Longwall Research Articles

Distributed acoustic sensing (DAS) for longwall coal mines

Distributed acoustic sensing (DAS) for longwall coal mines

Temporal and spatial comparison of coal mine ventilation methane emissions and mitigation quantified using PRISMA satellite data and on-site measurements.

Temporal and spatial comparison of coal mine ventilation methane emissions and mitigation quantified using PRISMA satellite data and on-site measurements.

Longwall panel width design with prediction of the corresponding maximum induced ground surface subsidence

Longwall mining is one of the most commonly used methods in underground coal mining. With advancing the coalface, the created flexural cracks at panel roof gradually transmit upwards, towards the ground surface that may induce ground surface subsidence. Since the resulting subsidence depends upon the bulking factor of the goaf materials, a new equation to estimate the initial fractured bulking factor has been first proposed. Then, the paper continues to present two more new analytical methods for a suitable longwall panel width design and subsequently to predict the corresponding maximum induced ground surface subsidence. To investigate the impact of the parameters incorporated into the new developed methods, a sensitivity analysis was carried out. The effects of parameters including; extracted coal seam thickness, depth of cover, angle of draw, initial and ultimate bulking factors have also been examined and evaluated. The present proposed methods have been compared with the current comparable methods and then verified with the results of in-situ measurements for both subcritical and critical/ supercritical panel widths. Finally, it has been concluded that the present proposed analytical methods can reliably be used to design a longwall panel width and to predict the corresponding maximum induced ground surface subsidence.

Numerical analysis of building damage caused by the exposure of a terrain threshold as a result of underground mining-induced subsidence

Underground mining exploitation causes deformations on the ground surface as a result of the filling of the resulting voids. In certain situations, apart from mild continuous deformations, discontinuous deformations may occur in the form of, e.g., steps in the ground. Unexpectedly occurring discontinuous deformations cause significant damage to buildings protected against the influence of continuous deformations, but do not lead to their complete destruction. For this reason, the aim of this paper is to present a numerical analysis of such an impact case, which, on the one hand, is sufficiently accurate and reflects the behaviour of the real structure, and on the other hand, it will be a guide for experts who will aim to determine the safety of similar structures. In the presented case, the multiple longwall mining of coal ended in the same place resulting in the formation of a step in the ground about 15 cm high under a residential building. Not protected building against such deformations, suffered significant damage. The numerical analysis of the residential building was carried out with the advanced ATENA software package. In order to accurately represent the building and the impacts, the structure and the surrounding ground were modelled. The structure of building and the ground were modelled with tetrahedron- and hexahedral-shaped volumetric elements. On the contact surface of the structure elements and the ground, flat contact elements were used. The loads on the structure were introduced in the form of displacements caused by the appearance of a terrain threshold. The results of numerical calculations are presented in the form of color stress maps. The obtained calculation results are very close to the actual damages, which confirms the correctness of the analysis.

Determining the abutment angle in longwall coal mining using NLMR, GEP and GEO techniques

Determining the abutment angle in longwall coal mining using NLMR, GEP and GEO techniques

Visualization analysis of potential fracture in overburden strata induced by longwall coal mining

Visualization analysis of potential fracture in overburden strata induced by longwall coal mining

Seismic behavior of cold-formed steel framed multi-panel and two-story shear walls

This paper presents an experimental investigation on the seismic behavior of cold-formed steel (CFS) shear wall systems. Two sets of cyclic lateral loading tests were conducted on OSB sheathed CFS shear wall specimens. The first part of the study deals with walls constructed by connecting multiple individual wall panels with different connection methods. Focus of the second part is the lateral load response of two-story shear walls with different framing details between wall panels in neighboring floors. In both parts, the behavior of wall panels was examined with combinations of one side sheathing and a coarse fastener layout, as well as double-side sheathing and a dense fastener layout. For the multi-panel shear walls, eight full-scale specimens were tested, featuring varying configurations of CFS framing and OSB sheathing. The experiments indicate that the use of different connection details between individual wall segments does not cause any appreciable difference in wall response. Significant excessive base slip was observed in longer walls with double-side sheathing due to increased shear force demand at the base, highlighting the importance of adequate fastener layout. In the investigation of two-story shear walls, eight specimens were tested. Platform and ledger framing details were explored, each with different methods of connecting wall panels between floors. The results demonstrated the influence of framing detail on the overall behavior and failure mechanisms of the shear walls. Notably, the presence of additional OSB sheathing panels between floors enhanced the load capacity and stiffness of the specimens, mitigating damage to CFS members within the connection region. Based on the experimental findings, practical recommendations were presented for multi-panel walls and interaction between wall panels and floor support system in multi-story CFS construction.

