TunnelsThe Dutch soil does not very well permit application of the so-called'shield method', which is often used elsewhere for tunnel construction.The country is low and this, combined with the fairly high groundwaterlevel, presents extra problems in this respect. For many years, thesefactors have undoubtedly formed a great obstacle to tunnel construc-tion in Holland, which moreover has no mountains fit for tunnellingso that there has never been cause for a tradition to grow in this res-pect.The increase in ocean-going shipping to Rotterdam and Amsterdam,and the growing land traffic which crosses the main waterways, haveaugmented the need for underwater tunnels, however. The 'immersionmethod', developed in about 1930 and a very appropriate example oflarge-scale prefabrication, furnished a suitable solution. The traffictunnel laid under the river Maas in Rotterdam in 1937-1942, the firsttunnel in Holland, was built according to this method as the firsttunnel rectangular in cross section. Ever since, the immersion methodhas been looked upon as a very suitable one for tunnel constructionunder Dutch conditions.The traffic tunnel at Velsen and the railway tunnel next to it, built in1953-1957 under the canal linking Amsterdam with the North Sea, wereyet constructed according to the 'excavation method'. This methodcould be followed here because the canal had to be widened thereanyway.At present five tunnels are under construction: two at Amsterdam (IJtunnel and Coen tunnel) and three at Rotterdam {Metro tunnel, Bene-lux tunnel and Heinenoord tunnel). Four of them are motor traffic tun-nels and one, the Metro tunnel, is built for the river crossing of theRotterdam Underground.Despite the difference in conditions which in all cases very much af-fected the construction, the underwater parts (lengths 630 + 180 m,60O m, 1040 m, 800 m and 600 m respectively) of these five tunnels areall laid according to the immersion method. The 2 km undergroundtunnel (including three stations) of the Rotterdam Metro is also builtthis way (see page 36 and page 37).In the Coen tunnel no prestressing is applied at all. In the Metro tun-nel, the Benelux tunnel and the Heinenoord tunnel prestressing ten-dons are temporarily applied to make it possible for the elements,which consist of sections ?oined by a flexible connection, to be trans-ported floating and then immersed, after which the tendons are re-leased and removed. Only the middle four elements of the Beneluxtunnel and the full length of the IJ tunnel have permanent prestressing.27. Benelux tunnel27.1. Benelux tunnel under constructionThis tunnel, schemed to be opened next year, will carry the west partof the new circular road around Rotterdam (see page 36) which is alsoa part of the new motorway from The Hague which leads throughthe tunnel, via the bridge over the Volkerak locks (see page 18) toAntwerp. The two open approaches to the tunnel, which has a totallength of 1,300 m, are made of reinforced concrete on a foundationof prestressed concrete piles. The underwater section, 740 m long, is23,9 m ? 7,84 m with a dual carriageway, is built up of eight elements,each about 93 m long which are placed according to the immersionmethod. As this part also curve horizontally (radius 1,300 m) theseeight elements also differ among each other. They are manufacturedin a dry dock, dug in the south bank near the approach to be laidthere.In order to limit effect of temperatures each element is made up offive sections (18.6 m long). The haunched ?oints are provided withwater stops and the entire tunnel is covered with a bituminousmembrane. Such flexible connections have also a favourable effectin the event of unequal settlements. To make it possible for anelement of 93 m long (net weight about 16,000 tons) to be transported-- after being made to float by means of water-tight end walls --and subsequently be immersed (by filling built-in water tanks),it is temporarily prestressed longitudinally with B.B.R.V. cables54 ? 6 mm; in total 92 cables for the whole tunnel.238 Cement XVIII (1966) Nr. 4 - 5Vhen it is immersed, the element is pushed close against the oneplaced previously, in such a way that a special rubber profile alonghe outer edge of the end wall ensures a perfectly water-tight seal.The space between the two end walls is then pumped dry, where-jpon the pressure of the water against the other end wall forceshe new element against the previous one. They can then be coupled.The longitudinal cables are then released and removed.Driginally the river has to provide a water depth of 13 m over avidth of 275 m, but in addition it was required to have later a depthof 16 m over 125 m. connection with the increased water and soil pressure the middleour elements would have to have a larger cross section. Thiswould call for a costly extension of the approaches. avoid these problems the above-mentioned four elements, having3 normal cross section, were partially prestressed transversely with inotal approx. 