Coal Seam Mining Research Articles

Dynamic Response Analysis of Roadway Surrounding Rock Induced by Dynamic Load under the Action of Hard and Thick Rock Stratum

In the process of coal seam mining, there are often hard thick key layers in the overlying strata. Due to the high strength and good integrity of the hard thick key layer, after the hard thick key layer is broken, the overlying strata will collapse and lose stability in a large area, which is very easy to induce dynamic disasters such as rock burst, mine earthquake, coal wall caving, and roof slab caving. Aiming at the hard and thick key layer overlying the working face, the dynamic response of the mine under the strong mine earthquake induced by the breaking of the main key layer of high-level magmatic rock is numerically simulated and analyzed by using FLAC2D numerical simulation software, and the variation laws of the stress field, displacement field, and velocity field of the coal seam roadway under different boundary conditions and different focal heights are studied. The research shows that the roof of solid coal roadway is prone to vibration in a small range, and the displacement increases and decreases with the disturbance. The displacement of the floor and two sides of the solid coal roadway and the top floor and two sides of the roadway along the goaf continues to increase in the initial stage of the disturbance, and the displacement will remain stable with the continuation of the disturbance. The displacement of both sides and roof and floor of gob roadway can reach stability in the later stage of disturbance, and with the increase of the number of adjacent goaf, the longer it takes for the displacement of surrounding rock to reach stability. When the focal height is lower than 90 m, the variation of surrounding rock response increases sharply with the decrease of focal height. When a strong earthquake occurs in the low rock stratum, the impact damage of roadway surrounding rock is almost inevitable. The influence degree of strong earthquake on the stability of roadway surrounding rock is arranged as follows: gob-side roadway (mined out on one side) > solid coal roadway (mined out on both sides) > solid coal roadway (mined out on one side). The evolution process also shows that the working face boundary conditions have an important influence on the energy propagation of mine earthquake. With the increase of the number of adjacent goafs, the faster the energy attenuation rate of mine earthquake propagation is. The research results have important reference significance for the safe mining of working face under similar geological conditions.

Study on Height Development Characteristics of Water-Conducting Fracture Zone in Fully Mechanized Mining of Shallow Thick Coal Seam under Water

The height of water-conducting fracture zone (HWCFZ) is one of the important technical parameters for water-preserved coal mining. The purpose of this paper is to acquire information about the height development characteristics of water-conducting fracture zone (WCFZ) in fully mechanized mining of shallow thick coal seam under water body in western mining area of China. The 91,105 fully mechanized mining face of Daheng coal mine under composite water body was taken as the research object, the development height, morphological characteristics, development and evolution process of WCFZ in working face mining were studied through underground up-hole water injection method by intervals, borehole TV and numerical simulation. The results show that the HWCFZ in 91,105 fully mechanized mining face is 52.7~53.6 m, and the fracture mining ratio is 12.55~12.76. The final development form is saddle-shaped with “large at both ends and small in the middle”. It is accurate and reliable to determine the development characteristics of overburden fractures and the HWCFZ by the field measurement of the combination of underground upward hole segmented water injection method and borehole TV. The development height of the water-conducting fracture zone obtained by numerical simulation is consistent with the field measured results. The development and evolution of the height of WCFZ presents four stages: “development–slow increase–sudden increase–stability”. When the WCFZ develops to a certain layer, the cracks generated by the weak strata in the fracture zone of overlying strata on the working face will automatically close with the advancement of the working face, resulting in “bridging phenomenon”, which inhibits the further development of the WCFZ. That is, the existence of soft rock with a certain thickness in overburden will become the key inhibiting layer for the development of WCFZ, effectively blocking the communication between water-conducting fracture and overlying aquifer. The research results are intended to provide guidance for the implementation of water preserving mining and ecological environment protection in ecologically fragile areas in western China.