Assessment of Groundwater Depressurisation due to Mining Considering Flow Nonlinearity in Connected Fractures

Longwall mining is a productive method for underground coal resource recovery, but usually leads to extensive fracture networks that facilitate groundwater drainage into mined-out areas. Accurately assessing the coverage and magnitude of induced groundwater depressurisation is crucial for sustainable mining practices, but is often constrained by simplified representations of fracture flow. This paper investigates the nonlinear flow behaviour in connected fractures and develops a governing equation applicable to field-scale models for improved groundwater impact assessments. Laboratory tests on intersected pathways demonstrate that inflows interact and redirect along curved paths with localised turbulence. Numerical upscaling reveals a negative correlation between pressure drop and pathway geometry, identifying the laminar flow threshold as Reynolds numbers (Re) ≤ 10. A modified cubic law (MCL) is derived from the best-fit linear relationship between hydraulic gradient and flow rate, defining a super-cubic correlation where the exponent increases asymptotically from 3.15 to 3.77 with apertures. Applying the MCL equation to a field-scale model reveals that the depressurised zone has a height of 0.86 times the panel width, aligning with the upper limit of horizontal stress relief and the significant outflow horizon measured by borehole acoustic scanning. The depressurisation remains confined below the claystone unit, which is interpreted as being associated with clay swelling upon water absorption. Comparisons with empirical equations suggest that integrating fluid flow analysis into numerical simulations allows more direct and comprehensive assessments for groundwater and sustainable purposes. The paper improves the understanding of flow nonlinearity in connected fractures and offers a practical numerical method for evaluating the hydrogeological impacts of mining activities.

A cyber-physical system based unmanned ground vehicles for safety inspection and rescue support in an underground mine

PurposeThe unmanned ground vehicle (UGV) described in this manuscript is a robot designed by the authors to map the underground mine environments. The UGV works to develop a computational intelligence-based cyber-physical system (CPS)-based analytical framework for mining operations. The UGV demonstrated excellent semi-autonomous navigation capabilities in the absence of GNSS signals. The UGV has a suite that works in unison to provide relevant information. These sensors are integrated to form a robust sensor fusion-based architecture, creating a CPS with a wide range of capabilities such as data acquisition and navigation in challenging underground environments. UGVs can be used to enhance the efficacy of safety inspections, rescue during underground emergencies and assist miners in hazardous conditions.Design/methodology/approachIn this research, an UGV was constructed whose operations are enabled by sensors including a D415i Red Blue Green (RGB) depth camera, a LiDAR, a FLIR C5 infrared camera and smart air quality sensors. This sensor fusion-based architecture forms a CPS. Data obtained remotely are processed by deep learning algorithms to achieve overall capabilities such as real-time image analysis for miner identification, object detection, posture analysis and identifying threats of roof falls and overhangs. Simultaneous localization and mapping (SLAM) algorithms create a 3D map, facilitate autonomous navigation and build a decision support system for delivering mine rescue support.FindingsThe aim of this study is to include this capacity in training situations when it has been validated and authorized by the Directorate General of Mines Safety (DGMS) Indian government regulatory agency for safety in mines and oil fields. The longwall demo mine, at IIT (ISM) is being used as the site of the first operations. Once approved by the respective enforcement agencies, this technology and the accompanying rescue and training process can be used in underground operations.Originality/valueIn fact, this paper is the first attempt at remotely operated UGVs based on CPSs, the CPS–UGV in Indian mine conditions, so as to revolutionize Indian mines based on the idea of Industry 4.0.

Environmental water requirements and climate sensitivity of Australia's upland swamps.

Environmental water requirements and climate sensitivity of Australia's upland swamps.

Angle effect of mining behavior of roof in longwall mining of steeply dipping coal seams

Angle effect of mining behavior of roof in longwall mining of steeply dipping coal seams

Innovative Cut-and-Fill Mining Method for Controlled Surface Subsidence and Resourceful Utilization of Coal Gangue

Existing coal filling mining technologies face significant challenges of controlled surface subsidence, efficient utilization of waste rock in coal mines, and a shortage of adequate filling materials. This study introduces an innovative cut-and-fill mining method designed to strategically partition the goaf into cutting and filling zones. In the cutting zone, in situ filling materials are employed to construct waste rock column supports adjacent to the filling zone, thereby achieving controlled surface subsidence. This approach is integrated with long-wall mining operations and implemented using advanced, comprehensive equipment. FLAC3D simulations were conducted to investigate the patterns of stress distribution, surface deformation, and plastic zone formation within the mining field. With the implementation of the cut-and-fill mining balance, key observations include a reduction in maximum principal stress near the center of the goaf, an increasing trend in minimum principal stress, regular displacement distributions, and intact plastic zones positioned vertically away from the stope and horizontally close to the center of the stope. Compared to traditional caving methods, the cut-and-fill technique significantly reduces maximum vertical displacement, by nearly 95%, and maximum horizontal displacement, by approximately 90%. Additionally, it minimizes energy accumulation, lowers overall energy release, and prolongs the release period. Importantly, this method facilitates the resourceful utilization of approximately 800 million tons of waste rock, potentially leading to an estimated reduction of 500 million tons in CO2 emissions. By achieving a balance of three effects—harmonizing coal extraction and filling capacity, aligning the supply and demand of filling materials, and optimizing the balance between filling costs and mining benefits—this method provides a sustainable and eco-friendly solution for the coal mining industry. The findings of this study are crucial for guiding the industry towards more environmentally responsible practices.

