Geotechnische Bedingungen in der Schachtanlage Konrad - Auffahrung von Strecken und Kammern in druckhaftem Gebirge

Geotechnical conditions at the Konrad mine - Excavation of drifts and rooms in squeezing rock.

The Konrad mine is a former iron ore mine near Salzgitter in Germany. The mine will be rebuilt in the next few years into a repository for low and intermediate level radioactive waste. During this conversion drifts and rooms for operating the repository are extended and newly constructed at shaft 2 on the 2nd floor level (depth 850 m). The planned useful life for the rooms is 40 years. In this period, maintenance-free operation has to be ensured. The bedrock is characterized by complex geology. In addition, the mudstone layers show partly a squeezing behavior. For the proof of stability and usability, the observation method is applied. Therefor numerical forecast models are necessary, which can reproduce the tree dimensional stress redistribution and convergences in the rock mass. These numerical calculations are flanked by an extensive geotechnical measurement program in order to detect the real behavior of the bedrock. The underground support system consists of a slotted lining with sliding anchors in the areas where squeezing rock is present. This allows converging of the bedrock. During the convergence period a bearing ring is formed within the rock mass. Afterwards the final lining is created in reinforced shotcrete. One major issue is the assessment of the convergence period taking into account the numerical forecast model and the measurement program.