Recent Development of New Austrian Tunneling Method

A support technique characterized by reliance on the carrying capacity of the rock or soil surround rather than on heavy wood, steel, or concrete support systems has evolved during the last decade in Europe. Carrying capacity is mobilized by the carefully timed and dimensioned provision of certain protective measures such as thin, seimirigid linings adhering directly to the surround (i.e., usually shotcrete) and system anchoring. Frequent measurements, experience, and a thorough theoretical understanding of time-deformation-stress relations of the rock or soil surround, of the measures to be provided, and their interaction are required to achieve optimum rock loads, made possible by the most advantageous stress distribution within the mostly self-carrying surround. Recent theoretical and experimental advances, and recent site experience at two large tunnel projects, are described.