Design and construction of tunnels in poor and faulted rock mass

In weak or faulted rock and high overburden considerable displacements occur during excavation of tunnels and galleries. In most cases the behaviour of the ground is not ductile, but governed by different failure modes. In the design stage it is important to
identify potential failure modes under the given boundary conditions to be able to select appropriate construction methods. A particular problem under such conditions is that the strains developing often exceed the deformability of standard linings,
frequently leading to severe damages and the necessity of costly repairs. To allow for safe and economical tunnel construction, strategies have to be used, which guarantee support characteristics compatible with the strains, and at the same time utilize the
supports as much as possible. Recent developments of ductile elements used in combination with shotcrete and rock bolts are shown, and their efficiency reviewed. For the design of such supports the development of the expected displacements must be predicted and the time dependent properties of shotcrete considered.
Special tools to predict displacements and a relatively simple analysis method to design shotcrete linings with integrated yielding elements, based on expected displacements and the transient lining properties are presented.
The methods described in this paper have been successfully used in the European Alps and on other projects around the world