A Recovery Method of Large-Scale Isolated Stopes Supported by Pre-Stressed Expandable Props in Deep Resource Mining: A Case Study

Abstract

This study proposes a recovery method for large-scale isolated stopes supported by pre-stressed expandable props in deep resource mining. Using a large isolated stope of the Danyin gold mine in Dandong, China as the case study, the field-tested isolated stope stability is analysed by numerical simulation and field monitoring. The numerical simulation results show that, compared to unsupported, the vertical deformation could be effectively limited by the expandable props with a maximum value of 39 mm and plastic failure of the stope roof. Field industrial test shows that, the load on the expandable props and the roof deformation increase during the mining of the isolated stope. Especially when the top layer of the isolated stope is completely excavated to penetrate the entire goaf, the increment of the roof stress and deformation is significant. After the isolated stope is mined, the closer the location of the expandable prop is to the lower boundary of the isolated stope or the central axis of the entire goaf, the larger the load on the expandable prop will be; here, the maximum force on the expandable props is 1864 kN. The roof vertical and tangential deformations in the upper portion of the isolated stope are larger than those of the lower portion, resulting in dislocation and slippage of expandable props. The maximum roof vertical deformation of the isolated stope is about 21.5 mm, compared with the numerical simulation, the deviation is only 0.5 mm. The stress concentration area shifts from the isolated stope to the deeper portion of the orebody, inducing the roof collapse and the roadway barriers spalling. Although the adjacent goaf near the isolated stope collapses, the expandable props and the isolated stope are visually stable and safe except for the cracked pumice in the bolt nets. In the field of economic benefits, the large-scale isolated stope can achieve a profit of US$16.4 million. The conclusions of this study can provide a theoretical and technical basis for safe mining of large-scale isolated stopes, improving the ore recovery rate and realizing the cleaner production of ore resources.

Keywords: Isolated stope, Expandable prop, Stope stability, Roof deformation, Bearing load