Stability analysis of tunnel under coal seam goaf: Numerical and physical modeling

The goaf formed by coal seam mining would dramatically reduce the strength and stiffness of the ground in and around the goaf, which is not conducive to tunnel excavation near the mined-out area. By establishing the Finite differential method and Discrete element method coupling numerical analysis method and conducting similar model test, the influence of dip angle, thickness and distance of coal seam goaf on the stability of unsupported tunnel excavation is studied. The results show that when the tunnel under the goaf is excavated, the circumferential stress increment increases first and then decreases along the radial direction of the tunnel, the radial stress increment gradually decreases to zero along the radial direction of the tunnel, the displacement is approximately distributed in a trough shape, and the maximum displacement is at the top of the tunnel. The area of the stress loosening zone (SLZ) is negatively correlated with the dip angle and the distance of the goaf, and positively correlated with the thickness. The SLZ near the goaf is larger, and the peak value of the asymmetry is about 1.35. When the thickness of the mined-out area is 1.8–2.1 m, the SLZ and displacement around the tunnel increase sharply and then become stable. When the dip angle of the mined-out area is greater than 30° or the distance exceeds 1.3 times tunnel diameter (D), the asymmetry converges. The research results of this paper are of great importance to the design and construction of tunnel support and the formulation of excavation schemes.

Study on the Mechanism and Control of Strong Rock Pressure in Thick Coal Seam Mining under the Goaf of Very Close Multiple Coal Seams

With the increasing proportion of close-distance coal seam mining in China, the problem of strong mining pressure during the mining of close-distance coal seams is becoming more and more severe. This article focuses on the complex stress environment and severe mining pressure encountered in the mining of thick coal seams under the multi-coal-seam goaf of Zhunnan Coal Mine. By using research methods, such as similar material simulation, theoretical analysis, and numerical simulation, it studies in depth the instability characteristics of the overlying rock structure of the W1701 working face, the inducing factors and mechanisms of strong mining pressure during the mining process, and control measures. The results show that the roof structure of the W1701 working face can be divided into “high-level key layer (hard rock)–giant thick soft and weak rock group–low-level key layer (hard rock)”, and the law of mining pressure manifestation presents a small cycle formed by the instability of “masonry beam” structure and a main large cycle formed by the periodic penetration and step-down of the giant thick soft and weak rock group, with the load on the support during the large cycle up to 5.4 times the rated working resistance. In addition, this article proposes the strategy of using layered mining to control the manifestation of strong mining pressure under the “hard sandwiched soft” overlying rock condition of the Zhunnan Coal Mine, optimizes the thickness of the layered mining of the thick coal seam, and finally, determines the upper layer thickness of 2.8 m and the lower layer thickness of 4 m, inducing the giant thick soft and weak rock formation to undergo incremental damage and releasing the fracture energy incrementally, effectively controlling the manifestation threat of strong mining pressure in the mining of thick coal seams under the close-distance coal seam goaf. As the proportion of close-range coal seam mining increases in China, the problem of strong mining pressure during the mining of close-range coal seams becomes more severe. This article focuses on the complex stress environment and severe mining pressure in the mining of thick coal seams under multiple mined-out areas in the Zhunnan coal mine. Similar material simulation, theoretical analysis, and numerical simulation methods were used to conduct in-depth research on the unstable characteristics of the overlying rock structure of the W1701 working face, the causes and mechanisms of strong mining pressure during the mining process, and control measures. The results show that the roof structure of the W1701 working face can be divided into “high-level key layer (hard rock)–thick soft weak rock group–low-level key layer (hard rock).” The law of mining pressure manifestation presents small cycles of instability formed by “block beams” and main cycles of pressure formed by vertically cracked periodic penetration and step sinking of the thick soft weak rock group. Moreover, during the main cycle of pressure, the load-bearing capacity of the support is up to 5.4 times the rated working resistance. Furthermore, it is proposed to use hierarchical mining to control the manifestation of strong mining pressure in the “hard-inlaid soft” overlying rock condition of the Zhunnan coal mine and optimize the thickness of layered mining of thick coal seams. Ultimately, the upper layer thickness was determined as 2.8 m; the lower layer thickness was determined as 4 m, and the layered mining induced the thick soft weak rock group to undergo gradual damage and energy release, effectively controlling the threat of severe mining pressure during the mining of thick coal seams under the close-range coal seam mining.

