Application of Precast SFRC Tunnel Segment Lining in HK and its Benefit

Abstract

Precast concrete tunnel segment lining reinforced with conventional steel rebar have been generally used with the Tunnel Boring Machine (TBM) since 1950s. As ample concrete cover needs to be provided to protect the steel reinforcement tunnel lining against corrosion and fire, concrete cover would be easily damaged during the segment handling, erection and TBM thrusting. This will induce different degrees of damaging to the precast tunnel segment lining which affects the long-term durability performance of the permanent lining and involves substantial maintenance to the tunnel structure. To tackle the subjected problems, steel fibres are adopted to replace the conventional steel reinforcement in precast concrete segment. The adoption of precast steel fibres reinforced concrete (SFRC) tunnel segment lining increased significantly in tunnel industry since 2000 with the increase on the understanding of SFRC behavior and enhancement on the quality assurance on production. Until now there is no precedent case project using precast SFRC segments as the permanent tunnel lining in Hong Kong, but Dragages Hong Kong (DHK) has stepped forward as a pioneer contractor to promote the adoption of precast SFRC segment as the temporary tunnel lining for pilot tunnel in two highway tunnel projects which can provide the foundation on expanding the usage of precast SFRC segment to the permanent tunnel lining in the near future. This paper is to present the general mechanical behavior and design principles on SFRC and discuss in detail for the appropriateness and benefit on the adoption of SFRC for the permanent precast concrete tunnel segment lining in Hong Kong. This paper also shares the local experience on using precast SFRC segments in HK.