Tangkou Coal Mine Research Articles

Identification of the Gas Explosion Hazardous Area in a Gob by Numerical Simulations-A Case study of the 6310 Working Face of Tangkou Coal Mine.

In the process of coal mining, gas explosion accidents occur frequently, which seriously affect the safety of mine production. Identifying the gas explosion hazardous zone in a gob is of specific guiding significance for the prevention and control of gas explosion in a coal mine. In this work, we analyze the porosity and gas concentration distribution in the gob after the working face was mined by combining the particle flow and finite-element simulation. A trianglular gas explosion hazardous zone is obtained by multielement coupling, and the CO2 injection simulation is then performed to eliminate the hazardous zone. The results show that the upper part of the gob and the edge of the return airway in the lower part are highly porous, and the porosities of other areas are relatively low with a value of 0.4. The gas concentrations in the upper left part and lower right part of the gob are relatively low, and the oxygen concentration distribution is the opposite. The gas explosion hazardous zone is mainly distributed near the oxidation zone. Yet, the simulation results reveal that after an injection of 97.5 m3/h of CO2, there is no area in the goaf that meets the gas explosion concentration conditions, that is, the oxygen concentration is greater than 12% and the methane concentration is greater than 5% but less than 16%, which can effectively eliminate the gas explosion hazardous zone.

Experimental and Numerical Simulations of Pore Structures and Seepage Characteristics of Deep Sandstones

Previously conducted studies have established that deep underground rock masses have complex pore structures and face complex geological conditions. Therefore, the seepage problem of such rock masses seriously affects engineering safety. To better explore the seepage law of deep rock masses and ensure engineering safety, indoor experimental methods such as casting thin sections, scanning electron microscopy, and mercury intrusion testing were utilized in this study. The microscopic pore shape, size, distribution, and other structural characteristics of sandstone in coal bearing strata were analyzed. The tortuosity calculation formula was obtained by the theoretical derivation method. And a numerical model was established for seepage numerical simulation research through microscopic digital image methods. The seepage law of surrounding rocks in the Tangkou Coal Mine roadway under different conditions is discussed. The research results indicate that the complexity of the pore structure in porous media leads to an uneven distribution of flow velocity and pressure within the medium. Meanwhile, with the change of physical properties, the fluid flow characteristics also undergo significant changes. The research results can effectively guide micropore water blocking, reduce the impact of groundwater on the environment, ensure the environment and safety of the project, and provide guidance for other geological projects.

The Optimization of Segmented Reaming Parameters and the Analysis of the Pressure Relief Effect in Impacted Coal Seams

This work focused on the insufficient or excessive pressure relief in large-diameter pressure relief by drilling. The influence of large-diameter pressure relief by drilling on the 6307 working face of the Tangkou coal mine on the roadway deformation was taken as the research background, with numerical simulations, indoor experiments, and on-site applications used. The influence of pressure relief drilling on roadway deformation was studied to propose segmented reaming pressure relief. The influences of parameters (e.g., reaming diameter, reaming depth, and borehole spacings) on the evolution characteristics of segmented reaming cracks and pressure relief were further investigated. The results showed that segmented reaming pressure relief reduced the roadway deformation and the peak elastic energy of coal in the impacted hazard area and improved the energy accumulation of the surrounding rocks of the roadway. The effect of segmented reaming pressure relief was positively correlated with the diameter and length of the reaming section; it was negatively correlated with borehole spacings. The optimized segmented reaming parameters of the 6307 working surface of Tangkou coal mine are as follows: the optimized reaming diameter of 240 mm, the reaming section depth of 15 m, and the borehole spacing of 1.6 m. Field tests proved that the optimized segmented reaming technology can improve the deformation of the surrounding rocks of the roadway and construction.