Suitability evaluation of land reclamation as arable land in coal mining area based on catastrophe theory

Niumasi Coal Mine (located in Shaodong City, Hunan Province, China) was an important producing area of high-quality coking coal in Hunan Province. After large-scale mining of underground coal seams in the area, there has been a large area of surface subsidence and serious land damage. The damaged land urgently needs to be reclaimed. In this paper, the suitability of land reclamation as arable land in Niumasi coal mining area was comprehensively evaluated, and a catastrophe progression model (CPM) for the suitability evaluation of land reclamation as arable land in coal mining area was put forward with the help of the catastrophe theory. The suitability classification was divided into four grades: suitable, moderately suitable, less suitable, and unsuitable. Eleven parameters including terrain slope grade, effective thickness of soil layer, soil parent materials, soil contamination, organic content, alkali hydrolyzable nitrogen (N), available phosphorus (P), available potassium (K), ground collapse, land destruction extent, and conditions of irrigation and drainage were selected as evaluation indicators, and the classification standards of each evaluation indicator was determined. Using MATLAB software to generate a total of 1200 samples (300 samples per level) between the arrays corresponding to each level of standards according to the normal distribution principle, of which 800 samples were used as training samples to establish the catastrophe progression criteria, and 400 samples as test samples to verify the reliability of the proposed criteria. According to CPM, the suitability status of the four land samples in Shuijingtou working area of Niumasi Coal Mine were identified. The evaluation results show that the suitability level of three lands are all ‘Moderately suitable’, and one sample is ‘Unsuitable’. Mining coal has the greatest damage to paddy fields, followed by the dry farming lands and vegetable lands, and the least impact to the forest lands. CPM can not only evaluate the suitability of land reclamation, and comprehensively compare the suitability degrees, but also can assess the damage degree of coal mining to different types of lands. This paper aims to provide a new idea for the study of quantitative evaluation methods of land reclamation suitability. The results have reference and guiding significance for the comprehensive evaluation of the suitability of land reclamation as arable land in coal mining areas.Article highlightsThe catastrophe theory can be used to evaluate the suitability of land reclamation as arable land in coal mining area. A catastrophe progression model for the suitability evaluation of land reclamation as arable land in coal mining area was put forward.Using MATLAB software to establish the catastrophe progression criteria according to the normal distribution principle.The results have reference and guiding significance for the comprehensive evaluation of the suitability of land reclamation as arable land in coal mining areas.

Impact of Underground Coal Seam Mining on Stability and Slippage of the Loess Slope

How to quantitatively characterise the impact of underground coal mining on the stability and slippage of loess slopes is a key problem in the evaluation of mining damage under loess slopes, but it is more difficult to study this problem under the impact of the particular mechanical properties and topographical features of loess slopes. In order to clarify the impact of underground coal seam mining on the stability and slippage of the loess slope, theoretical analysis, numerical simulation and physical similarity simulation experiments are used to address the problem based on the theory of slope stability and strata movement. The results show that the stability coefficient of a mining slope (Kms) is introduced to quantitatively characterise the stability of a mining loess slope, and to measure the degree of landslide risk. Due to the superposition of slope movement caused by mining subsidence and slope sliding tendency, the slope is more unstable when mining along the slope than when mining against the slope. The slope angle and slope height are the most important factors influencing the Kms. The ratio of rock stratum thickness to mining height and the ratio of rock stratum thickness to soil stratum thickness are positively correlated with Kms, and the correlation is relatively strong. The range of variation of the volume weight, internal friction angle and cohesion of the loess is small, and the influence on Kms is relatively weak. Probability integral theory is used to construct the relationship between stability and slippage of mining loess slopes. Taking the mining of a working face under the loess slope of Ningtiaota Coal Mine (China) as an example, the predicted results of the slope movement and deformation theory are in good agreement with the similar simulation test results, reaching 93.57~97.97%.

