Coal Working Face Research Articles

Preventing water-inrush from floor in coal working face with paste-like backfill technology

In the view of the situation where great economic loss often occurs during mining deep coal seams in Feicheng coal field due to water inrush from the floor Ordovician limestone aquifer, the floor "lower four-zone" theory was used as a guide. 81006 working face of Caozhuang Coalmine in Feicheng coal field was taken as the research background, and paste filling technology was proposed to inhibit or reduce the damaged floor depth caused by mine ground pressure in order to prevent water inrush from the floor Ordovician limestone aquifer. Glue material, coal gangue powder, and fly ash were selected as filling material, and a ground filling system, including a material production system, storage material system, power supply and water supply system, automatic control and measurement system, monitoring and control communications system, emergency response system, and underground filling system, including pipe conveyor system and working face blocking grout loss system, were established to achieve effective filling goaf. Field stress monitoring and floor damaged depth measurement showed that when reaching a steady state after a period of time, paste filling working face not only restored to the original stress state but also significantly reduced the floor's damaged depth caused by mine ground pressure. This verifies that working face with paste-like backfill technology is a very effective measure to prevent water-inrush from the floor.

Detection of geological anomalies in coal mining working faces using a scattered-wave imaging method

A concealed geological structure encountered during the excavation of a coal working face could connect the working face to high-pressure water in limestone strata, which can result in a serious or catastrophic water inrush accident. However, existing geophysical detection methods used to ensure the geological safety of working faces cannot detect small geological anomalies reliably. Based on the generalized theory of scattered waves, we have developed a novel and superior scattered wave imaging method for the detection at the roadway lateral wall, capable of wave vector extraction and multiwave imaging. In this method, the waves scattered from a geological anomaly can be dynamically and accurately extracted by the polarized filter function during the mapping processes of common scattering point (CSP) gathers. A numerical simulation was performed to study the seismic wave response characteristics of a small collapse column in a coal working face. The P and channel waves of the model were extracted and imaged using the novel imaging method. A field study of three-component seismic detection was performed in the Xuzhuang Coal Mine, demonstrating that the joint imaging of body and channel waves can detect small drop faults invisible to channel wave imaging alone. These results indicate that the proposed method can effectively image anomalous bodies on working faces in complex and noisy mine wavefields using multiwave information, providing a new approach for the reliable and timely detection of hazardous geological features hidden in working faces.

Study on time–space characteristics of gas drainage in advanced self‐pressure‐relief area of the stope

AbstractGas drainage is an important measure to ensure energy safety in coal mines. However, for mines with high gas content and low permeability, the critical question is how to enhance the drainage effect of drilling. By using the self‐unloading pressure effect on the coal body in front of the mine, the permeability of the coal body can be improved, which facilitates gas drainage. Therefore, establishing the fluid–solid model of gas‐bearing coal mass under the influence of mining, this paper simulates the advanced self‐pressure‐relief range in front of the coal working face and the permeability of coal seam at different heights. Through simulations and field tests, the reasonableness of the advanced self‐pressure‐relief gas drainage was verified, and the spatial and temporal characteristics of the gas drainage from the borehole were quantified and analyzed. The results show that the width of the advanced self‐pressure‐relief zone after simulated mining is 25 m, the vertical permeability of the coal seam increases first and then decreases with the increase of the height from the floor, and the maximum permeability of the layer is 2.6 m from the floor, which is 8.62 times higher than the initial permeability; the gas drainage effect of test boreholes has a periodic law with the coal seam recovery, which, divided into the initial drainage stage, the scalar volume of gas drainage increase stage, and the scalar volume of gas drainage decay stage. At a distance from the working face 20–40 m, the boreholes' scalar volume of gas drainage increased by 3.89 times compared with the initial drainage stage, and the scalar drainage volume of the boreholes through the seam increased by 8.01 times compared with the initial drainage stage; in the section of increasing scalar volume of drainage, the gas drainage volume of the boreholes at different heights of the coal seam had obvious “stratification” phenomenon. The test boreholes were optimally placed in the middle of the seam at the lower end. The study provides a reference for self‐pressure‐relief gas drainage technology and optimization of borehole placement.

