Rarely used “top-down” construction technique used to build new rail bridge at Milliken GO

Photo caption: Construction crews preparing to pour concrete for the bridge deck. (Metrolinx photo) Caption

Ontario Construction News staff writer

Construction has been underway since June on a new rail bridge is at Steeles Avenue East near Milliken GO Station in Toronto, recently completing a concrete pour of the bridge deck.

This was a significant milestone that connects the substructure elements (abutments and pier) with the superstructure (deck), and completes a critical phase of construction.

With the entire structure in place, several new phases of construction are ready to begin on the project that will see the existing Stouffville line tracks just east of Kennedy Road separated from the road.

According to the Metrolinx online blog, the big picture “road under rail” plan includes crews lowering existing Steeles Avenue East, between Silver Star Boulevard/Old Kennedy Road and Midland Avenue, so road users can move freely below, while GO trains and customers get to their destination above via a new rail and pedestrian bridge.

Crews from EllisDon are completing the construction in a rare “top-down” style, said Teresa Ko Metrolinx communications senior advisor.


“Building top-down involves constructing the bridge structure prior to completing the majority of the excavation for the underpass of the bridge. Localized excavations allowed for the north and south abutments to be built, and the centre pier was installed by drilling caissons.”

Once those elements of the substructure were complete, the bridge deck, or superstructure, used the existing ground level to support the falsework.

“This method eliminated the necessity for a significant shoring design that would typically be required of a bridge deck and allowed construction to be accelerated by eliminating the need to complete the entire excavation prior to building the structure,” Ko wrote.

The existing ground below the bridge will now be excavated to build the roadway that passes beneath, while at the same time the new tracks are constructed on top of the bridge. All part of the overall “road under rail” plan.

Here are some stats from the project:

  • Three weeks to install the reinforcing steel and engineered formwork to build the shape of the bridge deck. The formwork is used for the concrete pour to create the angles and shapes of the deck.
  • 1,600 working hours were spent to install the reinforcing steel for the main deck slab alone.
  • For the main deck pour, 570 cubic metres of concrete were used (enough to fill about 800 hot tubs), delivered in 70 concrete trucks, with two concrete pumps.
  • Main deck pour occurred in one day over 20 hours. The operation required a crew of 25 workers and approximately 500 working hours.

The completed bridge will include 1,400 cubic metres of concrete transported to site by 175 truckloads and about 8,000 working hours to build from start to end.


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