At its meeting on July 9, the TTC approved purchase of four tunnel boring machines from LOVAT Inc. for construction of the Spadina Subway extension at a cost of about $58-million. There was considerable discussion about this expense from the point of view of whether any could be recouped after construction, or what commonality there might be with Transit City requirements.
Various tidbits came out during the questions to staff from Commissioners.
The Sheppard tunnels are 5200mm inside diameter, whereas the Spadina tunnels will be 5400mm. The larger bore is required both to meet current fire code, and to allow trains to travel through curves with sufficient clearance. (The Sheppard line is, pardon the pun, rather boringly straight.) The larger tunnel size adds about $35-million to the cost of the 6km of bored tunnel on the Spadina line.
Transit City tunnel size will be determined by the dynamic envelope required for its cars and for the overhead power supply. These tunnels may not be the same diameter as those on the Spadina subway, but more to the point, the construction period for both Spadina and Eglinton overlap and using the Spadina machines for Eglinton will delay that project. It is conceivable that the Richmond Hill subway, if funded, might inherit the machines. Otherwise, the TTC expects to be able to sell them for about 30% of their original value.
This question will also affect the Sheppard tunnel at Don Mills, a short but necessary piece of work to get under Highway 404.
The TTC has canvassed the world market for second hand tunnelling machinery, but none which has the required bore diameter and soil condition design is available.
In a conversation after the meeting, I learned that although the single large bore tunnel (13m) proposed for Eglinton might be feasible, this large tunnel greatly increases the cost of removing spoil (earth and rock) because the tunnel structure is much larger than would be the case for two single tunnels. In turn, this begs the question of how much of the Eglinton line will be built cut-and-cover so that it is not dependent on the availability of tunnel boring equipment. We shall see in the fall when the next set of community meetings come around for the Eglinton corridor study.