Civil Engineering Reference
In-Depth Information
Fig. 10.8
Diagrammatic
representation of the
tail seal and grout
injection
4
1
475
475
475
450
3
2
2000
1 - Shield
2 - Lining
3 - Steel brushes
4 - Grease chambers
(measurements in mm)
should make it possible to reduce the pressure and in addition to carry out
repairs safely if any leaks should occur.
Relationship between depth and design of
the TBM
General
It has already been pointed out above that the boring machines had to be suit-
able to bore at great depths - the deepest point of the boring route was
60 metres
NAP. First of all, the depth had to be translated in the design into
the dimensioning of the boring shield: high soil and water pressures prevail at
great depths and the steel shield had to be able to withstand this sufficiently.
In addition, other features of the machines used also make it clear that they
were designed to be able to bore at great depths: built-in facilities for diving
work and the way in which the tail seal has been constructed.
Propulsion of the TBM and installation of the
tunnel ring segments
Discontinuous boring process
During the boring of the Westerschelde Tunnel, the boring shield was pro-
pelled linearly by means of 28 pairs of hydraulic jacks which were sub-
divided into 7 control groups. A spherical bearing transferred the reactive
force from these cylinders onto the main frame and the housing of the bor-
ing shield. The jacks thrust against the completed concrete tunnel section
which was last installed.
The boring and the subsequent construction of the lining can be charac-
terised as a discontinuous process. First, a length of 2 metres was bored, in
which the jacks were gradually extended.Then the boring stopped and several
pairs of jacks were retracted. Subsequently, a new tunnel segment could be
moved into the space created in this way.
The segments supplied by train and put on to one of the trailers in tempo-
rary storage were transferred by crane to the segment erector within the
shield of the TBM. The function of the segment erector was to pick up the
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