TBM Tunneling - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 678

Phase 2
The construction company Skanska took over as contractor in 1996 and continued ex-
cavating the tunnel with the drill and blast method. Heading was carried out from both
portals, and in addition an intermediate access (Fig. 21.14) was started in order to cope
with the delays caused earlier.
In summer 1996 large water inflow into the tunnel led to a lowering of the groundwater
table (Fig. 21.14), so that wells of the Hallandsas ridge, extensively used for agriculture
and recreation, dried up. As a consequence, grouting was carried out. On the basis of
extensive investigations a chemical grout named “Rhoca Gil” was used.

Due to common backflow of grout during the grouting process, water from tunnel
drainage contained Rhoca Gil. Unfortunately, this water was not purified before it was
discharged into the local creeks. As a consequence, fish and cattle died or became sick,
which caused major concerns among the residents. As a consequence, construction fi-
nally had to be stopped in October 1997.

Phase 3 and environmental conditions
After extensive investigations of the causes and restoration of the environment, new in-
vestigations were carried out regarding possible technology, environmental effects and
costs for continuation of the tunnel construction. The preconditions for a continuation
were not to lower the groundwater table and to provide extensive environmental con-
trols and information. In 2001, the Swedish Riksdag and Government decided for a
continuation of the project. In 2002, a consortium of the Swedish contractor Skanska
and the French contractor Vinci was awarded the corresponding contract. In 2003, the
Bastad Municipality granted a building permit with various conditions made by the
Environmental High Court.
Construction was finally restarted in 2004 with various environmental conditions, of
which the conditions related to groundwater inflow had the most decisive influence on
tunnel heading.

During construction, a maximum total removal of groundwater due to tunnel construc-
tion, excluding the access tunnel, was permitted of
-

100 l/s on a monthly average,

- 300 l/s on a weekly average,

- 400 l/s at any time.

For the access tunnel, the maximum permitted removal of groundwater amounted to
15 l/s. These values included the water inflow in the previously excavated sections of the
tunnel, which amounted to a total of approx. 30 l/s.
In view of the maximum water head of approx. 150 m above the tunnel's roof and the
comparatively high permeability that was locally to be expected, these were strict condi-
tions which required prompt and perfect sealing of the tunnel lining immediately after
excavation.