Longwall Mining Method Research Articles

Modelling surface subsidence of coal mines using a bonded block numerical method

Surface subsidence is common geologic hazard in coal mines when longwall mining method is applied. In this research, a Bonded Block Model (BBM) is selected to numerically simulate and analyze the surface subsidence of coal mines. Parametric study is conducted and key factors controlling the subsidence are characterized. BBM models with no bedding planes realistically simulate the maximum subsidence, but overestimate the subsidence levels above the panel edges. The bedding planes introduced in the BBM models potentially provide more realistic subsidence profile. The separation of the planes and downward bending of the layered strata, as commonly observed in coal mines, are simulated and captured. In addition, high horizontal stress plays a key role in simulating more realistic subsidence profiles. The methodologies and conclusions of this research are expected to improve our understandings of the surface subsidence of coal mines and provide reliable tools to analyze and characterize this challenging issue.

Examining the optimum panel pillar dimension in longwall mining considering stress distribution

Longwall mining method is widely used for underground coal production in the world. Additional stresses occur surrounding the longwall during underground mining. Stresses occurring surrounding the longwall are investigated by many researchers for years. How these stresses affect longwall production, gob, main gate, tailgate and main haulage road has been always an important issue. In this study, the effect of the safety pillar left at the end of the panel on the main haulage road is investigated. For this purpose, 6 models with different pillar distances are created and the stresses occurring in the main haulage road, tailgate and main gate at different pillar distances are examined. It has been demonstrated with numerical models that the optimum pillar distance according to these stress conditions does not damage the main haulage road, tailgate and main gate. In addition, the pillar distance of 10 m gives maximum coal recovery efficiency, and it has been shown by numerical models that the stresses occurring in the main haulage road, main gate and tailgate are not damaging to these galleries.

Analysis and Prevention of Rock Burst Risk of Working Face under the Influence of Continuous Irregular Triangular Coal Pillar Stress Concentration Area.

Irregular coal pillars inevitably appear in the layout of the current long-wall mining method, which easily forms stress concentrations and becomes a heavy disaster area of rock burst. In order to solve the impact risk of irregular coal pillar working face, it is necessary to study the instability mechanism of the coal pillar and put forward effective prevention and control measures. Based on the research background of 14320 working face of the Dongtan Coal Mine in the Yanzhou mining area of China, this paper studies the prediction and prevention of rock bursts in this kind of coal pillar by means of theoretical calculation, numerical simulation, engineering analogy, and field monitoring. The results show that (1) the absolute stability of coal pillar is that the width of coal pillar B reaches twice the support pressure of 2L, and the possibility of instability from large to small is coal pillars 2, 5, 3, 1, and 4. (2) The ratio of coal pillar strength to its average load determines the stability coefficient of the coal pillar, and it is judged that coal pillars 1 and 4 are in a stable state, coal pillars 3 and 5 are in a limit equilibrium state, and coal pillar 2 is in an unstable state. The numerical simulation shows that the maximum stress value inside the coal pillar during the mining process is basically consistent with the theoretical calculation of the bearing strength of the coal pillar. (3) The new evaluation method is used to evaluate the rock burst risk degree of the working face roadway: 156.75 m is a strong rock burst risk zone, 728.18 m is a medium rock burst risk zone, and 176.88 m is a weak rock burst risk zone. (4) Regional prevention and local prevention measures are proposed for the risk of rock burst in the roadway, which reduces the stress concentration of the coal pillar. It is verified that the pressure relief effect is remarkable, and the safe mining of such an irregular coal pillar working face is completed, which provides a solution for studying and solving such rock burst risk.

