Coal Strata Research Articles

Optimization of the Layer Location of Extraction Wells Based on the Unpressurized Gas Transport Law.

Protective layer mining is one of the most effective measures to control outbursts of coal seam gas in coal mines. Accurately grasping the overlying rock movement and pressure-relief gas migration patterns under protective layer mining conditions is a prerequisite for efficient surface coalbed methane extraction; it is the basis for green emission reduction in coal mines. A physical model was established using the Ji15-33200 working face of Pingmei Shi Mine as the research object, and a method combining theoretical calculation and numerical simulation was used to obtain the overlying rock movement. In situ stress distribution characteristics of the stope after the upper protective layer was mined to explore the upper protective layer migration rules of pressure-relief gas after mining. On this basis, the location and layer of surface coalbed methane production wells was determined. The research results show that the coal and rock formations on the floor of the goaf experienced a deformation process of compression → expansion → rebalance during the mining process; the stress changes of the overlying and underlying coal strata in the goaf have experienced a process of increasing → decreasing → rebalance; and gas migrates upward through the fissure zone in the coal layer and slowly diffuses in other microfissure areas. When the pressure reaches a certain value, it is enriched in the crack development area and the upper part of the fissure zone; combined with the relevant geological conditions of the study area, it was determined that the upper part of the roof of the Ji16-17 coal seam is a gas-rich area. By comparing three mining vertical wells at different positions in the horizontal direction, it was found that the extraction effect was significant in the "O″ ring, near the excavation face.

Timely Constructed and Enhanced Lining for Managing Extensive Deformations of Tunnel in Coal Stratum: A Case Study

Background The Sanlian Tunnel case study exemplifies that even after implementing the initial support within the coal stratum, the surrounding rocks exhibited ongoing deformation devoid of stabilization indications. Addressing this issue calls for innovative control technologies that mitigate extensive deformations and redefine safe and sustainable coal stratum tunnel construction. Methods The field experiment was adopted to select the appropriate technical measures to control extensive deformations. Three experiment schemes were developed and applied to the construction. Scheme One was the enhanced initial support structure, and Scheme Two was the combined use of enhanced initial support structure, lengthened sidewall anchor rods and added steel pipe piles. Scheme Three was the “timely constructed and enhanced lining structure” proposed on the basis of Scheme Two, and the secondary lining was applied if the horizontal displacement exceeded 450mm. Then, field observations of displacements and stresses were implemented to evaluate the effectiveness of different experimental schemes in controlling extensive deformations. Results Scheme One and Two cannot control extensive deformations effectively, as the displacement of the initial support continued to increase with no sign of stabilization. Regarding Scheme Three, structural deformation progressively attained a state of stability around 80 days subsequent to the secondary lining construction. Additionally, the stress within the support structure remains stable below the permissible threshold, affirming the secure condition. Conclusion Emanating from the field monitoring results, it is evident that the suggested “timely constructed and enhanced lining structure” scheme control technology holds substantial promise for practical implementation in engineering scenarios.

Mechanism of the pore and molecular structure evolution of coal exposed to acid mine drainage (AMD)

In the post-extraction epoch, wastewater from mining activities, particularly acid mine drainage (AMD) residing in sulfur-laden coal terrains, assumes a pivotal role in the safety stewardship of decommissioned coal mines. This research aims to investigate the mechanism behind coal characteristic deterioration from prolonged exposure to AMD. Immersion assays were performed on coal samples across pH 2 to 5 to assess the impact of acid mine drainage. Subsequently, the pore and molecular architecture was appraised using microscopic methodologies. Computed Tomography (CT) findings elucidate that post-immersion, the porosity, and fissures proliferated longitudinally along the coal strata, engendering a marked amplification in surface porosity contiguous to pre-existing pores. This escalation in surface porosity was further accentuated in correlation with the intensification of AMD acidity. Nuclear Magnetic Resonance (NMR) data indicated a marginal augmentation in the content of both micropores and macropores within a tepid AMD milieu. However, in a more virulent AMD context, the proportion of micropores diminished, whereas that of macropores and pore throat size (PTS) experienced an upswing, thereby transmuting adsorptive pores into permeable conduits and consequently enhancing coal permeability. Scanning Electron Microscopy (SEM) corroborated the NMR outcomes; as AMD acidity transitioned from mild to severe, the coal matrix manifested many erosive pores, matrix layer disintegration, and an expansion in cleat width. Therefore, the microscopic pore evolution can be succinctly encapsulated as follows: in a mild AMD environment, dissolution of minerals predominates, generating erosive pores, whereas, in a more acidic AMD milieu, the matrix undergoes partial contraction, thereby augmenting pore volume, enhancing permeability, and inducing structural degradation. Additionally, Fourier Transform Infrared Spectroscopy (FTIR) analysis substantiated that AMD compromised the pore architecture and catalyzed the disintegration of coal macromolecules into lower molecular weight constituents. Therefore, AMD degrades coal macromolecules into smaller compounds, heightening matrix layer porosity and impairing coal characteristics. This research yields vital insights for the security and efficient management of abandoned mine excavations.

