ABSTRACT
The Ontario Line South (OLS) is a critical component of Toronto’s expanding rapid transit network, connecting the Ontario Science Centre to Exhibition/Ontario Place. This 5.9 km underground segment includes twin-bored tunnels and seven stations, six of which are below ground. The station construction employs temporary support systems including shotcrete and rock bolts, while permanent structures include reinforced concrete linings and sheet waterproofing membranes. Twin-bored tunnels, constructed using tunnel boring machines (TBMs), feature fiber-reinforced concrete (FRC) precast segments, with waterproofing ensured by segmental gaskets. This paper presents a comprehensive durability evaluation of the OLS underground structures over their 100-year design life, focusing on the impact of ground and groundwater exposure. Durability design follows the Canadian CSA A23.1 (2019) standard and incorporates supplementary full probabilistic service life modeling based on fib Bulletin No. 34 (2006) to validate the prescriptive measures. Using CSA C-1 class concrete with 40% cement replaced by ground granulated blast-furnace slag (GGBS) as a supplementary cementitious material (SCM), the OLS meets its durability and embodied carbon reduction targets, aligning with sustainable infrastructure goals. Monte Carlo simulations show that the final concrete linings achieve a reliability index exceeding the target of 1.3 for up to 150 years, 1.5 times the required service life.
