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Community and Q&A

Building on Shale bedrock

Dustin_C | Posted in General Questions on

Hello Folks,

I’m building a stepped foundation on shale bedrock that runs from 4′ down on the one end of my building, up to the surface on the other end. It is a 20×32 footprint with a 3 wall perimeter foundation with 2×32′ walls tied together on the low end with a 20′ wall. There will be a 90 degree, 2′ strongback on the open end of the 32′ walls. Now the open end is the high end where the bedrock meets the surface of the grade. I am having a 18″ footing and I’m curious if I should try pinning the footing to the bedrock. The frost line where I’m at in Central B.C. is 42″ Should I be worried about heaving on the bedrock? My concern with pinning to bedrock is that the bedrock itself is shale and will probably crumble as soon as I hit it with the hammer drill. I have dug as deep as my machine will allow me. I will be forming the footings with 2×8 and the stem wall will be formed with 8″ ICF. Any advice is greatly appreciated. Thanks

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  1. Expert Member


    You need to consult a geo-technical engineer. They will assess the site and design an appropriate connection to the rock.

    1. ranson | | #2

      I second this. The cost of a couple hours of engineering time now will pale in comparison to foundation repair later. My understanding is that building on shale can be tricky. Depending on your site, the shale may be subject to frost heave. Regionally, some shales are expansive, and can heave a foundation significantly over time.

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