Characterization of the Sedimentary Environment of the Shanxi Formation in the Southeastern Ordos Basin Revealed by Detrital Zircon and Geochemical Analyses

The interpretation of the sedimentary paleogeographic environment of the Lower Permian Shanxi Formation (P1s) coal strata in the southeastern Ordos Basin remains a subject of significant debate. In this paper, based on detrital zircon U–Pb source analysis, paleosalinity assessment, the sandstone modal composition, and other methods, we analyzed the P1s source system and constructed a model of the sedimentary evolution. The findings reveal that the primary source of the clastic materials in the study area stems from a mixed-source within the recycling orogenic belt. During the deposition period, the Shanxi Formation developed two predominant material source systems: one in the north, primarily linked to the Paleo-Yinshan Fold Orogenic Belt (YFOB), and the other in the south, originating from the North Qinling Orogenic Belt (NQinOB). These two major source systems converged in the Yichuan–Fuxian area. From the early stages of the Shanxi Formation period (Shan1), there was a regional retreat of the sea in the area. The seawater receded in a southeastward direction, leading to a gradual reduction in the paleosalinity and Sr/Ba-ratio variability during the Shan1 period. The influence of the seawater diminished, transitioning into a deltaic depositional system. This shift towards a terrestrial lakeshore basin reached its full development during the Lower Xiashihezi period. This study concludes that the Shanxi Formation in this area represents the evolution of a deltaic depositional system originating from a shallow sea shelf. This evolution can be divided into three major stages: remnants of the shallow sea shelf, barrier island–lagoon–littoral, and deltaic deposition. Within this framework, the shoreline underwent frequent lateral migration, influencing a broad range of characteristics. In the vertical direction, numerous alternating sets of sandstone bodies and mudstone, shale, and coal beds formed, creating a significant relationship between coal hydrocarbon sources and reservoirs. This study also establishes the stratigraphic-sequence framework of the basin for this period. These results hold great importance for the expansion of natural gas exploration and development efforts.

Failure characteristics and conditions of rock-coal combination structure with weak layer under dynamic and static stresses

To comprehensively understand the mechanical response of a rock-coal combination structure containing a weak layer, a series of laboratory static loading and impact loading experiments were conducted. The results showed that under static load, the sliding process of the rock coal structure was relatively slow, and fragments can be observed. Under the action of horizontal impact loading, the whole coal stratum slipped out rapidly, and the process lasted only 0.05 s. Under the horizontal and axial impact loads, the coal stratum remained stable first, and then it slipped out as a whole under the action of static load. Additionally, a sliding instability criterion of a rock coal structure containing a weak layer was established based on theoretical analysis. The key parameter P value was checked through a numerical simulation experiment. It was found that the value was linearly related to the mechanical properties of the weak layer and overburden stress, and the experimental results coincided with the theoretical results. Finally, the relationship between sliding rockburst and strain rockburst was discussed, and these results can provide an important scientific basis for the prevention and control of dynamic disasters in deep mining.

Acoustic impedance inversion in coal strata using the priori constraint-based TCN-BiGRU method

Acoustic impedance inversion in coal strata using the priori constraint-based TCN-BiGRU method

Enrichment of Sulfate, Acidity and Mercury in Native outcropcoal, Southwest China.

The coal found in the Longtan Formation of the Late Permian is widely distributed in Southwest China, including the northwestern Guizhou, southeastern Sichuan, and northern Yunnan regions. This coal typically has a high sulfur content. Eighty-two coal samples were collected from the coal strata in 11 counties spanning this area, including underground mine coal, native outcrop coal and man-made outcrop coal. The mercury, total fluorine, total sulfur, and sulfate contents and pH values were determined. The results showed that the average mercury content in native outcrop coal was 2233ng/g, whereas that in underground mine coal was 306ng/g, and the relative enrichment factor could reach 6.6. There was no significant difference in the total fluorine content among the three types of coals; furthermore, the total sulfur content in native outcrop coal and man-made outcrop coal was higher than that in underground mine coal because of the local policy, which strictly prohibits the mining of high-sulfur coal. Native outcrop coal is acidic, with a total average pH of 3.54 and an average sulfate content as high as 13,390μg/g. In contrast, underground coal is almost neutral (average pH 7.33), with a low sulfate content (average 3221μg/g). These characterizations indicate that native outcrop coal has been subjected to long-term weathering and the mercury enrichment is likely due to migration, oxidation, and precipitation of Hg from the underground coal seam and enriched in loose and pulverized coal particles. Further investigation is needed to determine whether other outcrop areas are affected by this phenomenon.

