The highway 401 Rail Tunnel project consists of two tunnels, each 188m long with a maximum overburden of 2-5m. Dr. G. Sauer & Partners delivered the tunnel design for the Toronto Tunnel Partners (TTP) - a joint venture led by STRABAG along with EllisDon. The design consisted of IFC drawings, specifications, 3D FE analysis and detailed design reports, and was followed by Design Representation on Site.
The project started with excavation at the beginning of October 2019 and has continued since then without any Covid-19 interruptions. The tunnel 1 excavation is now 90 % complete and breakthrough is expected in the coming weeks. The tunnel 2 top heading excavation is 68m complete. The excavation completion of tunnel 2 is predicted later in the year.
In addition to the very low overburden, excavation below constant highway traffic, intercepting piles and wing walls from an adjacent structure, the ground conditions have their challenges as well. In the upper part of the tunnels the ground material is backfill that consists of a mixture of clay, silt, sand, some gravel, occasional cobbles, and organic and inorganic material. The lower part of the tunnels comprises glacial till with a firm to stiff consistency. All of this dictates a maximum excavation length of 1m per advance in the top heading which includes pocket excavation, followed by 2m advance in the invert area.