The storm surge barrier
in the Eastern Scheldt
Areas which wouid be periodicaliy fiooded if the Netheriands was not protected by dyices.
Cover illustrations
Storm surge barrier pier and gate construction
Vessels, from top to bottom: IVIytiius
Cardium Jan Heijmans Donax i and Macoma
Trias Tai<iift 4
The centuries oid struggle against the sea
Various stages in the
development of the southwest of the Netherlands
The Netheriands, the gateway to Europe, situated on the North Sea at the delta of three great rivers, the Rhine, the IVlaas and the Scheldt.
The Netherlands,
a country wrested from the sea
In the N e t h e r l a n d s water is both friend and foe: the inhabitants have s t r u g g l e d against it d o w n t h r o u g h the centuries, and have o v e r c o m e it by turning water into dry land. A m o n g the benefits w h i c h water has yielded is access for s h i p p i n g , w h i c h has been responsible for the b l o s s o m i n g trade for w h i c h the Netherlands is f a m o u s , while the freshwater rivers together with a d e q u a t e rainfall have e n s u r e d a successful agricultural industry on the fertile sea clay land. T h e relationship b e t w e e n the Dutch a n d the water has always been and indeed remains a love-hate o n e ; today it is e x p r e s s e d t h r o u g h the building and constant s t r e n g t h e n i n g of d y k e s , the construction of important trading links s u c h as the N e w W a t e r w a y and the North Sea Canal and the building of the Barrier D a m , w h i c h resulted not only in the reclamation of new tracts of land but also in increased safety and a freshwater lake.
T h e special relationship w h i c h the Netherlands has with the water is particularly noticeable in the province of Z e e l a n d , w h e r e the battle with the s e a is still c o n t i n u i n g , t h o u g h the province o w e s its fine t r a d i n g centres to that s a m e water, w h i c h has enabled It to remain a major pillar of t r a d e , industry and agriculture.
ZUIDERZEE PROJECT
AMSTERDAM
DELTA PROJL. T
"^ROTTERDAM RUN
'MAAS
A. Section of tiie Heinenoord road tunnei witii equipment for siniiing it into position
B. Dam buiiding in ttie iJsseimeer
C. Tite 5 i<ilometre iong Zeeiand Bridge over ttie Eastern Sciieidt
Ttie deveiopment of ever improved dredging and dustpan equipment goes on
The oii production piatform, Andoc, made iargeiy from concrete, on its way to its site in the North Sea
The iocation of Zuyder Zee and Deita Project operations D.
F.
Dutch hydraulic engineering
T h e Netherlands has long and varied e x p e r i e n c e of hydraulic e n g i n e e r i n g , and particularly of c o n s t r u c t i n g d y k e s , d i g g i n g c a n a l s , d r a i n i n g polders a n d building locks, b r i d g e s , t u n n e l s a n d ports. T h a t e x p e r i e n c e is also put to use in the off-shore industries - in the construction of p r o d u c t i o n platforms for e x a m p l e . W o r k i n g in and w i t h water has given the Dutch a world-wide reputation, a n d the Z u y d e r Z e e project, w h i c h not only protected large areas of the c o u n t r y f r o m flooding but also provided about 160,000 ha. of new land, and the Delta project, w h i c h is also to protect the N e t h e r l a n d s f r o m the ravages of the s e a , are o u t s t a n d i n g e x a m p l e s of their expertise in this field.
The Delta Project
This project proposed the closure of t h e main tidal estuaries and inlets in the s o u t h w e s t e r n part of the N e t h e r l a n d s with the exception of those giving access to the ports of Rotterdam and A n t w e r p . Not only w o u l d this s h o r t e n the c o u n t r y ' s coastline by h u n d r e d s of kilometres but, by forcing the saltwater further back t o w a r d s the s e a it w o u l d also provide significant i m p r o v e m e n t s to freshwater m a n a g e m e n t in the country.
After the floods of 1953, w h i c h e n g u l f e d large areas of this region, c l a i m i n g 1,835 lives, it w a s d e c i d e d to accelerate the i m p l e m e n t a t i o n of plans already in e x i s t e n c e .
In 1958 Parliament passed the Delta Act, w h i c h l a u n c h e d the Delta project, involving the closure of all tidal inlets except the N e w W a t e r w a y and the W e s t e r n Scheldt, the s h i p p i n g routes to R o t t e r d a m a n d
A n t w e r p .
T h e various parts of the project were u n d e r t a k e n , o n e after t h e other, without delay. All were c h a l l e n g i n g and interesting pieces of hydraulic e n g i n e e r i n g , e a c h o n e more c o m p l i c a t e d than the last.
T h e y were carried out in the following order: 1958: Storm s u r g e barrier in the Hollandse IJssel 1960: Z a n d k r e e k D a m
1 9 6 1 : Veerse D a m 1965: G r e v e l i n g e n D a m
1970: Volkerak D a m with lock c o m p l e x 1 9 7 1 : Haringvliet D a m with d i s c h a r g e sluices 1972: Brouwers D a m
The Eastern Scheldt
T h e final part of the project w a s to be a d a m closing off the Eastern Scheldt. This was c o n s i d e r e d to be the most c o m p l i c a t e d part of the w h o l e Delta project. However, t h a n k s to the e x p e r i e n c e g a i n e d during the earlier operations it w a s not regarded as a p r o b l e m . It w a s not l o n g , however, before voices w e r e raised in favour of keeping the Eastern Scheldt o p e n a n d m a i n t a i n i n g the tidal flow to preserve the original natural e n v i r o n m e n t of the area. A s public disquiet grew t h e Dutch G o v e r n m e n t ordered a new study to investigate w h e t h e r it was technically feasible to keep the Eastern Scheldt open while not only e n s u r i n g the safety of the population at all t i m e s , but also
maintaining the original natural e n v i r o n m e n t as m u c h as possible. T h e study proved positive a n d the decision w a s t a k e n to build the s t o r m s u r g e barrier with steel gates. T h e alternative, to keep the estuary open and to raise approximately 150 kilometres of dykes along the islands to the required height, w a s rejected. C o m p l e t e closure, for w h i c h c o n t r a c t s had already been a w a r d e d , c e a s e d to be a possibility. T h e Eastern Scheldt was to be kept o p e n in normal c i r c u m s t a n c e s , but w o u l d be closed w h e n s t o r m surges w e r e e x p e c t e d .
