Thick Seam Research Articles

Evaluation of water inrush risk from coal seam floors with an AHP–EWM algorithm and GIS

As coal mining is extended to ever-greater depths, the factors affecting the safe mining of coal seams are becoming increasingly complicated. High-pressure confined water in the coal seam floor can pose a major threat to the safety of coal mining. Therefore, based on the analysis of various factors that affect water inrush from coal seam floors, this study develops a geological engineering model of high-pressure confined water damage assessment for coal mine face floors. The model adopts six evaluation factors: coal mining depth, coal seam thickness, thickness of the aquiclude, hydrostatic pressure, brittle-rock thickness, and the distribution of faults and folds. The comprehensive weight of the six factors is obtained through analytic hierarchy processing (AHP) and the entropy weight method (EWM) to establish an AHP–EW risk index model (AEM). AEM is applied for the evaluation of two coalfaces in a study area in North China, and the water inrush risk zonation of the coalface floors is determined. Finally, the results given with AEM are compared with those from the traditional water inrush coefficient method, and its applicability in other mining areas is also validated. The results show that the proposed model provides more accurate evaluation results than the traditional method and that its application is more practical.

Research and Application of Support Technology for Re-mining Roadway in Goaf Under Regenerated Roof in Thick Coal Seam

Aiming at the problem of roadway support in the re-mining of residual coal in the goaf under the condition of regenerated roof in thick seam, this paper takes 6F301 re-mining face in Taiping Coal Mine as the background, combines with the roadway layout of the re-mining face, uses 3DEC simulation software to study the movement law of overlying rock in the re-mining face, and designs and studies the support scheme of the re-mining roadway according to the movement law of overlying rock. The results show that the shotcrete + steel roof support scheme can improve the strength parameters of surrounding rock, improve the stress state of surrounding rock and limit the yield failure of surrounding rock. The measured results show that the maximum relative displacement of roof and floor and two sides of roadway is 97 mm and 105 mm respectively, which effectively controls the deformation of surrounding rock strata with good supporting effect. Through on-site industrial test and application, it can effectively improve the average recovery rate of coal resources, improve the economic efficiency of coal mining, reduce the comprehensive cost of coal mining in coal mining enterprises, and has very important engineering application and research value.

Numerical analysis on the residual stress distribution and its influence factor analysis for Si3N4/42CrMo brazed joint

The residual stress distribution in Si3N4 ceramic-42CrMo steel joints brazed with TiNp-doped Ag–Cu–Ti composite filler has been investigated. The stress distribution in the specimens during cooling and four-point bending was simulated by finite element (FE) calculations using an elastic-plastic model. The FE simulation results indicate that the peak tensile axial residual stresses appear at the Si3N4 edge close to the interface. The experimentally determined joint strength based on the four-point bending test was compared with the results of the FE analysis, showing a reasonable agreement. The residual stress in the Si3N4-42CrMo joint decreases and then increases with the increase of TiNp content, resulting in an optimized joint strength. The consistency of the obtained results suggests that the stress distribution in the brazed joints can be reasonably predicted within the framework of this elastic-plastic FE model. Then the effect of the thickness of brazing layer and interfacial reaction layer on the stress distribution and joint strength was investigated. The FE results indicate that mechanical properties can be improved by increasing the brazing layer thickness and decreasing the thickness of the interfacial reaction layer. Nevertheless, to improve the experimental joint strength, we should carefully consider all critical properties of the joint rather than simply increasing the brazing seam thickness and decreasing the interfacial reaction layer thickness.

Field investigation of fractures evolution in overlying strata caused by extraction of the jurassic and carboniferous coal seams and its application: Case study

In multiple seam coal mining, the fractures induced by the mining of the lower coal seam may propagate to the goaf of the upper coal seam that is mined earlier. The fracture connection leads to the leakage of hazardous gas. To fully understand the gas leakage due to fracture evolution, the electromagnetic-based measurement system and the borehole televiewer were adopted in the panel No.8100 in Tongxin coal mine, Datong Coalfield, China. The coal seam thickness is 15 m and it was mined by top-coal caving method. The resistivity and fracture pattern in distinct zones of rock stratum were detected, and the correlation between them was explained clearly. We found that the fracture evolves in two stages as the panel working face advances, i.e., fracture propagation and fracture re-closure. The maximum height of fracture propagation is 150 m, in which the height of the caved and the fractured zones are 80 m and 70 m, respectively. These fractures start to be compacted and are re-closed at the distance of 80 m behind the working face. The extraction of the panel No.8100 results in the formation of a gas-bearing zone (GBZ) with separations and shear fractures rather than connecting the goafs of the carboniferous coal seam (CCS) and the jurassic coal seam (JCS). The GBZ is located in a region from 80 m to 150 m above the goaf and 80 m behind the working face. Based on the above findings, effective gas drainage approach is proposed to reduce the concentrations of the hazardous gases consisted of CH4 and CO. After gas drainage, the maximum concentrations of CH4 and CO drop to 0.5% and 16.63 ppm, with reductions of 53.7% and 33.9% respectively.

