Squeezing Rock - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 96

a length of a few meters are only conditionally effective. On the other hand, fully solid-
ified anchors of greater lengths and with fixed heads bear the risk of overstressing and
breaking off in the case of large displacements. Fig. 4.6, as an example, shows a yielding
anchor in form of an injection drill bolt with sliding head.
Figure 4.6 Yielding anchor (Minova Carbotech, WIBOREX 30/11, G32)
The installation of a slotted shotcrete membrane is frequently combined with the
use of yielding steel sets with sliding connections that transfer the thrust via fric-
tion. The axial force in the lining is then controlled by the frictional resistance of
the connections that must allow predetermined radial displacements of the tunnel's
contour to take place. In the past, yielding steel sets with top hat section, TH sec-
tion and H section were used (Fröhlich 1948, Wittke et al. 2005, Kovari et al. 2006,
Anagnostou & Cantieni 2007). As an example, Fig. 4.7 shows a yielding steel set
with top hat section.