Rock salt is particular impermeable to gases and liquids. The solution-mining method provides the means for the creation of large storage capacities at economic costs. The geotechnical behaviour of rock salt is well-known with sufficient details for dimensioning purposes. Due to its favourable geomechanical properties, halite remains stable over long periods of time without support.
However safety analysis has to be carried out in each case based on specific data. Such an analysis comprises engineering geological study of the site, laboratory and in-situ measurements. Model calculations are essential.
The study of uncertainties is fundamental part of the confidence building. The uncertainty of parameters (geometry, material behaviour, initial conditions, loading) given in a validated model can be expressed by a probability density function, but the model uncertainty is not a stochastic resp. probabilistic attribute. It can be described as a lack of dependability of a model to predict structural response assuming precisely defined parameters, Therefore the objective of model validation exercise must be the demonstration that a model is sufficiently accurate to predict structural response or migration of toxic particles by knowing the logic of idealization or justification of simplification (conservatism).
1. USE OF THE SOLUTION-MINED CAVERNS IN SALT FOR STORAGE AND DISPOSAL PURPOSES.
Salt deposits are increasingly being used throughout the world as a source of minerals (mining), for underground storage (cavern construction) and as repositories for various toxic wastes (Fig. 1). In earlier times these deposits were valued only for the salt reserves that they contained.
Various production proposes to recover salt have been recorded throughout ancient history. The first reported use of drilling to obtain salt brine was in China nearly 2,200 years ago. Brine recovered from wells drilled more than 1,000 meters deep flowed under artesian pressure to the surface, where the brine was boiled in kettles to evaporate the water to obtain the dry salt. One of the first documented uses of solar evaporation techniques was by the Mayan civilisation of Central America that introduced salt from coastal salt flats and inland brine springs more than 2,000 years ago. Other evidence indicates that salt probably was first produced about 1,000 B.C. in Yucatan. Rock salt mining in Europe was known to have been done as early as the late Bronze Age, about 1,400 B.C. The simple process of "salt boiling" evolved into a more sophisticated technique in 1887 through the use of a single-effect vacuum evaporator. This was the forerunner of the modern multiple-effect vacuum pan process. The four types of recovery methods - brine, solar, rock, and vacuum pan - yielded 9.3 million tons of salt worldwide in 1890 whereas world output reached about 190 million tons in 1990 (KOSTICK 1993).