Dealing with squeezing conditions in Alpine tunnels

In fault zones, excessive deformation during and after tunnel excavation is frequently encountered. Shoterete in combination with grouted rock bolts has successfully been used in many applications to control the deformation process. The magnitude of deformation frequently exceeds the deformability of the shotcrete lining. In the past, this problem has been solved by dividing the shotcrete lining into “segments” and leaving gaps between the segments to accommodate deformation without damage to the lining. The need for minimizing deformation in an extremely heterogeneous fault zone at the Galgenbergtunnel (Austria) led to the development of low cost yielding elements, installed between the shotcrete “segments” and the use of a new type of re-groutable brock bolts. New techniques in evaluating the results of displacement monitoring have improved the short term prediction.