Study on instability fracture and simulation of surrounding rock induced by fault activation under mining influence

The fault is potentially vulnerability's geological structure in the working face and its vicinity, and it is also a crucial geological factor affecting coal mine safety exploitation. To investigate the unstable failure of surrounding rock induced by fault activation under the influence of adoption, which was studied utilizing field case and numerical analysis for the deformation and failure process of surrounding rock near the fault-affected zone. Combined with field cases, this paper analyzes disturbance stress and roof abscission layer monitoring in effecting zones of fault activation. Using the discrete element 3DEC numerical analysis method, the model of surrounding rock unstable fracture induced by fault activation under adoption is established. The unstable fracture and stress variation characteristics of surrounding rock induced by fault activation during the excavation of the upper side wall and lower side wall of the faults are simulated and analyzed. Field analysis shows that as the coal working face continues to advance, the mining stress gradually increases. There is a zigzag wave on the relationship curve between coal mining and roof displacement near the fault, which reveals that the surrounding rock of the fault activation affected zone is in the superposition state of static load and dynamic load. Furthermore, the simulation results show that the stress and displacement of surrounding rock near the fault increase with the advance of coal mining face. The closer to the fault plane, the displacement gradually returns to zero, and the stress is also in a lower state.

Roof pressure prediction method of coal working face based on spatiotemporal correlation analysis

Roof pressure prediction method of coal working face based on spatiotemporal correlation analysis

Study on Reasonable Coal Pillar Width of Goaf-side Roadway Driving in Deep Island Working Face with Fully Mechanized Caving Mining

Goaf-side roadway driving with narrow coal pillars could obviously improve the coal recovery rates compared to traditional wide pillars of 15–40 m. However, it is difficult to control the stability of goaf-side roadway driving, especially in the deep island coal working face. To control the stability using fully mechanized caving, working face 4206 in Jianxin Coal Mine in the Shaanxi Province of China, field investigation, theoretical analysis, and numerical simulation were performed to obtain the main influencing factors of the surrounding rock deformation and reveal the characteristics of stress distribution, plastic zones, and deformations of the surrounding rock of roadways with coal pillars of different widths. Results show that the main influencing factors of surrounding rock deformation of roadways in the island working face 4206 in Jianxin Coal Mine include large, buried depth, thick coal seam, large coal pillars, and island working face with high stress concentration. Moreover, the reasonable coal pillar width is 8 m. The stress concentration and the damage of the 8-m-wide coal pillar are smaller, and the corresponding deformation is lower than that of the other pillars, which is beneficial to the stability of the Goaf-side roadway driving.

Seismic time-lapse monitoring of gas drainage in an underground coal working face

Gas drainage is a popular method used for preventing gas outbursts in coal seams. However, quantitative assessment of the drainage remains a challenging task. In this study, we conducted a seismic time-lapse monitoring study at the No. 15110 working face in the Sijiazhuang coal mine to evaluate the effectiveness of the gas drainage process. The result reveals that there is a remarkable difference in frequency bands and computed tomography (CT) image, inverted from the attenuation coefficients of the recorded channel waves, before and after the gas drainage. In the thick mylonitic coal zone, gas drainage operation generally decreases the wave frequency and wave attenuation. The comparable roof refractions from the monitored seismogram and CT-inverted velocity distributions demonstrate that changes in the coalbed roof during the gas drainage are minor. The attenuation differences are attributed mainly to the stress-relieving effects of the thick mylonitic coal zone. This observation is supported by the forward modeling of the channel waves. Time-lapse seismic monitoring employed in this study provides a useful tool for monitoring the impact of gas drainage on a coal working face, including its roof, for any coal mine with restively simple geological structures.