Economic Analysis of Natural Gas Reserves Addition from Coal Bed Methane in Nigeria

The aim of this project is to economically analyze Coal Bed Methane (CBM) development in Nigeria. This will offer an opportunity to use gas from the Nation huge coal reserves for domestic and exportation purposes to boost the economy of Nigeria. CBM can be used to generate power as well as manufacture alternative products. The profitability of coal bed methane (CBM) project depends on factors such as seam thickness, gas content, methane content, coal rank and permeability. Its economics are influenced by other variables, such as fiscal policy, depth of coal seam, volume of water disposal, access to market and price of gas. Potential and existing sites for coal bed methane extraction in Nigeria were identified. Kim’s equation was used to estimate the gas content. The gas-in-place was derived with Volumetric method. Methane quantification was estimated using Eddy curve. It is observed that the ultimate reserves, the capital costs, and the gas price have significant effect on the net present value (NPV) and internal rate of returns (IRR) and thus the economic viability of the project. Economic analysis of LNG and Pipeline projects for gas transmission were comparatively examined. It is observed that the gas price and demand at the market hub depend largely on the mode of transmission.

Economic Analysis of Natural Gas Reserves Addition from Coal Bed Methane in Nigeria

The aim of this project is to economically analyze Coal Bed Methane (CBM) development in Nigeria. This will offer an opportunity to use gas from the Nation huge coal reserves for domestic and exportation purposes to boost the economy of Nigeria. CBM can be used to generate power as well as manufacture alternative products. The profitability of coal bed methane (CBM) project depends on factors such as seam thickness, gas content, methane content, coal rank and permeability. Its economics are influenced by other variables, such as fiscal policy, depth of coal seam, volume of water disposal, access to market and price of gas. Potential and existing sites for coal bed methane extraction in Nigeria were identified. Kim’s equation was used to estimate the gas content. The gas-in-place was derived with Volumetric method. Methane quantification was estimated using Eddy curve. It is observed that the ultimate reserves, the capital costs, and the gas price have significant effect on the net present value (NPV) and internal rate of returns (IRR) and thus the economic viability of the project. Economic analysis of LNG and Pipeline projects for gas transmission were comparatively examined. It is observed that the gas price and demand at the market hub depend largely on the mode of transmission.

Case Studies of Rock Bursts in Tectonic Areas with Facies Change

Although tectonic areas with facies change (i.e., variation of coal seam thickness, coal seam dip angle, or coal quality) are one of the three major geological structures that induce rock bursts, case studies of rock bursts in these tectonic structures are rare. The main objective of this study is to illustrate this issue and provide case studies that may inspire future research. Based on several typical cases of rock bursts induced by tectonic areas with facies change, the conditions conducive for these bursts are introduced and investigated in detail. Subsequently, numerical simulation is performed, showing that stress concentration exists in regions with variable coal seam thicknesses or dip angle. When stoping or tunnelling approaches this region, the peak stress increases rapidly. Thus, the burst occurs via a mechanism involving the superposition of high in-situ stress from tectonic areas with facies change and abutment pressure from stoping or tunnelling, leading to high stress concentration. Strategies for mitigating rock bursts are also provided. Rock bursts induced by tectonic areas with facies change can be mitigated by avoiding regions of high tectonic stress concentration and reducing mining induced stress.

Experimental Investigation on Crack Development Characteristics in Shallow Coal Seam Mining in China

The development of cracks in mining is the scientific basis for the safety and environmental exploitation of shallow multiple-seam. According to the “thickness of coal seam, interactive distance, and buried depth,” four mining coal mines are selected in Shen Fu-Dong Sheng coalfield (SFDSC). To research the mining conditions of shallow coal seam under different base-load ratio mining conditions and different working faces by the physics simulation and in-sit measurement, the key roof caves are sketched by different colors. This study shows that the typical shallow coal seams in the thin overlying bedrock and thick loose sand layer (LSL) as well as the development of the setup entry cracks (SEC) is dominated by LSL arch damage. The surface cracks are almost directly above the setup entry. The flat seam mining and the SEC development is dominated by parabolic type. The surface cracks are located inside the setup entry. With the mining height increased typically in a shallow coal seam, the rate of crack development and the extent of damaged area increased significantly. The SEC and boundary cracks are fixed. The dynamic periodic cracks (DPC) show the ability of the strata to self-repair. During the multiple-seam mining, the above three kinds of cracks have the phenomenon of activation and development. Through the reasonable coal pillar distance arrangement, the development of boundary cracks can be effectively controlled and the relatively uniform surface settlement and crack closure can be achieved. The purpose of reducing damage mining can also be achieved. Furthermore, it provides scientific support for the green mining in the shallow coal seam.

