Longwall Face Research Articles

Interaction law between mining stress and fault activation and the effect of fault dip angle in longwall working face

Study of the interaction between fault activation and mining stress evolution in the longwall working face is helpful to provide a targeted area for fault type heavy mine pressure disaster control. Combining theoretical analysis, physical and numerical simulation, the mechanical mechanism of fault activation is analyzed, the interaction law between mining stress and fault activation is studied, and the influence of fault dip angle on the evolution of fault activation and mining stress is discussed. The minimum critical dip angles α of normal and reverse fault activation are π/4 + φ/2 and π/4-φ/2, respectively. During the mining process, the activation position of the fault surface, the peak values of stress and displacement gradually increase and transfer from the high position of the fault to the low position, and the peak value of the advance abutment pressure reaches the maximum at the fault. The advancing distance of the working face required for fault activation gradually decreases with the decrease of the fault dip angle, and the peak elevation area of the working face gradually increases with the decrease of the fault dip angle. Combined with the on-site microseismic monitoring results, it can be seen that when the working face is about 20 m away from the fault, the stress and energy increase sharply, which is the main control area of the impact disaster.

A NIRS-based recognition of coal and rock using convolution-multiview broad learning system

Achieving high production in the top coal caving process from thick coal seams is crucial. Thus, the timely decision of when to stop caving poses an urgent challenge to impact the mining loss rate and cost recovery. To address this issue, an innovative recognition system has been developed using Near-Infrared Spectroscopy (NIRS) technology. It stands out for its on-site usability, it enables rapid data collection and local recognition at the longwall face. Furthermore, to overcome the limitations of existing methods in adapting to variations in spectral data quality during on-site collection and the lack of integration of spectral data across different feature processing stages, a coal-rock recognition method has been developed which can ignore the influence of acquisition factors(granularity, light source angle, and detection sensor angle). This method incorporates the features of convolution and multi-view into the BLS model, the designed model structure exhibits a remarkable recognition accuracy of 99.78 %. The model was deployed into the recognition system, and experimental tests were conducted on the working face. The results showed that the recognition system can effectively identify the entire coal-caving process and achieve a recognition accuracy of 92.3 %. This capability is crucial for determining the optimal point to stop roof caving.

Reconstruction method of high-precision longwall mining floor curved surface model driven by data points fitting of equipment

Abstract High-precision coal seam model is the basis of intelligent mining. The longwall mining face floor model, which can provide data sources for the correction of the dynamic coal seam model, is difficult to measurement directly. To address this issue, this paper proposes a high-precision coal seam surface model reconstruction and correction method based on a large number of operating data points. Firstly, the coupling model of equipment and floor is obtained based on the coupling model of plane and surface. Subsequently, the plane data points of the equipment are corrected based on the coupling model of equipment and floor to obtain the floor reconstruction points. The Catmull–Clark surface subdivision method is then used to subdivide the plane formed by the equipment data points to obtain surface subdivision points. The floor model reconstructed using surface data points is validated and corrected using the physics engine in the Unity 3d platform. Finally, the verification of the reconstruction point selection method, the coupling principle between the equipment and the floor model, the reconstruction accuracy of the base plate and the correction principle were carried out based on the equipment and floor model in the laboratory. The experimental results show the feasibility of the floor reconstruction, verification and correction method, which can provide a new idea for the reconstruction of the floor of the longwall mining face and the correction of the dynamic coal seam.

Influence of rock shear processes on the methane content of longwall faces

Influence of rock shear processes on the methane content of longwall faces

Investigation on instability mechanism and control of abandoned roadways in coal pillars recovery face: A case study

The abandoned roadways (ARs) in front of the longwall face catastrophic instability will seriously hamper mining progress, which is a complicated process related to the stress environment, the roadway section, and the mechanical properties of the surrounding rock. The cusp catastrophe theory is employed to establish a state identification model for the irregular coal pillar-roof system (CPRS) formed by the ARs and re-mining entries. To begin, the state discrimination equation (Δp) for the gradual CPRS is derived, and the critical value at which the system transitions into an unstable state under quasi-static conditions is determined. The results indicated that when 16.49 m ≤ L ≤ 22.63 m (L denotes the equivalent span of the intersection roof) and 0 < Re ≤ 2.61 m (Re denotes the width of the elastic zone within the triangular coal pillar), the triangular CPRS is inherently unstable. Similarly, for trapezoidal CPRS configurations where the length Lm (the span of the right-angled trapezoid roof in the propulsion direction) varies from 4.0 to 12.60 m, the system is unstable as well. Subsequently, the model was further enhanced by accounting for the impact of the Pc (advance stress increment load), where a critical criterion for the catastrophic instability of the CPRS was proposed, which represented the external energy required to transition the CPRS from an unstable state to catastrophic instability in different mining stages. After that, the stability degree of the irregular coal pillar was categorized, and a coupling zoning control technology was applied to CPR operations. Field monitoring results demonstrated the effectiveness of the zoning control technology, providing valuable guidance for similar mining practices.

