Coal Mining Engineering Research Articles

Application Analysis of Roadway Tunneling and Support Technology in Coal Mining Engineering

Application Analysis of Roadway Tunneling and Support Technology in Coal Mining Engineering

Mining Process and Technology in Coal Mining Engineering

Mining Process and Technology in Coal Mining Engineering

Research on failure criteria and collapse height of roadway roof strata based on energy accumulation and dissipation characteristics

AbstractRoof collapse is a form of rock failure driven by energy release. The rectangular elastic thin plate (RETP) model, widely used in coal mining engineering research, reflects the law of the movement of overlying strata of a coal seam. The stress distribution regularity of each delamination can be analyzed using the theoretical model of RETPs. In this study, a new method for determining both the height of the caving zone and the damaged area of the roadway roof is developed based on the energy evolution law. The damaged area and the oval‐shaped boundary of each stratum are determined using the damage criterion deduced by calculating the strain energy of the elementary volume. As a case study, the collapse height was obtained by accumulating the thickness of damaged strata, and the length of bolts was increased from 2.2 m to 2.8 m, effectively preventing the reoccurrence of a roof collapse for the No. 30102 working face in Nanliang Coal Mine. In addition, the vertical boundary of the caved zone can be outlined by connecting and fitting the end vertexes of the minor axis in the oval‐shaped damaged area of the RETPs. The supporting angle of the bolts in two side walls of the roadway was decreased from 75° to 70°. This method was verified and applied in a roof collapse investigation by determining the length and drilling angle of the anchor rod and anchor cable required to develop reasonable support schemes. The results of this research can be used for ensuring safety in coal mining and subway or tunnel construction in China.

Dynamic Characteristics of Fault Structure and Its Controlling Impact on Rock Burst in Mines

As one of the most serious shock dynamic disasters in coal mining, rock burst only occurs under the certain geodynamic environment. Geodynamic is the necessary requirement for the occurrence of rock burst, and the disturbance of mining engineering is the sufficient requirement. In terms of the fault structure, the method of geodynamic zoning is used to classify fault structure forms of rock burst in mines, and a model of geological structure is established to reveal the connection between fault structure and mine engineering. Besides, the influence of fault structure on rock burst is analyzed, and the controlling mechanism of the fault structure on the tectonic evolution of the mine area and the occurrence of rock burst is revealed. This research provides a treatment plan for the prediction and prevention of rock burst and guides the safe production in the coal mining engineering.

An Innovative Non-Pillar Coal-Mining Technology with Automatically Formed Entry: A Case Study

• Innovative approach of non-pillar coal mining is accompanied by the automatically formed entry. • The mutual cooperation of three key techniques achieves non-pillar coal mining engineering. • A field test verified the feasibility and effectiveness of the non-pillar coal mining technology. • The proposed non-pillar coal mining technology is supposed to popularize on a large scale. A non-pillar coal-mining technology with an automatically formed entry is proposed, which reduces the waste of coal resources and the underground entry drivage workload. Three key techniques in this technology cooperate to achieve automatic formation and retaining of the gob-side entry, and to realize non-pillar mining. Constant-resistance large deformation (CRLD) support ensures the stability of the entry roof; directional presplitting blasting (DPB) separates the entry roof and the gob roof; and a blocking-gangue support system (BGSS) integrates the caved rock material as an effective entry rib. An industrial test was conducted to verify the engineering effects of these key techniques. The field application results showed that the retained entry was under the pressure-relief zone due to the broken-expansion nature of the caved rock mass within the DPB height. After going through a provisional dynamic pressure-bearing zone, the retained entry entered the stability zone. The final stable entry meets the requirements of safety and production. The research results demonstrate the good engineering applicability of this technology. By taking the framework of the technology design principles into consideration and adjusting the measures according to different site conditions, it is expected that the proposed non-pillar coal-mining technology can be popularized on a large scale.

