ABSTRACT
In rock tunnelling, the primary lining is traditionally viewed as temporary, but advancements in sprayed concrete technology have led to its increasing consideration as a permanent or at least semi-permanent support, particularly in highly fractured rock. This study investigates the limitations of empirical methods, such as the Terzaghi (1946) approach, for predicting tunnel lining pressures in complex conditions, including sloping ground. It explores load transfer mechanisms between primary and secondary linings in Double Shell Lined (DSL) tunnels through numerical modelling, focusing on the influence of interface stiffness, particularly where a sheet waterproof membrane is used. The findings suggest that, even after partial degradation, the primary lining continues to contribute significantly to structural support, allowing for reduced secondary lining thickness. The results highlight the potential for optimising tunnel designs, achieving material savings, and reducing carbon emissions through advanced numerical approaches.