Study on subsidence evolution induced by coal mining under highway based on finite element simulation

Accurate estimation of overlying strata subsidence and surface deformation caused by coal extraction is crucial for assessing the impact of mining activities on surface infrastructure. In this study, we investigated the subsidence evolution of overlying strata and ground surface induced by underground mining using finite element simulation and focus on a mining district in the Yu-Heng mining area of the central Ordos Basin and then, the influence of underground longwall mining on the surface roads was evaluated. A three-dimensional geological model of the mining district was constructed, considering the actual stratum structures and the deterioration effect of water on rock mechanical properties. The whole coal mining process was simulated to predict the evolution of the subsidence basin at different mining stages, and the surface deformation characteristics caused by coal mining were calculated. Results showed that the subsidence characteristics by numerical simulation were highly consistent with the records of surface subsidence in the adjacent areas, indicating that the constructed geological model can accurately reflect the actual geological conditions and the deformation behaviors of overlying strata. A comparative study revealed that the mechanical properties of the generalized layers determined by processing the mechanical parameters of dry core samples will be much higher than those of the natural strata under the in situ water-saturated condition, and then the subsidence caused by coal mining will be significantly underestimated. Thus, the water-induced mechanical property deterioration of overlying strata must be fully considered when constructing geological models.

Assessment of variations in shear strain energy induced by fault coseismic slip in deep longwall mining

Shear strain energy is a pivotal physical quantity in the occurrence of earthquakes and rockbursts during deep mining operations. This research is focused on understanding the changes in shear strain energy in the context of retreating longwall mining, which is essential for the optimized design and mitigation of rockbursts and seismic events. Through the application of innovative analytical models, this study expands its analytical range to include the variations in shear strain energy caused by fault coseismic slip. An integrated methodology is utilized, taking into account the changes in coseismic and fault friction parameters as well as enhancements in mining-induced stress and existing background stresses. Our numerical investigation highlights the significance of mining location and fault characteristics as key determinants of shear strain energy modifications. The analysis demonstrates significant spatial variability in shear strain energy, especially noting that fault slip near the mining face greatly increases the likelihood of rockburst. This finding emphasizes the need to integrate fault coseismic slip dynamics into the triggering factors of rock (coal) bursts, thus broadening the theoretical foundation for addressing geological hazards in deep mining operations. The results are further corroborated by observational data from the vicinity of the F16 fault zone, introducing the concept of mining-induced fault coseismic slip as an essential element in the theoretical framework for understanding rockburst triggers.

Overburden Fracture Propagation and Rib Spalling Control in Deep Longwall Mining with Large Panel Height

Overburden Fracture Propagation and Rib Spalling Control in Deep Longwall Mining with Large Panel Height

An attempt to determine the strong tremors causes during longwall mining of destressed bottom layer of a thick coal seam

An attempt to determine the strong tremors causes during longwall mining of destressed bottom layer of a thick coal seam

Research on the quantitative relationship between stress shadow effect of multiple thick and hard key layers and surface subsidence

For a long time, the management of surface structures such as villages and rivers affected by underground coal mining has been a popular and difficult issue in coal mining. With the further tightening of environmental protection requirements, it has become challenging for some underground coal mines that lack the conditions for filling and grouting to ensure the recovery of coal resources while controlling surface subsidence. Furthermore, many such common issues have emerged in the Yushen and Binchang mining areas of Shanxi Province, as well as in several other coalfields, severely constraining the development of coal energy and ecological environmental protection. Research on numerical simulation experiments and theoretical calculations via mechanical models suggests that the presence of multiple thick and hard key strata in the overlying rocks plays a crucial role in controlling surface displacement through the interlayer shading effect. A comparison of three mining methods, namely, fully mechanized top-coal caving with a large mining height (CMTC), longwall mining with a large mining height and full-height cutting (LMHT), and layered fully mechanized top-coal caving (LCMTC), reveals peak surface displacements of 3.818 m (CMTC), 3.649 m (LMHT), and 3.32 m (LCMTC), respectively, and peak vertical stresses of 7.3 MPa (CMTC), 5.9 MPa (LMHT), and 8.3 MPa (LCMTC), respectively. Based on these findings, an artificial buffer layer technology for controlling overlying rock displacement is proposed. This technology has a significant effect on effectively controlling surface subsidence by releasing stress in the overlying rock and provides a theoretical reference and methodological insights for mines with similar operating conditions.

