‘We want to be very thorough, right from the start’, says Bart-Jan Ruesink, Project Manager for Monitoring and Measuring at ZuidPlus. ‘Our surveyors have been working at various sites since the summer of last year. They are painstakingly mapping the routes of the road and the tunnels, and the site of Amsterdam Zuid railway station. We need this data to further refine the preliminary design of Zuidasdok. These measurements can also be used to check previously collected data. The designers can use these measurements to get an accurate view of the existing situation. By the same token, they will then be able to indicate – very precisely – what needs to be built, and where.’
Nails in the pavement
All these measurements are based on survey nails, which are driven into the asphalt or the pavement, for example. The precise locations of the nails are determined using GPS. These points serve as the basis for all the other measurements made. ‘Our work is accurate to within a millimetre, we leave nothing to chance’, says Bart-Jan.
Measuring in 3D
One commonly used measurement technique is 3D laser scanning. Here, the height, depth and width of the area being surveyed are ‘photographed’ with the aid of a laser beam. This ‘photograph’ of the existing situation is then compared to the new design, to check that everything is a perfect fit. Bart-Jan adds that ‘The survey team recently scanned the Minervapassage and the station platforms at Amsterdam Zuid. This is done manually, using laser scanners mounted on a tripod. Using the same technique, we will soon map out the spans and cellars of the Schinkelbrug bridge, as well as a number of roads. This involves driving around in a scanning car that scans every item of ‘street furniture’ (the road surface, the crash barrier, the lampposts, the signage, et cetera) in great detail. In this way, the designers know exactly where any given item is located. All in all, a massive job.’
Monitoring during construction
In addition to installing and operating the measuring equipment needed to determine exact locations, Bart-Jan’s team deploys measuring equipment that will be used to monitor the area during construction work. ‘We calculate the impact of our construction activities in advance, in terms of factors such as noise, subsidence, and vibration. This monitoring helps us to ensure that any impacts are kept within acceptable limits. It will enable us to ensure that Zuidasdok is implemented in a safe and controlled way, in the soft soil of Amsterdam. The construction companies will be using computer screens to monitor the site in real time. If we detect a signal, then we can take appropriate measures. The measuring equipment we have installed at various points around the site, will enable us to “keep a close eye on the surrounding area”. The type of measuring equipment used, and the locations in which it is to be installed, will depend on the planned construction activities and on the level of inconvenience they are expected to create. We are already working out the details.’
Moving buildings
As part of its preparatory work, and in consultation with the owners and managers concerned, ZuidPlus is currently inspecting the office buildings on either side of the planned tunnels (which will soon house a stretch of the southern section of the A10 orbital motorway). Buildings are constantly in motion, due to the effects of weather (wind and temperature) and use. ‘To monitor a building accurately, we must first assess its natural behaviour. In that way, we can subsequently identify any effects that might be caused by our construction work’, says Bart-Jan. The buildings are just the start of an extensive monitoring network. Next it’s the turn of the railway tracks, the groundwater level, the roads and the bridges. Plenty to keep Bart-Jan’s team busy for the time being.
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