Height Development Characteristics of Water-Conducting Fracture Zone in a Fully Mechanized Longwall Face with a Large Panel Width

Height Development Characteristics of Water-Conducting Fracture Zone in a Fully Mechanized Longwall Face with a Large Panel Width

A selection methodology on reasonable width of stabilized coal pillar for retracement channel in longwall working face

A selection methodology on reasonable width of stabilized coal pillar for retracement channel in longwall working face

Study on fault-slip process and seismic mechanism under dynamic loading of hard roof fracture disturbance

The dynamic stress disturbance induced by mining is a significant factor triggering fault-slip. To better understand the impact of mining-induced hard roof fracture on fault-slip, combined with the geological conditions of a longwall face in contact with the fault, a dynamic and static numerical model was established using FLAC3D. The influence of dynamic loading from hard roof fracture on fault stability was investigated. The characteristics of changes in fault shear stress, shear displacement, slip area, and seismic moment under dynamic loading were analyzed. Simultaneously, numerical results were compared and analyzed against microseismic (MS) monitoring records in the mining, validating the accuracy of the numerical results. The results indicate that dynamic loading is a critical factor in inducing fault-slip. As a geological weak surface, the fault impedes the transmission of shock waves and causes their attenuation. Under dynamic loading, when the fluctuation of fault shear stress and friction coefficient exceeds the threshold, the fault-slip. During the fault-slip process, accompanied by a sharp increase in shear displacement, the seismic moment increases. Finally, the influence of changes in seismic parameters (e.g. longwall–fault distance, seismic energy, and seismic location) on the fault-slip mechanism was analyzed. This study contributes to a better understanding of the disturbance mechanism of mining-induced dynamic loading on fault-slip and provides a theoretical basis for fault-slip rock bursts.

Research on coal mine longwall face gas state analysis and safety warning strategy based on multi-sensor forecasting models

Intelligent computing is transforming safety inspection methods and response strategies in coal mines. Due to the significant safety hazards associated with mining excavation, this study proposes a multi-source data based predictive model for assessing gas risk and implementing countermeasures. By examining the patterns of gas dispersion at the longwall face, utilizing both temporal and spatial correlation, a predictive model is crafted that incorporates safety thresholds for gas concentrations, four-level early warning method and response strategy are devised by integrating weighted predictive confidence with these correlations. Initially tested using a public dataset from Poland, this method was later verified in coal mine in China. This paper discusses the validity and correlation of multi-source monitoring data in temporal and spatial correlation and proposes a risk warning mechanism based on it, which can be applied not only for safety warning but also for regulatory management.

Regularities of rocks zonal disintegration and methane emissions periodicity in mine roadways

The article presents the results of studies on the establishment of stable relationships between methane emissions into degassing wells and their spatial location, stress-strain state of rock massif and mining operations process. Vibroacoustic and electrometric of mine control methods have been used to establish zoning and alternation of fractured zones in the rock massif during mining operations. Using the finite element method, zones of different permeability in the roof above the longwall face were determined, and a qualitative transition from compressive deformations to tensile deformations was revealed. Based on data from mine experiments at 157 degassing wells, patterns of repeatability of rocks zonal disintegration and periodicity of gas emissions into mine roadways depending on the distance to the moving longwall face have been determined for the first time. It has been established that the concentration of methane gas in a wells with distance from the longwall face changes according to a damped quasi-periodic dependence with recombinant changes in stress-strain states. For wells aimed at the goafs, the period of the quasi-periodic function increases by 40%, the amplitude decreases to 30%. The obtained dependencies make it possible to increase the efficiency of degassing.

