Cavities in salt for storage and final disposal — Geomechanical aspects

Caverns in salt domes and bedded salt lagers have been used successfully as storage vessels for hydrocarbons and gas storage all over the world. Based upon this general experience, the theoretical prediction of the rock mechanical behavior of these caverns has been developed to the present state of the art. As experience shows, the historical practice of disposing of hazardous waste in landfills has been determined to be detrimental to human health and the environment. The permanent containment of the post treatment hazardous residual constituents in repositories, constructed in geologically secure subsurface formations, is an attractive alternative. Extensive investigation and research has identified salt diapirs or domes as well as bedded salt layers as the prime candidate host formations for the perpetual containment repositories. This paper considers first the state of the art in the field of storage cavern design. This reflection includes a geomechanical design concept, characteristic material parameters, constitutive laws as well as the theoretical prognosis and the field data of an in situ test with a storage cavern Based on this experience secondly some effects of cavern behavior over time based upon the mechanical properties of the salt under conditions of both liquid and solid hazardous waste entombment are investigated. Mathemaaical modeling, based upon theoretical assumptions and actual in-situ experience in salt, is used to predict the performance of the cavern and its contents with respect to established rock mechanics principles. Movement of the waste, resulting from waste densities at odds with the lithostatic pressure gradients, is discussed and graphically depicted. The need for the containment of hazardous constituents over eons of time is considered.