Optimization of the Roof Protection Layer for Remnant Pillars via the Reengineering of the Mechanical Environment of an Overlying Artificial Roof

When remnant roof pillars are recovered under a loose tailings (waste rock) filling body, sufficient thickness should be reserved for the roof protection layer, which prevents loose tailing sands from leaking and blocking the workspace. Therefore, reducing the size of the roof protection layer while ensuring safe production is of great theoretical and practical significance for achieving the sustainable development of mines. In view of the aforementioned issues, we proposed mechanical environment reengineering technology for overlying an artificial false roof when recovering roof pillars to enhance the stability of an overlying filling body by integrating the solidified filling false roof, prestressed long anchor bolts, hanging wall, and footwall into a whole part. On this basis, the mean distribution load acting on the roof protection layer has been divided into the loose body zone and consolidation zone, respectively. The overlying roof protection layer was deduced based on Janssen’s bulk pressure theory and elastic mechanics theory, and the factors affecting the mean distribution load of the consolidation zone were also analyzed. The results show that after the mechanical environment reconstruction technology of the overlying artificial false roof is adopted, the strength of the filling body increases significantly after consolidation, and the shear resistance provided by the bolt (cable) reduces the uniform load value of the roof protection layer. The use of this technology ensures the safety of mining and reduces the thickness of the roof protection layer. Taking a lead–zinc mine in Inner Mongolia as a research object, the calculated size of the roof protection layer under the existing technology was reduced by 0.7 m compared with the original method, which significantly improved the resource recovery rate of remnant roof pillars. Numerical simulation and in situ monitoring results indicate that the displacement value and plastic zone of the roof protection layer were controlled within a small range, thereby verifying the reasonableness of the reduced size of the roof protection layer. This study greatly reduces the thickness of the roof protection layer and improves the benefit of the mine. The research results can provide a theoretical basis and technical guidance for the recovery of residual ore resources in similar mines.