CROSS CONNECTIONS - The Westerschelde Tunnel: Approaching Limits - page 200

Fig. 13.16
Application of an outer
lining of shotcrete
formwork, the final 0.4 metres thick reinforced concrete inner lining of
the cross connection was cast within the excavation. After this wall had
hardened, the freezing process was stopped completely. The behaviour
of the thawing frozen soil and the associated reduction of loads was only
monitored at the first two cross connections, but did not cause any problems
elsewhere.
Experiences
Necessity for insulation and cooling of tunnel tubes
The tunnel boring machine's electrical and hydraulic generators, the diesel
locomotives for the supply and discharge of materials, equipment and per-
sonnel and all other apparatus present in the tunnel, generated a great deal
of heat in the tunnel. Despite intensive ventilation, temperatures sometimes
measured over 25 °C in the tunnel. The result was that the lining also
warmed up, and therefore also the ground water which had to be frozen
on the outside of the tunnel at the location of the cross connection under
construction.
Active cooling
Originally, only a 100 mm thick insulation layer was fitted onto the lining
in the westerly tube. In the easterly tube the freezing pipes were fed through
the segments whereby these were cooled, and where active cooling was
already taking place in this tube. However, during the activities at the first
cross connection it was clear that merely a passive insulation in the west-
erly tunnel tube at the point of the lowest steel segment, was inadequate to
ensure a proper connection between the frozen soil and the tunnel tube: the