Research on the dynamic evolution law of fissures in shallow-buried and short-distance coal seam mining in Lijiahao Coal Mine

Aiming at the problem of spontaneous combustion of coal relics caused by the overburden fracture network penetrating the upper and lower coal seams in the process of shallow-buried and short-distance coal seam mining, the 31114 working face of Lijiahao coal mine was used as the research background to study the characteristics of overburden transport and fracture development in shallow-buried and short-distance coal seam mining by using physical similar simulation test; the fractal dimension and image processing techniques were used to quantify the overburden fractures; the classical mechanical models of "solid support beam" and "masonry beam" were combined to analyze the causes of fracture dynamic evolution. The results show that: (1) Before the key seam fracture, the stress in the upper rock seam only changes in a small amount, and the stress in the lower rock seam evolves similarly to the single coal seam mining; when the key seam fracture is broken, the stress in the upper and lower rock seams will change by jumps. (2) The fractal dimension of the fissures rised from 1.4 to 1.5, the total area of fissures is increased from 16,638 pixels to 17,707 pixels, and the total length is increased from 2217 to 3071 pixels; after the main key layer of the overlying rock is broken, the fractal dimension of the fissures is reduced from 1.56 to 1.5, and the total area of fissures is reduced from 31,451 pixels to 29,089 pixels, the total length has increased from 5657 to 6619 pixels. (3) Before the key layer between the coal seams is broken, it will be suspended to form a "fixed beam". After the first break, the broken rock above it will settle synchronously until the rock blocks form a hinged structure and then collapse. After the fall stops, the key layer periodically breaks to form a "masonry beam" structure, and the overlying stratum settles synchronously.

Study on the Instability Mechanism of Coal and Rock Mining under a Residual Coal Pillar in Gently Inclined Short-Distance Coal Seam with the Discrete Element

The collapse of overlying rocks caused by the instability of residual coal pillars during lower coal seam mining significantly impacts its safety. This paper focuses on the gentle dipping coal seam group and utilizes the discrete element method (DEM) as the basis to comprehensively consider multiple factors through orthogonal experiments. In so doing it reveals the influence mechanisms of various factors on mining at a close distance under a residual coal pillar. Firstly, the process of lower coal seam mining under residual coal pillars in gently-dipping coal seams was simulated and analyzed based on a case study at the Baoping coal mine. Comparing the evolution characteristics of coal–rock fractures, stress changes, and displacement changes during the mining process reveals the mechanism of the joint instability of the lower coal seam, interlayer rock, coal pillars, and overlying strata under the disturbed conditions of lower panel mining. Secondly, an orthogonal simulation experiment was established using the width of the coal pillar and the thickness of the lower coal seam as variables. By comparing the development process of cracks, stress distribution, and rock displacement under different conditions, the research results indicate that the width of coal pillars has an impact on the maximum amount of coal pillar subsidence, while the thickness of the underlying coal seam has an impact on the time of subsidence, when hd ≥ 4.2 m (hj/hd ≤ 4) and w ≤ 14 m (w/hm ≤ 2), a large-scale collapse of the overlying strata of the coal pillar occurs.

Optimization of Destressing Parameters of Water Jet Slits in Rock Burst Coal Seams for Deep Mining

Mining in deep coal seams is characterized by high ground stress, often accompanied by coal and rock dynamic disasters such as rock bursts. High-pressure water jet slotting technology can relieve pressure and reduce the stress concentration on the coal seam, which is one of the effective pressure relief measures in rock burst coal seams for deep mining. Reasonable pressure relief parameters are an important influence on the effectiveness of pressure relief achieved by a high-pressure water jet. This paper uses theoretical analysis and numerical simulation to analyze the principle of high-pressure water jet pressure relief and rock burst prevention, and a theoretical calculation model of six key pressure relief parameters is constructed. The optimal values of each pressure relief parameter are obtained, and good pressure relief effect is achieved in a certain rock burst risk area. The research results showed that (1) parameters such as drilling spacing–slit radius, drilling depth–slit length, and slotting cutting spacing–slotting cutting width have a great influence on the pressure relief effect, and there is a significant interaction between the parameters, while the strength of the coal seam also has a significant effect on the selection of the parameters and the pressure relief effect. (2) The displacement, vertical stress, plastic zone, elastic energy, impact risk index, and the cost of pressure relief can be used to comprehensively evaluate the quality and economy of the pressure relief effect, and the optimal pressure relief parameters of high-pressure water jet slotting under specific physical force properties of the coal seam can be obtained. (3) High-pressure water jet technology with optimal pressure relief parameters was applied to No. 3 connecting the roadway in the 730 mining area of a mine studied, and field monitoring showed that indicators such as microseismic frequency, total energy, and spatial concentration significantly decreased. Moreover, the accuracy of the theoretical model of high-pressure water jet slotting pressure relief parameter optimization is reliable in the relevant technical parameters of coal seam slotting. It is believed that the model can be used to design the high-pressure water jet slotting pressure relief parameters in deep rock burst coal seams.

