DEALING WITH SQUEEZING CONDITIONS IN ALPINE TUNNELS

In fault zones, excessive deformation during and after tunnel excavati on is frequently encountered. Shotcrete in combination with grouted ro ck bolts has successfully been used in many applications to control th e 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 extrem ely heterogeneous fault zone at the Galgenbergtunnel (Austria) led to the development of low cost yielding elements, installed between the s hotcrete ''segments'' and the use of a new type of re-groutable brock bolts. New techniques in evaluating the results of displacement monito ring have improved the short term prediction.