Influence of underground mining activities on the topographic surface, case study of Nui Beo Coal Mine (Vietnam)

Abstract

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.