Seed Home 2 Foundation

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HintLightbulb.png Hint: Moved on to slab on grade as the better option for load-bearing scalability


Soil Properties

  • What is a typical soil load capcity? [1]
    • 2000 PSF for clay, 12k PSF for bedrock. Just use a penetrometer.
    • Presumptive Loads - Utah Code - 1500 psf for clay - [2]

Helical Pier Design and Properties

Basics for calculation:

  • Size of helix can vary - 6-14"
  • Number of helices can vary to increase total bearing area. 1-3 helices per section
  • Pier shaft can vary - more load capacity. Hollow pier profiles can stand more lateral loads per weight of steel pier.
  • Screw force - force limit at a given radius = load bearing capacity, in the limit that we have not stripped out the soil (using a screw thread analogy)


When examining soil load bearing strength - is a Soil Penetrometer like this sufficient to get a good idea for the Building Package or engineering stamp? Who checks the soil bearing value in the process? I am assuming that if you select the minimum presumptive value (1500 psf), then they accept this value without contest?


  • Soil penetrometer $56 to measure compressive strength of soil - [3]
  • Review by DS - In my experience, when a soil test is required you will have to have an engineer provide a certified analysis—they provide insurance mostly. Outside of that, if you are not pouring a slab you won’t have that test either. Mostly when you are building, the idea is that unless there is clear evidence of poor soils, they allow you to build because you are taking the risk. That pentameter is worthless if you are using screw anchors to like 4 ft.