i WÊBmmmÊÊmm
ummaries
T e top layer of the sill
T piers of the Oosterschelde barrier are
p ked into a sill construction. This sill is
in nded to fulfill all its hydraulic and soil
n chanical functions under all imaginable
c umstances, also in the event of one gate
ft ing to close when a drop of 4,2 m may
01 ur; current velocities may then run up to 12
rr above the top layer of the sill. In order to
b able to stand up to such a current the top
It ar of the sill should consist of stones
w ghing approximately eight ton. Such stones
m y not be unloaded from the waterline, and
ce ainly not in the vicinity of vulnerable
ci. crete parts. These parts should first be
p tected with stone asphalt, which absorbs
th shock. A special processing apparatus has
bi n constructed which can place the stones
at urately: the top layer loader 'Trias'. With the
he p of a heavy sliding tube, the kelly, this
cr ne which is mounted on a pontoon, can
di ct a spoon or a steel chain container under
w sr. Afterwards a gauge sheet can establish
w therthe stones are lying correctly. Stones
w ch are lying too high can be pushed partly
in place by the gauge sheet.
Tl installation of the gates and the operating
m chanisms
Tl trestle 'Taklift 4' also installs the gates and
th operating mechanisms. It is in use for this
pi poses from autumn 1984 until the beginning
O; 986. The gates vary in height from 5,90 m
to i 1,90 m, and taking into consideration the
v: ying distances between the piers they also
di er in length. The hoisting frame of the
tr itle has been made adjustable for this
purpose. An ingenious construction enables
the hoisting frame to grasp the hoisting points
of the gate. The operating mechanisms are
raised onto the hoisting frame by means of
steel strops. Every twelve hours, at each low
tide mark, one installation is completed which
takes three or four hours. Order of installation
is as far as possible three gates and then three
operating mechanisms, leaving enough time
available to shift the grasp constructions.
Placing the road box girders
From May 1984 onwards road box girders have
been placed in the Oosterschelde barrier.
Together with the capping units they form the
upper cross connection between the piers.
Moreover they will bear the road which runs
over the barrier. In the design the possibility
for future widening of the bridge deck has
already been taken into account. The road box
girders are constructed initially in two halves
which are later joined together. Besides the
normal measurement of 45 m, six extra long
abutment road box girders have been
manufactured. The placing of the road box
girders is carried out by the trestle Taklift 4'
which is assisted by a second trestle for the
placing of the abutment road box girders.
When placing the road box girders, which is
always planned around low tide mark, ship
movement as a result of wave impulse is
acceptable up to 20 cm. The workability
percentage lies at 90 in the summer and at 70
in the winter. Up til now all placings have
proceeded according to plan.
Operational wave forecasting for the
construction of the storm surge barrier
From September 1983 onwards the
Flydro-Meteo-Centre in Zierikzee has provided
meteorological and hydraulogical weather
working forecasts for the benefit of the
construction of the Oosterschelde barrier. This
service is based on the intensive co-operation
between the Rijkswaterstaat, the K.N.M.I. and
the Hydraulic Laboratory. This article deals
with the wave forecasting system and its
evaluation. Wave models serve to describe the
evolution of a wave field in time and space. For
operational reasons use is generally made of
parametrical models, which only follow the
development of such parameters as significant
wave height and characteristic period, and also
of low frequency energy as a result of swell.
Due to intensive evaluation of the forecasting
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