Dynamics of gas release in highly gassy close-spaced coal seam mining

Dynamics of gas release in highly gassy close-spaced coal seam mining

Coal from the outburst hazardous mine seams: Spectroscopic study

Purpose is to analyze influence mechanisms of physicochemical coal properties on the degree of outburst risk as well as desorption kinetics of methane. Methods of scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), infrared spectroscopy (IR) and Raman scattering (RS) have been applied. The samples have been taken from Donbas coal seams varying in their ranks (i.e. carbonization degree). Findings. It has been identified that in the context of outburst hazardous zones, the ratio between integral intensity of spectral RS bands D and G, K = I(D)/I(G) shows abnormal dependence upon the nominal amount of volatile compounds connected with the impact by iron impurities. It has been defined that within the ferriferous coal samples, concentration of spins ns (i.e. the broken carbon bonds) correlates with iron content. Methane adsorption/desorption processes in the studied coal samples have been studied with the help of NMR method; in addition, they have been described using superposition of diffusion and filtration mechanisms. Originality. It has been understood that high iron content is typical for coal with a greater outburst hazardous degree. The abovementioned iron content and I(D)/I(G) and Ns correlation between the values determines the key role of iron impurities for coal metamorphism processes. For the first time, correlation between the outburst hazardous degree of coal seam and intensity of 3030 cm-1 IR band, stipulated by aromatic CH groups where hydrogen is in atomic status, has been identified. Practical implications. Predictability of outburst risk has been improved in the context of coal seam mining.

Stress Evolution and Surrounding Rock Control During Coal Seam Mining Under the Influence of Overlying and Adjacent Goafs

Stress Evolution and Surrounding Rock Control During Coal Seam Mining Under the Influence of Overlying and Adjacent Goafs

Evolution Mechanism and Control of Floor Heave in the Deep Roadway with Retained Bottom Coal

Roadways with retained bottom coal are common in thick coal seam mining, and floor heaving is a prominent problem. In this study, based on the interaction between the floor and two sides of the roadway-surrounding rock, a Winkler elastic foundation beam model is established to analyze the floor heave problem. A 3DEC model was used to analyze the failure range, failure mode, and migration law of the floor-surrounding rock with different bottom coal thicknesses and coal body strengths. The results show that (1) an increase in the thickness of the bottom coal results in a decrease in the stiffness of the roadway side coal body (the foundation of the supporting rock layer) and an increase in the bending deformation range, the amount of floor rock beam deformation, and the extrusion force. This leads to an expansion in the range of the sides of the coal body that are squeezed by the floor rock layer, resulting in additional failure and deformation of the coal body sides. Therefore, the damage to the floor rock layer is extended and increased. (2) The expansion of the floor pressure-bearing arch and surrounding rock in the arch are the causes of floor heave in the deep coal roadway with retained bottom coal. (3) Because of an increase in the thickness of the bottom coal and a decrease in the coal body strength, the floor pressure-bearing arch expands to the deeper part; thus, the range of surrounding rock in the arch with deformation and failure increases, resulting in an increase in floor heave. The field practice indicates that the support strategy of the “high prestressed strong rock bolt (cable) supporting two sides and bottom corners in time” can effectively control the floor heave of a roadway with retained bottom coal.

A Study on the Instability Mechanisms of Coal Pillars in Shallow Coal Seams Group Mining

To explore the instability mechanisms of coal pillars in the upper coal during coal seam group mining in the Yulin area and hence to achieve safe and green mining of the lower coal seams, the engineering geological condition for no. 3−1, no. 4−2, and no. 5−2 coal seams in the north-second panel area of Hongliulin Coal Mine was investigated in this article. Using the combination of physical simulation, FLAC3D numerical calculation, and theoretical analysis, the instability mechanisms, the characteristics of the fracture structure, and fracture evolution between the coal pillars and the interval rocks were all studied. The results showed that a layout position existed that induced instability and subsidence of the coal pillars of the upper coal seam. The instability mechanism was such that the concentrated stress of the upper and lower coal pillars caused shear plastic damage in the interval rock along the direction of stress-transfer influence angle. The phenomenon of “inclined step beam” fracture structure, falling fracture zone, and severe mine pressure happened during seam group mining. Furthermore, the minimum center offset formula was put forward to study the instability of the upper coal pillars. This study provides a theoretical basis for a reasonable layout on how to position coal pillars for shallow coal seams group mining.

