Doctor of Philosophy
Civil and Environmental Engineering
Prof. Dr. Moncef Nehdi
The use of precast concrete tunnel linings (PCTLs) has been escalating due to its efficient and economical installation process compared to that of normal cast in-situ lining practice. Normally, PCTL segments are designed for 100 years of service life. However, tunnel structures often suffer premature degradation primarily due to reinforcement corrosion, which requires costly repair and maintenance. Hence, addressing and solving such durability-sustainability dilemma of tunnels is a must. The main aim of this dissertation is to evaluate the structural and durability performance of full-scale conventional reinforced concrete (RC) PCTL segments in comparison to steel fibre-reinforced concrete (SFRC). Moreover, the potential for implementing ultra-high performance fibre-reinforced concrete (UHPFRC) in tunnel lining applications was also investigated. Tunnel lining segments behaviour was evaluated under simulated field-like conditions including physical and chemical loads encountered during the service life of PCTL segments.
Results showed that the peak load capacity of RC PCTL segments was higher than that of the corresponding SFRC segments; however, SFRC achieved higher cracking resistance and more progressive post-peak behaviour. The tested segments indicating the adequate ability to sustain TBM installation loads. The durability assessment showed that the chloride ion diffusion coefficient was a function of chloride concentration and exposure period. Results indicate that conventional RC PCTL segments are more vulnerable to corrosion damage compared to that of SFRC segments.
Moreover, the load carrying capacity of UHPFRC tunnel lining segments linearly increased with higher fibre dosage. UHPFRC exhibited higher cracking resistance, leading to better durability properties compared to that of conventional RC and SFRC owing to its very low porosity and denser micro-structure. Furthermore, no deterioration of UHPFRC mechanical properties was observed after various chloride ions exposures.
Based on structural and durability results, it can be concluded that the UHPFRC is a promising alternative for conventional RC and SFRC tunneling segments. The very high strength and ultra-durable nature of UHPFRC can allow reducing the cross-sectional dimensions of PCTL segments, leading to reduced material cost and more sustainable construction. In addition, UHPFRC PCTL segments can eliminate the costly manufacturing of rebar cages, which mitigates the corrosion problem, leading to enhanced service life of lining systems at low production cost.
Abbas, Safeer, "Structural and Durability Performance of Precast Segmental Tunnel Linings" (2014). Electronic Thesis and Dissertation Repository. 1865.