New ductile tunnel lining system

Tunnelling with high overburden in poor or faulted rock masses frequently leads to large displacements, damaging conventional supports. Ductile support systems allow accommodating the large strains imposed on the lining without damage. With an appropriate design and layout of the support, it can develop a controlled resistance, thus reducing displacements. Development of yielding elements has started many years ago, but only during the last 20 years, practical application has become common practice. Various requirements have to be considered in the design of ductile elements, which are integrated in the conventional supports. Among other factors, the time dependent development of the properties of shotcrete, as well as the development of the displacements with time – which again depends on the advance rate - play an important role. Graz University of Technology during the last two decades has worked on the development of ductile elements for shotcrete linings. The paper gives an overview of the development and the current state.