Purpose. On the basis of analysis and assessment of geological conditions, technological parameters and support methods of a longwall, the author has pointed out the causes and rules of the phenomenon of face spall and roof falling in fully mechanized longwall. From there, the author proposes some solutions to prevent this phenomenon to ensure the safety of the longwall. Methods. The statistical, survey and analysis methods of actual field data are used to achieve research results. Findings. The results of applying solutions to prevent the phenomenon of face spall and roof falling are relatively good. There are some effective solutions such as the technique of force-pumping chemicals directly into the coal seam to increase the connection among the coal masses, the solution of force-pumping water into the seam combined with enhanced support at the place of face spall and roof falling on a small scale. Originality. There are many reasons and factors that cause the phenomenon of face spall and roof falling in the longwalls. In the present paper, the author focuses on 5 main causes and factors ruling face spall and roof falling in longwalls. On that basis, the author proposes 5 solutions that can be applied to prevent the face spall and roof falling in geological conditions of longwalls in Quang Ninh coalfield, Vietnam. Practical implications. The research results presented in the article will help mines be proactive in production. These technical solutions, after being applied in actual production, allowed to achieve quite good results, and effectively handled the phenomenon of face spall and roof falling in the longwall according to each specific geological condition. Thus, it is possible to develop technical and technological solutions for troubleshooting in fully mechanized longwall at some current underground mines of Quang Ninh coalfield, Vietnam.
Purpose. Tunneling in the ground changes the initial equilibrium stress state of the rock, which is also the cause of displacement and deformation of the surrounding rock mass. To determine the impact of tunneling on surface construction works in order to ensure the safety of surface works by analyzing the displacements and deformations of the rock mass during tunneling in the IIsection of Seam 14 at Ha Lam Coal Mine. Methodology. To achieve the research results, actual field survey methods, data analysis and numerical modeling, as well as combined blasting vibration methods are used. Findings. After analyzing the numerical modeling results, an area has been identified in the II section of Seam 14 of the Ha Lam Coal Mine that affects the surface construction works and is located within a radius of about 20 m from the portal of two inclined shafts. The results of blasting vibrations are calculated on the basis of the passport of blasting operations in tunnels. Thus, the affected area has been identified within a radius of 30.5m. However, at a distance of 30.5 m, surface construction works are not in the area of influence. Originality. On the basis of FLAC software, the authors have developed a simulation model for tunneling, thereby analyzing and describing the best state of deformation and displacement of the surrounding rock mass. In this study, a numerical modeling method is applied to simulate the driving order for each tunnel, which is consistent with the actual production of underground mines. Based on the passport of drilling and blasting operations in tunnels, the authors calculated the impact of blasting vibrations on surface construction works. After that, the authors assessed and identified the affected area with the required degree of reliability. Practical value. The research results are used as a basis for implementation in actual production at Ha Lam Coal Mine. On the basis of analysis of the surrounding rock mass displacements and deformations, when tunneling in the II section of Seam 14 at Ha Lam Coal Mine, the affected area of the surface construction works has been determined. This is also the basis for Ha Lam Coal Mine when planning construction works on the site outside the determined affected areas to ensure the safety of such works.
Purpose. Coal mining activities by underground mining method will disrupt the equilibrium of the surrounding rock mass. In underground mining, determining the influence zone of exploiting the longwall on the topographic surface is extremely important.Through analyzing the displacement and deformation of the rock mass when exploiting the longwall 21103 in Seam 11 at Nui Beo Coal Mine, the influence is to be determined of exploiting this longwall on the topographic surface in order to forecast the boundary of the influence zone that may affect the surface works, ensuring the safety of such works. Methodology. To achieve the research results, actual field survey methods, data analysis and numerical modeling methods are used in this article. Findings. Analysis of the results from the numerical model determined that the total height of the collapsed and cracked area when exploiting the longwall 21103 in Seam 11 is about 85 m. The subsidence to the ground is about 10 cm from the center of the subsidence area. The analysis results from the numerical model also show that the roof collapse angle is 69°, thereby determining the area of influence on the topographic surface in the range of 55 m. Results on the cross-sections show that the boundary of the influence of mining on the topographic surface is the closest section 6–6, which is about 12 m. The stability time of the collapsed rock mass is determined to be about 5 months. Originality. On the basis of UDEC (Universal Distinct Element Code) software, the authors have developed a simulation model for the mining process of the longwall 21103 in Seam 11. Analysis of the results from the model has shown the state of displacement and deformation of the surrounding rock mass. In this study, the numerical modeling method is applied to simulate the displacement of the longwall, which is consistent with the actual production of the underground mine. This enabled the authors to assess and identify the affected area with the required degree of reliability. Practical value. The research results of the paper are used as a basis for implementation in actual production at Nui Beo Coal Mine. On the basis of the analysis of the surrounding rock mass displacements and deformations, when exploiting the longwall 21103 in Seam 11 at Nui Beo Coal Mine, the affected boundary of the topographic surface has been determined. At the same time, the stability time of the collapsed rock mass is also calculated. So, this is also the basis for Nui Beo Coal Mine to plan construction works on the site outside the determined affected areas to ensure the safety of such works.