T h e decision to build a storm surge barrier also necessitated the c o n s t r u c t i o n of two auxiliary d a m s ,
the Philips D a m and the Oester D a m . T h e s e d a m s have a twofold f u n c t i o n . Firstly, they reduce the area of the tidal basin b e h i n d the storm surge barrier, thus maintaining a greater tidal range at Y e r s e k e (3.00 metres) t h a n w o u l d o t h e r w i s e have been possible. Secondly, they create a tide-free shipping route b e t w e e n A n t w e r p a n d the Rhine.
The Eastern Scheldt storm surge barrier
T h e decision to build a storm surge barrier in one of the most f o r m i d a b l e estuaries along the D u t c h coast had c o n s i d e r a b l e c o n s e q u e n c e s . In order not to interfere w i t h the c h a n n e l configuration in the Eastern Scheldt the storm surge barrier had to be built in the three tidal c h a n n e l s , the deepest part of the estuary. E x p e r i e n c e g a i n e d f r o m previous projects now proved to be insufficient. T h e d e v e l o p m e n t of even more new t e c h n i q u e s , never before t e s t e d , was called for. It w a s d e c i d e d to prefabricate as m a n y c o m p o n e n t s as possible in a d v a n c e as construction operations in situ w o u l d not only affect the tidal currents in the c h a n n e l s and c a u s e e n v i r o n m e n t a l p r o b l e m s but c o u l d also prove hazardous to those w o r k i n g on t h e m . T h e y w o u l d t h e n only have to be installed or a s s e m b l e d on the spot.A s the new storm surge barrier had to be operational by 1985 the d e s i g n process and the s t u d y of
c o n s t r u c t i o n m e t h o d s w e r e started simultaneously. From the outset the Public W o r k s D e p a r t m e n t (Rijkswaterstaat) w h i c h c o m m i s s i o n e d the work, and the c o n t r a c t o r s , D o s b o u w , w o r k e d in close c o o p e r a t i o n , assisted by advisers and consultants f r o m a w i d e range of specialised areas. It soon b e c a m e clear that c o m p l e t i o n of the s t o r m s u r g e barrier w o u l d have to be deferred till 1986.
Various alternative p l a n s w e r e s t u d i e d and d e v e l o p e d , and within a few years a basic d e s i g n w a s p r o d u c e d a c c o m p a n i e d by s u g g e s t i o n s as to c o n s t r u c t i o n m e t h o d s and the e q u i p m e n t to be u s e d . A l t h o u g h the details of d e s i g n , t e c h n i q u e s a n d m a t e n a l s had still to be w o r k e d out, the b r o a d outline of the project w a s a g r e e d .
A. The mouth of the Eastern Scheldt
B. Piers in the construction docif C. The storm surge barrier in detaii
1 pier
2 quarry stone dam for land abutment construction 3 beam supporting operating
equipment 4 hydraulic cylinders 5 capping unit 6 upper beam 7 gate 8 sill beam 9 road
10 road box girder and
machinery for gate operation 11 power supply duct
12 sand filling of sill beam 13 top layer of sill 14 core of sill
15 sand fiiling of pier base slab
16 sill beam stops/bearings 17 upper mattress
18 grout filling 19 bioci< mattress 20 bottom mattress
21 compacted sand under the bed of the Eastern Scheldt 22 gravel bag
The storm surge barrier in the Eastern Scheldt
1 the island of Schouwen 2 the Hammen channel 3 the Roggenplaat
construction island 4 the Schaar van
Roggenplaat channel 5 service building
6 Neeltje Jans outer harbour 7 former pier construction
dock 8 beach
9 Roompot lock inner harbour
10 Roompot lock outer harbour
11 Roompot lock
12 depth approximately 30 • metres
S C H A A R VAN R O G G E N P L A A T 1265 m 10 20 3 0 -4 0 ^ - / I AOD H A M M E N 1965 m B.
Cross-sections of ttie tiiree tidai ciiannels in wtiicii ttie piers are being positioned.
1 piers 2 siii beam 3 underwater sill 4 deptii compaction 5 seabed improvement 6 original bed profile
Ttie Neeltje Jans construction island
T h e final plan for the construction of the s t o r m s u r g e barrier c a n be d e s c r i b e d as follows.
T h e s t o r m s u r g e barrier, in all 3,000 metres l o n g , w a s to be built in the three tidal c h a n n e l s , H a m m e n , S c h a a r v a n Roggenplaat, and R o o m p o t . It w a s to consist of 65 prefabricated c o n c r e t e piers, b e t w e e n w h i c h 62 sliding steel gates w e r e to be installed. W i t h the g a t e s in a raised position, the difference b e t w e e n the high a n d low tide behind the barrier w o u l d be m a i n t a i n e d at least three-quarters of its original range, sufficient to preserve the natural e n v i r o n m e n t of t h e Eastern Scheldt b a s i n . W h e n s t o r m s a n d d a n g e r o u s l y high w a t e r levels are forecast the gates c a n be c l o s e d , thus s a f e g u a r d i n g the population of the islands f r o m the ravages of the North Sea.
In c o n n e c t i o n with the initial plans to build a d a m across the Eastern Scheldt s o m e islands (Roggenplaat and Geul) had already been c o n s t r u c t e d at shallow points in the estuary. T h e construction islands, Neeltje J a n s a n d N o o r d l a n d , are c o n n e c t e d by G e u l , w h i c h is in fact a section of d a m . T h e s e raised parts will f o r m the d a m sections of the storm s u r g e barrier.
In view of its convenient situation and t h e facilities w h i c h had already been c o n s t r u c t e d there, Neeltje J a n s w a s t u r n e d into a construction island f r o m w h e r e operations w e r e c o n d u c t e d . T h e greater part of the prefabricated c o m p o n e n t s were also built here - the
piers, the sill b e a m s and upper b e a m s , and the f o u n d a t i o n mattresses. T h e stone to-be d u m p e d to f o r m the u n d e r w a t e r sill a r o u n d the piers was stockpiled- here too.
