Influences of filling abandoned salt caverns with alkali wastes on surface subsidence

Abandoned salt caverns, particularly those that allow free draining of brine, are serious potential causes of subsidence above salt mines. Filling such caverns with alkali wastes may eliminate these troubles. Based on the filling project in Jingshen salt mine of China, the influences of filling abandoned free-draining salt caverns with alkali wastes on surface subsidence are discussed. The deposition characteristics of alkali waste slurry were studied by laboratory simulation tests. It is found that alkali waste slurry has good flowability during injection into a cavern. Based on the results of compression tests under drained conditions, a distribution model of void ratio of sediment is established. A method for determining the ultimate subsidence value is presented based on the distribution model. The relationship of average effective stress and void ratio of the sediment is also established. Further, a method for predicting development process of surface subsidence is presented. Finally, the specific application procedure of the prediction methods is discussed. According to the research results, filling free-draining salt caverns with alkali wastes can restrain surface subsidence successfully. The reasons can be summed up as: Volume convergence of salt caverns slows down after the caverns are filled owing to the supporting effect of alkali wastes on the rock surrounding caverns, and then, subsidence slows down and decreases, and finally, subsidence stops when the fill material is compacted to its compressed limit.