Civil Engineering Reference
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4 metres and the section where, in order to apply the underwater concrete, a
filling layer of gravel with a thickness of at least 500 mm was needed.
Fig. 8.12
Construction pit and
construction of basin
structure
Concrete work - the sections which connect onto the caisson
The design of the northern access ramp is the same as the design of the
southern access ramp where it concerns the staggered entrance and exit,
the columns and wall with recesses in the central reservation and the orna-
ments in the outside walls.
Due to the backfill within the dyke, the northern access ramp has been car-
ried out with high walls. Although the retaining height - approximately 11
metres - is not exceptional, it was difficult to comply with the set flexure
requirement for the cantilevered walls of the sections positioned deeper.
In order to overcome this problem, the cantilevered walls over the section
where the exit end is still closed, were strutted on the roof of this closed sec-
tion. For each section, on either side of the expansion joint, two concrete
struts with a 0.80 metre diameter were applied. In connection with the risk
of a possible collapse of these struts, the requirement was set that they had
to be resistant against a hydrocarbon fire lasting for two hours at a maxi-
mum temperature of 1,100 °C.
Taking the normal forces into consideration, the spalling of the concrete was
considered as normative. The strut was therefore carried out in a relatively
low concrete quality B35 which is less sensitive to spalling and which was
provided with a heat-resistant epoxy coating.
The structural floor of the concrete basin structure was cast without a
spread or slide layer, directly onto the underwater concrete. This has an
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