Stability and potential failure mode of tunnels and underground rock caverns are directly related to the magnitude and orientation of the in-situ rock stress. In some cases, the high horizontal in-situ stress is essential in maintaining cavern stability, whilst in other cases the high rock stress may bring forth additional difficulties in tunnel construction and rock support design. It is crucial to take into account the in-situ rock stress in designing of the shape and orientation of underground works and selecting of excavation methods and rock support. With a number of examples of real projects the paper describes the impact of the in-situ rock stress on the tunnel/cavern stability and corresponding rock support design. The hazardous effects resulting from spalling and rock burst associated with very high in-situ rock stress are addressed with the example of the world longest road tunnel – the Lærdal
tunnel.