Ground stability analysis and control of large-scale isolated stopes by a combined support of reinforced concretes and expandable props

Abstract

In this study, a recovery method for large-scale isolated stopes is proposed by building a combined support construction of the reinforced concrete and pre-stressed expandable pillars in deep resource mining. Using a large isolated stope of the Danyin gold mine in Dandong, China as the case study, the isolated stope roof stability is analysed by numerical simulation and field monitoring during the isolated stope is mined. The results by numerical simulation show that, compared to unsupported, the vertical deformation with a maximum value of 39 mm and the plastic failure of the stope roof can be effectively limited supported by the expandable props. Field industrial test shows that, the bearing load on 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 deformation and the release of the roof stress are significant. After the isolated stope is completely 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 bearing load on the expandable prop will be; here, the maximum force on 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 the dislocation and slippage of expandable props. The maximum vertical deformation of the isolated stope roof is about 21.5 mm, and there is only a deviation of 0.5 mm with the numerical simulation. The stress concentration area shifts from the isolated stope roof to the deeper unmined portion of the orebody, inducing the roadway 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.