Abstract
The twin tube, 1,765 m long Hanekleiv road tunnel is located in Southeast Norway. Ten years after completion of the tunnel, a serious rock fall occurred in the southbound tube, approximately 1.1 km from the northern tunnel entrance, in a fault zone containing swelling clay. In addition to swelling, gravitational collapse due to the very low internal friction played an important role in the development of the instability. Numerical analysis has been carried out for the rock slide. Modelling based on the support actually applied indicated cracks during tunnel excavation as well as the tunnel collapse. Simulation showed that even reinforced shotcrete ribs or 25 cm thick concrete lining, based on the Q-system, may not be sufficient for the fault zone.
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