Prediction of Surface Subsidence Due to Mining

Ground subsidence caused by mining is increasing day by day, and some enormous disasters have been brought. Some scholars have carried out some results by a single factor analysis, but did not consider the multi-working conditions, resulting in a certain deviation from the actual project. Accurate and effective prediction of subsidence caused by coal mining is an urgent problem to be solved. In this paper, the main factors affecting surface subsidence in mining area, which are coal seam thickness and mining depth, are studied by means of composite analysis method. At the same time, three-dimensional finite element method is employed to simulate different engineering conditions. According to the simulation maximum value settlements, fitting through MATLAB software, the corresponding predicted models are established. Comparing with the actual engineering survey data, it is proved that the settlement prediction curve is in good agreement with each other. This research has reference value for actual coal mine engineering and construction engineering.

Automatic Coal and Gangue Segmentation Using U-Net Based Fully Convolutional Networks

Sorting gangue from raw coal is an essential concern in coal mining engineering. Prior to separation, the location and shape of the gangue should be extracted from the raw coal image. Several approaches regarding automatic detection of gangue have been proposed to date; however, none of them is satisfying. Therefore, this paper aims to conduct gangue segmentation using a U-shape fully convolutional neural network (U-Net). The proposed network is trained to segment gangue from raw coal images collected under complex environmental conditions. The probability map outputted by the network was used to obtain the location and shape information of gangue. The proposed solution was trained on a dataset consisting of 54 shortwave infrared (SWIR) raw coal images collected from Datong Coalfield. The performance of the network was tested with six never seen images, achieving an average area under the receiver operating characteristics (AUROC) value of 0.96. The resulting intersection over union (IoU) was on average equal to 0.86. The results show the potential of using deep learning methods to perform gangue segmentation under various conditions.

Deformation Analysis of Bending Stratum Based on Displacement Function Method

Bending strata is an inevitable consequence of coal mining, which will waste mineral resources and influence their production. In this paper, the displacement function suitable for curved beam in polar coordinates is introduced, and the partial differential governing equation of curved beam is obtained by theoretical analysis. Then, the expressions of displacement components and stress components are expressed by displacement function. On this basis, the program for solving the partial differential equation is compiled using the difference principle. Finally, these theoretical formulas of curved beam are applied to analyze the displacement distribution of bending rock and the influencing factors of deformation in coal mining. These main results show that the value of deformation is increasing with the increase of inner radius, tectonic stress and mining depth, while it is decreasing with the increase of thickness of overburden layer. Moreover, the advancing angle effects significantly not only the value of deformation, but also the position of max value. The value of deformation is more suitable for mining position at about 30°. Obviously, the inner radius and advancing angle have more effect on deformation than other factors. These conclusions provide scientific basis and reference for coal mine engineering.

Effects of Flaw Geometry on the Fracturing Behavior of Rock‐Like Materials Containing Two Arch‐Like Parallelogram Flaws

To increase understanding of the strength and failure mechanism of rocks with arch‐like fractures generated in the overlying strata above a gob during coal mining, a series of uniaxial compression tests on rock‐like specimens containing two preexisting parallelogram flaws at inclination angles varying from 45° to 75° were made using a rock mechanics servocontrolled testing system. Based on the experimental results, the effects of the inclination angles of two flaws having the same area on the mechanical parameters and fracturing process of the specimens were analyzed in detail. By adopting photographic monitoring, the crack initiation, propagation, coalescence, and failure modes in rock‐like specimens were observed and characterized. The crack initiation stress and the second initiation stress were distinctly related to the flaw inclination angles, although the crack initiation stress presented a change trend generally similar to that of the crack second initiation stress with increasing flaw angle. Four modes of ultimate macroscopic failure morphology and the crack coalescence and failure modes of three types could be summarized. The research reported here could provide some theoretical support for the arch‐like fracture evolution in the overburden during the excavation in underground engineering, especially in coal mining engineering.

