Did you know that there is a good chance your home, sunroom, cottage or deck has been built on a foundation designed using soil assumptions?
What exactly is a soil assumption? In Manitoba (and most other places) many of the new residential and cottage country structures are resting on foundations (concrete or steel) designed to established norms. Often in Winnipeg an assumption that the soil’s capacity will be 1,500 psf (~75 kPa) is a standard.
For example, if you purchase a ground anchor / screw pile from a local Manitoba building centre it will likely be approved to support your deck because it has been engineered for a specified capacity. But when you look at the engineering there is fine-print that might say something like – “5,000lbs capacity in 1,500 psf soil, contact engineer to recalculate loading if other soil capacity.” Clearly in this example, a building official who approves a permit based on the DIY 5,000lbs rated screw pile is making an assumption that the soil will be 1,500 psf or greater.
What’s alarming about the way its been done for so long is that MANITOBA SOILS ARE ANYTHING BUT PREDICTABLE.
Our company has done two things over the past 5 years that have helped us come to the conclusion that soil assumptions need to be brought round back and shot:
- We’ve reviewed a ton of geotechnical reports and commissioned many geotechnical investigations in and around Winnipeg.
- We have 5 years experience monitoring torque while installing screw piles in the area and there is a proven empirical relationship between torque and soil capacity.
At a 10 foot depth we have encountered 24 kPa soils to 250 kPa soils around Winnipeg and from our experience, 75 kPa soil is at the high end of average. We have not necessarily found an obvious reason for poor soil capacity either. You might think, “we aren’t close to the river, our soil must be good”, you’re thinking logically but you could be very wrong from our experience.
I hate to gamble, I simply don’t like to leave things to chance – especially when I’m investing hard-earned money!
Want to learn about HOW SCREW PILES CAN BE INSTALLED WITHOUT SOIL ASSUMPTIONS? Check out this technical brief: http://www.manitobascrewpiles.ca/wp-content/uploads/2013/12/Technical-Brief-Torque-Installation-of-Screw-Piles-Limits-Liability.pdf