Deformation mechanism of gob‐side entry at top coal caving mining face: A numerical study

AbstractTo investigate the significant deformation of the surrounding rock within the dynamic pressure zone of the gateroad, this study utilized the tailgate of the 1506 longwall face in Anyang Coal Mine as the engineering context. A combined approach of field measurement and numerical analysis was employed to explore the deformation and failure mechanisms of the surrounding rock under dynamic pressure. The findings indicate that before the exploitation of the 1506 longwall face, there was a notable reduction in stress across the floor and immediate roof, with minimal stress concentration observed in the coal pillar and the entity rib side. The plastic zone surrounding the tailgate was limited, suggesting a high degree of stability in the entry's surrounding rock. However, during the extraction of the 1506 longwall face, the tailgate, extending 60 m ahead of the working face, was subjected to dynamic pressure, leading to a marked increase in stress within the floor, coal pillar, and immediate roof. Stress concentration was more pronounced on the entity rib side than on the pillar rib side. This resulted in significant fissuring and severe deformation of the entry's surrounding rock. The primary failure mechanism involved damage to both the roof and floor corners, with the severity of damage escalating alongside the stress in the surrounding rock. This culminated in the failure of roof corner bolts and anchor cables, thereby compromising the stability of the entry within the dynamic pressure zone.

Coal burst mechanism in large-scale panel under extra-thick key strata

Extra-thick key strata (ETKS) are a key factor causing coal bursts. In this study, field monitoring, physical and numerical modelling, and theoretical analysis were comprehensively adopted to investigate the effect of ETKS on the static and dynamic stress and its impact on coal bursts. Firstly, the coal bursts and the stability of ETKS were investigated. The roof strata structure and the mining-induced stress in a large scale panel under ETKS were analyzed. Then, the coal burst mechanism under ETKS is discussed. The results show that when the panel reaches the 4th and 5th longwall faces, the inferior ETKS and the main ETKS break, respectively, and large-scale cantilever-articulated structures involving the ETKS are formed. This moment, the overburden load is transferred downwards massively, and the coal seam becomes overstressed and accumulates massive elastic energy. Meanwhile, the collaborative collapse of multiple strata in the large cantilever-articulated structures causes the sudden release of elastic energy and high-energy seismicity, which exerts strong dynamic disturbances on the overstressed coal mass and leads to coal burst. Finally, strategies for coal burst control under ETKS including deep-hole pre-splitting blasting and panel size optimization are proposed and validated.

Steel Arch and Rock Bolt Support in Terms of the Gateroad Stability Maintaining behind the Longwall Face

The longwall system is an extraction system commonly used in coal mining in many countries, including Poland. One of the methods for reducing extraction costs is the dual use of the gateroad. In the first instance, the gateroad serves as the tailgate, and during the exploitation of the second coal panel, it functions as the headgate. Such a situation requires maintenance of the roadway behind the longwall face, which is typically challenging, due to significant stress-related loads on the support and its substantial deformation. The support design for this kind of roadway should take into consideration the dual impact of exploitation pressure and the caved zone influence behind the longwall face. This article presents the results of in-situ research conducted on two roadways behind the longwall face. In both roadways, the effectiveness of specially designed steel arch frames and rock bolt patterns were examined to minimize roadway deformations and maintain their functionality. The research project was comprised of several stages. Initially, mining and laboratory studies were conducted to determine the geomechanical parameters of the rocks. Subsequently, excavation stability and functionality forecasts were performed based on the authors’ empirical indicators. Then, numerical analyses were carried out to design support schemes (steel arches and rock bolt) in both roadways. A fully automated monitoring system with programmed data loggers was designed to check the behaviour of a specific rock mass and the support elements. The load on the steel arch support was measured with the help of load cells, while the load on the rock bolt support was carried out with the help of measurement bolts. Behind the longwall face, the loads on the wooden cribs set from the goaf side were also monitored. Additionally, the measurement station was equipped with extensometers to monitor the movement of roof layers and stress meters to determine changes in rock mass stress. Laser scanning or traditional surveying methods were also used to verify the support schemes through roadway convergence measurements. The obtained results allowed us to draw conclusions regarding the optimization of support schemes and to give recommendations for the practical application of specific reinforcements in excavations maintained behind the longwall face.

Stability of longwall face adjacent to gateroads

Longwall is the widely used mining method in the word and in Vietnam due to the high production and high level of safety. To maintain production as scheduled, the stability of a longwall face is of great importance, especially at areas adjacent to gateroads where ground pressure is strongly concentrated. This paper presents a study on the stability of longwall faces adjacent to gateroads under medium and hard-to-cave roofs. By using theoretical and field measurement methods, the authors conclude that in such geological conditions, the ground pressure at face adjacent to gateroads increases and decreases cyclically. At the study site, the ground pressure fluctuates in the range of 20÷26 MPa, and the piston chainage changes in the range of 0.6÷0.9 m. The face stability is closely related to ground pressure and roof stability. The study demonstrates that the face area near tailgate appears to be less stable compared to that near maingate, and initial signs of roof weighting can occur. The paper’s results serve as fundamental science assisting mining engineers in better identifying longwall face stability, from which effective prevention and remedy measures can be developed.

