Sunday, August 16, 2009

150 Slater progress: Piles of fun III

In the previous post on 150 Slater's progress, I documented the construction of retaining walls around the former Rideau Winter Club building.

I also briefly mentioned a negative space becoming a positive one. Such a transition is even more pronounced on another part of the 150 Slater site, which will be the topic of today's post.

The Premier building, whose history and final days I documented in Down, Down, Down, Update 1, was separated from the building at 235 Laurier by a small alley. Looking at the building, you barely noticed it. Being a negative space, it was defined by the absence of anything between two very definable structures.

Let's get our bearings for a moment. In the image below, we see O'Connor Street in the foreground, with 235 Laurier squarely framed. You can see how some of the original siding was not replaced when the blue and glass cladding was added earlier this decade. In the foreground are some patches in the asphalt where holes had been dug to cut off services to the now-demolished buildings on the 150 Slater site.

Here's a closeup of the former siding. It's made from that ugly reinforced institutional glass with a grid of metal wires inside. The glass is filthy with years of dirt and grime. If this part of the wall is too far out of sight to re-clad, evidently it isn't worth cleaning, either. But having them here gives insight on how the new cladding relates to the old exterior: The new cladding essentially enshrouds these concrete fins, as it comes out further and has a lip below them. though I'm sure there was much work behind the glass as well.

At the back of the building, right below the old wall, are a pair of emergency exits, a gas connection and some ventilation panels. Since the building is still in use, the emergency exits must remain usable during the construction at 150 Slater. So a little structure was built to protect the accessway during the demolition of the Premier.

When the Premier's remains were extracted in mid-May and its site became an empty hole, the former alley became an enclosed passageway. In effect, negative and positive switched places.

By mid-June, the Premier's foundation walls had been demolished and the hole was filled in. Evidently, the demolition was very thorough, as a makeshift wooden walkway needed to be built to preserve access from the fire exit.

Under the boardwalk is revealed a gaping hole leftover from the foundation wall's demolition.

And in early July, piles had been driven and a retaining wall was built (as documented in the previous two posts on 150 Slater).

The gap under the walkway is still there, but the walkway is better supported now on the piles. You can also see a yellow hose--the gas line that comes from under the street to the back of the building. A worker is measuring the distance for the final segment of four-by-eights.

The machine used to install the tiebacks set me on a bent to learn more about construction of retaining walls. It's a very curious looking machine, which looks to me like the Predator alien from various films I haven't seen. It's rather photogenic, too, since its 'head' is suspended in the air at an angle.

Zooming in on the photo, I see the brand name Interoc, which suggests it may be an Interoc AN 140 Multi-purpose hydraulic drill rig. I believe this is the manufacturer's writeup. It's used to intall tiebacks, which is one fo the three primary ways of supporting retaining walls in construction sites, as illustrated in this diagram.

This particular rig, which is identified as unit number 05-28 in large black lettering on the back, is now being used at the construction site for 120 University, just over the Rideau Canal. A photo I have of the rig there has clearly written in the back, identifying the owner as Forages M.S.E. Drilling, Inc. of Ste-Martine, Quebec.

The previously-linked California PDF manual on foundations (28MB) has a good writeup on tiebacks beginning on page 11-1 (page 193 of the PDF), and a useful cross-section diagram on the following page.

In short, a cavity is drilled at the end of an angled hole behind the wall, and a steel wire is anchored into the cavity with concrete (the weight and firmness of the soil keeps it in place). A stretch of wire between the anchor and the wall, surrounded loosely by a shroud, can be tensioned to put pressure on the wall, holding it in place. Once tightened, a cap is placed on the wire to hold its position, and your wall is retained.

And that's it for the progress updates on 150 Slater. Let me show you the exit:

For all photos of 150 Slater's development, see previous posts marked with the "150 Slater" label.

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