Deciphering soil bacterial community structure in subsidence area caused by underground coal mining in arid and semiarid area

Subsidence caused by underground coal mining results in soil degradation. However, little is known about bacterial community structure and its response to a 1-year-old coal mining subsidence area in arid and semiarid areas northwest China. Soil samples from 5 unexplored areas (MC, RC, YC, LC and ZC) and a 1-year-old subsidence area above a coal working face were collected and soil biogeochemical properties and bacterial community structure were determined. Results showed electrical conductivity (EC), soil water content (SWC), soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), dissolved organic carbon (DOC), available nitrogen (AN), available phosphorus (AP) and available potassium (AK) decreased with depth. The microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and the activity of β-1,4-glucosidase (BG), β-1,4-N-acetylglucosaminidase (NAG), alkaline phosphatase (PP) and catalase (CAT) were also reduced. The nutrients, BG, PP and MBC in subsidence of marginal zone of a coal working face were significantly lower than those in control, suggesting subsidence led to a loss in nutrients and a reduction in microbial biomass. High-throughput sequencing revealed that the Sphingomonas, Gemmatimonas, Pseudomonas and Gp6, involved in C and N nutrient cycles, were dominant in this region. The relative abundances of Sphingomonas, Pseudomonas and Arthrobacter were decreased in subsidence due to the nutrient leakage and microbial biomass reduction. The predicted abundances of genes for metabolisms of xenobiotics via cytochrome P450 pathways and nitrogen were low in marginal zone, while peroxidase was high, indicating low capacities of degrading for xenobiotics and polycyclic aromatic hydrocarbons (PAHs) occurred marginal zone, while resistance to hydrogen peroxide was strengthened. Redundancy analysis (RDA) revealed EC, SWC and soil depth governed bacterial community structure. Overall, subsidence caused losses in soil water, nutrients and microbial biomass, alteration of bacterial community structure, and ultimately reduced soil nutrient conversion. Therefore, the cracks in the subsidence area should be filled manually in time, especially in marginal zone.

Stability analysis of coal face based on coal face-support-roof system in steeply inclined coal seam

Rib spalling is a major issue affecting the safety of steeply inclined coal seam. And the failure coal face and support system can be affected with each other to generate a vicious cycle along with inducing large-scale collapse of surrounding rock in steeply inclined coal seam. In order to analyze failure mechanism and propose the corresponding prominent control measures of steeply inclined coal working face, mechanical model based on coal face-support-roof system and mechanical model of coal face failure was established to reveal the disaster mechanism of rib spalling and the sensitive analysis of related factors was performed. Furthermore, taking 3402 working face of Chen-man-zhuang coal mine as engineering background, numerical model by using FLAC3D was built to illustrate the propagation of displacement and stress fields in steeply inclined coal seam and verify the theory analysis as mentioned in this study. The results show that the coal face slide body in steeply inclined working face can be observed as the failure height of upper layer smaller than that of lower layer exhibiting with an irregular quadrilateral pyramid shape. Moreover, the cracks were originated from the upper layer of sliding body and gradually developed to the lower layer causing the final rib spalling. The influence factors on the stability of coal face can be ranked as overlying strata pressure (P) > mechanical parameters of coal body (e.g., cohesion (c), internal fraction angle (𝛟)) > support strength (F) > the support force of protecting piece (F

Top corner gas concentration prediction using t‐distributed Stochastic Neighbor Embedding and Support Vector Regression algorithms

