Experimental study on hybrid precast tunnel segments reinforced by macro-synthetic fibres and glass fibre reinforced polymer bars

Abstract

Increasing the popularity of using fibres in precast structures has brought questions about their usability in segmental tunnel linings as an alternative to the conventional reinforced lining. Most prior studies have already revealed that the replacement of conventional steel reinforcement is possible with steel fibres. However, the usability of macro-synthetic fibres (MSFs) as reinforcements in precast tunnel segments is still unclear and one of the controversial questions to be answered. As such, this study aims to evaluate the structural applicability of using polypropylene (PP) MSFs in precast tunnel segments by means of an experimental program on full-scale specimens. Within this framework, totally fourteen full-scale precast tunnel segments of Mecidiyekoy – Mahmutbey underground railway tunnel in Istanbul/Turkey characterized by four different reinforcement cases were analysed: i) typical conventional steel reinforcement; ii) the combination of MSFs and conventional reinforcement; iii) the combination of MSFs and glass fibre reinforced polymer (GFRP) rebars; and iv) MSFs only. Flexural tests were carried out to compare the flexural behaviour of specimens at the allowable crack opening width, while point load tests were conducted to observe the structural performance of precast tunnel segments under the effect of design thrust forces. The experimental results showed that the combination of MSFs and GFRP could be an innovative solution for precast tunnel segments in case of using a suitable quantity that satisfied the project requirements. Although PP fibres exhibited adequate spalling and splitting stress control, it is observed that they could not overcome high flexure forces without using reinforcement bars at a low volume of fractions. Thus, more comprehensive studies need to perform on GFRP + MSFs segments because of having the advantages of corrosion resistance in the presence of an aggressive surrounding environment.