The city of Toronto has embarked on the largest and most significant stormwater management program in the city’s history. Coxwell Bypass Tunnel is the first project of the City of Toronto’s Wet Weather Flow Master Plan that will virtually eliminate the release of combined sewer overflows into Lake Ontario. The project consists of five work shafts, 12 drop shafts and 10.5 km of 6.3 m diameter tunnel. Secant piles were utilized as support of excavation for the work shafts while the drop shafts were drilled. The tunnel will be excavated in shale and lined with precast concrete segments.