RD&D-Programme 2004 - SKB

The methods deemed possible for excavation of the deposition holes today are: full-face boring
with a shaft boring machine (SBM) or drilling of a pilot hole followed by reaming with a larger
drill bit as shown in Figure 10-2 (a and b). Core drilling and percussion drilling have been
discussed for making deposition holes but judged not to be competitive alternatives.
Full-scale full-face boring of deposition holes has been demonstrated at the Äspö HRL, where a
total of 17 deposition holes have been drilled with SBM. Posiva has made two full-sized deposition
holes by pilot hole drilling followed by reaming to full diameter in one step /10-1/.
A variant of reaming is called raise boring, and this technique is being discussed for excavation
of deposition tunnels and other chambers. The technique is normally used for excavating shafts
between two chambers in a mine. Figure 10-2 describes the principle of the technique. First a
pilot hole (a) is drilled and then a drill bit is attached to the drill string and a shaft or tunnel is
created by pulling and rotating the bit (back reaming) (c). Shafts with a diameter of about six
metres can be created by means of back reaming. If larger diameters are desired, reaming can be
done in stages by changing after the first stage to a bit with a larger diameter. It is also possible
to push and rotate the bit (down reaming) instead of pulling it so that a shaft or tunnel is created.
Horizontal deposition of the canisters is currently being studied by SKB and Posiva in cooperation
and a demonstration of the KBS-3H method is planned at the Äspö HRL. In the KBS-3H
method, the canisters with buffer are deposited in a perforated steel container one after the other
in long deposition drifts 1.85 metres in diameter, see section 10.7. The deposition drifts that
will be drilled for the demonstration must be straight and must meet narrow tolerances on e.g.
diameter. A drilling rig based on water hammer technology was built and tested in the autumn
of 2003. Alternative methods exist for boring horizontal deposition drifts for KBS-3H, and one
alternative that is being discussed is drilling of a pilot hole followed by down or back reaming
to the desired diameter of the deposition drifts.
a) Drilling of pilot hole b) Boring by pushing the bit c) Boring by pulling the bit
from one side of a chamber between two chambers/
(back reaming)
tunnels (back reaming)
Figure 10-2. Sequence of operations in down and back reaming.
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