ABSTRACT
For sinking the Mol N° 2 shaft in Belgium (for EIG Praclay, a consortium representing SCK • CEN, the Belgian nuclear energy research center, and NIRAS, the Belgian institute for radioactive waste disposal) the freezing method combined with rigid and yielding outer lining systems was successfully used to sink the shaft through the waterbearing unstable strata into the top area of the Boom formation, a firm overconsolidated tertiary clay. The outer lining consists mainly of shotcrete, suitable for extremely deep temperatures, and where necessary, intermediate yielding layers. The design of the outer lining was accommodated during the sinking procedure to the actual freeze wall thicknesses and the measured convergency behaviour of the rock. In view of watertightness, the inner shaft lining consists of a steel reinforced concrete composite with asphalt backfill. The lining was premanufactured at surface in single rings. Only the horizontal welds were done underground.
