A numerical design framework for unloading excavations in deep potash mining

The stability of deep underground structures in potash mining is challenged by significant rock pressure and the inhomogeneous structure of the enclosing rock mass, often requiring innovative support strategies beyond conventional methods. This study investigates the deliberate use of unloading excavations as a safety measure for underground structures in potash salt rock masses at depths ranging from 300 to 1200 m. Through an extensive series of finite element method (FEM) simulations incorporating an original complex limit state criterion, the effectiveness of this approach is evaluated by comparing the extent of limit state zones across the investigated depth range. The FEM model was indirectly validated against long-term field deformation data from a single mining excavation at the Starobin potash deposit, demonstrating its ability to capture the displacement field over a one-year period. Numerical results demonstrate that the strategic placement of unloading excavations can reduce the computed size of limit state zones by 7% to over 90% across the studied scenarios. For the conditions of the Starobin deposit, the analysis suggests design parameters including a 3-meter diameter for the unloading excavation and a placement distance of 1.5-7 m from the main excavation, with a distance of 5-6 m being the most significant in reducing limit state zones. The findings provide initial approximations and preliminary design guidelines, indicating that this technique can contribute to enhancing the stability of deep geotechnical structures in potash mining, while also pointing to its potential relevance for other geotechnical projects.