Longwall Research Articles

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

Explainable artificial intelligence and advanced feature selection methods for predicting gas concentration in longwall mining

Explainable artificial intelligence and advanced feature selection methods for predicting gas concentration in longwall mining

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.

Development of geomechanical model for determination of elastic modulus and study on law of caving span induced by mechanized longwall mining

Development of geomechanical model for determination of elastic modulus and study on law of caving span induced by mechanized longwall mining

Prediction of Dynamic and Final Vertical and Horizontal Movements Due to Longwall Mining

Prediction of Dynamic and Final Vertical and Horizontal Movements Due to Longwall Mining

Influence of mining depth and panel length in longwall underground coal mining on the distribution of principal stresses along the barrier pillars

Abstract The production increase in longwall underground coal mining is in line with the dimension changes of the mining panel that subsequently affect changes in stress distribution and disrupts roadway stability. This paper studies the effect of panel dimensions on stress distribution around the roadway using the finite element method to model the panel conditions numerically, drawing height and shape of the goaf from empirical data. In this study, the length of the panels made varied between 500 and 1500 meters and the depth of the panels varied between 200 and 1000 meters from the surface. Based on the modelling results, stress changes due to differences in panel size occurred at the depth of 800 and 1000 meters, the longer the panel, the greater the stress that occurs. The further from the surface, the greater the pressure on the barrier pillar, at a depth of 200 meters the main pressure is 3.4 times the vertical pressure at the end of the excavation, while at a depth of 1000 meters the pressure increases to 5 times the vertical pressure.

Experiences of longwall mining alongside the Nepean Fault at Tahmoor mine

Experiences of longwall mining alongside the Nepean Fault at Tahmoor mine

An attempt to determine the cause of the strong tremor responsible for a rockburst in a hard coal mine based on numerical modeling and spectral parameter

Seismic and rockburst hazards represent significant challenges during the longwall mining of coal seams. One analytical approach to assess the potential for rockburst hazards involves reconstructing the stress conditions within the rock mass. This article reports on the findings from three-dimensional (3D) numerical modeling aimed at examining the distribution of maximum shear stress within the rock mass amid the longwall mining operations of the 703/1 coal seam in a mine situated in the Upper Silesian Coal Basin, Poland which was disrupted by a rockburst incident. On the day of the rockburst, substantial concentrations of maximum shear stress were identified in a thick sandstone layer proximate to the boundary of the overlying 624 coal seam located significantly above the 703/1 coal seam. The calculated maximum shear stress demonstrated an increase of approximately 80% over the values observed in the absence of edge effects. Furthermore, a higher concentration of maximum shear stress was identified within the geologically weaker strata adjacent to the 703/1 coal seam. These observations facilitated the classification of the examined rockburst as a stress-stroke phenomenon. Additionally, the study determined the spectral parameters of the tremor, which possessed an energy of 9.8 × 107 J and triggered the analyzed rockburst. The ratio of the seismic energy of S and P-waves confirmed a shear mechanism in the focus. The scope of inelastic deformation within the focal zone was also quantified. Following the event, the rock mass that had been destressed due to the significant tremor and subsequent rockburst exhibited reduced seismic activity upon the resumption of longwall mining of the 703/1 coal seam.

Ground motion characteristics induced by high-magnitude events with different source mechanisms of longwall mining

Rockbursts have become one of the most serious hazards in underground mines worldwide. While the characteristics of ground motions before rockbursts (or high-magnitude events (HMEs)) have not been studied. In this study, the peak ground velocity (PGV) and cumulative absolute displacement (CAD) before HMEs were examined based on seismic monitoring in a coal mine. It’s found that the source mechanisms vary significantly across different zones of the longwall, attributed to the low correlation between rock fracture types, stress levels, and seismic intensity. This correlation is mainly related to the distribution of primary fractures within the rock mass. The non-overlap of CAD peak with HME and the induction of delayed rockbursts are mainly caused by the unavoidable creep and additional energy input into the coal mass under disturbances before instability. The energy conversion process of the entire system is determined to be controlled by the stiffness ratio between the roof-floor system and the loaded coal, in accordance with the concept of dynamic and static load superposition. A high static load, strong dynamic disturbances, and a low rigidity ratio between surrounding rock and coal are identified as the most hazardous factors.

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.