The Research on the Effect of Humidity on the Rheological Model of Swelling Rock

The research on the rheological mechanical behaviour of swelling rock in the condition of humidity field has a significant meaning for large rock engineering, such as deep coal mining, tunnelling, and slope engineering. Based on the Nishihara model, considering on the effect of humidity factor on swelling rock, the rheological elements are established and the effects of humidity on the damage of rock, the viscosity, and the elasticity are introduced. Moreover, the viscoelastic plasticity constitutive equations are established under the coupling of swelling rock stress and humidity. Afterward, considering the effects of humidity on the damage, elasticity, and viscosity, the creeping, unloading, and relaxation equations have been deduced. From this research, under the state of low stress (σ3P < σS), the Nishihara model which considers the effect of humidity shows the properties of stable creeping. In addition, the unloading curves contain instantaneous elasticity, elastic after effect, and the viscosity flow induced by the humidity. However, under the state of high stress (σ3P ≥ σS), it is an unstable creeping model. The unloading curves include instantaneous elasticity, elastic after effect, and the viscosity flow induced by the stress and the humidity. This model reflects the rheological properties of swelling rock comprehensively, and it can be used for rock rheological analysis.

Novel Segmented Roadside Plugging-Filling Mining Method and Overlying Rock Mechanical Mechanism Analyses

The no-pillar mining method is widely used in coal mining engineering because of its superiority in resolving mine pressure hazards and protecting natural resources. In view of the geological conditions of stable strata in a coal mine of the Shandong Coal Zone, a novel segmented roadside plugging-filling mining method is proposed by introducing the filling coefficient into roadside filling. The operation process is designed with a new grouting filling forming device. Based on the relationship between the theoretical deflection of a cantilever beam and geometric settlement and parallel settlement models, strength formulas applicable to the segmented roadside plugging-filling (SRPF) method at different migration stages are obtained, and the deformation formulas of a roadway toward a rock slab are solved by an elastic equivalent model. Further, the determination procedure of the filling mode under the mining method is clarified. The SRPF method was implemented on a test stope, and the test results indicated that the theoretical deformation produced by the SRPF method was small and can meet the mining requirements. Through on-site test monitoring, the deformation of surrounding rock was 0–160 mm and the filling body under the SRPF method could maintain its own strength and the stability of the surrounding rock. In addition, entire successful mining been completed in the working stope, which further proves the applicability of this method. The backfilling cost of the gob-side filling was reduced by approximately 50%, and the backfilling efficiency was improved in the mine. The description of the novel mining method may provide theoretical and practical guidance for coal mining in similar geological conditions.

Curved beam elasticity theory based on the displacement function method using a finite difference scheme

A displacement function suitable for plane curved beam in polar coordinates is introduced, and a partial differential governing equation of plane curved beam is obtained by theoretical analysis. Then, the formulation of displacement components and stress components is expressed by the displacement function. On this basis, a finite difference scheme of the partial differential governing equation, displacement components, and stress components of an elastic body in polar coordinates is presented. Finally, the finite difference equations of theoretical formulation are applied to analyze the stress distribution of curved rock, which will provide scientific basis and reference for coal mining engineering.

Experimental Study on Mechanical Characteristics and Fracture Patterns of Unfrozen/Freezing Saturated Coal and Sandstone.

The thermomechanical behavior of coal and sandstone during excavation using the freezing method is a new challenge for coal mining and geotechnical engineering. In this paper, the influence of temperature on the mechanical characteristics and fracture patterns of two types of saturated rocks (coal and sandstone) were investigated. A series of laboratory tests, including the Brazilian tensile strength (BTS), uniaxial compressive strength (UCS), and triaxial compressive strength (TCS), were conducted at temperatures of 20, −4, −10, and −15 °C. The results indicated a significant increase in their strength when the temperature was reduced from 20 to −15 °C, especially near the phase-transition point. Then, a theoretical model was proposed to predict rock strength change with temperature, based on the phase-transition theory. To evaluate this model, the predicted results were compared with experimental data, where a good correlation was identified. In addition, four failure patterns were observed in indirect tensile tests (i.e., layer activation, central fracture, noncentral fracture, and central and layer activation), and three types of failure modes in compression tests (i.e., axial splitting, shearing along a single plane, multiple fracturing). The evolution of the rock damage was divided into four stages: Crack closure, fracture initiation, critical energy release, and rupture. These results could be applied to evaluate and predict the mechanical behavior of saturated coal and sandstone during excavation using the freezing method.

