Summaries
The conversion of the vessel 'Jan Heymans'
into a dumping vessel
The asphalting vessel 'Jan Heymans' has been
converted into a stone dumping barge for the
purpose of filling in the spaces between the
foundation-mattresses on which the piers of
the Oosterschelde barrier are to be positioned.
The vessel will also perform preparatory
activities such as: the removal of sand and of
temporary scouring protection of the edges of
mattresses. The 'Jan Heymans' has been
equipped with two supply pipes, a 'dustpan'
attachment and a nozzle-beam. The dumping
material will be stored in silos and from there
transported by conveyor belts to the supply
pipes; the silos have been built on either side
of the vessel. There are also provisions for
taking any required measurements. On
December 11, 1981, test trials were started.
Execution of the sill
Over 5 million tons of stone are being used for
the construction of the sill of the Oosterschelde
barrier. Each layer of dumped stones will vary
in thickness. As the stones vary in type and
size, different dumping techniques are required.
For the lowest layer split barges and
selfpositioning dumping equipment will be
used. The top layer consists of stones weighing
over 1000 kg each. To avoid possible damage
to piers and sill-beams, these will not be
dumped from the waterline but lowered with
special equipment. A kelly with a loading
capacity of 20 tons can be lowered and opened
under the watersurface; the progress of the
dumping activities can be screened on the
monitor.
Practical experience gained in compacting the
subsoil on which the Oosterschelde barrier is
being built
From April 1980 - March 1981, the compaction
vessel 'Mytilus' was activily engaged in the
axis of the Oosterschelde barrier. As the
expected results were rather disappointing
-the effectiveness averaged only 50 percent -
experimental tests were made with the
horizontal and withdrawn step distances and
with the compaction-method itself. Efforts
were made to optimalize the function of the
enterprise. Thus, investigations were made
into the possibility of improving such relevant
factors as the efficiency of the enterprise, the
turnover time, the horizontal step distance and
the 'value' of the vibrating needles. It appeared
that only the efficiency of the latter item could
be improved significantly by utilizing more
spare parts. Due to this and by more shift-work,
the desired operation rate could finally be
achieved.
Prediction of the vertical and horizontal tides
by using the harmonic tide-analysis.
For the execution of the Oosterschelde works,
exact predictions on the progress of the
water-level and current-velocity are of the
greatest importance. Tidal movement is
caused, in the first place, by the power of
attraction of the moon and the sun; this is
called the astronomical tide. When weather
conditions are quiet, the actual tide will be as
predicted, but variations in meteorological
conditions can lead to deviations from the
norm. It is possible on the basis of a series of
measurements of the water-level and
current-velocities at a particular place, to
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