Formation Mechanism of “Large-Area Sweating” Water Seepage from Deep Mine Sandstone Pores

The groundwater in nonkarst areas can be divided into two categories: pore water and fracture water. Unlike fracture seepage, sandstone pore seepage in deep mines manifests as a large area of “sweating,” rather than an area of local “spray,” and is difficult to plug via conventional grouting methods. This study focused on pore seepage in deep mine sandstone to improve the grouting effect. Taking the deep mine sandstone in the southwest Shandong coal field, where “large-area sweating” seepage occurs, as the study object, this study examined the pore structure, petrological characteristics, physical properties, and grain sizes of the sandstone by analyzing experimental data from thin sections and scanning electron microscopy samples. The formation mechanism of the “large-area sweating” seepage was then analyzed. The range of permeability in which “large-area sweating” seepage may occur in the sandstone was discussed. The results indicate that the process of “large-area sweating” seepage in deep mine sandstone can be divided into a matrix softening stage, a matrix erosion stage, and a “large-area sweating” water seepage formation stage. According to the case analysis on the “large-area sweating” seepage in the Tangkou coal mine of the Southwest Shandong coalfield, the lower limit of permeability of the “large-area sweating” sandstone is approximately 0.25 mD. Thus, this type of seepage can occur in deep mine sandstone with a permeability of greater than 0.25 mD and affect typical mining production. The results of this study provide information about the formation mechanism of “large-area sweating” water seepage from sandstone pores and can theoretically inform the development of a new permeation grouting technique.

Study on the Pressure Relief Mechanism and Engineering Application of Segmented Enlarged-Diameter Boreholes

Ensuring the stability of surrounding rock while conducting pressure relief is key to roadway stability control and preventing rock burst. In this paper, segmented enlarged-diameter borehole destressing technology is proposed. The stress distribution around the borehole is analysed based on the theory of elasto-plastic mechanics, and the mechanism of pressure relief for segmented enlarged-diameter boreholes is studied. Secondly, The effects of the diameter of enlarged-diameter section, length of the enlarged-diameter section, and borehole space on pressure relief and roadway deformation were investigated. Finally, the optimal drilling parameters for Tangkou coal mine 6307 working face are analysed. The key parameters of segmented enlarged-diameter borehole pressure relief technology for the 6307 working face were determined and applied in field practice. Field monitoring results showed that the accumulated energy can be effectively reduced using segmented enlarged-diameter pressure relief boreholes, effectively controlling roadway deformation and providing reference for rock burst prevention and roadway stability control.

Study on Pore Structure Change Characteristics of Water-Immersed and Air-Dried Coal Based on SEM-BET

ABSTRACT The pore structure of coal affects spontaneous combustion to a certain extent. The pore structure of the coal body will be altered after prolonged waterlogging and is highly susceptible to spontaneous combustion in the presence of elevated ground temperatures. To study the pore structure changes in the coal body after immersion and drying. The coal samples from the Jinjitan coal mine in Yulin, Shaanxi Province, the Tangkou coal mine in Jining, Shandong Province, and the Gaojiapu coal mine in Shaanxi Province were scanned by electron microscopy and low-temperature nitrogen adsorption experiments. This study indicates that after water immersion, the fracture pores of the coal body are developed, the morphology changes, and the percentage of pore fracture area increases significantly. With the increase in immersion time, the pore types of Coal samples A and C did not change, being delicate necked bottle-shaped pores and open, permeable pores, respectively. Coal sample B pore type developed from impermeable pores to open pores. The cumulative pore volume of coals from all three areas increased for the same pore size. The contribution of micropores to the BET specific surface area and total BJH pore volume was more significant than the original coal samples. The specific surface area of A90, B30, and C60 was larger than that of the other coal samples for the soaking time, so it can be assumed that A90, B30, and C60 have a higher propensity for spontaneous combustion. Underwater immersion, the pore type of coal samples from coal mines in Northwest China did not change, but the pore types of coal samples from coal mines in East China changed. Therefore, the pore structure of gas coal was easily changed underwater dissolution.

