Cd, Fe, Mn, SO42−, Al, and F- to enter the food chain, thereby endangering the life and health of villagers in Yudong River area. [ABSTRACT FROM AUTHOR]

The roof usually collapses when exposed to the repeated underground mining; this will potentially lead to the instability of coal wall and even cause serious mining disasters. Based on this specific mining hazard, this work investigates the roof leak characteristics and corresponding control technology based on a coal mine in Guizhou province, China. The theoretical analysis, numerical simulation, and physical testing were carried out. By establishing a physical model, the roof structure and roof "pressure" law under repeated mining are studied, and the instable conditions of face-end roof are analyzed, so as to determine the influencing factors of face-end roof instability. By analyzing different roof structures, the working resistance of hydraulic support with stable face-end roof under repeated mining is determined. The leakage of face-end roof under different support working resistance, tip-to-face distance, and surrounding rock strength is simulated, and different methods are proposed to control face-end roof leaks. The results show that in the process of 17# coal seam mining, the roof collapse is serious, the roof pressure is frequent, and the broken roof instability would form the "granular arch" structure. Through the analysis of the roof structure, the tip-to-face distance, the strength of granular arch structure, and the working resistance of the hydraulic support affect the stability of the face-end roof. Using UDEC simulation software, it is obtained that the higher the strength of roof and surrounding rock, the smaller the tip-to-face distance, the more stable the face-end roof is. The prevention measures such as strengthening the broken face-end roof under repeated mining, improving the support strength of the working face hydraulic support and controlling the reasonable tip-to-face distance are put forward. Through field application, the face-end roof leaks have been effectively controlled, which has played a good reference for the prevention and control of face-end roof leaks under repeated mining. [ABSTRACT FROM AUTHOR]

Thin coal seams in mines usually lack gas data. Thus, preventing and controlling gas outbursts of thin coal seams are difficult. In this study, a coal structure index, which is used to express the damage degree of coal, was estimated by logging curve. In accordance with the contour line of the floor of the coal seam, structural curvature was calculated to express the complexity of the coal seam structure quantitatively. Subsequently, relationships among the burial depth, thickness, coal structure index, structural curvature were analyzed on the basis of the gas pressure of coal seam. The gas pressure values of the coal seams of Nos. 22, 24, and 27 in the study area were predicted by multiple linear regression (MLR) and were then verified and analyzed. The deviation rate of the MLR method was 6.5%–19.7%, with an average of 13.0%. The average deviation rate between the predicted value and the measured value was 11.6%, except for the measuring point of No. 2, which had a large deviation. Results show that the prediction accuracy of the aforementioned method is acceptable and has practical value in the prediction of gas pressure in thin coal seams without measured data. The results in the gas pressure prediction provide a basis for evaluating the risk of gas outbursts in thin coal seams. [ABSTRACT FROM AUTHOR]

The spatial patterns, ecological risks, and sources of heavy metals (HMs), including Pb, Zn, Mn, Cu, Cd, Hg, and As in river sediments, were identified around a lead-zinc mine of Danzhai, Guizhou, China. The concentrations of selected HMs and their coefficient variations indicated that the river sediments around this typical lead-zinc mine were obviously contaminated with HMs. Anthropogenic activities had further enhanced the accumulation of HMs. The higher contents of the most common selected HMs were mainly distributed in the area close to the lead-zinc mine. Based on the combined evaluations of the single factor pollution index, geo-accumulation index, and potential ecological risk index, it indicated that the ecological risks of Hg, Cd, Zn, and Pb were high or extremely high, and of Mn, Cu, and As were slight or none in the sediments around this lead-zinc mine. It was found that lead-zinc mining and smelting activities, coal mining activities, and agricultural activities (livestock and poultry breeding) are the primary sources of selected HMs, based on the results of correlation analysis together with principal component analysis (PCA) and positive matrix factorization (PMF) model. The pollution of HMs in the river sediments around a lead-zinc mine was predominantly caused by lead-zinc mining and smelting activities. Therefore, for environmental persistence, lead-zinc mining and smelting activities should be given careful consideration and under close surveillance. [ABSTRACT FROM AUTHOR]