Research on Permeability Enhancement Model of Pressure Relief Roadway for Deep Coal Roadway Strip

Aiming at the problem of permeability enhancement in deep coal roadway strip, it proposed a pressure relief roadway permeability enhancement model, and the model was verified through experiments, theoretical calculations, and field tests. The experiment reveals that the unloading of gas-containing coal can achieve the effect of permeability enhancement. Theoretical calculation shows that with the increase of the distance from the coal seam, the overlying coal seam’s permeability enhancement multiple and the width of the significant permeability enhancement zone gradually decrease, and the width of the general permeability enhancement zone gradually increases and then stabilizes. Field tests show that the pressure relief roadway is arranged 9 m directly below the coal seam; the overlying coal strata has a significant pressure relief and permeability enhancement effect. This research can provide reference value for the high-efficiency permeability enhancement in the deep coal roadway strip.

Laboratory and field investigations of different bolting configurations for coal mine roadways in weak coal strata

Laboratory and field investigations of different bolting configurations for coal mine roadways in weak coal strata

DISCRETE ELEMENT SIMULATION FOR CRACK FRACTAL EVOLUTION LAWS ASSOCIATED WITH SLICING MINING IN SUPER THICK COAL STRATUM

This paper presents an approach of combining fractal geometry theory and UDEC discrete element numerical simulation method to study the fractal evolution law of mining-induced fracture of overburden rock. It can be applied to quantitatively evaluate development characteristics of mining fracture network in weakly consolidated overburden under the high-intensity mining in the western mining area. The research result indicates the following findings. The development and expansion of overlying rock fractures have good self-similarity under high-intensity mining conditions and the fractal dimension is between 0.461 and 1.488. The law of evolution can be divided into four stages including the dimensionality rapidly increasing stage,quickly reducing stage,stable stage,and periodically varying stage. In addition,the fractal dimension at each stage and the number of mining meet the logarithmic relationship,linear relationship and quadratic function relationship,respectively. With slice mining in huge coal stratum,the fitting curve of fractal dimension shows a high degree of similarity,has a certain periodicity,and shows a power function relationship. The research results provide scientific basis and technical reference for safe mining in western mining area and protection of water resources.

Prediction of the Water-Bearing Capacity of Coal Strata by Using the Macro and Micro Pore Structure Parameters of Aquifers

Accurate prediction of the water-bearing capacity of aquifers is crucial for protecting the surface ecological environment and ensuring safety during coal mining. In this study, a macro–micro combination was used to investigate the water-bearing capacity of bedrock aquifers. At the micro-level, the micro pore parameters of various sandstones were determined through cast sheeting. At the macro-level, the porosity and water absorption rate of various sandstones were determined experimentally. After that, a new index weighting method was proposed to comprehensively evaluate the water-bearing capacity index of sandstone. According to this method, the water-bearing capacity of aquifers in the Guojiahe coalmine were evaluated. The research results revealed that the water-bearing capacity of sandstone was mainly related to its pore connectivity, and the water-bearing capacity of sandstone in the Luo’he and Zhi’luo formation was considerably greater than that in the Yan’an formation. The water bearing capacity of strata in the eastern part of the mining area is lower than that in the western part of the mining area. The research results can provide considerable money savings for coal mining and protect the ecological environment and groundwater resources in the region.

Study on Dynamic Evolution of Roof Crack and Support Timing of Secondary Tunneling for Large Section Open-Off Cut in Deep Mines

The stability of large section open-off cut in deep mines (LODM) is the key factor affecting the normal equipment installation and safe mining in fully mechanized top-coal caving face. The mechanical model shows that the deflection of the roof of the LODM is proportional to the cubic of span. In this paper, UDEC Trigon model is established, and the parameters of different coal measures strata are modified in detail. The evolution law, failure mode, and damage degree of roof cracks in secondary tunneling are studied, and the roof support effect is analyzed. The numerical simulation results show that the process of roof crack evolution after the primary excavation section and the second excavation section can be divided into three stages according to microseismic activities, and the reasonable supporting time can control the propagation of roof microcracks and reduce the development height of macrocracks. The rock bridge existing in the roof rock stratum after the combined support of long and short anchor cables can effectively limit the formation of macrocracks and their interaction; especially the key support in the interface area can reduce the development height of roof cracks in secondary tunneling and weaken the damage degree of roof rock stratum in the LODM. The field test shows that the moved volume of rib-to-rib and roof-to-floor of the LODM is stable at about 350 mm and 550 mm, respectively. The numerical simulation in this paper is helpful to understand the failure mode of roof in LODM with large mining height and provides a method for the design of its control technologies.