Analysis of inclined length effect of roof fracture and overlying strata catastrophe in steeply inclined longwall face: A case study

In order to determine the optimal inclined length of steeply inclined working face, the fracture field, strain field, displacement field and strata movement trend of steeply inclined working face were monitored through physical simulation test and digital speckle technique. At the same time, combined with theoretical analysis, the movement law of overlying strata and the catastrophe mechanism of working face caused by the length effect of working face are deeply studied. The research results show that with the increase of working face length, the length and growth rate of middle extremely unstable region are always largest, followed by lower and upper. The spreading failure characteristics of “roof-overlying strata-roof” appear along the inclined direction. When the working face length is less than 125 m, the larger vertical displacement and horizontal displacement are concentrated in the middle extremely unstable region. When the working face length is greater than 140 m, the larger vertical displacement is transferred to the lower stable region and the larger horizontal displacement is transferred to the upper unstable region. Based on this, it is obtained that the working face boundary length of roof and overlying strata catastrophe is 125 m and 140 m respectively. Furthermore, it is put forward that the optimal working face length is 95 m ∼ 125 m on the premise of effectively controlling the hanging space instability in the upper goaf and the flying gangue disaster in the working face. The application of digital speckle technique in large deformation measurement of large-scale physical models is realized.

Research on mining-induced surface soil cracking mechanism and development depth of downward fracture

In order to reveal the cracking mechanism of surface soil layer caused by coal seam mining, and explore theoretical methods for predicting the development depth of downward fractures during mining. Based on the background of the No. 1–2 upper coal seam mining in Daliuta Coal Mine, combining with fracture mechanics, soil mechanics, physical similarity simulation and numerical calculation methods. The mining-induced cracking mechanism and criterion of surface soil layer were analyzed, the crack development pattern and expansion mechanism were revealed, and the prediction formula of downward crack development depth of surface soil layer was put forward. The research results show that surface cracks mainly occur in the tensile zone, the concentrated tensile stress produced by the subsidence of overburden in the tensile zone can lead to soil cracking. When the surface maximum horizontal tensile deformation exceeds the limit horizontal deformation of soil, the soil layer cracks, and the cracking criterion of the surface soil layer was given accordingly. The soil crack of coal seam mining belongs to the mixed mode crack, and the soil cracks tip starts cracking and expanding along the direction of the maximum principal stress, therefore, the initiation crack angle of soil crack tip was obtained, and the fracture criterion of soil crack was proposed. With the crack propagation and development, the microcosmic crack becomes the macroscopic downward fracture. When the horizontal stress of the soil decreases to the cohesive force of the soil, the downward fracture stops develop, and the calculation formula for the development depth of mining-induced downward fracture was proposed. The development and evolution law of downward fracture was revealed, after the surface cracks, with the advance of the longwall face, the downward crack continues to extend and develop to the deep. Downward fracture develops on the ground surface at the open cut side, the mined-out area and in front of the longwall face, the maximum development depth of downward fracture tends to be stable when the longwall face advances to a certain distance. According to the physical simulation, numerical calculation and theoretical calculation, the development depth of downward fracture in No 1–2 upper coal seam mining is 8.11 m, 8.21 m and 8.14 m respectively. The theoretical prediction formula is reliable, and the results can provide a new method for the research of the development depth of mining-induced surface downward fracture.