Design and application of a dust suppression technology of the forcing air curtain in fully mechanized rock tunnelling faces.

To effectively reduce high dust concentrations and keep clean air in fully mechanized rock tunnelling faces in coal mine, this study carried out a research of dust suppression technology of the forcing air curtain. First, the mechanism of dust diffusion controlled by the forcing air curtain was introduced in this study. Then, numerical simulations of the formation of the forcing air curtain as well as the influence for dust diffusion under the different distance between forcing air duct outlet and heading end were carried out. Moreover, a dust suppression technology of the forcing air curtain was designed and tested in a fully mechanized rock tunnelling face of southern return air tunnel which was located in the Tangkou coal mine of China. It shows that the numerical simulation results were in good agreement with the in situ tests. The average removal rate of total and respirable dust could reach up to 95.1% and 96.1%, respectively, at manned working areas in the tunnel. Research results show that the dust suppression technology of the forcing air curtain is an effective method of dust control in fully mechanized rock tunnelling faces.

Research on the Influence of Natural Wind Pressure in Deep Mines on Ventilation Stability

Deep mines are greatly affected by changes in natural wind pressure because of their large buried depths and long ventilation paths. Changes in natural wind pressure do affect the air flow of the underground ventilation system, and even change the direction of individual branches. If the dynamic changes of natural wind pressure are not monitored constantly, it is very likely to cause disasters such as gas overrun and may even lead to heavy casualties. In this paper, the changes of natural wind pressure and the air volume entering the mine are measured on‐site in the 630 mining area in the south wing of Tangkou Coal Mine, Then, compare the change law of natural wind pressure with the change law of ventilation air volume. Finally, through numerical simulation by FLUENT, the change of internal flow in the gob where there is a loosely closed condition is simulated. Through research, the annual natural wind pressure change and the change of air intake in the 630 mining area of the south wing of Tangkou Coal Mine were obtained; The influence of changes in external conditions on the ventilation air volume of deep mines is obtained; The importance of the influence of natural wind pressure on the stability of the deep mine ventilation system is verified.

Determination of roof horizontal long drilling hole layout layer by dynamic porosity evolution law of coal and rock

The key to the layout of the roof horizontal long drilling hole is to accurately locate the range of gas-conducting fracture zone. In this paper, the discrete element method (DEM) is firstly adopted to quantitatively simulate the porosity distribution in goaf from a microscopic perspective, with the 6306 working face of the Tangkou coal mine as an engineering example. Then, the three-dimensional porosity distribution data is extracted and converted into a two-dimensional array form, which was verified by the mathematical model established by previous work. After that, combining the DEM data and mathematical model result, user-defined function (UDF) codes are written and imported into computational fluid dynamics (CFD) software to simulate the gas distribution in the goaf before and after the drilling of the working face. The results show that the gas in goaf is mainly distributed in the upper position after drilling, and the proportion of gas in the bottom position is largely reduced. The boreholes arrangement in the gas-guiding fissure zone is reasonable effectively reducing the gas concentration in goaf.

Disaster Control of Roof Falling in Deep Coal Mine Roadway Subjected to High Abutment Pressure

The roof falling accident is a serious threat to the lives of miners in deep coal mining, especially when the coal mine is more than 1000 meters deep. In regard to the 5306 coalface in the Tangkou coal mine, Shandong, China, the depth of coal seam is 992.8 m and the stress concentration coefficient of the roadway surrounding rock is 3.33. This leads to a serious deformation of the roadway roof, thereby producing a high risk of the roof falling disaster. In this pursuit, based on the mechanical analysis of roadway roof subjected to a high abutment pressure, the mathematical expressions of the setting load and movable column length of supports were introduced. Furthermore, the stability control mechanism of the roadway roof was analyzed and the optimized support parameters of supports are provided. The results showed that the longtime effective support of the roadway roof required the strength and deformation coupling of supports and anchored surrounding rock. The support length of the belt roadway should be at least 57.7 m, with 0-30 m away from the coalface supported by hydraulic supports and 32-57.7 m supported by single props. In addition, the maximum setting load and movable column length of hydraulic supports were 21.67 MPa and 280.3 mm and 12.44 MPa and 177.1 mm for single props, respectively. By applying the optimized support parameters of supports to the belt roadway of the 5306 coalface, the effective control of the roadway roof and the disaster control of roof falling were realized.