Evaluation Model on Activation Classification of Coal Mine Goaf Ground Considering High-Speed Railway Loads

The construction and expansion of high-speed railway networks in China has been occurring at a fast pace, resulting in some lines crossing through coal mine goaf sites. However, the embankment and train loads may trigger the activation of the coal mine goaf ground, posing a threat to traffic safety. To ensure the safety of construction and railway lines, an evaluation model on the activation classification of coal mine goaf ground, taking into account the high-speed railway load, is proposed, which is mainly applicable for middle–deep and level goaf areas using a longwall mining method. Firstly, 12 influencing factors are selected as the underlying evaluation indexes, and the catastrophe progression method model for evaluating the coal mine goaf ground stability is constructed. The findings of the evaluation were found to align with the actual results, indicating the reliability of the model. Then, the additional stress calculation model for high-speed railway ground with different embankment heights, train speeds, and axle loads was established, and the train load disturbance depth with a 5% criterion was determined. The influence degree of load on high-speed railway was divided, and the weight of each factor was determined. Finally, the extension comprehensive evaluation method was used to unite the stability grade of the coal mine goaf site and the influence degree of the train, so the evaluation model on activation classification was proposed. The accurateness and reliability of the proposed model was verified using the Taijiao high-speed railway cases and the model test.

DETERMINATION BY NUMERICAL MODELING OF STRESS-STRAIN VARIATIONS RESULTING FROM GALLERY CROSS-SECTION CHANGES IN A LONGWALL TOP COAL CAVING PANEL

As a major pillar of global energy production, coal mining requires continuous advancements in efficiency to contribute to the broader goal of energy sustainability, all the while the shift towards more sustainable energy sources is underway. Mechanized excavation systems employed in underground coal mines, particularly within the longwall mining method, enable high-tonnage coal production. The Longwall Top Coal Caving (LTCC) method, one of the longwall mining techniques, has been developed for the effective extraction of coal from thick coal seams. However, as mining operations delve deeper, various complex issues, such as gallery cross-sectional variation, emerge. Gallery cross-sectional variation can increase the risk of collapse by affecting the stress distribution in the rock mass, posing a threat to worker safety. This study centers on the numerical modeling and analysis of gallery cross-sectional variation in the Ömerler underground mine, operated by the Turkish Coal Enterprises (TKI), West Lignite Enterprise (GLI). To achieve this objective, an extensive database was established through field and laboratory rock mechanics studies. This database was then utilized in the Fast Lagrangian Analysis of Continua 3D (FLAC3D) (v6.0) program to simulate the cross-sectional variations of the A6 panel in the Ömerler underground mine. The numerical simulation results provide valuable insights into the secondary stress-deformation changes associated with gallery cross-sectional variation.

Numerical modelling approach for estimation of a yield zone in the face of a deep longwall panel

In the Longwall mining method, the coal face is being supported with two-legged or four-legged shield supports which improve better roof control between the face and canopy tip. The development of load on the face increases with the face retreating rate or the increase of the overhung length behind the shield support and as a result, the coal face tends to yield/fail. The yield/failure zone in the face extends depending on intensity of developed load due to the depth of mining, panel size, height of excavation and geometry of the overhung. The broken coal from the yielded face may fall on the shearer, armoured flexible conveyor (AFC), shield supports or may hit the deployed manpower in the face and causes the face stoppage which in turn results in to the loss of the project. It is therefore, a study is conducted to understand the face yield/failure behaviour considering various geo-mining conditions based on input parameters such as main roof thickness, overhung length, and material type and setting load. This paper develops a unique statistical model to predict the yield/failure zone in the longwall face. For this purpose, a total of fifty-four (54) three-dimensional finite element models in ANSYS software are developed and analyzed considering Drucker-Prager failure criterion.

Preliminary Design and On-Site Testing Methodology of Roof-Cutting for Entry Retaining in Underground Coal Mine.