T h e following gives a brief description of the chief c o m p o n e n t s of the s t o r m surge barrier and other important related s u b j e c t s .
AIB. Schaar construction doci<. The piers are buiit in
compartments 1, 2 and 3 and the siii beams in compartment 4 C. Piers being constructed
D. Compieted piers
Pier construction
T h e prefabricated piers of prestressed c o n c r e t e , with a dry w e i g h t of up to 18,000 t o n n e s , are built in t h e Schaar c o n s t r u c t i o n d o c k , a gigantic building dock, covering an area of one square kilometre. It w a s s u r r o u n d e d by a ring d y k e and p u m p e d dry; the base of the d o c k is 15.2 metres below s e a level.
T h e construction d o c k is divided into four
c o m p a r t m e n t s by m e a n s of d y k e s . A s soon as all piers in o n e c o m p a r t m e n t are ready an o p e n i n g is m a d e in the ring d y k e , and t h e c o m p a r t m e n t is f l o o d e d . D e p e n d i n g on the tide the water in the flooded c o m p a r t m e n t reaches è d e p t h of 13 to 17 metres, sufficient for the d r a u g h t of the lifting vessel w h i c h lifts the piers and transports t h e m , o n e by one, to their d e s i g n a t e d locations. T h e y develop their o w n b u o y a n c y of about 9,000 t o n n e s per pier and a hoisting capacity of 10,000 t o n n e s is therefore a d e q u a t e to lift even the heaviest pier and transport it to its site.
T o keep the c o n s t r u c t i o n d o c k dry a deep-well d r a i n i n g system has been installed consisting of a great n u m b e r of wells s u n k into the s u r r o u n d i n g d y k e . A n y water seeping t h r o u g h f r o m t h e outside collects there a n d c a n be p u m p e d out.
T h e construction of the piers is a story in itself. Each pier is a c o n c r e t e building varying in height f r o m 30.25 to 38.75 metres. T h e lower part, the caisson s e c t i o n , is hollow and will be filled with sand d u r i n g the final c o n s t r u c t i o n phase of the barrier, o n c e all the piers have been installed.
T h e c o n s t r u c t i o n period for o n e pier w a s almost a year and a half. Every two w e e k s w o r k w a s started on a new pier so that at any given t i m e , more than 30 piers w e r e under c o n s t r u c t i o n , each in a different state of c o m p l e t i o n . A well-planned organisation w a s required to c o m p l e t e these extensive and c o m p l i c a t e d c o n c r e t e c o n s t r u c t i o n operations within the time s c h e d u l e . During the c o n s t r u c t i o n of the piers, the c o n s t r u c t i o n d o c k w a s in fact one huge open-air c o n c r e t e factory, w h e r e a total of 450,000 cubic metres of c o n c r e t e w a s p r o c e s s e d b e t w e e n IVlarch 1979 and the b e g i n n i n g of 1983.
A. The stages in which a pier is constructed 1 base slab
2 interior wails 3 outer walls
4 roof of caisson section 5 connecting section 6 middle section 7 top section
B. Timetable of construction stages of the piers, as planned in 1979
Installation of the piers
T o transport ttiese concrete giants, w e i g t i i n g 18,000 t o n n e s , a n d to position t t i e m accurately to wittiin a few c e n t i m e t r e s in 30 metres deep c h a n n e l s at a centre to centre d i s t a n c e of 45 metres is a far f r o m s i m p l e j o b . T w o of t h e most important vessels involved are. the O s t r e a , the lifting, transport and installation v e s s e l , and the M a c o m a w h i c h , apart f r o m p e r f o r m i n g several other f u n c t i o n s , acts as a mooring pontoon for the lifting vessel d u r i n g the installation of the piers. T h e O s t r e a (Oyster) is s h a p e d like a letter U a n d c a n therefore , , e m b r a c e " a pier in the c o n s t r u c t i o n dock, lift it a few metres and transport it f r o m the S c h a a r c o n s t r u c t i o n d o c k to the site in the Eastern Scheldt. W i t h its load the O s t r e a ' s d r a u g h t is 12 metres and it therefore has to m a k e a considerable detour w h e n t r a n s p o r t i n g a pier f r o m the Schaar c o n s t r u c t i o n d o c k to any location in either the H a m m e n or the R o o m p o t c h a n n e l . A s this involves extra time the operation is in principle only carried out w h e n a s o m e w h a t longer period of reasonably g o o d weather c a n be e x p e c t e d . T h e O s t r e a is e q u i p p e d with a 9,000 hp e n g i n e of its o w n with four rudder propellers, two at t h e bow a n d two at the stern, e n a b l i n g the vessel to m a n o e u v r e itself in the construction dock. For longer j o u r n e y s in the Eastern Scheldt itself it is assisted by t u g s . W i t h its
10,000 t o n n e s lifting c a p a c i t y and its two t o w e r i n g gantry c r a n e s , the O s t r e a is u n d o u b t e d l y the flagship of the fleet. O n arrival w i t h the pier at the appropriate location the O s t r e a meets up with the M a c o m a . T h e M a c o m a (the n a m e of another mollusc f o u n d in the Eastern Scheldt) is e q u i p p e d as a m o o r i n g p o n t o o n for the Ostrea and the two vessels are s e c u r e d to each other by m e a n s of a c o u p l i n g device capable of
w i t h s t a n d i n g a load of 600 t o n n e s . T h e role of the M a c o m a is to keep the O s t r e a accurately positioned while the pier is b e i n g lowered onto the s e a b e d . T h e exact positioning of the piers is of vital i m p o r t a n c e for the correct f u n c t i o n i n g of the storm surge barrier. A s the M a c o m a runs out its m o o r i n g lines in a d v a n c e the c o m b i n e d craft O s t r e a / M a c o m a c a n be m a n o e u v r e d into position without delay, thus reducing installation t i m e .