Numerical simulation and application of entrainment dust collector for fully mechanized mining support based on orthogonal test method

In order to alleviate the dust pollution in the fully mechanized mining face, the novel negative pressure entrainment dust collector was optimized by the method of orthogonal experimental design and numerical simulation. The influences of nozzle distance, throat diameter and diffusion angle on the atomization efficiency of the proposed dust collector was investigated. The obtained results showed that the optimum ejection dust removal performance of the developed negative pressure entrainment dust collector was obtained for throat diameter 80 mm, throat distance 60 mm and diffusion angle 20 degrees. Under these conditions, air suction rate at the entrance of contraction section was 17.48 m3/min and the average droplet size and mass concentration were 62.99 μm and 0.034 kg/m3, respectively. Here, we have proposed a local closed atomization control dust removal technology for hydraulic support areas based on the optimized negative pressure entrainment dust collector. After the application of the developed system in 2307 fully mechanized mining face in Tangkou Coal Mine, the average total dust of measuring points was decreased from 337.90 to 49.53 mg/m3 and average exhaust dust was decreased from 271.80 to 41.40 mg/m3. The average dust removal rates of total dust and exhaled dust were 85.17% and 84.74% respectively, and dust removal efficiency of the proposed system was obviously confirmed.

Intelligent remote control technology for fully-mechanized roadheader of Tangkou Coal Mine

Intelligent remote control technology for fully-mechanized roadheader of Tangkou Coal Mine

An innovative approach to theoretical analysis of partitioned width & stability of strip pillar in strip mining

The strip mining method is preferred to the extraction of coal resources under surface buildings, water bodies and railways in China. Strip pillars with appropriate widths play a significant role in controlling stress distribution and surface subsidence. The strip mining activity at Tangkou coal mine in Eastern China is taken as the engineering background in the paper. In order to evaluate the general strip pillar design of mining area no. 430, an innovative analytical model is developed to determine the yield width and the elastic core width of the strip pillar under the stress superimposition effect in this paper. In the proposed model, the strip pillar is divided into the yield zone and the elastic core zone on the basis of the existing reasonable structural division of the strip pillar. Based on the Drucker-Prager criterion which considers the influence of the intermediate principal stress, the formulae of the partitioned width of the strip pillar are inferred. The yield width of the strip pillar with one-sided goaf is derived based on the limit equilibrium theory and the Drucker-Prager criterion. The yield width of the strip pillar with two-sided goafs is obtained based on the stress superimposition method. The elastic core width of the strip pillar is obtained by the semi-inverse method with the consideration of mine pressure and the application of the Drucker-Prager criterion. As a case study, the proposed model is used to determine the yield width and the elastic core width of the strip pillar at Tangkou coal mine in China. Comparing the obtained results with the in-situ measurement data, it can be concluded that the proposed analytical model is effective in calculating the yield width and the elastic core width of the strip pillar. In order to evaluate the effects of the parameters in the proposed model on the yield width of the strip pillar with one-sided goaf and the elastic core width of the strip pillar with two-sided goafs, a detailed sensitivity analysis is conducted based on the actual data at from Tangkou coal mine.

