The highway 401 Rail Tunnel project in Ontario comprises two tunnels, each 188m long with a maximum overburden of 2-5m. Dr. Sauer & Partners designed the tunnels for the joint venture led by STRABAG along with EllisDon to form the Toronto Tunnel Partners (TTP). The design delivered, consisted of the IFC drawings, specifications, 3D FE analysis and detailed design reports, with subsequent Design Representation on Site.
Excavation began at the beginning of October 2019 and Tunnel 1 excavation completed at the beginning of August this year. The waterproofing and final lining invert pour is on the way followed by waterproofing, reinforcement installation and the final lining arch pour.
Sunday 15th November 2020 marked the next major milestone for the project, breakthrough of Tunnel 2 was executed and with this the most difficult and challenging part of excavation for the project completed.
To complete the entire excavation on the 401 Crossing Project, 100m of Tunnel 2’s invert remains - this should be finalised by January 2021. The two tunnels are connected with two cross passages (CP) where the excavation of CP2 is already complete and CP1 planned to also complete by the end of this year.
The upper part TH of Tunnel 2 excavation is performed in loose sand with limited stand up time, and the lower part in soft clay, silty sand ground material. In such ground conditions, additional spile installations must be carried out. The tube spiles were grouted with chemical injections with adjacent ground also injected to provide better support and to stabilise the loose ground. An additional challenge was the steel-wood wall obstruction that was encountered between TM 134.50 up to TM 122.50. Exceptional care was taken with each round of excavation in this area due to the unstable sand material that was unveiled almost every time part of the obstruction was removed. The repercussions of this was a reduced advance rate and slight settlement encasement in the affected surface and subsurface areas.
Worth noting is that the excavation has been carried out and continues to progress with the cooperation of the on-site wildlife!