T h e M a c o m a also acts as a kind of v a c u u m cleaner. No sand c a n be allowed to collect between f o u n d a t i o n bed a n d pier as it might be w a s h e d away at a later stage c a u s i n g s e t t l e m e n t of the pier and j a m m i n g of the gates. It is vital, therefore, that the sand be r e m o v e d .
This is easier said t h a n d o n e . W i t h e a c h high tide great quantities of sand are shifted into the estuary to be swept back again at low tide, m a k i n g it very difficult to keep a surface free f r o m s a n d for any lenght of 14
DIE.
Diagramatic representation of tfie transportation and instaUation of a pier by tiie Ostrea
The routes taicen by the Ostrea
The Ostrea transporting a pier
The Ostrea moored to the IViacoma during an instaUation operation Grouting and baiiasting a pier 1 grout suppiy
2 grout pump 3 iayer of grout 4 sand/water mixture 5 sand baiiast
t i m e . Just before the pier is put in position the M a c o m a therefore removes any last traces of s a n d . Both vessels have to perform s u c h unique f u n c t i o n s that no existing vessel or e q u i p m e n t w o u l d have been able to c o p e . T h e Ostrea and M a c o m a had to be specially d e s i g n e d a n d built for this part of the Eastern Scheldt project.
W h e n the u n d e r w a t e r sill (see later) has been partly raised to the required height the cavity b e t w e e n the base of the piers and the f o u n d a t i o n bed is filled with grout, a mixture of s a n d , c e m e n t and water, t h u s providing uniform bearing conditions over the entire base slab area. G r o u t i n g is done t h r o u g h the hollow c o m p a r t m e n t inside the pier once it has b e e n locked into position and p u m p e d dry.
T o give the piers a d d e d stability they are filled w i t h sand d u r i n g the final construction p h a s e by p u m p i n g a sand/water mixture into the caisson s e c t i o n . After the sand has settled, the water is p u m p e d out a g a i n . This system e n s u r e s that the caissons are 90 percent filled.
SEABED IMPROVEMENT CU NETTE DEPTH COMPACTION 15 m max. BOTTOM MATTRESS 200 nn 60 m UPPER MATTRESS BLOCK MATTRESS
A
INSTALLED PIER A. Construction of tlie foundations B. Diagramatic representation of seabed compaction by the MytiiusJULUL
C. Seaiing the joint between
two sets of mattresses 1 bottom mattress 2 upper mattress 3 sea gravei 4 quarry stone
5 gravei baiiast mattress
Foundation bed
T h e piers are the bacl<bone of the storm s u r g e barrier, s u p p o r t i n g the s u p e r s t r u c t u r e w h i c h consists of steel g a t e s , a roadway and the b e a m s . W h e n storms o c c u r a n d the gates are c l o s e d , the barrier will be s u b j e c t e d to e n o r m o u s forces w h i c h the piers must transfer to the f o u n d a t i o n b e d . This bed must be c o n s t r u c t e d in s u c h a w a y that it does not cause m o v e m e n t of the pier, w h i c h might result in j a m m i n g of t h e g a t e s . It is, therefore, as in any c o n s t r u c t i o n , of vital i m p o r t a n c e . T h e piers of the Eastern Scheldt s t o r m s u r g e barrier are positioned on the seabed without pile f o u n d a t i o n s . First, a c u n e t t e w a s e x c a v a t e d a n d , w h e r e necessary, unsuitable sand replaced by better quality s a n d . T h e deepest parts of the tidal c h a n n e l s were raised a n d covered with gravel to prevent erosion. T o improve the bearing c a p a c i t y of the s e a b e d further a n d to prevent settlement of the piers, it w a s c o m p a c t e d over a d i s t a n c e of 80 metres around the piers. This w o r k w a s carried out by the Mytiius (mussel), a c o m p a c t i n g rig, specially d e s i g n e d a n d built for the p u r p o s e . By driving its four giant vibrating needles into the subsoil t h e rig c a n c o m p a c t layers of up to 18 metres t h i c k over an area of 6 x 25 metres. In this w a y it w a s possible to c o m p a c t a n d strengthen the subsoil of all three tidal c h a n n e l s over a period of three years.
In order to survey the condition of the s e a b e d before a n d after c o m p a c t i o n the J o h a n V., a purpose-built
geotechnical survey p o n t o o n , e q u i p p e d with a conventional drilling rig a n d a diving bell, was u s e d . W i t h the aid of the diving bell soil s a m p l i n g a n d density m e a s u r e m e n t s c a n be carried out under water. After c o m p a c t i o n a n d inspection and before
installation of the piers, the s e a b e d has to be d r e d g e d a n d levelled off to the correct d e p t h and covered with a prefabricated f o u n d a t i o n mattress, m e a s u r i n g 200 x 4 2 metres x 36 c e n t i m e t r e s laid under e a c h pier. T h e s i m u l t a n e o u s d r e d g i n g of t h e s e a b e d and positioning of the f o u n d a t i o n m a t t r e s s e s are carried out by the C a r d i u m (cockle), another special purpose-built rig, and the J a n H e i j m a n s . T h e piers and the mattresses are positioned at a centre to centre d i s t a n c e of 45 metres leaving a g a p of about three metres b e t w e e n t h e 42 metres w i d e mattresses.
Apart f r o m assisting with t h e laying of the mattresses the J a n H e i j m a n s is responsible for filling in the s p a c e s b e t w e e n t h e mattresses with loose sea gravel t o p p e d by two layers of heavier s t o n e . T h e J a n H e i j m a n s , formerly an asphalt laying barge, u n d e r w e n t drastic conversion for this particular o p e r a t i o n .
To reinforce the f o u n d a t i o n structure, w h i c h does after all have to bear t h e w e i g h t of the pier, a s e c o n d smaller mattress, m e a s u r i n g 60 x 29 metres a n d again 36 c m t h i c k is t h e n placed by the C a r d i u m on 16
top of the first o n e . T h e foundation b e d , therefore, consists of a lower and an upper mattress.
T h e placing of the lower mattress is the most crucial o p e r a t i o n , b e c a u s e this is what ultimately d e t e r m i n e s the levelness of the foundation on w h i c h the piers are to be installed.