Investigation of ground subsidence response to an unconventional longwall panel layout

Ground subsidence caused by extraction of longwall panels has always been a great concern all over the world. Conventional longwall mining system (CLMS) gives rise to wavy subsidence causing great damage to surface structures. A coal mine in Shanxi, China, utilizes a split-level longwall layout (SLL) for a sub-horizontal No. 8 coal seam to improve the cavability of mudstone interlayer and top coal. This layout, however, also produced unexpectedly favorable surface subsidence. Subsidence of No. 6 and No. 8 longwall panels was monitored while mining was conducted. Field instrumentation and numerical simulation were carried out. It is demonstrated that an asymmetric subsidence profile with stepped subsidence and cracks occurred on the tailgate side but relatively mild and smooth deformation on the other. Due to elimination of conventional parallelepiped gate pillar, No. 6 and No. 8 gobs were connected. Extraction of two SLL panels acted as one supercritical panel. The maximum possible subsidence was reached which lowers the likelihood of potential future secondary subsidence as underground gob fractures and voids have closed. Therefore, SLL is more favorable for post-mining land reuse as gobs are more consolidated underground.

Solutions to improving the efficiency of production organization at semi-mechanized longwall face I-6-2, Bac Quang Loi coal mine

Dong Bac Corporation is the second largest coal producer in Vietnam with output accounting for more than 14% of the country's total production. According to the plan, coal production from underground mines is expected to increase to 60% of the total Corporation’s production by 2025. To increase coal production in longwall mining, Dong Bac Corporation applies advanced technological solutions to modernize production stages, with the notable implementation of the semi-mechanized longwall mining technology. This technology uses a single-drum shearer and mobile hydraulic supports. The use of the technology has encountered challenges and difficulties, resulting in low production efficiency. The highest output achieved in the longwall face only reached 70% of the initial design capacity. The article presents the current status of technological innovation in underground coal mining of Dong Bac Corporation. The primary research subject is the semi-mechanized longwall face I-6-2 at Bac Quang Loi coal mine of Company 790, Dong Bac Corporation. Based on analysing the causes of difficulties, the authors provide solutions to improving production efficiency, safety, and the environment. Some solutions have been used in practice and have achieved positive and promising effects. Adjustment of production cycle organization chart to align with mining conditions has resulted in an increase in effective working time and a 17% rise in coal output. Accordingly, the authors propose technological orientations for the development of underground coal mining at Dong Bac Corporation.

Mining impacts peatland hydrology reducing discharge and water storage volumes

Peatlands cover about 3% of the Earth’s land surface, but are the largest terrestrial carbon store and are important for freshwater storage. In Australia, nationally protected peatlands (called upland swamps) exist in the catchment headwaters for Sydney’s drinking water supply. In this region, longwall mining of underground coal seams can result in subsurface fracturing, land subsidence, and, potentially, peatland drainage. This study presents the water balance modelling results for an upland peat swamp before and after it was undermined in 2020. Following a detailed field campaign, a conceptual lumped hydrology model was developed to estimate the local water balance, with a Nash Sutcliffe Efficiency of 0.85 for the modelled storage of the intact swamp. After undermining, the water balance of the swamp changed, with higher deep seepage rates and reduced surface water discharge rates. For the first time, these findings detail the hydrologic effects of longwall mining on peatland environments. Based on these findings, broader catchment management initiatives are recommended to prevent or limit further water extraction from upland swamps, including incidental water losses associated with subsidence.

Numerical analysis of fissure development and self-healing mechanism on surface due to longwall mining

Numerical analysis of fissure development and self-healing mechanism on surface due to longwall mining

Three-Dimensional Physical Test Study on the Overburden Breaking Behavior of Non-Penetrating Pre-Splitting in Small-Coal-Pillar Roadway Roofs

In longwall coal mining, significant deformation of small-pillar roadways presents challenges for the safe and efficient retreat of mining panels. Non-penetrating directional pre-splitting alters the roof structure of these roadways and effectively manages their stability under high stress during mining operations. In this study, a three-dimensional experimental model for the non-penetrating pre-splitting of small-coal-pillar roadway roofs was established, the apparent resistivity change in the rock layer during mining of the working face was determined, the propagation law of high-frequency electromagnetic waves in the overlying rock was studied, and the stress distribution law of the surrounding rock was investigated. After non-penetrating pre-splitting in the roof, the apparent resistivity change rate of the overlying rock increased and the electromagnetic waveform exhibited scattering and diffraction, forming a short cantilever beam. After mining, the stress in the adjacent mining panel gateway reduced, resulting in a pressure relief effect on the surrounding rock. These findings were further validated through field application, where the overall deformation of the roadway was reduced by 57%. The research results shed light on the management of roof control in small-coal-pillar roadways and the rational determination of non-penetrating pre-splitting parameters.