Insight into proactive inertisation strategies for spontaneous combustion management during longwall mining of coal seams with various orientations

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

Application of Gob-Side Entry Driving in Fully Mechanized Caving Mining: A Review of Theory and Technology

China has abundant coal resources, and the distribution of coal seams is complex. Thick coal seams account for more than 45% of all coal seams. Fully mechanized top coal caving mining has the advantages of large production, high efficiency, and low cost. In fully mechanized caving mining, especially in fully mechanized caving mining of extra-thick coal seams, the mining space is ample, the mine pressure is severe, and the roadway maintenance is complex. As a result, it is necessary to summarize and discuss the gob-side entry driving of fully mechanized caving in theory and technology, which will help to promote the further development of fully mechanized caving gob-side entry driving technology. First, in recent years, the research hotspots of gob-side entry driving have focused on the deformation mechanism and the control method of the roadway surrounding rock. Secondly, this paper discusses the theoretical models of the “triangle-block” and “beam” for the activity law of the overlying strata in gob-side entry driving, including the lateral breaking “large structure” model, compound key triangle block structure model in the middle and low position, the high and low right angle key block stability mechanics model, elastic foundation beam model, low-level combined cantilever beam + high-level multilayer masonry beam structure model, and the vertical triangular slip zone structure model. It introduces the “internal and external stress field theory” and the “stress limit equilibrium zone model”. Thirdly, it summarizes several numerical simulation analysis methods in different conditions or research focuses and selects appropriate constitutive models and simulation software. Finally, it introduces surrounding rock control technology, including two ribs, the roof, and under challenging conditions. It provides a method reference for support in similar projects.

Study on the Bearing Mechanism and Stability of Surrounding Rock in Original Roadway Filling and Nonpillar Tunneling

This study is focused on the problem that with the increase of coal seam mining depth, it is difficult to continuously replace mining due to complex roadway layout and unreasonable stope layout. By taking the mining geological conditions of the 62210 fully mechanized mining face of Xinzhuangzi Coal Mine in Huainan mining area, China, as the background, it explores the stress characteristics of the original roadway filling body as well as the stress distribution and deformation characteristics of roadway surrounding rock in original roadway filling and nonpillar tunneling (ORFNPT) through theoretical analysis and numerical simulation. The following findings are obtained. The required strength for the filling body is primarily determined by two factors, i.e., the span of the hanging roof that lies over the filling body and the width of the filling body. The span of the hanging roof is positively correlated with the required strength of the filling body. However, when the width of the filling body reaches a certain value, its further increase fails to change the required strength of the filling body. Compared with gob-side entry driving with small coal pillars, when the ORFNPT technology is applied to the lower-section roadway, the peak stress position in the solid coal on the lower side of the roadway is closer to the roadway sides, and the filling body is of a much higher stress than the small coal pillars. Besides, the roadway surrounding rock undergoes milder deformation. According to the on-site application and measurement data, the roof-to-floor convergence and side-to-side displacement amounts of the roadway are about 89 mm and 58 mm during tunneling of the 62310 working face, and the two amounts are about 910 and 1,290 mm during recovery of the 62310 working face, respectively. This tunneling method achieves an excellent roadway control effect.

