These levels and the foundation levels of the
piers have been established in the meantime.
Hydraulic research into the length of the
protective bottom-revetment
The hollows caused by scouring at the
downstream side of the storm-surge barrier
should not exceed a depth of 25 m, and the
occurence of spontaneous liquefaction should
be avoided. The measures to be taken will be
determined by model research.
The hydraulic properties of the storm-surge
barrier will be fed into models with a smaller
scale, via a so called schemetical research,
whereby accurate tests are made to find out
which form the storm-surge barrier must have
in the model to come to the same
discharge-coefficient as in the design.
Model research and computer calculations
combined can determine the requisite length of
the protective bottom-revetment in order to
remain within the acceptable limits of scouring,
even after 10 years.
Research into the filter-system for the design of
the base
At the design of the base for the storm-surge
barrier there was great concern about the
stability of the interface between the bottom
material and the lowest layer of the
foundationbed. Due to the wave action heavy
cyclical surface energy gradients were exerted
at these places. Little is known about the
behaviour of filters under cyclical loads; it was
deemed necessary therefore to undertake
elementary research into these loads in three
test cases, in combination, if so required, with
surface energy gradients running in other
directions.
The best solution of the problem at hand proved
to be 'the two layer solution': between the
bottom and the first layer of the foundationbed
an extra layer of coarse rubble is added
consisting of a graded mixture of loose stones
with a diameter of between 0.3 and 32 mm. This
will ensure both the stability and the filter action.
Report of studies and preparations related to
the storm-surge barrier, first semester of 1978
In so far as they have not been discussed in
separate reports, some changes in the details of
the design of the storm-surge barrier which
have been introduced in the first semester of
1978, are mentioned in this publication.
It appeared possible to reduce the assumed t >tal
perpendicular wave-load by 20%. In view oft ie
discharge-coefficient and the necessary
reserves the gross wet cross-section has bee
fixed at 18.000 m2. The retaining height was
increased up to N.A.P. 5.8 m. The piers will bf
positioned, directly and without correction
afterwards, on the flat foundationbed. It isthi s
possible to decrease the magnitude of the
soil-compaction. The design of the compaction
vessel shortly to be built can be adjusted
accordingly.
Tests with the second gate of the storm-sur< a
barrier in the Hollandse IJssel
The oldest Delta-construction, the movable
storm-surge barrier in the Hollandse IJssel, t e
building of which started in 1954 already, wa
not equipped with a second gate until 1976.1 his
second gate will become operational in the r aar
future. Preceding this event a number of test
have been made to determine the properties af
the new gate and to observe at the same tirrv
the behaviour of the barrier during opening i nd
closing procedures at the time of tidal flow a d
at a difference in water-level across the barri r.
These manoeuvres prove to be possible with act
adverse effects for the hydraulic structure or ts
surroundings.
Re-adjustment works in the southern Delta
area
As a result of the hydraulic constructions in t ie
Delta area the system of water-control in the
western part of the Netherlands will have to )e
re-adjusted: everywhere water-levels are ch n-
ging. As the original plans related to the Oos er-
schelde have been changed, the surroundint
territories must also be re-adjusted. Especia y
when the storm-surge barrier is closed, sue!
high water-levels may occur on the Ooster-
schelde, that none of the six surrounding pu n-
ping stations is capable, with their present c. pa-
city, of handling the discharges adequately, le-
adjustment, however, can be completed in t ne.
324