Analysis on Rock Burst Risks and Prevention of a 54 m-Wide Coal Pillar for Roadway Protection in a Fully Mechanized Top-Coal Caving Face

A case study based on the 401103 fully mechanized caving face in the Hujiahe Coal Mine was carried out in this research to analyze the rock burst risks in a 54 m-wide coal pillar for roadway protection. Influencing factors of rock burst risks on the working face were analyzed. Stress distribution characteristics on the working face of the wide coal pillar for roadway protection were discussed using FLAC3D numerical simulation software. Spatial distribution characteristics of historical impact events on the working face were also investigated using the microseismic monitoring method. Results show that mining depth, geological structure, outburst proneness of coal strata, roof strata structure, adjacent mining area, and mining influence of the current working face are the main influencing factors of rock burst on the working face. Owing to the collaborative effects of front abutment pressure of the working face and lateral abutment pressure in the goaf, the coal pillar is in the ultimate equilibrium state and microseismic events mainly concentrate in places surrounding the coal pillars. Hence, wide coal pillars become the regions with rock burst risks on the working face. The working face adopts some local prevention technologies, such as pressure relief through presplitting blasting in roof, pressure relief through large-diameter pores in coal seam, coal seam water injection, pressure relief through large-diameter pores at bottom corners, and pressure relief through blasting at bottom corners. Moreover, some regional prevention technologies were proposed for narrow coal pillar for roadway protection, including gob-side entry, layer mining, and fully mechanized top-coal caving face with premining top layer.

Development of a rotatable similar simulation experimental system for steep coal seam mining

Purpose Currently, the existing similar simulation is still limited in the following aspects: un-rotatable laboratory devices, the difficulty in the pavement on steep seams and great error of the experimental data. Design/methodology/approach To address above-mentioned problems, this study combined theoretical analysis and numerical simulation and developed a rotatable experimental system for similar simulation on steep coal seam mining on the premise of ensuring experimental safety. Findings The present experimental system mainly consists of the model support, the rotation system and the bearing system. By taking into account the experimental requirements and actual laboratory space, the sizes of the model support and the bearing system were determined. Considering the requirements in space limit and rotation stability, the rotation mode of vertical sliding on the left side and the horizontal sliding on the lower side was designed. Originality/value Using programmable logic controller automatic angle control technology, the rotation angle, velocity and displacement of the model can be automatically adjusted and controlled so as to achieve safe rotation and precise control. Finally, the calculation method of the mass of the required similar materials for paving the coal strata at different inclination angles and in different horizons was analyzed, and the related mass proportion calculation software was developed.

Prevention and Control of Hydrogen Sulphide Accidents in Mining Extremely Thick Coal Seam: A Case Study in Wudong Coal Mine

Hydrogen sulphide is a toxic gas often present in coal seams and seriously threatens the lives and health of underground workers in coal mines. In this study, we theoretically modelled hydrogen sulphide generation in extremely thick underground coal mines with the +575 level #45 coal seam of Wudong Coal Mine as an example and obtained the on-site hydrogen sulphide emission pattern and spatial distribution features by combining field measurements and computational fluid dynamics simulation. The results showed that hydrogen sulphide mainly exists in the coal porous system in an adsorbed state. Because hydrogen sulphide has a molecular weight greater than the average molecular weight of air molecules, its concentration decreases with the increase of altitude to the bottom plate. When mining the upper stratified coal stratum, it diffuses widely in the working space; while when mining the lower coal stratum, it mainly concentrates at the bottom of the working face. Based on these analyses, on-site treatments were carried out using mixtures with different concentrations of sodium carbonate and sodium bicarbonate. In addition, different combinations of catalysts as well as type A and type B wetting agents were also tested. Eventually, a neutral KXL-I absorbent was developed, and the process of preinjecting absorbent and spraying absorbent was designed. The results showed that the newly developed KXL-I absorbent has high hydrogen sulphide absorption ability and is suitable for use as an absorbent in Wudong Coal Mine; preinjecting and spraying the absorbent can effectively prevent hydrogen sulphide disasters in the +575 level #45 coal seam in Wudong Coal Mine with the optimal final concentration of 0.9% and the absorption rate of 87% at the shearer of 66.6% at the support. Overall, our study provides valuable information for the prevention and control of hydrogen sulphide disasters in coal mines.

