c ivered with quarry stones as a protective
r ieasure against current attacks or pressure
c fferences. Should any perforation occur this
cduId lead to scouring. It now appears that there
i insufficient adhesion between the layers of
b ^phalt mastic when the contact layer is
c Dvered by sand. As a consequence, the barge
an Heymans', which lays the asphalt mastic
f >r the aprons, has to clean the work done the
p evious day by hosing the last layer with jets
t sfore another layer can be added. The fact
t at, owing to seepage pressure, the layers of
a ïphalt mastic can be pushed upwards is
i significant, as long as a limit of one metre is
r )t exceeded.
F ïsearch and design of the dam approaches
e id the concrete land abutments
final design has been drawn upforthe interim
s ructures to be built between the fixed and
r lovable components of the Oosterschelde
t arrier. They will consist of a dam approach, a
c jncrete land abutment, a bridge girder and
r :bble mould, to be built between the dam
a tproaches and the end piers. In the
v orking-scheme, priority has been given to the
c instruction of the dam approaches. The
c stance between the end pier and the land
a jutment has been shortened to 65 metres and
v ill be spanned by a concrete bridge girder.
I this chapter further information is given
6 >out the construction of various components.
f ttention is paid to the extensive model
r search that was needed to calculate the exact
c mensions of the various components of the
i terim construction with relevance to their load
t ;aring properties.
F -st results of the experimental
c «charge-programme of the Volkerak-sluices
F r experimental purposes, the discharge of
f ;sh water into the Oosterschelde, near the
V >lkerak-sluices, was doubled from 50 m3 to
1 0 m3 between November 1979 and March
1 80. The test forms part of an investigation
P ogramme, to gain insight into the control of
t e salinity of the Oosterschelde. For the benefit
c the submarine biology, in particular the
r ussels, a number of restrictive pre-conditions
v 3s set. Throughout this test the permissible
v lues were not significantly below the
r ference level. Extensive measurements were
t, <en at various times to determine the impact
o the salinity of the Oosterschelde. The results
c these tests are now being worked out.
Simultaneously the condition of the mussels
was constantly checked.
Heavy metals in the Delta area
Heavy metals occur in the waters of the Delta
area either in a dissolved form or in cohesion
with silt. The latter form mostly settles in the
downstream rivers. An inventory of the amount
of heavy metals in the silt of the bottom equated
with a 'basic level', which was based on former
bottom samples, led to surveys as shown in
figures 1 and 2.
It appears that the level of heavy metals in the
Oosterschelde and the mouth of the
Westerschelde, in contrast with that found in all
other waters, is still in conformity with the
natural basic level.
A combined biological geochemical research
team has tried to evaluate the effect of heavy
metals on the biomass in the water. In this case
field work data were collected of the specific
influence of four different modes of heavy metals
on the flora and fauna each in accordance with
its own growth and behaviour pattern. The
research was specifically aimed at the
accumulation of heavy metals in mussels and
green algae.
Geological research
In aid of the works in the Oosterschelde the
Governmental Geological Service has spent
much time and effort investigating the
geological and morphological phenomena of
the seabed, especially in the mouth of the
estuary. Through studies, surveys and
laboratory research the profiles could be
determined of the stratigraphical layers of the
bottom in the axis of the stormsurge barrier. On
the old pleistosene layers, situated between
N.A.P. - 39 and - 29 m, more recent holocene
formations have been found the
'Westlandformation'. It appears that the
'Deposit of Duinkerke' is poorly consolidated
and susceptible to liquefaction. An accurate
survey of the Deposit was necessary to mark the
exact location under the barrier where the
seabed must be compacted by vibration.
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