Entry retaining via roof cutting is a new longwall mining method that has emerged in recent years, and is characterized by high resource utilization and environmental friendliness. Due to the complexity of this method, a field study is commonly employed for process optimization. Roof blasting is a key operation for retaining the entry, and the current practice involves dynamically adjusting blasting parameters through on-site testing and postblasting monitoring. However, the existing literature lacks detailed descriptions of blasting operations, making it difficult for field engineers to replicate the results. In this study, based on a roof cutting project for entry retaining, a preliminary design of blasting parameters is made based on theories and on-site geological conditions. The on-site test methods and equipment for roof-cutting blasting are described in detail, and the fractural patterns under different blasting parameters are analyzed. After the retreat of the working face, the state of roof caving in the goaf is analyzed based on monitoring data, and the effectiveness of top cutting is evaluated through reverse analysis, leading to dynamic adjustments of the blasting parameters. This research provides a reproducible construction method for roof-cutting operations and establishes the relationship between blasting parameters and post-mining monitoring data. It contributes to the development of fundamental theories and systematic technical systems for entry retaining via roof cutting, offering high-quality case studies for similar geological engineering projects.

Failure mechanism and bulking characteristic of goaf roof in no-pillar mining by roof cutting technology

It is of significant importance to mining engineering by investigating the control method and technology of reducing mining damage to overlying strata. A novel no-pillar longwall mining method (NPLM) by roof cutting technology (RCT) was proposed in China, it can mitigate mining damage by increasing the volume of gangue bulking through RCT theoretically. Considering the NPLM by RCT industrial test as a case study, this paper conducted a comparative analysis of the gangue bulking characteristic at different positions in roof-cutting working face employing in-situ monitoring. The results demonstrated that the RCT can significantly increase gangue bulking and minimize mining pressure concentration. Based on the results of in-situ monitoring, the failure mechanism of goaf roof rock under different mining methods was further studied by theoretical analysis and numerical simulation. The analysis results indicated that RCT can create a free surface in the goaf roof, greatly reducing the minimum principal stress and increasing the failure range of roof rock. It can enhance the height of caving zone, preserve the integrity of overlying strata and reduce the subsidence of surface. This study has significant consequences for the security, productivity, and environmental protection of underground coal mines.

Seismoacoustic Monitoring of a Longwall Face Using Distributed Acoustic Sensing.

Violent, dynamic failures of rockmasses in underground mines pose significant hazards to workers and operations. Over the past several decades, hardrock mines have widely adopted seismic monitoring to help address such risks. However, coal mines, particularly those employing the longwall mining method, have struggled to implement similar monitoring strategies. This is because typical longwall mines are much larger and mine more rapidly than hardrock mines. Moreover, regulations place significant restrictions on the subsurface use of electronics in coal mines due to potentially explosive atmospheres. We present a new monitoring concept that uses distributed acoustic sensing (DAS) to turn an entire longwall face into a seismoacoustic array. After exploring the acoustic response of our sensors in the laboratory, we deployed the array at an active underground longwall mine for several days. We examine 33 events recorded by both the in-mine DAS array and a surface seismic network. We observed that the array records both seismic vibrations traveling through rock and mining equipment as well as sound waves propagating in the workings. We show that waveform moveouts are clearly visible, and that the standard deviation of the audio recordings is a straightforward yet promising metric that could help quantify burst damage. Although improvements are needed before mines can routinely use this monitoring strategy, DAS-based seismoacoustic arrays may assist in understanding coal-burst mechanisms and managing associated risks in underground longwall mines as well as enable better understanding of damage associated with dynamic failures in other underground environments.

A Field Study Implementing New Monitoring Technology for Roof Caving and Systematic Monitoring for Gob-Side Entry Retaining via Roof Cutting in Underground Coal Mining