Failure Characterization of Three Typical Coal-Bearing Formation Rocks Using Acoustic Emission Monitoring and X-ray Computed Tomography Techniques

In coal mining engineering, the mechanical properties of rocks in coal-bearing formations are important for mining safety. In addition, lithological properties are among the most crucial factors affecting the mechanical properties of a given rock. To preliminarily address this important issue, several uniaxial compression tests were conducted on three types of rocks in coal-bearing formations: argillaceous siltstone, mudstone and silty mudstone. In all of the experiments, the acoustic emission (AE) technique was employed to detect the initiation and evolution of microcracks during the testing process, and the computed tomography method was then employed to further investigate the failure patterns of the different types of rock mass. The AE results showed that failure initiated at stress levels of approximately 0.18, 0.48 and 0.05 times the peak stresses for argillaceous siltstone, mudstone and silty mudstone, respectively. Furthermore, in the argillaceous siltstone, the accumulated AE events increased gradually during loading until macrofailure occurred; in contrast, obvious plateaus in the AE parameter curves existed in the stress regions at 60–70% and 35.5–50% peak stress for mudstone and silty mudstone, respectively. In the crack coalescence stage, a large number of low-energy microfractures occurred in the argillaceous siltstone, whereas a small number of high-energy microfractures occurred in the mudstone and silty mudstone. The results revealed that (1) the argillaceous siltstone was essentially destroyed by splitting, while the mudstone and silty mudstone samples were broken by shear fracture propagation; (2) for all of the coal-bearing formation rocks investigated in this work, when the fracture surface area was larger, the strain energy to be translated into surface energy was greater, and thus, more input energy was required when the peak strength was greater. Clearly, lithological properties, especially microstructural features, play a critical role in the mechanical properties of coal-bearing formation rocks. Therefore, a comprehensive evaluation should be considered in any analysis of mining safety.

An innovative yielding prop with high stable load capacity and long shrinkage distance in coal mine

ABSTRACTConventional free standing supports, such as wooden cribs, hydraulic prop in coal mine and other underground engineering have some disadvantages, such as low stiffness for wooden cribs, costly, overweight and inconvenient for hydraulic prop, etc. This paper introduced a new yielding prop with high stable load capacity and long shrinkage distance, which is mainly consisted of an inner and outer prop and a circle of steel balls. The stable load capacity is generated by the plastic flow induced by the contact behavior among inner prop, steel balls and outer prop and the supporting height could be adjustable by the connected height by the inner and outer prop. The mechanical and mathematical model are developed based on contact mechanics and a serial of full-scale tests were conducted to verify the theoretical model. The test results are well corresponded to the calculated stable load capacity and four batch of props with stable load capacity from 200 kN to 1400 kN were designed. The load capacity of the prop can be adjusted with a small change made to its geometry. The on-site experiment results show that supporting method with this new prop can enhance the stability of surrounding rock and can resist dynamic pressures generated by excavation compared with the wooden cribs. In addition, relative to original supporting costs, new prop can reduce overall supporting costs by 63.8%.

Analysis of Dynamic Surface Subsidence at the Underground Coal Mining Site in Velenje, Slovenia through Modified Sigmoidal Function

In underground coal mining engineering, one of the most important tasks is to monitor, predict and manage the surface subsidence due to underground coal excavation. The impact of underground mining excavation reflects as subsidence of the overlying strata and the formation of surface depressions soon after excavation. The surface subsidence is one of many natural processes that exhibit a progression from small beginnings that accelerate and approach a climax over time. When detailed data is lacking, a logistic function is often used. In this paper, the analysis of the surface subsidence above underground mining sites in the Velenje Coal Mine by using a modified sigmoid function (surrogate of logistic function), with the common “S” shape, is introduced. Furthermore, the time estimation of the next and the final epoch measurement is considered.

