Investigation into the Long-Term Stability of Carnallite Pillars Considering Creep Influence

In subterranean potash mines utilizing the room-and-pillar mining method, maintaining the long-term stability of carnallite pillars is imperative for the safety and ongoing viability of operations. This study undertakes uniaxial compression creep tests on carnallite samples sourced from the Dongtai Potash and Magnesium Salt Mine in Laos. The durability of carnallite pillars is evaluated using an advanced Burgers creep model combined with Flac3D numerical simulations. Results indicate that the creep strength of carnallite is approximately 60%–70% of its immediate strength, demonstrating significant creep behavior. The refined Burgers model provides an accurate representation of the carnallite’s creep characteristics. Post-excavation, the internal compressive stress within the pillars progressively increases, registering an approximate rise of 1 MPa, and stabilizes under pressure after one year. After three years of continuous observation through creep tests and Flac3D simulations, the maximum deformations detected in the roof and floor of the mining house, as well as the adjacent rock masses, were 60mm and 20mm, respectively, indicating minimal overall deformation. The width of the plastic zone within the pillars exhibits time-dependent growth, with rapid expansion occurring in the internal plastic zone and a significant deformation rate within the first six months post-excavation. To ensure the long-term stability of the mining pillars and voids, it is recommended that backfilling operations be conducted within six months following the excavation.