Lifting buildings with pancakes and potatoes

Over the centuries buildings in Amsterdam have been sinking steadily in the soft, swampy grounds underneath the city. Over the past few years however some buildings have started rising. According to Johan Bosch, a professor at the faculty of Civil Engineering and Geosciences (CEG), and until recently the technical manager of the North South metro line project in Amsterdam, buildings situated along the Rokin, the Dam square and the Munt Tower have been lifted up half a centimeter by compensation grouting.

This measure, which involves pumping huge quantities of a mixture of cement, bentonite and water at dozens of spots in the ground underneath a building, must compensate for settlements that occur during the drilling of the tunnels. The drilling will start in a couple of months, Bosch stated last week during the ‘Frontiers in Shallow Subsurface Technology’ conference, held at TU Delft.
Until now contractors have only partially dug out the metro stations, yet they’ve already had to deal with numerous setbacks, most importantly the subsiding of houses along the Vijzelgracht, which sank up to 25 centimeters due to leakage in the casing of the station.

So what might we expect from the most crucial part, the actual drilling of the tunnels? That will work out all right, Bosch says reassuringly (and not surprisingly). But PhD student and grout expert, Adam Bezuijen (CEG, and also employed by Deltares), warns that the lifting of the buildings prior to the tunneling, the so-called pregrouting stage, is the easiest part of the settlement compensation.

During the drilling, more grout may have to be added underneath the buildings. And, Bezuijen says, this compensation must be done simultaneously with the tunneling, in order to keep the settlements of the buildings within certain limits. “If the settlement caused by the tunneling cannot be compensated for fast enough, the drilling has to be slowed down or even stopped temporarily. They should be able to drill and compensate simultaneously”, Bezuijen concludes. “But I do wonder how easy it will be.”
Bezuijen focused his research on finding the physical mechanisms that play a role during compensation grouting and how these can be influenced by the grout mixtures for different soils. The problem with grouting is that it is not known in what geometrical form the mixtures end up in the ground; therefore, the reaction of the soil and the buildings is continuously monitored.
In his laboratory Bezuijen tried to figure out how the composition of the grout influences its shape in the ground. “In the laboratory we experimented by injecting grout in layers of sand kept under high pressure”, he explains. “We then washed away the sand to see the shape of the grout. Ideally you’d like the grout to split up the sand layer and form a pancake that has a diameter of a couple of meters and that lifts up the top sand layer. But the grout often ended up looking like a potato.”

By adding more water to the mixture, the grout tends to form into a shape more like a pancake. Add too much water however and the grout particles get mixed up between the grains of sand. That’s not good either. The ideal mixture depends on the size of the grains of sand, among other factors. All in all it’s no easy feat to obtain the best mixture.
Jan Bijkerk, who is now in charge of the construction of the metro line, isn’t worried that houses will subside. “We can’t give 100 percent guarantees, but we’re convinced the technique works. It has been used successfully around the world. Preventing houses from subsiding is our priority.”

Alles bij elkaar opgeteld betaalt de overheid in 2009 bijna 4,3 miljard euro aan R&D. Dat blijkt uit het jaarlijkse overzicht van de totale onderzoeksfinanciering (TOF). Het leeuwendeel komt bij OCW vandaan: 2,9 miljard, inclusief de onderzoeksbekostiging van Wageningen Universiteit en TNO. Met 641 miljoen euro staat het ministerie van Economische Zaken op de tweede plaats.

Maar dat is lang niet alles. Zo trekt Landbouw, Natuurbeheer & Voedselkwaliteit 210 miljoen euro voor onderzoek uit, nog afgezien van de bekostiging van Wageningen. De ministeries van Verkeer & Waterstaat (138 miljoen) en Volksgezondheid, Welzijn & Sport (103 miljoen) spenderen ook flinke bedragen.

Enige ruis zit er wel in de cijfers. Het Centraal Bureau voor de Statistiek komt meestal op een lager eindbedrag uit, schrijven de ambtenaren. Want het CBS gaat uit van de ontvanger, terwijl de overheid van de betaler uitgaat. Soms spreekt de overheid van R&D, terwijl de ontvanger dat geen goede benaming vindt. Die vindt bijvoorbeeld dat zijn arbeid onder het kopje ‘innovatie’ zou moeten vallen. Het is een dunne lijn.

Ten opzichte van het BBP stijgen de overheidsuitgaven van 0,66 procent in 2007 naar 0,72 in 2009. Het valt niet exact na te gaan of het CBS hier hetzelfde over denkt. Sinds 2003 heeft het CBS geen financieringscijfers meer gepubliceerd door ‘problemen met het vaststellen van de R&D-uitgaven van de universiteiten’.

Overigens kunnen de overheidsuitgaven voor R&D de inflatie niet bijbenen. Die was vorig jaar 2,5 procent. Dit betekent dat de overheid 56,5 miljoen euro meer had moeten uitgeven als tegenwicht voor de inflatie. Ook de Lissabon-doelstellingen zijn nog ver weg. Om daadwerkelijk één procent van het BBP aan onderzoek uit te geven, moet de overheid nog één miljard euro inlopen. Maar de weg naar boven is gevonden, schrijven de ambtenaren.