Civil Engineering Reference
In-Depth Information
Heinenoord Tunnel. The application of triplex caused a drastic decrease of
damages: triplex is far more rigid and can therefore, in comparison with
kaubit, transfer a greater force via friction. Due to the friction, a coupling is
brought about between the rings: in other words, the rings can lean against
each other better, so that smaller mutual deformation occurs, the dowels
are less loaded and less damage is the result.
Due consideration was given to the durability of the triplex and the effect on
the Dowel-Recess joint. It has been investigated that after wear and tear of
the triplex in the end situation, the Dowel-Recess joint is still acceptable.
Dowels are given more space
In the ideal situation the dowel (Nocke) falls into the recess (Topf) which
involves an evenly distributed 'latitude' around the dowel. When charting
the possible causes of the damages, it was also examined whether some-
thing perhaps went amiss with the play in the building-in of the segments
into a ring. In general, it is of utmost importance in the construction of a ring
to push the longitudinal joints together properly. If this does not happen,
then it results in a greater circumferential length than intended. If this 'mis-
take' is repeated in the placing of every segment, that leads - in the worst
case - to too little space for the placing of the keystone.
This is also of vital importance for the position of the dowels, because, in
the case of not pushing the longitudinal joints together properly, the dowel
in the circumferential direction would continue to lie further away from the
ideal position. Sometimes, even so far, that when placing a segment there
is contact already. Then even if the slightest thing happens the dowel will
shear. It is because of this problem also possibly occurring during the bor-
ing and construction of the Westerschelde Tunnel, that the dowels were
made smaller so that they had a bit more space.
Relationship with the sealing profile
As the abovementioned shows, it is best to construct the tunnel rings as
'tight-fitting' as possible, whereby the segments are pushed optimally against
each other at the position of the longitudinal joint. However, in practice, the
pushing together often appeared to happen laboriously and naturally the
question about its cause arose.The answer was closely connected to the seal
used which was applied around the segments in order to guarantee the water-
tightness. Originally, a high and simultaneously too extremely rigid profile
was used which appeared to be awkwardly compressible. When the longitu-
dinal joints are not pushed together to the maximum during the ring con-
struction, then this occurs at the moment that the ring is outside the shield -
in the advancement of the TBM - sand and water pressures complete the
'task'. The result is that the rings amongst themselves deform, which again
could lead to damage. The solution to the problem was found in the use of a
lowered and broadened profile which was easier to push together.
Key stone
The recurrent leakages which occurred during the boring of the first couple of
hundred metres, were particularly concentrated around the closing stone
(keystone).The idea was that here a problem may also have occurred with the
seal: perhaps it was damaged during the placing, or possibly the sliding in
of the stone caused damage to the concrete. In order to shed light on the
problem, an extensive investigation was set up amongst other things, by the
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