Tome Architecture and management of a geological repository - Andra

6 – C waste repository zone6.6.3 Construction of disposal boreholesDisposal boreholes are bored using a micro-tunnel boring machine modified to operate vertically.Construction is based on the demonstrations carried out by SKB in the Äspö laboratory to excavate adisposal borehole for spent fuel.Figure 6.6.2Disposal borehole in the Äspö laboratory (source: SKB)This method has been adopted since it is suited for constructing small diameter vertical shafts fromsmall section drifts and because it causes very slight damage at the excavation wall.The drill head thrust system and the removal of broken muck (Figure 6.6.3) are the main areasmodified to enable the micro-tunnel boring machine to operate vertically. The thrust is power-assistedby four independent hydraulic jacks. Steel casings, approximately the same height as the jack stroke,transmit the thrust to the drill head. By adding steel casings, boring is carried out. The jacks leanagainst the drift arch [50].The broken muck is raised by reverse air circulation in a suction column installed in the body of themicro-tunnel boring machine. Suction is controlled by a vacuum pump installed in the handling drift.A filtration system removes dust from the air and collects the broken muck into a closed bin.Improvements are planned so that boreholes can be excavated deeper than the Äspö laboratory ones.As well, a pilot hole is also envisaged to steer the drill head.Dossier 2005 granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY184/228