采矿工程专业在坚守中理性变革

煤炭是国家的能源支柱，采矿工程专业是煤炭开采的主干专业。煤炭鼎盛十年过后，在行业发展与人才培养方面两者正面临着巨大的困难与挑战。煤炭高校采矿工程专业信心受到了极大冲击，许多学生感到前途迷茫，心理波动较大。在煤炭经济形势的新常态下，煤炭高校采矿工程专业的人才培养模式要主动理性变革与适应；进一步加强采矿工程专业内涵建设，丰富培养手段，实现小班制精英式教育，是当前的采矿工程专业的重要变革手段。 Coal is the nation’s energy pillar. Mining engineering major is an important part of a coal mining. Peak after ten years, both in terms of industry development and personnel training are facing great difficulties and challenges. Coal mining engineering professional confidence is heavily in-fluenced by the impact of colleges and universities, many students feel lost, future psychological volatile. In coal economic situation under the new normal, universities in coal mining engineering major personnel cultivating mode need to active the rational transformation and adaptation. To further strengthen the construction of mining engineering major connotation, rich culture, to achieve a small elite education, is an important task of the current mining engineering.

Key technology of 3D geosciences modeling in coal mine engineering

A new method for simulation technology of laneway engineering seamless excavation based on 3D geoscience modeling (3DGM) was proposed to overcome the deficiency in current research. The generalized triprism (GTP) data model was used as the basic modeling element in this method. The models of geological body were created by the method of rock pillar body partition (RPBP) modeling. The laneway engineering models were built with component method, while the corresponding triangles in sections were connected and transformed into tunnel GTP models. All the GTP models were converted into tetrahedron models based on the smallest vertex identifier (SVID). The simulation and spatial analysis of laneway engineering seamless excavation could be realized through the local hierarchical intersection (LHI) algorithm. The application case showed that the method was fast and effective, and it could meet the needs of design and spatial analysis for mine laneway engineering.

Enrichment and Separation of Coal Mine Ventilation Methane and Engineering Education

Due to the large flow, low concentration, low enrichment efficiency, potential safety hazards and the difficulty of comprehensive utilization, it is a big challenge for the development and application of enrichment and separation technology for coal mine ventilation methane (CMVM) at home and abroad. And many countries paid more and more attentions to resolve this problem. In this paper, we comprehensively introduce the research progress in the field of gas enrichment and separation of CMVM, and analyze the related research and application situation. Then, we put forward the enrichment and separation of CMVM in the future development will focus on high efficient adsorbent and adsorption & separation & enrichment technology and equipment, etc. in order to effectively form the system technology of separation & enrichment of CMVM. So we can provide technical support and auxiliary equipment for the domestic related enterprises, and ensure the mine safety and CMVM utilization. The application of CMVM in the laboratory can make mining engineering students learn how to use environmental technology to realize energy saving and emission reduction in coal mine.

An Experimental Investigation of Permeability Measurement of Water Flow in Crushed Rocks

Due to the high permeability of water flow in crushed rocks, flow catastrophes and water inrush accidents are apt to take place in the broken zones of aquifers in coal mining engineering. The pore, crack and fracture geometries needed for water transport are strongly influenced by grains diameter size and axial displacement conditions. In order to inspect and quantify the influence, we designed and manufactured a water flow apparatus that can be connected to the electro-hydraulic servo-controlled test system MTS815.02 which provides loading pressure in the experiment. Using the apparatus and MTS system, we tested crushed mudstone, limestone and sandstone specimens and obtained the relationship between permeability and variable grain diameter of a (2.5–5 mm), b (5–10 mm), c (10–15 mm), d (15–20 mm) and e (mixed sizes) under variable axial displacement (10, 15, 20, 25, 30, 35 and 40 mm). In particular, the permeability calculation based on collection of water flow velocity and pore pressure gradient difference has involved the influence of non-Darcy flow. The results show that (1) The porosity decreases with the increase of axial displacement and decrease of bigger particle size, respectively. Particle crushing during compaction is a main cause of size 0–2.5 mm appearing, some fine particles be washed away is a main cause of weight loss because of the effect of water seepage. (2) Water flow properties of crushed rocks are found to be strongly influenced by axial displacement and grain diameter size; in general, the permeability decreases with the increase of axial displacement and the decrease of grain diameter, respectively. (3) The fluctuations of permeability–axial displacement are especially intense for mudstone and sandstone than that for limestone. The permeability of crushed rocks is not only related to loading levels but also to grain diameters, style of arrangement. (4) To each grain diameter sizes, the permeability change of sandstone has a greater value than that of mudstone and limestone. The permeability of crushed mudstone shows much less than that of limestone and sandstone.