RD&D-Programme 2004 - SKB

• Methods exist for full-face drilling of the deposition holes. Such drilling of deposition holes
has been demonstrated at the Äspö HRL.
Based mainly on existing information and knowledge, selection and further development of
excavation methods, machinery and equipment can take place in parallel with the gathering of
design-basis data for construction and detailed characterization of the underground part of the
deep repository facility. Freedom of choice with regard to methods for excavation of deposition
tunnels and holes will remain even after deposition has begun.
Newfound knowledge since RD&D 2001
A new tunnel, The Apse tunnel, was built at the Äspö HRL at a depth of 450 metres during
the spring and summer of 2003, see Figure 10-1. The tunnel is about 70 metres long and was
excavated by drilling and cautious blasting.
The blast-damaged zone around the new tunnel has so far been preliminarily investigated in the
tunnel floor. The results of these investigations indicate that:
• Drilling procedure is of importance for the damaged zone.
• Modern alignment instruments on the drilling rig provide a satisfactory means for controlling
drilling precision and thereby indirectly also the blast-damaged zone.
• Of 13 cored boreholes in the tunnel floor, macroscopic fractures with a depth of about
10 centimetres were observed in 12 of the holes, and 30 centimetres in one of the holes.
• In three holes bored in the tunnel floor (diameter 1.75 metres), the picture from the cored
holes is confirmed as regards the depth of the fractures. The macroscopic fractures are
natural fractures sheared or opened by blasting and/or stress redistributions. Since the
induced fractures are only partially plane-parallel with the tunnel contour, the extent of
the damaged zone appears to be heterogeneous.
Figure 10-1. The new Apse tunnel at the Äspö HRL excavated during the summer of 2003 by
controlled drill-and-blast.
114 RD&D-Programme 2004