The North/South subway in Amsterdam is by far one of the most complex urban projects in the Netherlands. The city is divided by the river IJ and the subway connects both parts. After a long political debate from the 1950s onwards, the work finally started in 2003 and is still to be completed. The line will be 9.7 kilometres long with stops at eight stations. The majority, some 7.1 kilometres, will be underground, below water, the railway station and the historic centre. The riverbed of the Amstel was chosen to avoid damage in the historic district. There was a general intention to not disturb heritage above the ground. However, the river bed is of course an archaeological ‘hot spot’ and severe erosion could not be avoided. The city archaeologists were consulted early in the process. As early as 1997 a desk based assessment was presented to the planners indicating where to expect archaeological remains [Veerkamp 1998].
The complexity of the project is due to the weak soil combined with a historic city centre that is now a World Heritage site. The engineers have used a new type of drill especially designed for weak soils. The drill has a diameter of 6.88m and is 84m in length. In total 6.2 km will be drilled. It is the first time engineers have used a drill instead of sinking tunnel cases. The great advantage of drilling is in preventing demolition of historic houses. As all the historic houses are funded on long beams that go well into the peat to the first sandy layer, the drill needs to stay away from an underground forest of beams. The city archaeologists developed a master plan for archaeological research well beneath street level (25-33m) based on preconditions set by engineering [Kranendonk 2003 and 2005]. The drilling technique itself excludes the possibility of research. Three locations were selected for excavation, two stations and one part of the trajectory where the drill needed to be put into place to start its work. Excavations led to complex working conditions without much daylight. Among other things archaeologists needed to be instructed about decompression sickness.
At some other locations the archaeological work was limited to assessments such as the Bijenkorf location at Dam square [Kranendonk 2010]. Here finds material was collected from dumped soil from vertical drilling work by engineers. Methods could not be influenced to gain more archaeological insight.