Civil Engineering Reference
In-Depth Information
involved a risk that sand and ground water could enter into the tunnel. Besides,
stopping the supply could also lead to the collapse of the excavation front.
Provisional solution
The first attempts to stop the leakage were concentrated on the injecting of
a chemical agent through the segments at the position of the leak. Yet this
agent needed time to react with the soil and the water. However, due to the
rate at which the bentonite solution flowed into the TBM and the tunnel,
there was no time. That is why the flow of the water/bentonite first had to be
stopped. In order to achieve that, the dowels of a segment were removed,
while an insulation membrane - which originated from the activities on the
cross connections - was applied. Then, by means of the erector, this seg-
ment was then pushed against the hole and the shield.The small quantity of
bentonite which then still flowed in could be stopped by plugging the
remaining holes with fabric. Due to this the supply flow reduced to such an
extent, that the injecting of the chemical agent thereafter was successful:
after 13 hours the leakage was under control.
Fig. 11.15
The sealing of the leak
by placing the
'membrane segment'
The brush seal was replaced in the same manner as described at the leak-
age of the tail seal of the westerly machine.
Ring construction and damages
During the boring of a tunnel and the building-in of the tunnel rings, there is
always a chance of damage to the tunnel ring segments also being caused
by the tremendous jack forces exerted onto the segments. As such, not
every kind of damage is avoidable; it's different when a structural damage-
pattern becomes apparent.The building-in of a tunnel ring is an irreversible
process. Damages could indeed be repaired, but the replacement of a
damaged segment with a new one is 'impossible'. Certainly taking into
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