Recall that the new O-Train corridor cycling path parallels the tracks on their east side. To get under Somerset Street, the City is constructing a new underpass for the multi-user path.
The north portal has been cut out; here is the view from the top of the hole in Somerset:
Notice how thick is the base of the wall of the viaduct. There is no further foundation — the wall just bulbs out and rests on the dirt. It reminds me of those blocks sold to hold up decks — rather than digging a deep hole and filling it up with cement, the pier simply rests on the soil and either rides the frost heave up and down (fine for a deck) or in the case of the Somerset viaduct the sheer mass of the cement footing probably keeps it stable.
And here is a pic of a bunch of City white hats looking at the hole, this time seen from ground level on the north side. Look ma, one big cavity!
The underpass will have more clearance than it shows in the picture. The contractor will remove about another metre of soil from the base.
On the south wall of the viaduct, the cement cutting guys are busy making the second portal. Instead of using a really giant saw blade (imagine the diameter of the saw required to cut through that cement wall!) they are using a simple pulley system. A continuous loop of steel cable with diamond-tipped blades attached to it runs round and round on four pulleys, cutting two slices into the cement at the same time. It is running about 16 hours a day. Here is a view looking straight down into the hole:
In a few days, precast tunnel sections will be delivered an installed into the hole, cemented into place, and waterproofed. After that, it remains to fill in the hole with fresh crushed stone and repave the street above.
The first segment of the bike path, from Bayview Station to either Somerset or on a bit further to Gladstone, is planned for construction in 2012.