This paper reports on the petrological and geochemical compositions of K9 and K4 coals in the Late Permian Longtan Formation in the Gemudi Mine, which is located in the western Guizhou, southwest (SW) China. Critical metal concentrations have not been reported and there is a significant difference in the V concentration between the lower part and the upper part in the K9 coal of Gemudi Mine. Thus, it is a good research object of the enrichment mechanism of V. The studied coals are medium volatile bituminous coals that are characterized by a medium–high ash yield (21.7% and 37.7% on average, respectively) and a low sulfur content (0.81% and 0.18% on average, respectively). Vitrinite is the major maceral group in both coals, and collotelinite and collodetrinite contribute the most to it. Clay minerals (mainly kaolinite, illite, and illite/smectite mixed) are the majority of the minerals, quartz, carbonite minerals and pyrite are also found in the coal samples. Correspondingly, SiO 2 and Al 2 O 3 are the major components in ash, and both of them are highly correlated with the ash yield. Vanadium (213 μg/g on average) is the single enriched element in K9 coal, and it is also enriched in K4 coal. Vanadium is significantly enriched in the lower part of K9 coal, but it is depleted in the upper portion. A correlation analysis indicated that V in K9 coal mainly has an organic association, and it is positively related to telinite. Whereas, the cell and crack filling chlorite is likely to be the predominant occurrence mineral of V. Terrigenous detritus from the Emeishan basalt in the Kangdian Upland represents main origin of V in Gemudi coals, and hydrothermal fluids reformed some part of V in the K9 coal. The reducing depositional environment provides the preservation conditions as well. • Vanadium is significantly enriched in the lower part of K9 coal, but it is depleted in the upper part. • Telinite and chlorite are the main organic association and clay mineral that V occurred in the Gemudi coal. • Terrigenous detritus was the main origin of V in Gemudi coals, and hydrothermal fluids reformed some part of K9. [ABSTRACT FROM AUTHOR]

Acid Mine Drainage (AMD) from coal mining is a serious environmental issue which affects water quality, ecology, and the overall landscape of the basin. A large number of coal mine tailings in the mountainous regions of Guizhou Province, China were unattended and iron-rich AMD was directly discharged to the rivers. This discharge leaves the river "yellow" and heavily polluted. This study tries to find an efficient and economical method for treating iron-rich AMD. We sampled AMD water in two sites: Yangliujie town of Duyun city (hereafter, called Yangliujie), and Xinglong Coal Mine, Duliu town of Guiding county (hereafter, called Xinglong). We performed iron removal laboratory experiment with Cement-Bentonite Agent (CBA, 80% cement and 20% bentonite) in 500 mL AMD water from Yangliujie, scale-up experiment in 15 L AMD water from both Yangliujie and Xinglong, and engineering application in Xinglong respectively. Laboratory experiment results showed the iron removal rate can reach 99.8% and the removal rate depends on the CBA dosage and the treatment time. In the scale-up experiment, we found that Fe concentration could be reduced from 587.0 to 0.2 mg/L when adding 20 g/L CBA to the AMD water and aerating for 3 hours. As sampled water in Xinglong has a very high Fe concentration (Fe 1019.8 mg/L) and the concentration varies with seasons, it is not economical to add the CBA directly to the AMD water. Considering the abundant and cheap limestone resources in Guizhou, we used a twostep treatment method, first we added CaCO3 to raise the pH, and then we took the supernatant liquor and added CBA to the liquor. It was shown that 15 g/L of CBA was a good dosage for iron removal with Fe concentration being reduced from 1019.8 to 0.3 mg/L when CaCO3 was used to raise the pH. The best treatment realized over 99.9% iron removal, 99.2% NH3-N removal, 98.9% CODMn removal, and heavy metals in the treated water were reduced to under the limit stipulated in the "Environmental Quality Standards of Surface Water in China". Thus in the engineering application, we used this two-step treatment method. After the treatment, the pH of the iron-rich AMD (pH 2.86, Fe 2624.6 mg/L) increased to 8.53, the concentration of Fe was reduced to 59.5 mg/L, NH3-N decreased from 16.15 to less than 0.05 mg/L, CODMn decreased from 323.33 to 24.57 mg/L, heavy metals except Fe and Mn were reduced to under the limit of surface water. In conclusion, the use of CBA can effectively remove Fe and other heavy metals from the iron-rich AMD and adjust the pH value to the range of a natural water body. [ABSTRACT FROM AUTHOR]

The stability of coal mine roadways in jointed soft rock masses is an important issue for safe and efficient mining production in underground mines. Taking a main haulageway of a coal mine in Guizhou Province in China as the research background, the instability failure caused by large deformation of a roadway in a cracked rock mass was analysed, and its support control measures were put forward. First, the stability of the surrounding rock was evaluated by field investigation on the failure characteristics and statistics for the development of joints and fissures in the surrounding rock. Second, the corresponding numerical model was established by using FLAC3D software, and the influence of the lateral pressure coefficient λ on the plastic zone and principal stress were analysed quantitatively. In addition, the evolution process of the plastic zone over time was summarized. Furthermore, the key points of the reinforcement plan and support parameter design were provided on the basis of the technical approach for deformation control of the surrounding rock of the roadway. The original supporting scheme was optimized step by step, and the combined supporting scheme with "short bolt, long anchor cable and two-step grouting shell" serving as the main concept was put forward. Finally, the results of numerical calculation and field practice showed that the optimized scheme could effectively restrain the local deformation in the plastic zone of the surrounding rock of the roadway. The overall deformation was in a controllable range. In addition, the reinforced anchor cable was anchored to the deep part of the surrounding rock, ensuring the safety and stability of the roadway. [ABSTRACT FROM AUTHOR]