616 B.B.R.V. cables 44 ? 6 mm (1 m c.o.c). The tensile?tresses in the roofing and the bottom of the elemnt (max. 18 kg/cm2)caused by the weight was changed into a compressive stress of18 kg/cm2by this partial prestress.The tunnel will provisionally be run as a toll tunnel until it is takenover by the State.27.2. cross-section with cablesEmployer: Benelux-Tunnel N.V.Design and Supervision: Rijkswaterstaat, Directie Sluizen en Stuwen(Ministry of Transport, Department Locks and Weirs)Contractor: N.V. NESTUM II (formed byN.V. Amsterdamsche Ballast Mij./AmsterdamChristian! & Nielsen N.V./The HagueVan Hattum & Blankevoort N.V./BeverwijkH.B.M. Nederland N.V./The HagueN.V. Intern. Gewapendbeton-Bouw/BredaN.V. Ned. Aann. Mij. v/h Fa. Boersma/The HagueN.V. Nederl. Betonmaatschappij 'Bato'/The Hague)28. Other tunnelsa. IJ tunnelIn a few years' time, this tunnel is to provide the main linkaetween the two parts of Amsterdam which are separated bywater, the IJ. On one side of this water is the town centre withseveral new districts, an the other side a part which has grownsubstantially in recent years. For a great many years the connectionsnave consisted of a few ferries which fail to keep pace with thencreasing amount of traffic.The closed part of the 2,250 m tunnel, also crossing underneath theDijksgracht which runs parallel to the IJ, is over 1,000 m long. Itsconstruction is adapted to the various situations and possibilitieswhich present themselves, and therefore varies as follows, goingFrom north to south:-- on the north bank of the IJ, about 100 m in an open trench;-- under the IJ, 7 immersed elements, each about 90 m long;-- under the railway embankment between the IJ and the Dijksgracht,about 130 m according to the 'caisson method';-- under the Dijksgracht, 2 immersed elements, each about 90 mlong.The tunnel is 24.8 m X 8.85 m in cross section, with a dual carriage-way. As the stratum which has sufficient bearing capacity is at greatdepth, the two underwater parts were placed on a foundation ofconcrete bored piles 60-80 m long. As this pile foundation combinedwith the tunnel cover produces but little friction, special provisionswere called for to permit movement caused by temperature differ-ences. Each underwater section was therefore provided with two?oints: one for expanding and contracting movements and one forcontractions only. To take up the temperature stresses in the longsection under the IJ, use will be made of max. 12 continuous KAcables (Philipp Holzmann), each consisting of 40 oval wires, section40 mm2, longitudinally in the parts which are separated by joints.Upon immersion, the tunnel elements are placed against each otherin the same way as in the Benelux tunnel, viz. with the applicationof a special rubber profile on one of the end walls. The elementsare then joined by means of 12-16 short KA cables, about 9 m long,likewise consisting of 40 oval wires 40 mm2, in order to take up theelasticity of the rubber profiles.Design: Publieke Werken Amsterdam (Public Works Amsterdam)Contractor: Combinatie Bouw IJ-tunnel (COBIJT) (formed byN.V. Ned. Aann. Mij. v/h Fa. H. F. Boersma/The HagueN.V. Bataafsche Aann. Mij. v/h Fa. J. v. d. Wal & Zn./The HagueN.V. Aann. Bedrijf v/h J. P. Broeckhoven N.V./ArnhemN.V. tot Aanneming van Werken v/h H. J. Nederhorst/GoudaHollandsen Aann. bedrijf Zanen-Verstoep N.V./The HaguePhilipp Holzmann A. G./Frankfurt a.M. (Germany)Wayss & Freytag .G./Frankfurt a.M. (Germany))28.1. transport of an element of the IJ-tunnelb. Metro tunnelLike elements for the Benelux tunnel, those for the underwater partof the Metro tunnel in Rotterdam, each 90 m long, are temporaritylongitudinally prestressed to aid their floating transport and immer-sion. Each elements is made up of six sections of 15 m each. As thenet weight (about 4,500 tons) was lower in this case, the prestressingunits (Dywidag bars) could be fitted inside the tunnel, viz. in thefour corner points (see page 37).c. Heinenoord tunnelThis tunnel, which was started as the last of the mentioned fivetunnels, is being constructed south of Rotterdam as a replacementof the bridge near Barendrecht. The total lenght is 1,070 m, and theclosed part will be about 600 m long. As with the other tunnels, thecross section is rectangular (30.7 m ? 8.8 m). The fairly large widthwas necessary because in addition to a dual carriageway, the tunnelwill also accommodate two parallel roads. As for the Benelux tunnel,the underwater part of this tunnel is made up of elements, one of111 m and four of 115 m, which are much heavier (max. 30,000 tons)on account of the larger width. Each tunnel element will as in theother tunnels consist of a number of sections joined by flexibleconnections. The sections are temporarily combined by longitudinalprestressing to facilitate floating transport and immersion.Design: Rijkswaterstaat, Directie Sluizen en Stuwen (Ministry of Transport,Department Locks and Weirs)Contractor: N.V. NESTUM II (see Benelux tunnel)Cement XVIII (1866) Nr. 4-5 239