Apart from the theoretical and technical laboratory investigations for the dimensioning of serviceable and stable caverns, extensive in-situ measurements are necessary during and after cavern establishment in order to verify the calculated bearing behaviour predictions. As the salt caverns are not accessible, measurement techniques otherwise usual in rock cavity constructions cannot be applied. At present the measurements are restricted to the echometric assessment of the cavern form as well as the detection of well head pressures, discharge rates and temperature distribution in the cavern axis. Based on the existing measurement results from a cavern project the problem of their evaluation and interpretation is illustrated.
For energy and environmental protection policy reasons cavity construction in the salt rock has won increasing significance worldwide over the past years, as experience has shown that these cavities are ideally suited for the storage of liquid and gaseous energy carriers such as natural oil or gas. According to a survey by RUh1 (1978), in the North West of the Federal Republic of Germany alone a total of 95 caverns for crude oil, middle distillates and heavy fuel oil as well as 14 caverns for natural gas and 2 for compressed air have been completed and put into operation by the end of 1977. The development in this field is recognizable last but not least by the almost erratic rise in the number of publications dealing with salt cavern construction research topics such as e.g. the material behaviour of salt rocks or the theoretic investigation of cavern bearing behaviour. (Anderson (1975), Fossum (1977), Thoms/Martinez (1978), Langer/Kern (1979), Langer (1979), Lux/Rokahr (1980)).
Closely connected with the growing· requirement for cavities in salt rocks, the multiplicity of uses and the resultant very varied stress conditions is the question regarding their dimensioning, i.e. processes and criteria which lead to the design of serviceable and stable caverns. Alongside fundamental geological studies, technical laboratory investigations on core material and theoretic simulations of possible boundary conditions in the cavern bearing behaviour, comparisons between theoretic prognoses and actual behaviour in particular are of fundamental importance as only in this way can the evidential strength allocated to the theoretic models be ascertained. Unfortunately only few measurement results are available to date which can be referred to for such a comparison.
As the caverns created by solution-mining are not accessible and are located at very great depths the measurements procedures otherwise usual in rock cavity construction cannot be applied. A direct continuous observation of individual measuring points in the immediate vicinity of the caverns during the operation phase is at present not yet possible so that conclusions regarding the bearing behaviour of the cavern can only be drawn indirectly with the aid of results of surface measurements of wellhead pressures, discharge rates or ground level subsidences. Some of the difficulties occurring during evaluation of such measurements and statements for interpretation with theoretic simulation models shall be discussed in the following. In doing so reference is made to measuring results from a cavern project in North Germany.