Analytical study to estimate rib spalling extent and support requirements in thick seam mining

In order to better understand the mechanism behind the poor stability of support and surrounding rocks at mechanized working faces with increased mining height (MWMH), a conceptual model of the support and rocks surrounding the MWMH, under different structural conditions of the main roof, is established in this study. On the basis of the mechanical model, the interaction among the coal wall, support and roof in MWMH is studied. The analytical analysis reveals that the coal wall and support interact more significantly in the MWMH than conventional approaches (e.g., conventional longwall mining). With the increase in the depth of rib spalling in coal wall, the support strength, needed to control the roof, increases linearly. While as the support strength increases, the depth of rib spalling in coal wall showed a hyperbolic-like decrease. Based on these results, the expression, which describes the relationship of the interaction between the rib spalling in coal wall and support strength in the MWMH, is proposed. Rib spalling is then controlled in real working face in a soft, thick coal seam. The field experiment demonstrates that the advanced long-hole hydrostatic pre-injection can control rib spalling in coal wall and guarantee the stability of support and surrounding rock, which enables a high-efficiency mining of the MWMH.

Investigation of coal discharge modes on brassboards of powered roof support unit

Physical and analytical modeling of caved top coal discharge by adjustable feeders on armored face conveyor during underground mining of thick flat seams has been performed. The process of top coal caving is studied using laboratory installation with the feeders operating in wave and areal modes. Based on 3D discrete element method (DEM), gravity flow of coal and its interaction with the powered roof support unit is modeled numerically.

Sand Body Provenance Analysis of Taiyuan Formation in Datong Coal Basin

Coal provenance analysis is an important part of coal research, of referential significance for coal-seeking direction determination, coal-rock formation comparison, coal enrichment zone location prediction, exploration of coal seam thickness variation laws, and estimation of coal reserves/resources.

Development of the fracture zone water flow level in the overburden

Abstract The Guojiahe coalmine was studied to estimate the maximum water level in the fractured zone in the overburden of a thick seam in Linyou mining area, where extraction is fully-mechanized. Using a predictive model of the movement and deformation of the upper rock/soil layer in the overburden fracture zone, the free water level in the overburden was determined. Physical and numerical simulations were performed to study the development characteristics of water-flow in the fractured zone under different conditions, and the maximum water level in the fracture zone was determined. The maximum height of the fracture zone is 185 ∼ 193 m from the roof of the coal seam, and the relationship between it and the distance to the working face has a step-like function, revealing the controlling effects on water level of the key strata in the overburden.

Coal Seam Thickness Prediction Based on Transition Probability of Structural Elements

Coal seam thickness prediction is crucial in coal mine design and coal mining. In order to improve the prediction accuracy, an improved Kriging interpolation method on the basis of efficient data and Radial Basis Function (RBF-Kriging) is firstly proposed to interpolate the cutting data that is obtained in pre-mining, especially at the edge of the geological surface of coal seam by taking into account the spatial structure and the efficient spatial range, ensuring the integrity of the edge data during the movement of structural elements. Subsequently, a structural element transition probability based Gaussian process progression (STTP-GPR) method is proposed to predict the coal seam thickness from the interpolated coal seam data. The experimental results demonstrated that the proposed STTP-GPR method has superior performance in coal seam thickness prediction. The average absolute error of thickness prediction for thin coal seams is 0.025 m, which significantly improves the prediction accuracy in comparison to the existing back propagation (BP) neural networks, support vector machine, and Gaussian process regression methods.

A quantitative evaluation method of coal burst hazard based on zone division and an analytic hierarchy process: a case study on Yanbei coal mine, Gansu Province, China

