Design and Construction of Temporary Works to Facilitate the Construction of Go Rail Tunnel Under the Highway 401 and 409

Toronto Tunnel Partners (TTP), under the contract to Metrolinx, recently completed the construction of two 10mtall, 8.5mwide rail tunnels crossing 21 lanes of Highway 401 at the Highway 409 interchange to facilitate the future expansion of the GO transit rail corridor. The tunnels were advanced by use of the Sequential ExcavationMethod (SEM) and required the use of a pre-support pipe canopy to assist with the ground support above the tunnel crowns. A 26 m x 10 m x 9.8 m deep strutted sheet pile shaft was constructed occupying the full median space between Highway 401 and 409 lanes to facilitate auger boring operation necessary to install this pipe canopy. The shaft also aided in the temporary support to the adjacent existing rail tunnel and bridge wing walls that were partially exposed during construction. The shaft also needed to be designed to allow for pipes to be installed through the load resisting sheet pile walls, and later the unbalanced loading during the tunnel construction. At the tunnel portals, a custom thrust frame was required to allow the contractor to complete auger boring up to 4.5 m above grade and was required to resist a 250-tonne thrust load at this height. Retaining walls and work platforms were also required at the portals to facilitate installation of monitoring equipment and temporary support of equipment on the active railway during short duration closures. This paper will provide a comprehensive overview of the design and installation of the unique temporary structures which helped facilitate the construction of this challenging project.