Purpose. Nowadays, in Quang Ninh coalfield, the mining activity in quarries is increasing. For this purpose, mine roadways are dug and supported. After the mine roadways are dug, they are mainly supported by steel arches. Statistics in fact show that about 85 % of the roadway support structure at the underground coal mines in Quang Ninh are supported by the steel arch support made of SVP profile. The purpose of the study is to calculate and determine a reasonable steel support distance for the roadways located under the open-pit mine to ensure their stability and the safety of exploitation. Methodology. In this study, the numerical simulation method was used. On the basis of Phase2 software and geological conditions of the mine, the authors established a simulation model to determine the pressure acting on the roadway and select a reasonable support distance. Findings. The study considered different steel arch support structure distance following the structure of the rock mass under the 790 open-pit area at the Mong Duong Coal Mine, the internal forces in SVP steel arch support structure distance were also studied for one-lane railway and two-lane railways roadway. From the results of internal forces in the steel support structure, a reasonable SVP-22 steel arch distance was selected, which is 0.7 m for the one-lane railway roadway, as well as SVP-27, which is 0.7 m for the two-lane railway roadway. Originality. Using Phase2 software, the authors created a simulation model of the roadways in Seam L7 located on the West side of Mong Duong Coal Mine, which allowed analyzing and describing the condition of the surrounding rock mass. This study utilized a numerical modeling approach to simulate and establish the bending moment and axial force of both single and double lane railway roadways, across a range of support distances. Based on the results of pressure calculation for the roadways, the authors have selected a reasonable support distance for each corresponding roadway. Practical value. The findings of the study serve as the foundation for the practical application of production methods at the Mong Duong Coal Mine. On the basis of calculating the pressure acting on the roadways at the Seam L7 in the West Side under the 790 open-pit area, the distance of steel arch support was determined, from which the roadway support plan has been developed. This research result will also serve as a basis for other mines with similar geological conditions in Quang Ninh coalfield to consider and apply.
Purpose. It is important to conduct a study to identify the displacement zone caused by mining operations. By numerical modeling the process of mining the longwall 31104 in Seam 11 at the Nui Beo Coal Mine, Vietnam, the authors have deter-mined the total height of the rock mass displacement zone and the boundary of the affected area on the topographic surface. Methods. In this study, the authors use a numerical modeling method. The models are developed based on the UDEC (Universal Distinct Element Code) software. In addition, field survey methods and statistical analysis methods are used. Findings. Based on the analysis of the numerical modeling results, it has been determined that the total height of the displacement zone, when exploiting the longwall 31104 in Seam 11, is about 63 m. The analysis of the numerical modeling results also shows that the roof collapse angle is 52°, which determines the area of influence on the topographic surface in the range of 160 m. Originality. Based on the UDEC software, the authors have developed a simulation model for the mining process of the longwall 31104 in Seam 11. Analysis of the model results has shown the state of the displacement zone of the surrounding rock mass. In this study, the numerical modeling method is applied to simulate the longwall displacement zone, which is consistent with the actual production of the underground mine. Practical implications. Based on the analysis of the surrounding rock mass displacements zone, when exploiting the longwall 31104 in Seam 11 at the Nui Beo Coal Mine, the affected boundary on the topographic surface has been determined. At the same time, the height of the rock mass displacement zone has also been calculated. Thus, the research results can be used as a basis for implementation in actual production at the Nui Beo Coal Mine.
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