Surface Subsidence Control during Deep Backfill Coal Mining: A Case Study

Deep resource exploitation is imperative, but it is facing with more complicated mining environment and more dangerous mining disturbances to induce the potential catastrophe process. Solid backfill technology, which can control the strata movement and prevent potential hazards, has been used as the primary method in deep mining for surface subsidence control and ecosystem protection. In this study, taking backfill mining area no. 930 in the Tangkou coal mine as background, the probability integral model was adopted to predict the surface subsidence at different mining depths and filling ratios. The filling ratio was designed for deep mining based on the regression analysis of the predicted surface subsidence results. The study shows that the backfilling ratio at the Tangkou deep coal mining area should be controlled at a level greater than 82.5%, and the mining damage to the surface under this condition was analyzed. Furthermore, control strategies for deep backfill mining are proposed in which the backfill density can be enhanced by optimizing the tamping machine, material composition, and tamping process. Finally, the measurement of the backfill mass and surface subsidence showed that the actual filling ratio was controlled at 82.57%, which ensures adequate protection of the surface buildings during the mining process.

Coal fire prevention in large areas over long term with a composite inert gas—a case study in Tangkou coal mine, China

ABSTRACT In order to effectively control the serious spontaneous combustion of residual coal in large areas over long term, and reduce the cost of fire prevention process, ensure the safety of fire prevention process, we injected a composite inert gas (1:1 v/v CO2 and N2) into the goaf at the 5306 working face of the Tangkou coal mine. Thanks to its special properties, the composite inert gas overcame some shortcomings of using only N2 or CO2 as the inert gas and showed some unique features. Field test results at the 5306 working face showed that 9 days after the injection of the composite inert gas, the CO concentration rapidly decreased from 14.9 ppm to 0.1 ppm and from 4821 ppm to 21 ppm in the return airflow and in the corner of the return air at the working face, respectively. Meanwhile, the concentration of CO2 in the return airflow never exceeded 1500 ppm (Maximum allowable concentration) after the injection of composite inert gas into the goaf. Therefore, the composite inert gas, which is also cheaper than CO2, could effectively reduce fire risk in goaf over an extended time without compromising the safety of underground workers.

Research on Distribution Law of Advanced Abutment Pressure in Deep Soft Rock Working Face

In view of the characteristics of deep buried depth and weak rock strata in Tangkou coal mine, the method of combining RFPA numerical simulation and field measurement is used to study the peak position of the advanced abutment pressure and the influence range of the advanced abutment pressure in the fully mechanized caving face, fully mechanized mining face and hard rock face. According to the results, when other conditions are met, the influence range, peak position and coal wall damage depth of the advanced abutment pressure of the caving mining face are greater than those of the fully mechanized mining stope. When other conditions are certain, the two soft working faces show that the advanced abutment pressure has a wide influence range, a far peak position, a large depth of damage of the coal wall, a small peak of the advanced abutment pressure, and a small stress concentration coefficient.

Mechanism by Which Backfill Body Reduces Amount of Energy Released in Deep Coal Mining

Deep coal mining is unavoidable, and the complex mining environments and the increasing dangers associated with ultrahigh energy accumulation and release from mining disturbances renders it extremely difficult to maintain a safe and stable stope. Solid backfilling technology directly uses coal gangue and other solid wastes in the mining area to fill the gob after mining. Support from the backfill body can inhibit the movement of overlying rock strata and significantly alleviate the influence of mining. In this study, the correlations between the deformation of gangue filling material and the characteristics of energy dissipation were examined under lateral uniaxial compression. The strain energy density distributions of backfilling and caving mining methods were simulated using numerical modeling. The results showed that the strain energy density distribution of backfilling mining was less concentrated, and its peak value was lower than that of caving mining by 51.0%, indicating that backfilling could effectively reduce the amount of energy released from mining rocks. The dense backfill mining area of the No. 9301 face in Tangkou Coal Mine was used as a case study. Measures for controlling the backfill body compaction for reducing the amount of energy released from mining rocks were proposed. These measures include optimizing the support structure and filling material formula, controlling the preroof subsidence, and ensuring an appropriate number of tamping strokes. The monitoring results of the backfilling quality, surface subsidence, and microseismic energy of No. 9301 working face in Tangkou Coal Mine showed that when the backfill body filling ratio control value was 82.28%, the total number of microseisms and the amount of energy released from the mining working face were significantly lower compared to those of the caving method. This study demonstrated that the backfill body could effectively reduce the amount of energy released from mining rocks, thereby realizing management of mine earthquake and sustainable deep coal mining.

