Keeping it quiet below Berlin

DB ProjeckBau GmbH is building a four-track railway under the heart of Berlin, Germany, to create a 9km link between the northern and southern sides of the city's inner rail ring. About 3.5 km of the route runs underground under the commercial centre and government district. Consultants Dr Heiland were commissioned to model the transmission of vibrations from the tunnel floor into adjacent buildings. Mass-spring measures were used to reduce vibration and noise. Instead of being fixed to the tunnel floor, the track sits in a rigid concrete trough supported by polymer bearings with a range of geometries. Assembly of the heavy mass-spring systems involved installing a lining on the tunnel floor, pouring the concrete slab in situ, lifting the slab in 200 m sections with hydraulic jacks, positioning the bearings using a sliding gauge and lowering the trough. For the light mass-spring systems, the concrete is poured directly onto pre-installed full-surface elastic mats. Tests have shown that forecast levels of vibration and noise in surrounding buildings have been achieved.