ABSTRACT
This paper examines a series of scenarios in which possible failure mechanisms involving shrinkage-induced cracking, delamination, and creep of a shotcrete lining are assessed to identify the possible causes of a recent shotcrete lining collapse observed in a Sydney tunnel. Derivations of structural behaviour based on shrinkage, creep, cracking and de-bonding, have been developed from basic engineering principals. Typical geometries for recently built linings in Sydney have been used to determine which of several postulated scenarios are likely to actually occur. This has been done by comparing tensile stresses generated within the lining and at the boundary with the substrate against estimated tensile and adhesive bond strengths. The results indicate that drying shrinkage cracking is highly likely at the exposed surface of a lining, and that these cracks are likely to induce de-bonding of the lining from the substrate in the immediate vicinity.
