Vibrations due to hydroshield tunnelling

The Hubertus tunnel in Den Hague, the Netherlands, is a 1.5 km long bored tunnel, mostly below groundwater
level, constructed with a hydro-shield Tunnel Boring Machine in 2006 and 2007. The vibrations due to the tunnelling have been
recorded both inside the tunnel and at ground surface. No harmful vibrations were observed while the Hubertus tunnel was
being bored, although unexpected vibration nuisance did occur. This is an effect that is widely known when tunnelling in rock,
but was not expected when tunnelling in beach sand. Analyses of the recorded vibrations showed that the vibrations were mainly
caused by the trembling motion of the TBM in the sand as a result of the stick-slip effect. This creates shear waves along the
TBM shaft and pressure waves at the bore front. Both waves travel in an axial direction.