Assessment of factors and mechanism contributing to groundwater depressurisation due to longwall mining

Assessment of mining impact on groundwater is one of critical considerations for longwall extension and sustainability, however usually constrained by limited data availability, hydrogeological variation, and the complex coupled hydro-mechanical behaviour. This paper aims to determine the factors and mechanism of groundwater depressurisation and identify knowledge gaps and methodological limitations for improving groundwater impact assessment. Analysis of dewatering cases in Australian, Chinese, and US coalfields demonstrates that piezometric drawdown can further lead to surface hydrology degradation, while the hydraulic responses vary with longwall parameters and geological conditions. Statistical interpretation of 422 height of fracturing datasets indicates that the groundwater impact positively correlates to panel geometry and depth of cover, and more pronounced in panel interaction and top coal caving cases. In situ stress, rock competency, clay mineral infillings, fault, valley topography, and surface–subsurface water interaction are geological and hydrogeological factors influencing groundwater hydraulics and long-term recovery. The dewatering mechanism involves permeability enhancement and extensive flow through fracture networks, where interconnected fractures provide steep hydraulic gradients and smooth flow pathways draining the overlying water to goaf of lower heads. Future research should improve fracture network identification and interconnectivity quantification, accompanied by description of fluid flow dynamics in the high fracture frequency and large fracture aperture context. The paper recommends a research framework to address the knowledge gaps with continuous data collection and field-scale numerical modelling as key technical support. The paper consolidates the understanding of longwall mining impacting mine hydrology and provides viewpoints that facilitate an improved assessment of groundwater depressurisation.

Implication of fault seal analysis method to evaluate the sealing conditions of major fault planes at Barapukuria basin, North-West Bangladesh

The Barapukuria coal basin stands as Bangladesh’s sole active underground coal mining site. The geological setting of this basin is marked by two major faults, the Eastern Boundary Fault and FB fault encircling the basin perimeter, alongside several smaller faults and those induced by underground longwall mining activities. A major concerning issue of this mine is the water inrush into the mine area from the extensive groundwater aquifer, Upper DupiTila (UDT). Using the Fault Seal Analysis technique employed by (Yielding et al. in Am Assoc Pet Geol Bull 81:897–917, 1997) algorithm, this analysis attempts to identify susceptible areas and potential unsealed faults that could provide the risk of water invasion into the mine area. Evaluation of Fault Seal Analysis reveals varying Shale Gauge Ratio (SGR) values: 0.08 and 0.13 for the major Eastern Boundary Fault, 0.05 for the second largest FB fault, 0.35 and 0.53 for FB-1, and 5.65, 1.69, and 1.22 for the smaller faults BGP-N-F11, BGP-N-F2, and F-24, respectively. According to SGR values, the Eastern Boundary Fault and the FB fault plane are anticipated to be unsealed and dip westward at an angle of 75°-80°, rendering them vulnerable to water inflow through the fault planes. The analysis also suggests that the Lower DupiTila (LDT) aquiclude which can impede the groundwater flow from the UDT aquifer into the mine area, is very thin or absent in the northern region of the basin making this region highly susceptible to water inundation.

ANALYSIS AND REMEDIATION OF ENDOGENOUS FIRE AT LONGWALL TOTAL COAL THICKNESS MINING OF THE MAIN COAL SEAM IN RASPOTOČJE MINE OF ZENICA BROWN COAL MINES

Mining of the thick coal layers that include roof caving operation can results in residual coal quantities in the gob as a potential threat causing occurence of spontaneous oxidation process, smoldering, and endogenous mine fire that can affect the safety and regular mine operations. Endogeneous fire occurences in Zenica coal mines are directly linked to complex natural conditions reflecting in complex geological conditions, great depth of mining, high methane content in coal seams, and tendency of coal to spontaneous oxidation process. The subject of the paper is the analysis of endogenous fire supression method applyed in conditions of complete coal thickness longwall mining in Raspotočje mine, that has been rehabilitiated upon the endogeneous fire and then reactivated. The following methods were used in fire fighting: passive fire fighting methods (sealing of the area affected by the fire), active method (injection of electrofilter ash) and ventilation methods. Furthermore additional data (position of gob area and sealing objects, air flow regulators, routes of possible air migration, suggested technical solutions, etc) were added in the linear and canonic schemes for the purpose of defining efficient solutions for fire fighting. Key words: endogenous fire, longwall mining, advancing mining, fire fighting.