Many areas of Ottawa have been built on sensitive clay, and the same can happen in Tewin, according to an engineer employed by the group who wants to build the city’s fourth suburb.
The new official plan, to be voted on in the city council this month, adds hundreds of acres to a dense urban community in the southeastern country, where land conditions have been talked about for decades.
Residents of Piperville Road have questioned the cost and feasibility of building in the countryside, far from transit and pipes, and on poor soils.
They know full well that neighbors have paid for expensive repairs after the foundation has been replaced, while new homes need to be surrounded by a lightweight material similar to styrofoam, rather than heavier fillings.
The city of Ottawa has not surveyed the soil in the Tewin area in the eight months since February’s controversial council vote.
But a senior geotechnical engineer at Paterson Group, who was hired by Tewin landowners Taggart Investments and Algonquins of Ontario (AOO), says he’s not too worried.
“Yes, development over clay deposits is something we need to be careful about,” said David Gilbert, director of Paterson’s geotechnical division, a company that has worked with Ottawa’s largest developers.
“But I want to say this: the designers in Ottawa are very conscious of clay deposits, and Tewin does not pose any significant concern to me.”
Correct technique already used in Ottawa
Gilbert pointed to neighborhoods in southern Orléans, Riverside South and Kanata that have the same clay from the Champlain Sea that covered the Ottawa area thousands of years ago.
Highrises can be built if hundreds of steel pipes are driven through the ground to the bedrock and filled with concrete. This technique is often used in the city, Gilbert said, pointing to newer buildings at Petrie’s Landing in Orleans.
Midrise buildings, meanwhile, can be built on “timber foundations,” with solid concrete extending from one side of the building to the other, he said.
So far, the Paterson Group has not produced a complete report on Tewin, just a much shorter geotechnical summary for Taggart Investments.
“Our knowledge is not easy. We have a significant number of gaps out here, so it’s something we’m very sure of,” Gilbert said, adding more studies and analyzes.
Tewin landowners also gave CBC News another four-page preliminary report conducted for Taggart Investments by Golder Associates Ltd. in November 2020. In the report, Golder reviewed his own data from studies of the area between 1973 and 1975 and described how taller buildings would need deeper foundations.
At the February 10 council meeting, councilors voted down a move to give staff years to study the Tewin area. Mayor Jim Watson said it would be an “abdication of leadership” to delay city boundary expansion and instead described the “extra care” that would take place in Tewin before the official plan was approved.
City staff have not resolved the land issue themselves, but said there was no time for such extensive investigations.
They have focused on mapping the area, developed a long list of future surveys to be conducted on Tewin, and come up with a financial arrangement so the suburb pays for itself.