TBM Tunneling - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 704

Ground conditions
Figure 21.43 shows the geotechnical longitudinal section of the tunnels San Simone
and Collecervo. The latter has an overburden of up to 345 m. Both tunnels are located
in the so-called Flysch H1, which consists of an alternating sequence of sandstones and
marlstones with intercalations of clay. It is horizontally bedded and vertically joint-
ed and tends to weathering at the ground surface (Fig. 21.44). The rock mechanical
parameters given by the consultant vary with overburden height and location. In the
area of fault zones and in completely undisturbed areas deformability and strength are
significantly different (Fig. 21.43).
Figure 21.43 Tunnels Collecervo and San Simone, longitudinal section (Wittke et al. 2006)
The steeply dipping fault zones occur at regular intervals and strike predominantly with
acute angles to the tunnel. According to the results of site investigations, the fault zones
are composed of an alternating sequence of plastic clays, a re-cemented material, and
sound rock mass.
The Collecervo tunnel is completely located underneath the groundwater table. The
design water pressure was specified as 6 bar (Fig. 21.43).
The Caighei and Gorleri tunnels are located in similar ground. The Bardellini tunnel
over 60% of its length also crosses the Flysch H1. The remaining tunnel sections are lo-
cated in the Flysch H2 as well as in the so-called Pog-Zone. In the Flysch H2, mudstone
and siltstone layers dominate. The Pog-Zone consists of highly compacted clayey silty
sand with gravels and partly with larger cobbles which are firmly bound into the matrix.
As a consequence, the rock mass parameters all-in-all are even worse.