The longwall mining method with gob-side entry retaining via roof cutting is a new underground coal mining method which has the characteristics of a high resource recovery ratio and environmental friendliness. Due to the complexity of this method, the research method of case-based dynamic on-site monitoring, analysis, adjustment, and optimization is usually adopted. Based on a roadway retaining via roof cutting project, in addition to the traditional indirect monitoring method of hydraulic support pressure, this study innovatively establishes a direct monitoring method for roof caving by monitoring the gangue pressure in the goaf, which provides data for the roof cutting effect and offers a new method for studying the overlying strata movement. In the project, a comprehensive monitoring and analysis system was established, including gangue pressure, cable bolt stress, bracket pressure, roadway deformation, and roof separation, which was used to dynamically analyze the effect of roof cutting and optimize the support design. The results show that the pressure of the hydraulic support close to the roof cutting is low, indicating that roof cutting is favorable in the roadway retaining mining method. The roadway deformation in the advanced abutment pressure area of the working face is small. The mining-induced stress caused by the collapse and compaction of the overlying strata in the goaf is the dominant factor affecting the effect of roadway retaining, especially in the 50-100 m range behind the working face, where the dynamic load causes high bearing capacity of the support elements, large roadway convergence, and roof separation. Temporary support and supplementary reinforcement should be added when necessary. The monitoring system presented in this study is highly comprehensive, simple, reliable, and low in cost, providing a reference for roof cutting roadway retaining projects and roof caving-related studies.

Impact of the Hydrogeological Conditions on the Calculated Surface Uplift above Abandoned and Flooded Coal Mines

Upward surface movement or uplift has been extensively observed above abandoned and flooded deep coal mines, which used the longwall mining method, i.e., a caving method. Detailed analysis of satellite measurements indicated that the process of uplift is one of the more complex phenomena in ground control. The observed uplift is linked to the flooding of the underground infrastructure and rock mass. This was confirmed by conducting analytical calculations. The distribution of water pressure at the end of the mining phase and their increase during the flooding is an important aspect in all estimations. The main objectives of the study are to compare the impact of various hydrogeological conditions of this distribution at the start of the flooding phase and to select the most realistic one. They range from a zero-water pressure to a linear decrease from the top to the bottom longwall panel. Different scenarios of how the water pressures change as a function of time are also compared, i.e., from filling an open reservoir from bottom to top, to a systematic change in the linear downward trend. The main conclusion is that a linear trend, i.e., the original assumed scenario, is the best option in comparison to the other scenarios evaluated. It provides the best fit between the estimated uplift values and the large amount of remote sensing measurements along north–south transects in the Belgian Campine coal basin.

Roof-cutting and energy-absorbing method for dynamic disaster control in deep coal mine

Deep mining roadways are often under high-stress conditions and strong mining-induced disturbances. In the traditional longwall mining method, stress concentration and energy accumulation take place in the surrounding rock of the roadway, often causing dynamic disasters. To this end, the roof-cutting and energy-absorbing (RCEA) control method is proposed. Directional roof presplitting is used to transfer the roof stress and release the energy accumulated in the rock. Importantly, a roadway is automatically formed and coal pillars are eliminated. Moreover, new constant resistance energy-absorbing bolt and cable with high prestress and high elongation are used to control the roadway roof, which are independently developed. As a result, the self-supporting capacity of the rock is improved, and the energy released by the rock deformation is effectively absorbed by the support system. To verify the fidelity of the RCEA method, the numerical comparison test between the automatically formed roadway (AFR) method and the gob side entry driving method is carried out. Compared with the latter, the energy per unit length of AFR is reduced by 4.59*10 6 J, and the maximum energy density is reduced by 36.6%, which shows that AFR has profound effect on the energy release. Subsequently, the mechanical tests on the new bolt (cable) are carried out. The forces at fracture of the new bolt and cable are 1.63 times and 2.80 times that of the common bolt, and the maximum energy absorbed per unit length are 3.05 times and 2.89 times that of the common bolt. The new bolt (cable) has characteristics of high strength and high energy absorption. Finally, the strength-energy combined support design method and the field application are carried out. Field monitoring results show that the RCEA method can effectively release the energy accumulated in the rock and ensure the safety and stability of the roadway.

