There are two common methods of salt mining--dry underground mining and solution mining. When dry mining (or the room-and-pillar method) is used, underground mining is usually confined to a single bed. Pillars are left to support the roof, as in the photo directly below.
Carey Salt Company mine, Hutchinson, Kansas, showing light and dark banding in the Hutchinson Salt (from Walters, 1978). Photograph courtesy of Underground Vaults and Storage, Inc.
The following illustrations refer to solution mining, where water is injected into a salt formation and brine is withdrawn. Because we cannot enter solution mines, sonar is used to estimate cavern dimensions. See sonar images of cavities or jugs at the Yaggy storage facility (which were formed by salt solution) under Gas Storage-Yaggy.
Sketch depicting brine well and cavity (after Lomenick, 1972)
Solution mining schematics (from Myers et al., 1972)
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