Measurement of CBM Bubble Parameters by Double-Sensor Conductivity Probe

Since the current commonly used bubble detection method cannot meet the requirements of real-time bubble detection in terms of the detection target and volume, this paper proposes a method of real-time detection of coal-bed methane (CBM) bubble parameters in a borehole with a double-sensor conductivity probe and designs the corresponding test device. The ellipsoid correction algorithm was adopted for the calculation of the bubble volume to reduce the error. Simulation test results indicated that the proposed device can quickly and reliably measure local bubble parameters, including void fraction, bubble velocity, and bubble volume. This technique can be applied to monitor the fluid parameters of different strata of main coal in CBM well simultaneously and provide a basis for the comparison of reservoir properties of different main coal seams and the effect of CBM well exploitation.

Exploration and application of directional long boreholes in coal measure strata

two roadways in adjacent working face of Baode Mine may have the risk of water inrush at the same time, so it is necessary to construct long borehole to cover the roadway excavation. On the basis of the hydrogeological conditions of the mine, the safe water insulation thickness and water inrush coefficient of coal seam No .8 are calculated. The results show that the water inrush coefficient is 0.035-0.037 MPa/m, which is less than the critical value 0.06 MPa/m and the bottom plate has no sudden water hazard. In the construction of No .10 coal seam, the directional long borehole is used to detect whether there is a hidden structure communicating with the floor limestone and to drain water. The test shows that there is no effluent phenomenon in the borehole, which proves that there is no hidden structure in No .10 coal seam.

Determine method of effective experimental period of similar material model for improving the simulation results

ABSTRACT Similar material simulation methods have been extensively applied to investigate stratum movement in mining technology. The similarity between similar material models and prototypes is directly associated to the reliability of simulation results. Considering that the mechanical strength changes of similar material model made at a certain ratio is closely related to its humidity and moisture content, the effective time period for simulating excavation and model monitoring should be determined based on the changes in humidity and moisture content of similar material models, but there is currently no such method. According to the relation of humidity and moisture content of the similar material model obtained through mechanical experiments, an approach is proposed for determining the effective experimental time for similar material model for coal mine stratum movement. The new device designed can effectively monitor the humidity changes of similar model materials, so that the simulation excavation and monitoring time process of similar material models can be scientifically controlled. This paper solves the difficult issue that the model dynamics similarity can hardly guarantee during the experiment of similar materials simulation, and the findings can offer a scientific basis for monitoring period of similar material models and reliability improvement for model simulation results.

Critical issues for the ground control of shallow roadways in weak ground: a case study

The roadways located in weak ground experience strong and cyclic dynamic loading induced by the thick coal seam extraction, which caused costly support and delay of normal production. This paper discusses the critical issues and support strategy for such roadways through a case study on a roof collapsed roadway which was excavated in a coal stratum at a depth of 120 m in Shanxi Province, China. A 2-m-high void between the concrete support and the exposed roof strata was left untreated due to poor roadway construction. The roadway collapse reached up to approximately 6 m in the roof strata, which was attributed to the large untreated void as well as the highly fractured rock mass. A combination support method of the void filling, the fracture grouting, and rock bolting was proposed to rebuild and reinforce the roadway. The deformation of the roadway was effectively controlled, and the maximum roof displacement reached 135 mm. The failure mechanism of the roadway was numerically investigated using discontinuous deformation analysis (DDA) based on specific geological conditions. The numerical findings suggested that the void above the roadway could significantly impact on the stability of the overlying strata.

Study and Test on Development Regularity of Mining Speed of Coal Seam Separated from Overburden Strata

In the sedimentary coal stratum, rock stratum exhibits layered feature and has an obvious level. Overlying rock often produces separation along the level after the underground coal mining. But, due to the difference in the layers of rocks, the change of the mining process, the difference height in the level and other factors, the rule of separation is extremely complex. Therefore, in this paper, the allometric phenomenon, feature and laws of mining overburden separated strata are found by means of experiment and numerical simulation. The paper reveals the mechanical mechanism of allometric development of overburden separated strata, establishes its development formula based on the theory of beam in the mechanics, analyzing the space-time law of mining subsidence and overburden separation, and finally finds the relationship between surface subsidence and allometric growth of mining overburden separated strata, establishing the subsidence model based on allometric growth of mining overburden separated strata.