Both upper and lower mattresses are m a n u f a c t u r e d in the filter mattress plant, specially built for this p u r p o s e on the w o r k island, Neeltje J a n s . T h e y are called filter mattresses b e c a u s e of the w a y in w h i c h they are c o n s t r u c t e d - in three layers of graded material (sand, fine g r a v e l , coarse gravel). T h e function of the
mattresses is to absorb the c h a n g i n g water pressure in the subsoil so that it does not w e a k e n a n d to e n s u r e that the fine sand on the s e a b e d is not w a s h e d away. T h e filter mattresses are an essential part of the w h o l e
f o u n d a t i o n structure w l i i c h is d e s i g n e d to prevent settlement of tfie piers.
T h e levelling w h i c h c a n be achieved by the C a r d i u m may still vary by s o m e 30 centimetres however, w h e r e a s the ribs under the piers require an even more level s u r f a c e . If surveys of the upper mattress indicate that the f o u n d a t i o n s are not sufficiently level, a blocl< mattress c a n be positioned immediately under the pier. This consists of concrete blocks varying in t h i c k n e s s f r o m 15 to 60 centimetres in order to s m o o t h out any u n e v e n n e s s .
T h e s e block mattresses are m a n u f a c t u r e d in a plant at S o p h i a harbour, formerly used to m a k e c o n c r e t e w e i g h t e d erosion mats (see later under S e a b e d Protection) a n d now converted for this p u r p o s e . T h e y are w o u n d onto a floating cylinder, the Donax II, (Donax is a kind of mollusc), towed to the converted p o n t o o n , D o n a x I,.and m o o r e d to the M a c o m a , w h i c h positions the mattress on the s e a b e d .
T h e r e is a d a n g e r that the layer of q u a r r y stone c o v e r i n g t h e joints b e t w e e n the mattresses m i g h t be d a m a g e d by u n e x p e c t e d high currents or t u r b u l e n c e a r o u n d the piers, and the joints are therefore protected by a 200 m long and 13,5 m w i d e gravel-ballast mattress w h i c h consists of a flexible steel w o v e n mat to w h i c h rolls of quarry stone (ballast) p a c k e d in a wire m e s h are a t t a c h e d diagonally. T h e n u m b e r and w e i g h t
A. Jan Heijmans B. Cardium
C. Fiiter mattress factory on Neeitje Jans D. Composition of a fiiter mattress E. How a biocic mattress is used
of the rolls are c h o s e n so as to ensure that the mattress will be able to w i t h s t a n d the current in any c i r c u m s t a n c e s .
This mattress is m a d e on a special site with loading facilities at S o p h i a - h a v e n . It is rolled up a n d
t r a n s p o r t e d on board the Sepia (a kind of o c t o p u s ) , an a d a p t e d pontoon with w i n d i n g e q u i p m e n t w h i c h earlier b e l o n g e d to the J a n H e i j m a n s . T h e Sepia c a n be tied up to the J a n Heijmans or to the Donax I (with M a c o m a ) a n d c a n , in this c o m b i n a t i o n , unroll the ballast-mattress over the joints.
T h e f o u n d a t i o n bed is t h e n ready to receive the pier.
/ H
A. Stockpile of stone on the construction island B. Stone deposition barge Trias
C. Diagramatic representation of top-layer dumping D. Stone dumping pontoon Libra
opposite: installation of a gate
Sill construction
T o increase the stability of the piers o n c e they have been installed, a sill, built up of g r a d e d layers of stone is c o n s t r u c t e d under water around the base of the piers. This also helps reduce the o p e n i n g in the Eastern S c h e l d t estuary, as the ultimate intention is that only that part w h i c h can be closed off by the gates will remain o p e n .
T h e stone used in the sill is g r a d e d , the stones in e a c h layer b e c o m i n g larger the nearer the top they are, so that the larger stones in the upper layers prevent the smaller stones in the lower layers f r o m being swept away. T h e c o n s t r u c t i o n of the sill thus follows the s a m e filter principle as that used in the f o u n d a t i o n mattresses. T h e top layer on the Eastern Scheldt side consists of basalt blocks w e i g h i n g 6-10 t o n n e s in order to e n s u r e that, s h o u l d a gate fail to close, the stone will not be carried away by the c u r r e n t s , thus e n d a n g e r i n g the barrier.
Pieces of s t o n e like these c a n n o t be d u m p e d f r o m the surface of the water as they would d a m a g e the c o n c r e t e structure of the piers. T h e y are therefore put in position by a pontoon e q u i p p e d with a specially a d a p t e d c r a n e , the stone depositing b a r g e . Pieces of one t o n n e or less are d u m p e d f r o m stone d u m p e r s fitted with a d y n a m i c positioning s y s t e m , w h i c h enables the s l i i p to be kept in position or m a n o e u v r e d
slowly with the aid of m o v a b l e thrusters and without the assistance of other vessels. A p a r t f r o m the stone d u m p e r s p o n t o o n s are also used to c o m p a c t t h e d u m p e d layers of s t o n e , to remove excess s a n d a n d to survey the u n d e r w a t e r operations.
T h e most vital parts of the piers, e.g. the a n c h o r a g e sockets for the prestressing t e n d o n s , are specially protected against stones being d u m p e d f r o m the surface of the water. W h e n very heavy pieces of stone (6 -10 tonnes) are being d u m p e d a protective layer of asphalt is applied to t h e piers in order to prevent the c o n c r e t e f r o m being d a m a g e d or c r a c k e d if they are hit directly, thus e n d a n g e r i n g the life s p a n of the barrier, w h i c h has been d e s i g n e d to last for 200 years. S o m e five million t o n n e s of stone had to be put in position within the s p a c e of about two years. A s it w a s practically impossible to tailor the supply of stone to the i m m e d i a t e n e e d , the stone w a s brought in over a period of four years a n d stockpiled on the w o r k Island. It c o m e s f r o m G e r m a n y , Finland, S w e d e n and
B e l g i u m , a n d has a high density (2.8 - 3.0 tonnes/m^), w h i c h prevents it f r o m being too easily swept away by the currents.