A Simulation Experimental Study on the Advance Support Mechanism of a Roadway Used with the Longwall Coal Mining Method

Aiming to advance a support problem for roadways used with the longwall coal mining method, the S1202 working face of the Ningtiaota Coal Mine is taken as the engineering background. The monitoring and analysis of bolt force, anchor cable force and surrounding rock deformation of two types of roadways within the whole advance pressure influence range are carried out in the present paper. Based on this, a numerical calculation model consistent with the field is established, and numerical comparison tests under different influencing factors are carried out. The rationality of the numerical test results is verified by using the field monitoring data. At the same time, quantitative evaluation indexes, such as characterization deformation, are established, and the deformation law of roadways surrounding rocks under different advance passive support forces is analyzed. The advance support mechanism of the roadway used with the longwall coal mining method is clarified. The test shows that under the condition of no advance passive support, the maximum characteristic deformation of surrounding rock in the haulage roadway and ventilation roadway is 7.1 cm and 10.1 cm, respectively. The above surrounding rock deformation still meets the requirements of on-site safety production. The research results can provide experimental support for the advance support parameters of the roadway used with the longwall coal mining method.

Impact of the closure of a coal district on the environmental issue of long-term surface movements

<abstract> <p>The environmental impact of deep underground coal mines using the longwall mining method is diverse, e.g., short- and long-term subsidence, damage to surface infrastructure, disturbance of the hydrogeological conditions, and the quality of groundwater and surface water. The study presented focusses on the long-term surface movements after the closure of an entire coal district. Due to the flooding of the underground infrastructure and rock mass, an upward surface movement or uplift is observed. For a specific site in the Campine coal district, Belgium results are presented of satellite data (radar-interferometry). However, the main aim of the study is to better understand the process of uplift and to determine the various mechanisms that are involved. For this purpose, an analytical framework was developed recently, and it was applied successfully in a relatively easy case. The case study of the paper is more challenging, but the usefulness of the analytical framework is clearly confirmed. The most important conclusions are that (i) the uplift is induced by an increase in water pressure after the closure, i.e., re-establishing the original hydraulic gradient, (ii) the expansion of both the goaf volumes and the volumes of the non-collapsed rock mass must be considered, and (iii) the assumption of a linear decrease of water pressure variation from the top to the bottom of the mined area at the end of the mining phase provides the most realistic results. However, the next step in the analysis should focus on a more advanced hydrogeological model of the complex underground environment.</p> </abstract>

Review on the Development of Mining Method Selection to Identify New Techniques Using a Cascade‐Forward Backpropagation Neural Network

The most crucial event in a mining project is the selection of an appropriate mining method (MMS). Consequently, determining the optimal choice is critical because it impacts most of the other key decisions. This study provides a concise overview of the development of multiple selection methods using a cascade‐forward backpropagation neural network (CFBPNN). Numerous methods of multicriteria decision‐making (MCDM) are discussed and compared herein. The comparison includes several factors, such as applicability, subjectivity, qualitative and quantitative data, sensitivity, and validity. The application of artificial intelligence is presented and discussed using CFBPNN. The Chengchao iron mine was selected for this investigation to pick the optimum mining method. The results revealed that cut and fill stoping is the most appropriate mining method, followed by sublevel and shrinkage stoping methods. The least appropriate method is open‐pit mining, followed by room and pillar and longwall mining methods.

Automated planning of open mining for longwall mining methods in the mgis mineframe

Automated planning of open mining for longwall mining methods in the mgis mineframe

Predicting roof displacement of roadways in underground coal mines using adaptive neuro-fuzzy inference system optimized by various physics-based optimization algorithms

