Chienberg Tunnel: Rehabilitation using yielding elements of the section in Keuper sediments affected by heave / Chienbergtunnel: Instandsetzung der Hebungsstrecke im Gipskeuper mit Knautschkörpern

Rocks containing clay and anhydrite exhibit the property of increasing their volume by absorbing water. The paper first discusses the mechanisms causing swelling and outlines their effects on tunnels. Next the hazard scenario of heaving of the tunnel tube as a whole, the structural consequences of this and the concept of the Modular Yielding System for tunnelling in stretches where heave is unavoidable are discussed. Taking the case of the Chienberg road tunnel in Switzerland, the paper also reports on experience during construction and field measurements after putting the repaired sections into operation. Special attention is given to the technical aspects of yielding supports with cement as a basic constituent for loads up to 10 MN and a yielding capacity of up to 50 %.