Screw Piles in Chestermere, AB

Below the surface in Chestermere

The lake that gives Chestermere its name is man-made: a reservoir within the Western Irrigation District canal network, held back by a dam and supplied from the Bow. Keep that in mind whenever you think about groundwater in this city. The soil around it is the same heavy clay found across the plain east of Calgary, but along the shore and beside the canals the water table is high, and it rises and falls with how the irrigation system is run rather than just with the weather — the WID lowers the lake every fall before freeze-up.

Clay that stays saturated loses strength, and close to the lake that softness can extend well past the level where an ordinary footing would bear. The answer is to take the screw pile through the soft layer and into firmer ground below, confirming it with installation torque — on this soil, picking a depth ahead of time is a guess. The practical upside is that water in the ground does not get in a helical pile’s way the way it floods an open hole. Excavating for a footing beside the lake means pumping and fighting slumping walls; turning a pile through that same soil does not.

Move back from the shoreline and the newer subdivisions are on typical high-plasticity prairie clay, swelling and shrinking much as it does in northeast Calgary or Airdrie. In effect Chestermere is two separate foundation markets — a wet band along the water and an ordinary clay-plain suburb inland — and each calls for its own design.

The projects we see locally

Waterfront properties generate jobs that do not come up elsewhere in our service area: decks that step down the bank toward the lake, gazebos at the shore, supports for boat lifts and gangways, and stairs set on soft ground where pouring concrete would be awkward and likely to shift. All of it stands in wet, weak soil and gets pushed sideways and pulled upward by wind, ice and everyday use, so a screw pile foundation here has to be designed for tension and corrosion as well as bearing.

Inland it is another job altogether: back decks, hot tub bases, detached garages, home additions and stabilising foundations moved by the clay, on newer houses with plenty of room for equipment. The same municipality and the same permit counter, but a completely different engineering question.