The occurrence of coal bursts affects the safety of coal mines while coal burst hazard evaluation exerts a guiding influence preventing future coal bursts. Therefore, a method for quantitatively evaluating coal burst hazard was proposed based on zone division and an analytic hierarchy process (AHP). On this basis, by considering the distribution of influence factors of coal bursts in coal mining face (CMF) and means of influencing weight changes, the research aimed to enhance the accuracy and pertinence of coal burst hazard evaluation. By investigating the LW250204 of Yanbei Coal Mine in Gansu Province, China, it can be speculated that the CMF was influenced by various factors (including extra-thick coal seam, syncline and anticline tectonics, mining- induced disturbance, dip angle of coal seams, and mining depth) and thus suffered significant threat of coal burst. The results revealed the following three points: firstly, the degree of coal burst hazard had a positive correlation with the thickness of the coal seams, the mining depth, and mining-induced disturbance, while it exhibited a negative correlation with syncline and anticline tectonics. Moreover, it showed a parabolic correlation with the dip angle of the coal seams. Secondly, the zone division of the CMF was carried out according to the range of influence and changes in various factors. Based on AHP and the degree of influence of different factors on coal burst hazard, an evaluation matrix for the weights of influence factors driving coal bursts was established to quantify the differences between weights of various influence factors. Thirdly, based on the evaluation matrix for weights of influence factors, the relative coal burst hazard index was constructed to quantify the coal burst hazard in a given zone. Through testing, the goodness of fit between the distribution of the global relative coal burst hazard indices of the LW250204 and mininginduced tremors (MITs), as located, reached 90.8%, which validated the accuracy of the evaluation results. The research can provide a reference for quantitative evaluation of coal burst hazard in coal mines.

Application of structural equation modeling to evaluate coal and gas outbursts

Coal mines have sudden, usually unexpected expulsions of gas in conjunction with coal into the mine workings. The gas is mainly consisted of methane making this so-called coal and gas outburst a major hazard affecting the safety and productivity of an underground coal mine. Several parameters affect this outburst hazard. In this study, a statistical method namely structural equation modeling (SEM) was applied to identify the relationships between the parameters affecting the coal and gas outbursts for an underground coal mine in Turkey and to analyze multiple interactions between them. The model includes main factors (mining depth, coal seam gas content and moisture content) and contributor factors (seam thickness, seam inclination and distance from fault). The results indicate that mining depth is the most efficient factor in main factors and distance from fault is the most significant contributor to outburst.

Hydraulic Fracturing Effect on Filtration Resistance in Gas Drainage Hole Area in Coal

Features of stress state and jointing as well as their effect on hydraulic fracture propagation direction in coal seams are considered. The flow resistance in drainage areas is analyzed depending on hydrofracture orientation, thickness of seams and spacing of holes. The comparison of one-stage and multi-stage hydrofractures created in-plane and orthogonally to hole axes is given. In simulated reservoir conditions, permeability of dense coal is studied without a fracture and with a through propped fracture subjected to confining pressure. The recommendations are developed for improving efficiency of gas drainage in coal seams based on in-mine hydraulic fracturing.

Modeling Top Coal Disintegration in Thick Seams in Longwall Top Coal Caving

The geomechanical model of the powered roof support-top coal-roof rock system is developed. For investigation of disintegration processes in top coal of thick seam, numerical modeling with finite element discretization of a study domain is carried out using the authors’ original code. The computational experiment reveals stress distribution in rock mass, as well as evaluates position, shape and size on uncontrolled caving zones in top coal.

Discovery of anomalous molybdenum enrichment in lower Carboniferous coal and its availability and origin

Less attention has been paid to element variations in lower Carboniferous coal (South China) due to the relatively thin coal-bearing seam thickness, but these variations are of great significance for broad industrial utilization and to evaluate the environmental effects of these coals. This study investigated 34 elemental varations of Carboniferous M2 coal-bearing seam collected from Guizhou Province in South China. The new findings include that molybdenum (Mo) is abnormally enriched in these coals with an mean of 945 mg/kg (0.12–7928 mg/kg), which is 782 and 306 times more than Mo of upper continental crust and Chinese coals. The studied coal bed (Moavg = 2264.89 mg/kg, range = 474 to 7928 mg/kg, ca. 1 m thick) may be utilized as a Mo resource. The Mo origin of the studied Carboniferous coal is influenced by terrigenous inputs and hydrothermal fluids, but the leading Mo source of the Carboniferous coals with anomalous Mo enrichment was derived from the hydrothermal fluids. In addition, Ga and Li have potential applications after recycling, and coal from this seam could be considered to be a Se-rich fertilizer after grinding.

Modeling Top Coal Disintegration in Thick Seams in Longwall Top Coal Caving

Modeling Top Coal Disintegration in Thick Seams in Longwall Top Coal Caving

Research on Prevention and mitigation of Deep Mine Hazards in Ningzheng Mining Area

Ningzheng Mining Area, as one of the key mining areas of Longdong Energy Base in Gansu Province, whose average overburden depth of coal seams is more than 800 meters and average thickness of coal seams ranges from 8m to 14m. This paper analyzed the typical characteristics of water damage, heat damage, high mine pressure and gas disaster in Ningzheng mining area. Disaster prevention measures and two resource utilization prevention technologies (namely EMS cooling technology, Gas power generation and cogeneration system cooling technology) were put forward, the rearch has a realistic significance for the safety exploitation, comprehensive utilization of deep coal resources in China, energy conservation and emission reduction and development of circular economy.