Tunneling in Swelling Rock - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 765

The excavation of the tunnel was carried out by means of blasting. To avoid loosening
of the rock mass and access of moisture into the area near the tunnel contour, a 0.5 -
1.0 m thick rock zone around the tunnel contour was not blasted but removed with a
road header in a separate working step (Fig. 23.16). During excavation, the rock mass
was carefully protected from water. The excavation with the road header was also
done dry. Because of intense dust development this sometimes led to considerable
interference of the excavation works. Immediately after excavation, the rock surface
was always sealed with just a 3 - 5 cm thick shotcrete layer (Wittke 1978, Wittke &
Pierau 1979).
Figure 23.16 Use of a road header (Wittke 1978)
Until the installation of the internal lining, which took place one year after excavation
of the tunnel, the tunnel was held stable with this sealing. Thus, as predicted from the
results of the stability analyses, the tunnel proved to be stable without any statically
effective support (Fig. 23.17).