PEMB Foundation Uplift

[BubbaJ]

Can you use the dead load of the soil above a formed spread footing in a PEMB foundation to resist uplift? Typically the foundations I have worked on have been on very poor soil with a resulting large footing required. In this instance, I have very good soil, thus the dead load of the "required" footing for soil bearing is not sufficient to resist the uplift forces imposed.

 

[dylansdad]

Sure. I do it all the time.

 

[MWPC]

I typically use an inverted truncated cone of soil to help resist the uplift. By using a cone shaped volume of soil, lowering the top of the footing a little helps a lot. You can also make use of the weight of the grade beam/foundation wall by designing it for the uplift. Depending on the depth and footing spacing, minimum reinforcing may be enough. Be careful at the corners though. The manufacturers often just use a typical frame at the ends and do not reduce the loads. Good luck.

 

[BubbaJ]

Thanks, I was pretty sure that was an acceptable practice, but it's always nice to hear it from someone else

 

[eric1037]

You should be careful about the groundwater level. If it's above the bottom of the foundation, you should only use the buoyant weight of the concrete and/or soil.

 

[BubbaJ]

ground water is 10 feet or more below finished grade. foundations will be at -4'; so, not an issue on this project.