A Prediction Approach Based on Clustering Reconstruction for Abnormal Mining Pressure of Longwall Face under Residual Coal Pillars

In multi-coal seam mining, when the lower coal seam mining face passes over the goaf, residual coal pillars, and other geological anomaly areas of the overlying coal seam, abnormal mine pressure appears, and the hydraulic support monitoring system is inaccurate in identifying the pressure, which brings great hidden dangers to the safe production of the mining face. It is very necessary to carry out the prediction and early warning of the mine pressure of this kind of mining face. In order to improve the reliability of the prediction model, this paper takes the 31317 mining faces of the Chahasu coal mine as the engineering background, studies the mechanism of the disaster caused by the abnormal mine pressure of the residual coal pillar, uses the clustering analysis algorithm to divide the abnormal mine pressure area of the mining face, reconstructs the abnormal mine pressure type and number based on the prediction results of CEEMDAN–Transformer deep learning, and proposes the disaster criterion of the abnormal mine pressure. The research results show that, when the 31317 mining face enters the goaf of the overlying 31203 and 31201 coal seams, the residual coal pillars are accompanied by the instability of the interlayer rotation, and the dynamic and static loads are superimposed to form the additional stress of the residual coal pillars and transfer downward, causing the abnormal mine pressure of the mining face to appear; based on the hydraulic support resistance data of the mining face within the range of 3921.4–5050.4 m advance, the clustering analysis results show that there are six abnormal mine pressures during this period, and the types are cutting eye, residual coal pillar, square breaking, previous working face goaf square breaking, double square breaking, and geological damage zone. The clustering analysis is used to reconstruct the abnormal mine pressure area based on the prediction results of the mine pressure time series (MPTS) after interpolation completion, decomposition, and noise reduction preprocessing, and the MAE values are all lower than 2000 kN, predicting that there will be one abnormal pressure between the 80#–129# hydraulic supports in the process of advancing to 5050.4–5219.5 m, corresponding to the 18th square breaking area of the working face. Through the verification in the actual production, the prediction result is accurate; when the predicted value of the hydraulic support working resistance is greater than 19,000 KN, measures should be taken to speed up the advancing speed of the mining face, quickly pass through the abnormal mine pressure area, and prevent the disaster caused by the abnormal mine pressure. The prediction clustering analysis reconstruction abnormal pressure analysis method based on mining working face mine pressure data proposed in this paper provides a new direction and guidance for the abnormal mine pressure prediction analysis of mining working face and has good foresight, good intelligent prediction, and a good analysis method for the intelligent empowerment of mine safety production.

Research on Stress Change and Deformation Monitoring of Coal Pillar Between Two Longwall Coal Faces

Research on Stress Change and Deformation Monitoring of Coal Pillar Between Two Longwall Coal Faces

Characterizing the effect of longwall retreating speeds on overburden and surface synergistic subsidence behaviors with a thick coal seam: intensive field measurements

Abstract The 12 401 longwall face in the Shangwan coal mine currently boasts one of the largest mining height (&amp;gt;8.0 m) longwall faces in the world. In-depth field measurements, including overburden movement, surface subsidence and fissure, and shield support loads, were conducted to elucidate the subsidence and damage behaviors induced by high-intensity mining. The findings identified three control rock strata (CRS1, CRS2, and CRS3), which dominate the formation of two subsidence modes (‘two zones’ and ‘three zones’) depending on longwall retreating speed. CRS1 and CRS2 collectively affect the variation of shield support loads. CRS2 governs the movement of the entire overburden, and its rupture precipitates swift subsidence. CRS3, characterized by thick soft rock with robust expansion and bending resistances, serves as a buffer, mitigating displacements caused by the breakage of CRS2. It is instrumental in shaping the ‘three-zone’ overburden structure. At lower retreating speeds, the height of the water-conduction fracture zone (Hwf) is ∼200 m, contrasting with 120.47–134.46 m for higher retreating speeds. The CRS2 manifests as a ‘step rock beam’ at lower retreating speeds, causing a maximum surface subsidence of 6315 mm. Conversely, under higher retreating speeds, it adopts a ‘masonry beam’ structure, resulting in a maximum surface subsidence of 4947 mm. The distribution of ground fissures is significantly affected by retreating speed, aligning closely with the breakage steps of the control rock strata. Our study offers robust scientific insights into preventing mining damage and promoting ecologically sustainable mining practices.

The use of the open-source software QGIS for the assessment of the risk caused by mining the longwall face to buildings on the ground surface

The aim of our work is to present a variant analysis of the threat to buildings in the event of mining the underground coal seam using longwall face. QGIS, the currently open-source spatial information system, was used to assess the threat to buildings. The assessment consisted of comparing the hazard category of the mining area with the resistance category of the building. In the case of mines, an inventory of the resistance of buildings is carried out during the development of mining plans. The second important aspect of our work is the transition from traditional CAD technology to the use of GIS technology. The new technology makes it easier and quicker to carry out analyses such as the threat posed by mining to listed buildings. It helps to produce annexes to the mining plan, such as hazard maps for buildings and a table listing buildings at risk.