Summaries
Progress in the design of the Oosterschelde
barrier
The design of the Oosterschelde barrier as a
whole has not been discussed in the
Driemaandelijks Bericht (Quarterly Review)
since February 1979. The aims, the terms of
reference and the basic data will therefore now
be reviewed.
It is apparent that some elements have not been
satisfactorily studied or set down in detail. This
applies in particular to the excavations, the
aprons, the compaction works and the
foundation mattress, which items will be
discussed below.
Prognosis of the topography of the
Oosterschelde during the construction stage
During the construction of the barrier, each
stage of the construction will cause changes in
the existing hydraulic and morphological
conditions and, in particular, in the profile of the
seabed. In a so-called 'construction research
programme', data are being collected to be able
to make reliable prognoses. The hydraulic
models M 1000 and M 1001 are being used for
this. The input material used are sounding data
regarding the changing bed-profile, gathered
between 1972 and 1977 and supplemented
wherever possible by data collected in later
years. The area to be investigated for this
purpose has been dividend into 160,000
squares of 25 x 25 metres. By extrapolating
data, a prognosiscould be made ofthe probable
bed-profile in 1982. This prognosis has been
used in the models. With the aid of current
patterns predicted for 1981-1983, prognoses
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are now being made aboutthe probable bed-
profile in 1984.
Experience gained with the soil improvements
during construction in the centre line of the
closure gaps
To prevent the occurrence of liquefaction 2,5
million m3 of an inferior quality of subsoil will
have to be removed from the closure gaps in
the Oosterschelde barrier and subsequently be
replaced by clean sand.
The dredging of this inferior subsoil required
the modification of a suction dredger into a
'dustpan' dredger. The clean sand is delivered
by hoppers. The sand is unloaded by opening
the wells of the dredger. The sand descends
vertically through 30 or 40 metres of water, in
which there are sometimes rather strong tidal
currents, before reaching the bed ofthe estuary
The drift ofthe sand and other turbulent
phenomena cause great losses of sand during
the dumping. As a consequence, efforts to fill
the trenches at one go failed. A step by step
procedure, by which a wider sedimentation
sphere was created, gives a more satisfactory
result. Nevertheless the loss of sand still
amounts to 50
Further investigation of the asphalt mastic
layers used for the aprons
The aprons, situated just outside the centre line
ofthe axis of the closure gaps ofthe barrier, wil
be built in overlapping layers of asphalt mastic,
laid in the same manner as roof-tiles. If these
layers are properly fitted they need not be