Numerical Simulation of Appropriate Design for Selecting Tunnel Support Systems in Squeezing Grounds (Tunnel No. 2 in Tabas Coal Mine, Iran)

Tunnel No. 2 of the mechanized Tabas coal mine and access entry to E5 panel serve as the primary routes for coal extraction from the longwall mining panel. The main objective of this research is to strengthen and select the optimal support system in the area after the intersection of main tunnel No. 2 with the access tunnel E5 panel, using numerical modeling (FLAC 3D software). The results of numerical modeling have indicated that due to coal seam dip and its partial intersection with tunnel No. 2 at the junction of the main tunnel and the eastern access tunnel at levels 2410–2430, along with the presence of the coal seam above this area, there is less rock mass resistance to the induced stresses. Consequently, significant displacements have been occurred in the floor, walls, and roof of the main tunnel. The numerical modeling results indicated displacements of approximately1.4 m in the sidewalls, 0.8 m in the roof, and 1.2 m in the floor, which correlated with the field measurements. The best way to reinforce and optimize the support system was determined by evaluating the supporting effects of mixed support systems, such as truss bolts, flexi bolts, and different steel frames. Therefore, the best support system arrangement was suggested as adding three 6‐m‐long flexi bolts in the sidewalls and two 3‐m‐long truss bolts in the tunnel floor, steel frame TH40, eleven 2.7‐m rock bolts, and one 9‐m cable bolt in the ceiling and walls was proposed. This support system arrangement reduces the tunnel convergence to 90%. This system has been successfully implemented in the mine and reduced the squeezing‐related problems to the lowest degree.

Stability analysis of ‘roof-coal pillar’ structure in longwall multi-section mining of steeply dipping coal seam

To solve the problem of stability control of coal pillar in steeply dipping coal seam (SDCS), based on the characteristics of surrounding rock structure and stress environment of the coal pillar, a special bearing structure of ‘roof-coal pillar’ combination is proposed through theoretical analysis. The mechanical model of inclined ‘roof-coal pillar’ structure is established, and the stress and strength characteristics of each element in the structure are deduced. Combining numerical calculations (PFC2D-FLAC2D coupling model) and physical similarity simulation, the stress evolution characteristics and failure mechanism of the ‘roof-coal pillar’ structure under the influence of mining were revealed. The results show that the coal pillar of SDCS is easy to form a ‘roof-coal pillar’ combined bearing structure with the roof strata. Under the influence of mining, the stress distribution and deformation evolution within the ‘roof-coal pillar’ structure show strong non-uniform and asymmetric characteristics. Among them, the stress distribution shows an ‘ellipse’ shape which is offset to the upper section, and the main deformation zone of the structure is a diagonal deformation distribution zone that runs through the coal and rock in the same direction as the stress offset. The failure of the ‘roof-coal pillar’ structural firstly occurs in the coal area near the coal-rock interface on the side of the lower section, and finally forms a diagonal failure crack running through the coal and roof, which is manifested as a diagonal shear failure mode. The findings can provide a theoretical basis for the stability control of coal pillars in multi-section mining of SDCSs and improve the safety production technology level of the working face.

Stress Zoning Characteristics and Migration of Leaked Methane from Gas Wells Penetrating Protective Coal Pillars in Longwall Mining Areas

There are a large number of abandoned or casing-damaged oil/gas wells in the western mining areas of China. Under the influence of mining-induced stress, the methane leaked from the oil and gas wells will be transported through fracture within the coal pillar to the longwall working face, which will seriously threaten the safe mining of coal resources. There is no mandatory standard for the practice of coal pillars in coal and gas wells in coal/gas overlapping areas, and the problems of oversized coal pillars and waste of coal resources have occurred during the implementation. In this study, through finite element numerical simulation, three different sizes of protective coal pillars are modeled in the background of Shuangma Coal Mine. The impacts of different heights and widths of protective coal pillars on the evolution of stresses and the diffusion process of leaked methane are explored, and the spatial and temporal migration law of leaked methane under multi-field coupling is revealed. The results show that under mining-induced stress, the size of the protective coal pillar has a significant effect on the stress distribution and methane transport law. Compared with the 130 m coal pillar, the peak stress of the 150 m coal pillar decreased by 6.7%, and the peak stress of the 180 m coal pillar decreased by 9%. At 150 m and 180 m widths, the permeability difference between the two sides is only 1 mD, and the diffusion ranges are similar. From the stress distribution and gas diffusion law, it is shown that the effect achieved by 150 m and 180 m coal pillars is similar. This work is of great significance for the reasonable remaining protective coal pillars for oil/gas wells penetrating longwall mining areas, as well as the prevention and control of disasters caused by leaked methane from wells.