Innovative Design of Fibre Reinforced Concrete Tunnel Segments

Tunnels have been playing a significant role throughout the history of civilisation. In recent years, precast fibre reinforced concrete (FRC) tunnel segments have been increasingly used worldwide. Compared to normal concrete, FRC has higher tensile strength, increased toughness and reduced crack, making it an ideal material for tunnel lining design. Also, as fibres can be easily incorporated into concrete mix, reinforced steel cages can be significantly reduced or even eliminated, which provides a cost-effective and environmentally friendly alternative to traditional reinforced concrete (RC) tunnel segments, and opens up an opportunity for innovative tunnel segment design. In traditional shield tunnel, segmental joints are the most vulnerable parts of a tunnel structure due to their considerably low bending capacity caused by bolted connection. Leakage is a notorious issue in tunnel structure due to joint opening, which can cause severe joint deformation and instability of lining, leading to tremendous losses of life and property. Joint opening usually occurs during long-term operation, while severe damage of tunnel segment and significant joint opening can be caused by impacts from occasional train derailments and car collision. Although substantial research has been conducted to evaluate the structural performance of FRC tunnel lining, most of the existing studies have been focused on the segments and FRC mix design only. The performance of FRC segmental joint has not been well explored. Moreover, the dynamic response of FRC tunnel lining has not been reported in literature. Consequently, it is essential to optimise FRC segmental joint design and investigate the dynamic response of FRC tunnel lining under impact loading. As an innovative design concept for developing new materials and structures, topological interlocking has great potential to be applied to optimise the geometry of precast FRC tunnel segments. Interlocking structures display a number of desirable characteristics, such as improved bending flexibility, strong fracture resistance and high tolerance to locally damaged or missing elements. In this thesis, a novel non-planar interlocking design of FRC tunnel segment is proposed to optimise the segmental joint and enhance the impact resistance of tunnel structure. Both experimental and numerical studies are carried out to investigate the performance of the new tunnel segment design, and the recommendations are also provided.

A novel non-planar interlocking element is firstly proposed, which has a symmetrical geometry with six curved side surfaces to be interlocked with adjacent elements. A tunnel can be simply constructed by assembling a number of these identical elements without mortar, and the movement of each element is naturally restricted in all directions. The structural behaviour of the concrete tunnel assembled with the proposed non-planar interlocking element is investigated numerically. It is found that the interlocking assembled concrete tunnel has a lower peak contact force and a higher energy absorption capacity under impact load compared to the concrete tunnel constructed with normal segment and monolithic concrete tunnel. To further investigate the performance of the interlocking assembled tunnel made of FRC, lab-scale drop weight tests are carried out. An aluminum mould is designed to cast non-planar interlocking steel fibre reinforced concrete (SFRC) segments, making the fabrication process easy and cost-effective. To impact the inner surface of the tunnel specimen, a sophisticated test setup is proposed, and a customised steel frame is fabricated. The influences of the initial impact velocity and the confining load on the impact resistance of the interlocking assembled SFRC tunnel are examined. Furthermore, a finite element model and modelling techniques that can accurately predict the impact performance of the interlocking assembled SFRC tunnel are developed. In particular, the constitutive model for SFRC is carefully calibrated in the present model. The structural details of the experimental setup, such as the frictions and constraints between different components are considered. Once the numerical model is validated by the experimental results, a parametric study is conducted to evaluate the effect of the geometric design of segmental joint. Finally, the recommendations for the optimisation design of SFRC tunnel segment are provided.