ABSTRACT
The standard construction method of the sprayed concrete lining (SCL) in soft ground tunnelling comprises a temporary primary lining of sprayed concrete, a permanent cast-in-situ or sprayed secondary lining and a waterproofing membrane interface between them. In the last twenty years, a novel design philosophy suggests the primary lining to be part of the permanent structure contributing to the long-term structural response of the tunnel’s SCL system. Also, if the sheet membrane is substituted with a sprayed one, some bond and shear capacity can be assumed between the concrete linings. This could lead to a composite behaviour and load sharing between the linings, potentially reducing the secondary concrete lining thickness and improving the overall system’s efficiency, e.g., by reducing excavation volumes and lining material consumption. This paper presents research for this composite configuration by use of mechanical shear connection in relation to the tunnel’s geometry. This is further compared to the boundary situations with frictionless interfaces and full monolithic bond. This paper delivers first insights on this novel concrete lining philosophy aiming to significantly improve the overall sustainability and life-cycle load bearing performance of critical underground infrastructure assets.
