Problems Solved During Shaft-Sinking into Gorleben Salt Dome

摘要

Anisotropic stress accumulated above the salt dome at Gorleben, north central Germany, through large loading during the ice ages. Its retention in clay formations rendered the drilling of the freeze boreholes for the proposed nuclear waste repository more difficult. It led to the failure of the preliminary shaft lining and endangered the whole project through potential fractures of the freeze pipes. Further problems arose from brine flows in the salt deposit. The penetration of brines into the salt formation followed cracks which occurred laterally and below the frost body and were caused by the low-temperature freezing of the salt rock. The numerous injection techniques used in the sealing operation are described. In future undertakings of this kind potential stresses in the rock formations should be investigated thoroughly and taken into account in the planning process. For future projects it is recommended that freezing be confined to unstable formations of the water-bearing overburden, the freezing of stable rock strata be avoided and injection be implemented immediately when water and brine flows are encountered.