Experimental and numerical-based design of hybrid steel fibre-reinforced concrete tunnels

Hybrid steel fibre-reinforced concrete (HSFRC) composites, constituted from different geometries of steel fibres, benefit from positive performances of different fibre geometries. When applied in segmental tunnels, different aspects of their structural performance should be adequately evaluated to ensure a safe and durable design. In this paper, the flexural behaviour of segmental joints and performance under tunnel-boring machine (TBM) thrust forces for HSFRC segments is separately investigated through an experimental and numerical campaign. Experimental tests are used to evaluate the mechanical characteristics of the HSFRC composites, specifically the nonlinear tensile performance. Numerical models are then developed to study the aforementioned structural aspects in HSFRC segmental tunnels. Currently, guidelines and standards do not provide relationships specifically for the flexural design of segmental joints and TBM jack loads in HSFRC segmental linings. With the intention of meeting this deficit, simplified engineered relations are proposed.