Determination of Long Horizontal Borehole Height in Roofs and Its Application to Gas Drainage

Accurately determining the height of the gas-guiding fracture zone in the overlying strata of the goaf is the key to find the height of the long horizontal borehole in the roof. In order to determine the height, in this study we chose the 6306 working face of Tangkou Coal Mine in China as a research example and used both the theoretical model and discrete element method (DEM) numerical simulation to find the height of the gas-guiding fracture zone and applied the height to drill a long horizontal borehole in the roof of the 6303 working face. Furthermore, the borehole was utilized to deep into the roof for coalbed methane drainage and the results were compared with conventional gas drainage measures from other aspects. The height of the gas-guiding fracture zone was found to be 48.57 m in theoretical model based on the bulk coefficient and the void ratio and to be 51.19 m in the DEM numerical simulation according to the temporal and spatial variation characteristics of porosity. Taking both the results of theoretical analysis and numerical simulation into consideration, we determined that gas-guiding fracture zone is 49.88 m high and applied it to drill a long horizontal borehole deep into the roof in the 6303 working face field. Compared with conventional gas drainage measures, we found that the long horizontal borehole has the high stability, high efficiency and strong adaptability for methane drainage.

Deep-hole water injection technology of strong impact tendency coal seam—a case study in Tangkou coal mine

The implementation of coal-seam water injection can change the physical and mechanical properties of coal, can improve the coal storage limit, prevent and control rock burst, prevent coal and gas outburst, and reduce dust concentration in underground operations. However, there are still many shortcomings such as the poor sealing effect and the lack of coal seam permeability. In order to study coal softening through water injection and its effect of reducing the coal’s impact tendency, we examine the impact tendency, coal seam injection, water injection additive, water injection hole sealing, and coal seam stress-relief effect of coal seam on LW5304 experimentally and through engineering application. The results show that this method can be used to reduce the coal’s impact tendency, if the samples are soaked. Triton X-100 additive can effectively reduce the polarity of water and the surface tension, while improving the coupling effect of water and coal and the wettability of coal. The “pure polyurethane + cement slurry + cement mortar” sealing process can be used to avoid water injection leaking. The water content of LW5304 coal seam is 3.2~4.2% after water injection, and the average increase of moisture content is 1~2.5%. In addition, the number of coal-stress early warning is reduced, and micro-seismic monitoring shows that the average energy is reduced as well. Therefore, water injection in coal seam is considered a good method for relieving stress.

Investigation lateral deformation and failure characteristics of strip coal pillar in deep mining

In deep mining, the lateral deformation of strip coal pillar appears to be a new characteristic. In order to study the lateral deformation of coal-mass, a monitoring method and monitoring instrument were designed to investigate the lateral deformation of strip coal pillar in Tangkou Coalmine with the mining depth of over 1000 m. Because of without influence of repeated mining, the bedding sandstone roof is easy to break and the angle between maximum horizontal stress and the roadway is small, the maximum lateral deformation is only about 287 mm lower than the other pillars in the same coalmine. In deep mining, the energy accumulation and release cause a discontinuous damage in the heterogeneous coal-mass, and the lateral deformation of coal pillar shows discontinuity, step and mutation characters. These coal-masses not only show a higher plasticity but also the high brittleness at the same time, and its burst tendency is more obvious. According to the monitoring results and theoretical calculations, the yield zone of the coal pillar width is determined as 15.6 m. The monitoring results presented through this study are of great significance to the stability analysis and design of coal pillar.