SummaryThe excess of gas concentration in the top corner of coal working face has always been the main factor restricting the safe productivity of coal mines. Therefore, the rapid and accurate prediction of top corner gas concentration is an effective method to prevent gas disasters. At the same time, the development of the Internet of things has made the gas monitoring data collected by the coal mine safety monitoring system exhibit nonlinear big data characteristics. In order to mine the characteristic data related to the gas concentration of the top corner from a high‐dimensional and nonlinear monitoring datasets, a model that integrates the t‐distributed Stochastic Neighbor Embedding algorithm (t‐SNE) and the Support Vector Regression (SVR) algorithm to predict the gas concentration of the top corner on the coal working face is proposed. First, the multidimensional monitoring data are nonlinearly dimension‐reduced by t‐SNE algorithm, which enabled the spatial feature data of the monitoring data to be extracted. After that, the SVR algorithm was used to construct the nonlinear regression model between the spatial feature data and the actual gas concentration of the top corner to predict the gas concentration of the top corner. The experimental results show that the predictive model based on t‐SNE and SVR was better than the multiple linear regression, SVR, Principal Components Analysis (PCA) + SVR. The results show the model based on t‐SNE and SVR was more stable and could provide more accurate predictions, anomaly sensitivity, and the fitness is 0.55628405, which can better fit the actual gas concentration of the top corner.

Experimental Study on the Effect of Advancing Speed and Stoping Time on the Energy Release of Overburden in an Upward Mining Coal Working Face with a Hard Roof

In order to study the influence of advancing speed and stoping time of a coal face on the scale and frequency of rock burst, the energy release characteristics of an overburden fracture under six advancing speeds and four stoping times are studied by theoretical analysis and similar simulation experiments. The distribution characteristics of microseismic events before and after stoppage are compared, and the load/unload response ratio is introduced to analyze the relationship between the synergistic effect of advancing speed and stoping time and the characteristics of microseismic events in coal and rock mass. The mechanism of rock burst induced by the advancing speed and stoping time effect in the working face is studied, and the coordinated regulation and mitigation of advancing speed and stoping time are analyzed and completed. The results show that the effect of advancement speed and stoping time is very important to the energy release of overburden. The energy released by microseismic events during stoping is exponentially related to the advancing speed. The change of advancing speed causes the change of microseismic event characteristics, reflecting the evolution process of overburden structure and its energy. During stoping, the secondary microseismic events disturbed by mining occur frequently, leading to the significant difference of energy released by microseismic events during stoping. After stoping, the microseismic energy is more than four times higher than that during the stop period, and the risk of coal seam impact is high during the stope period. The synergetic change of advancement speed and stoping time changes the cycle of energy accumulation and release. The response ratio of loading and unloading considering the effect of advancement speed and stoping time is established by using the corresponding ratio of loading and unloading, and the impact risk of the coal seam is quantitatively analyzed. Based on the monitoring and analysis of microseismic events, the safety mining index of coordinated control with the energy of a single microseismic event of 180 J is established, and the best advancing speed of the working face is determined to be 4 m/d. According to the corresponding ratio of loading and unloading, the reasonable stoping time of different advancing speeds and the corresponding advancing speed of different stoping times after the resumption of mining are determined, so as to provide a reference for the safe and efficient mining of similar rock burst mines.

Study on Rule of Overburden Failure and Rock Burst Hazard under Repeated Mining in Fully Mechanized Top-Coal Caving Face with Hard Roof

The dynamic disasters caused by the failure of hard roof in the process of mining coal seriously affect the safe production in coal mines. Based on the W1123 mining coal working face of Kuangou coal mine, the physical similar material simulation experiment and acoustic emission (AE) monitoring method are used to study the failure law and AE characteristics of overburden in the process of coal mining. The stress evolution law is revealed through numerical simulation, the dangerous areas and rock burst hazard under the repeated mining with hard roof are studied combined with microseismic monitoring on site. The results show that the energy of W1123 working face released by the overburden damage under B4-1 solid coal is higher than that of the gob, and the peak value of the AE energy appears near the W1145 open-off cut. Through the statistics of the AE data, the large energy rate of AE event is defined, and the AE events with large energy rate appear in the scale of 82.4–231.2 cm within the model. This area is shown as a stress superposition area according to the numerical simulation. On the basis of comparing with the characteristics of energy distribution in the field, it is considered that the main control factors of rock burst in this area are hard roof of the working face and the stress concentration caused by the repeated mining. It provides a scientific guidance for the prevention and control measures of rock burst in this type of mining condition.

