Bottom of the hole
Starting at the bottom of the hole, the drill borer drills gradually through the ca. 20-m thick wall up to the emplacement chamber.
Prior to the start of drilling a steel pipe is concreted four metres into the wall, the so-called stand-pipe. Upon this the preventer is placed. That is a protection device which prevents that hazardous substances are released in an uncontrolled manner during the drilling process.