Characteristic Developments of the Water-Conducting Fracture Zones in Weakly Cemented Overlying Strata of Jurassic Coal Mines in Western China

The overlying weakly cemented, and poorly performing strata in Jurassic mines of western China have mechanical properties that are generally lower than those in the Carboniferous-Permian coal mines of central and east China. During coal mining, the overlying strata easily deform and fracture. These then formed water-conducting channels, triggering a series of eco-environmental issues, including ground fracturing, collapsed surfaces, declined underground water levels, deserted lands, and even severe water/sand burst accidents. To study the fracture characteristics of weakly cemented overlying strata and the evolution law of water-conducting fractures in Jurassic coal mines in western China, this study selected Tashidian Erjingtian Mine in Korla, Xinjiang, as the research object. Based on the simulation data obtained with physical analog model testing and field monitoring results, the authors investigated the development of water-conducting fractures in the weakly cemented overlying strata during the coal seam mining process. We simultaneously determined the location of key strata in the working face based on key stratum theory. According to the present research results, key strata controlled the development height of water-conducting fractures. When the primary key stratum or sub-key stratum was not fractured, the development of water-conducting fractures was stagnant; water-conducting fractures developed abruptly when the primary key stratum or sub-key stratum was cracked. The heights of water-conducting fractures in the weakly cemented overlying strata of western China exceeded that of similar stopes of central and east China. These research results provided theoretical and technical support for safety in production at Tashidian Coal Mine. In addition, they offered a reference for green and safe production in Jurassic coal mines of western China.

An extended ITL-VIKOR model using triangular fuzzy numbers for applications to water-richness evaluation

Jiaozuo coalfield is the most typical in Northern China type coalfield. When it mined the Permian coal seams, it was threatened by water inrush from the confined aquifer of thin karst fissure limestone in the lower Carboniferous. How to scientifically evaluate and predict the water-richness of thin karst fissure limestone in Carboniferous system has become the most important work in mine water control and prevention. Taking the mining of coal seam No. 21 of Shanxi Formation in Guhanshan coal mine as an example, this paper analyzed the water-richness main controlling factors of L8 Limestone Aquifer of Taiyuan Formation, and selected four evaluation indexes, i.e. water inflow of drilling, the thickness of L8 Limestone Aquifer, the water level of L8 Limestone Aquifer and fault fractal dimension. The 2-tuple linguistic weights of all factors were obtained by the use of interval 2-tuple linguistic method extended by triangular fuzzy numbers. Following the above outlines, the mathematical model for the 2-tuple linguistic evaluation of water-richness was established based on ITL-VIKOR method extended by triangular fuzzy numbers. The data of geophysical exploration were collected to test the accuracy of the model. In addition, the results of 2-tuple linguistic assessment of water-richness and geophysical exploration were used to evaluate the water-richness of L8 Limestone Aquifer, which extends the evaluation and prediction of water abundance for karst fractured aquifers to dyadic array. These results have been applied to guide the safe mining in Guhanshan coal mine, and will be further extended to the mines with similar geological conditions. It is our goal to establish an intelligent application system to ensure safe production in coal mines, which is great beneficial to the technical personnel engaged in mine water prevention and control.

Coevolution mechanism and branch of pillar‐overburden fissures in shallow coal seam mining

AbstractThe large‐scale mining of coal resources promotes the formation of section coal pillar groups between working faces. The overlying strata are supported by coal pillars, which leads to the formation of a unique fracture‐bearing structure in the key stratum, resulting in the evolution of fissures (cracks) and a generally high load on the supports. Studying the fracture‐bearing structure formed by coal pillars and overlying strata (fissures) is the basis for realizing rational mining of working faces. Here, the evolution characteristics of coal pillar‐overburden rock (fissures) in shallow coal seam mining and the working resistance of the support with stable fracture bearing structure of section coal pillar and overburden rock were studied in the No. 1‐2 coal mining of Longhua Coal Mine in Shenmu City, Northern Shaanxi. The fissure evolution characteristics on both sides of the coal pillar and the fracture‐bearing structure of the rock stratum were obtained by physical similarity simulation experiment. The mechanical calculation model of the coal pillar‐overburden rock (fissure) structure was established by theoretical derivation and calculation, and the working resistance of advanced support with a stable mechanical structure was studied. The research shows that the fracture evolution and rock fracture characteristics of a shallow coal seam mining face can be divided into three zones. Through the reanalysis of the mechanical structure of coal pillar‐overburden rock (fissure), the combined mechanical structure of the subkey stratum consisting of a lagging broken step rock beam structure and the main key stratum consisting of a hinged rock beam structure was obtained. Combined with the failure characteristics of the section coal pillar, a mechanical structure calculation method suitable for the bearing characteristics of section coal pillar support in shallow coal buried layers was obtained, and the field measurement results were verified.