As a result of the mining of a C3 coal seam in a mine in Guizhou, perilous rock masses on the surface collapsed. In this study, the stability of perilous rock masses on the surface of the coal mine before and after mining was calculated and examined, and the movement law of the overlying strata in the goaf, the movement and deformation law, and the failure mode of perilous rock were analyzed. This study provides a theoretical basis for the treatment of unstable rock and coal seam mining, and has important guiding significance for the safe and efficient production of the mine. The results show that: (1) The perilous rock is in a basically stable state without the influence of mining. Through theoretical analysis and the construction of the collapse model of perilous rock, it is judged that perilous rocks W1, W3, W4, and W7 were basically stable, perilous rocks W2 and W5 were in an unstable state, and perilous rock W6 was stable without heavy rainfall. (2) As a result of the mining of the C3 coal seam, the cracks in the upper strata began to develop to the surface, and the longitudinal separation cracks gradually appeared between the surface perilous rock and the rock matrix. Due to the existence of these cracks, the perilous rock had a downward shear force. In addition, due to the heavy rainfall in the Guizhou area, the transient saturated zone of perilous rock is expanding and the strength of perilous rock is reduced. The seepage increases the sliding force of the perilous rock and aggravates the opening of cracks at any time. (3) The stability of the surface perilous rock mass is largely affected by the mining of underground coal mines. The simulation analysis was repeated using the method of setting coal pillars. When 45 m permanent protection coal pillars are set at both ends, and 15 m local protection coal pillars are set at 60 m, the safety of coal mining can be ensured without affecting the surface and perilous rock. [ABSTRACT FROM AUTHOR]

A new species of permineralized ovule is reported from a previously undocumented diverse fossil plant assemblage preserved in volcaniclastic tuff from the Late Permian Xuanwei Formation at the Huopu coal mine in Guizhou Province, China. The ovule is large and platyspermic, with 180° rotational symmetry. It has a pronounced commissure that distally divides the integument into two valves. The integument comprises a two-part sarcotesta, a sclerotesta also divided into two parts, and an endotesta that is unusually thick in the central part of the ovule and at the apex. Fusion of the nucellus to the integument occurs only at the chalaza, and the nucellar apex is small, consisting of a proximal pollen chamber and a distally extending tubular projection. A single vascular bundle enters the base of the ovule and divides in the major plane at the boundary of the inner and outer sarcotesta to form two integumentary bundles, one to each side of the ovule, with the nucellar bundle continuing to the base of the nucellus, where it forms a small vascular cup. The gross morphology and the pattern of vascularization of the ovule fit the circumscription of the morphogenus Cardiocarpus Brongniart, to which the ovule is here assigned, but are distinct from previously recognized morphospecies leading to the erection of Cardiocarpus huopuensis sp. nov. In C. huopuensis sp. nov., tissues of the outer sarcotesta are rarely preserved and where present occur external to a zone of poorly preserved cells that suggests exfoliation of the outer sarcotesta through ontogeny. Although the identity and, hence, affinity of the parent plant for C. huopuensis sp. nov. are unknown, previous evidence shows ovules of this kind to be produced by either a coniferophyte or a seed fern (pteridosperm). [ABSTRACT FROM AUTHOR]

Acid mine drainage (AMD) from abandoned coal mines can lead to serious environmental problems due to its low pH and high concentrations of potentially toxic elements. In this study, soil pH, sulfur (S) content, and arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), zinc (Zn), iron (Fe), manganese (Mn), and mercury (Hg) concentrations were measured in 27 surface soil samples from areas in which coal-mining activities ceased nine years previously in Youyu Catchment, Guizhou Province, China. The soil was acidic, with a mean pH of 5.28. Cadmium was the only element with a mean concentration higher than the national soil quality standard. As, Cd, Cu, Ni, Zn, Mn, Cr, and Fe concentrations were all higher than the background values in Guizhou Province. This was especially true for the Cd, Cu, and Fe concentrations, which were 1.69, 1.95, and 12.18 times their respective background values. The geoaccumulation index of Cd and Fe was present at unpolluted to moderately polluted and heavily polluted levels, respectively, indicating higher pollution levels than for the other elements in the study area. Spatially, significantly high Fe and S concentrations, as well as extremely low pH values, were found in the soils of the AMD sites; however, sites where tributaries merged with the Youyu River (TM) had the highest Cd pollution level. Iron originated mainly from non-point sources (e.g., AMD and coal gangues), while AMD and agricultural activity were the predominant sources of Cd. The results of an eco-risk assessment indicated that Cd levels presented a moderate potential ecological risk, while the other elements all posed a low risk. For the TM sites, the highest eco-risk was for Cd, with levels that could be harmful for aquatic organisms in the wet season, and may endanger human health via the food chain. [ABSTRACT FROM AUTHOR]