Superstructure
O n c e the u n d e r w a t e r sill has been c o m p l e t e d the s u p e r s t r u c t u r e will be put in place. This consists in order of a s s e m b l y , of road bridge box girders, pier c a p p i n g units, gates, sill b e a m s and upper b e a m s . . Each c o m p o n e n t has a specific function a n d presents its o w n p r o b l e m s of m a n u f a c t u r e , and they are therefore all briefly d e s c r i b e d here.
T h e road bridge box g i r d e r s , 45 metres l o n g , m a d e
of prestressed c o n c r e t e and each w e i g h i n g 1,200 t o n n e s at t h e t i m e of assembly, will be placed on t h e piers. T h e s p a c e within t h e m houses the gate o p e r a t i n g m a c h i n e r y and the road will be c o n s t r u c t e d on top of t h e m , hence their n a m e . A p a r t f r o m the 62 box girders resting on the piers, there are six additional girders, w h i c h are especially long
(80 metres) and will link the first pier in each section of the barrier w i t h the land or island adjacent to it. T h e s e are m a d e of lightweight c o n c r e t e .
T h e c a p p i n g units are prefabricated a n d also m a d e of
prestressed c o n c r e t e a n d they increase t h e height of the piers so as to a c c o m m o d a t e the gate structure. Each pier has t w o c o n n e c t e d c a p p i n g units, together w e i g h i n g b e t w e e n 250 to 460 t o n n e s .
T h e sill b e a m s , 39 metres l o n g , 8 metres w i d e and 8
metres h i g h , are hollow b e a m s , e a c h w e i g h i n g 2,500
t o n n e s , w h i c h are installed b e t w e e n the piers on top of the u n d e r w a t e r sill. O n c e t h e sill b e a m s have been positioned, stone will be placed against t h e m on both sides to improve the flow profile of the barrier. T h e y are m a d e of prestressed c o n c r e t e and will be finished to their exact lenght only w h e n the exact position of the piers, w h i c h m a y deviate f r o m that p l a n n e d , is k n o w n . After final c o n s t r u c t i o n they will be filled with s a n d .
T h e upper b e a m s f o r m the upper e d g e of the
o p e n i n g s in the barrier w h i c h can be closed by the gates. T h e y are hollow rectangular b e a m s m e a s u r i n g 5 x 4 metres and are m a d e of prestressed c o n c r e t e ; they w e i g h about 1,100 t o n n e s e a c h .
T h e sill b e a m s are m a n u f a c t u r e d in the fourth c o m p a r t m e n t of the Schaar construction dock, w h i l e the other concrete c o m p o n e n t s are m a d e at the former Z e e l a n d bridge c o n s t r u c t i o n site at Kats. Production at this c o m p l e x c o n c r e t e factory must be continually tailored to the progress of c o n s t r u c t i o n at the barrier site.
T h e 62 steel gates will be installed b e t w e e n the piers. W h e n the gates are raised the Eastern Scheldt will be o p e n , i.e. the barrier will have an o p e n i n g of
14.000 m 2 , allowlrig sufficient water to pass t h r o u g h in order to maintain three-quarters of the original tidal range at Y e r s e k e .
G G.
The gate system
1 gate raised, normai position
2 gate towered, oniy in stormy conditions 3 cyiinder in the hydraulic operating system
Diagramatic representation of fhe hydraulic operating system
1 piston rod 2 cyiinder 3 cardan ring 4 gate
To carry out maintenance worlc the gates wiii be rased another 1.30 m
installation of a gate
T h e g a t e s , m a d e of steel, have a s p a n of about 42 metres. T h e exact d i m e n s i o n s c a n only be d e t e r m i n e d only after the precise distance b e t w e e n the piers c o n c e r n e d is k n o w n . T h e height of the gates varies f r o m 5.90 to 11.90 metres as the flow profile of the barrier roughly follows the bottom profile of the tidal c h a n n e l s , w h i c h is d e e p e r in the centre a n d shallower at the sides. T h e gates in the middle of the tidal c h a n n e l s are therefore m u c h higher t h a n t h o s e at the sides. Their w e i g h t varies f r o m 300 to 500 t o n n e s . T h e gate structure consists of a vertical plate on the Eastern Scheldt side, and of horizontal and vertical truss girders m a d e of tubular steel on the North S e a side. T h e gates are d e s i g n e d to w i t h s t a n d the loads c a u s e d by the different water levels on either side, a n d c a n be closed and o p e n e d under even the most adverse conditions.
A hydraulic system has been c h o s e n to operate t h e gates. Each gate is o p e n e d and closed with the aid of two hydraulic cylinders. All 124 cylinders are operated f r o m t h e central control building.
T h e gates and the o p e r a t i n g e q u i p m e n t are
c o n s t r u c t e d , s u p p l i e d and installed by O S T E M , a joint undertaking c o m p r i s i n g Grootint BV of Z w i j n d r e c h t a n d Hollandia Kloos NV of K r i m p e n a/d IJssel, w h i c h w a s a w a r d e d the contract by Rijkswaterstaat, the Public W o r k s D e p a r t m e n t .
All the parts of the s u p e r s t r u c t u r e mentioned above are being installed by the 1600 t o n n e floating crane Taklift 4. After the installation of the sill b e a m s stone and c o n c r e t e blocks will be d u m p e d on both sides.