Due to the rapid industrialization and the development of the economy in each country, the demand for energy is increasing rapidly. The coal mines have to pace up the mining operations with large production to meet the energy demand. This requirement has led underground coal mines to go deeper with more difficult conditions, especially the mining hazards, such as large deformations, rockburst, coal burst, roof collapse, to name a few. Therefore, this study aims at investigating and predicting the stability of the roadways in underground coal mines exploited by longwall mining method, using various novel intelligent techniques based on physics-based optimization algorithms (i.e. multi-verse optimizer (MVO), equilibrium optimizer (EO), simulated annealing (SA), and Henry gas solubility optimization (HGSO)) and adaptive neuro-fuzzy inference system (ANFIS), named as MVO-ANFIS, EO-ANFIS, SA-ANFIS and HGSO-ANFIS models. Accordingly, 162 roof displacement events were investigated based on the characteristics of surrounding rocks, such as cohesion, Young's modulus, density, shear strength, angle of internal friction, uniaxial compressive strength, quench durability index, rock mass rating, and tensile strength. The MVO-ANFIS, EO-ANFIS, SA-ANFIS and HGSO-ANFIS models were then developed and evaluated based on this dataset for predicting roof displacements in roadways of underground mines. The results indicated that the proposed intelligent techniques could accurately predict the roof displacements in roadways of underground mines with an accuracy in the range of 83%–92%. Remarkably, the SA-ANFIS model yielded the most dominant accuracy (i.e. 92%). Based on the accurate predictions from the proposed techniques, the reinforced solutions can be timely suggested to ensure the stability of roadways during exploiting coal, especially in the underground coal mines exploited by the longwall mining. • Roof displacements in underground coal mines were investigated. • Physics-based optimization algorithms were applied in this regard. • ANFIS was applied to determine the relationship of surrounding rocks. • Four AI techniques were proposed to predict roof displacements. • The SA-ANFIS model provided the highest accuracy in predicting roof displacements.

An investigation of longwall failure using 3D numerical modelling – A case study at a copper mine

AbstractIt is well-known that the longwall mining method (with roof caving) is widely used in underground mining extraction for bedded deposits (e.g. coal) due to its numerous advantages. Generally, this method is not commonly applied for ore deposits such as copper deposit. In Poland, the longwall mining method has been tested for thin copper deposits at the Polkowice-Sieroszowice copper mine (KGHM). Various failure modes were observed during longwall operation in the 5A/1 panel. This paper aims to examine these occurred failures. To do so, an analysis has been conducted using 3D numerical modelling to investigate the failure mode and mechanism. Based on the 3D numerical modelling results with extensive in situ measurements, causes of failure are determined and practical recommendations for further copper longwall operations are presented.

Validation study of no‐pillar mining method without advance tunneling: A case study of a mine in China

AbstractStudies regarding the reuse of a gob‐side roadway formed by the N00 longwall mining method are scarce. To investigate the mine pressure behavior characteristics during roadway reuse, the anchor cable force, roof‐to‐floor deformation, and working resistance of the hydraulic support obtained from the verification working face were analyzed. Test results show that the influence range of the mining‐induced pressure was 0‐90 m in front of the working face. The ratios of the first and periodic weighting steps between the entry‐retaining and non‐roof‐cutting sides were 20.25 and 1.94, respectively. However, the ratios of the ground pressure strengths at the two sides were 1.07 and 1.31, respectively. The results indicate that the monitored roadway can be classified into three deformation zones based on the severity of the mine pressure behavior: large, intermediate, and creep. The main roof between the adjacent working faces exhibited a failure type comprising the “O‐X” and “O‐Y” states, which resulted in an unconventional mine pressure behavior. This study provides insights into the N00 longwall mining method as well as important guidance for tackling similar geological conditions when using this mining method.

An Innovative Technology for Monitoring the Distribution of Abutment Stress in Longwall Mining

Fracturing roofs to maintain entry (FRME) is a novel longwall mining method, which has been widely used in China, leading a new mining revolution. In order to research the change law of side abutment pressure and movement law of overlying strata when using the FRME, a new abutment pressure monitoring device, namely, the flexible detection unit (FDU), is developed and is applied in the field. The monitoring results show that compared with the head entry (also called the non-splitting entry), the peak value of the lateral abutment pressure in the tail entry (also termed the splitting entry) is reduced by 17.2% on average, and the fluctuation degree becomes smaller. Then, finite difference software FLAC3D is used to simulate the stress change of the solid coal on both sides of the panel. The simulation results show that the side abutment pressure of the tail entry decreases obviously, which is consistent with the measured results. Comprehensive analysis points out that after splitting and cutting the roof, the fissures can change the motion state of the overlying strata, causing the weight of the overburden borne by the solid coal to reduce; therefore, the side abutment pressure is mitigated.