Stability Control of a Goaf-Side Roadway under the Mining Disturbance of an Adjacent Coal Working Face in an Underground Mine

Goaf-side roadway driving could not only notably reduce the loss of coal resources and improve the coal recovery rates, but also greatly mitigate the imbalance between excavation speed and production needs, which are able to prolong the service life of the mine and are pivotal to sustainable and efficient development of underground coal mines. However, it is difficult to control the stability of the goaf-side roadway, especially under mining disturbance of another adjacent coal working face. In order to control the stability of the goaf-side roadway, Haulageway 1513 in the Xinyi Coal Mine of China, under mining disturbance, theoretical analysis, numerical simulation, and engineering practice were carried out to reveal the mechanism of overburden key strata fracture, stress distribution, and deformation characteristics of the surrounding rock of the goaf-side roadway due to mining disturbance. Results showed that some key strata above Goaf 1512 did not fracture due to the influence of the strata caving angles. However, these key strata would fracture and break into rock blocks when suffering from mining disturbance of the adjacent coal working face, which changed the stress distribution and increased the deformations of the surrounding rock of the goaf-side roadway. The combined techniques of pressure relief and bolt support were proposed and carried out to control the stability of the goaf-side roadway. Engineering practice indicated that the maximum deformations of the roof and sidewall-to-sidewall were 220 mm and 470 mm, respectively. The deformations of the goaf-side roadway under mining disturbance were efficiently controlled.

Study on Gas Outburst Forecast Sensitivity Index for 2# Coal Working Face of Xuecun Mine

According to the Xuecun mine field measured data, the gas outburst prediction index is analysed by the qualitative. It is the use of gray relational analysis and the “three rate” calculated quantitatively predict the sensitive indicators of Xuecun mine. The results show that the results of qualitative analysis and quantitative are agreement. It initially came to the prominence predictor of Δh2, the sensitivity of which is better. It improves the reliability of sensitivity index for 2# coal working face of xuecun mine.

Estimation of hydrogen release and conversion in coal-bed methane from roof extraction in mine goaf

In order to effectively utilize the coal bed methane (CBM) resources extracted from underground coal mines, an evaluation method of hydrogen production capacity from CBM is established by means of experiments and theoretical models. The main components of CBM collected from coal working face are measured by gas chromatography, and the release law of trace hydrogen is obtained. Considering gas extraction technology in goaf roof, a computational fluid dynamics model for seepage problem in porous media is presented. The law of gas migration in goaf under extraction conditions is obtained by simulation, and the extraction rate of CBM and methane/hydrogen content are predicted. The technology of producing hydrogen from CBM extracted from goaf under low gas concentration is discussed, and the effect of methane content on auto-thermal conversion efficiency is analyzed. Under the condition of this study case, the theoretical estimation of pure hydrogen produced from goaf extraction can reach more than 10,000 m3 per day. The presented results could provide a new route for the utilization of CBM by underground extraction.

Study on the mechanism of water inrush in the arid western mining area

The analysis found that the coal mining process in the western mining area has the mining loss and disaster effect of the water-rich aquifer of the coal seam roof, which is mainly manifested by the overburden water in the roof. On this basis, the formation and development of the separation water of the roof is proposed, and the mechanism of the water inrush from the layer is revealed. It is found that there is hydrostatic pressure and hydrodynamic pressure in the separated water, under the combined action of bed separation water pressure, the mining-induced fracture and water-isolation layer tension fracture are connected, which causes water inrushing in the coal working face of the mine, and provides a theoretical guarantee for the large-scale development of coal resources in western mining areas.

