Sonotubes vs. Steel Piles: Which Foundation is Right for Me?
/Deck Foundations
While there are many different types of foundations available for building deck structures, we've found that driven steel piles, helical steel piles and concrete sonotubes are the best suited options for the Alaskan environment and soil conditions. And importantly, all three are approved for use by the Municipality of Anchorage Building Safety Department.
Often the type of foundation support we use is dependent on both access to the site as well as the specific ground soil type and conditions.
Driven Steel Piles
This is a foundation consisting of a steel pipe that is driven into the ground. Treeline Construction likes to use this style of foundation in rocky soil conditions like Eagle River and the Anchorage Hillside area as well as for lake docks where an extended depth is required.
These are installed with a vibratory hammer attachment on a backhoe that pounds them to a point of refusal. The refusal depth can vary quite a bit however in the Anchorage bowl, but the average depth is about 15-18 foot deep. Pipe diameter size is determined by the load that it is supporting. Both 2 inch and 3 inch diameter pipes are the most commonly used for our deck builds.
Helical Steel Piles
Helical piles consist of a steel pipe with a helical screw blade welded to the bottom. Instead of hammering like the driven piles, helical piles are screwed into the ground. Treeline Construction likes to use this style in less rocky soils like in the lower Anchorage bowl area.
These are installed to a minimum torque pressure at a minimum depth. Pipe diameter size is determined by the load that it is supporting, but 3 inch diameter pipe is the most used for our deck builds.
Concrete Sonotubes:
Sonotubes are round cylinders of concrete reinforced with rebar, poured in place. Because they are a lot more labor intensive to construct and more prone to frost heaving, we at Treeline don'e use sonotubes very often for our foundation supports.
That being said, concrete sonotubes still serve a purpose and work well for their intended use. Typically we use them when we don't have access to bring in the equipment to drive steel piles or if the intended location is too close to marked utilities which would make driving piles less safe.
Again, size of the sonotube will be determined by the load that it will be supporting.