Concrete weighted erosion mat factory at Sophiahaven near Kamperiand
Seabed protection 1 erosion guiiy
2 concrete weighted erosion mat
3 bottom foundation mattress 4 upper foundation mattress 5 bloci< mattress
6 mastic asphait slabs 7 siii
8 gravel bag 9 pier
Seabed protection and anchor piles
To protect ttie s e a b e d f r o m erosion c a u s e d by tiie increased s p e e d of the currents a 500-600 metre w i d e area on either side of the barrier had to be c o v e r e d . Had this not been done the channels m i g h t have e r o d e d to s u c h an extent that the barrier w o u l d be e n d a n g e r e d . T h e protection consists of c o n c r e t e w e i g h t e d erosion mats, aprons of stone filled asphalt a n d stone w e i g h t e d mastic asphalt slabs. Highly a d v a n c e d t e c h n i q u e s w e r e d e v e l o p e d especially for this o p e r a t i o n . T h e concrete w e i g h t e d erosion mats, m a n u f a c t u r e d in the factory at the S o p h i a harbour later used to m a k e the block mattresses, w e r e laid by Dos I, w h i c h w a s later converted into Donax I. T h e asphalting operations w e r e carried out by the J a n H e i j m a n s , o w n e d by Bitumarin BV, w h i c h has later been converted into a gravel/stone d u m p e r to be used for filling in the space b e t w e e n the f o u n d a t i o n filter mattresses.A s the anchors of the various craft used in the c o n s t r u c t i o n of the storm surge barrier w o u l d have d a m a g e d the s e a b e d protection, anchor piles w e r e driven into the s e a b e d within the w o r k i n g area in a c c o r d a n c e with a particular pattern. T h e s e piles c a n w i t h s t a n d a load of 200 t o n n e s and c a n be used for several a n c h o r i n g lines simultaneously.
A special d e p a r t m e n t has been set up to coordinate and handle all a n c h o r i n g a n d transport operations. It has several tugs at its d i s p o s a l , s o m e hired a n d s o m e o w n e d by the Public W o r k s Department, one of w h i c h is the Area (a mollusc), w h i c h was specifically built as an auxiliary a n c h o r i n g craft.
Temporary bridge
T o facilitate the daily transport of more than a
t h o u s a n d e m p l o y e e s to a n d f r o m the c o n s t r u c t i o n site, a t e m p o r a r y bridge, nearly three kilometres l o n g , was built b e t w e e n the w o r k island, Neeltje J a n s , and the island of S c h o u w e n - D u i v e l a n d . T h e bridge is also used to transport materials not carried by ship. A s soon as traffic across the barrier itself is possible the bridge will be d i s m a n t l e d .
Laying of concrete weigiited erosion mat by tiie Dos i Position of anciior iines wiien tiie Ostrea is moored to the iViacoma
The Area, an anchoring vessei The anchoring system
1 anchor post
2 protective rubber covehng 3 steei cabie 4 baiiast bioci< 5 hauiing cabie 6/7 buoy Temporary bhdge 25
Roompot lock
In the s o u t h e r n part of D a m Section G e u l , w h i c h is called N o o r d l a n d , a lock has been built for the use of small v e s s e l s , fishing boats and leisure craft. T h e lock c h a m b e r m e a s u r e s 100 x 16.5 metres a n d its floor lies 6.5 metres below A O D . T h e r e is an inner harbour on the Eastern Scheldt side and an outer harbour on the North S e a side with f e n d e r s and m o o r i n g points.
Diagram of moutii of Eastern Sciieidt
1 Sciiouwen 2 dam extensions 3 i-iammen 4 Roggenpiaat
5 Sctiaar van Roggenpiaat 6 Neeitje Jans
7 Roompot iocl< 8 Noordiand 9 Roompot 10 Noord-Beveiand Dam extension and iand abutment
1 dam extension 2 foundation mattress 3 quarry stone 4 rougii quarry stone 5 cyiindricai eiements 6 iand abutment 7 quarry stone dam 8 iand abutment box road
girder 9 pier
Land abutment construction 1 outer wails
2 cylindrical eiements Roompot ioci<
Abutments
T h e s p a c e s b e t w e e n the first pier in e a c h section of the barrier and the adjacent bank or island have to be b r i d g e d . T h e c o n s t r u c t i o n s d e s i g n e d to do this
c o m p r i s e four s e c t i o n s : a f o u n d a t i o n layer rising t o w a r d s the land, w h i c h s u p p o r t s the land a b u t m e n t , a quarry-stone d a m b e t w e e n this a n d the first pier, and a bridge b e a m .
T h e s u b s t r u c t u r e of the land a b u t m e n t consists of 7 prefabricated cylindrical e l e m e n t s w h i c h are placed on the level f o u n d a t i o n b e d and i m m e d i a t e l y filled with c o n c r e t e . T h e s u p e r s t r u c t u r e and the outer walls are c o n s t r u c t e d on site. T h e land a b u t m e n t constitutes part of the barrier and links the land, the f o u n d a t i o n layer and the quarry-stone d a m , w h i c h in t u r n f o r m s the barrier linking the land a b u t m e n t a n d the first pier. T h e q u a r r y stone d a m is c o n s t r u c t e d in m u c h t h e s a m e w a y as the sill b e t w e e n the piers in the s t o r m surge barrier, the filter principle again being u s e d , w i t h layers of stone increasing in size and w e i g h t f r o m the bottom u p w a r d s .
A. Construction cranes - tieavy users of energy B. Power plant
Power supply
T h e power r e q u i r e m e n t s during the c o n s t r u c t i o n operations, especially for the c o n t i n u o u s deepwell draining system of the Schaar c o n s t r u c t i o n dock, are very heavy. In the early s t a g e s , therefore, a power plant w a s built on the w o r k island w h i c h has a c a p a c i t y of 12,000 kVA, sufficient to meet the electricity
d e m a n d s of a t o w n with a population of about 4 5 , 0 0 0 . T h e plant houses 15 diesel generators, ten of w h i c h w e r e o v e r h a u l e d a n d installed in the service b u i l d i n g .
Electronics
It is n o w a d a y s virtually unthinkable for m o d e r n plant and e q u i p m e n t not to use applied electronics. Within the context of t h e Eastern Scheldt s t o r m s u r g e barrier operations s u c h s y s t e m s including a highly
s o p h i s t i c a t e d position fixing s y s t e m , are all classified as , , s u r v e y " . This classification, however, is inaccurate b e c a u s e t h e e q u i p m e n t does m u c h more t h a n just survey. It i n c l u d e s , for e x a m p l e :
- t h e latest e q u i p m e n t for automatic c o n t i n u o u s position fixing w h i c h is accurate to within 5 c m at a d i s t a n c e of 2 k m offshore;
- newly d e v e l o p e d s o u n d i n g t e c h n i q u e s e n a b l i n g u n d e r w a t e r position fixing a n d t e c h n i q u e s for
m e a s u r i n g t h e e v e n n e s s of t h e s e a b e d a n d d e t e c t i n g s a n d deposits less than a few c e n t i m e t r e s thick; - t h e use of g y r o s c o p e s a n d a c c e l e r o m e t e r s ;
- c o m p u t e r s y s t e m s o n board t h e various w o r k vessels m a k i n g it possible to read, c h e c k , process, present, r e c o r d , store a n d retrieve information f r o m h u n d r e d s of sensors.
