Collapse mechanism of the overlying strata above a salt cavern by solution mining with double-well convection

In solution mining of salt formations, unreasonable salt cavities formed may lead to surface collapse hazards. In this paper, a mathematical model was proposed to analyze the collapse mechanism of the overlying strata above a salt cavern induced by solution mining with double-well convection. In the proposed model, the collapses of the overlying strata were supposed to occur layer by layer, and a thin plate with four edges clamped was introduced to calculate the critical collapse span of each layer. The limit breaking distance of the thin plate can be solved by setting the corresponding surrounding condition. According to the solution, the limit breaking distance is related to the dimensions, the mechanical properties of the rock, the buried depth, and the force status. For the convenience of calculation, a span criterion was introduced to distinguish the limit breaking distance. To keep the immediate roof more stable, the span criterion should be larger. As a case study, the collapse incidents at Dongxing Salt Mine were analyzed by the proposed model, and the collapses were verified to be inevitable under its mining and geological conditions. Discussions were finally carried out to study the influences of the thickness of the immediate roof, tension strength, Poisson ratio, and buried depth on the collapses. Above all, the collapses will occur more easily with the decrease of the thickness, tension strength, and Poisson ratio of each stratum. Especially, the collapse depth will not increase linearly with the buried depth, because of the bulking effect of the overlying strata.