The Konrad mine is the first legally approved repository in Germany. The former iron ore mine in Salzgitter in northern Germany is currently being reconstructed to meet the requirements for the final disposal of low- and intermediate-level radioactive waste.
In the area of the bottom landing of shaft 2 at a depth of 850 m existing mine openings are being enlarged to ensure the needed infrastructure for the transshipment of waste containers from the pit cage to the transport vehicles. In detail a clear cross-section with a diameter of 10 m in the drift is required. Taking into account the supporting system and an additional allowance a cross-section with a diameter of more than 13 m needs to be excavated over a length of 60 m. The excavation is divided into three partial steps, the driving of the base, crown and bench.
The geology of the bedrock is characterized by layers of limestone and claystone, which partly shows a squeezing behavior, intersected by a set of discontinuities. Due to the complex geology and the large cross-section a support system consisting of a slotted lining with sliding anchors was chosen to allow the bedrock to converge. Once the convergence period is concluded and a bearing ring is formed within the rock mass the final lining is created with reinforced shotcrete.
In order to observe the actual behavior of the bedrock an extensive geotechnical measurement program is being carried out. The measurements taken are then evaluated against threshold values calculated via numerical forecast models. This paper presents the challenges of developing large cross sections in squeezing rock.
The Konrad mine (Fig. 1) is a former iron ore mine in Salzgitter in Northern Germany. The mine operated for 12 years from 1964 until 1976, when hauling became no longer profitable. The mine workings consist of six levels in depths of 800 m to 1300 m, which can be accessed through two mineshafts.