Civil Engineering Reference
In-Depth Information
Figure 4.8
Typical examples of
the arrangement of
rock bolts/dowels
within tunnels (after
Woodward 2005)
Zone stressed
Reinforced
arch in rock
Rock reinforcement
Shotcrete
lining
Rock reinforcement
Sliding
blocks
Buckling
•
larger spans in fractured rock will require primary, secondary and even
tertiary reinforcement.
(Note: dowels and bolts are also applicable for soft ground.)
Figure 4.9 shows an anchor installation associated with sprayed concrete
lining in the Heidkopf Tunnel (HKT), Göttingen, Germany. This tunnel
was constructed through sandstone and limestone and consisted of a twin
tube, 2-lane road tunnel, 1720 m long (each tube) and a cross section of
88-129 m
2
(approx. width 12 m). Figure 4.10 shows the load testing of
an anchor as part of the construction of the Lainzer Tunnel LT31, Vienna
(see section 8.3 for further details of this tunnel).
4.2.5 Forepoling
This technique is aimed at limiting the decompression in the crown im-
mediately ahead of the face (ITA/AITES 2007). Longitudinal bars (dowels)
or steel plates (forepoling plates) are installed ahead of the tunnel from
the periphery of the face, typically over the upper third or quarter of the
