DETERMINATION OF OPTIMUM TUNNEL SHAPE BY THREE-DIMENSIONAL BACK ANALYSIS. PROCEEDINGS OF THE SIXTH INTERNATIONAL CONFERENCE ON NUMERICAL METHODS IN GEOMECHANICS, 11-15 APRIL 1988, INNSBRUCK, AUSTRIA. VOLUMES 1 - 3

A method to assess the optimum tunnel shape as well as the optimum excavation and support system is shown after evaluating the equivalent mechanical properties by a three dimensional back analysis. The method has been applied to a practical tunnel in an extremely squeezing ground and the optimum tunnel shape has been determined. The appropriateness of the method is evaluated by comparing the results obtained by the method with those obtained in the field. A simple figure to back analyze the maximum and the minimum principal stresses of the ground and the direction of these stresses in a tunnel cross section is proposed. This enables engineers to determine such stresses in situ. (Author/TRRL)