A petrographic coal structure of Late Permian coals from the Liupanshui coalfield, Western Guizhou, SW China, has been distinguished for its novel macro-lithological characteristics. Petrographic, mineralogical and geochemical studies have been conducted for a typical coal sample (No.3 coal, Songhe coalmine, Panzhou County, China) and its geological genesis and significance for coalbed methane (CBM) evaluation is accordingly discussed. It was found that coal is characterized by a banded structure with intensively fractured vitrain sublayers, where a great number of fractures were developed and filled with massive inorganic matter. The study of coal quality, coal petrography, mineralogy and lanthanides and yttrium (REY) geochemistry of the infilling mineral matter (IMM) indicates that this fractured coal structure resulted from the tissues of coal-forming plants or coal matrix shrinkage, as well as the precipitation of calcium rich groundwater and the addition of terrigenous materials. The coal depositional environment and coal-forming plant are considered to have played a role in inducing the special fractures. This provides a scientific reference for the study of CBM for coal with this fractured structure, such as the Late Permian coal from the western border of Guizhou Province, SW China. [ABSTRACT FROM AUTHOR]

In view of problems with roadways with a compound roof, such as the occurrence of instability in the roof strata, ease of separation of the layer caving, difficulty of maintenance, and poor safety, we established a mechanical calculation model of a roadway with compound roof using the elastic mechanics theory, taking the stability control of a roadway with compound roof at a coal mine in Guizhou Province, China as the research background, and based on the actual characteristics of the coal seam and the roof and floor slate. Expressions of the separation layer and instability limit load of compound roof were derived, and the calculation and verification were carried out in combination with the actual conditions. By means of numerical simulation, the distribution and evolution laws of stress, displacement and plastic zone of roadways with a compound roof were studied, and the deformation characteristics and instability mechanism of roadways with a compound roof were revealed: (1) in early stage deformation of roadway, the amount is large, the speed is fast, and the scale is wide; (2) compound roofs are vulnerable to abscission and instability, the bearing capacity of the two sides is low due to softness and cracking, the shear failure of side angles and vertex angles weakens the strength of surrounding rock, and the self-bearing capacity of surrounding rock is low; (3) the bolt and anchor bear relatively large tensile force, and the support structure is easy to be broken up. On this basis, the stability control principle of a roadway with compound roof tunnel was put forward: fast and timely support; high-strength bolt strong support; improving the stability of the roof and the bearing capacity of the two sides; restraining the shear failure of the key bearing parts such as the side angles and the bottom angles, and targeted stability control technology for roadways with a compound roof was developed. The field industrial test showed that the deformation of this roadway with a compound roof was effectively controlled and the overall stability of the roadway was effectively improved. The results of this study could provide useful reference for a roadway with a compound roof under similar conditions. [ABSTRACT FROM AUTHOR]

Various sizes of coal pillars will be formed after the mining of close-distance coal seams. The concentrated stress formed on the coal pillars can cause serious deformation and failure to the roadway below (floor roadway). Wantian coal mine in Guizhou was taken as an example to study the stress propagation and distribution of roadway by Kirsch equations. Based on the stope condition, a numerical model was established to analyze the changes of stress, displacement, and plastic zones around roadways, and the cause for roadway deformation during the mining of the upper coal seams. The new support scheme was designed and applied at the study site. The results show that the vertical stress, the maximum shear stress, and the plastic zones of the rock surrounding the roadway increase with the mining of the upper working faces. Roadway deformation and failure mainly occurs at floor, sides, and corners. The key of roadway support was to control floor heave, and then to recover the integrity and strength of the surrounding rock of two sides. The developed omnidirectional rotatable drilling equipment can guarantee the success rate of floor drilling. The broken surrounding rock of floor was enhanced through grouting. The high prestress cable was used to support the roof and two sides, and the birdcage cable was for the floor. By the new support system, the roadway deformation was controlled, which could meet the support requirements. [ABSTRACT FROM AUTHOR]