Highly Deformable Shotcrete Lining - Design and Experience

Shotcrete has proved to be the most appropriate lining material for many applications when
tunnelling through different types of rock mass. Under “squeezing ground” conditions the magnitude of deformation often far exceeds the deformability of the shotcrete lining. In order to provide more ductility and avoid damage to the support, one solution, first introduced in 1970, was the division of the shotcrete lining into circumferential “segments”, leaving gaps between these “segmental arches”.
This approach in combination with a dense rock bolt pattern was successfully used on many alpine tunnels, on tunnel projects in foreign countries and in mines. The shortcoming of this support system is the missing thrust transmission between the lining “segments”, resulting in a rather low radial support pressure.
Recently in Austria low-cost, yielding-steel-elements called LSC (“Lining Stress Controller”) have been introduced. These consist of multiple steel pipes in a concentric assembly which are installed
between the shotrcete “segments”. This system proved to be very efficient in terms of reducing
displacements and controlling stresses in the shotcrete support, hence avoiding failures of the lining,
increasing support resistance and safety. Other objectives of such devices are lightness, ease of
construction and a high potential of energy absorption with a constant average collapse load at
failure. The capacity of the energy absorbing elements can be custom-tailored to individual
requirements depending on the geological and stress conditions on site by using different
combinations of steel pipe dimensions. Numerical simulation is used for the design of elements. The
support system can be used with any type of lining e.g. concrete, steel, segmental, shotcrete etc