Thing: Deep dark hole

>> How to dig a crater and how to stop the neighbouring streets and buildings from caving into it

by PHILIP PREVILLE

In the shadow of Queen Victoria's statue, a once-empty lot (about 350 feet long and 120 feet wide) is now being excavated. A highrise will eventually stand in its place but for now, all anyone will say is that they're building "a three-storey underground parking garage."

Digging a hole is never easy in the city: in this case, there's metro access tunnels on the left, high-tension hydroelectric wires at the far end (beneath Her Majesty's likeness) and St-Antoine itself on the right. When you dig three storeys deep, you risk having all that other stuff cave in--which would result in no end of lawsuits and other mundane hassles. How do you prop it up?

1. On the left side, adjacent to the metro tunnels, they do it the old-fashioned way: they build a wall from wooden planks and prop it up with these huge, round steel beams. For construction crews, these beams are a pain in the ass because they get in the way of the backhoes and other industrial machinery. They still have to dig down another storey on this side, and they'll have to work around the beams to do it.

2. On the right side, beneath St-Antoine, the wall seems to hold up on its own--but that's hardly the case. There are no underground tunnels of any kind here, nothing but sand, earth and stone. Using what's known as a rock anchor, they drill 70 feet down into the earth at a 45-degree angle. They then insert a bunch of re-bar (the big wires you see sticking out here) into the hole and fill it with a special epoxy cement. The wire-and-cement combination "anchors" the wall into the ground, allowing crews and machinery to work without the hassle of protruding steel beams.

Final factoid: Every day, over 100 trucks enter the site and leave with a truckload of earth. It's been going on for over a month now, causing traffic havoc at the foot of Beaver Hall Hill, and will continue for at least another month. Worse still, during pothole-repair season, the city requires all trucks to lighten their load--which means all those trucks are only filled to the halfway point. :