Civil Engineering Reference
In-Depth Information
Fig. 13.17b
Freezing leads to
inward deformation of
the tunnel lining in
Boom clay
20.0
18.0
16.0
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0.0
Starting excavation cross connection
2.0
0
7
14
21
28
35
42
49
56
63
70
77
84
Time (day)
twenty-six) the choice was made for active cooling of the steel segment by
means of a small cooling system.
The segment was cooled down on the inside to approximately 0 °C.
Leakages
Aside from the laborious achievement of a proper connection due to
the inadequate insulation, another problem occurred during the construc-
tion of the first cross connection: leakage of ground water through the final
inner lining. The cause was due to a problem with the - perhaps too lightly
dimensioned - vibrating formwork which is why the compacting of the con-
crete had to be halted. The result: an inner lining which was not properly
watertight.
Presumably the water penetrated the cross connection via the circular and
longitudinal joints between the circular tunnel segments.These joints are so
deep within the surface of the lining, that they could never be completely
filled with shotcrete with which the outer lining of the cross connection was
made. In this way these joints form channels through which the ground
water could penetrate the non-watertight concrete of the final construction -
spaces were also observed around the reinforcement bars.
Application of membrane is necessary
The experience gained in the construction of the first cross connection had
led to the fact that the vibrating formwork was adapted. Despite this meas-
ure, problems with the water tightness continued to exist, so too in the con-
struction of the second cross connection. That is why, from the third cross
connection onwards, an extra membrane sealing was fitted between the
shotcrete (the outer lining) and the inner lining of reinforced concrete.
The membrane sealing consists of a drain foil, the actual sealing layer and
a studded protection layer.The single sealing layers were welded watertight
to each other and fastened to the flange which was welded around the door
of the cross connection. Thus the possibility of water seeping in via the
joints was counteracted. Especially the realization of the transition of the
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