Summaries
Quality guarantee for hydraulic engineering
materials used for the Oosterschelde barrier
Since 1976, efforts have been made to set up a
systematic quality control of the materials to
be used for the barrier and its subsidiary
works. Previously this was inadequate. In
particular, the quality control procedures
initially met with some resistance as these
seemed to hamper the progress of the works.
In fact, in some cases, the control is more a
guidance signal in case the quality of the
material deteriorates, than a selection mecha
nism. The investigation is aimed at an evaluation
of the quality control method and its results for
such materials as concrete, synthetic fibres,
asphalt, stone-asphalt and loose materials such
as gravel, sand and slags. In many cases,
experience with these materials in road-con
struction proved to be helpful.
Soundings made for the storm-surge barrier
The storm-surge barrier is being constructed
from pre-fabricated elements; accurate and
frequent soundings in the operational area are,
therefore, of major importance. Success or
failure depends on the accuracy of the position-
finding. In the Oosterschelde, a multi-user
radiographic position-finding system is being
used. To measure the depth, hydrographic
echo soundings with increased accuracy are
being used.
The procedure is completely automated as
result of which a 250 km long sounding line
can be processed. By increasing the efficiency
of the sounding activities in all kinds of ways,
only two sounding vessels were required to do
the job well into 1981. At present, three vessels
are in use, which will be the maximum, even in
the very active future period.
Tidal amplitude at Yerseke after the implemen-
ation of the works on the Oosterschelde
n order to ensure an average tidal amplitude of
2,70 m at Yerseke under almost all conditions a
vet cross-section of 14,000 m2 was chosen for
he storm surge barrier, with additional allowan-
e for maintenance and certain hydraulic
jncertainties. Thus the net effective wet
ross-section came to 16,480 m2. Now it
ippears that an average tidal amplitude of 3,10
can be reached at Yerseke using this wet
cross-section.
The chance that the required average tidal
amplitude of 2,70 m will not be reached has
been reduced to less than 1%. On the other
hand 120 tides per year may occur in which the
actual tidal amplitude is less than 2,70 m.
Investigation into the current resistance of the
temporary protection of the soil improvement
under the piers of the Oosterschelde barrier
Some time will elapse before the soil improve
ment in the axis of the Oosterschelde barrier
can be covered by foundation mattresses.
During the interim period, a temporary layer of
gravel is dumped, which will later be removed
by suction by the 'Cardium', but, in the mean
time, will have to be adequately current
resistant. In fact, the stability of this gravel
protection needs to be further investigated.
Calculations were made and measurements
taken to investigate how much of the gravel
protection was displaced at certain current
velocities; also below the so-called 'critical bed
shear stress', where, according to the existing
theory, no transport could take place.
It appears that the margin between stability
and instability is unclear and that the duration
of the exposure has indeed some effect. This
could be demonstrated by the sand corrugations
which had developed on the gravel protection.
In some places, the thickness of the gravel
layers had to be somewhat increased.
Falling stones
For the construction of the barrier-sill stones
are being used that weigh from 10 ups to 10 000
kg. It is to be expected that the piers will suffer
some damage particularly by the larger stones
if they fall freely from the water surface. This
has been theoretically and practically investi
gated. Initially, the results of these calculations
were highly exaggerated. Practical investiga
tions proved that, around the piers, stones
weighing over 3000 kg, would have to be
replaced by slabs of stone-asphalt which would
not damagethe piers even in free fall. Additional
equipment has been developed which reduces
the fall of the stones, weighing between 1 and
3 tons, to 2 metres maximum. Moreover, the
piers will be protected by a thicker concrete layer
and by wide protection aprons along the edges.
Integration of ecological aspects in coastal
hydraulic engineering projects
For centuries, flood-defences and land reclama-
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