Wednesday, October 7, 2009

Foundations when ground is soft

Preston Street is the former runoff route from Dow's Great Swamp down to the Ottawa River at Nepean Bay, until Colonel By built the dam that QE Driveway runs along the top of. This means significant portions of the ground along Preston are peat or soft materials.

At the site of a new three storey infill on Preston (six apts above 3 retail) crews bored supporting pipes deep into the ground. The pipes were cut off at the same level down in the future basement. A concrete "box" was poured in place on top of each post. Gravel was poured into the basement between the posts and packed down. Then the footings shown in the fourth picture were poured in place on top of the concrete boxes on top of the steel posts, plumbing was put in, and gravel packed in to make the subfloor. All this, just to get to the basement floor level.

Then the plywood forms shown in the fourth picture were unpacked and set out for the walls to be poured, as shown in picture 5. the basement consists of tiny rooms, probably lockers. Note that the building on the right - Photo Lux - is supported by a steel beam and concrete footings. The old wood frame brick veneer house that previously occupied this site was on such a tilt that it made me seasick just looking at it. Its kitchen must have been crazy  like the one at the museum of science and technology.


  1. Fascinating post, one of the reasons I stop by to read this blog a few times a week.

    How wide was the run off from Dows swamp as I did not see these foundation methods used at the Domicile tower on Loretta ?

  2. It has been too many decades since I took surficial geology, civic engineering, and geography courses at Carleton to remember the details of where runoff occured. Pockets of peat subsoil cause foundation problems at Primrose/Booth, Elm between Booth and Rochester and along City Centre Ave but these are from former Ottawa River elevations. Dows swamp drained roughly down Preston as far as Pouffe Park/Plant Pool then a bit westward to the Otrain alignment to the River, a drainage pattern blocked a century ago when Somerset was raised to go over the rail tracks. Some of the bays in the City Centre complex have experienced significant settlement due to the poor subsoil. During the great fire of 1902 the dam at Dow's Lake was breached, permitting the Lake to flood down Preston and stopping the fire in its tracks. The dam is somewhat hard to see, being covered by the QE Driveway, but is most apparent when you stand in Commissioners Park near Carling and realize that Dows Lake is way up HIGHER than you are.
    Thanks for reading.