T h e C a r d i u m has been e q u i p p e d not only w i t h t h e s e ' s u r v e y ' s y s t e m s but also with a semi-automatic w a r p i n g s y s t e m . This enables the rig to be m o v e d more or less automatically while attached to its anchor cables over a distance of 2 0 0 metres a n d w i t h i n an a c c u r a c y of about 50 c m , while actually d r e d g i n g a n d
A. Position-finding and inspection 1 Cardium
2 Wiji<er Rib 3 Portunus
4 infra-red position-finding
5 Radio position-finding using ttie Trident iii B. Steering ttie Portunus from ttie Wijicer Rib
C. Position-finding using ttie automatic traci<ing tiieodolite, tViiniiir, and the distance meter AGA 112.
D. The Portunus on a test drive over a concrete weighted blocic matress
E. Trigia inspects the hoiiow gap under the pier
laying mattresses. S h o u l d this system fail, there is still a s o m e w h a t simpler w a r p i n g s y s t e m to fall back o n . 28
Underwater inspection
Various craft have been d e v e l o p e d for u n d e r w a t e r i n s p e c t i o n , including the Portunus ( n a m e d after a type of crab), an u n m a n n e d vehicle w h i c h m e a s u r e s 6 x 4
metres and w e i g h s 6.5 t o n n e s on land and 5 under water. It c o m p r i s e s two parts: the vehicle itself, including the e n g i n e , a n d the inspection trawler, w h i c h is attached to the vehicle by a system of metal rods. T h e latter is e q u i p p e d w i t h three ,,Klar Sicht V o r s a t z " blocks, e a c h of w h i c h acts as light and w i d e angle lens for two black and white television c a m e r a s . T h e
pictures t a k e n by the c a m e r a s are t r a n s m i t t e d to the Wijker Rib, a vessel positioned a b o v e , t h r o u g h the c o n n e c t i n g cable. T h e inspection c o m p a r t m e n t is also fitted with sensors w h i c h m e a s u r e the t h i c k n e s s of layers of s a n d . U n d e r normal c i r c u m s t a n c e s the Portunus m o v e s on caterpillar tracks (0.5 m/sec.) but it has to use four castors to t u r n sharply in any d i r e c t i o n . It c a n either be steered manually f r o m the Wijker Rib or p r o g r a m m e d In a d v a n c e to follow a given c o u r s e . T h e c o n n e c t i n g c a b l e is 7 c m t h i c k and 250 metres long and provides all the energy needed on board the Portunus, t r a n s m i t s m e a s u r e m e n t s f r o m the sensors and acts as a lifting cable.
T h e Trigia, a small self-propelled device w h i c h c a n be operated by remote c o n t r o l , has been d e v e l o p e d to inspect the g a p b e t w e e n the f o u n d a t i o n s and t h e installed pier. It is tubular (900 x 42.5 m m ) and also has television c a m e r a s a n d sensors for m e a s u r i n g the t h i c k n e s s of layers of s a n d . It travels t h r o u g h the grout c h a n n e l s in the base of the pier in order to get under t h e pier.
A. Measuring platform witli sensors for obtaining information on ttie weatfier and sea conditions
B. 'Tfie ir. J. W. Topshiuis'
C. Tiie control panel in tiie service buiiding c
The Hydro-Meteo Centre
Most sections of the storm surge barrier are
prefabricated and therefore have to be t a k e n to their ultimate site and placed in position - for e x a m p l e , f o u n d a t i o n mattresses have to be laid, the piers a n d sills have to be positioned, and so o n . T h e s e operations c a n only be carried out in g o o d w e a t h e r and w h e n the seas are suitable. This m e a n s that highly a c c u r a t e forecasts have to be available for periods of several days at a t i m e and in order to facilitate this a special meteorological a n d hydrological centre, the Hydro-Meteo C e n t r e , has been set u p , w h e r e experts process information f r o m d o z e n s of m e a s u r i n g points in the North Sea relating to water levels, the speed of the currents, w a v e fields, water t e m p e r a t u r e s , salinity and w i n d . It is particularly important to know w h e n w a v e fields are a p p r o a c h i n g as they may c a u s e a long swell in the estuary, s o m e t h i n g to w h i c h the special e q u i p m e n t involved in the project is particularly sensitive.
A direct link with the Royal Netherlands Meteorological Institute and a c o n n e c t i o n with the international meteorological network also provide s o m e of the information on w h i c h forecasts are b a s e d , a n d f r e q u e n t bulletins are issued to all c o n c e r n e d ; d u r i n g positioning operations these are updated minute by m i n u t e .
Service building
All 62 gates will be centrally operated f r o m the service building on the c o n s t r u c t i o n island, Neeltje J a n s , ' T h e Ir. J . W. T o p s h u i s ' . T h e top two floors of this building also houses a p e r m a n e n t exhibition on the Delta Project in general a n d the Eastern Scheldt barrier in particular.
A, Personne! facilities at iVioermond B. l\/loermond Castie
Personnel amenities - Moermond
A b o u t 60 per cent of all personnel c o m e f r o m the province of Z e e l a n d . T h e remaining 40 per cent live in the rest of the country. Fore s o m e the distance b e t w e e n h o m e and worl< is too great to travel or shift w o r k prevents t h e m f r o m g o i n g h o m e e a c h day. T e m p o r a r y living quarters were therefore built in the g r o u n d s of M o e r m o n d Castle in Renesse w h i c h c a n a c c o m m o d a t e 260 people. T h e y have their o w n k i t c h e n , c a n t e e n a n d recreation rooms.T h e castle itself is used by the Public W o r k s D e p a r t m e n t and D o s b o u w for m e e t i n g s etc.