Fuzzy fault tree analysis for gas explosion of coal mining and heading faces in underground coal mines

During the past decade, gas explosions have been one of the most serious types of disasters in China, threatening the lives of miners and causing significant losses in terms of national property. This article, by constructing the fuzzy fault tree model of gas explosion on the coalface and heading face, deduces the minimum cut sets and minimum path of the fault tree, analyzes the importance of the fault tree structure, and obtains the ratio of gas explosion. The results show that the isolation of gas and heat sources is the most effective way to prevent gas explosion. In addition, a close detection of gas concentration and appropriate treatment can also avoid explosive accidents by reducing the ratio of explosion to below 0.059%, which is the critical value of explosion. The probability of gas explosion occurred in coal working face is about 0%–2.055%, and the most likely probability is 0.059%. However, the probability of gas explosion occurred in heading face is about 0%–8.543%, and the most probability likely to occur is 0.772% which is larger than that in coal working face. The fuzzy fault tree can not only be applied in the analysis of the coal mining gas explosion, but it also provides the theoretical basis for the precaution and prevention of coal mining accidents.

Research on Monitoring and Prewarning System of Accident in the Coal Mine Based on Big Data

More and more big data come from sensor nodes. There are many sensor nodes placed in the monitoring and prewarning system of the coal mine in China for the purpose of monitoring the state of the environment. It works every day and forms the coal mine big data. Traditional coal mine monitoring and prewarning systems are mainly based on mine communication cable, but they are difficult to place at coal working face tunnels. We use WSN to replace mine communication cable and build the monitoring and prewarning system. The sensor nodes in WSN are energy limited and the sensor data are complicated so it is very difficult to use these data directly to prewarn the accident. To solve these problems, in this paper, a new data aggregation strategy and fuzzy comprehensive assessment model are proposed. Simulations compared the energy consumption, delay time, cooperation cost, and prewarning time with our previous work. The result shows our method is reasonable.

大海则煤矿超大采高工作面片帮治理技术研究

通过对脆性煤层工作面煤壁片帮的机理和影响因素分析，并运用PFC软件对回采过程进行离散元数值模拟分析，对超大采高回采过程中可能形成的片帮情况以及片帮规模有了定量的预测。明确了大海则煤矿大采高工作面片帮属于典型的拉张型板裂破坏，与煤岩层的受力、结构的变形、煤岩物理力学性质有关。制定了采用提高围岩支护强度，提升煤体强度，优化液压支架结构设计，改进回采工艺以及保证煤层节理与煤壁倾向的综合治理技术方案，来减少煤壁片帮。 Through analyzing mechanism and influencing factors of the brittle coal working face coal wall, and using PFC software to simulate discrete element analysis of the process of mining, there is quantitative prediction in the situation about the formation of wall caving in the process of extra large mining height and spalling scale. It is clear that the working face of mining height in coal mine belongs to typical tensile fracture failure, which is related to the stress of coal and rock strata, the deformation of structure and the physical and mechanical properties of coal rock. The formulation is adopted to improve the surrounding rock supporting strength, improve coal strength, optimize the structure of hydraulic support design, improve the mining process and ensure the comprehensive treatment scheme of coal bed joints and coal wall inclination, to reduce the coal wall spalling.

Gas Emission Prediction Model of Coal Mine Based on CSBP Algorithm

In view of the nonlinear characteristics of gas emission in a coal working face, a prediction method is proposed based on cuckoo search algorithm optimized BP neural network (CSBP). In the CSBP algorithm, the cuckoo search is adopted to optimize weight and threshold parameters of BP network, and obtains the global optimal solutions. Furthermore, the twelve main affecting factors of the gas emission in the coal working face are taken as input vectors of CSBP algorithm, the gas emission is acted as output vector, and then the prediction model of BP neural network with optimal parameters is established. The results show that the CSBP algorithm has batter generalization ability and higher prediction accuracy, and can be utilized effectively in the prediction of coal mine gas emission.